title: Proteasomes are tightly associated to myofibrils in mature skeletal muscle.
abstract: Proteasomes are the major actors of nonlysosomal cytoplasmic protein degradation. In particular, these large protein complexes (about 2500 kDa) are considered to be responsible for muscular degradation during skeletal muscle atrophy. Despite their unusual and important size, they are widely described as soluble and mobile in the cytoplasm. In mature skeletal muscle, we have previously observed a sarcomeric distribution of proteasomes, as revealed by the distribution of alpha1/p27K, a subunit of the 20S core-particle (prosome) of proteasome. Here, we extend these observations at the electron microscopic level in vivo. We also show that this sarcomeric pattern is dependent of the extension of the sarcomere. Using isolated myofibrils, we demonstrate that proteasomes are still attached to the myofibrils after the isolation procedure, and reproduce the observations made in vivo. In addition, the extraction of actin by gelsolin largely removes proteasomes from isolated myofibrils, but some of them are held in place after this extraction, showing a sarcomeric disposition in the absence of any detectable actin, and suggesting the existence of another molecular partner for these interactions. From these results, we conclude that most of detectable 20S proteasomes in skeletal muscle cells is tightly attached to the myofibrils.
authors.affiliation: Laboratoire CRRET, CNRS FRE 2412, Faculté des Sciences, Université Paris 12-Val de Marne, Créteil, France. bassaglia@univ-paris12.fr
authors.forename: Yann
authors.initials: Y
authors.lastname: Bassaglia
authors.forename: José
authors.initials: J
authors.lastname: Cebrian
authors.forename: Silvia
authors.initials: S
authors.lastname: Covan
authors.forename: Monica
authors.initials: M
authors.lastname: Garcia
authors.forename: Jean
authors.initials: J
authors.lastname: Foucrier
mesh_terms: D000199:Actins / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D003546:Cysteine Endopeptidases / Q000378:metabolism / Q000648:ultrastructure*; D005455:Fluorescent Antibody Technique; D019084:Fluorescent Antibody Technique, Indirect; D018260:Gelsolin / Q000378:metabolism; D008297:Male; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000648:ultrastructure*; D009210:Myofibrils / Q000378:metabolism* / Q000648:ultrastructure; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000199:Actins; D018260:Gelsolin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex