INTERLEUKIN-1-ALPHA AND TUMOR-NECROSIS-FACTOR-ALPHA (TNF ALPHA) INHIBIT GROWTH AND INDUCE TNF MESSENGER-RNA IN MCF-7 HUMAN BREAST-CANCER CELLS

We studied the effects of interleukin-1-alpha (IL-1) and tumor necrosis factor-alpha (TNF), alone and in combination, on MCF-7 breast cancer cells to determine whether these cytokines alter cell growth, TNF gene expression, and TNF secretion. We found that IL-1 alone and TNF alone inhibited cell growth in a dose-dependent manner. Each cytokine arrested growth in the G0/G1 phase of the cell cycle, with maximum growth inhibition at 1000 U/ml (P < 0.05) and 100 U/ml (P < 0.01), respectively. However, the combination of these two cytokines did not result in greater growth inhibition or a greater percentage of cells arrested in the G0/G1 phase of the cell cycle compared with each cytokine alone. We examined the effect of exogenous IL-1 and TNF on TNF gene expression by Northern blot analysis. In the absence of any cytokine, these cells do not express TNF mRNA. Exposure to IL-1 (1000 U/ml) induced TNF mRNA at 3 h; however, mRNA levels diminished thereafter to barely detectable levels by 24 h. Exposure to TNF (1000 U/ml) also induced TNF mRNA at 3 h, but in contrast to IL-1, the level of enhanced expression persisted at these levels through 72 h of exposure. Secretion of TNF by these cells is induced by exogenous TNF, but not by IL-1. IL-1 and TNF in combination do not produce greater inhibition of growth, greater amounts of TNF mRNA at 3 h, or greater secretion of TNF than that produced by TNF alone. These findings indicate that these two cytokines, while inhibiting cell growth, have different effects on TNF gene expression and secretion, suggesting different modes of action. In contrast to their actions on other cell types, these cytokines are not additive or synergistic in their effects on these breast cancer cells. The finding that TNF induces gene expression and secretion of TNF also indicates an important potential regulatory role of the cytokine on these cells.