Article

Dystrophin is a microtubule-associated protein

Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
The Journal of Cell Biology (Impact Factor: 9.69). 09/2009; 186(3):363-9. DOI: 10.1083/jcb.200905048
Source: PubMed

ABSTRACT Cytolinkers are giant proteins that can stabilize cells by linking actin filaments, intermediate filaments, and microtubules (MTs) to transmembrane complexes. Dystrophin is functionally similar to cytolinkers, as it links the multiple components of the cellular cytoskeleton to the transmembrane dystroglycan complex. Although no direct link between dystrophin and MTs has been documented, costamere-associated MTs are disrupted when dystrophin is absent. Using tissue-based cosedimentation assays on mice expressing endogenous dystrophin or truncated transgene products, we find that constructs harboring spectrinlike repeat 24 through the first third of the WW domain cosediment with MTs. Purified Dp260, a truncated isoform of dystrophin, bound MTs with a K(d) of 0.66 microM, a stoichiometry of 1 Dp260/1.4 tubulin heterodimer at saturation, and stabilizes MTs from cold-induced depolymerization. Finally, alpha- and beta-tubulin expression is increased approximately 2.5-fold in mdx skeletal muscle without altering the tubulin-MT equilibrium. Collectively, these data suggest dystrophin directly organizes and/or stabilizes costameric MTs and classifies dystrophin as a cytolinker in skeletal muscle.

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    • "To explain the orthogonal grid of MTs, we must involve dystrophin, the protein missing in DMD. Dystrophin is a MAP (Prins et al., 2009) Figure 4. MTs are nucleated on Golgi elements that concentrate -tubulin and pericentrin . To investigate MT nucleation, plated FDB fibers were treated with NZ to depolymerize MTs and fixed after different periods of recovery . "
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    ABSTRACT: Skeletal muscle microtubules (MTs) form a nonclassic grid-like network, which has so far been documented in static images only. We have now observed and analyzed dynamics of GFP constructs of MT and Golgi markers in single live fibers and in the whole mouse muscle in vivo. Using confocal, intravital, and superresolution microscopy, we find that muscle MTs are dynamic, growing at the typical speed of ∼9 µm/min, and forming small bundles that build a durable network. We also show that static Golgi elements, associated with the MT-organizing center proteins γ-tubulin and pericentrin, are major sites of muscle MT nucleation, in addition to the previously identified sites (i.e., nuclear membranes). These data give us a framework for understanding how muscle MTs organize and how they contribute to the pathology of muscle diseases such as Duchenne muscular dystrophy.
    The Journal of Cell Biology 10/2013; 203(2). DOI:10.1083/jcb.201304063 · 9.69 Impact Factor
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    • "This is based on our immunohistochemical and biochemical data indicating strongly reduced dystroglycan expression in non-regenerating muscle fibers of mdx muscles, and on the observed destabilization of the dystroglycan-Cavin1 complex. One possible mechanism by which loss of dystrophin may indirectly destabilize “free” dystroglycan complexes at the myofiber membrane is through the disorganization of the microtubular and sub-membranous actin networks [27,69]. Alternatively, these “free” dystroglycan complexes may be post-translationally altered in the absence of dystrophin and remain trapped in microsomes [70]. "
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    ABSTRACT: The dystroglycan complex contains the transmembrane protein β-dystroglycan and its interacting extracellular mucin-like protein α-dystroglycan. In skeletal muscle fibers, the dystroglycan complex plays an important structural role by linking the cytoskeletal protein dystrophin to laminin in the extracellular matrix. Mutations that affect any of the proteins involved in this structural axis lead to myofiber degeneration and are associated with muscular dystrophies and congenital myopathies. Because loss of dystrophin in Duchenne muscular dystrophy (DMD) leads to an almost complete loss of dystroglycan complexes at the myofiber membrane, it is generally assumed that the vast majority of dystroglycan complexes within skeletal muscle fibers interact with dystrophin. The residual dystroglycan present in dystrophin-deficient muscle is thought to be preserved by utrophin, a structural homolog of dystrophin that is up-regulated in dystrophic muscles. However, we found that dystroglycan complexes are still present at the myofiber membrane in the absence of both dystrophin and utrophin. Our data show that only a minority of dystroglycan complexes associate with dystrophin in wild type muscle. Furthermore, we provide evidence for at least three separate pools of dystroglycan complexes within myofibers that differ in composition and are differentially affected by loss of dystrophin. Our findings indicate a more complex role of dystroglycan in muscle than currently recognized and may help explain differences in disease pathology and severity among myopathies linked to mutations in DAPC members.
    PLoS ONE 08/2013; 8(8):e73224. DOI:10.1371/journal.pone.0073224 · 3.23 Impact Factor
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    • "In specimens from mdx mice, MT networks were found to be reduced and disorganized (particularly in subsarcolemmal regions) compared to wt mice. Disorganization of MT networks in mdx mice, originally reported by Percival et al. [36], has recently been attributed to the loss of dystrophin’s MAP-like MT-stabilizing function [37]. In sharp contrast, in cKO and more so in dKO mice, MT networks were more prominent, appearing more robust compared to wt mice. "
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    ABSTRACT: BACKGROUND: Duchenne muscular dystrophy (DMD) is one of the most frequent forms of muscular disorders. It is caused by the absence of dystrophin, a core component of the sarcolemma-associated junctional complex that links the cytoskeleton to the extracellular matrix. We showed previously that plectin 1f (P1f), one of the major muscle-expressed isoforms of the cytoskeletal linker protein plectin, accumulates at the sarcolemma of DMD patients as well as of mdx mice, a widely studied animal model for DMD.Hypothesis: Based on plectin's dual role as structural protein and scaffolding platform for signaling molecules, we speculated that the dystrophic phenotype observed after loss of dystrophin was caused, at least to some extent, by excess plectin. Thus, we hypothesized that elimination of plectin expression in mdx skeletal muscle, while probably resulting in an overall more severe phenotype, may lead to a partial phenotype rescue. In particular, we wanted to assess whether excess sarcolemmal plectin contributes to the dysregulation of sugar metabolism in mdx myofibers. METHODS: We generated plectin/dystrophin double deficient (dKO) mice by breeding mdx with conditional striated muscle-restricted plectin knockout (cKO) mice. The phenotype of these mice was comparatively analyzed with that of mdx, cKO, and wild-type mice, focusing on structural integrity and dysregulation of glucose metabolism. RESULTS: We show that the accumulation of plectin at the sarcolemma of mdx muscle fibers hardly compensated for their loss of structural integrity. Instead, it led to an additional metabolic deficit by impairing glucose uptake. While dKO mice suffered from an overall more severe form of muscular dystrophy compared to mdx or plectin-deficient mice, sarcolemmal integrity as well as glucose uptake of their myofibers were restored to normal levels upon ablation of plectin. Furthermore, microtubule (MT) networks in intact dKO myofibers, including subsarcolemmal areas, were found to be more robust than those in mdx mice. Finally, myotubes differentiated from P1f-overexpressing myoblasts showed an impairment of glucose transporter 4 translocation and a destabilization of MT networks. CONCLUSIONS: Based on these results we propose that sarcolemma-associated plectin acts as an antagonist of MT network formation in myofibers, thereby hindering vesicle-mediated (MT-dependent) transport of glucose transporter 4. This novel role of plectin throws a bridge between extra-sarcomeric cytoarchitecture and metabolism of muscle fibers. Our study thus provides new insights into pathomechanisms of plectinopathies and muscular dystrophies in general.
    06/2013; 3(1):14. DOI:10.1186/2044-5040-3-14
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