Dystrophin glycoprotein complex-associated Gbetagamma subunits activate phosphatidylinositol-3-kinase/Akt signaling in skeletal muscle in a laminin-dependent manner.
Previously, we showed that laminin-binding to the dystrophin glycoprotein complex (DGC) of skeletal muscle causes a heterotrimeric G-protein (Galphabetagamma) to bind, changing the activation state of the Gsalpha subunit. Others have shown that laminin-binding to the DGC also leads to Akt activation. Gbetagamma, released when Gsalpha is activated, is known to bind phosphatidylinositol-3-kinase (PI3K), which activates Akt in other cells. Here, we investigate whether muscle Akt activation results from Gbetagamma, using immunoprecipitation and immunoblotting, and purified Gbetagamma. In the presence of laminin, PI3K-binding to the DGC increases and Akt becomes phosphorylated and activated (pAkt), and glycogen synthase kinase is phosphorylated. Antibodies, which specifically block laminin-binding to alpha-dystroglycan, prevent PI3K-binding to the DGC. Purified bovine brain Gbetagamma also caused PI3K and Akt activation. These results show that DGC-Gbetagamma is binding PI3K and activating pAkt in a laminin-dependent manner. Mdx mice, which have greatly diminished amounts of DGC proteins, display elevated pAkt signaling and increased expression of integrin beta1 compared to normal muscle. This integrin binds laminin, Gbetagamma, and PI3K. Collectively, these suggest that PI3K is an important target for the Gbetagamma, which normally binds to DGC syntrophin, and activates PI3K/Akt signaling. Disruption of the DGC in mdx mouse is causing dis-regulation of the laminin-DGC-Gbetagamma-PI3K-Akt signaling and is likely to be important to the pathogenesis of muscular dystrophy. Upregulating integrin beta1 expression and activating the PI3K/Akt pathway in muscular dystrophy may partially compensate for the loss of the DGC. The results suggest new therapeutic approaches to muscle disease.
Xiong
Yongmin
Y
Key Laboratory of Environment and Genes Related to Disease, Department of Public Health, Xi'an Jiaotong University College of Medicine, Xi'an, Shaanxi Province, People's Republic of China.
Zhou
Yanwen
Y
Jarrett
Harry W
HW
D000730:Androstadienes / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002460:Cell Line; D016189:Dystrophin / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D044387:GTP-Binding Protein beta Subunits / Q000235:genetics / Q000378:metabolism*; D044388:GTP-Binding Protein gamma Subunits / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism; D007797:Laminin / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D015398:Signal Transduction / Q000502:physiology; D000077191:Wortmannin
D000730:Androstadienes; D016189:Dystrophin; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019012:Integrin beta1; D007797:Laminin; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D021122:Protein Subunits; D051057:Proto-Oncogene Proteins c-akt; D000077191:Wortmannin