Interactions Between Sorting Protein-Related Receptor And Calcineurin To Activate Renal Na-K-2cl Cotransporter

Activity of the Na‐K‐2Cl cotransporter (NKCC2) of thick ascending limb (TAL) depends on its phosphorylation. The sorting protein‐related receptor SORLA facilitates this process, but the underlying mechanism is still elusive. We hypothesized that SORLA may interfere with kinases or phosphatases relevant for NKCC2 phosphorylation. We have studied the regulation of the proline/alanine‐rich kinase (SPAK), oxidative stress responsive kinase 1 (OSR1), and calcineurin phosphatase A (CnA) in wildtype (WT) and SORLA‐deficient (SORLA−/−) kidneys in vivo and in cell culture. Knockdown of SPAK/OSR1 in cultured rat TAL cells decreased, whereas inhibition of calcineurin with cyclosporin A (CsA) increased NKCC2 phosphorylation thus confirming their relevance for the transporter. SORLA‐deficiency was associated with decreased NKCC2 phosphorylation (−84%), unchanged abundance and distribution of SPAK and OSR1 kinases, and increased abundance of CnAβ isoform in the apical compartment of TAL epithelia (+201%). Short term administration of CsA to SORLA−/− mice restored their decreased NKCC2 phosphorylation. Coimmunoprecipitations from rat kidney revealed interactions between CnAβ, NKCC2, and SORLA. Our results suggest that SORLA participates in calcineurin degradation in TAL thereby supporting activating phosphorylation of NKCC2.