Regulation of Cl−in signaling and ion transport by IRBIT‐mediated recruitment of multiple kinase and phosphatase pathways

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IRBIT is a multifunctional protein that also controls the activity of IP3 receptors and multiple Cl− and HCO3− transporters, including NBCe1‐B, CFTR and Slc26a6, by unknown mechanisms. With the ubiquitous NBCe1‐B, IRBIT interacts with the autoinhibitory domain (AID), exposing two cryptic GXXXP motifs to confer regulation by Cl−in. Here, we report that IRBIT‐dependent combinatorial dephosphorylation of S232/S233/S235 controls NBCe1‐B close and open states by determining autoinhibition and regulation by Cl−in. The pS233/pS235 conformer is fully active, no longer activated by IRBIT or inhibited by Cl−in. The pS232/pS235 conformer is similar to wild‐type NBCe1‐B, while the pS232/pS233 conformer is partially active, but retains inhibition by Cl−in. IRBIT then recruits the kinases SPAK and CaMKII to control phosphorylation of S65 and S12, respectively, which determine inhibition by Cl−in at the 32GXXXP36 and 194GXXXP198 motifs. Recruitment by IRBIT of PP1 and calcineurin dephosphorylates S65 and S12, respectively, and relieves inhibition by Cl−in. These findings reveal how multiple kinase/phosphatase pathways use multiple phosphorylation sites to fine tune a transport function, which has important implications for epithelial fluid and HCO3− secretion.Support or Funding InformationAll the work was supported by NIH fundingThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.