Distinct calcium/calmodulin-dependent serine protein kinase domains control cardiac sodium channel membrane expression and focal adhesion anchoring

Abstract

Background: Membrane-associated guanylate kinase (MAGUK) proteins function as adaptor proteins to mediate the recruitment and scaffolding of ion channels in the plasma membrane in various cell types. In the heart, the protein CASK (Calcium/CAlmodulin-dependent Serine protein Kinase) negatively regulates the main cardiac sodium channel, NaV1.5, which carries the sodium current (INa) by preventing its anterograde trafficking. CASK is also a new member of the dystrophin-glycoprotein complex, and like syntrophin, binds to the C-terminal domain of the channel. Objective: To unravel the mechanisms of CASK-mediated negative INa regulation, and interaction with the dystrophin-glycoprotein complex in cardiac myocytes. Methods: CASK adenoviral truncated constructs with sequential single functional domain deletions were designed for overexpression in cardiac myocytes: CASK CAMKII , CASK L27A , CASK L27B , CASK PDZ , CASK SH3 , CASK HOOK , and CASK GUK. Combination of whole-cell patch-clamp recording, total internal reflection fluorescence microscopy (TIRFm) and biochemistry experiments were conducted in cardiac myocytes to study the functional consequences of domain deletions. Results: We show that both L27B and GUK domains are required for the negative regulatory effect of CASK on INa and NaV1.5 surface expression and that the HOOK domain is essential for interaction with the cell adhesion dystrophin-glycoprotein complex. Conclusions: This study demonstrates that the multi-modular structure of CASK confers an ability to simultaneously interact with several targets within cardiomyocytes. Through its L27B, GUK, and HOOK domains, CASK potentially provides the ability to control channel delivery at adhesion points in cardiomyocyte.

Remodeling of Ion Channel Trafficking and Cardiac Arrhythmias

“…Interestingly, when Na V 1.5 is overexpressed, internalization of Kir2.1 appears to be reduced, suggesting that the channels regulate each other in part through retrograde trafficking [ 24 ]. Recently characterized in the myocardium, the MAGUK protein CASK negatively regulates the surface expression of Na V 1.5 by impeding the Golgi-to-plasma-membrane trafficking of the channel [ 27 , 28 ] and reduces the Kir2.x-mediated I K1 current (personal unpublished data). Of note, previous publications have reported that SAP97 and CASK act synergistically to regulate the trafficking and targeting of Kir2.2 potassium channels at the basolateral membrane of epithelial cells [ 23 ].…”

“…As a syntrophin, CASK is restricted to the LM in the costameric dystrophin–glycoprotein complex and interacts with the Na V 1.5 channel through its C -terminal PDZ-binding motif SIV [ 27 ]. In contrast to other Na V 1.5 partners, CASK negatively regulates the I Na current by impeding the early forward trafficking of Na V 1.5 to the LM of cardiomyocytes [ 27 , 28 ]. Given its multi-modular structure, CASK can control channel delivery at adhesion points in cardiomyocytes, linking channel expression to structural organization of cardiomyocytes [ 28 ].…”

Complete loss of CASK causes severe ataxia through cerebellar degeneration in human and mouse

“…Although often considered to be a component of presynaptic terminals, CASK in fact is ubiquitously expressed in the body and has been implicated in a variety of functions 21, 22 . Outside of the brain, CASK has been shown to participate in cell proliferation 23 , cell polarization 24 , gap junctions and wound healing 25 , insulin secretion and signaling 26, 27 , hypoxia response 28, 29 , renal development and disease 30, 31 , spermatogenesis and sperm motility 32, 33 , and cardiac conductivity 34, 35 , to name a few examples. In the brain, CASK has been examined as both a pre- and post-synaptic molecule 36, 37 .…”

Complete Loss of CASK Causes Severe Ataxia Through Cerebellar Degeneration

“…Although often considered to be a component of presynaptic terminals, CASK in fact is ubiquitously expressed in the body and has been implicated in a variety of functions (Hata et al 1996;Stevenson et al 2000). Outside of the brain, CASK has been shown to participate in cell proliferation (Ojeh et al 2008), cell polarization (Caruana 2002), gap junctions and wound healing (Marquez-Rosado et al 2012), insulin secretion and signaling (Wang et al 2006;Zhu et al 2014), hypoxia response (Su et al 2007;Weigand et al 2012), renal development and disease (Ahn et al 2013;Beaudreuil et al 2019), spermatogenesis and sperm motility (Aravindan et al 2012;Burkin et al 2004), and cardiac conductivity (Beuriot et al 2020;Eichel et al 2016), to name a few examples. In the brain, CASK has been examined as both a pre-and post-synaptic molecule (Butz et al 1998;Hsueh et al 1998).…”