Urotensin II-induced endothelin-1 expression and cell proliferation via epidermal growth factor receptor transactivation in rat aortic smooth muscle cells

Urotensin II (U-II) is implicated in vascular smooth muscle cell proliferation, which results in vascular remodeling. We recently demonstrated that both reactive oxygen species (ROS) generation and epidermal growth factor receptor (EGFR) transactivation play critical roles in U-II signal transduction. However, the detailed intracellular mechanism of U-II in vascular smooth muscle cells remains unclear. In this study, we used rat aortic smooth muscle cells treated with U-II to investigate the connection between ROS generation and EGFR transactivation. U-II treatment was found to stimulate endothelin-1 (ET-1) expression and cell proliferation through the phosphorylation of EGFR and ROS generation. NAD(P)H oxidase inhibitor apocynin and ROS scavenger N-acetylcysteine (NAC) inhibited the EGFR transactivation induced by U-II. In contrast, AG-1478 (an EGFR inhibitor) failed to inhibit intracellular ROS generation induced by U-II. Src homology 2-containing tyrosine phosphatase (SHP-2) was shown to be associated with EGFR during U-II treatment by EGFR coimmunoprecipitation. ROS have been reported to oxidize the catalytic cysteine of SHP-2 and inhibit its activity. We examined the effect of U-II on SHP-2 in smooth muscle cells using a modified malachite green phosphatase assay. SHP-2 was oxidized during U-II treatment; and this oxidization could be repressed by NAC treatment. In SHP-2 knockdown cells, U-II-induced EGFR phosphorylation, ET-1 secretion, and cell proliferation were enhanced, and were not influenced by NAC. Our data suggest that U-II-mediated ROS generation can inhibit SHP-2 activity to facilitate the EGFR transactivation and mitogenic signal transduction in rat aortic smooth muscle cells.