The NHE3 interacting PDZ protein NHERF2 determines the lipid raft association of the apical Na+/H+ exchanger NHE3 in murine small intestine

Abstract

BackgroundIntestinal NHE3 is scaffolded and differentially regulated by Na+/H+Exchanger Regulatory Factor (NHERF) PDZ‐adaptors. NHE3 partially resides in lipid rafts of the Brush Border Membrane (BBM).AimTo investigate if there is a cross talk between NHERFs and membrane rafts, specifically if NHERFs associate differentially with the raft and non‐raft fraction of NHE3, and whether they influence the function and distribution of NHE3 in these microdomains.Methods and ResultsMurine BBM was detergent‐solubilised and lipid rafts isolated by density gradient floatation. NHE3 was partially, NHERF2 strongly and NHERF1 weakly raft‐associated, and NHERF3 exclusively in the non‐raft fraction. In absence of NHERF2, raft‐associated NHE3 was strongly decreased. Increasing the membrane sphingomyelin/ceramide ratio, increased NHE3‐dependent small intestinal fluid absorption in vivo, as well as overall NHE3 in the lipid rafts, suggesting a positive correlation between NHE3 function and raft association.ConclusionsIn murine small intestinal BBM, NHE3 differentially associates with the different NHERFs in the raft and non‐raft fraction. NHE3 raft‐association is NHERF2‐dependent. NHE3 and NHERF raft‐association and function are modulated by changes in the lipidic environment. This suggests that PDZ‐scaffolding proteins are involved in the retention of membrane proteins within lipid raft platforms.