Contribution of Casein Kinase 2 and Spleen Tyrosine Kinase to CFTR Trafficking and Protein Kinase A-Induced Activity

Abstract

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 cellattached 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.

Detection of Phospho-Sites Generated by Protein Kinase CK2 in CFTR: Mechanistic Aspects of Thr1471 Phosphorylation

“…While the PKA sites, whose phosphorylation has been validated in vivo are concentrated in the R domain (where they play a prominent role in the activation of the channel function) the potential CK2 sites are also localized outside the R domain and, by analogy with other CK2 targets whose phosphorylation commits them to degradation (see e.g. [10]–[12]), they may be implicated in the premature proteolysis of CFTR, also consistent with the outcome of recent mutational studies [13], [14]. It should be noted in fact that, although wild type CFTR is much more stable than its Phe508del counterpart, it nevertheless undergoes a very stringent quality control as well, resulting in perhaps 50% of the protein being discarded and proteolytically degraded [15].…”

Encephalomyocarditis Virus Leader Is Phosphorylated by CK2 and Syk as a Requirement for Subsequent Phosphorylation of Cellular Nucleoporins

“…Luz et al found that CK2 and Syk cophosphorylate CFTR, the protein responsible for cystic fibrosis. Those data attributed the primary phosphorylation event to Syk, with the consequence as altered CFTR trafficking (43).…”

Protein Kinase CK2 and Angiogenesis

“…By phosphorylating [57][58][59] or interacting with Akt [60,61], CK2 can modulate the activity of several angiogenic mediators simultaneously. Furthermore, CK2 is acting upstream of ERK1/2 and p38 MAPK and might thus also modulate the MAP kinase pathway, which is initiated by VEGF and IGF-1 [62,63].…”