Laminin-Induced Activation of Rac1 and JNKp46 Is Initiated by Src Family Kinases and Mimics the Effects of Skeletal Muscle Contraction

Abstract

Laminin-binding to dystroglycan in the dystrophin glycoprotein complex2 causes signaling through dystroglycan-syntrophin-grb2-SOS1-Rac1-PAK1-JNK. Laminin-binding also causes syntrophin tyrosine phosphorylation to initiate signaling. The kinase responsible was investigated here. PP2 and SU6656, specific inhibitors of Src family kinases, decreased the amount of phosphotyrosinesyntrophin and decreased active Rac1 in laminin-treated myoblasts, myotubes or skeletal muscle microsomes. c-Src and c-Fyn both phosphorylate syntrophin and inhibition of either with specific siRNAs diminish syntrophin phosphorylation. When the rat gastrocnemius was contracted, Rac1 activation increased compared to the relaxed control muscle and Rac1 co-localized with β-dystroglycan. Similar results were obtained when the muscle was stretched. Contracted muscle also contained more activated c-Jun N-terminal Kinase, JNKp46. E3, an expressed protein containing only laminin domains LG4-5, increased proliferation of myoblasts and PP2 prevented cell proliferation. In addition, Src family kinases co-localized with activated Rac1 and with lamininSepharose in solid-phase binding assays. Thus, contraction, stretching, or laminin-binding cause Srcfamily kinase recruitment to the dystrophin glycoprotein complex, activating Rac1 and inducing downstream signaling. The DGC likely represents a mechanoreceptor in skeletal muscle regulating muscle growth in response to muscle activity. Src-family kinases play an initiating and critical role.In skeletal muscle, dystrophin, dystroglycan and syntrophins are found in the dystrophin glycoprotein complex, whose defects cause muscular dystrophies. Duchenne muscular dystrophy is the absence of dystrophin and the most common progressive muscle-wasting disease in human (1). Congenital muscular dystrophy results from alterations in laminindystroglycan interaction (2). Either type of muscular dystrophy would disrupt the normal DGC interaction with laminin. We showed that laminin binding causes signaling through dystroglycan-syntrophin-grb2-SOS1-Rac1-PAK1-JNK that ultimately results in the phosphorylation of c-jun on Ser 63 (3). We have proposed that this or other cell signaling, which results from the DGC-laminin interaction, may serve a role in these pathologies. Although many activities of the DGC are known, its function is unclear.1 This work was supported by the National Institutes of Health (grant AR051440) and the Muscular Dystrophy Association (grant 3789).2 Abbreviations Used: DGC, dystrophin glycoprotein complex; JNKp46, the 46,000 molecular mass isoform of c-Jun N-terminal Kinase;LG, laminin globular domains; E3, an expressed protein containing only α1-laminin domains LG4-5; αDG , α-dystroglycan; βDG , β-dystroglycan; αSG, α-sarcoglycan; Syn, syntrophin; PCR, polymerase chain reaction; DMEM, Dulbecco's modified Eagle's medium; GST, glutathione S-transferase; PAK1, p21-activated kinase; Laminin is an αβγ heterotrimer. It binds to both dystroglycan and integrins in five globular domains (i.e., LG domains)...

Fukutin, identified by the Escherichia coli ampicillin secretion trap (CAST) method, participates in tumor progression in gastric cancer

“…It indicated that the loss of function of FKTN results in defective glycosylation of a-dystroglycan, a central component of the dystrophinglycoprotein complex, leading to the disruption of the linkage between the basal lamina and the cytoskeleton. The binding of laminin to a-dystroglycan causes signaling through the dystorglycan-syntrophin-Grb2-SOS1-Rac1-PAK1-JNK cascade, which is initiated by Src family kinases and which also causes syntrophin tyrosine phosphorylation to begin signaling [29]. Disruption of the linkage between a-dystroglycan and laminin is predicted to have profound effects on muscle-cell viability, because it causes destabilization of the sarcolemma against contraction-stretch stress, hampers signal transduction, and inhibits the assembly of extracellular matrix proteins.…”

Functional diversity of dystroglycan

“…The same signal cascade seems to be activated by muscle tension (Zhou et al, 2007;Xiong et al, 2009). …”

Basement Membranes: Cell Scaffoldings and Signaling Platforms

“…In one study, laminin-111 binding to Schwann cells was reported to activate Src family members in a dystroglycan-and sulfatide-dependent manner, affecting cell survival (Li et al 2005b). In other studies, Src kinase-dependent syntrophin tyrosine phosphorylation leading to Rac1 activation, heterotrimeric G protein binding syntrophin, and calcium mobilization was detected following the binding of laminins (and laminin terminal LG fragments) to muscle sarcolemmal-rich microsomes (Zhou et al 2005;Zhou et al 2006;Zhou et al 2007;Xiong et al 2009). Similar effects seen with muscle contraction/stretching led to the proposal that dystroglycan acts as a mechanoreceptor.…”