Ankyrin-B Regulates Kir6.2 Membrane Expression and Function in Heart

Abstract

Ankyrin polypeptides are critical for normal membrane protein expression in diverse cell types, including neurons, myocytes, epithelia, and erythrocytes. Ankyrin dysfunction results in defects in membrane expression of ankyrin-binding partners (including ion channels, transporters, and cell adhesion molecules), resulting in aberrant cellular function and disease. Here, we identify a new role for ankyrin-B in cardiac cell biology. We demonstrate that cardiac sarcolemmal K ATP channels directly associate with ankyrin-B in heart via the K ATP channel ␣-subunit Kir6.2. We demonstrate that primary myocytes lacking ankyrin-B display defects in Kir6.2 protein expression, membrane expression, and function. Moreover, we demonstrate a secondary role for ankyrin-B in regulating K ATP channel gating. Finally, we demonstrate that ankyrin-B forms a membrane complex with K ATP channels and the cardiac Na/K-ATPase, a second key membrane transporter involved in the cardiac ischemia response. Collectively, our new findings define a new role for cardiac ankyrin polypeptides in regulation of ion channel membrane expression in heart.Ankyrins are multivalent adapter proteins required for the proper membrane expression of ion channels, transporters, cell adhesion molecules, and structural and signaling molecules in excitable and non-excitable cells (1). Three genes (ANK1, ANK2, and ANK3) encode a host of structurally similar but functionally distinct ankyrin polypeptides (ankyrin-R, ankyrin-B, and ankyrin-G, respectively) with specific roles in erythrocyte membrane structure, cardiac excitability, polarized epithelial ion regulation, and neuronal development. In heart, ankyrins regulate membrane excitability by coordinating the expression of voltagegated Na ϩ and Ca 2ϩ channels, cytoskeletal elements, key membrane transporters and pumps, and signaling proteins (2, 3). The importance of cardiac ankyrins for normal physiology is demonstrated by human disease associated with dysfunction in ankyrinbased pathways. For example, dysfunction in the ankyrin-G-based cellular pathway for voltage-gated Na ϩ channel membrane expression is associated with the potentially fatal Brugada syndrome cardiac arrhythmia due to reduced membrane sodium current (4, 5).In heart, ankyrin-B is critical for regulating membrane protein expression, with ankyrin-B dysfunction linked to cardiovascular disease in humans and mice (6 -10). Humans harboring ANK2 loss-of-function gene variants display a complex cardiac phenotype that may include sinus node disease, conduction defects, ventricular arrhythmia, and sudden death (6 -8, 10). Mice lacking one functional allele of Ank2 (ankyrin-B ϩ/Ϫ mice) display similar phenotypes and have been utilized to identify and validate potential ankyrin-B protein partners that contribute to the human disease phenotype (6). More recently, ANK2 variants have been linked with arrhythmia susceptibility in the general human population (11). Furthermore, ankyrin-B dysfunction has been identified following myocardial infarction (12, 13), sug...

KATPChannels in the Cardiovascular System

“…In addition to this list of candidates, there is evidence that syntaxin 1A may interact with SURx subunits and that this interaction regulates the function of K ATP channels in pancreatic ␤-cells and in cardiac myocytes (104,108,421,422,634) and that this binding may depend on PIP 2 levels (883). In cardiac muscle, ankyrin-B was found to interact directly with the Kir6.2 subunit and to regulate the membrane expression and function of K ATP channels in the heart (494). The interaction with ankyrin-B is likely to reflect a trafficking or membrane anchoring function, and it is possible that ␤IV-spectrin may have a similar role, as has been described for the pancreatic K ATP channel (449).…”

β IV -Spectrin and CaMKII facilitate Kir6.2 regulation in pancreatic beta cells

“…2D). We previously demonstrated that AnkB directly associates with Kir6.2 (12,16) and AnkB/ SUR1 interactions require Kir6.2 (Fig. S2).…”

Evidence of a Structural and Functional Ammonium Transporter RhBG·Anion Exchanger 1·Ankyrin-G Complex in Kidney Epithelial Cells

“…An important finding is that RhBG (2) and possibly kAE1 need to associate with ankyrin-G to be functional. Previous reports demonstrated a similar link between ankyrin binding and activity of an ion channel: ankyrin-G for cardiac Nav1.5 and neuronal Nav1.6 sodium channels (36,37) and ankyrin-B for cardiac K ATP channel (38). A very recent study showed a physical and functional interaction between kAE1 and Na ϩ ,K ϩ -ATPase in renal ␣-intercalated cells (39), and Na ϩ ,K ϩ -ATPase is known to bind ankyrin-G (26).…”