Browsing by Author "Amaral, M.D."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Antagonistic Regulation of CFTR Cell Surface Expression by Protein Kinases WNK4 and Spleen Tyrosine KinasePublication . Mendes, A.I.; Matos, P.; Amaral, M.D.; Jordan, P.Members of the WNK (with no lysine (K)) subfamily of protein kinases regulate various ion channels involved in sodium, potassium and chloride homeostasis by either inducing their phosphorylation or regulating the number of channel proteins expressed at the cell surface. Here, we describe that WNK4 promotes the cell surface expression of the cystic fibrosis transmembrane conductance regulator (CFTR) in mammalian cells. The mechanism by which WNK4 acts on CFTR involves interaction with spleen tyrosine kinase (Syk), which we find to phosphorylate Tyr512 in the first nucleotide-binding domain (NBD) 1 of CFTR. The presence of WNK4 prevents the phosphorylation of NBD1 by Syk in vitro in a kinase-independent manner. In baby hamster kidney cells stably expressing CFTR, catalytically active Syk reduces while WNK4 promotes the cell surface expression of CFTR. This is shown by biotinylation of cell surface proteins, immunofluorescence microscopy and functional efflux assays. Mutation of Tyr512 to either glutamic acid or phenylalanine is sufficient to alter CFTR surface levels. Together, our results identify that Tyr512 phosphorylation is a novel signal regulating the prevalence of CFTR at the cell surface and describe an antagonistic role of WNK4 and Syk in this process.
- Contribution of casein kinase 2 and spleen tyrosine kinase to CFTR trafficking and protein kinase A-induced activityPublication . Luz, S.; Kongsuphol, P.; Mendes, A.I.; Romeiras, F.; Sousa, M.; Schreiber, R.; Matos, P.; Jordan, P.; Metha, A.; Amaral, M.D.; Kunzelmann, K.; Farinha, C.M.Previously, the pleiotropic "master kinase" casein kinase 2 (CK2) was shown to interact with CFTR, the protein responsible for cystic fibrosis (CF). Moreover, CK2 inhibition abolished CFTR conductance in cell-attached membrane patches, native epithelial ducts, and Xenopus oocytes. CFTR possesses two CK2 phosphorylation sites (S422 and T1471), with unclear impact on its processing and trafficking. Here, we investigated the effects of mutating these CK2 sites on CFTR abundance, maturation, and degradation coupled to effects on ion channel activity and surface expression. We report that CK2 inhibition significantly decreased processing of wild-type (wt) CFTR, with no effect on F508del CFTR. Eliminating phosphorylation at S422 and T1471 revealed antagonistic roles in CFTR trafficking: S422 activation versus T1471 inhibition, as evidenced by a severe trafficking defect for the T1471D mutant. Notably, mutation of Y512, a consensus sequence for the spleen tyrosine kinase (SYK) possibly acting in a CK2 context adjacent to the common CF-causing defect F508del, had a strong effect on both maturation and CFTR currents, allowing the identification of this kinase as a novel regulator of CFTR. These results reinforce the importance of CK2 and the S422 and T1471 residues for regulation of CFTR and uncover a novel regulation of CFTR by SYK, a recognized controller of inflammation.