Requirement for protein kinase C theta for cell cycle progression and formation of actin stress fibers and filopodia in vascular endothelial cells.

Activation of the protein kinase C (PKC) family with phorbol esters induces endothelial proliferation and angiogenesis, but which of the events that constitute angiogenesis are affected by individual members of the PKC family is unknown. In rat capillary endothelial (RCE) cells, serum stimulation increased expression of a single PKC isoenzyme, PKCtheta, and its translocation to the periphery. Conditional overexpression of a dominant-negative mutant of PKCtheta markedly inhibited RCE proliferation, as well as closure of a "wound" by RCE migration and formation of capillary rings and tubules in vitro. PKCtheta inhibition delayed the endothelial cell cycle at the G2/M phase and prevented formation of actin stress fibers and filopodia but not lamellipodia. The defect in cell morphology and wound closure in PKCtheta-kn cells was reversed by overexpressing kinase-active PKCtheta, indicating that these RCE functions depend upon PKCtheta substrates. Thus, PKCtheta is required for multiple processes essential for angiogenesis and wound repair, including endothelial mitosis, maintenance of a normal actin cytoskeleton, and formation of an enclosed tube.