Giα but not Gqα is linked to activation of p21 ras in human airway smooth muscle cells

Abstract

Airway smooth muscle hypertrophy contributes to the narrowing of asthmatic airways. Activation of the mitogen-activated protein kinases is an important event in mediating cell proliferation. Because the monomeric G protein p21 ras is an important intermediate leading to activation of mitogen-activated protein kinases, we questioned which heterotrimeric G protein-coupled receptors were linked to the activation of p21 ras in cultured human airway smooth muscle and which of the heterotrimeric G protein subunits (α or βγ) transmitted the activation signal. Carbachol and endothelin-1 increased GTP-bound p21 ras in a pertussis toxin-sensitive manner [ratio of [32P]GTP to ([32P]GTP + [32P]GDP): control, 30 ± 1.7; 3 min of 1 μM carbachol, 39 ± 1.1; 3 min of 1 μM endothelin-1, 40 ± 1.2], whereas histamine, bradykinin, and KCl were without effect. Transfection of an inhibitor of the G protein βγ-subunit [the carboxy terminus (Gly495–Leu689) of the β-adrenoceptor kinase 1] failed to inhibit the carbachol-induced activation of p21 ras . These data suggest that Gi- but not Gq-coupled receptors activate p21 ras in human airway smooth muscle cells, and this effect most likely involves the α-subunit.