Transforming growth factor-beta1 (TGF-beta1) has been shown to down-regulate NO synthesis in a variety of normal cells. In the present study, we investigated the influence of TGF-beta1 upon NO production in tumor cells and its consequences for tumor development. During the growth of PROb colon carcinoma cells intraperitoneally injected in syngeneic BDIX rats, intratumoral concentration of TGF-beta1 increases while NO concentration stays very low. Tumor regression induced by intraperitoneal injections of a lipid A is associated with a decrease in TGF-beta1 and an increase in NO intratumoral concentration. In these tumors, PROb tumor cells are the NO- and TGF-beta1-secreting cells. Using PROb cells transfected with an expression vector coding for TGF-beta1 antisense mRNA, we demonstrate in vitro that there is an inverse correlation between the amount of TGF-beta1 secreted and the ability of PROb cells to secrete NO. As the same results were obtained in the presence of an anti-TGF-beta type II receptor neutralizing antibody, and as exogenous TGF-beta1 is without any effect on NO secretion by PROb cells, TGF-beta1 apparently down-regulates NO synthesis in PROb cells by an intracellular mechanism. These results suggest that endogenous TGF-beta1 constitutes a potential target in a search for new antitumoral agents.

Transforming Growth Factor-b1 (TGF-b1) inhibits the proliferation of most cells, but stimulates some mesenchymal cell types, including murine NIH3T3 ®broblasts. We show here that TGF-b1 growth stimulation of NIH3T3 ®broblasts is reversed when these cells are transformed by SV40 or are transfected with a plasmid encoding the SV40 Large T antigen. Inversion of the TGF-b1 growth stimulation of NIH3T3 cells is not observed when these cells are transfected with plasmids expressing either a mutant Large T, unable to bind P53, or the E1A adenovirus oncoprotein which binds the retinoblastoma protein pRB but not P53. But when the TGF-b1-growth stimulated cells are transfected with a plasmid expressing a mutant form of Large T capable of binding to P53, but not to pRB, or with one expressing the E1B-55 kD adenovirus oncoprotein, which also binds to P53 but not to pRB, the cells are growth-inhibited by TGF-b1. The cdk inhibitor p21Waf is decreased in TGFb1-stimulated NIH3T3 ®broblasts and increased in TGFb1-inhibited SV40-transformed cells. Finally, we show that T12 ®broblasts, from a P53 knockout mouse, are growth inhibited by TGF-b1 and that they remain so upon transfection with a P53 which is mutant at restrictive temperature, but become growth-stimulated by this factor at permissive temperature when P53 is functional. These data strongly suggest that growthstimulation of ®broblasts by TGF-b1 depends on the presence of a functional P53 protein and that inversion of this response occurs if P53 is absent or inactivated.

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In tissue culture conditions, exogeneous active transforming growth factor-b1 (TGF-b1) enhances the lethal effect of DNA-damaging agents (UV-C, gamma rays, cisplatin, methotrexate and 5-fluorouracil) toward human A549 cells and mink Mv1Lu cells, as detected by the loss of their capacity to give rise to colonies; both these cell lines harbor a wild-type p53, as determined by immunoprecipitation. Contrastingly, the sole effect of the cytokine used alone is to inhibit reversibly the multiplication of the same cells without further impairing, once withdrawn from their environment, their capacity to divide and give rise to colonies. The lethal synergy between TGF-b1 and UV-C was studied on mink and human cell lines, and the biomodulation by TGF-b1 of cell killing by cisplatin, gamma rays, 5-fluorouracil or methotrexate was tested only on human cells. As investigated with UV-Cirradiated human A549 cells, TGF-b1 appears to enhance apoptosis rather than to disturb the repair of DNA photolesions (mainly pyrimidine dimers) by the nucleotidic excision repair pathway according to results of nucleosomal ladder and comet tests. Our data raise the possibility that, in vivo, TGF-b1 might affect the curative and/or undesirable secondary side effects of cancer therapy. Int.