[Show abstract][Hide abstract]ABSTRACT: The bio-effects of cellular repressor of E1A-stimulated genes (CREG) have been proposed to depend on its N-glycosylation and binding to mannose-6-phosphate/insulin-like growth factor-2 receptor (M6P/IGF2R). The present study aimed to investigate the detailed mode and specific sites for their binding and the functional relevance of this binding in the phenotypic modulation of vascular smooth muscle cells (SMCs). Wild-type and glycosylation mutant human CREG (wtCREG and mCREG) proteins were expressed and isolated from HEK293 cells. CREG knocked-down SMCs were used to evaluate their biological activity. Both wtCREG and mCREG arrest cell cycle progression of CREG knocked-down SMCs when added to the culture medium. In vitro binding assay revealed that CREG bound to M6P/IGF2R extracellular domains 7-10 and 11-13 in a glycosylation-dependent and -independent manner, respectively. Further blocking experiments using soluble M6P/IGF2R fragments and M6P/IGF2R neutralizing antibody suggest that the binding to domains 11-13, as well as to 7-10, is adequate for CREG to modulate SMC proliferation. These data suggest that soluble CREG protein can exert its biological function via glycosylation-independent binding to the extracellular domains 11-13 of cell surface M6P/IGF2R, and thereby provide novel insights into CREG modulation of SMC phenotypic switching from contractile to proliferative.
Article · Dec 2010 · Journal of Molecular and Cellular Cardiology
[Show abstract][Hide abstract]ABSTRACT: Vascular smooth muscle cell (VSMC) apoptosis accelerates atherosclerosis and promotes restenosis following vascular injury. The current study examined the effects of cellular repressor of E1A-stimulated genes (CREG), a novel glycoprotein inhibiting transcription activation, on the regulation of VSMC apoptosis. Serum starvation or treatment of human VSMCs with apoptosis inducers (STS or VP-16) significantly reduced CREG expression and caused caspase-3 activation. CREG downregulation and caspase-3 activation were inversely related, suggesting that reduced CREG expression may contribute to VSMC apoptosis. Both loss-of-function (CREG-DW produced by retroviruses expressing CREG shRNAs) and gain-of-function (CREG-UP produced by retroviral infection with vector pLNCX-CREG) studies were performed to confirm this hypothesis. CREG-DW significantly increased VSMC apoptosis, whereas CREG-UP significantly reduced apoptosis. Moreover, p38 and JNK mitogen-activated protein kinases were significantly upregulated in CREG-DW and significantly reduced in CREG-UP VSMCs. More importantly, CREG-DW-induced VSMC apoptosis was blocked by the p38-specific inhibitor SB203580 or by overexpression of a dominant-negative P38 alpha (p38 alpha AGF). Balloon injury-induced vascular caspase-3 activation was significantly inhibited by treatment with recombinant CREG protein. These results demonstrated for the first time that CREG plays a key role in modulating VSMC apoptosis through the p38 and JNK signal transduction pathways, both in vitro and in situ.
Article · Jun 2010 · Journal of Molecular and Cellular Cardiology