The Interplay between Palmitoylation and Phosphorylation of NHE1 in the Regulation of Cell Proliferation.

Abstract

The Na+‐H+ Exchanger Isoform 1 (NHE1) is key to the regulation of cell cycle progression and cell proliferation. NHE1 is a 12‐pass transmembrane transport protein that exchanges one extracellular Na+ for one intracellular H+ with the primary function of intracellular pH regulation. This pH regulation is essential to the control of cell proliferation and migration. The exchanger’s transmembrane domain is involved in ion exchange and the extended cytoplasmic tail functions as the protein’s regulatory domain. The regulation of NHE1 is extremely complex and involves protein and lipid binding sites including phosphorylation and palmitoylation sites. NHE1 transport activity is regulated by a series of signaling pathways which include kinases such as MEK, Erk, Rsk, Rock, and Akt. Recently, it was recognized that NHE1 also undergoes reversible palmitoylation. Here we evaluate the impact of the inhibition of phosphorylation and palmitoylation of NHE1 on cell proliferation to identify the interplay between these two covalent modifications of NHE1. We hypothesize that the combined impact of inhibition of palmitoylation and phosphorylation will have a synergistic impact inhibiting cell growth. Cell proliferation was evaluated utilizing Chinese hamster lung fibroblasts (PSN cells), which express human NHE1, in the presence of the inhibitors Mk‐2206 (Akt), PD98059 (MEK), Y27632 (Rock), 2‐BP (Palmitoylation), and EIPA (NHE1).