title: Transcriptional repression of telomerase RNA gene expression by c-Jun-NH2-kinase and Sp1/Sp3.
abstract: Telomerase is essential for immortalization of most human cancer cells. Expression of the core telomerase RNA (hTR) and reverse transcriptase (hTERT) subunits is mainly regulated by transcription. However, hTR transcriptional regulation remains poorly understood. We previously showed that the core hTR promoter is activated by Sp1 and is repressed by Sp3. Here, we show that the mitogen-activated protein kinase kinase kinase 1 (MEKK1)/c-Jun-NH(2)-kinase (JNK) pathway represses hTR expression by a mechanism that involves Sp1 and Sp3. Promoter activity was induced by the JNK inhibitor SP600125 and was repressed by activated MEKK1. Repression by MEKK1 was blocked by SP600125 or enhanced by coexpression of wild-type but not phosphoacceptor mutated JNK. SP600125 treatment also increased levels of endogenous hTR. Mutations in the hTR promoter Sp1/Sp3 binding sites attenuated SP600125-mediated promoter induction, whereas coexpression of MEKK1 with Sp3 enhanced hTR promoter repression. Chromatin immunoprecipitation showed that levels of immunoreactive Sp1 associated with the hTR promoter were low in comparison with Sp3 in control cells but increased after JNK inhibition with a reciprocal decrease in Sp3 levels. No corresponding changes in Sp1/Sp3 protein levels were detected. Thus, JNK represses hTR promoter activity and expression, apparently by enhancing repression through Sp3.
authors.affiliation: Centre for Oncology and Applied Pharmacology, University of Glasgow, Scotland, UK.
authors.forename: Alan E
authors.initials: AE
authors.lastname: Bilsland
authors.forename: Katrina
authors.initials: K
authors.lastname: Stevenson
authors.forename: Stuart
authors.initials: S
authors.lastname: Atkinson
authors.forename: Walter
authors.initials: W
authors.lastname: Kolch
authors.forename: W Nicol
authors.initials: WN
authors.lastname: Keith
mesh_terms: D000873:Anthracenes / Q000494:pharmacology; D001665:Binding Sites; D045744:Cell Line, Tumor; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D012313:RNA / Q000096:biosynthesis / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051705:Sp3 Transcription Factor / Q000378:metabolism*; D019098:Telomerase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D000873:Anthracenes; C497121:SP3 protein, human; D016329:Sp1 Transcription Factor; D051705:Sp3 Transcription Factor; C432165:pyrazolanthrone; D012313:RNA; D048031:JNK Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D019098:Telomerase