title: Muscle-specific calpain-3 is phosphorylated in its unique insertion region for enrichment in a myofibril fraction.
abstract: CAPN3 (also called p94/calpain-3) is a skeletal muscle-specific calpain, an intracellular cysteine protease. Loss of CAPN3 protease activity and/or structural functions cause limb-girdle muscular dystrophy type 2A (LGMD2A). However, the precise mechanism of action of CAPN3 in skeletal muscles in vivo remains largely elusive. By studying the protein modifications that regulate CAPN3 activity, we found that CAPN3 was phosphorylated. By performing mutagenesis and mass spectrometry analyses, we identified two Ser residues at positions 629 and 636 in human CAPN3 that are phosphorylated and showed that S629 is a major phosphorylation site. Intriguingly, rapid and exhaustive autolysis of CAPN3 was slightly attenuated by the substitution of S629. In skeletal muscles, phosphorylated CAPN3 was enriched in the myofibril fraction. These results imply that phosphorylated CAPN3 is a myofibril structural component and/or participates in myofibril-based signaling pathways, rather than functions as a protease. We evaluated the relationship between phosphorylated CAPN3 and the pathology of LGMD2A. The level of phosphorylated CAPN3 was greatly reduced in LGMD2A muscles. Our findings suggest that phosphorylated CAPN3 is involved in the pathology of LGMD2A through defects in myofibril integrity and/or signaling pathways. This is the first report that phosphorylation of CAPN3 may be involved in its physiological function.
authors.affiliation: Animal Products Research Division, NARO Institute of Livestock and Grassland Science, 2 Ikenodai, Tsukuba, Ibaraki, 305-0901, Japan; Calpain Project, Department of Advanced Science for Biomolecules, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Ojima
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ono
authors.forename: Shoji
authors.initials: S
authors.lastname: Hata
authors.forename: Satoru
authors.initials: S
authors.lastname: Noguchi
authors.forename: Ichizo
authors.initials: I
authors.lastname: Nishino
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sorimachi
mesh_terms: D000293:Adolescent; D000818:Animals; D019556:COS Cells; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D049288:Muscular Dystrophies, Limb-Girdle / Q000378:metabolism / Q000473:pathology; D016254:Mutagenesis, Insertional; D009154:Mutation; D009210:Myofibrils / Q000378:metabolism*; D010766:Phosphorylation; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D055815:Young Adult
chemical_list: D009124:Muscle Proteins; D012694:Serine; C105884:CAPN3 protein, human; D002154:Calpain