EGF Receptor Transactivation by Endothelin-1 Increased CHSY-1 Mediated by NADPH Oxidase and Phosphorylation of ERK1/2

Objective: Growth factors [transforming growth factor-beta (TGF-beta), epidermal growth factor (EGF), endothelin-1 (ET-1)] stimulate proteoglycan synthesis resulting in retention and accumulation of low density lipoprotein (LDL) in vessel intima and leading to atherosclerosis development. This study investigated the role of ET-1 on the expression of CHSY1, proteoglycan synthesizing enzyme, through both EGF and TGF-beta receptor transactivation in human vascular smooth muscle cells (VSMCs). Also, we explored the involvement of NADPH oxidase (NOX), an important intermediate of redox signaling, in ET-1 transactivated EGF receptor (EGFR) through endothelin receptors. Materials and Methods: In this experimental study, phosphorylated ERK1/2 and CHSY1 protein levels in the human VSMCs were measured by Western blot analysis using anti phospho-ERK1/2 (Thr202/Tyr204) and anti CHSY1 antibodies. Results: ET-1 (100 nM) and EGF (100 ng/ml) stimulated ERK1/2 phosphorylation and inhibited in the presence of bosentan (ET receptor inhibitor), AG1478 (EGFR inhibitor), and DPI (NOX antagonist). Also, ET-1 treatment increased CHSY1 enzyme level; this response was suppressed by bosentan, AG1478, DPI, and SB431542, TGF-beta receptor antagonist. This study revealed that ET-1 increases expression of CHSY1 through transactivation of EGF and TGF-beta receptors. Conclusion: Transactivation through the EGF receptor mediated by phospho-ERK1/2 leads to expression of CHSY1 protein. EGF receptor transactivation by ET-1 is shown for the first time, to be dependent on NOX enzymes.