The molecular basis by which transforming growth factor (TGF)-beta 1 protects certain tumor cells from tumor necrosis factor (TNF) cytotoxicity was investigated. When pretreated with TGF-beta 1, -beta 2, and -beta 3, murine L929S fibroblasts developed resistance to TNF cytotoxicity, Time course experiments revealed that TGF-beta 1 initially induced both cellular protein-tyrosine phosphorylation and simultaneous secretion of a novel extracellular matrix TNF-resistance triggering (TRT) protein(s), which closely preceded the acquisition of TNF-resistance, TGF-beta 2 and -beta 3 also increased tyrosine phosphorylation, However, both molecules failed to stimulate TRT secretion, The increased levels of phosphorylation, particularly to 9 specific protein tyrosine kinase inhibitor-sensitive cellular proteins, appeared to alter the TNF killing pathway, TGF-beta 1-induced TRT secretion required participation of unknown serum factors, TRT adhered strongly to polystyrene plates and resisted treatment with heat (60 degrees C, 30 min), collagenase, alpha(2)-macroglobulin, heparin, antibodies against TGF-beta s, and limited trypsin digestion, Notably, TRT promoted TNF-resistance via activation of tyrosine and serine/threonine kinase functions in L929S. Thus, the molecular pathway involves TGF-beta 1-mediated initiation of a rapid tyrosine phosphorylation of cellular protein substrates (which alters TNF cytotoxic pathway), and a simultaneous secretion of TRT, which in turn signals the cells to maintain the levels of phosphorylation, thereby sustaining the TNF-resistance.
