RGS4 controls airway hyperresponsiveness through GAP-independent mechanisms

Regulators of G protein signaling (RGS proteins) constrain G protein-coupled receptor (GPCR)-mediated and other responses throughout the body primarily, but not exclusively, through their GTPase activating (GAP) activity. Asthma is a highly prevalent condition characterized by airway hyper-responsiveness (AHR) to environmental stimuli resulting in part from amplified GPCR-mediated airway smooth muscle (ASM) contractility. Rgs2 or Rgs5 gene deletion in mice enhances AHR and ASM contraction whereas RGS4 knockout (KO) mice unexpectedly have decreased AHR due to increased production of the bronchodilator prostaglandin E2 (PGE2) by lung epithelial cells. Here we found that knockin mice harboring Rgs4 alleles encoding a point mutation (N128A) that sharply curtails RGS4 GAP activity had increased AHR, reduced airway PGE2 levels, and augmented GPCR-induced bronchial contraction compared to either RGS4 KO mice or WT controls. RGS4 interacted with the p85a subunit of PI3 kinase (PI3K) and inhibited PI3K-dependent PGE2 secretion elicited by TGFb in airway epithelial cells. Together these findings suggest that RGS4 affects asthma severity in part by regulating the airway inflammatory milieu in a G protein-independent manner.