Protein phosphatase 2A subunit B55 alpha is required for angiotensin type 2 receptor elicited natriuresis.

Angiotensin type 2 receptor (AT(2)R) activation promotes natriuresis, thereby contributing to sodium balance and blood pressure regulation. In this study, we explored a novel intermediate in AT(2)R signaling, protein phosphatase 2A (PP2A) regulatory subunit B55α. Probing for PP2A subunit-AT(2)R interactions in vivo using proximity ligation assays on kidney sections prepared from rats after renal interstitial (RI) infusion of vehicle or the AT(2)R agonist compound 21 (C21), we observed a sixfold increase in AT(2)R-B55α interaction in apical brush border membranes of renal proximal tubule cells (RPTCs) with C21 stimulation. In vitro binding of purified AT(2)R and B55α supported a direct interaction between these two proteins. To test whether B55α is required for renal AT(2)R signaling, we administered siRNA targeting B55α to rats in vivo by RI infusion, which resulted in a ∼70% decrease in B55α in proximal but not distal tubules. Remarkably, RPTC B55α knockdown abolished C21-induced natriuresis and simultaneously prevented C21-mediated AT(2)R redistribution to apical brush border membranes and sodium transporter Na(+)/H(+) exchanger-3 (NHE-3) retrieval. Furthermore, B55α knockdown prevented cellular Src (c-Src) phosphorylation with C21 stimulation, increased AT(2)R colocalization with lysosomal marker lysosomal-associated membrane protein 1 (LAMP1) by four to sixfold, and reduced AT(2)R colocalization with early and late endosomal markers early endosome antigen 1 (EEA1) and Rab7 by 50%. In conclusion, our results show that RPTC PP2A B55α binds to activated AT(2)R and is required for AT(2)R signaling to natriuresis and AT(2)R intracellular trafficking. We thus establish RPTC PP2A B55α as a key AT(2)R signaling intermediate and potential therapeutic target to promote sodium excretion in hypertensive individuals.NEW & NOTEWORTHY Protein phosphatase 2A (PP2A) B55α is required for angiotensin type 2 receptor (AT(2)R) natriuretic signaling and AT(2)R intracellular trafficking in renal proximal tubule cells (RPTCs). RPTC PP2A B55α is thus a key AT(2)R signaling intermediate and potential therapeutic target to promote sodium excretion in hypertensive individuals. This study introduces knocking down B55α in vivo specifically in RPTCs using renal interstitial infusion of siRNA as a novel and unique approach to investigate physiological protein function in the kidney.