Epidermal Growth Factor Activates Na+/H+ Exchange in Podocytes through a Mechanism that Involves Janus Kinase and Calmodulin

Abstract

Previous studies from our laboratory have shown that the NHE-1 can be activated by G protein-coupled receptors or hypertonic medium, through janus kinase 2 (Jak2)-dependent phosphorylation of calmodulin (CaM) and subsequent interaction between CaM and NHE-1. Therefore, we wanted to determine whether the EGF receptor regulated NHE-1 activity through Jak2 and CaM. EGF induced concentration-dependent increases in proton efflux in renal podocytes as accessed using a Cytosensor microphysiometer. Stimulation of proton efflux by EGF in podocytes was diminished in the presence of MIA or a sodium-free solution, which demonstrates that EGF stimulates a sodium-dependent proton efflux that can be attenuated by a selective NHE-1 inhibitor in podocytes. Furthermore, inhibitors of Jak2 and calmodulin attenuated EGF-induced NHE-1 activity. Co-immunoprecipitation studies determined that EGF induced formation of complexes between Jak2, CaM, and NHE-1. We found that there were increased amounts of NHE-1 and calmodulin assembled with Jak2 upon EGF stimulation. The results suggest that EGF induces NHE-1 activity in podocytes through Jak2 and increased interaction between CaM and NHE-1. This work was supported by Veterans Affairs Merit Award and NIH R01DK052448.