Shear‐induced platelet‐derived growth factor gene expression in human endothelial cells is mediated by protein kinase C

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Abstract
Our previous studies have shown that steady shear stress causes a transient increase of platelet‐derived growth factor (PDGF) A and B chain mRNA levels in human umbilical vein endothelial cells (HUVEC). In the present study, we elucidated the signaling pathway of shear stress in HUVEC by examining the roles of protein kineses, intracellular calcium, cyclooxygenase, and guanine nucleotide‐binding proteins (G proteins) in the PDGF gene induction by shear. The protein kinase C inhibitors, H7 and staurosporine, strongly inhibited the shear‐induced PDGF gene expression in HUVEC. In contrast, HA1004, a cAMP‐ and cGMP‐dependent protein kineses inhibitor, was only slightly inhibitory. BAPTA/AM, an intracellular calcium chelator, partially (50%) inhibited the shear‐induced PDGF gene expression. The cyclooxygenase inhibitors, ibuprofen and indomethacin, were slightly inhibitory. A 35–50% inhibition of shear‐induced PDGF gene expression was found with GDP‐β‐S, an inhibitor of G proteins. These results suggest that shear‐induced PDGF gene expression in HUVEC is mainly mediated by protein kinase C activation and requires intracellular calcium. Furthermore, G proteins seem to be involved in this process, whereas prostaglandin synthesis via cyclooxygenase pathway is not. We propose a mechanism of shear‐induced gene expression in HUVEC: Shear stress, either directly or indirectly (G protein‐mediated), enhances the membrane phosphoinositide turnover via phos‐pholipase C, producing diacylglycerol, an activator of protein kinase C. The activated protein kinase C then triggers the subsequent PDGF gene expression.

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