TRPM8 in prostate cancer cells: a potential diagnostic and prognostic marker with a secretory function?

During the past 5 years it has emerged that the transient receptor potential (TRP) family of Ca(2+)-and Na(+)-permeable channels plays a diverse and important role in cell biology and in pathology. One member of this family, TRPM8, is highly expressed in prostate cancer cells but the physiological and pathological functions of TRPM8 in these cells are not known. Here we address these questions, and the issue of whether or not TRPM8 is an effective diagnostic and prognostic marker in prostate cancer. TRPM8 is known to be activated by cool stimuli (17-25 degrees C) and cooling compounds such as menthol. The activation mechanism(s) involves voltage sensing of membrane potential, phosphatidylinositol 4,5-bisphosphate and Ca(2+). In addition to prostate cancer cells, TRPM8 is expressed in sensory neurons where it acts as a sensor of cold. In prostate epithelial cells, expression of TRPM8 is regulated by androgen and is elevated in androgen-sensitive cancerous cells compared with normal cells. While there is some evidence that in prostate cancer cells Ca(2+) and Na(+) inflow through TRPM8 is necessary for survival and function, including secretion at the apical membrane, the function of TRPM8 in these cells is not really known. It may well differ from the role of TRPM8 as a cool sensor in sensory nerve cells. Androgen unresponsive prostate cancer is difficult to treat effectively and there are limited diagnostic and prognostic markers available. TRPM8 is a potential tissue marker in differential diagnosis and a potential prognostic marker for androgen-unresponsive and metastatic prostate cancer. As a consequence of its ability to convey Ca(2+) and Na(+) and its expression in only a limited number of cell types, TRPM8 is considered to be a promising target for pharmaceutical, immunological and genetic interventions for the treatment of prostate cancer.