| Breast cancers are characterized by tumor cell proliferation and extensive angiogenesis. The mammary tumor stroma often contains macrophages (M&phis;s), dendritic cells, monocytes, neutrophils, and fibroblasts. Tumor promotion may be controlled by cytokines and growth factors secreted by tumor-associated macrophages (TAMs). Tumor growth outstrips local blood supply resulting in areas of hypoxia, which stabilizes hypoxia inducible factor-1alpha (HIF-1alpha) and upregulates vascular endothelial growth factor (VEGF). Tumor angiogenesis is mainly mediated through VEGF, a potent angiogenic cytokine.; Although mammary tumors express both alpha and beta estrogen receptors (ERalpha and ERbeta), signal transduction is mainly mediated through ERalpha. Tamoxifen (TMX), the most widely used drug for the treatment of breast cancer, binds to ERalpha and abrogates estrogen signaling. TMX induces apoptosis in breast cancer cells; however, its effects on stromal cells have not been studied. This investigation was designed to test the hypothesis that TAMs may inhibit TMX-induced apoptosis of breast cancer cells by providing survival signaling through the release of proinflammatory and angiogenic cytokines; and that the use of inhibitors of macrophage function can increase the effectiveness of TMX killing of breast cancer cells. This study assessed the effects of TMX on M&phis;s co-cultured with MCF-7 breast cancer cells in a simulated tumor environment. More specifically, it assessed the ability of TMX to modify the gene expression profiles of inflammatory cytokines and growth factors in both M&phis;s and MCF-7 cells by utilizing pathway-focused cDNA microarrays and reverse transcription polymerase chain reaction (RT-PCR). The results showed that (1) co-culture of MCF-7 cells with THP-1-derived macrophages alone and with TMX induced the expression of the proinflammatory cytokine genes MIF, TGF-beta1, TGF-beta3 and IL-1beta in MCF-7 cells, (2) VEGF was expressed in both THP-1-derived M&phis;s and MCF-7 cells under normoxia and hypoxia but its expression was blocked by TMX in MCF-7, (3) HIF-1alpha was constitutively expressed in both THP-1-derived M&phis;s and MCF-7, and (4) THP-1-derived M&phis;s increased the growth of and protected MCF-7 cells from TMX-induced apoptosis. Surprisingly, TMX upregulated IL-1beta in both THP-1-derived M&phis;s and MCF-7 cells. The cumulative results suggest that although TMX inhibits tumor cell growth, it may promote tumor invasion and metastasis by upregulating several proinflammatory and angiogenic cytokines in both tumor and stromal cells. |
