HoxC5 and Pbx4 repress hTERT to limit telomerase activity

Telomere elongation by telomerase is critical for the proliferation of human stem cells and >85-90% of cancer cells. The repression of telomerase activity during cellular differentiation promotes replicative aging and function as a physiological barrier for tumorigenesis in long-lived mammals, including humans. However, the underlying mechanisms remain unclear. We found that HoxC5 repressed hTERT, via a previously uncharacterized upstream enhancer element. HoxC5 interacts with co-repressors Pbx4 and Meis3, and recruits Class I histone deacetylases, to mediate repression of hTERT. The upstream enhancer element are conserved in long-lived primates, and HOXC5 are activated upon differentiation, consistent with diminished telomerase activity. Thus, HoxC5/Pbx4/Meis3 together constitute a developmental-controlled regulatory loop that coordinates transcriptional repression of hTERT. Overall design: Endogenous and overexpressed Hoxc5 and PBX4 ChIP-seq in prostate cancer cell line (PC-3)