title: Human muscle LIM protein dimerizes along the actin cytoskeleton and cross-links actin filaments.
abstract: The muscle LIM protein (MLP) is a nucleocytoplasmic shuttling protein playing important roles in the regulation of myocyte remodeling and adaptation to hypertrophic stimuli. Missense mutations in human MLP or its ablation in transgenic mice promotes cardiomyopathy and heart failure. The exact function(s) of MLP in the cytoplasmic compartment and the underlying molecular mechanisms remain largely unknown. Here, we provide evidence that MLP autonomously binds to, stabilizes, and bundles actin filaments (AFs) independently of calcium and pH. Using total internal reflection fluorescence microscopy, we have shown how MLP cross-links actin filaments into both unipolar and mixed-polarity bundles. Quantitative analysis of the actin cytoskeleton configuration confirmed that MLP substantially promotes actin bundling in live myoblasts. In addition, bimolecular fluorescence complementation (BiFC) assays revealed MLP self-association. Remarkably, BiFC complexes mostly localize along actin filament-rich structures, such as stress fibers and sarcomeres, supporting a functional link between MLP self-association and actin cross-linking. Finally, we have demonstrated that MLP self-associates through its N-terminal LIM domain, whereas it binds to AFs through its C-terminal LIM domain. Together our data support that MLP contributes to the maintenance of cardiomyocyte cytoarchitecture by a mechanism involving its self-association and actin filament cross-linking.
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Céline
authors.initials: C
authors.lastname: Hoffmann
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Flora
authors.initials: F
authors.lastname: Moreau
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Michèle
authors.initials: M
authors.lastname: Moes
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Carole
authors.initials: C
authors.lastname: Luthold
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Monika
authors.initials: M
authors.lastname: Dieterle
authors.affiliation: Laboratory of Cardiovascular Research, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Emeline
authors.initials: E
authors.lastname: Goretti
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: Katrin
authors.initials: K
authors.lastname: Neumann
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg.
authors.forename: André
authors.initials: A
authors.lastname: Steinmetz
authors.affiliation: Laboratory of Cellular and Molecular Oncology, Public Research Center for Health, Luxembourg, Luxembourg clement.thomas@crp-sante.lu.
authors.forename: Clément
authors.initials: C
authors.lastname: Thomas
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D009202:Cardiomyopathies / Q000235:genetics / Q000473:pathology; D002460:Cell Line; D006801:Humans; D060588:LIM Domain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D032342:Muscle Cells / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D011485:Protein Binding; D055503:Protein Multimerization; D012518:Sarcomeres / Q000378:metabolism; D015398:Signal Transduction; D022502:Stress Fibers / Q000378:metabolism
chemical_list: D060588:LIM Domain Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; C090114:cysteine and glycine-rich protein 3