The growth of cells is determined by the balance between growth-stimulatory and growth-inhibitory signals. In the present study, we demonstrate that the transfection of NIH 3T3 cells with a ...platelet-derived growth factor (
PDGF-B/c-sis) gene induces resistance to the anticellular effects of tumor necrosis factor (TNF). Human tumor cell lines that express elevated levels of
c-sis (e.g. epidermoid carcinoma, A-431) are also TNF resistant, whereas those that express no significant levels of this gene (e.g. breast adenocarcinoma, MCF-7) are TNF sensitive. Transfection of cells with the
c-sis gene leads to down-modulation of TNF receptors and also a decrease in intracellular glutathione levels. Thus, our results demonstrate that over-expression of
PDGF-B/c-sis by certain tumor cells can lead to their protection from the anticellular effects of TNF.
While some tumor cells are sensitive to the antiproliferative effects of tumor necrosis factor (TNF), others are resistant. The molecular basis for cellular resistance to TNF is not completely ...understood. Previously we have shown that transfection of cells with an oncogene
HER2/neu/erb B2, a receptor tyrosine kinase, leads to resistance to the anticellular effects of TNF (1988) Proc. Natl. Acad. Sci. USA 85, 5102-5106. In the present study, we demonstrate that the overexpression of another oncogenic tyrosine kinase, pp60
v-src
also induces resistance to TNF. In contrast to
HER2, however, pp60
v-src
transfection of cells did not lead to down-modulation of TNF receptors but rather to decreased intracellular glutathione levels. The pp60
v-src
-induced cellular resistance to TNF could be abrogated by interferon-γ. Thus, these results indicate that the resistance of certain tumors to TNF may also be due in part to the overexpression of
pp60
v-src
oncogene.
The limited life span in culture of normal human diploid fibroblasts (HDF) has provided a model of cellular senescence. The short-term growth of these cells in culture is regulated by a number of ...different cytokines, including tumor necrosis factor (TNF), interleukin-1 (IL-1), and fibroblast growth factor (FGF). However, the effect of senescence on the responsiveness of HDF to these cytokines is not known. In the present report, we examined the effects of TNF on foreskin-derived HDF at different passage levels. We compared the response of HDF cells at population doubling (PD) 23 (young) with that of cells at PD 70 (senescent). Young cells proliferated in response to TNF in a dose-dependent manner. Under these conditions TNF had no effect on senescent HDF. The decrease in TNF responsiveness was found to be dependent on PD. The lack of response of senescent HDF was not unique to TNF, since FGF and IL-1 were also ineffective. In contrast to senescent HDF, TNF-dependent proliferation of young HDF could be further potentiated by IL-1 and FGF, suggesting an independent signaling mechanism. On exposure to TNF, senescent HDF produced IL-6 and IL-8, but to a much lower degree than that produced by young HDF. The diminished responsiveness of senescent HDF to TNF does not appear to be due to the difference in either receptor number or affinity, since senescent cells had two-to threefold higher number of TNF receptors than young HDF but the same affinity. TNF induced the activation of a nuclear transcriptional factor, NF-
k
B, equally in both young and senescent cells, which indicates the lack of a defect in the early events of TNF signal transduction in senescent fibroblasts. Overall, our results indicate that there is an age-dependent decline in TNF-induced proliferation and in the production of interleukins by fibroblasts; this unresponsiveness appears not to be due to TNF receptors or NF-
K
B activation. These results may have importance in understanding the diminished immune response, inflammation, and wound healing associated with aging.
Suramin, a polysulfonated naphthylurea, is an antitrypanosomal and antifilarial drug. Because of its anti-reverse transcriptase activity and antiproliferative activity, suramin is also used for the ...treatment of acquired immunodeficiency syndrome and cancer. In spite of these uses, very little is known about its effects on the immune system. In this report, we investigated the effects of suramin on peripheral blood mononuclear cells. We found that natural killer (NK) cell-mediated cytotoxicity against human erythroblastoid cell line K562 was completely inhibited by suramin in a dose-dependent manner. It also completely blocked lymphokine-activated killer (LAK) cell-mediated cytotoxicity against the human B lymphoblastoid cell lines Raji and Daudi. The cytotoxicity against the human melanoma tumor cell line A-375 mediated by unstimulated and stimulated monocytes was also suppressed by suramin. Maximum inhibition of monocyte-mediated cytotoxicity was observed when suramin was present during both the activation and the effector phases of cytotoxicity. Besides its effects on cell-mediated cytotoxicity, suramin also inhibited the cytotoxic effects of tumor necrosis factor (TNF) against different tumor cell lines. Furthermore, we found that suramin interferes with the binding of TNF with its receptor. Thus our results indicate that suramin overall downregulates the immune system by inhibiting cell-mediated and TNF-mediated cytotoxicity against different tumor cells.
Differences in the number of the antigenic determinants of A1 and B erythrocytes were exploited to study the influence of the sensitization on antibody-dependent monocyte- and complement-mediated ...cytotoxicity. Lysis was compared in direct and cold target competition assays. The findings were: (1) Monocyte mediated lysis of both targets was similar; A1 erythrocytes, however, showed stronger competitive inhibition than B cells; (2) the competitive inhibition was influenced by the antiserum concentration in a range where the direct lysis was not; (3) in the presence of optimal concentrations of hyperimmune antisera and complement, A1 erythrocytes were lysed, while B erythrocytes were not; and (4) A1 cells exposed to suboptimal concentrations of complement consumed complement, while B cells did not. It was concluded that the cold target competition assay is more sensitive than the direct cytotoxicity test to detect differences in the sensitization of erythrocytes.
Anti-D antibody-dependent cellular cytotoxicity of peripheral blood mononuclear cells was measured against O, Rh (D)-positive erythrocytes in 20 healthy pregnant women (chosen from all trimesters), ...and in 16 toxemic patients; it was then compared to the cytotoxic activities of 20 women 3 months after parturition and to that of 42 nonpregnant women. The application of an enzyme-like kinetic model for measurement of maximal cytotoxic function has permitted sensitive determination of the K cell function. It was found that during normal pregnancy maternal K cell activity did not change, whereas it was significantly decreased in preeclampsia.
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