CHARACTERIZATION OF LATENT TRANSFORMING GROWTH-FACTOR-BETA-2 FROM MONKEY KIDNEY-CELLS

Serum-free medium conditioned by BSC-40 cells was analyzed for the presence of transforming growth factor-beta-2 (TGF-beta-2)-related proteins. Western blot analysis was performed using site-specific antipeptide antibodies directed against the pro- and mature regions of the TGF-beta-2 precursor. When conditioned medium was analyzed by polyacrylamide gel electrophoresis under reducing conditions, proteins with mol wt of 53 kDa (containing both mature and proregion sequences), 34-38 kDa (containing proregion sequences only), and 12 kDa (containing mature sequences) were detected. Under nonreducing conditions, complexes of 60- to 80-kDa, 160- to 200-kDa, as well as 24-kDa mature dimers were seen. Cleavage of mature TGF-beta-2 from its precursor was inhibited by monensin and chloroquin, but not by ammonium chloride or methylamine. Two peaks of bioactivity were detected after fractionation on a TSK column corresponding to mol wt of 130 and 400 kDa. These peaks contained TGF-beta-2 and pro-TGF-beta-2 proteins. Partial purification of the 130-kDa complex followed by N-glyconase digestion indicated that the pro-TGF-beta-2 proteins were glycosylated. These data demonstrate that BSC-40 cells secrete mature TGF-beta-2 complexed with proregion-containing proteins and suggest that this association may contribute to the latency phenomena observed with respect to this growth regulator.