Novel role of cold/menthol-sensitive transient receptor potential melastatine family member 8 (TRPM8) in the activation of store-operated channels in LNCaP human prostate cancer epithelial cells

Recent cloning of a cold/menthol-sensitive TRPM8 channel ( transient receptor potential melastatine family member 8) from rodent sensory neurons has provided the molecular basis for the cold sensation. Surprisingly, the human orthologue of rodent TRPM8 also appears to be strongly expressed in the prostate and in the prostate cancer-derived epithelial cell line, LNCaP. In this study, we show that despite such expression, LNCaP cells respond to cold/ menthol stimulus by membrane current (I-cold/menthol) that shows inward rectification and high Ca2+ selectivity, which are dramatically different properties from "classical" TRPM8-mediated I-cold/menthol. Yet, silencing of endogenous TRPM8 mRNA by either antisense or siRNA strategies suppresses both I-cold/menthol and TRPM8 protein in LNCaP cells. We demonstrate that these puzzling results arise from TRPM8 localization not in the plasma, but in the endoplasmic reticulum ( ER) membrane of LNCaP cells, where it supports cold/menthol/icilin-induced Ca2+ release from the ER with concomitant activation of plasma membrane ( PM) store-operated channels ( SOC). In contrast, GFP-tagged TRPM8 heterologously expressed in HEK-293 cells target the PM. We also demonstrate that TRPM8 expression and the magnitude of SOC current associated with it are androgen-dependent. Our results suggest that the TRPM8 may be an important new ER Ca2+ release channel, potentially involved in a number of Ca2+- and store-dependent processes in prostate cancer epithelial cells, including those that are important for prostate carcinogenesis, such as proliferation and apoptosis.