INTERLEUKIN-6 AND TUMOR-NECROSIS-FACTOR-ALPHA SYNERGISTICALLY BLOCK S-PHASE CELL-CYCLE AND UP-REGULATE INTERCELLULAR-ADHESION MOLECULE-1 EXPRESSION ON MCF7 BREAST-CARCINOMA CELLS

The effect of IL-6 and TNFalpha were studied on human MCF7 breast cancer cells. Synergistic interaction between IL-6 and TNFalpha, on the growth inhibition (50% reduction in the percentage of S-phase cells) and the upregulation of ICAM-1 expression (4 to 11-fold increase) was shown using flow cytometric methods. IL-6 and TNFalpha alone had negligible effect on the cell cycle. The individual effect of IL-6 resulted in down-regulation of ICAM-1 expression (30-35%), while TNFalpha always upregulated ICAM-1 (1.5 to 4-fold increase). The combined effect of IL-6 and TNFalpha consistently caused an increased expression of ICAM-1, which was greater than the sum of each one alone and also sustained for 72 h following cytokine withdrawal.