Role of protein kinase Cζ in Ras-mediated transcriptional activation of vascular permeability factor/vascular endothelial growth factor expression

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF), a multifunctional cytokine, is regulated by different factors including degree of cell differentiation, hypoxia, and certain oncogenes namely, ras and src, The up-regulation of VPF/VEGF expression by Ras has been found to be through both transcription and mRNA stability. The present study investigates a novel pathway whereby Ras promotes the transcription of VPF/VEGF by activating protein kinase C zeta (PKC zeta), The Res-mediated overexpression of VPF/VEGF was also found to be inhibited by using the antisense or the dominant-negative mutant of PKC zeta In co-transfection assays, by overexpressing oncogenic Ha-Ras (12 V) and PKC zeta, there was an additive effect up to 4-fold in activation of Spl-mediated VPF/VEGF transcription. It has been shown through electrophoretic mobility shift assay that Ras promoted the PKC zeta -induced binding of Spl to the VPF/VEGF promoter. In the presence of PDK-1, a major activating kinase for PKC, the Ras-mediated activation of VPF/VEGF promoter through PKC zeta was further increased, suggesting that PKC zeta can serve as an effector for both Ras and PDK-1, In other experiments, with the use of a dominant-negative mutant of phosphatidylinositol 3-kinase, the activation of VPF/VEGF promoter through Ras, PDK-1, and PKC zeta was completely repressed, indicating phosphatidylinositol 3-kinase as an important component of this pathway. Taken together, these data elucidate the signaling mechanism of Res-mediated VPF/VEGF transcriptional activation through PKC zeta and also provide insight into PKC zeta and Spl-dependent transcriptional regulation of VPF/VEGF.