Signaling of short‐ and long‐term regulation of intestinal epithelial type 1 Na + /H + exchanger by interferon‐ γ

1 The present study evaluated the effect of interferon‐ γ (IFN‐ γ ) on intestinal Na + /H + exchange (NHE) activity and the intracellular signaling pathways set into motion after IFN‐ γ receptor activation. 2 Caco‐2 cells express endogenous NHE1, NHE2 and NHE3 proteins, as detected by immunoblotting. Short‐ (0.5 h) and long‐ (24 h) term exposure of Caco‐2 cells to IFN‐ γ resulted in a concentration‐dependent decrease in NHE activity. Inhibition of NHE activity by IFN‐ γ was absent in cariporide‐treated cells, but not in cells treated with S‐3226. The long‐term exposure to IFN‐ γ was accompanied by a 20% increase in surface NHE1 abundance and no changes in total NHE1 abundance. 3 Inhibition of Raf1, mitogen‐activated protein kinase kinase (MAPKK/MEK) and p38 MAPK with, respectively, GW 5074, PD 98059 and SB 203580 and downregulation of protein kinase C (PKC) with phorbol‐12,13‐dibutyrate (100 n M for 24 h) prevented inhibition of NHE activity by IFN‐ γ (0.5 and 24 h exposure). The signal transducer and activator transcription factor 1 (STAT1) inhibitor epigallocatechin‐3‐gallate (EGCG) prevented inhibition of NHE activity by long‐ but not the short‐term treatment with IFN‐ γ . 4 Treatment with IFN‐ γ activated phospho‐p38 MAPK, this effect being detected as early as 1 h, persisting over 3 h and decreasing after 24 h. IFN‐ γ produced a sustained action of phospho‐STAT1 that was prevented by EGCG and partially attenuated by SB 203580 and insensitive to downregulation of PKC. 5 In conclusion, short‐ and long‐term inhibition of NHE1 activity by IFN‐ γ involves a complex signaling pathway that includes PKC activation and STAT1 phosphorylation, respectively, but is not accompanied by downregulation of NHE1.British Journal of Pharmacology (2005) 145 , 93–103. doi: 10.1038/sj.bjp.0706167