Publications by authors named "Jan van Riggelen"

20 Publications

  • Page 1 of 1

Expression regulation and function of PD-1 and PD-L1 in T lymphoma cells.

Cell Immunol 2021 Aug 17;366:104397. Epub 2021 Jun 17.

Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA; Georgia Cancer Center, Augusta, GA 30912, USA; Charlie Norwood VA Medical Center, Augusta, GA 30904, USA. Electronic address:

T lymphoma cells may constitutively express PD-1 and PD-L1. The relative role of PD-1 and PD-L1 in T lymphoma is incompletely understood. We report here that PD-1 PDL-1 human T lymphoma cells exhibit constitutive hyperactivation of the TCR signaling and do not respond to PD-L1-mediated suppression in vitro. Knocking out PD-1 or PD-L1 has no effects on T lymphoma cell apoptosis and proliferation in vitro, but significantly increased tumor-bearing mouse survival. Our findings determine that the constitutively active TCR signaling pathway maintain T lymphoma cell growth in vitro and that both PD-1 and PD-L1 promote T lymphoma growth in vivo.
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http://dx.doi.org/10.1016/j.cellimm.2021.104397DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8327398PMC
August 2021

Glycine decarboxylase is a transcriptional target of MYCN required for neuroblastoma cell proliferation and tumorigenicity.

Oncogene 2019 12 23;38(50):7504-7520. Epub 2019 Aug 23.

Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta University, Augusta, GA, 30912, USA.

Genomic amplification of the oncogene MYCN is a major driver in the development of high-risk neuroblastoma, a pediatric cancer with poor prognosis. Given the challenge in targeting MYCN directly for therapy, we sought to identify MYCN-dependent metabolic vulnerabilities that can be targeted therapeutically. Here, we report that the gene encoding glycine decarboxylase (GLDC), which catalyzes the first and rate-limiting step in glycine breakdown with the production of the one-carbon unit 5,10-methylene-tetrahydrofolate, is a direct transcriptional target of MYCN. As a result, GLDC expression is markedly elevated in MYCN-amplified neuroblastoma tumors and cell lines. This transcriptional upregulation of GLDC expression is of functional significance, as GLDC depletion by RNA interference inhibits the proliferation and tumorigenicity of MYCN-amplified neuroblastoma cell lines by inducing G1 arrest. Metabolomic profiling reveals that GLDC knockdown disrupts purine and central carbon metabolism and reduces citrate production, leading to a decrease in the steady-state levels of cholesterol and fatty acids. Moreover, blocking purine or cholesterol synthesis recapitulates the growth-inhibitory effect of GLDC knockdown. These findings reveal a critical role of GLDC in sustaining the proliferation of neuroblastoma cells with high-level GLDC expression and suggest that MYCN amplification is a biomarker for GLDC-based therapeutic strategies against high-risk neuroblastoma.
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http://dx.doi.org/10.1038/s41388-019-0967-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6908766PMC
December 2019

MYC deregulates TET1 and TET2 expression to control global DNA (hydroxy)methylation and gene expression to maintain a neoplastic phenotype in T-ALL.

Epigenetics Chromatin 2019 07 2;12(1):41. Epub 2019 Jul 2.

Department of Biochemistry and Molecular Biology, Augusta University, 1410 Laney-Walker Blvd., Augusta, GA, 30912, USA.

Background: While aberrant DNA methylation is a characteristic feature of tumor cells, our knowledge of how these DNA methylation patterns are established and maintained is limited. DNA methyltransferases and ten-eleven translocation methylcytosine dioxygenases (TETs) function has been found altered in a variety of cancer types.

Results: Here, we report that in T cell acute lymphoblastic leukemia (T-ALL) the MYC oncogene controls the expression of TET1 and TET2 to maintain 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) patterns, which is associated with tumor cell-specific gene expression. We found that cellular senescence and tumor regression upon MYC inactivation in T-ALL was associated with genome-wide changes in 5mC and 5hmC patterns. Correlating with the changes in DNA (hydroxy)methylation, we found that T-ALL overexpress TET1, while suppressing TET2 in a MYC-dependent fashion. Consequently, MYC inactivation led to an inverse expression pattern, decreasing TET1, while increasing TET2 levels. Knockdown of TET1 or ectopic expression of TET2 in T-ALL was associated with genome-wide changes in 5mC and 5hmC enrichment and decreased cell proliferation, suggesting a tumor promoting function of TET1, and a tumor suppressing role for TET2. Among the genes and pathways controlled by TET1, we found ribosomal biogenesis and translational control of protein synthesis highly enriched.

Conclusions: Our finding that MYC directly deregulates the expression of TET1 and TET2 in T-ALL provides novel evidence that MYC controls DNA (hydroxy)methylation in a genome-wide fashion. It reveals a coordinated interplay between the components of the DNA (de)methylating machinery that contribute to MYC-driven tumor maintenance, highlighting the potential of specific TET enzymes for therapeutic strategies.
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http://dx.doi.org/10.1186/s13072-019-0278-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6604319PMC
July 2019

Indispensable role of the Ubiquitin-fold modifier 1-specific E3 ligase in maintaining intestinal homeostasis and controlling gut inflammation.

Cell Discov 2019 29;5. Epub 2019 Jan 29.

2Department of Biochemistry & Molecular Biology, Georgia Cancer Center, Medical College of Georgia, Augusta University, Augusta, GA 30912 USA.

Intestinal exocrine secretory cells, including Paneth and goblet cells, have a pivotal role in intestinal barrier function and mucosal immunity. Dysfunction of these cells may lead to the pathogenesis of human diseases such as inflammatory bowel disease (IBD). Therefore, identification and elucidation of key molecular mechanisms that regulate the development and function of these exocrine cells would be crucial for understanding of disease pathogenesis and discovery of new therapeutic targets. The Ufm1 conjugation system is a novel ubiquitin-like modification system that consists of Ufm1 (Ubiquitin modifier 1), Uba5 (Ufm1-activating enzyme, E1), Ufc1 (Ufm1-conjugating enzyme, E2) and poorly characterized Ufm1 E3 ligase(s). Recent mouse genetic studies have demonstrated its indispensable role in embryonic development and hematopoiesis. Yet its role in other tissues and organs remains poorly defined. In this study, we found that both Ufl1 and Ufbp1, two key components of the Ufm1 E3 ligase, were highly expressed in the intestinal exocrine cells. Ablation of either Ufl1 and Ufbp1 led to significant loss of both Paneth and goblet cells, which in turn resulted in dysbiotic microbiota and increased susceptibility to experimentally induced colitis. At the cellular and molecular levels, deficiency caused elevation of endoplasmic reticulum stress and activation of the Unfolded Protein Response (UPR) and cell death program. Administration of small molecular chaperone partially prevented loss of Paneth cells caused by acute Ufbp1 deletion. Taken together, our results have provided unambiguous evidence for the crucial role of the Ufm1 E3 ligase in maintenance of intestinal homeostasis and protection from inflammatory diseases.
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http://dx.doi.org/10.1038/s41421-018-0070-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6349939PMC
January 2019

Targeting the MYC Oncogene in Burkitt Lymphoma through HSP90 Inhibition.

Cancers (Basel) 2018 Nov 16;10(11). Epub 2018 Nov 16.

Department of Biochemistry and Molecular Biology, Augusta University, 1410 Laney-Walker Blvd., Augusta, GA 30912, USA.

Overexpression of the MYC oncogene is a key feature of many human malignancies including Burkitt lymphoma. While MYC is widely regarded to be a promising therapeutic target, a clinically effective MYC inhibitor is still elusive. Here, we report an alternative strategy, targeting MYC indirectly through inhibition of the HSP90 machinery. We found that inhibition of HSP90 function reduces MYC expression in human Burkitt lymphoma through suppression of MYC transcription and destabilization of MYC protein, thereby diminishing the proliferation of tumor cells. Consistently, treatment of Burkitt lymphoma cell lines with HSP90 inhibitors (17-AAG or 17-DMAG) was accompanied by downregulation of canonical MYC target genes. Combination treatment with 17-DMAG and the proteasome inhibitor, MG-132, led to accumulation of MYC protein, indicating that upon HSP90 inhibition, MYC is degraded by the proteasome. Using co-immunoprecipitation, we furthermore demonstrated a direct interaction between MYC and HSP90, indicating that MYC is an HSP90 client protein in Burkitt lymphoma. Together, we report here the use of HSP90 inhibitors as an alternative approach to target the MYC oncogene and its network in Burkitt lymphoma.
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http://dx.doi.org/10.3390/cancers10110448DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6266960PMC
November 2018

FGFR1 fusion kinase regulation of MYC expression drives development of stem cell leukemia/lymphoma syndrome.

Leukemia 2018 11 2;32(11):2363-2373. Epub 2018 Apr 2.

Georgia Cancer Center, Augusta University, Augusta, GA, 30912, USA.

Oncogenic transformation of hematopoietic stem cells by chimeric fusion kinases causing constitutive activation of FGFR1 leads to a stem cell leukemia/lymphoma (SCLL) syndrome, accompanied by widespread dysregulation of gene activity. We now show that FGFR1 activation is associated with upregulation of MYC and pharmacological suppression of FGFR1 activation leads to downregulation of MYC and suppression of MYC target genes. Luciferase reporter assays demonstrate that FGFR1 can directly regulate MYC expression and this effect is enhanced in the presence of chimeric FGFR1 kinases. In SCLL cells, a truncated form of FGFR1 is generated by granzyme B cleavage of the chimeric kinases, producing a nucleus-restricted derivative that can bind MYC regulatory regions. Mutation of the granzyme B cleavage site prevents relocation to the nucleus but does not suppress MYC activation, suggesting additional mechanisms of MYC activation in the presence of cytoplasm-restricted chimeric kinases. We show that one of these mechanisms involves activating cytoplasmic STAT5, which upregulates MYC independent of the truncated FGFR1 kinase. Targeting MYC function using shRNA knockdown and 10054-F8 in SCLL cells leads to inhibition of cell proliferation and synergizes with the BGJ398 FGFR1 inhibitor, suggesting a combination therapy that could be used in the treatment of SCLL.
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http://dx.doi.org/10.1038/s41375-018-0124-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6168426PMC
November 2018

DNMT3B overexpression contributes to aberrant DNA methylation and MYC-driven tumor maintenance in T-ALL and Burkitt's lymphoma.

Oncotarget 2017 Sep 10;8(44):76898-76920. Epub 2017 Aug 10.

Augusta University, Department of Biochemistry and Molecular Biology, Augusta, GA 30912, USA.

Aberrant DNA methylation is a hallmark of cancer. However, our understanding of how tumor cell-specific DNA methylation patterns are established and maintained is limited. Here, we report that in T-cell acute lymphoblastic leukemia (T-ALL) and Burkitt's lymphoma the oncogene causes overexpression of DNA methyltransferase (DNMT) 1 and 3B, which contributes to tumor maintenance. By utilizing a tetracycline-regulated transgene in a mouse T-ALL (EμSRα-tTA;tet-o-MYC) and human Burkitt's lymphoma (P493-6) model, we demonstrated that DNMT1 and DNMT3B expression depend on high MYC levels, and that their transcription decreased upon MYC-inactivation. Chromatin immunoprecipitation indicated that MYC binds to the and promoters, implicating a direct transcriptional regulation. Hence, shRNA-mediated knock-down of endogenous MYC in human T-ALL and Burkitt's lymphoma cell lines downregulated DNMT3B expression. Knock-down and pharmacologic inhibition of DNMT3B in T-ALL reduced cell proliferation associated with genome-wide changes in DNA methylation, indicating a tumor promoter function during tumor maintenance. We provide novel evidence that MYC directly deregulates the expression of both and maintenance DNMTs, showing that MYC controls DNA methylation in a genome-wide fashion. Our finding that a coordinated interplay between the components of the DNA methylating machinery contributes to MYC-driven tumor maintenance highlights the potential of specific DNMTs for targeted therapies.
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http://dx.doi.org/10.18632/oncotarget.20176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5652751PMC
September 2017

MYC-Master Regulator of the Cancer Epigenome and Transcriptome.

Genes (Basel) 2017 May 13;8(5). Epub 2017 May 13.

Augusta University, Department of Biochemistry and Molecular Biology, 1410 Laney-Walker Blvd., Augusta, GA 30912, USA.

Overexpression of is a hallmark of many human cancers. The oncogene has long been thought to execute its neoplastic functions by acting as a classic transcription factor, deregulating the expression of a large number of specific target genes. However, MYC's influence on many of these target genes is rather modest and there is little overlap between MYC regulated genes in different cell types, leaving many mechanistic questions unanswered. Recent advances in the field challenge the dogma further, revealing a role for MYC that extends beyond the traditional concept of a sequence-specific transcription factor. In this article, we review MYC's function as a regulator of the cancer epigenome and transcriptome. We outline our current understanding of how MYC regulates chromatin structure in both a site-specific and genome-wide fashion, and highlight the implications for therapeutic strategies for cancers with high MYC expression.
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http://dx.doi.org/10.3390/genes8050142DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5448016PMC
May 2017

p19ARF is a critical mediator of both cellular senescence and an innate immune response associated with MYC inactivation in mouse model of acute leukemia.

Oncotarget 2015 Feb;6(6):3563-77

Division of Oncology, Departments of Medicine and Pathology, Molecular Imaging Program, Stanford University, Stanford, California, United States of America.

MYC-induced T-ALL exhibit oncogene addiction. Addiction to MYC is a consequence of both cell-autonomous mechanisms, such as proliferative arrest, cellular senescence, and apoptosis, as well as non-cell autonomous mechanisms, such as shutdown of angiogenesis, and recruitment of immune effectors. Here, we show, using transgenic mouse models of MYC-induced T-ALL, that the loss of either p19ARF or p53 abrogates the ability of MYC inactivation to induce sustained tumor regression. Loss of p53 or p19ARF, influenced the ability of MYC inactivation to elicit the shutdown of angiogenesis; however the loss of p19ARF, but not p53, impeded cellular senescence, as measured by SA-beta-galactosidase staining, increased expression of p16INK4A, and specific histone modifications. Moreover, comparative gene expression analysis suggested that a multitude of genes involved in the innate immune response were expressed in p19ARF wild-type, but not null, tumors upon MYC inactivation. Indeed, the loss of p19ARF, but not p53, impeded the in situ recruitment of macrophages to the tumor microenvironment. Finally, p19ARF null-associated gene signature prognosticated relapse-free survival in human patients with ALL. Therefore, p19ARF appears to be important to regulating cellular senescence and innate immune response that may contribute to the therapeutic response of ALL.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414137PMC
http://dx.doi.org/10.18632/oncotarget.2969DOI Listing
February 2015

High throughput automated chromatin immunoprecipitation as a platform for drug screening and antibody validation.

Lab Chip 2012 Jun 8;12(12):2190-8. Epub 2012 May 8.

Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.

Chromatin immunoprecipitation (ChIP) is an assay for interrogating protein-DNA interactions that is increasingly being used for drug target discovery and screening applications. Currently the complexity of the protocol and the amount of hands-on time required for this assay limits its use to low throughput applications; furthermore, variability in antibody quality poses an additional obstacle in scaling up ChIP for large scale screening purposes. To address these challenges, we report HTChIP, an automated microfluidic-based platform for performing high-throughput ChIP screening measurements of 16 different targets simultaneously, with potential for further scale-up. From chromatin to analyzable PCR results only takes one day using HTChIP, as compared to several days up to one week for conventional protocols. HTChIP can also be used to test multiple antibodies and select the best performer for downstream ChIP applications, saving time and reagent costs of unsuccessful ChIP assays as a result of poor antibody quality. We performed a series of characterization assays to demonstrate that HTChIP can rapidly and accurately evaluate the epigenetic states of a cell, and that it is sensitive enough to detect the changes in the epigenetic state induced by a cytokine stimulant over a fine temporal resolution. With these results, we believe that HTChIP can introduce large improvements in routine ChIP, antibody screening, and drug screening efficiency, and further facilitate the use of ChIP as a valuable tool for research and discovery.
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http://dx.doi.org/10.1039/c2lc21290kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4117344PMC
June 2012

Lymphomas that recur after MYC suppression continue to exhibit oncogene addiction.

Proc Natl Acad Sci U S A 2011 Oct 3;108(42):17432-7. Epub 2011 Oct 3.

Division of Oncology, Department of Medicine and Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA.

The suppression of oncogenic levels of MYC is sufficient to induce sustained tumor regression associated with proliferative arrest, differentiation, cellular senescence, and/or apoptosis, a phenomenon known as oncogene addiction. However, after prolonged inactivation of MYC in a conditional transgenic mouse model of Eμ-tTA/tetO-MYC T-cell acute lymphoblastic leukemia, some of the tumors recur, recapitulating what is frequently observed in human tumors in response to targeted therapies. Here we report that these recurring lymphomas express either transgenic or endogenous Myc, albeit in many cases at levels below those in the original tumor, suggesting that tumors continue to be addicted to MYC. Many of the recurring lymphomas (76%) harbored mutations in the tetracycline transactivator, resulting in expression of the MYC transgene even in the presence of doxycycline. Some of the remaining recurring tumors expressed high levels of endogenous Myc, which was associated with a genomic rearrangement of the endogenous Myc locus or activation of Notch1. By gene expression profiling, we confirmed that the primary and recurring tumors have highly similar transcriptomes. Importantly, shRNA-mediated suppression of the high levels of MYC in recurring tumors elicited both suppression of proliferation and increased apoptosis, confirming that these tumors remain oncogene addicted. These results suggest that tumors induced by MYC remain addicted to overexpression of this oncogene.
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http://dx.doi.org/10.1073/pnas.1107303108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198348PMC
October 2011

TGFβ-dependent gene expression shows that senescence correlates with abortive differentiation along several lineages in Myc-induced lymphomas.

Cell Cycle 2010 Dec;9(23):4622-6

Theodor Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany.

Deregulated expression of Myc under the control of an immunoglobulin enhancer induces lymphoma formation in mice. The development of lymphomas is limited by TGFβ-dependent senescence and high levels of Myc expression are continuously required to antagonize senescence. The biological processes underlying senescence are not fully resolved. We report here a comprehensive analysis of TGFβ-dependent alterations in gene expression when the Myc transgene is switched off. Our data show that Myc-induced target genes are downregulated in a TGFβ-independent manner. In contrast, TGFβ is required to upregulate a broad spectrum of genes that are characteristic of different T-cell lineages when Myc is turned off. The analysis reveals a significant overlap between these Myc-repressed genes with genes that are targets of polycomb repressive complexes in embryonic stem cells. Therefore, TGFβ-dependent senescence is associated with gene expression patterns indicative of abortive cellular differentiation along several lineages.
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http://dx.doi.org/10.4161/cc.9.23.14211DOI Listing
December 2010

The interaction between Myc and Miz1 is required to antagonize TGFbeta-dependent autocrine signaling during lymphoma formation and maintenance.

Genes Dev 2010 Jun;24(12):1281-94

Department of Medicine, Division of Oncology, Stanford University, School of Medicine, Stanford, California 94304, USA.

The Myc protein suppresses the transcription of several cyclin-dependent kinase inhibitors (CKIs) via binding to Miz1; whether this interaction is important for Myc's ability to induce or maintain tumorigenesis is not known. Here we show that the oncogenic potential of a point mutant of Myc (MycV394D) that is selectively deficient in binding to Miz1 is greatly attenuated. Binding of Myc to Miz1 is continuously required to repress CKI expression and inhibit accumulation of trimethylated histone H3 at Lys 9 (H3K9triMe), a hallmark of cellular senescence, in T-cell lymphomas. Lymphomas that arise express high amounts of transforming growth factor beta-2 (TGFbeta-2) and TGFbeta-3. Upon Myc suppression, TGFbeta signaling is required to induce CKI expression and cellular senescence and suppress tumor recurrence. Binding of Myc to Miz1 is required to antagonize growth suppression and induction of senescence by TGFbeta. We demonstrate that, since lymphomas express high levels of TGFbeta, they are poised to elicit an autocrine program of senescence upon Myc inactivation, demonstrating that TGFbeta is a key factor that establishes oncogene addiction of T-cell lymphomas.
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http://dx.doi.org/10.1101/gad.585710DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885663PMC
June 2010

MYC as a regulator of ribosome biogenesis and protein synthesis.

Nat Rev Cancer 2010 Apr;10(4):301-9

Division of Oncology, Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.

MYC regulates the transcription of thousands of genes required to coordinate a range of cellular processes, including those essential for proliferation, growth, differentiation, apoptosis and self-renewal. Recently, MYC has also been shown to serve as a direct regulator of ribosome biogenesis. MYC coordinates protein synthesis through the transcriptional control of RNA and protein components of ribosomes, and of gene products required for the processing of ribosomal RNA, the nuclear export of ribosomal subunits and the initiation of mRNA translation. We discuss how the modulation of ribosome biogenesis by MYC may be essential to its physiological functions as well as its pathological role in tumorigenesis.
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http://dx.doi.org/10.1038/nrc2819DOI Listing
April 2010

Myc and a Cdk2 senescence switch.

Nat Cell Biol 2010 Jan;12(1):7-9

Cdk2 has been shown to have an unanticipated role in suppressing Myc-induced senescence. This has implications for how c-Myc overcomes failsafe mechanisms to induce tumorigenesis and suggests that the inhibition of Cdk2 may have therapeutic efficacy in the treatment of cancer.
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http://dx.doi.org/10.1038/ncb0110-7DOI Listing
January 2010

Cellular senescence is an important mechanism of tumor regression upon c-Myc inactivation.

Proc Natl Acad Sci U S A 2007 Aug 30;104(32):13028-33. Epub 2007 Jul 30.

Department of Medicine, Division of Oncology, Stanford University School of Medicine, CA 94305, USA.

Oncogene-induced senescence is an important mechanism by which normal cells are restrained from malignant transformation. Here we report that the suppression of the c-Myc (MYC) oncogene induces cellular senescence in diverse tumor types including lymphoma, osteosarcoma, and hepatocellular carcinoma. MYC inactivation was associated with prototypical markers of senescence, including acidic beta-gal staining, induction of p16INK4a, and p15INK4b expression. Moreover, MYC inactivation induced global changes in chromatin structure associated with the marked reduction of histone H4 acetylation and increased histone H3 K9 methylation. Osteosarcomas engineered to be deficient in p16INK4a or Rb exhibited impaired senescence and failed to exhibit sustained tumor regression upon MYC inactivation. Similarly, only after lymphomas were repaired for p53 expression did MYC inactivation induce robust senescence and sustained tumor regression. The pharmacologic inhibition of signaling pathways implicated in oncogene-induced senescence including ATM/ATR and MAPK did not prevent senescence associated with MYC inactivation. Our results suggest that cellular senescence programs remain latently functional, even in established tumors, and can become reactivated, serving as a critical mechanism of oncogene addiction associated with MYC inactivation.
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http://dx.doi.org/10.1073/pnas.0701953104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1941831PMC
August 2007

Sustained regression of tumors upon MYC inactivation requires p53 or thrombospondin-1 to reverse the angiogenic switch.

Proc Natl Acad Sci U S A 2006 Oct 20;103(44):16266-71. Epub 2006 Oct 20.

Departments of Medicine and Pathology, Division of Oncology, Stanford University School of Medicine, CCSR Building, Room 1120, 269 Campus Drive, Stanford, CA 94305-5151, USA.

The targeted inactivation of oncogenes offers a rational therapeutic approach for the treatment of cancer. However, the therapeutic inactivation of a single oncogene has been associated with tumor recurrence. Therefore, it is necessary to develop strategies to override mechanisms of tumor escape from oncogene dependence. We report here that the targeted inactivation of MYC is sufficient to induce sustained regression of hematopoietic tumors in transgenic mice, except in tumors that had lost p53 function. p53 negative tumors were unable to be completely eliminated, as demonstrated by the kinetics of tumor cell elimination revealed by bioluminescence imaging. Histological examination revealed that upon MYC inactivation, the loss of p53 led to a deficiency in thrombospondin-1 (TSP-1) expression, a potent antiangiogenic protein, and the subsequent inability to shut off angiogenesis. Restoration of p53 expression in these tumors re-established TSP-1 expression. This permitted the suppression of angiogenesis and subsequent sustained tumor regression upon MYC inactivation. Similarly, the restoration of TSP-1 alone in p53 negative tumors resulted in the shut down of angiogenesis and led to sustained tumor regression upon MYC inactivation. Hence, the complete regression of tumor mass driven by inactivation of the MYC oncogene requires the p53-dependent induction of TSP-1 and the shut down of angiogenesis. Notably, overexpression of TSP-1 alone did not influence tumor growth. Therefore, the combined inactivation of oncogenes and angiogenesis may be a more clinically effective treatment of cancer. We conclude that angiogenesis is an essential component of oncogene addiction.
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http://dx.doi.org/10.1073/pnas.0608017103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637571PMC
October 2006

Loss of net as repressor leads to constitutive increased c-fos transcription in cervical cancer cells.

J Biol Chem 2005 Feb 16;280(5):3286-94. Epub 2004 Nov 16.

Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 242, 69120 Heidelberg, Germany.

We have investigated the expression of c-fos in cervical carcinoma cells and in somatic cell hybrids derived therefrom. In malignant cells, c-fos was constitutively expressed even after serum starvation. Dissection of the c-fos promoter showed that expression was mainly controlled by the SRE motif, which was active in malignant cells, but repressed in their non-malignant counterparts. Constitutive SRE activity was not mediated by sustained mitogen-activated protein kinase activity but because of inefficient expression of the ternary complex factor Net, which was either very low or even barely discernible. Chromatin immunoprecipitation assays revealed that Net directly binds to the SRE nucleoprotein complex in non-tumorigenic cells, but not in malignant segregants. Small interfering RNA targeted against Net resulted in enhanced c-fos transcription, clearly illustrating its repressor function. Conversely, stable ectopic expression of Net in malignant cells negatively regulated endogenous c-fos, resulting in a disappearance of the c-Fos protein from the AP-1 transcription complex. These data indicate that loss of Net and constitutive c-fos expression appear to be a key event in the transformation of cervical cancer cells.
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http://dx.doi.org/10.1074/jbc.M409915200DOI Listing
February 2005

Ectopic expression of nonliganded retinoic acid receptor beta abrogates AP-1 activity by selective degradation of c-Jun in cervical carcinoma cells.

J Biol Chem 2004 Oct 11;279(44):45408-16. Epub 2004 Aug 11.

Angewandte Tumorvirologie, Abteilung Virale Transformationsmechanismen, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 242, 69120 Heidelberg, Germany.

Expression of the nuclear retinoic acid receptor beta2 (RARbeta2) gene is often disturbed in cervical carcinoma cells. One important mechanism by which RARbeta2 can exert growth inhibitory function is based on its ability to repress the AP-1 transcription factor in a ligand-dependent manner. Because less is known about the biological effects of RARbeta in the absence of ligand, the corresponding cDNA was stably introduced into HPV18-positive HeLa cervical carcinoma cells. In the present study we describe a novel mechanism by which AP-1 becomes inactivated. Constitutive expression of nonliganded RARbeta abrogated both AP-1 binding affinity and activity by a selective degradation of the c-Jun protein as major dimerization partner, without substitution by other members of the Jun family. Blockage of the proteasomal pathway completely rescued c-Jun and reconstituted the AP-1 function. Moreover, HeLa RARbeta2 clones treated either with tumor necrosis factor-alpha or transfected with a constitutive active upstream mitogen-activated protein kinase (MEKK1Delta) also resulted in c-Jun phosphorylation and restoration of AP-1 affinity and functionality similar to that found in nontransfected parental HeLa cells. These data revealed an important cross-talk between trans-repression of AP-1 and nonliganded RARbeta in human papillomavirus-positive cells. Because AP-1 activity was not irreversibly disturbed, but could be switched on through activation of the Jun N-terminal kinase pathway, a model for the transient activation of AP-1 even in the presence of RARbeta as repressor is suggested.
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http://dx.doi.org/10.1074/jbc.M401818200DOI Listing
October 2004

Disturbance of tumor necrosis factor alpha-mediated beta interferon signaling in cervical carcinoma cells.

J Virol 2002 Jan;76(1):280-91

Forschungsschwerpunkt Angewandte Tumorvirologie, Abteilung Tumorvirus-Immunologie, Deutsches Krebsforschungszentrum, Heidelberg, Federal Republic of Germany.

In the present study we show that malignant human papillomavirus (HPV)-positive cells lost their ability to synthesize endogenous beta interferon (IFN-beta) upon tumor necrosis factor alpha (TNF-alpha) treatment. IFN-beta transcription, however, was reinducible in nonmalignant HPV-positive cells, which was confirmed in functional protection assays against encephalomyocarditis virus or vesicular stomatitis virus infections. Addition of neutralizing antibodies against IFN-beta blocked the antiviral effect, excluding the possibility that other IFN types were involved. Conversely, both malignant and immortalized cells could be protected against viral cytolysis when either IFN-beta, IFN-alpha, or IFN-gamma was added exogenously. This indicates that only the cross talk between TNF-alpha and the IFN-beta pathways, and not IFN-alpha/beta and IFN-gamma signaling in general, is perturbed in cervical carcinoma cells. Notably, full virus protection was restricted exclusively to nonmalignant cells, indicating that the antiviral effect correlates with the growth-inhibitory and virus-suppressive properties of TNF-alpha. The IFN-regulatory factors IRF-1 and p48 (ISGF3gamma) emerged as key regulatory molecules in the differential IFN-beta response, since their transcription was either absent or only inefficiently enhanced in tumorigenic cells upon treatment with TNF-alpha. Inducibility of both genes, however, became reestablished in cervical carcinoma cells, which were complemented to nontumorigenicity after somatic cell hybridization. Complementation was paralleled by the entire reconstitution of cytokine-mediated IFN-beta expression and the ability of TNF-alpha to exert an antiviral state. In contrast, under conditions where tumor suppression was not accomplished upon somatic cell hybridization, neither expression of IRF-1, p48, and IFN-beta nor antiviral activity could be restored.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC135709PMC
http://dx.doi.org/10.1128/jvi.76.1.280-291.2002DOI Listing
January 2002
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