RNAi-mediated knockdown of protein kinase C-alpha inhibits cell migration in MM-RU human metastatic melanoma cell line

Protein kinase C (PKC) is a multigene family of serine/threonine protein kinases involved in cell signaling pathways of proliferation and motility. PKC interacts with Rho GTPases in the regulation of the actin cytoskeleton. The PKC-alpha isozyme binds the Rho GTPase cdc42, and both are coordinated with the Rac-phosphatidylinositol-3 kinase (PI3K) signaling pathway in melanoma cell invasion and migration on extracellular matrix proteins. To further define the role of PKC-alpha in melanoma cell migration, we tested the effect of PDBu and Ca dependent activation of PKC-alpha as well as treatment with the PKC-alpha inhibitors calphostin C and Go6976. Furthermore, we transfected siRNA targeted against PKC-alpha into human melanoma cells and performed time-lapse analysis of cell migration followed by western immunoblotting. We found that significant enhancement of cell migration at 0.5 h after PDBu treatment directly correlated with Ca dependent activation of PKC-alpha and was inhibited by the PKC-alpha inhibitor calphostin C. PKC-alpha siRNA transfection nearly abrogated PKC-alpha expression and significantly reduced melanoma cell migration compared with siRNA controls. These findings provide further evidence that PKC-alpha plays an important role in melanoma cell migration and may have implications in therapies designed to disrupt melanoma cell motility by alteration of PKC-alpha signaling.