Properties of extracellular adhesion-mediating particles in myoblast clone and its adhesion-deficient variant.

Abstract

Both the skeletal muscle myoblast cell line L6 and an adhesion-deficient variant of L6 released glycoprotein complexes, termed adherons, into their culture medium. The adherons from the variant, M3A, differed from those of L6 in a number of properties. M3A adherons were much less effective in promoting the cell-substratum and cell-cell adhesion of myoblasts than L6 particles. The adherons from the two cell lines also differed in their relative sedimentation velocities in sucrose gradients and had different chemical compositions. The M3A particle lacked chondroitin and contained relatively less collagen and fibronectin than the L6 adheron. Both L6 and M3A particles adhered to plastic surfaces and cells equally well in the absence of calcium ions. Neither cell-cell adhesion nor particle aggregation occurred in calcium-free medium. However, in the presence of calcium, the L6 adherons aggregated completely and M3A particles aggregated poorly. These data suggest that at least two sets of interactions are required for adheron-mediate@ adhesion: a calcium-independent binding of the adheron to the cell, and a calcium-dependent interaction between particles that is directly responsible for adhesion. The M3A variant is blocked afthe calcium-dependent step, resulting in an adhesion deficiency.Myogenic cells release into their culture medium a glycoprotein complex which aggregates myoblasts and alters the adhesion of cells to the substratum of plastic petri dishes (13). When adsorbed onto culture dish surfaces, the material from clonal L6 skeletal muscle myoblasts stimulated the adhesion of myoblasts and inhibited the adhesion of a clone of sympathetic nervelike cells. The adhesion-mediating activity had a sedimentation value of 16 S in sucrose gradients in the absence of calcium; it aggregated in the presence of calcium. This 16 S myoblast particle, termed an adheron, was composed of glycosaminoglycans (GAGs) and several proteins, including collagen and fibronectin.We selected a variant of the L6 skeletal muscle myoblast cell line which adheres poorly to the surface of culture dishes (14, 15). The variant line, designated M3A, was selected from an unmutagenized L6 population for its ability to grow on a nonadhesive agar surface; the parental L6 line was anchorage dependent for growth. A comparison of the protein and GAG composition of these two cell lines and the material they release into the culture medium showed that the M3A variant had lost the ability of its L6 parent to synthesize extracellular chondroitin and complete collagen a chains (14). A further analysis of this pair of cells showed that the substrate-attached material adsorbed to the culture dish surface from growth-conditioned 108 medium of L6 cells was very effective in stimulating the adhesion of myoblasts, while the substrate-attached material from M3A was relatively less active (15). Since the adhesionpromoting activity in the conditioned medium of the parental L6 cell line was a 16 S glycoprotein complex, it was possible that the diminished adh...

Characterization of toposomes from sea urchin blastula cells: a cell organelle mediating cell adhesion and expressing positional information.

“…In this respect our complex resembles other external cell surface proteins, and it is probable that, like fibronectin, it is attached through a specific site to an integral membrane protein receptor (18,19). Our results, when viewed in the context of recent work in other systems, suggest that the very large glycoprotein complexes of the type represented by our 22S particles and the adherons (18,20) are a novel class of cell organelles specialized in mediating cell-cell and cell-substratum interaction as well as conveying positional information. Schubert and LaCorbiere (20) have shown that adherons, particles of a uniform size that are released into the medium by a variety of higher vertebrate cells, are taken up by cells to promote cell-cell and cell-substratum interaction.…”

Studies on Extracellular Matrix Components That Promote Neurite Outgrowth

“…The properties of this factor, therefore, resemble those of the adhesion-mediating particles described by Schubert andLaCorbicre (1980a,b, 1982), which contain a mixture of glycosaminoglycans, collagen , and glycoproteins. The factor from BCE CMsF.…”

Characterization of a 140Kd cell surface glycoprotein involved in myoblast adhesion

“…Recent studies by Schubert et a1 [28,29] have demonstrated that the skeletal muscle myoblast cell line L6 secretes particles known as adherons which appear to be high molecular weight complexes composed of glycosaminoglycns and "matrix"-type glycoproteins, including fibronectin and collagen. It has also been shown by Damsky et a1 1231 that epithelial cells, which contain a 120Kd cell-surface molecule implicated in cell-cell adhesion, also shed an 80Kd fragment of this protein into the medium.…”