Arhgef5 Binds α-Dystrobrevin 1 and Regulates Neuromuscular Junction Integrity

Abstract

The neuromuscular junctions (NMJs) connect muscle fibers with motor neurons and enable the coordinated contraction of skeletal muscles. The dystrophin-associated glycoprotein complex (DGC) is an essential component of the postsynaptic machinery of the NMJ and is important for the maintenance of NMJ structural integrity. To identify novel proteins that are important for NMJ organization, we performed a mass spectrometry-based screen for interactors of α-dystrobrevin 1 (aDB1), one of the components of the DGC. The guanidine nucleotide exchange factor (GEF) Arhgef5 was found to be one of the aDB1 binding partners that is recruited to Tyr-713 in a phospho-dependent manner. We show here that Arhgef5 localizes to the NMJ and that its genetic depletion in the muscle causes the fragmentation of the synapses in conditional knockout mice. Arhgef5 loss in vivo is associated with a reduction in the levels of active GTP-bound RhoA and Cdc42 GTPases, highlighting the importance of actin dynamics regulation for the maintenance of NMJ integrity.

The Dystrophin Node as Integrator of Cytoskeletal Organization, Lateral Force Transmission, Fiber Stability and Cellular Signaling in Skeletal Muscle

“…Myocilin, a modulator of muscle hypertrophy was shown to be linked to alpha-syntrophin [ 169 ]. Interestingly, alpha-dystrobrevin was demonstrated to interact with the cytoskeletal linker protein alpha-catulin, which acts as a scaffold structure for G-protein signaling pathways, [ 170 , 171 , 172 ], and is also linked to liprin and the guanidine nucleotide exchange factor Arhgef5 at the neuromuscular junction [ 173 , 174 ].…”

A Role for Caveolin-3 in the Pathogenesis of Muscular Dystrophies

“…It is, therefore, not surprising that the mutations in most of the core DGC proteins lead to muscular dystrophies. The core of the DGC additionally recruits several peripherally-associated proteins such as signaling molecules nNOS and PI3K, scaffold proteins such as GRB2 and α-Catulin, or cytoskeleton-organizing proteins such as Liprin-α1 and Arhgef5 [ 148 , 149 , 150 , 151 ]. For more comprehensive reviews on DGC, see [ 146 , 152 ].…”

Tks5 Regulates Synaptic Podosome Formation and Stabilization of the Postsynaptic Machinery at the Neuromuscular Junction

“…Moreover, the fact that after Tks5 knockdown other phenotypes unrelated to remodeling of cluster topology were observed indicates that this protein has multiple functions at the postsynaptic apparatus. Thus, considering that Tks5 is also an essential podosomal scaffold, chances are that its other functions can be mediated by the actin cytoskeleton [ 20 , 36 ]. We therefore performed PLA to check whether association of actin with rapsyn (anchoring AChRs to cortical actin filaments) was affected by the absence of Tks5.…”

“…In order to elicit the function of αDB1, our laboratory has previously identified a number of its interacting partners. Among those were proteins such as Rho guanine nucleotide exchange factor 5 (Arhgef5), growth factor-receptor bound protein 2 (Grb2) and liprin-α-1 [ 20 , 21 , 22 ]. All of them are involved in regulation of the muscle postsynaptic machinery, highlighting the importance of αDB1 in synapse organization.…”