Publications by authors named "Paola Menichini"

38 Publications

Evaluating the Influence of a G-Quadruplex Prone Sequence on the Transactivation Potential by Wild-Type and/or Mutant P53 Family Proteins through a Yeast-Based Functional Assay.

Genes (Basel) 2021 Feb 15;12(2). Epub 2021 Feb 15.

Mutagenesis and Cancer Prevention Unit, IRCCS Ospedale Policlinico San Martino, 16132 Genoa, Italy.

P53, P63, and P73 proteins belong to the P53 family of transcription factors, sharing a common gene organization that, from the P1 and P2 promoters, produces two groups of mRNAs encoding proteins with different N-terminal regions; moreover, alternative splicing events at C-terminus further contribute to the generation of multiple isoforms. P53 family proteins can influence a plethora of cellular pathways mainly through the direct binding to specific DNA sequences known as response elements (REs), and the transactivation of the corresponding target genes. However, the transcriptional activation by P53 family members can be regulated at multiple levels, including the DNA topology at responsive promoters. Here, by using a yeast-based functional assay, we evaluated the influence that a G-quadruplex (G4) prone sequence adjacent to the p53 RE derived from the apoptotic target gene can exert on the transactivation potential of full-length and N-terminal truncated P53 family α isoforms (wild-type and mutant). Our results show that the presence of a G4 prone sequence upstream or downstream of the P53 RE leads to significant changes in the relative activity of P53 family proteins, emphasizing the potential role of structural DNA features as modifiers of P53 family functions at target promoter sites.
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http://dx.doi.org/10.3390/genes12020277DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7919268PMC
February 2021

Potential Role of miRNAs in the Acquisition of Chemoresistance in Neuroblastoma.

J Pers Med 2021 Feb 7;11(2). Epub 2021 Feb 7.

Department of Experimental Medicine, University of Genova, 16100 Genova, Italy.

Neuroblastoma (NB) accounts for about 8-10% of pediatric cancers, and the main causes of death are the presence of metastases and the acquisition of chemoresistance. Metastatic NB is characterized by amplification that correlates with changes in the expression of miRNAs, which are small non-coding RNA sequences, playing a crucial role in NB development and chemoresistance. In the present study, miRNA expression was analyzed in two human -amplified NB cell lines, one sensitive (HTLA-230) and one resistant to Etoposide (ER-HTLA), by microarray and RT-qPCR techniques. These analyses showed that miRNA-15a, -16-1, -19b, -218, and -338 were down-regulated in ER-HTLA cells. In order to validate the presence of this down-regulation in vivo, the expression of these miRNAs was analyzed in primary tumors, metastases, and bone marrow of therapy responder and non-responder pediatric patients. Principal component analysis data showed that the expression of miRNA-19b, -218, and -338 influenced metastases, and that the expression levels of all miRNAs analyzed were higher in therapy responders in respect to non-responders. Collectively, these findings suggest that these miRNAs might be involved in the regulation of the drug response, and could be employed for therapeutic purposes.
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http://dx.doi.org/10.3390/jpm11020107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7916079PMC
February 2021

Antitumor Effects of PRIMA-1 and PRIMA-1 (APR246) in Hematological Malignancies: Still a Mutant P53-Dependent Affair?

Cells 2021 Jan 7;10(1). Epub 2021 Jan 7.

Mutagenesis and Cancer Prevention Unit, IRCCS Ospedale Policlinico San Martino, 16132 Genoa, Italy.

Because of its role in the regulation of the cell cycle, DNA damage response, apoptosis, DNA repair, cell migration, autophagy, and cell metabolism, the tumor suppressor gene is a key player for cellular homeostasis. gene is mutated in more than 50% of human cancers, although its overall dysfunction may be even more frequent. mutations are detected in a lower percentage of hematological malignancies compared to solid tumors, but their frequency generally increases with disease progression, generating adverse effects such as resistance to chemotherapy. Due to the crucial role of P53 in therapy response, several molecules have been developed to re-establish the wild-type P53 function to mutant P53. PRIMA-1 and its methylated form PRIMA-1 (also named APR246) are capable of restoring the wild-type conformation to mutant P53 and inducing apoptosis in cancer cells; however, they also possess mutant P53-independent properties. This review presents the activities of PRIMA-1 and PRIMA-1/APR246 and describes their potential use in hematological malignancies.
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http://dx.doi.org/10.3390/cells10010098DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7827888PMC
January 2021

Comparison of ibrutinib and idelalisib plus rituximab in real-life relapsed/resistant chronic lymphocytic leukemia cases.

Eur J Haematol 2021 Apr 28;106(4):493-499. Epub 2021 Jan 28.

Biothecnology Research Unit, AO of Cosenza, Cosenza, Italy.

Objectives: To compare the capacity of ibrutinib (IB) and idelalisib-rituximab (IDELA-R) of prolonging overall survival (OS) as in CLL patients, previously treated with chemotherapy only.

Methods: A real-life cohort of 675 cases has been identified and investigated in the database of the groups participating in the study.

Results: At an unadjusted univariate analysis, a significant death risk reduction was observed favoring IB (IDELA-R vs IB HR = 0.5, 95% CI = 0.36-0.71) although with some limitations due to the non-randomized and retrospective nature of the study and to the lower number of patients in the IDELA-R group (112 cases) related to the current prescribing practice. To overcome the potential problem of confounding by indication, we adjusted the association between the type of therapy and mortality for all variables significantly associated with OS at Cox univariate analysis. Furthermore, those variables, differently distributed between the two study groups, were introduced into the multivariate Cox model to improve the effectiveness of the analysis. By introducing all these variables into the multiple Cox regression model, we confirmed the protective effect of IB vs IDELA-R (HR = 0.67, 95% CI = 0.45-0.98, P = .04) independent of potential confounders.

Conclusions: Although our analysis presents some constraints, that is, the unavailability of additional potential confounders, and the retrospective nature of the study, this observation may be of help for the daily clinical practice, particularly in the absence of randomized trials comparing the two schedules.
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http://dx.doi.org/10.1111/ejh.13573DOI Listing
April 2021

MicroRNA-Mutant P53 Crosstalk in Chemoresistance: A Hint to Monitor Therapy Outcome.

Microrna 2020 ;9(5):322-335

Mutagenesis and Cancer Prevention Unit, IRCCS Ospedale Policlinico San Martino, Largo R. Benzi 10, Genoa, Italy.

The chemoresistance of cancer cells is a multifactorial mechanism in which de-regulated apoptotic pathways, the oxidative response and cancer cell migration play a crucial role. A key player in the control of such pathways is the tumor suppressor gene TP53, also defined as the "guardian of the genome", encoding the P53 tetrameric transcription factor. P53, following cell injuries, can activate the transcription of several target genes crucial for the induction of apoptosis, cell cycle arrest, modulation of senescence, DNA repair, autophagy and metabolism. Importantly, TP53 gene is mutated in nearly 50% of human cancers, implying an altered expression of target genes in cancer cells. The presence of TP53 mutations can also affect the expression of several small noncoding RNAs (microRNAs or miRNAs) involved in the same regulation of the apoptotic signaling, cell cycle regulation and cell migration. In mutant P53 expressing tumors, some miRNAs resulted in being down-regulated, while others appeared to be up-regulated as demonstrated by in vitro and in vivo studies. Thus, the expression level of specific P53 responsive miRNAs could be used as a marker of cancer progression and therapy performance. In the present review, we will summarize the role of P53-related miRNAs and their clinical relevance in monitoring therapy outcome and progression of cancers with mutant P53.
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http://dx.doi.org/10.2174/2211536609666201209151659DOI Listing
January 2020

Heterogeneity of Mutations and P53 Protein Residual Function in Cancer: Does It Matter?

Front Oncol 2020 28;10:593383. Epub 2020 Oct 28.

Mutagenesis and Cancer Prevention Unit, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS) Ospedale Policlinico San Martino, Genoa, Italy.

The human locus, located on the short arm of chromosome 17, encodes a tumour suppressor protein which functions as a tetrameric transcription factor capable of regulating the expression of a plethora of target genes involved in cell cycle arrest, apoptosis, DNA repair, autophagy, and metabolism regulation. is the most commonly mutated gene in human cancer cells and germ-line mutations are responsible for the cancer-prone Li-Fraumeni syndrome. When mutated, the gene generally presents missense mutations, which can be distributed throughout the coding sequence, although they are found most frequently in the central DNA binding domain of the protein. mutations represent an important prognostic and predictive marker in cancer. The presence of a mutation does not necessarily imply a complete P53 inactivation; in fact, mutant P53 proteins are classified based on the effects on P53 protein function. Different models have been used to explore these never-ending facets of mutations, generating abundant experimental data on their functional impact. Here, we briefly review the studies analysing the consequences of mutations on P53 protein function and their possible implications for clinical outcome. The focus shall be on Chronic Lymphocytic Leukemia (CLL), which also has generated considerable discussion on the role of mutations for therapy decisions.
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http://dx.doi.org/10.3389/fonc.2020.593383DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7655923PMC
October 2020

Time to first treatment and P53 dysfunction in chronic lymphocytic leukaemia: results of the O-CLL1 study in early stage patients.

Sci Rep 2020 10 28;10(1):18427. Epub 2020 Oct 28.

Biotechnology Research Unit, Aprigliano, A.O./ASP of Cosenza, 87100, Cosenza, Italy.

Chronic lymphocytic leukaemia (CLL) is characterised by a heterogeneous clinical course. Such heterogeneity is associated with a number of markers, including TP53 gene inactivation. While TP53 gene alterations determine resistance to chemotherapy, it is not clear whether they can influence early disease progression. To clarify this issue, TP53 mutations and deletions of the corresponding locus [del(17p)] were evaluated in 469 cases from the O-CLL1 observational study that recruited a cohort of clinically and molecularly characterised Binet stage A patients. Twenty-four cases harboured somatic TP53 mutations [accompanied by del(17p) in 9 cases], 2 patients had del(17p) only, and 5 patients had TP53 germ-line variants. While del(17p) with or without TP53 mutations was capable of significantly predicting the time to first treatment, a reliable measure of disease progression, TP53 mutations were not. This was true for cases with high or low variant allele frequency. The lack of predictive ability was independent of the functional features of the mutant P53 protein in terms of transactivation and dominant negative potential. TP53 mutations alone were more frequent in patients with mutated IGHV genes, whereas del(17p) was associated with the presence of adverse prognostic factors, including CD38 positivity, unmutated-IGHV gene status, and NOTCH1 mutations.
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http://dx.doi.org/10.1038/s41598-020-75364-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7595214PMC
October 2020

TP53 dysfunction in chronic lymphocytic leukemia: clinical relevance in the era of B-cell receptors and BCL-2 inhibitors.

Expert Opin Investig Drugs 2020 Aug 27;29(8):869-880. Epub 2020 Jun 27.

Department of Experimental Medicine, University of Genoa , Genoa, Italy.

Introduction: Patients with dysfunction, assessed by del(17p) or mutations, respond poorly to chemo-immunotherapy and fare better with the new therapies (BCR and BCL-2 inhibitors); however, it is unclear whether their response is similar to that of patients without anomalies or whether there is currently an adequate determination of dysfunction.

Area Covered: A literature search was undertaken on clinical trials and real-world experience data on patients with dysfunction treated with different protocols. Moreover, data on the biological function and on the tests currently employed for its assessment were reviewed.

Expert Opinion: Although dysfunction has less negative influence on the new biological therapies, patients with these alterations, particularly those with biallelic inactivation of , have a worst outcome with these therapies than those without alterations. At present, a determination of , particularly with next generation sequencing (NGS) methodologies, may be sufficient for the identifications of the patients unsuitable for chemo-immunotherapy, although integration with del(17p) would be advisable. For the future, more extensive determinations of the status, including functional assays, may become part of the current armamentarium for a better patient stratification and treatment with newer protocols.
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http://dx.doi.org/10.1080/13543784.2020.1783239DOI Listing
August 2020

NEAT1 Long Isoform Is Highly Expressed in Chronic Lymphocytic Leukemia Irrespectively of Cytogenetic Groups or Clinical Outcome.

Noncoding RNA 2020 Mar 13;6(1). Epub 2020 Mar 13.

Department of Oncology and Hemato-oncology, University of Milan, 20122 Milan, Italy.

The biological role and therapeutic potential of long non-coding RNAs (lncRNAs) in chronic lymphocytic leukemia (CLL) are still open questions. Herein, we investigated the significance of the lncRNA NEAT1 in CLL. We examined NEAT1 expression in 310 newly diagnosed Binet A patients, in normal CD19+ B-cells, and other types of B-cell malignancies. Although global NEAT1 expression level was not statistically different in CLL cells compared to normal B cells, the median ratio of NEAT1_2 long isoform and global NEAT1 expression in CLL samples was significantly higher than in other groups. NEAT1_2 was more expressed in patients carrying mutated genes. Concerning cytogenetic aberrations, NEAT1_2 expression in CLL with trisomy 12 was lower with respect to patients without alterations. Although global NEAT1 expression appeared not to be associated with clinical outcome, patients with the lowest NEAT1_2 expression displayed the shortest time to first treatment; however, a multivariate regression analysis showed that the NEAT1_2 risk model was not independent from other known prognostic factors, particularly the IGHV mutational status. Overall, our data prompt future studies to investigate whether the increased amount of the long NEAT1_2 isoform detected in CLL cells may have a specific role in the pathology of the disease.
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http://dx.doi.org/10.3390/ncrna6010011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7151605PMC
March 2020

P63 modulates the expression of the WDFY2 gene which is implicated in cancer regulation and limb development.

Biosci Rep 2019 12;39(12)

Mutagenesis and Cancer Prevention Unit, IRCCS Ospedale Policlinico San Martino, Largo R. Benzi, 10, Genoa 16132, Italy.

TP63 is a member of the TP53 gene family, sharing a common gene structure that produces two groups of mRNAs' encoding proteins with different N-terminal regions (ΔN and TA isoforms); both transcripts are also subjected to alternative splicing mechanisms at C-terminus, generating a variety of isoforms. p63 is a master regulator of epidermal development and homoeostasis as well as an important player in tumorigenesis and cancer progression with both oncogenic and tumour suppressive roles. A number of studies have aimed at the identification of p63 target genes, allowing the dissection of the molecular pathways orchestrated by the different isoforms. In the present study we investigated in more detail the p63 responsiveness of the WDFY2 (WD repeat and FYVE domain containing 2) gene, encoding for an endosomal protein identified as a binding partner of the PI-3K/AKT signalling pathway. We showed that overexpression of different p63 isoforms was able to induce WDFY2 expression in TP53-null cells. The p63-dependent transcriptional activation was associated with specific response elements (REs) that have been identified by a bioinformatics tool and validated by yeast- and mammal-based assays. Interestingly, to confirm that WDFY2 belongs to the p63 network of cancer regulation, we analysed the impact of WDFY2 alterations, by showing its frequent deletion in different types of tumours and suggesting its expression level as a prognostic biomarker. Lastly, we identified a chromosomal translocation involving the WDFY2 locus in a patient affected by a rare congenital limb anomaly, indicating WDFY2 as a possible susceptibility gene placed downstream p63 in the network of limb development.
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http://dx.doi.org/10.1042/BSR20192114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6914664PMC
December 2019

Autophagy induced by SAHA affects mutant P53 degradation and cancer cell survival.

Biosci Rep 2019 02 19;39(2). Epub 2019 Feb 19.

Mutagenesis and Cancer Prevention Unit, IRCCS Ospedale Policlinico San Martino, Genoa 16132, Italy

Missense mutations in the gene produce mutant p53 (mutp53) proteins which may acquire oncogenic properties favoring chemoresistance, cell migration, and metastasis. The exploitation of cellular pathways that promote mutp53 degradation may reduce cell proliferation and invasion as well as increase the sensitivity to anticancer drugs, with a strong impact on current cancer therapies. In the last years, several molecules have been characterized for their ability to induce the degradation of mutp53 through the activation of autophagy. Here, we investigated the correlation between autophagy and mutp53 degradation induced by suberoylanilide hydroxamic acid (SAHA), an FDA-approved histone deacetylase inhibitor. In the human cancer lines MDA-MB-231 (mutp53-R280K) and DLD1 (mutp53-S241F), SAHA induced a significant mutp53 degradation. However, such degradation correlated with autophagy induction only in MDA-MB-231 cells, being counteracted by autophagy inhibition, which also increased SAHA-induced cell death. Conversely, in DLD1 cells SAHA triggered a low level of autophagy despite promoting a strong decrease in mutp53 level, and autophagy inhibition did not change either mutp53 levels or sensitivity to this drug. We conclude that autophagy can be a relevant pathway for mutp53 degradation induced by SAHA, but its contribution to mutp53 destabilization and the consequences on cell death are likely context-dependent.
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http://dx.doi.org/10.1042/BSR20181345DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6379511PMC
February 2019

Etoposide-resistance in a neuroblastoma model cell line is associated with 13q14.3 mono-allelic deletion and miRNA-15a/16-1 down-regulation.

Sci Rep 2018 09 13;8(1):13762. Epub 2018 Sep 13.

Department of Experimental Medicine, General Pathology Section, University of Genova, Genova, Italy.

Drug resistance is the major obstacle in successfully treating high-risk neuroblastoma. The aim of this study was to investigate the basis of etoposide-resistance in neuroblastoma. To this end, a MYCN-amplified neuroblastoma cell line (HTLA-230) was treated with increasing etoposide concentrations and an etoposide-resistant cell line (HTLA-ER) was obtained. HTLA-ER cells, following etoposide exposure, evaded apoptosis by altering Bax/Bcl2 ratio. While both cell populations shared a homozygous TP53 mutation encoding a partially-functioning protein, a mono-allelic deletion of 13q14.3 locus, where the P53 inducible miRNAs 15a/16-1 are located, and the consequent miRNA down-regulation were detected only in HTLA-ER cells. This event correlated with BMI-1 oncoprotein up-regulation which caused a decrease in p16 tumor suppressor content and a metabolic adaptation of HTLA-ER cells. These results, taken collectively, highlight the role of miRNAs 15a/16-1 as markers of chemoresistance.
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http://dx.doi.org/10.1038/s41598-018-32195-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6137223PMC
September 2018

TP63 mutations are frequent in cutaneous melanoma, support UV etiology, but their role in melanomagenesis is unclear.

Oncol Rep 2017 Oct 14;38(4):1985-1994. Epub 2017 Aug 14.

UOC Mutagenesis, Ospedale Policlinico San Martino, I-16132 Genova, Italy.

In contrast to TP53, cancer development is rarely associated with mutations in the TP63 and TP73 genes. Recently, next generation sequencing analysis revealed that TP63 mutations are frequent, specifically in cutaneous melanomas. Cutaneous melanoma represents 4% of skin cancers but it is responsible for 80% of skin cancer related deaths. In the present study, we first determined whether all three members of the P53 family of transcription factors were found mutated in cutaneous melanomas by retrieving all TP53, TP63 and TP73 mutations from cBioPortal (http://www.cbioportal.org/). TP53 and TP63 were frequently mutated [15.0% (91/605) and 14.7% (89/605), respectively], while TP73 [1.5% (9/605)] was more rarely mutated (p<0.0001). A UV-mutation fingerprint was recognized for TP63 and TP73 genes. Then, we tried to evaluate the potential role of TP63 mutations as drivers or passengers in the tumorigenic process. In the former case, the amino acid substitutions should cause significant functional consequences on the main biochemical activity of the P63 protein, namely transactivation. The predicted effects of specific amino acid substitutions by two bioinformatics tools were rather different. Using a yeast-based functional assay, the observed hotspot mutant R379CP63 protein exhibited a substantial residual activity compared to the wild-type (>70%). This result does not support a major role of the mutant P63 protein in melanomagenesis while it is still consistent with the TP63 gene being a recorder of UV exposure. The TP63 mutation spectrum from cutaneous melanomas, when compared with that observed at the germinal level in patients affected by P63-associated diseases [ectodermal dysplasia syndromes, (EDs)], revealed significant differences. The TP63 mutations were more frequent at CpGs sites (p<0.0001) in EDs and at PyPy sites (p<0.0001) in cutaneous melanomas. The two spectra differed significantly (p<0.0001). We conclude that TP63 mutations are frequent in cutaneous melanoma, support UV etiology, but their role in melanomagenesis is unclear.
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http://dx.doi.org/10.3892/or.2017.5903DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5652947PMC
October 2017

The inhibition of 45A ncRNA expression reduces tumor formation, affecting tumor nodules compactness and metastatic potential in neuroblastoma cells.

Oncotarget 2017 Jan;8(5):8189-8205

Department of Experimental Medicine (DIMES), University of Genova, Genova, Italy.

We recently reported the in vitro over-expression of 45A, a RNA polymerase III-transcribed non-coding (nc)RNA, that perturbs the intracellular content of FE65L1 affecting cell proliferation rate, short-term response to genotoxic stress, substrate adhesion capacity and, ultimately, increasing the tumorigenic potential of human neuroblastoma cells. In this work, to deeply explore the mechanism by which 45A ncRNA contributes to cancer development, we targeted in vitro and in vivo 45A levels by the stable overexpression of antisense 45A RNA.45A downregulation leads to deep modifications of cytoskeleton organization, adhesion and migration of neuroblastoma cells. These effects are correlated with alterations in the expression of several genes including GTSE1 (G2 and S phase-expressed-1), a crucial regulator of tumor cell migration and metastatic potential. Interestingly, the downregulation of 45A ncRNA strongly affects the in vivo tumorigenic potential of SKNBE2 neuroblastoma cells, increasing tumor nodule compactness and reducing GTSE1 protein expression in a subcutaneous neuroblastoma mouse model. Moreover, intracardiac injection of neuroblastoma cells showed that downregulation of 45A ncRNA also influences tumor metastatic ability. In conclusion, our data highlight a key role of 45A ncRNA in cancer development and suggest that its modulation might represent a possible novel anticancer therapeutic approach.
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http://dx.doi.org/10.18632/oncotarget.14138DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5352393PMC
January 2017

Gambogic acid counteracts mutant p53 stability by inducing autophagy.

Biochim Biophys Acta Mol Cell Res 2017 Feb 27;1864(2):382-392. Epub 2016 Nov 27.

U.O.C. Mutagenesi, IRCCS AOU San Martino-IST, 16132 Genova, Italy. Electronic address:

Mutant p53 (mutp53) proteins are frequently present at higher levels than the wild-type (wt) protein in tumors, and some of them can acquire oncogenic properties. Consistently, knockdown of mutp53 protein in human cancer cell lines leads to reduced cell proliferation and invasion as well as to an increased sensitivity to some anticancer drugs. Therefore, the exploitation of cellular pathways and/or molecules that promote mutp53 degradation may have a therapeutic interest. Recently, autophagy is emerging as an important pathway involved in the stability of mutp53. In this paper, we explored the autophagic potential of gambogic acid (GA), a molecule that stimulates the degradation of mutp53 and increases the sensitivity of cancer cells to chemotherapeutic agents. We demonstrated that GA may induce mutp53 degradation through autophagy in cancer cells expressing the p53-R280K (MDA-MB-231) and the p53-S241F (DLD1) proteins. The inhibition of autophagy with bafilomycin A1 or chloroquine counteracted mutp53 degradation by GA. However, the autophagy induction and mutp53 degradation affected cell survival and proliferation only at low GA concentrations. At higher GA concentrations, when cells undergo massive apoptosis, autophagy is no longer detectable by immuno-fluorescence analysis. We concluded that autophagy is a relevant pathway for mutp53 degradation in cancer cells but it contributes only partially to GA-induced cell death, in a time and dose-dependent manner.
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http://dx.doi.org/10.1016/j.bbamcr.2016.11.023DOI Listing
February 2017

∆N-P63α and TA-P63α exhibit intrinsic differences in transactivation specificities that depend on distinct features of DNA target sites.

Oncotarget 2014 Apr;5(8):2116-30

TP63 is a member of the TP53 gene family that encodes for up to ten different TA and ∆N isoforms through alternative promoter usage and alternative splicing. Besides being a master regulator of gene expression for squamous epithelial proliferation, differentiation and maintenance, P63, through differential expression of its isoforms, plays important roles in tumorigenesis. All P63 isoforms share an immunoglobulin-like folded DNA binding domain responsible for binding to sequence-specific response elements (REs), whose overall consensus sequence is similar to that of the canonical p53 RE. Using a defined assay in yeast, where P63 isoforms and RE sequences are the only variables, and gene expression assays in human cell lines, we demonstrated that human TA- and ∆N-P63α proteins exhibited differences in transactivation specificity not observed with the corresponding P73 or P53 protein isoforms. These differences 1) were dependent on specific features of the RE sequence, 2) could be related to intrinsic differences in their oligomeric state and cooperative DNA binding, and 3) appeared to be conserved in evolution. Sicen genotoxic stress can change relative ratio of TA- and ∆N-P63α protein levels, the different transactivation specificity of each P63 isoform could potentially influence cellular responses to specific stresses.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4039150PMC
http://dx.doi.org/10.18632/oncotarget.1845DOI Listing
April 2014

Comparison of the biological effects of MMS and Me-lex, a minor groove methylating agent: clarifying the role of N3-methyladenine.

Mutat Res 2014 Jan 7;759:45-51. Epub 2013 Nov 7.

Molecular Mutagenesis and DNA Repair Unit, Istituto di Ricerca e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino-IST-Istituto Nazionale per la Ricerca sul Cancro, Genoa 16132, Italy. Electronic address:

N3-methyladenine (3-mA), generated by the reaction of methylating agents with DNA, is considered a highly toxic but weakly mutagenic lesion. However, due to its intrinsic instability, some of the biological effects of the adduct can result from the formation of the corresponding depurination product [an apurinic (AP)-site]. Previously, we exploited Me-lex, i.e. {1-methyl-4-[1-methyl-4-(3-methoxysulfonylpropanamido)pyrrole-2-carboxamido]-pyrrole-2 carboxamido}propane, a minor groove equilibrium binder with selectivity for A/T rich sequences that efficiently reacts with DNA to afford 3-mA as the dominant product, to probe the biology of this lesion. Using human p53 cDNA as a target in a yeast system, a weak increase in mutagenicity was observed in the absence of Mag1 (3-methyladenine-DNA glycosylase 1, mag1), the enzyme devoted to remove 3-mA from DNA. Moreover, a significant increase in mutagenicity occurred in the absence of the enzymes involved in the repair of AP-sites (AP endonucleases 1 and 2, apn1apn2). Since methyl methanesulfonate (MMS) has been extensively used to explore the biological effects of 3-mA, even though it produces 3-mA in low relative yield, we compared the toxicity and mutagenicity induced by MMS and Me-lex in yeast. A mutagenesis reporter plasmid was damaged in vitro by MMS and then transformed into wild-type and Translesion Synthesis (TLS) Polζ (REV3) and Polη (RAD30) deficient strains. Furthermore, a mag1rad30 double mutant strain was constructed and transformed with the DNA plasmid damaged in vitro by Me-lex. The results confirm the important role of Polζ in the mutagenic bypass of MMS and Me-lex induced lesions, with Polη contributing only towards the bypass of Me-lex induced lesions, mainly in an error-free way. Previous and present results point towards the involvement of AP-sites, derived from the depurination of 3-mA, in the observed toxicity and mutagenicity.
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http://dx.doi.org/10.1016/j.mrfmmm.2013.10.004DOI Listing
January 2014

Transactivation specificity is conserved among p53 family proteins and depends on a response element sequence code.

Nucleic Acids Res 2013 Oct 26;41(18):8637-53. Epub 2013 Jul 26.

Laboratory of Transcriptional Networks, Centre for Integrative Biology (CIBIO), University of Trento, TN, 38060 Italy, Molecular Mutagenesis and DNA Repair Unit, IRCSS Azienda Ospedaliera Universitaria San Martino-IST-Istituto Nazionale per la Ricerca sul Cancro, Genoa 16132, Italy, Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA, 92093, USA and Chromosome Stability Group, Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, NIEHS, NIH, RTP, NC, 27709, USA.

Structural and biochemical studies have demonstrated that p73, p63 and p53 recognize DNA with identical amino acids and similar binding affinity. Here, measuring transactivation activity for a large number of response elements (REs) in yeast and human cell lines, we show that p53 family proteins also have overlapping transactivation profiles. We identified mutations at conserved amino acids of loops L1 and L3 in the DNA-binding domain that tune the transactivation potential nearly equally in p73, p63 and p53. For example, the mutant S139F in p73 has higher transactivation potential towards selected REs, enhanced DNA-binding cooperativity in vitro and a flexible loop L1 as seen in the crystal structure of the protein-DNA complex. By studying, how variations in the RE sequence affect transactivation specificity, we discovered a RE-transactivation code that predicts enhanced transactivation; this correlation is stronger for promoters of genes associated with apoptosis.
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http://dx.doi.org/10.1093/nar/gkt657DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3794606PMC
October 2013

PRIMA-1 induces autophagy in cancer cells carrying mutant or wild type p53.

Biochim Biophys Acta 2013 Aug 29;1833(8):1904-13. Epub 2013 Mar 29.

IRCCS Azienda Ospedaliera Universitaria San Martino-IST, Genova, Italy.

PRIMA-1 is a chemical compound identified as a growth suppressor of tumor cells expressing mutant p53. We previously found that in the MDA-MB-231 cell line expressing high level of the mutant p53-R280K protein, PRIMA-1 induced p53 ubiquitination and degradation associated to cell death. In this study, we investigated the ability of PRIMA-1 to induce autophagy in cancer cells. In MDA-MB-231 and HCT116 cells, expressing mutant or wild type p53, respectively, autophagy occurred following exposure to PRIMA-1, as shown by acridine orange staining, anti-LC3 immunofluorescence and immunoblots, as well as by electron microscopy. Autophagy was triggered also in the derivative cell lines knocked-down for p53, although to a different extent than in the parental cells expressing mutant or wild type p53. In particular, while wild type p53 limited PRIMA-1 induced autophagy, mutant p53 conversely promoted autophagy, thus sustaining cell viability following PRIMA-1 treatment. Therefore, the autophagic potential of PRIMA-1, besides being cell context dependent, could be modulated in a different way by the presence of wild type or mutant p53. Furthermore, since both cell lines lacking p53 were more sensitive to the cytotoxic effect of PRIMA-1 than the parental ones, our findings suggest that a deregulated autophagy may favor cell death induced by this drug.
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http://dx.doi.org/10.1016/j.bbamcr.2013.03.020DOI Listing
August 2013

A novel snRNA-like transcript affects amyloidogenesis and cell cycle progression through perturbation of Fe65L1 (APBB2) alternative splicing.

Biochim Biophys Acta 2013 Jun 26;1833(6):1511-26. Epub 2013 Feb 26.

Dept. of Experimental Medicine, University of Genova, Genova, Italy.

FE65 proteins constitute a family of adaptors which modulates the processing of amyloid precursor protein and the consequent amyloid β production. Thus, they have been involved in the complex and partially unknown cascade of reactions at the base of Alzheimer's disease etiology. However, FE65 and FE65-like proteins may be linked to neurodegeneration through the regulation of cell cycle in post-mitotic neurons. In this work we disclose novel molecular mechanisms by which APBB2 can modulate APP processing. We show that APBB2 mRNA splicing, driven by the over-expression of a novel non-coding RNA named 45A, allow the generation of alternative protein forms endowed with differential effects on Aβ production, cell cycle control, and DNA damage response. 45A overexpression also favors cell transformation and tumorigenesis leading to a marked increase of malignancy of neuroblastoma cells. Therefore, our results highlight a novel regulatory pathway of considerable interest linking APP processing with cell cycle regulation and DNA-surveillance systems, that may represent a molecular mechanism to induce neurodegeneration in post-mitotic neurons.
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http://dx.doi.org/10.1016/j.bbamcr.2013.02.020DOI Listing
June 2013

EEC- and ADULT-associated TP63 mutations exhibit functional heterogeneity toward P63 responsive sequences.

Hum Mutat 2013 Jun 2;34(6):894-904. Epub 2013 Apr 2.

Molecular Mutagenesis and DNA Repair Unit, Istituto di Ricerca e Cura a Carattere Scientifico Azienda Ospedaliera Universitaria San Martino-IST-Istituto Nazionale per la Ricerca sul Cancro, Genoa, Italy.

TP63 germ-line mutations are responsible for a group of human ectodermal dysplasia syndromes, underlining the key role of P63 in the development of ectoderm-derived tissues. Here, we report the identification of two TP63 alleles, G134V (p.Gly173Val) and insR155 (p.Thr193_Tyr194insArg), associated to ADULT and EEC syndromes, respectively. These alleles, along with previously identified G134D (p.Gly173Asp) and R204W (p.Arg243Trp), were functionally characterized in yeast, studied in a mammalian cell line and modeled based on the crystal structure of the P63 DNA-binding domain. Although the p.Arg243Trp mutant showed both complete loss of transactivation function and ability to interfere over wild-type P63, the impact of p.Gly173Asp, p.Gly173Val, and p.Thr193_Tyr194insArg varied depending on the response element (RE) tested. Interestingly, p.Gly173Asp and p.Gly173Val mutants were characterized by a severe defect in transactivation along with interfering ability on two DN-P63α-specific REs derived from genes closely related to the clinical manifestations of the TP63-associated syndromes, namely PERP and COL18A1. The modeling of the mutations supported the distinct functional effect of each mutant. The present results highlight the importance of integrating different functional endpoints that take in account the features of P63 proteins' target sequences to examine the impact of TP63 mutations and the associated clinical variability.
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http://dx.doi.org/10.1002/humu.22304DOI Listing
June 2013

3-Methyl-3-deazaadenine, a stable isostere of N3-methyl-adenine, is efficiently bypassed by replication in vivo and by transcription in vitro.

DNA Repair (Amst) 2011 Aug 14;10(8):861-8. Epub 2011 Jun 14.

Molecular Mutagenesis and DNA Repair Unit, Department of Epidemiology and Prevention, National Cancer Research Institute (IST), 16132 Genova, Italy.

The goal of the present work was to determine the impact of N3-methyladenine (3-mA), an important lesion generated by many environmental agents and anticancer drugs, on in vivo DNA replication and in vitro RNA transcription. Due to 3-mA chemical instability, the stable isostere 3-methyl-3-deazaadenine (3-m-c(3)A) was site specifically positioned into an oligodeoxynucleotide. The oligomer was, then incorporated into a vector system that is rapidly converted to ssDNA inside yeast cells and requires DNA replication opposite the lesion for plasmid clonal selection. For control purposes, an adenine or a stable apurinic/apyrimidinic (AP)-lesion was placed at the same site. The presence of each lesion in the oligonucleotide was confirmed by MALDI-TOF analysis. Plasmids were then transfected into yeast cells. While the AP-site dramatically reduced plasmid replication in all strains, the 3-m-c(3)A had a slight effect in the rad30 background which significantly increased only in a rev3rad30 background. Considering TLS events opposite 3-m-c(3)A, the lack of Polη was associated with a substantial increase in AT>GC transitions (p=0.0011), while in the absence of Polζ only events derived from an error free bypass were detected. The 3-m-c(3)A also did not affect in vitro transcription, while the AP-site was a strong block to T7 RNA progression when located in the transcribed strand. We conclude that, in these experimental systems, 3-m-c(3)A is efficiently bypassed by replication in vivo and by transcription in vitro.
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http://dx.doi.org/10.1016/j.dnarep.2011.05.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3146564PMC
August 2011

p53 transactivation and the impact of mutations, cofactors and small molecules using a simplified yeast-based screening system.

PLoS One 2011 2;6(6):e20643. Epub 2011 Jun 2.

Unit of Molecular Mutagenesis, National Institute for Cancer Research, IST, Genoa, Italy.

Background: The p53 tumor suppressor, which is altered in most cancers, is a sequence-specific transcription factor that is able to modulate the expression of many target genes and influence a variety of cellular pathways. Inactivation of the p53 pathway in cancer frequently occurs through the expression of mutant p53 protein. In tumors that retain wild type p53, the pathway can be altered by upstream modulators, particularly the p53 negative regulators MDM2 and MDM4.

Methodology/principal Findings: Given the many factors that might influence p53 function, including expression levels, mutations, cofactor proteins and small molecules, we expanded our previously described yeast-based system to provide the opportunity for efficient investigation of their individual and combined impacts in a miniaturized format. The system integrates i) variable expression of p53 proteins under the finely tunable GAL1,10 promoter, ii) single copy, chromosomally located p53-responsive and control luminescence reporters, iii) enhanced chemical uptake using modified ABC-transporters, iv) small-volume formats for treatment and dual-luciferase assays, and v) opportunities to co-express p53 with other cofactor proteins. This robust system can distinguish different levels of expression of WT and mutant p53 as well as interactions with MDM2 or 53BP1.

Conclusions/significance: We found that the small molecules Nutlin and RITA could both relieve the MDM2-dependent inhibition of WT p53 transactivation function, while only RITA could impact p53/53BP1 functional interactions. PRIMA-1 was ineffective in modifying the transactivation capacity of WT p53 and missense p53 mutations. This dual-luciferase assay can, therefore, provide a high-throughput assessment tool for investigating a matrix of factors that can influence the p53 network, including the effectiveness of newly developed small molecules, on WT and tumor-associated p53 mutants as well as interacting proteins.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0020643PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3107237PMC
September 2011

Dominant-negative features of mutant TP53 in germline carriers have limited impact on cancer outcomes.

Mol Cancer Res 2011 Mar 22;9(3):271-9. Epub 2011 Feb 22.

Molecular Mutagenesis and DNA Repair Unit, Department of Epidemiology and Prevention, National Cancer Research Institute (IST), Largo Rosanna Benzi, 10, Genova 16132, Italy.

Germline TP53 mutations result in cancer proneness syndromes known as Li-Fraumeni, Li-Fraumeni-like, and nonsyndromic predisposition with or without family history. To explore genotype/phenotype associations, we previously adopted a functional classification of all germline TP53 mutant alleles based on transactivation. Severe deficiency (SD) alleles were associated with more severe cancer proneness syndromes, and a larger number of tumors, compared with partial deficiency (PD) alleles. Because mutant p53 can exert dominant-negative (DN) effects, we addressed the relationship between DN and clinical manifestations. We reasoned that DN effects might be stronger in familial cancer cases associated with germline TP53 mutations, where mutant alleles coexist with the wild-type allele since conception. We examined 104 p53 mutant alleles with single amino acid substitutions described in the IARC germline database for (i) transactivation capability and (ii) capacity to reduce the activity of the wild-type allele (i.e., DN effect) using a quantitative yeast-based assay. The functional classifications of p53 alleles were then related to clinical variables. We confirmed that a classification based on transactivation alone can identify familial cancer cases with more severe clinical features. Classification based on DN effects allowed us to highlight similar associations but did not reveal distinct clinical subclasses of SD alleles, except for a correlation with tumor tissue prevalence. We conclude that in carriers of germline TP53 mutations transactivation-based classification of TP53 alleles appears more important for genotype/phenotype correlations than DN effects and that haplo-insufficiency of the TP53 gene is an important factor in cancer proneness in humans.
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http://dx.doi.org/10.1158/1541-7786.MCR-10-0496DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3077904PMC
March 2011

PRIMA-1 cytotoxicity correlates with nucleolar localization and degradation of mutant p53 in breast cancer cells.

Biochem Biophys Res Commun 2010 Nov 12;402(2):345-50. Epub 2010 Oct 12.

Molecular Mutagenesis and DNA Repair Unit, Department of Epidemiology and Prevention, National Cancer Research Institute (IST), 16132 Genova, Italy.

PRIMA-1 has been identified as a compound that restores the transactivation function to mutant p53 and induces apoptosis in cells expressing mutant p53. Studies on subcellular distribution of the mutant p53 protein upon treatment with PRIMA-1Met, a methylated form of PRIMA-1, have suggested that redistribution of mutant p53 to nucleoli may play a role in PRIMA-1 induced apoptosis. Here, we specifically investigated the influence of PRIMA-1 on cellular localization of mutated p53-R280K endogenously expressed in tumour cells. By using immunofluorescence staining, we found a strong nucleolar redistribution of mutant p53 following PRIMA-1 treatment. This subcellular localization was associated to p53 degradation via ubiquitylation. When cells were treated with adriamycin, neither nucleolar redistribution nor mutant p53 down modulation and degradation were observed. Interestingly, cells where p53-R280K was silenced were more sensitive to PRIMA-1 than the parental ones. These results indicate that in some cellular context, the cell sensitivity to PRIMA-1 could depend on the abolition of a gain-of-function activity of the mutated p53, through a protein degradation pathway specifically induced by this compound.
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http://dx.doi.org/10.1016/j.bbrc.2010.10.031DOI Listing
November 2010

XRCC1 deficiency influences the cytotoxicity and the genomic instability induced by Me-lex, a specific inducer of N3-methyladenine.

DNA Repair (Amst) 2010 Jul 14;9(7):728-36. Epub 2010 May 14.

Department of Epidemiology and Prevention, National Cancer Research Institute, Genova, Italy.

Me-lex is a sequence-specific alkylating agent synthesized to preferentially (>90%) generate N3-methyladenine (3-mA) in the minor groove of double-strand DNA, in A-T rich regions. In this paper we investigated the effect of XRCC1 deficiency in the processing of 3-mA adducts generated by Me-lex, through the molecular analysis of the Hprt mutations and the evaluation of cytogenetic end points such as sister chromatid exchanges (SCEs), micronuclei (MN) and nucleus fragmentation. EM-C11 cells, deficient in XRCC1 activity, showed a 2.5-fold higher sensitivity to the toxicity of Me-lex compared to the DNA repair proficient parental CHO-9 cells, but were not hyper mutable. The spontaneous mutation spectrum at the Hprt locus generated in EM-C11 cells revealed a high percentage of genomic deletions. After Me-lex treatment, the percentage of genomic deletions did not increase, but a class of mutations which appeared to target regulatory regions of the gene significantly increased (p=0.0277), suggesting that non-coding Hprt genomic sequences represent a strong target for the rare mutations induced by Me-lex. The number of SCEs per chromosome increased 3-fold above background in 50mucapital EM, Cyrillic Me-lex treated CHO-9 cells, while at higher Me-lex concentrations a sharp increase in the percentage of MN and fragmented nuclei was observed. In EM-C11 cells the background level of SCEs (0.939+/-0.182) was approximately 10-fold higher than in CHO-9 (0.129+/-0.027) and higher levels of multinucleated cells and MN were also found. In EM-C11, even low doses of Me-lex (25microM) led to a significant increase in genomic damage. These results indicate that XRCC1 deficiency can lead to genomic instability even in the absence of an exogenous genotoxic insult and low levels of Me-lex-induced lesions, i.e., 3-mA and/or a BER intermediate, can exacerbate this instability.
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http://dx.doi.org/10.1016/j.dnarep.2010.03.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2893271PMC
July 2010

Mutagenicity of N3-methyladenine: a multi-translesion polymerase affair.

Mutat Res 2010 Jan;683(1-2):50-6

Department of Epidemiology and Prevention, National Cancer Research Institute (IST), Genova, Italy.

We recently demonstrated that Polzeta and Rev1 contribute to alleviate the lethal effects of Me-lex, which selectively generates 3-methyladenine, by error prone lesion bypass. In order to determine the role of Poleta in the biological fate of Me-lex induced lesions, the RAD30 (Poleta) gene was deleted in the yIG397 parental strain and in its rev3 (Polzeta) derivative, and the strains transformed with plasmid DNA damaged in vitro by Me-lex. While deletion of RAD30 increased the toxicity of Me-lex, the impact on mutagenicity varied depending on the concentration of Me-lex induced DNA damage and the overall TLS capacity of the cells. For the first time the Me-lex induced mutation spectrum in rad30 strain was determined and compared with the spectrum previously determined in WT strain. Overall, the two mutation spectra were not significantly different. The effect on mutation frequency and the features of the Me-lex induced mutation spectra were suggestive of error prone (significant decrease of mutation frequency and significant decrease of AT>TA at a mutation hotspot in rad30 vs RAD30) but also error free (significant increase of AT>GC in rad30 vs RAD30) Poleta dependent bypass of lesions. In summary, our previous results with Polzeta and Rev1 mutants, the present results with Poleta, and the known physical and functional interactions among TLS proteins, lead us to propose that the bypass of Me-lex induced lesions is a multi-DNA polymerases process that is mostly effective when all three yeast TLS polymerases are present.
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http://dx.doi.org/10.1016/j.mrfmmm.2009.10.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794908PMC
January 2010

High frequency of genomic deletions induced by Me-lex, a sequence selective N3-adenine methylating agent, at the Hprt locus in Chinese hamster ovary cells.

Mutat Res 2009 Dec 1;671(1-2):58-66. Epub 2009 Sep 1.

Molecular Mutagenesis and DNA Repair Unit, Department of Epidemiology and Prevention, National Cancer Research Institute (IST), L.go R. Benzi, 10, 16132 Genova, Italy.

We have investigated the mutagenicity induced at the Hprt locus in Chinese hamster ovary (CHO) cells treated with increasing concentrations of Me-lex, a minor groove selective methylating agent that efficiently generates more than 90-95% of 3-MeA DNA adducts. Me-lex treatment was cytotoxic but weakly mutagenic, resulting in up to 7-fold induction above background in the Hprt mutation frequency. The molecular nature of 43 Hprt mutations induced by Me-lex was determined by sequence analysis of the Hprt cDNA and genomic analysis of the gene locus. Base pair substitutions represented about 25% of Me-lex induced mutations. The mutation spectrum revealed a high percentage of genomic deletions (51%) comprising single/multiple exon(s) and even the loss of the complete locus. When the distribution of mutations among different classes was considered, the difference between the spontaneous and Me-lex induced CHO spectra was statistically significant (p<0.012), indicating that the sites where mutations occurred were Me-lex specific. Based upon these results we hypothesize that a large proportion of mutations may result from the processing of 3-MeA, the main adduct induced by Me-lex, within A/T rich sequences in non-coding regions of the Hprt gene. The processing of these lesions by DNA polymerases could result in recombination and genomic deletions, thus representing a severe threat for genome integrity.
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http://dx.doi.org/10.1016/j.mrfmmm.2009.08.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2783936PMC
December 2009

Rev1 and Polzeta influence toxicity and mutagenicity of Me-lex, a sequence selective N3-adenine methylating agent.

DNA Repair (Amst) 2008 Mar 7;7(3):431-8. Epub 2008 Jan 7.

Department of Epidemiology and Prevention, National Cancer Research Institute (IST), L.go R. Benzi, 10, 16132 Genova, Italy.

The relative toxicity and mutagenicity of Me-lex, which selectively generates 3-methyladenine (3-MeA), is dependent on the nature of the DNA repair background. Base excision repair (BER)-defective S. cerevisiae strains mag1 and apn1apn2 were both significantly more sensitive to Me-lex toxicity, but only the latter is significantly more prone to Me-lex-induced mutagenesis. To examine the contribution of translesion synthesis (TLS) DNA polymerases in the bypass of Me-lex-induced lesions, the REV3 and REV1 genes were independently deleted in the parental yeast strain and in different DNA repair-deficient derivatives: the nucleotide excision repair (NER)-deficient rad14, and the BER-deficient mag1 or apn1apn2 strains. The strains contained an integrated ADE2 reporter gene under control of the transcription factor p53. A centromeric yeast expression vector containing the wild-type p53 cDNA was treated in vitro with increasing concentrations of Me-lex and transformed into the different yeast strains. The toxicity of Me-lex-induced lesions was evaluated based on the plasmid transformation efficiency compared to the untreated vector, while Me-lex mutagenicity was assessed using the p53 reporter assay. In the present study, we demonstrate that disruption of Polzeta (through deletion of its catalytic subunit coded by REV3) or Rev1 (by REV1 deletion) increased Me-lex lethality and decreased Me-lex mutagenicity in both the NER-defective (rad14) and BER-defective (mag1; apn1apn2) strains. Therefore, Polzeta and Rev1 contribute to resistance of the lethal effects of Me-lex-induced lesions (3-MeA and derived AP sites) by bypassing lesions and fixing some mutations.
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http://dx.doi.org/10.1016/j.dnarep.2007.11.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2289995PMC
March 2008

Transcriptional properties of feline p53 and its tumour-associated mutants: a yeast-based approach.

Mutagenesis 2007 Nov 18;22(6):417-23. Epub 2007 Oct 18.

Istituto Zooprofilattico Sperimentale del Piemonte Liguria e Valle d'Aosta, Genoa, Italy.

Mutations at the tumour suppressor gene TP53 are associated with nearly half of human cancers, but they appear to be rare ( approximately 10%) in feline neoplasms. The reasons for this difference are presently unclear but might be related to evolutionary divergence of p53 functions. To begin exploring this issue, we developed a yeast-based functional assay to measure the transcriptional ability of wild-type (wt) or mutant feline p53 (fe_p53) in comparison with human or murine p53 (hu_p53, mo_p53). fe_p53 cDNA was cloned and expressed in a panel of yeast reporter strains engineered to contain the ADE2 or the luciferase gene under p53 control via different p53 response elements. We established that wt fe_, hu_ and mo_p53 can act as transcription factors in yeast with overlapping DNA sequence specificities. Random mutagenesis and phenotypic evaluation of fe_ and hu_p53 cDNAs was also performed, revealing equal susceptibility to deleterious mutations. Five tumour-associated fe_p53 mutants exhibited a similar impact on the transactivation capacity (partial or complete loss) compared to the corresponding hu_p53 mutants. Given the high conservation of the intrinsic functional properties of fe_p53, further studies will be needed to clarify the role of p53 in feline carcinogenetic pathways.
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http://dx.doi.org/10.1093/mutage/gem038DOI Listing
November 2007