Interleukin-8 (IL-8) has been identified as an angiogenesis factor (AF) as well as a tumor cell chemotactic factor and mitogen. Recent in vivo studies have demonstrated the expression of IL-8, IL-1 and TNF, as well their receptors, on various sub-populations of tumor cells in human breast cancer (HBC). Since pro-inflammatory cytokines such as IL-1 and TNF are known inducers of IL-8 in non-tumor cells, we hypothesize that IL-1/TNF may act as an IL-8 inducer in HBC, and thus enhance HBC tumor progression. To begin to test this hypothesis, we evaluated the ability of: a) human breast cancer cell lines (BCC) and normal human breast epithelial cell lines (BEC) to produce IL-8 in vitro; and b) IL-1 and TNF to regulate the expression of IL-8. In general, basal IL-8 expression was low in all 8 cell lines examined. TNF-α and TNF-β induced a 3- to 24-fold increase in IL-8 protein expression of BEC, and a 2- to 8-fold increased IL-8 expression in estrogen-independent BCC cell lines and no significant IL-8 expression in estrogen-dependent cell lines. Conversely, IL-1α and IL-1β, induced a 5- to 104-fold stimulation of BEC and a 330 to 1,138-fold increase in IL-8 expression in estrogen independent BCC. These observations demonstrate the ability of HBC cells to produce IL-8 in vitro and further indicate that IL-1 is a potent inducer of IL-8 expression by BEC and BCC. Furthermore, this in vitro data support the hypothesis, that within the HBC tumor microenvironment, tumor cells exist that respond to pro-inflammatory cytokine (IL-1) stimulation (i.e. MDA-MB-231) and those that do not (i.e. MCF-7). Additionally, HBC tumor cell lines that can be induced to express high levels of IL-8 tend to be associated with a more aggressive phenotype.

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