Publications by authors named "Christoforos Giatzakis"

15 Publications

  • Page 1 of 1

Mutation Spectrum of the Gene in a Greek Cohort with Stargardt Disease: Identification of Novel Mutations and Evidence of Three Prevalent Mutated Alleles.

J Ophthalmol 2018 30;2018:5706142. Epub 2018 Apr 30.

Department of Ophthalmology, University of Crete School of Medicine, Heraklion, Greece.

Aim: To evaluate the frequency and pattern of disease-associated mutations of gene among Greek patients with presumed Stargardt disease (STGD1).

Materials And Methods: A total of 59 patients were analyzed for mutations using the ABCR400 microarray and PCR-based sequencing of all coding exons and flanking intronic regions. MLPA analysis as well as sequencing of two regions in introns 30 and 36 reported earlier to harbor deep intronic disease-associated variants was used in 4 selected cases.

Results: An overall detection rate of at least one mutant allele was achieved in 52 of the 59 patients (88.1%). Direct sequencing improved significantly the complete characterization rate, that is, identification of two mutations compared to the microarray analysis (93.1% versus 50%). In total, 40 distinct potentially disease-causing variants of the gene were detected, including six previously unreported potentially pathogenic variants. Among the disease-causing variants, in this cohort, the most frequent was c.5714+5G>A representing 16.1%, while p.Gly1961Glu and p.Leu541Pro represented 15.2% and 8.5%, respectively.

Conclusions: By using a combination of methods, we completely molecularly diagnosed 48 of the 59 patients studied. In addition, we identified six previously unreported, potentially pathogenic mutations.
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http://dx.doi.org/10.1155/2018/5706142DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952432PMC
April 2018

Does somatostatin have a role in the regulation of cortisol secretion in primary pigmented nodular adrenocortical disease (ppnad)? a clinical and in vitro investigation.

J Clin Endocrinol Metab 2014 May 10;99(5):E891-901. Epub 2014 Feb 10.

INSERM Unité 982 (Z.B., E.L., H.L.), Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, Institute for Research and Innovation in Biomedicine, University of Rouen, 76821 Rouen, France; Section on Endocrinology and Genetics (P.X., D.A., C.G., M.N., R.C., C.A.S.), Program on Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Pediatric Endocrinology Inter-Institute Training Program (M.F.K., C.A.S.), National Institute of Child Health and Human Development, National Institutes of Health, and Clinical Center (N.S.), National Institutes of Health, Bethesda, Maryland 20892; Erasmus Medical Center (L.J.H.), 3015 GE Rotterdam, The Netherlands; and Department of Endocrinology (H.L.), Institute for Research and Innovation in Biomedicine, University Hospital of Rouen, 76031 Rouen, France.

Context: Somatostatin (SST) receptors (SSTRs) are expressed in a number of tissues, including the adrenal cortex, but their role in cortisol secretion has not been well characterized.

Objectives: The objective of the study was to investigate the expression of SSTRs in the adrenal cortex and cultured adrenocortical cells from primary pigmented nodular adrenocortical disease (PPNAD) tissues and to test the effect of a single injection of 100 μg of the SST analog octreotide on cortisol secretion in patients with PPNAD.

Setting And Design: The study was conducted at an academic research laboratory and clinical research center. Expression of SSTRs was examined in 26 PPNAD tissues and the immortalized PPNAD cell line CAR47. Ten subjects with PPNAD underwent a randomized, single-blind, crossover study of their cortisol secretion every 30 minutes over 12 hours (6:00 pm to 6:00 am) before and after the midnight administration of octreotide 100 μg sc.

Methods: SSTRs expression was investigated by quantitative PCR and immunohistochemistry. The CAR47 and primary cell lines were studied in vitro. The data of the 10 patients were analyzed before and after the administration of octreotide.

Results: All SSTRs, especially SSTR1-3, were expressed in PPNAD at significantly higher levels than in normal adrenal. SST was found to differentially regulate expression of its own receptors in the CAR47 cell line. However, the administration of octreotide to patients with PPNAD did not significantly affect cortisol secretion.

Conclusions: SSTRs are overexpressed in PPNAD tissues in comparison with normal adrenal cortex. Octreotide did not exert any significant effect on cortisol secretion in a short clinical pilot study in a small number of patients with PPNAD, but long-acting SST analogs targeting multiple SSTRs may be worth investigating in this condition.
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http://dx.doi.org/10.1210/jc.2013-2657DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4010701PMC
May 2014

Identification of two novel mutations in the RET proto-oncogene in the same family.

Thyroid 2010 Apr;20(4):401-6

Department of Endocrinology-Endocrine Oncology, Theagenio Cancer Hospital , Thessaloniki, Greece.

Background: Activating germline mutations of the RET gene cause multiple endocrine neoplasia type 2 and familial medullary thyroid carcinoma (FMTC), conditions that are inherited in an autosomal dominant manner. In addition, somatic RET mutations have been identified in a variable proportion (about 30-70%) of sporadic (nonfamilial) MTC cases.

Methods: We describe a Greek family with two novel likely pathogenic sequence variants of the RET gene. The first is a C to T transition at position 2458 (c.2458C>T) that causes an arginine to cysteine substitution (p.R820C) in exon 14 in the intracellular region of the kinase. This sequence variant was identified in an apparently healthy woman who had a recently deceased sister with confirmed aggressive MTC (age of onset 37 years). To assess the pathogenicity of this novel missense sequence variant, screening was performed on all available relatives: her two sons, the mother, and a second sister, including an MTC tumor sample from the deceased sister of the proband. At the time of the investigation, no clinical symptoms suggestive of multiple endocrine neoplasia type 2 or MTC were present in any of the individuals screened.

Results: The c.2458C>T transition was found in one son, the living sister, and the mother. Interestingly, it was not present in the tumor sample from the deceased sister. Instead, an in-frame deletion of 54 nt in exon 10 resulting in a protein missing 18 amino acids from I590 to G608 (c.1766_1819del 54) was found. Both genetic alterations were present in heterozygous state.

Conclusions: These data suggest that the novel in-frame deletion was the disease-causing mutation in the deceased sister. The effect of the 2458C>T mutation on the activity of the kinase is under investigation.
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http://dx.doi.org/10.1089/thy.2009.0262DOI Listing
April 2010

A novel germline mutation of the VHL gene in a Greek family with Von Hippel-Lindau disease.

BMJ Case Rep 2009 19;2009. Epub 2009 Aug 19.

Endocrine Unit, Second Department of Internal Medicne-Propaedeutic, Research Institute and Diabetes Center, Athens University Medical School, Attikon University Hospital, 1 Rimini Street, Athens, Greece.

Von Hippel-Lindau disease (VHL) is an autosomal dominant disorder, caused by mutations of the VHL gene showing a strong genotype-phenotype correlation. The present report concerns a 16-year-old girl with VHL (retinal, spinal cord and cerebellar haemangioblastomas and pancreatic cysts), her father (retinal and spinal cord haemangioblastomas) and the phenotypically healthy mother and younger brother and sister. DNA extraction, PCR and direct sequencing of the VHL entire coding and intronic flanking sequences, were performed according to standard procedures. In the index patient and her father a novel heterozygous germline was identified; nonsense mutation (p.145X) in exon 2 of VHL, leading to a truncated VHL protein lacking the last 66 amino acids. This is the first report of a novel VHL mutation in patients with VHL associated with haemangioblastomas and pancreatic cysts but not renal cell carcinoma.
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http://dx.doi.org/10.1136/bcr.02.2009.1574DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3029452PMC
November 2011

Phorbol-12-myristate 13-acetate acting through protein kinase Cepsilon induces translocator protein (18-kDa) TSPO gene expression.

Biochemistry 2008 Dec;47(48):12886-99

Department of Biochemistry & Molecular and Cell Biology, Georgetown University Medical Center, Washington, DC 20057, USA.

Translocator protein (TSPO) is an 18-kDa cholesterol-binding protein that is expressed at high levels in steroid synthesizing and several cancer cells where it is involved in steroidogenesis and cell proliferation, respectively. The factors regulating Tspo expression are unknown. We analyzed Tspo transcriptional responses to the tumor promoter, phorbol-12-myristate 13-acetate (PMA), in cells with varying TSPO levels. PMA induced Tspo promoter activity and Tspo mRNA levels in TSPO-poor nonsteroidogenic cells (NIH-3T3 fibroblasts and COS-7 kidney) but not in TSPO-rich steroidogenic cells (MA-10 Leydig) with high basal Tspo transcriptional activity. The stimulatory effect of PMA was mediated by an 805-515-bp region upstream of the transcription start site. Electrophoretic mobility shift assay (EMSA) revealed that PMA induced binding of c-jun and GA-binding protein transcription factor (GABP-alpha) to their respective activator protein 1 (AP1) and v-ets erythroblastosis virus E26 oncogene homologue (Ets) sites in this region. Protein kinase C (PKC)-specific inhibitors blocked PMA induction of Tspo promoter activity with an inhibition profile suggestive of involvement of PKCepsilon. PKCepsilon expression correlated with TSPO content in the three cell lines. In NIH-3T3 cells, PKCepsilon overexpression induced Tspo promoter activity and mRNA levels and enhanced PMA-induced up regulation of c-jun and TSPO. In MA-10 cells, a PKCepsilon-specific translocation inhibitor peptide reduced basal Tspo promoter activity. PKCepsilon siRNA pool reduced PKCepsilon and TSPO levels in MA-10 cells indicating a role for PKCepsilon in regulating TSPO expression. Taken together, these data suggest that elevated TSPO expression in steroidogenic cells may be due to high constitutive expression of PKCepsilon that renders them unresponsive to further induction while PMA activation of PKCepsilon drives inducible TSPO expression in nonsteroidogenic cells, likely through AP1 and Ets.
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http://dx.doi.org/10.1021/bi8012643DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2645926PMC
December 2008

A cAMP-specific phosphodiesterase (PDE8B) that is mutated in adrenal hyperplasia is expressed widely in human and mouse tissues: a novel PDE8B isoform in human adrenal cortex.

Eur J Hum Genet 2008 Oct 23;16(10):1245-53. Epub 2008 Apr 23.

Section on Endocrinology & Genetics, Program on Developmental Endocrinology & Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.

Bilateral adrenocortical hyperplasia (BAH) is the second most common cause of corticotropin-independent Cushing syndrome (CS). Genetic forms of BAH have been associated with complex syndromes such as Carney Complex and McCune-Albright syndrome or may present as isolated micronodular adrenocortical disease (iMAD) usually in children and young adults with CS. A genome-wide association study identified inactivating phosphodiesterase (PDE) 11A (PDE11A)-sequencing defects as low-penetrance predisposing factors for iMAD and related abnormalities; we also described a mutation (c.914A > C/H305P) in cyclic AMP (cAMP)-specific PDE8B, in a patient with iMAD. In this study we further characterize this mutation; we also found a novel PDE8B isoform that is highly expressed in the adrenal gland. This mutation is shown to significantly affect the ability of the protein to degrade cAMP in vitro. Tumor tissues from patients with iMAD and no mutations in the coding PDE8B sequence or any other related genes (PRKAR1A, PDE11A) showed downregulated PDE8B expression (compared to normal adrenal cortex). Pde8b is detectable in the adrenal gland of newborn mice and is widely expressed in other mouse tissues. We conclude that PDE8B is another PDE gene linked to iMAD; it is a candidate causative gene for other adrenocortical lesions linked to the cAMP signaling pathway and possibly for tumors in other tissues.
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http://dx.doi.org/10.1038/ejhg.2008.85DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2671148PMC
October 2008

In vitro functional studies of naturally occurring pathogenic PRKAR1A mutations that are not subject to nonsense mRNA decay.

Hum Mutat 2008 May;29(5):633-9

Section on Endocrinology & Genetics, Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.

Patients presenting with primary pigmented nodular adrenocortical disease (PPNAD), Carney complex (CNC), or sporadic tumors were previously found to carry germline mutations in the human type Ialpha regulatory subunit (RIalpha) of adenosine 3',5'-cyclic monophosphate (cyclic AMP [cAMP])-dependent protein kinase (PKA; PRKAR1A). Although about 90% of disease-causing PRKAR1A mutations lead to premature stop codon generation and subsequent degradation of the mutant message by nonsense-mediated mRNA decay (NMD), here we describe seven PRKAR1A mutations whose mRNAs do not seem to undergo NMD and instead result in an expressed mutant RIalpha protein. The expressed mutations (p.Ser9Asn, p.Glu60_Lys116del [Delta-exon 3], p.Arg74Cys, p.Arg146Ser, p.Asp183Tyr, p.Ala213Asp, and p.Gly289Trp) were spread over all the functional RIalpha domains, and all of them exhibited increased PKA activity, which we attribute to decreased binding to cAMP and/or the catalytic subunit. Our data further corroborate the previous finding that altered PRKAR1A function, not only haploinsufficiency, is enough to elevate PKA activity which is apparently associated with tumorigenesis in tissues affected by CNC. In some cases, as with the Delta-exon 3 mutation, we may even conclude that the presence of a mutant PRKAR1A protein may be more harmful than allelic loss.
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http://dx.doi.org/10.1002/humu.20688DOI Listing
May 2008

Large deletions of the PRKAR1A gene in Carney complex.

Clin Cancer Res 2008 Jan;14(2):388-95

Section on Endocrinology and Genetics and Pediatric Endocrinology Training Program, Developmental Endocrinology Branch, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA.

Purpose: Since the identification of PRKAR1A mutations in Carney complex, substitutions and small insertions/deletions have been found in approximately 70% of the patients. To date, no germ-line PRKAR1A deletion and/or insertion exceeded a few base pairs (up to 15). Although a few families map to chromosome 2, it is possible that current sequencing techniques do not detect larger gene changes in PRKAR1A -- mutation-negative individuals with Carney complex.

Experimental Design: To screen for gross alterations of the PRKAR1A gene, we applied Southern hybridization analysis on 36 unrelated Carney complex patients who did not have small intragenic mutations or large aberrations in PRKAR1A, including the probands from two kindreds mapping to chromosome 2.

Results: We found large PRKAR1A deletions in the germ-line of two patients with Carney complex, both sporadic cases; no changes were identified in the remaining patients, including the two chromosome-2-mapping families. In the first patient, the deletion is expected to lead to decreased PRKAR1A mRNA levels but no other effects on the protein; the molecular phenotype is predicted to be PRKAR1A haploinsufficiency, consistent with the majority of PRKAR1A mutations causing Carney complex. In the second patient, the deletion led to in-frame elimination of exon 3 and the expression of a shorter protein, lacking the primary site for interaction with the catalytic protein kinase A subunit. In vitro transfection studies of the mutant PRKAR1A showed impaired ability to bind cyclic AMP and activation of the protein kinase A enzyme. The patient bearing this mutation had a more-severe-than-average Carney complex phenotype that included the relatively rare psammomatous melanotic schwannoma.

Conclusions: Large PRKAR1A deletions may be responsible for Carney complex in patients that do not have PRKAR1A gene defects identifiable by sequencing. Preliminary data indicate that these patients may have a different phenotype especially if their defect results in an expressed, abnormal version of the PRKAR1A protein.
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http://dx.doi.org/10.1158/1078-0432.CCR-07-1155DOI Listing
January 2008

The role of Ets transcription factors in the basal transcription of the translocator protein (18 kDa).

Biochemistry 2007 Apr 3;46(16):4763-74. Epub 2007 Apr 3.

Department of Biochemistry and Molecular and Cellular Biology, Georgetown University Medical Center, 3900 Reservoir Road NW, Washington, DC 20057, USA.

The translocator protein (18 kDa; TSPO), previously known as peripheral-type benzodiazepine receptor, is a high-affinity cholesterol- and drug-binding mitochondrial protein involved in various cell functions including steroidogenesis, apoptosis, and proliferation. TSPO is highly expressed in secretory and glandular tissues, especially in steroidogenic cells, and its expression is altered in certain pathological conditions such as cancer and neurological diseases. In this study, we characterized the regulatory elements present in the region of the TPSO promoter extending from 515 to 805 bp upstream of the transcription start site, an area previously identified as being important for transcription. Promoter fragments extending 2.7 kb and 805 bp upstream of the transcription start site were able to direct enhanced green fluorescent protein expression to Leydig cells of the testis, theca cells of the ovary, and cells of the adrenal cortex in transgenic animals. This expression pattern perfectly mimicked endogenous TSPO expression. Functional characterization of the 515-805 bp region revealed the presence of one specificity protein 1/specificity protein 3 (Sp1/Sp3) and two v-ets erythroblastosis virus E26 oncogene homologue (Ets) binding sites that are important for transcriptional activity in both MA-10 mouse Leydig tumor cells and NIH/3T3 whole mouse embryo fibroblasts. GA-binding protein alpha (GABPalpha), a member of the Ets family of transcription factors, was found to be associated with the endogenous TSPO promoter. We conclude that Sp1/Sp3 and members of the Ets family of transcription factors bind to specific binding sites in the TSPO promoter to drive basal TSPO gene transcription.
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http://dx.doi.org/10.1021/bi062208oDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2529463PMC
April 2007

Adrenal hyperplasia and adenomas are associated with inhibition of phosphodiesterase 11A in carriers of PDE11A sequence variants that are frequent in the population.

Cancer Res 2006 Dec;66(24):11571-5

Section on Endocrinology and Genetics, Developmental Endocrinology Branch, National Institute of Child Health and Human Resources, NIH, Bethesda, MD 20892, USA.

Several types of adrenocortical tumors that lead to Cushing syndrome may be caused by aberrant cyclic AMP (cAMP) signaling. We recently identified patients with micronodular adrenocortical hyperplasia who were carriers of inactivating mutations in the 2q-located phosphodiesterase 11A (PDE11A) gene. We now studied the frequency of two missense substitutions, R804H and R867G, in conserved regions of the enzyme in several sets of normal controls, including 745 individuals enrolled in a longitudinal cohort study, the New York Cancer Project. In the latter, we also screened for the presence of the previously identified PDE11A nonsense mutations. R804H and R867G were frequent among patients with adrenocortical tumors; although statistical significance was not reached, these variants affected significantly enzymatic function in vitro with variable increases in cAMP and/or cyclic guanosine 3',5'-monophosphate levels in HeLa and HEK293 cells. Adrenocortical tissues carrying the R804H mutation showed 2q allelic losses and higher cyclic nucleotide levels and cAMP-responsive element binding protein phosphorylation. We conclude that missense mutations of the PDE11A gene that affect enzymatic activity in vitro are present in the general population; protein-truncating PDE11A mutations may also contribute to a predisposition to other tumors, in addition to their association with adrenocortical hyperplasia. We speculate that PDE11A genetic defects may be associated with adrenal pathology in a wider than previously suspected clinical spectrum that includes asymptomatic individuals.
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http://dx.doi.org/10.1158/0008-5472.CAN-06-2914DOI Listing
December 2006

A genome-wide scan identifies mutations in the gene encoding phosphodiesterase 11A4 (PDE11A) in individuals with adrenocortical hyperplasia.

Nat Genet 2006 Jul 11;38(7):794-800. Epub 2006 Jun 11.

Section on Endocrinology & Genetics, Developmental Endocrinology Branch, US National Institute of Child Health and Human Development, US National Institutes of Health, Bethesda, Maryland 20892, USA.

Phosphodiesterases (PDEs) regulate cyclic nucleotide levels. Increased cyclic AMP (cAMP) signaling has been associated with PRKAR1A or GNAS mutations and leads to adrenocortical tumors and Cushing syndrome. We investigated the genetic source of Cushing syndrome in individuals with adrenocortical hyperplasia that was not caused by known defects. We performed genome-wide SNP genotyping, including the adrenocortical tumor DNA. The region with the highest probability to harbor a susceptibility gene by loss of heterozygosity (LOH) and other analyses was 2q31-2q35. We identified mutations disrupting the expression of the PDE11A isoform-4 gene (PDE11A) in three kindreds. Tumor tissues showed 2q31-2q35 LOH, decreased protein expression and high cyclic nucleotide levels and cAMP-responsive element binding protein (CREB) phosphorylation. PDE11A codes for a dual-specificity PDE that is expressed in adrenal cortex and is partially inhibited by tadalafil and other PDE inhibitors; its germline inactivation is associated with adrenocortical hyperplasia, suggesting another means by which dysregulation of cAMP signaling causes endocrine tumors.
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http://dx.doi.org/10.1038/ng1809DOI Listing
July 2006

Characterization of the cholesterol recognition amino acid consensus sequence of the peripheral-type benzodiazepine receptor.

Mol Endocrinol 2005 Mar 4;19(3):588-94. Epub 2004 Nov 4.

Département de Biologie Joliot Curie/Service de Biophysique des Fonctions Membranaires and Unité de Recherche Associée Centre National de la Recherche Scientifique 2096, Gif-sur-Yvette Cedex, France.

We previously defined a cholesterol recognition/interaction amino acid consensus sequence [CRAC: L/V-X (1-5)-Y-X (1-5)-R/K] in the carboxyl terminus of the peripheral-type benzodiazepine receptor (PBR), a high-affinity drug and cholesterol-binding protein present in the outer mitochondrial membrane protein. This protein is involved in the regulation of cholesterol transport into the mitochondria, the rate-determining step in steroid biosynthesis. Reconstituted wild-type recombinant PBR into proteoliposomes demonstrated high-affinity 2-chlorophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinolinecarboxamide and cholesterol binding. In the present work, we functionally and structurally characterized this CRAC motif using reconstituted recombinant PBR and nuclear magnetic resonance. Deletion of the C-terminal domain of PBR and mutation of the highly conserved among all PBR amino acid sequences Y152 of the CRAC domain resulted in loss of the ability of mutant recPBR to bind cholesterol. Nuclear magnetic resonance analysis of a PBR C-terminal peptide (144-169) containing the CRAC domain indicated a helical conformation for the L144-S159 fragment. As a result of the side-chain distribution, a groove that could fit a cholesterol molecule is delineated, on one hand, by Y152, T148, and L144, and, on the other hand, by Y153, M149, and A145. The aromatic rings of Y152 and Y153 assigned as essential residues for cholesterol binding constitute the gate of the groove. Furthermore, the side chain of R156 may cap the groove by interacting with the sterol hydroxyl group. These results provide structural and functional evidence supporting the finding that the CRAC domain in the cytosolic carboxyl-terminal domain of PBR might be responsible for the uptake and translocation of cholesterol into the mitochondria.
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http://dx.doi.org/10.1210/me.2004-0308DOI Listing
March 2005

Differential utilization of the promoter of peripheral-type benzodiazepine receptor by steroidogenic versus nonsteroidogenic cell lines and the role of Sp1 and Sp3 in the regulation of basal activity.

Endocrinology 2004 Mar 20;145(3):1113-23. Epub 2003 Nov 20.

Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20057, USA.

The peripheral-type benzodiazepine receptor (PBR) is involved in many cellular functions, including steroidogenesis, oxidative processes, cellular proliferation, and apoptosis. Secretory and glandular tissues, especially steroid hormone-producing cells, are particularly rich in PBR. To understand the mechanisms of PBR expression and regulation, we established an mRNA expression profile in mouse tissues and cell lines and subsequently mapped the transcription start site and characterized the promoter of the gene. Our findings indicate that PBR tissue mRNA levels are relatively high in kidney, spleen, muscle, lung, adrenal gland, thymus, and stomach; are intermediate in pancreas, uterus, prostate, heart, and testis; and are low in brain and liver. Relatively high levels of PBR mRNA were also observed in the steroid-synthesizing MA-10 mouse Leydig tumor cells compared with adrenocortical Y1 mouse cells and nonsteroidogenic NIH-3T3 mouse fibroblasts, although PBR protein levels were much higher in both steroidogenic cells compared with fibroblasts. Transcription was initiated primarily at an adenine nucleotide 61 nucleotides upstream of the translation start site, but internal initiation was also observed. A 2.7-kb fragment of the mouse PBR promoter was cloned and sequenced. Sequence analysis revealed the absence of TATA or CCAAT boxes, but the presence of many putative transcription factor-binding sites, including Sp1/Sp3, AP2, Ik2, AP1, SOX, GATA, and SRY. Functional characterization revealed that two Sp1/Sp3 sites in the proximal promoter are important for basal activity in all cell lines tested and that the steroidogenic MA-10 and Y1 cells use different areas of the promoter compared with nonsteroidogenic NIH-3T3 cells.
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http://dx.doi.org/10.1210/en.2003-1330DOI Listing
March 2004

In vivo and in vitro peripheral-type benzodiazepine receptor polymerization: functional significance in drug ligand and cholesterol binding.

Biochemistry 2003 Apr;42(15):4506-19

Division of Hormone Research, Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20057, USA.

Peripheral-type benzodiazepine receptor (PBR) is an 18 kDa high-affinity drug ligand and cholesterol binding protein involved in various cell functions. Antisera for distinct PBR areas identified immunoreactive proteins of 18, 40, and 56 kDa and occasionally 72, 90, and 110 kDa in testicular Leydig and breast cancer cells. These sizes may correspond to PBR polymers and correlated to the levels of reactive oxygen species. Treatment of Leydig cells with human chorionic gonadotropin rapidly induced free radical, PBR polymer, and steroid formation. UV photoirradiation generates ROS species, which increased the size of intramembraneous particles of recombinant PBR reconstituted into proteoliposomes consistent with polymer formation, determined both by SDS-PAGE and by freeze-fracture electron microscopy. Spectroscopic analysis revealed the formation of dityrosines as the covalent cross-linker between PBR monomers. Moreover, photoirradiation increased PK 11195 drug ligand binding and reduced cholesterol binding capacity of proteoliposomes. Further addition of PK 11195 drug ligand to polymers increased the rate of cholesterol binding. These data indicate that reactive oxygen species induce in vivo and in vitro the formation of covalent PBR polymers. We propose that the PBR polymer might be the functional unit responsible for ligand-activated cholesterol binding and that PBR polymerization is a dynamic process modulating the function of this receptor in cholesterol transport and other cell-specific PBR-mediated functions.
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http://dx.doi.org/10.1021/bi0267487DOI Listing
April 2003