AHEART February 47/2

Iwasaki, Hiroaki, Satoru Eguchi, Hikaru Ueno, Fumiaki Marumo, and Yukio Hirata. Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor. Am. J. Physiol. Heart Circ. Physiol. 278: H521–H529, 2000.—We have studied whether activation of epidermal growth factor receptor (EGFR) is involved in stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and protein synthesis in cultured rat vascular smooth muscle cells (VSMC). Cyclic stretch (1 Hz) induced a rapid (within 5 min) phosphorylation of ERK1/2, an effect that was time and strength dependent and inhibited by an EGFR kinase inhibitor (AG-1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG-1296). The stretch rapidly (within 2 min) induced tyrosine phosphorylation of several proteins, among which 180kDa protein was shown to be EGFR as revealed by blockade with AG-1478 as well as immunoprecipitation with antiEGFR antibody coupled with immunoblotting with antiphosphotyrosine antibody. The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione-S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies. Transfection of a dominant-negative mutant of H-Ras also inhibited stretch-induced ERK1/2 activation. Treatment with a stretch-activated ion channel blocker (Gd31) and an intracellular Ca21 antagonist (TMB-8) inhibited stretch-induced phosphorylation of EGFR and ERK1/2. Treatment with AG-1478 and a mitogen-activated protein kinase kinase inhibitor (PD-98059), but not AG-1296, blocked [3H]leucine uptake stimulated by a high level of stretch. These data suggest that ERK1/2 activation by mechanical stretch requires Ca21-sensitive EGFR activation mainly via stretch-activated ion channels, thereby leading to VSMC growth.