Calpains mediate integrin attachment complex maintenance of adult muscle in Caenorhabditis elegans.
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Copyright: © 2012 Etheridge et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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.
This work was supported by a grant from the UK Medical Research Council (G0801271) to NJS and by a grant from the US National Institutes of Health (NIH) National Institute for Arthritis and Musculoskeletal and Skin Diseases (AR-054342) to NJS and LAJ. EAO was also supported by personal awards from the Pennsylvania Space Grant Agency, the Biochemical Society, and the Barry M. Goldwater Scholarship Program. EAO and BDF were also summer research participants under an Undergraduate Science Education grant from the Howard Hughes Medical Institute. The monoclonal antibodies against DEB-1, developed by Dr. Robert H. Waterson (named MH24, ); myosin heavy-chain A, developed by Dr. Henry F. Epstein (named 5–14); actin, developed by Jim Jung-Ching Lin (named JLA20, ); and beta-galactosidase, developed by T.L. Mason/Judith A. Partaledis (named JIE7), were obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the US NIH National Institute of Child Health and Human Development and maintained by The University of Iowa, Department of Biology. Many of the mutant alleles utilized in this work were obtained from the Caenorhabditis Genetics Center, which is funded by the US NIH National Center for Research Resources. All Bioinformatic work was conducted utilizing WormBase , which is funded by the US NIH National Human Genome Research Institute and the British Medical Research Council. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Research Support, N.I.H., Extramural
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Vol. 8, Iss. 1, e1002471 -
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