Abstract 1350: Macrophages induce COX-2 expression in breast cancer cells: Role of IL-1β dependent signal transduction pathways

Abstract Macrophages are a major component of the inflammatory infiltrate observed in many tumors including carcinoma of the breast. Evidence suggests that tumor associated macrophages (TAMs) are a part of an inflammatory “loop” that promotes tumor progression. In the breast, the presence of high numbers of TAMs is associated with a poor prognosis. However, the mechanisms underlying the interactions between TAMs and breast cancer cells are not clearly understood. In this regard, cyclooxygenase-2 (COX-2) is over expressed in approximately 40% of breast cancers, and is associated with a poor prognosis. COX-2 derived prostaglandin E2 (PGE2) promotes the growth and metastasis of breast cancers. To determine whether TAMs regulate COX-2 expression in breast cancer cells, PMA-treated THP-1 cells grown on porous inserts were co-cultured with HCC1954 breast cancer cells. The presence of THP-1 cells led to increased COX-2 expression in the breast cells and elevated levels of PGE2 in conditioned media. Similar results were observed when THP-1 cells were incubated with HCC1937 cells and when peripheral blood-derived mononuclear cells were incubated with HCC1954 cells. To identify potential paracrine factors that mediated COX-2 induction in breast cancer cells, levels of pro-inflammatory cytokines in THP-1/HCC1954 co-culture conditioned media were measured. The levels of IL-1β rose rapidly in co-culture conditioned media. Moreover, the expression of IL-1β in both breast cancer cells and macrophages was increased as a result of co-culture. This increased expression was blocked in both cells by IL-1 receptor antagonist (IL-1ra) suggesting an autocrine loop. Importantly, the addition of IL-1ra or IL-1β neutralizing antibody blocked the induction of COX-2 in HCC1954 cells. These data suggest that IL-1β is a major mediator of COX-2 induction. Co-culture conditioned media triggered production of reactive oxygen species (ROS) in naïve HCC1954 cells. Blocking ROS production by DPI (a NADPH oxidase inhibitor) or knocking down the expression of p67 subunit of the NADPH oxidase complex led to inhibition of COX-2 induction in HCC1954 cells. ROS production in HCC1954 cells triggered activation of Src kinase, and subsequently the downstream MAP kinases (ERK, p38, and JNK). Blocking the activity of Src or MAP kinases, utilizing specific inhibitors or siRNA, attenuated COX-2 induction. In summary, we identified that IL-1β was a major mediator of COX-2 induction in HCC1954 cells co-cultured with THP-1 macrophages. We also showed that co-culture induced COX-2 expression was a consequence of IL-1β dependent ROS→Src→MAP kinases signaling. These findings provide new insights into the mechanisms of interactions between TAMs and breast cancer cells and potential intervention targets in TAM-positive breast cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1350.