title: Calpains mediate integrin attachment complex maintenance of adult muscle in Caenorhabditis elegans.
abstract: Two components of integrin containing attachment complexes, UNC-97/PINCH and UNC-112/MIG-2/Kindlin-2, were recently identified as negative regulators of muscle protein degradation and as having decreased mRNA levels in response to spaceflight. Integrin complexes transmit force between the inside and outside of muscle cells and signal changes in muscle size in response to force and, perhaps, disuse. We therefore investigated the effects of acute decreases in expression of the genes encoding these multi-protein complexes. We find that in fully developed adult Caenorhabditis elegans muscle, RNAi against genes encoding core, and peripheral, members of these complexes induces protein degradation, myofibrillar and mitochondrial dystrophies, and a movement defect. Genetic disruption of Z-line- or M-line-specific complex members is sufficient to induce these defects. We confirmed that defects occur in temperature-sensitive mutants for two of the genes: unc-52, which encodes the extra-cellular ligand Perlecan, and unc-112, which encodes the intracellular component Kindlin-2. These results demonstrate that integrin containing attachment complexes, as a whole, are required for proper maintenance of adult muscle. These defects, and collapse of arrayed attachment complexes into ball like structures, are blocked when DIM-1 levels are reduced. Degradation is also blocked by RNAi or drugs targeting calpains, implying that disruption of integrin containing complexes results in calpain activation. In wild-type animals, either during development or in adults, RNAi against calpain genes results in integrin muscle attachment disruptions and consequent sub-cellular defects. These results demonstrate that calpains are required for proper assembly and maintenance of integrin attachment complexes. Taken together our data provide in vivo evidence that a calpain-based molecular repair mechanism exists for dealing with attachment complex disruption in adult muscle. Since C. elegans lacks satellite cells, this mechanism is intrinsic to the muscles and raises the question if such a mechanism also exists in higher metazoans.
authors.affiliation: School of Graduate Entry Medicine and Health, University of Nottingham, Royal Derby Hospital, Derby, United Kingdom.
authors.forename: Timothy
authors.initials: T
authors.lastname: Etheridge
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Oczypok
authors.forename: Susann
authors.initials: S
authors.lastname: Lehmann
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Fields
authors.forename: Freya
authors.initials: F
authors.lastname: Shephard
authors.forename: Lewis A
authors.initials: LA
authors.lastname: Jacobson
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Szewczyk
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques / Q000379:methods; D007136:Immunoglobulins / Q000378:metabolism; D016023:Integrins / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D032342:Muscle Cells / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism; D059748:Proteolysis; D034622:RNA Interference
chemical_list: D029742:Caenorhabditis elegans Proteins; D015815:Cell Adhesion Molecules; C480418:DIM-1 protein, C elegans; D007136:Immunoglobulins; D016023:Integrins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D009124:Muscle Proteins; D011509:Proteoglycans; C411729:UNC-112 protein, C elegans; C117451:UNC-97 protein, C elegans; C082396:unc-52 protein, C elegans; D002154:Calpain