Response gene to complement 32 is required for C5b-9 induced cell cycle activation in endothelial cells

Abstract

Proliferation of vascular endothelial cells (EC) and smooth muscle cells (SMC) is a critical event in angiogenesis and atherosclerosis. We previously showed that the C5b-9 assembly during complement activation induces cell cycle in human aortic EC (AEC) and SMC. C5b-9 can induce the expression of Response Gene to Complement (RGC)-32 and over expression of this gene leads to cell cycle activation. Therefore, the present study was carried out to test the requirement of endogenous RGC-32 for the cell cycle activation induced by C5b-9 by knocking-down its expression using siRNA. We identified two RGC-32 siRNAs that can markedly reduce the expression of RGC-32 mRNA in AEC. RGC-32 silencing in these cells abolished DNA synthesis induced by C5b-9 and serum growth factors, indicating the requirement of RGC-32 activity for S-phase entry. RGC-32 siRNA knockdown also significantly reduced the C5b-9 induced CDC2 activation and Akt phosphorylation. CDC2 does not play a role in G1/S transition in HeLa cells stably overexpressing RGC-32. RGC-32 was found to physically associate with Akt and was phosphorylated by Akt in vitro. Mutation of RGC-32 protein at Ser 45 and Ser 47 prevented Akt mediated phosphorylation. In addition, RGC-32 was found to regulate the release of growth factors from AEC. All these data together suggest that cell cycle induction by C5b-9 in AEC is RGC-32 dependent and this is in part through regulation of Akt and growth factor release.

Expression of RGC32 in human normal and preeclamptic placentas and its role in trophoblast cell invasion and migration

“…Recently, some studies have reported that Akt activation participated in C5a-induced RGC32 expression in breast cancer cells [30] and hyperglycemia-or hyperinsulinemia-induced RGC32 expression in endothelial cells [31]. Meanwhile, other studies have shown that RGC32 silencing inhibited C5b-9-mediated Akt phosphorylation in human aortic vascular endothelial cells [32]. The above studies implied that the relationship between AKT and RGC32 is changeable at different conditions and in different cells.…”

Response gene to complement 32 (RGC-32) expression on M2-polarized and tumor-associated macrophages is M-CSF-dependent and enhanced by tumor-derived IL-4

“…These results are in contrast with previously reported data on the RGC-32-mediated activation of AKT in endothelial cells. 36 In addition, An et al 16 reported that RGC-32 had no significant effect on the phosphorylation of Akt in human umbilical vein endothelial cells. 16 The disparities among these reports might reflect differences in RGC-32 functions in different cell types.…”

Sub-lytic C5b-9 induces functional changes in retinal pigment epithelial cells consistent with age-related macular degeneration

“…Upon complement activation, its individual components C5b, C6, C7, C8, and C9 combine to form a lytic pore on the surface of target cell membranes in response to activated complement, capable of inducing cell lysis and inflammatory processes, as well as activating various cell signalling pathways. 6,7 The formation of MAC is regulated by the membrane bound complement regulatory protein CD59, which controls activation of complement by inhibiting the incorporation of C9 into the forming complex, and thereby preventing assembly of a functional pore. 8,9 CD59 is strongly expressed in the normal human retina and in cultured retinal pigment epithelial (RPE) cells.…”