Physical and functional links between anion exchanger-1 and sodium pump.

ABSTRACT: Anion exchanger-1 (AE1) mediates chloride-bicarbonate exchange across the plasma membranes of erythrocytes and, via a slightly shorter transcript, kidney epithelial cells. On an omnivorous human diet, kidney AE1 is mainly active basolaterally in ?-intercalated cells of the collecting duct, where it is functionally coupled with apical proton pumps to maintain normal acid-base homeostasis. The C-terminal tail of AE1 has an important role in its polarized membrane residency. We have identified the ?1 subunit of Na(+),K(+)-ATPase (sodium pump) as a binding partner for AE1 in the human kidney. Kidney AE1 and ?1 colocalized in renal ?-intercalated cells and coimmunoprecipitated (together with the catalytic ?1 subunit of the sodium pump) from human kidney membrane fractions. ELISA and fluorescence titration assays confirmed that AE1 and ?1 interact directly, with a Kd value of 0.81 ?M. GST-AE1 pull-down assays using human kidney membrane proteins showed that the last 11 residues of AE1 are important for ?1 binding. siRNA-induced knockdown of ?1 in cell culture resulted in a significant reduction in kidney AE1 levels at the cell membrane, whereas overexpression of kidney AE1 increased cell surface sodium pump levels. Notably, membrane staining of ?1 was reduced throughout collecting ducts of AE1-null mouse kidney, where increased fractional excretion of sodium has been reported. These data suggest a requirement of ?1 for proper kidney AE1 membrane residency, and that activities of AE1 and the sodium pump are coregulated in kidney.

SUBMITTER: Su Y 

PROVIDER: S-EPMC4310651 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature