Cyclic stretch activates ERK1/2 via G proteins and EGFR in alveolar epithelial cells

MechanicaI stimuli are transduced into intracellular signals in lung alveolar epithelial cells (AEC). We studied whether mitogen-activated protein kinase (MAPK) pathways are activated during cyclic stretch of AEC. Cyclic stretch induced a rapid (within 5 min) increase in extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in AEC. The inhibition of Na⁺, L-type Ca²⁺ and stretch-activated ion channels with amiloride, nifedipine, and gadolinium did not prevent the stretch-induced ERK1/2 activation. The inhibition of Grb2-SOS interaction with an SH3 binding sequence peptide, Ras with a farnesyl transferase inhibitor, and Raf-1 with forskolin did not affect the stretch-induced ERK1/2 phosphorylation. Moreover, cyclic stretch did not increase Ras activity, suggesting that stretch-induced ERK1/2 activation is independent of the classical receptor tyrosine kinase-MAPK pathway. Pertussis toxin and two specific epidermal growth factor receptor (EGFR) inhibitors (AG-1478 and PD-153035) prevented the stretch-induced ERK1/2 activation. Accordingly, in primary AEC, cyclic stretch activates ERK1/2 via G proteins and EGFR, in Na⁺ and Ca²⁺ influxes and Grb2-SOS-, Ras-, and Raf-1-independent pathways.