Activation and translocation of PKCδ is necessary for VEGF-induced ERK activation through KDR in HEK293T cells

VEGF-KDR/Flk-1 signal utilizes the phospholipase C-γ-protein kinase C (PKC)-Raf-MEK-ERK pathway as the major signaling pathway to induce gene expression and cPLA2 phosphorylation. However, the spatio-temporal activation of a specific PKC isoform induced by VEGF-KDR signal has not been clarified. We used HEK293T (human embryonic kidney) cells expressing transiently KDR to examine the activation mechanism of PKC. PKC specific inhibitors and human PKCδ knock-down using siRNA method showed that PKCδ played an important role in VEGF-KDR-induced ERK activation. Myristoylated alanine-rich C-kinase substrate (MARCKS) translocates from the plasma membrane to the cytoplasm depending upon phosphorylation by PKC. Translocation of MARCKS-GFP induced by VEGF-KDR stimulus was blocked by rottlerin, a PKCδ specific inhibitor, or human PKCδ siRNA. VEGF-KDR stimulation did not induce ERK phosphorylation in human PKCδ-knockdown HEK293T cells, but co-expression of rat PKCδ-GFP recovered the ERK phosphorylation. Y311/332F mutant of rat PKCδ-GFP which cannot be activated by tyrosine-phosphorylation but activated by DAG recovered the ERK phosphorylation, while C1B-deletion mutant of rat PKCδ-GFP, which can be activated by tyrosine-phosphorylation but not by DAG, failed to recover the ERK phosphorylation in human PKCδ-knockdown HEK293T cell. These results indicate that PKCδ is involved in VEGF-KDR-induced ERK activation via C1B domain.