Protein kinase C-epsilon coordinately regulates changes in cell growth and shape. Cells overproducing protein kinase C-epsilon spontaneously acquire a polarized morphology and extend long cellular membrane protrusions that are reminiscent of the morphology observed in ras-transformed fibroblasts. Here we report that the regulatory C1 domain contains an actin binding hexapeptide motif that is essential for the morphogenic effects of protein kinase C-epsilon in cultured NIH3T3 murine fibroblasts. The extension of elongate processes by protein kinase C-epsilon transformed fibroblasts appeared to be driven by a kinase-independent mechanism that required organized networks of both actin and microtubules. Flow cytometry of phalloidin-stained cells demonstrated that protein kinase C-epsilon significantly increased the cellular content of polymerized actin in NIH3T3 cells. Studies with a cell-free system suggest that protein kinase C-epsilon inhibits the in vitro disassembly of actin filaments, is capable of desequestering actin monomers from physiologically relevant concentrations of thymosin beta4, and increases the rate of actin filament elongation by decreasing the critical concentration of actin. Based on these and other observations, it is proposed that protein kinase C-epsilon may function as a terminal downstream effector in at least one of the signaling pathways that mitogens engage to initiate outgrowth of cellular protrusions.
Copyright 2001 Wiley-Liss, Inc.