Giα but not Gqα is linked to activation of p21ras in human airway smooth muscle cells

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 (alpha or beta gamma) transmitted the activation signal. Carbachol and endothelin-l increased CTP-bound p21(ras) in a pertussis toxin-sensitive manner [ratio of [P-32]GTP to ([P-32]GTP + [P-32]GDP): control, 30 +/- 1.7; 3 min of 1 mu M carbachol, 39 +/- 1.1; 3 min of 1 mu M endothelin-l, 40 +/- 1.2], whereas histamine, bradykinin, and KCl were without effect. Transfection of an inhibitor of the G protein beta gamma-subunit [the carboxy terminus (Gly(495)-Leu(689)) of the beta-adrenoceptor kinase 1] failed to inhibit the carbachol-induced activation of p21(ras). These data suggest that G(i)- but not G(q)-coupled receptors activate p21(ras) in human airway smooth muscle cells, and this effect most likely involves the alpha-subunit.