title: Multiple molecular interactions implicate the connectin/titin N2A region as a modulating scaffold for p94/calpain 3 activity in skeletal muscle.
abstract: p94/calpain 3 is a skeletal muscle-specific Ca(2+)-regulated cysteine protease (calpain), and genetic loss of p94 protease activity causes muscular dystrophy (calpainopathy). In addition, a small in-frame deletion in the N2A region of connectin/titin that impairs p94-connectin interaction causes a severe muscular dystrophy (mdm) in mice. Since p94 via its interaction with the N2A and M-line regions of connectin becomes part of the connectin filament system that serves as a molecular scaffold for the myofibril, it has been proposed that structural and functional integrity of the p94-connectin complex is essential for health and maintenance of myocytes. In this study, we have surveyed the interactions made by p94 and connectin N2A inside COS7 cells. This revealed that p94 binds to connectin at multiple sites, including newly identified loci in the N2A and PEVK regions of connectin. Functionally, p94-N2A interactions suppress p94 autolysis and protected connectin from proteolysis. The connectin N2A region also contains a binding site for the muscle ankyrin repeat proteins (MARPs), a protein family involved in the cellular stress responses. MARP2/Ankrd2 competed with p94 for binding to connectin and was also proteolyzed by p94. Intriguingly, a connectin N2A fragment with the mdm deletion possessed enhanced resistance to proteases, including p94, and its interaction with MARPs was weakened. Our data support a model in which MARP2-p94 signaling converges within the N2A connectin segment and the mdm deletion disrupts their coordination. These results also implicate the dynamic nature of connectin molecule as a regulatory scaffold of p94 functions.
authors.affiliation: Department of Enzymatic Regulation for Cell Functions (Calpain Project), The Tokyo Metropolitan Institute of Medical Science (Rinshoken), Tokyo, Japan.
authors.forename: Chikako
authors.initials: C
authors.lastname: Hayashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ono
authors.forename: Naoko
authors.initials: N
authors.lastname: Doi
authors.forename: Fujiko
authors.initials: F
authors.lastname: Kitamura
authors.forename: Mai
authors.initials: M
authors.lastname: Tagami
authors.forename: Reiko
authors.initials: R
authors.lastname: Mineki
authors.forename: Takao
authors.initials: T
authors.lastname: Arai
authors.forename: Hayao
authors.initials: H
authors.lastname: Taguchi
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Yanagida
authors.forename: Stephanie
authors.initials: S
authors.lastname: Hirner
authors.forename: Dietmar
authors.initials: D
authors.lastname: Labeit
authors.forename: Siegfried
authors.initials: S
authors.lastname: Labeit
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sorimachi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002154:Calpain / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D064211:Connectin; D005786:Gene Expression Regulation; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D064211:Connectin; D009124:Muscle Proteins; C577285:TTN protein, human; D011494:Protein Kinases; D006867:Hydrolases; C063440:ADP-ribosyl protein hydrolase C; D010447:Peptide Hydrolases; C105884:CAPN3 protein, human; D002154:Calpain; C491373:Capn3 protein, mouse; C078134:calpain p94