Cellular repressor of E1A-stimulated genes inhibits human vascular smooth muscle cell apoptosis via blocking P38/JNK MAP kinase activation

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 P38α (p38α 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.