Phosphorylation and Palmitoylation Dynamically Regulate Sodium Hydrogen Exchanger Isoform 1 (NHE1) Activity: Implications in Health and Disease

Abstract

The SLC9 family is made up of nine isoforms of sodium hydrogen exchangers (NHE) which regulate pH by exchanging an intracellular proton for an extracellular sodium ion. Isoform 1 (NHE1) is ubiquitously expressed and plays a vital role in multiple cellular processes in addition to regulating pH such as cellular migration and proliferation, control of cell volume, and stress fiber formation. Additionally, NHE1 is a scaffolding protein that organizes protein complexes to regulate various signaling pathways within the cell. Therefore, it is important to understand the factors contributing to NHE1 regulation as maintenance of these critical cellular functions is vital ensure a healthy cell. Regulation of NHE1 occurs onthe large intracellular C‐terminus where binding partners and posttranslational modifications (PTMs) influence the exchanger in both short‐ and long‐term manners. Phosphorylation and palmitoylation are both dynamic reversible posttranslational modifications (PTMs) that regulate proteins to influence critical cellular processes. Multiple studies have shown phosphorylation and palmitoylation can work together in a barcode to regulate proteins and alter cellular functions. Previous work in our lab has shown NHE1 is regulated by palmitoylation and that inhibition of palmitoylation in cells expressing NHE1 decreases NHE1 activity, as well as NHE1 associated cellular functions such as stress fiber formation and cell migration. NHE1 is regulated by phosphorylation of multiple sites through various kinase pathways. To better understand the relationship between palmitoylation and phosphorylation on NHE1 we used various stimuli known to regulate multiple kinase pathways that impact NHE1 phosphorylation and measured the impact on NHE1 palmitoylation. Using lysophosphatidic acid (LPA) and phorbol 12‐myristate (PMA) to increase NHE1 phosphorylation leads to increased palmitoylation of NHE1, while activation of the NHE1 phosphorylation with insulin leads to decreased NHE1 palmitoylation. Furthermore, we have shown that using these stimuli NHE1 activity increases with NHE1 palmitoylation and this can be attenuated by irreversibly inhibiting palmitoylation using 2‐bromopalmitate (2BP). Using this information, we have begun to understand how the presence or absence of palmitoylation and phosphorylation in a coordinated manner contributes to a barcode that dictates a regulatory outcome and cellular response involving the sodium hydrogen exchanger isoform 1 (NHE1). Future studies will target specific kinases involved in these pathways to further explore the mechanism through which palmitoylation is altered.Support or Funding InformationThis work was supported by the University of North Dakota School of Medicine and Health Sciences and P20 GM103442 (to U.N.D.) from the INBRE program of the National Institute of General Medical Sciences. ND EPSCoRDoctoral Dissertation Assistantship UND0023386