Identification of moesin as NKCC2-interacting protein and analysis of its functional role in the NKCC2 apical trafficking.

BACKGROUND INFORMATION: The renal Na(+) -K(+) -2Cl(-) co-transporter (NKCC2) is expressed in kidney thick ascending limb (TAL) cells, where it mediates NaCl reabsorption regulating body salt levels and blood pressure. RESULTS: In this study we used a well-characterized NKCC2 construct (c-NKCC2) to identify NKCC2 interacting proteins by an antibody shift assay coupled with Blue Native/SDS-PAGE (BN/SDS-PAGE) and Mass Spectrometry (MS). Among the interacting proteins we identified moesin, a protein belonging to ERM (Ezrin, Radixin, Moesin) family. Co-immunoprecipitation experiments confirmed that c-NKCC2 interacts with the N-terminal domain of moesin in LLC-PK1 cells. Moreover, c-NKCC2 accumulates in intracellular and sub-apical vesicles in cells transfected with a moesin dominant negative GFP-tagged construct. In addition, moesin knockdown by siRNA decreases by about 50% c-NKCC2 surface expression. Specifically, endocytosis and exocytosis assays showed that moesin knockdown does not affect c-NKCC2 internalization but strongly reduces exocytosis of the co-transporter. CONCLUSIONS: Our data clearly demonstrate that moesin plays a critical role in apical membrane insertion of NKCC2, suggesting a possible involvement of moesin in regulation of Na(+) and Cl(-) absorption in the kidney.