Activation of EGF receptor by oxidized LDL

Abstract

Oxidized low density lipoproteins (oxLDL) are thought to play a major role in atherosclerosis. OxLDL exhibit a wide variety of biological effects resulting from their ability to interfere with intracellular signaling. The cellular targets and primary signaling events of oxLDL are unknown. We report that oxLDL elicit, in intact cells, tyrosine phosphorylation of the epithelial growth factor receptor (EGFR) and activation of its signaling pathway. This activation triggered by oxLDL was associated with derivatization of reactive amino groups of EGFR and was mimicked by 4-hydroxynonenal (4-HNE, a major lipid peroxidation product of oxLDL). Immunopurified EGFR was derivatized and activated in vitro by oxLDL lipid extracts and 4-HNE, thus indicating that 1) EGFR may be a primary target of oxidized lipids and 2) EGFR derivatization may be associated with activation. The reported data suggest that EGFR acts as a sensor for oxidized lipids. We therefore propose a novel concept of the mechanism by which oxidized lipids (contained in oxLDL or more generally produced during oxidative stress) are able to activate receptor tyrosine kinase and subsequent signaling pathways, resulting finally in a gain of function.

Phenolic antioxidants trolox and caffeic acid modulate the oxidized LDL‐induced EGF‐receptor activation

“…Cells were routinely grown in RPMI 1640 medium (Life Technologies-Gibco) containing 10% foetal calf serum (Biowhittaker, Gagny, France) as described (Suc et al, 1998;Vieira et al, 2000). The B82LK+ cells (transduced with wild type EGFR) (Wright et al, 1995), were a generous gift from Dr M. Weber (Charlottesville, VA, U.S.A.), and were grown in DMEM containing 10% foetal calf serum.…”

“…Free amino groups were labelled by an aminereactive probe, N-succinimidyl [2,3- (Staros et al, 1986), as previously described (Suc et al, 1998). The immunoprecipitates were washed three times in borate bu er, boiled in SDScontaining bu er and were resolved by SDS ± PAGE.…”

“…OxLDL induce a variety of biological e ects potentially involved in atherogenesis, such as foam cells and fatty streak formation, alterations in gene expression, cell migration, motility and contractility, cell proliferation, cell viability, local immune response, vasomotor tone (Witztum & Steinberg, 1991;Hajjar & Haberland, 1997). These biological responses are triggered by oxidized lipids contained in oxLDL that alter the activity of various cellular signalling pathways (Hajjar & Haberland, 1997), for instance calcium (Escargueil-Blanc et al, 1994), phospholipase D (Natarajan et al, 1995(Natarajan et al, ), trimericet al 1996, EGF-receptor (EGFR) (Suc et al, 1998), PI3-kinase (Martens et al, 1998), PPARgamma (Nagy et al, 1998), rho-kinase (Essler et al 1999).…”

“…Among the cell proteins derivatized by 4-HNE, we have shown that EGFR is a target of 4-HNE from oxLDL which induce 4-HNE-adducts formation and activation of the EGFR (Suc et al, 1998).…”

“…In mammals, the EGFR family consists of four members, EGFR (or ErbB1), HER2 (or ErbB2/neu), HER3 (or ErbB3) and ErbB4 which are able to bind multiple peptide ligands (EGF, TGFa, amphiregulin, NDF, neuregulins, heregulins, HB-EGF, betacellulin and epiregulin) and, subsequently, to form homo-and heterodimeric complexes (Riese & Stern, 1998;Moghal & Sternberg, 1999;Hackel et al, 1999). Beside ligand-induced activation, EGFR can also be activated through ligandindependent mechanisms, for instance upon exposure of cells to ultraviolet radiations, oxidants, alkylating agents (Hackel et al, 1999) and oxidized lipids (Suc et al, 1998).…”