Mechanisms Underlying p-Agonist and Prostaglandin E2 Inhibition of Airway Smooth Muscle Growth

摘要

Previous studies have reported the ability of both p-agonists and prostaglandin E2 (PGE2) to inhibit mitogen-stimulated growth of airway smooth muscle (ASM) cells in culture, suggesting that asthma therapies effective at bronchodilation may also be useful in managing excessive ASM growth. However, the molecular mechanisms mediating these effects are poorly defined, and the presumed role of the cAMP-dependent protein kinase (PKA) in enabling P-agonist-mediated bronchodilation and ASM growth inhibition has been questioned by two recent studies. To overcome limitations of pharmacologic antagonism of PKA, we expressed a GFP chimera of the PKA inhibitory peptide (PKI-GFP) in human ASM cultures and compared the ability of various p-agonists and PGE2 to stimulate intracellular PKA activity, inhibit mitogenic signaling (p42/p44 MAPK phosphorylation), and inhibit ASM [3H] thymidine incorporation stimulated by EGF. In GFP control cells, the p-agonists tested (isoproterenol, salmeterol, and albuterol) were similar in their efficacy in stimulating intracellular PKA and inhibiting EGF-stimulated growth (^25% inhibition), and exhibited modest inhibition of p42/p44 phosphorylation. Alternatively, PGE2 promoted a very strong activation of PKA and inhibition of p42/p44 phosphorylation lasting up to at least 18 hours; this corresponded with a maximal approximately 80 % inhibition of ASM growth. In PKI-expressing cells, effects of p-agonists and PGE2 on signaling events and growth inhibition were almost completely reversed. These findings suggest an association between PKA-dependent inhibition of p42/p44 activity and the antimitogenic effect of Gs-coupled receptor agonists on ASM.