Regulation of apical membrane enrichment and retention of plasma membrane Ca ATPase splice variants by the PDZ-domain protein NHERF2.

The localization of plasma membrane calcium ATPase (PMCA) isoforms in specified membrane compartments is crucial for their function in local Ca(2+) handling. PMCA2w/b is present in the apical membrane whereas alternative splice variants PMCA2x/b and 2z/b reside in the basolateral membrane in polarized epithelial cells. Here we found that the apical scaffolding protein NHERF2 greatly enhances the apical concentration of PMCA2w/b by tethering the pump to the underlying actin cytoskeleton. The interaction requires the C-terminal PDZ binding sequence in PMCA2b and results in increased membrane retention and decreased lateral mobility of the pump. In contrast, PMCA2x/b remains exclusively basolateral even when NHERF2 is overexpressed. Our results suggest that the alternatively spliced intracellular loop in PMCA2 imposes dominant membrane targeting information. NHERF2-mediated recruitment may be an effective means for polarized cells to regulate the abundance of PMCA2w/b in the apical membrane to meet an increased demand for local Ca(2+) extrusion.