title: Effects of growth factors on the antiproliferative activity of tumor necrosis factors.
abstract: Tumor necrosis factors (TNFs) are a class of cytokines secreted by activated effector cells involved in host defense against tumor progression. Epidermal growth factor (EGF) and recombinant human transforming growth factor-alpha (rHuTGF-alpha) were shown to interfere with the in vitro antiproliferative effects of recombinant human tumor necrosis factor-alpha (rHuTNF-alpha) and -beta on a human cervical carcinoma cell line, ME-180. The inhibitory effect could be observed at EGF or rHuTGF-alpha concentrations of 100 pg/ml, and was maximal between 1 and 10 ng/ml. This response was not due to down regulation of the TNF receptor or to alteration of the affinity of TNF-alpha for its receptor. Since the antiproliferative effect of recombinant human interferon-gamma was not significantly affected by the presence of EGF or rHuTGF-alpha, the inhibition was specific for recombinant TNFs and was not due solely to enhanced proliferation induced by the growth factors. Neither growth factor had a substantial protective effect on the synergistic cytotoxicity observed when tumor cells were exposed simultaneously to rHuTNF-alpha and recombinant human interferon-gamma. TGF-beta can also interfere with the antiproliferative effects of rHuTNF-alpha in vitro. At concentrations of less than 1 ng/ml, TGF-beta significantly antagonized the cytotoxic effects of rHuTNF-alpha on NIH 3T3 fibroblasts. Since EGF, platelet-derived growth factor, and TGF-beta all enhanced NIH 3T3 cell proliferation, but only TGF-beta interfered with rHuTNF-alpha cytotoxicity, the protective effects of TGF-beta were not related in a simple manner to enhanced cell proliferation. rHuTGF-alpha and TGF-beta did not have a significant protective effect against rHuTNF-alpha-mediated cytotoxicity on two other tumor cell lines, BT-20 and L-929 cells. Based upon these observations we suggest that growth factors might enhance tumor growth in vivo by a combination of distinct mechanisms: (a) by autocrine stimulation tumor cell growth; and/or (b) by interfering with normal effector mechanisms of host defense.
mesh_terms: D000818:Animals; D001943:Breast Neoplasms; D002294:Carcinoma, Squamous Cell; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D006023:Glycoproteins / Q000494:pharmacology*; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D007739:L Cells / Q000166:cytology / Q000187:drug effects; D051379:Mice; D013329:Structure-Activity Relationship; D014409:Tumor Necrosis Factor-alpha; D002583:Uterine Cervical Neoplasms
chemical_list: D006023:Glycoproteins; D006133:Growth Substances; D014409:Tumor Necrosis Factor-alpha