Angiogenesis, the formation of new blood vessels, plays a crucial role in normal physiological processes and in various pathological conditions. In the present study, we have investigated the physiological function of a newly described serine/threonine protein kinase D2 (PKD2) in aspects of endothelial cell biology involved in angiogenesis. We found that PKD2 was expressed in primary human endothelial cells from different tissues and was a critical PKD isoform mediating the phosphorylation of PKD substrates in endothelial cells. By using small interference RNAs that target different PKD2 regions, we found that silencing PKD2, but not PKD1 isoform, markedly inhibited the proliferation, migration, and in vitro angiogenesis of endothelial cells cultured in EGM-2 complete medium. We further showed that PKD2, but not PKD1, was required for the expression of vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 that are two key growth factor receptors involved in angiogenesis. These findings indicate that PKD2 plays a pivotal role in endothelial cell proliferation and migration necessary for angiogenesis at least in part through modulation of the expression of vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1.Angiogenesis is the fundamental physiological process by which new blood vessels are generated from pre-existing vasculature. It plays a crucial role in embryonic development in addition to numerous normal physiological processes. Angiogenesis is critically involved in a wide variety of human diseases including ischemic vascular diseases, tumor growth and metastasis, diabetic retinopathy, age-related macular degeneration, and rheumatoid arthritis (1-3). Emerging evidence indicates that angiogenesis also plays a critical role in the development and progression of atherosclerosis, a chronic inflammatory disease of the vessel wall (4 -7). For these reasons, an understanding of the complex mechanisms that regulate angiogenesis is seen not only as a fundamental problem in human biology but also critical in fulfilling the important goal of biomedical research to develop more specific and efficacious pro-and antiangiogenesis therapies.The process of angiogenesis depends on endothelial cell (EC) 2 proliferation, migration, and differentiation. It is controlled by a variety of positive and negative signals. Vascular endothelial growth factor (VEGF, also termed VEGF-A) is the most critical and potent of all the known proangiogenic factors, and its proangiogenic effect is mediated through the VEGF receptor 2 (VEGFR2, also termed Flk-1 or KDR) that is selectively expressed in vascular ECs (8). Besides VEGF, fibroblast growth factors (FGFs) and their receptors that are expressed on ECs also play a crucial role in angiogenesis (9). ECs express the FGF receptor 1 (FGFR1), and under some circumstances, FGFR2. Activation of FGFR1 or FGFR2 promotes EC proliferation, migration, and angiogenesis (9). Additionally, angiopoietins, transforming growth factors, cytokine...

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Emerging evidence indicates that vascular endothelial growth factor (VEGF) plays a critical role in host inflammatory responses in several disease states, including atherosclerosis, sepsis, and rheumatoid arthritis. In this study, we determined the effect of VEGF on endothelial induction of proinflammatory cytokines and investigated the responsible signal pathways. By using a cytokine antibody array that detects the end point protein products released from endothelial cells (ECs), we found that VEGF, via VEGF receptor 2 (VEGFR2), predominantly induced the production of proinflammatory cytokine interleukin (IL)-6 and CXC chemokines IL-8 and growth-related oncogene-α (GRO-α) in ECs but not in leukocytes among 36 cytokines in the array. The production of these inflammatory cytokines by VEGF was much stronger than the induction of cell adhesion molecule in ECs. We further found that the cytokine production by VEGF was essentially mediated by the Gö-6976-sensitive protein kinase D (PKD) family kinases. Importantly, the VEGF-induced production of IL-6, IL-8, and GRO-α was inhibited ∼70%, 40%, or 37% by PKD1 silencing (more than 90% knockdown) with three small interference RNAs that target different PKD1 regions. Moreover, silencing PKD2 downregulated VEGFR2 and markedly inhibited the cytokine production by VEGF in ECs. Our results indicate that VEGF, via VEGFR2-PKD1 axis, induces the production of proinflammatory cytokine IL-6, IL-8, and GRO-α in ECs but not in leukocytes, which may offer new insights into the mechanism of the proinflammatory activity of VEGF.

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