Protein kinase G increases antioxidant function in lung microvascular endothelial cells by inhibiting the c-Abl tyrosine kinase

Oxidant injury contributes to acute lung injury (ALI). We previously reported that activation of protein kinase G(I) (PKG(I)) posttranscriptionally increased the key antioxidant enzymes catalase and glutathione peroxidase 1 (Gpx-1) and attenuated oxidant-induced cytotoxicity in mouse lung microvascular endothelial cells (MLMVEC). The present studies tested the hypothesis that the antioxidant effect of PKG(I) is mediated via inhibition of the c-Abl tyrosine kinase. We found that activation of PKG(I) with the cGMP analog 8pCPT-cGMP inhibited c-Abl activity and decreased c-Abl expression in wild-type but not PKG(I)(-/-) MLMVEC. Treatment of wild-type MLMVEC with atrial natriuretic peptide also inhibited c-Abl activation. Moreover, treatment of MLMVEC with the c-Abl inhibitor imatinib increased catalase and GPx-1 protein in a posttranscriptional fashion. In imatinib-treated MLMVEC, there was no additional effect of 8pCPT-cGMP on catalase or GPx-1. The imatinib-induced increase in antioxidant proteins was associated with an increase in extracellular H2O2 scavenging by MLMVEC, attenuation of oxidant-induced endothelial barrier dysfunction, and prevention of oxidant-induced endothelial cell death. Finally, in the isolated perfused lung, imatinib prevented oxidant-induced endothelial toxicity. We conclude that cGMP, through activation of PKG(I), inhibits c-Abl, leading to increased key antioxidant enzymes and resistance to lung endothelial oxidant injury. Inhibition of c-Abl by active PKG(I) may be the downstream mechanism underlying PKG(I)-mediated antioxidant signaling. Tyrosine kinase inhibitors may represent a novel therapeutic approach in oxidant-induced ALI.