title: Regulation of telomerase activity by the p53 family member p73.
abstract: The terminal ends of eukaryotic chromosomes, termed telomeres, progressively shorten during each round of cell division eventually leading cells into senescence. Tumor cells typically overcome this barrier to unlimited proliferation by activation of the human telomerase reverse transcriptase (hTERT) gene. In contrast, in most human somatic cells hTERT expression is tightly repressed by multiple tumor suppressors. Here, we studied the regulation of hTERT by the p53 family member p73. We show that forced expression of p73 or activation of endogenous p73 by E2F1 results in the downregulation of telomerase activity. Vice versa, siRNA-mediated knockdown of p73 induces hTERT expression. Responsiveness to p73 is conferred by Sp1 binding sites within the hTERT core promoter. In tumor cells, p73 isoforms lacking the transactivation domain (DeltaNp73) are frequently overexpressed and believed to function as oncogenes. We show that DeltaNp73 antagonizes the repressive effect of the proapoptotic p53 family members on hTERT expression and, in addition, induces hTERT expression in telomerase-negative cells by interfering with E2F-RB-mediated repression of the hTERT core promoter. These data provide evidence that the p73 gene functions as an important regulator of telomerase activity with implications for embryonic development, cellular differentiation and tumorigenesis.
authors.affiliation: Molecular Tumor Biology Group, Rudolf-Virchow-Center (DFG Research Center for Experimental Biomedicine), University of Würzburg, Versbacher Strasse 9, Würzburg 97078, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Beitzinger
authors.forename: C
authors.initials: C
authors.lastname: Oswald
authors.forename: R
authors.initials: R
authors.lastname: Beinoraviciute-Kellner
authors.forename: T
authors.initials: T
authors.lastname: Stiewe
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D017209:Apoptosis / Q000502:physiology; D001665:Binding Sites; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D016147:Genes, Tumor Suppressor; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins
chemical_list: D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D016329:Sp1 Transcription Factor; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C000606369:delta Np73 protein, human; D019098:Telomerase