C-terminal amino acids 290–328 of LPTS/PinX1 confer telomerase inhibition

LPTS/PinX1, a telomerase inhibitor composed of 328 amino acids, binds to the telomere associated protein Pin2/TRF1 and to the telomerase catalytic subunit hTERT. However, the mechanism by which LPTS/PinX1 regulates telomerase activity remains unclear. Here we show, for the first time, that LPTS/PinX1 uses different domains to interact with Pin2/TRF1 and hTERT. The LPTS/PinX1254–289 fragment specifically binds to Pin2/TRF1, and LPTS/PinX1290–328 can associate with hTERT. Compared with the full-length LPTS/PinX1 protein, LPTS/PinX1290–328 shows stronger in vitro telomerase inhibitory activity. Moreover, the LPTS/PinX1 protein was recruited to telomeres for binding to Pin2/TRF1. Overexpression of LPTS/PinX1290–328, which contains a nucleolus localization signal, in cells resulted in telomere shortening and progressive cell death. Conversely, telomere elongation was induced by expression of the dominant-negative LPTS/PinX11–289. Our results suggest that the C-terminal fragment of LPTS/PinX1 (LPTS/PinX1290–328) contains a telomerase inhibitory domain that is required for the inhibition of telomere elongation and the induction of cell crisis. Our studies also provide evidence that LPTS/PinX1 interaction with Pin2/TRF1 may play a role in the stabilization of telomeres.

Research highlights
► LPTS/PinX1, a telomerase inhibitor composed of 328 amino acids, uses different domains to interact with Pin2/TRF1 and hTERT.
► Telomere localization of LPTS/PinX1 is mediated by Pin2/TRF1.
► The C-terminal LPTS/PinX1290–328 has the strongest telomerase inhibitory activity in vitro.
► LPTS/PinX1290–328 induces telomere shortening, but LPTS/PinX11–289 elongates telomere length in cells.
► LPTS/PinX1290–328 inhibits cell growth and induces cell death.