Modulation of extracellular proteolytic activity and anchorage-independent growth of cultured cells by sarcoma cell-derived factors: Relationships to transforming growth factor-β

We have previously described a factor(s) produced by 8387 fibrosarcoma cells, which can affect plasminogen activator (PA) activity of cultured cells. Since then, transforming growth factor-β (TGFβ) has, been established as a major growth factor/growth inhibitor that regulates both the expression and activity of PAs and their endothelial-type inhibitor (PAI-1). The present study was undertaken to characterize the 8387 fibrosarcoma cell-derived factor(s) and to investigate its relationships to TGFβ by analysis of modulation of PA activity and cell growth. The fibrosarcoma cell-derived proteins were partially purified from serum-free conditioned culture medium using Bio-Gel P-10 chromatography. Two separate fractions with apparent molecular weights of 16,000 and 12,000 contained activities that both decreased the secretion of PA activity by human lung fibroblasts and inhibited the soft agar growth of A549 lung adenocarcinoma cells. Both factors affected similarly the production of urokinase-type PA and PAI-1 in various cell lines and enhanced anchorage-independent growth of murine AKR-2B fibroblasts. The effects of these factors thus resembled those of TGFβ. The immunological relationships between the M_r 16,000 and M_r 12,000 factors and TGFβ were therefore studied using neutralizing anti-TGFβ antibodies. The TGFβ antibodies efficiently inhibited the effects of the M_r 16,000 factor but not those of the M_r 12,000 factor in cell culture assays. The results suggest that 8387 fibrosarcoma cells produce two major growth inhibitors, one of which is closely related to TGFβ.