The Pin2/TRF1-interacting protein PinX1 is a potent telomerase inhibitor.

Telomerase activity is critical for normal and transformed human cells to escape from crisis and is implicated in oncogenesis. Here we describe a novel Pin2/TRF1 binding protein, PinX1 that inhibits telomerase activity and affects tumorigenicity. PinX1 and its small TID domain bind the telomerase catalytic subunit hTERT and potently inhibit its activity. Overexpression of PinX1 or its TID domain inhibits telomerase activity, shortens telomeres, and induces crisis, whereas depletion of endogenous PinX1 increases telomerase activity and elongates telomeres. Depletion of PinX1 also increases tumorigenicity in nude mice, consistent with its chromosome localization at 8p23, a region with frequent loss of heterozygosity in a number of human cancers. Thus, PinX1 is a potent telomerase inhibitor and a putative tumor suppressor.