|Title:||Calpains/caveolae interactions during muscle cell differentiation (abstract : congrès international de Myologie, 2005)|
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|Authors:||Congrès international de myologie 2005 (International Congress of Myology 2005; 9-13 mai 2005; Nantes, France) ; Goudenege S ; Poussard S ; Cottin P|
|Keywords :||actin ; calpains ; caveolae ; caveolins ; cell fusion ; cytoskeleton ; G proteins ; MARCKS protein ; muscle differentiation ; myoblast ; myogenesis ; NO synthase ; protein kinase C ; rippling muscle disease ; skeletal muscle ; striated muscle fibers ; symposium|
Communication n° 365. Introduction : We have previously shown that calpain promotes myoblast fusion by acting on protein kinase Ca and MARCKS (Myristoylated Alanine Rich C kinase Substrate), a protein involved in actin cytoskeleton dynamic and membrane trafficking. In other cell types, calpains as well PKCa and MARCKS are associated with caveolae. In muscle cells, these specialised RAFT are essential for fusion and differentiation and are also implicated in a type of muscular dystrophy (LGMD1C). Caveolin, the main protein in theses structures, is central to the organisation of proteins and lipids that are associated with caveolae. Caveolin interacts with numerous mediating proteins (PKC, Nitric Oxyde Synthase, G protein, Src) through a "Caveolin Scalfolding Domain".
Objectives : This work was performed in order to verify the presence of calpains in myoblast caveolae and their eventual activities on caveolae associated PKCa signalling.
Methods : Caveolae were isolated from C2C12 myoblasts using a sucrose density fractionation.
Results : We have evidenced that only m-calpain (CAPN2) is associated with caveolae. Using a calcium ionophore A23187 and a specific inhibitor of calpains (CS peptide) we have also demonstrated for the first time that activated m-calpain is able to decrease both PKCa and MARCKS levels in caveolae. In addition, the presence of PMA (an activator of PKCa) inducing both PKCa and m-calpain tranlocation towards caveolae results in a significant reduction of MARCKS in caveolae, event abolished in the presence of Gö (an inhibitor of PKCa).
Conclusions : We demonstrate hence that the positioning of biologically active m-calpain within myoblast caveolae strategically places it in close proximity to PKCa, regulates its breakdown and modulates MARCKS translocation. According to our previous works and the essential role of caveolae during the fusion process this study allows us to claim that such a localised signalling event is essential for myoblast differentiation.