Biosynthesis of plasma-membrane proteins during myogenesis of skeletal muscle in vitro

Abstract

1. Surface labelling of plasma-membrane proteins with 125I, catalysed by lactoperoxidase, and radioactive l-fucose incorporation into glycoprotein were used as plasma-membrane markers for skeletal-muscle cells in culture. 2. Plasma membranes were prepared at various stages of myogenesis in vitro and rates of synthesis and accumulation of proteins in the membranes were compared. 3. Increased synthesis and accumulation of a protein of apparent mol.wt. 70000 occurred in the plasma-membrane fraction concomitant with the onset of myoblast fusion. 4. In cultures in which fusion of myoblasts was inhibited by 5'-bromo-2-deoxyuridine, synthesis and accumulation of the protein of apparent mol.wt. 70000 was selectively inhibited. 5. It is suggested the protein of apparent mol.wt. 70000 may be involved in the process of myoblast fusion.

The fusion of myoblasts

“…Changes in other myoblast surface proteins have also been observed. Cates & Holland (1978) reported both increased synthesis and accumulation of a protein of apparent M, of 70000, concomitant with the onset of myoblast fusion. The relative amount of a cell surface protein of Mr 200000-250000 has been found to increase during the fusion of the L6 myoblast cell line, but was not found in a nonfusion variant (M3A).…”

Humoral autoimmunity to cartilage in rheumatoid arthritis?

“…Chondrocyte membrane preparations: Chondrocyte membranes were prepared from chicken and calf sterna as well as from surgically removed human nasal septa with a stepwise gradient with 40, 17.5 and 8.5% w/w sucrose [3]. After crude homogenization of the tissue the homogenate was centrifuged at 1500 g at 4~ for 15 minutes to remove the matrix.…”

Correlation between fusion and the developmental regulation of membrane glycoproteins in L6 myoblasts.

“…The effect of BrdUrd, a potent inhibitor of myoblast fusion and differentiation (7), has also been studied. Only minor changes in membrane proteins have been reported and no good correlation with the adhesion or fusion process has been found (5,8,9).Recent studies by Couch and Strittmatter (10, 11) indicate that an endogenous metalloendoprotease plays a role in myoblast fusion. Inhibition of the metalloendoprotease by various inhibitors was shown to correlate with the inhibition of myoblast fusion in primary rat myoblast cultures as well as in the rat cell line L6.…”

“…The effect of BrdUrd, a potent inhibitor of myoblast fusion and differentiation (7), has also been studied. Only minor changes in membrane proteins have been reported and no good correlation with the adhesion or fusion process has been found (5,8,9).…”