CHIP Promotes Human Telomerase Reverse Transcriptase Degradation and Negatively Regulates Telomerase Activity

The maintenance of eukaryotic telomeres requires telomerase, which is minimally composed of a telomerase reverse transcriptase (TERT) and an associated RNA component. Telomerase activity is tightly regulated by expression of human (h) TERT at both the transcriptional and post-translational levels. The Hsp90 and p23 molecular chaperones have been shown to associate with hTERT for the assembly of active telomerase. Here, we show that CHIP (C terminus of Hsc70-interacting protein) physically associates with hTERT in the cytoplasm and regulates the cellular abundance of hTERT through a ubiquitin-mediated degradation. Overexpression of CHIP prevents nuclear translocation of hTERT and promotes hTERT degradation in the cytoplasm, thereby inhibiting telomerase activity. In contrast, knockdown of endogenous CHIP results in the stabilization of cytoplasmic hTERT. However, it does not affect the level of nuclear hTERT and has no effect on telomerase activity and telomere length. We further show that the binding of CHIP and Hsp70 to hTERT inhibits nuclear translocation of hTERT by dissociating p23. However, Hsp90 binding to hTERT was not affected by CHIP overexpression. These results suggest that CHIP can remodel the hTERT-chaperone complexes. Finally, the amount of hTERT associated with CHIP peaks in G(2)/M phases but decreases during S phase, suggesting a cell cycle-dependent regulation of hTERT. Our data suggest that CHIP represents a new pathway for modulating telomerase activity in cancer.