Regulation of anion exchanger Slc26a6 by protein kinase C

Abstract

(CFEX, PAT1) is an anion exchanger expressed in several tissues including renal proximal tubule, pancreatic duct, small intestine, liver, stomach, and heart. It has recently been reported that PKC activation inhibits A6-mediated Cl/HCO 3 exchange by disrupting binding of carbonic anhydrase to A6. However, A6 can operate in HCO 3-independent exchange modes of physiological importance, as A6-mediated Cl/ oxalate exchange plays important roles in proximal tubule NaCl reabsorption and intestinal oxalate secretion. We therefore examined whether PKC activation affects HCO 3-independent exchange modes of Slc26a6 functionally expressed in Xenopus oocytes. We found that PKC activation inhibited Cl/formate exchange mediated by Slc26a6 but failed to inhibit the related anion exchanger pendrin (SLC26A4) under identical conditions. PKC activation inhibited Slc26a6-mediated Cl/formate exchange, Cl/oxalate exchange, and Cl/Cl exchange to a similar extent. The inhibitor sensitivity profile and the finding that PMA-induced inhibition was calcium independent suggested a potential role for PKC-␦. Indeed, the PKC-␦-selective inhibitor rottlerin significantly blocked PMA-induced inhibition of Slc26a6 activity. Localization of Slc26a6 by immunofluorescence microscopy demonstrated that exposure to PKC activation led to redistribution of Slc26a6 from the oocyte plasma membrane to the intracellular compartment immediately below it. We also observed that PMA decreased the pool of Slc26a6 available to surface biotinylation but had no effect on total Slc26a6 expression. The physiological significance of these findings was supported by the observation that PKC activation inhibited mouse duodenal oxalate secretion, an effect blocked by rottlerin. We conclude that multiple modes of anion exchange mediated by Slc26a6 are negatively regulated by PKC-␦ activation.oxalate; formate; chloride; duodenum SLC26A6 (CFEX, PAT1) is a member of the SLC26 gene family of anion transporters and is expressed in many tissues including renal proximal tubule, pancreatic ducts, small intestine, liver, stomach, and heart (22,25,27,35,39,41). Functional expression studies have indicated that A6 can mediate multiple modes of anion exchange including Cl/formate, Cl/oxalate, Cl/HCO 3 , and Cl/OH exchanges (18,22,23,39,41). The physiological significance of A6 is indicated by defects in apical membrane Cl/base exchange in the proximal tubule and intestine of Slc26a6-null mice (6,17,40).Recent studies have begun to elucidate the molecular mechanisms regulating A6 transport activity. In particular, Cl/HCO 3 exchange activity of A6 is negatively regulated by ␣-adrenergic stimulation and angiotensin II, effects that are mediated by protein kinase C (PKC) activation (1, 2). Inhibition by PKC was attributed to PKC-mediated displacement of carbonic anhydrase II from binding to SLC26A6 and consequent disruption of the HCO 3 transport metabolon (2). Inhibition of A6 by PKC may explain the observation that agonists acting through PKC inhibit HCO 3 secretion in the pancreas (1...

Two PKC consensus sites on human acid-sensing ion channel 1b differentially regulate its function

“…Another possibility is that the PKC activators cause membrane retrieval of the channel, therefore decreasing its functional expression. This has been reported for other membrane proteins expressed in oocytes like ␣␤␥-rENaC (1), type II Na ϩ -P i cotransporters (16), glutamate transporter EAAC1 (35), and anion exchanger SLC26A6 (22). The effects of PMA on membrane retrieval could be specific to the membrane protein expressed in oocytes or general endocytosis of the plasma membrane (1).…”

Activated PKCδ and PKCϵ Inhibit Epithelial Chloride Secretion Response to cAMP via Inducing Internalization of the Na+-K+-2Cl− Cotransporter NKCC1

“…This is a novel finding because our previous pharmacological studies revealed that PMA-induced internalization of NKCC1 is dependent upon isoform PKC⑀ (12). In other studies, nPKC and cPKCs have been suggested to regulate membrane protein surface expression, but in all these instances the identity of the specific PKC isoform is only inferable through the use of pharmacological inhibitors (19,60,61). Knockdown of the PKC isoforms did not change steadystate TER (Table 1), suggesting it does not affect the constitutive maintenance of tight junction integrity under these conditions.…”

Solution Structure of the Guanine Nucleotide-binding STAS Domain of SLC26-related SulP Protein Rv1739c from Mycobacterium tuberculosis

“…The STAS domains of human SLC26A3 (29) and human SLC26A9 (53) interact in vitro with the phosphorylated R domain of CFTR, but the reported regulatory interactions of SLC26 polypeptides and CFTR in vitro and in vivo have varied. PKC phosphorylation of the human SLC26A6 STAS domain has been suggested to regulate Cl Ϫ /HCO 3 Ϫ exchange activity through CAII binding (54), but this phosphorylation did not regulate oxalate transport (55), and its relationship to CFTR is unknown. Although the R domain of CFTR is not shared among other ABC proteins, Rv1739c might function as a regulator of the M. tuberculosis ABC family sulfate permease CysTWA (15).…”