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Journal of Lipid Research, Vol. 44, 1667-1675, September 2003
Copyright © 2003 by American Society for Biochemistry and Molecular Biology

OxLDL induces mitogen-activated protein kinase activation mediated via PI3-kinase/Akt in vascular smooth muscle cells

Ming-Wei Chien^*, Chin-Sung Chien^*, Li-Der Hsiao^*, Ching-Hsuan Lin^* and Chuen-Mao Yang^1,*,

^* Department of Physiology and Pharmacology, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan
Graduate Institute of Natural Products, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan

¹ To whom correspondence should be addressed. e-mail: chuenmao{at}mail.cgu.edu.tw

Oxidized low-density lipoprotein (OxLDL) is a risk factor in atherosclerosis and stimulates multiple signaling pathways, including activation of phosphatidylinositol 3-kinase (PI3-K)/Akt and p42/p44 mitogen-activated protein kinase (MAPK), which are involved in mitogenesis of vascular smooth muscle cells (VSMCs). We therefore investigated the relationship between PI3-K/Akt and p42/p44 MAPK activation and cell proliferation induced by OxLDL. OxLDL stimulated Akt phosphorylation in a time- and concentration-dependent manner, as determined by Western blot analysis. Phosphorylation of Akt stimulated by OxLDL and epidermal growth factor (EGF) was attenuated by inhibitors of PI3-K (wortmannin and LY294002) and intracellular Ca²⁺ chelator (BAPTA/AM) plus EDTA. Pretreatment of VSMCs with pertussis toxin, cholera toxin, and forskolin for 24 h also attenuated the OxLDL-stimulated Akt phosphorylation. In addition, pretreatment of VSMCs with wortmannin or LY294002 inhibited OxLDL-stimulated p42/p44 MAPK phosphorylation and [³H]thymidine incorporation. Furthermore, treatment with U0126, an inhibitor of MAPK kinase (MEK)1/2, attenuated the p42/p44 MAPK phosphorylation, but had no effect on Akt activation in response to OxLDL and EGF. Overexpression of p85-DN or Akt-DN mutants attenuated MEK1/2 and p42/p44 MAPK phosphorylation stimulated by OxLDL and EGF.

These results suggest that the mitogenic effect of OxLDL is, at least in part, mediated through activation of PI3-K/Akt/MEK/MAPK pathway in VSMCs.

Supplementary key words oxidized LDL • phosphatidylinositol 3-kinase • protein kinase C • Ca²⁺ • DNA synthesis • epidermal growth factor

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