Phosphorylation of α-syntrophin is responsible for its subcellular localization and interaction with dystrophin in muscle cells

Abstract

Syntrophin is a well-known adaptor protein that links intracellular proteins with the dystrophin-glycoprotein complex (DGC) at the sarcolemma. However, little is known about the underlying mechanism that regulates the intracellular localization of α-syntrophin and its interaction with dystrophin. In this study, we demonstrate that α-syntrophin phosphorylation determines its intracellular localization and interaction with dystrophin in muscle cells. α-Syntrophin, a predominant isoform in skeletal muscles, directly interacts with ion channels, enzymes, receptors, and DGC proteins. Despite α-syntrophin being a potential signaling molecule, most studies focus on its function as a dystrophin-associated protein. However, we previously reported that α-syntrophin has a variety of DGC-independent functions to modulate cell migration, differentiation, survival, and protein stability. According to the results of the <em>in vitro</em> phosphorylation assays using subcellular fractions, the phosphorylated α-syntrophin accumulated only at the plasma membrane, and this event occurred regardless of dystrophin expression. However, the α-syntrophin interacting with dystrophin at the membrane was not in a phosphorylated state. We also identified that protein kinase C (PKC) was involved in the phosphorylation of α-syntrophin, which restricted α-syntrophin to interact with dystrophin. In conclusion, we demonstrate that the phosphorylation of α-syntrophin by PKC regulates its intracellular localization and interaction with dystrophin.