Ion .channel TRPM8 promotes hypoxic growth of prostate cancer celfs via an O_2-independent and-RACK1-mediated mechanism of HIF-Ia stabilization

摘要

The growth adaptation of cancer cells to a hypoxic tumour microenvironment is mostly regulated by hypoxia-induced transcription factor HIF-1, HIF-1 transcriptional activity is strictly controlled by protein levels of the HlF-1oc subunit, which is tightly regulated by a well-characterized O2-dependent ubiquitin ligase-proteasomal degradation pathway. The cold-sensitive Ca2+ channel protein TRPM8 exhibits increased expression in advanced prostate cancer. However, its exact functional roles in prostate cancer growth regulation are unclear and controversial. In this work, we show that TRPM8 promotes in vitro hypoxic growth capacities, drug resistance, and in vivo tumourigenicity, accompanied with enhanced HlF-1a protein levels. These effects are further potentiated by TRPM8 agonists but suppressed by TRPM8 gene knockdown and blocking with antagonists or TRPM8 antibody. TRPM8-induced suppression of HIF-1a ubiquitination and enhanced HIF-1 transactivation were attenuated by forced RACK1 expression and TRPM8 overexpression reduced phospho-RACK1 levels, thus affecting its dimerization status, and promoted RACK1 binding to HlF-1a and calcineurin. These data indicate that TRPM8-induced increase of HlF-1a protein in hypoxia- or normoxia-exposed prostate cancer cells was mediated through a newly characterized Ca2+-dependent but O2-independent mechanism involving binding of RACK1 to HIF-1 a and RACK1 -mediated ubiquitination of HIF-la. Collectively, our study not only provides a mechanistic insight into howTRPM8 promotes the hypoxic growth adaptation of cancer cells via its promotion of RACK1 -mediated stabilization of HIF-1oj but also suggests a potential therapeutic strategy for prostate cancer by targeting TRPM8.