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

A dyskerin motif reactivates telomerase activity in X-linked dyskeratosis congenita and in telomerase-deficient human cells

“…Conversely, treatment with the JNK inhibitor SP60125 was able to activate this promoter (data not shown), as has been previously described. 9 These results indicate that the activity of GSE24-2 was specific for hTERT expression.Dyskerin was originally identified as the human cbf5 homologue 53 showing 85% identity to S cerevisiae Cbf5 gene at the protein level. 54 Therefore, we cloned the yeast S cerevisiae cbf5 gene sequence equivalent to GSE24-2 ( Figure 1D) into the pLNCX vector.…”

Activation of KLF8 Transcription by Focal Adhesion Kinase in Human Ovarian Epithelial and Cancer Cells

“…Indeed, recent studies have identified Sp1 as an important mediator of gene transcription induced by diverse signaling stimuli, including oncogenes, growth factors, and cytokines (42), despite the fact that Sp1 has been implicated in controlling the basal transcription of many "housekeeping" genes. For example, Sp1 binding sites are required for stimulation by the ERK, Akt, and JNK pathways of promoters of several genes, including the urokinase plasminogen activator, vascular endothelial growth factor, and p21 (37,(43)(44)(45). Interestingly, we noticed that other Sp1 binding sites located between Ϫ705 and Ϫ97 of the KLF8 promoter may mediate an additional contribution to the promoter activation by FAK, since deletion of this region also led to some loss of the promoter activity compared with the fulllength promoter (see Fig.…”

Modulation of Telomerase Promoter Tumor Selectivity in the Context of Oncolytic Adenoviruses

“…Postinfection, cells were rinsed extensively and trypsinized to remove extraneous virus. Genomic DNA was prepared from cell pellets, and QPCR was done in triplicate using GRI Opticon monitor equipment and software (Genetic Research Instrumentation, Essex, United Kingdom) as described previously (40). Penton DNA was monitored using the primers 5 ¶-GAGG-CAAGCACACAGACCATC-3 ¶ and 5 ¶-CGTTTCTTGCTGTCCTCTGTCA-3 ¶, and cellular GAPDH genomic DNA was detected with the primers 5 ¶-ACCA-CAGTCCATGCCATCAC-3 ¶ and 5 ¶-TCCACCACCCTGTTGCTGTA-3 ¶.…”