Exchange Protein Directly Activated by Cyclic AMP Increases Melanoma Cell Migration by a Ca2+-Dependent Mechanism

Melanoma has a poor prognosis due to its strong metastatic ability. Although Ca2+ plays a major role in cell migration, little is known about the role of Ca2+ in melanoma cell migration. We recently found that the exchange protein directly activated by cyclic AMP (Epac) increases melanoma cell migration via a heparan sulfate-related mechanism. In addition to this mechanism, we also found that Epac regulates melanoma cell migration by a Ca2+-dependent mechanism. An Epac agonist increased Ca2+ in several different melanoma cell lines but not in melanocytes. Ablation of Epac1 with short hairpin RNA inhibited the Epac agonist-induced Ca2+ elevation, suggesting the critical role of Epac1 in Ca2+ homeostasis in melanoma cells. Epac-induced Ca2+ elevation was negated by the inhibition of phospholipase C (PLC) and inositol triphosphate (IP3) receptor. Furthermore, Epac-induced cell migration was reduced by the inhibition of PLC or IP3 receptor. These data suggest that Epac activates Ca2+ release from the endoplasmic reticulum via the PLC/IP3 receptor pathway, and this Ca2+ elevation is involved in Epac-induced cell migration. Actin assembly was increased by Epac-induced Ca2+, suggesting the involvement of actin in Epac-induced cell migration. In human melanoma specimens, mRNA expression of Epac1 was higher in metastatic melanoma than in primary melanoma, suggesting a role for Epac1 in melanoma metastasis. In conclusion, our findings reveal that Epac is a potential target for the suppression of melanoma cell migration, and, thus, the development of metastasis. Cancer Res; 70(13); 5607-17. (C)2010 AACR.