Androgen receptor in melanoma progression: the role of TRPM8 and its intersection with androgen signaling

1. INTRODUCTION AND BACKGROUND Background Melanoma is one of the most aggressive skin cancer, because of its metastatic potential and drug-resistance. Recent data from our laboratory have shown that the androgen receptor (AR) promotes the migratory phenotype and immune-escape in melanoma-derived cells. On the other, the transient receptor potential melastatin 8 (TRPM8) channel, a calcium-permeable and non-selective cation channel, has been identified as an androgen-responsive protein, capable of interacting with AR and influencing the calcium-dependent signaling pathway in prostate cancer and melanoma-derived cells. This study aims at investigating the intersection between TRPM8 and the AR-mediated signaling in melanoma progression. Methods Data from The Cancer Genome Atlas (TCGA-SKCM) showed that both AR and TRPM8 are upregulated in metastatic melanoma, as compared with the primary and normal counterparts. Western blot analysis confirmed these findings. Studies with new TRPM8 pharmacological modulators have shown that TRPM8 blockade reduces androgen-induced migration in both metastatic and primary melanoma cells. TRPM8 blockade also prevents the androgen-induced cytoskeletal changes and ruffle’s formation, as shown by immunofluorescence analysis. Co-immunoprecipitation and co-localization approaches have shown that hormone stimulation rapidly promotes the assembly of AR/TRPM8 complex. Blockade of TRPM8 perturbs the complex assembly. Androgen exposure induces a rapid phosphorylation of PKC, FAK, and ERK, which was counteracted by TRPM8 inhibitors. These signaling effectors control the cell locomotion mediated by the androgen-coupled AR in various cell types. At last, hormone stimulation upregulates PD-L1 levels. AR blockade by the antagonist, bicalutamide, and inhibition of TRPM8 both prevent such effect. Similar results were achieved by inhibiting FAK or ERK. Conclusions Our findings identify TRPM8 as a mediator of the androgen-driven signaling in melanoma cells. The AR/TRPM8 axis orchestrates calcium-dependent activation of PKC, FAK, and ERK, fostering cell motility on one hand. On the other, PD-L1 upregulation and the consequent immune-escape follow. TRPM8 blockade interferes with these responses. In sum, pharmacological inhibition of TRPM8 might be envisaged to counteract the hormone-mediated invasion of melanoma and amplify its responsiveness to immune therapy in clinical setting.