Inhibition of dystroglycan binding to laminin disrupts the PI3K/AKT pathway and survival signaling in muscle cells

Abstract

Dystroglycan is a component of the dystrophin-glycoprotein complex (DGC) in muscle and a cell surface receptor for laminin. Numerous muscular dystrophies are the result of disruption of proteins comprising the DGC, but the underlying pathogenetic mechanisms are unknown. Because apoptosis is an early feature of muscular dystrophy in vivo, and perturbation of cell-extracellular matrix associations is known to induce apoptosis, we investigated the role of dystroglycan-laminin interactions in the propagation and maintenance of cell survival signals in muscle cells. We found that disrupting the interaction between alpha-dystroglycan and the extracellular matrix protein laminin induces apoptosis in muscle cells. This increase in apoptosis is mediated in part by caspase activation and can be blocked by a caspase-3 inhibitor. We demonstrate a role for the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway in muscle cell-survival signaling using a pharmacological inhibitor of PI3K. Treatment with this inhibitor resulted in decreased phosphorylation of AKT and its downstream effector glycogen synthase kinase (GSK)-3beta and induced apoptosis in muscle cell cultures. Disruption of dystroglycan-laminin interactions resulted in decreased phosphorylation of AKT and GSK-3beta. Furthermore, activation of AKT prior to the disruption of dystroglycan-laminin protected the muscle cells from the induction of apoptosis. These results support a role for the PI3K/AKT pathway in the propagation of cell-survival signals mediated by the DGC and provide new insight into the molecular pathogenesis associated with the development of muscular dystrophies.