title: UNC-87 isoforms, Caenorhabditis elegans calponin-related proteins, interact with both actin and myosin and regulate actomyosin contractility.
abstract: Calponin-related proteins are widely distributed among eukaryotes and involved in signaling and cytoskeletal regulation. Calponin-like (CLIK) repeat is an actin-binding motif found in the C-termini of vertebrate calponins. Although CLIK repeats stabilize actin filaments, other functions of these actin-binding motifs are unknown. The Caenorhabditis elegans unc-87 gene encodes actin-binding proteins with seven CLIK repeats. UNC-87 stabilizes actin filaments and is essential for maintenance of sarcomeric actin filaments in striated muscle. Here we show that two UNC-87 isoforms, UNC-87A and UNC-87B, are expressed in muscle and nonmuscle cells in a tissue-specific manner by two independent promoters and exhibit quantitatively different effects on both actin and myosin. Both UNC-87A and UNC-87B have seven CLIK repeats, but UNC-87A has an extra N-terminal extension of ~190 amino acids. Both UNC-87 isoforms bind to actin filaments and myosin to induce ATP-resistant actomyosin bundles and inhibit actomyosin motility. UNC-87A with an N-terminal extension binds to actin and myosin more strongly than UNC-87B. UNC-87B is associated with actin filaments in nonstriated muscle in the somatic gonad, and an unc-87 mutation causes its excessive contraction, which is dependent on myosin. These results strongly suggest that proteins with CLIK repeats function as a negative regulator of actomyosin contractility.
authors.affiliation: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322.
authors.forename: Kanako
authors.initials: K
authors.lastname: Ono
authors.affiliation: Department of Biology, Faculty of Science, Chiba University, Chiba 263-8522, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Obinata
authors.affiliation: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322.
authors.forename: Sawako
authors.initials: S
authors.lastname: Yamashiro
authors.affiliation: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322.
authors.forename: Zhongmei
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322 sono@emory.edu.
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Ono
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009130:Muscle, Smooth / Q000502:physiology; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D029742:Caenorhabditis elegans Proteins; D009124:Muscle Proteins; D020033:Protein Isoforms; C089652:UNC-87 protein, C elegans; D000205:Actomyosin