Isolation and characterization of a multiplication-stimulating activity (MSA)-like polypeptide produced by a human...

A human fibrosarcoma cell line, 8387, produces and secretes multiplication-stimulating activity (MSA)-like polypeptide growth factors, which are associated with a high molecular weight binding protein. The purification of 8387-MSA involved concentration of serum-free media conditioned by 8387 cells, dialysis, and chromatography of the acid-soluble growth-promoting activity on Bio-Gel P-100 in 1 M acetic acid and subsequently on carboxymethylcellulose. The purification was followed by a radioreceptor assay specific for MSA and an assay for growth-stimulating activity. Both activities chromatographed through the purification steps of 8387-MSA. 8387-MSA competes with 125I-labeled rat MSA for binding on rat cells with a specific activity 5 times lower than that of rat MSA and stimulates [3H]-thymidine incorporation into DNA of normal rat fibroblasts at comparable concentrations. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the MSA-competing activity co-migrated with a single band of protein that behaved heterogeneously on discpolyacrylamide gels in the presence of 6 M urea, yielding two bands associated with biological activity. 8387-MSA is a single chain polypeptide with an apparent molecular weight of 14,500.