Human transforming growth factor. Production by a melanoma cell line, purification, and initial characterization

A low molecular weight human transforming growth factor (hTGFs) was isolated from serum-free medium conditioned by a human metastatic melanoma tumor line, A2058. The purification of hTGFs was achieved by gel permeation chromatography of the acid-soluble growth-promoting activity on Bio-Gel P-10 in 1 M acetic acid, followed by reverse phase high pressure liquid chromatography on muBondapak C18 support using a linear gradient of acetonitrile in 0.045% trifluoroacetic acid, and subsequently by rechromatography of the human transforming growth factor-containing fractions with a linear 1-propanol gradient in 0.035% trifluoroacetic acid on the same column. The estimated molecular weight of hTGFs is 7400. It is a single chain polypeptide with three intrachain disulfide bridges and no free sulfhydryl groups. Lacking tyrosine and methionine, but containing three phenylalanine residues, hTGFs is unlike human and mouse epidermal growth factor (EGF). hTGFs competes with 125I-labeled EGF for binding to A431 human carcinoma cells completely and equivalently, and thus is functionally related to EGF. In contrast, hTGFs enabled normal anchorage-dependent rat kidney cells to grow in soft agar, whereas EGF did not stimulate growth of these cells in semisolid medium. The half-maximal growth-stimulating response of hTGFs was reached with one EGF-competing unit or 1.1 ng of hTGFs.