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

Year: 2025

Type: article

Abstract: ABSTRACT Background Angiotensin type 2 receptor (AT 2 R) activation promotes natriuresis in renal proximal tubule cells (RPTCs) counteracting sodium retention stimulated by the AT 1 R. Early signaling events mediating the natriuretic response with AT 2 R activation in RPTCs are currently unknown. Our previous research suggested protein phosphatase 2A (PP2A) functions downstream of the AT 2 R. In this study, we investigated the interaction of PP2A regulatory subunit B55α with the AT 2 R and requirement for B55α in AT 2 R signaling and natriuresis. Methods and Results Rats were subjected to renal interstitial (RI) infusion of vehicle or Compound 21 (C21), a non-peptide specific AT 2 R agonist, and kidney sections were probed for interactions between PP2A subunits and the AT 2 R using a proximity ligation assay. A dramatic 6-fold increase in AT 2 R-B55α interaction in apical brush border membranes of RPTCs was observed with C21 stimulation. In vitro binding of purified AT 2 R and B55α supported a direct interaction between these two proteins. To determine the requirement for B55α in renal AT 2 R signaling, siRNA targeting B55α was administered to rats in vivo by RI infusion which resulted in a ∼70% decrease in B55α in RPTCs but not distal tubules. In rats with B55α knockdown in RPTCs, natriuresis in response to C21 was abolished. Simultaneously, C21-elicited AT 2 R redistribution to and sodium transporter Na + /H + exchanger-3 (NHE3) retrieval from apical brush border membranes was lost, as observed with confocal immunofluorescence microscopy. Consistent with impaired AT 2 R signaling, B55α knockdown prevented c-Src phosphorylation in response to C21. B55α knockdown also led to a dramatic 4 to 6-fold increase in AT 2 R co-localization with the lysosomal marker LAMP1, and a 50% reduction in AT 2 R co-localization with EEA1 and Rab 7, markers for early and late endosomes, respectively. Conclusions PP2A B55α directly binds to the activated AT 2 R and is required for AT 2 R-elicited natriuresis, AT 2 R signaling and intracellular trafficking in RPTCs.

Source: American Journal of Physiology-Renal Physiology

DOI: 10.1152/ajprenal.00256.2025