Interferon-γ-induced STAT1-mediated membrane retention of NHE1 and associated proteins ezrin, radixin and moesin in HT-29 cells

This study evaluated the effect of interferon-γ (IFN-γ) upon the function and expression of type 1 Na+/H+ exchanger (NHE1) in human intestinal epithelial HT-29 cells, namely that concerning the abundance of surface NHE1 and NHE1 binding to the ezrin, radixin and moesin (ERM) family of proteins. HT-29 cells express endogenous NHE1 and the ERM family of proteins that retain the localization of NHE1 in the membrane. Long-term exposure (24 h) of HT-29 cells to IFN-γ resulted in a concentration-dependent decrease in NHE1 activity. Inhibition of NHE1 activity by IFN-γ was absent after pretreatment with cariporide. The long-term exposure to IFN-γ was accompanied by increase in surface NHE1 and ERM abundance and no changes in total NHE1 and ERM abundance. Inhibition of signal transducer and activator transcription factor 1 (STAT1) with epigallocatechin-3-gallate (EGCG) prevented the inhibitory effect of IFN-γ. Treatment with IFN-γ activated phospho-STAT1 was markedly attenuated by EGCG. The IFN-γ-induced increase in surface NHE1 and ERM abundance was prevented by EGCG. In conclusion, long-term inhibition of NHE1 activity by IFN-γ involves STAT1 phosphorylation and is accompanied by increased abundance of surface NHE1 and the NHE1 membrane anchoring ERM proteins.