It has been reported that IL-1beta is present in tissue extracts from benign breast lesions, ductal carcinomas in situ (DCIS) and invasive breast carcinomas. IL-1beta levels were found to be relatively high in invasive breast carcinomas and correlated with estrogen receptor negativity, high tumor grade, p53 positivity, and bcl-2 negativity, suggestive of aggressive tumor biology. Our recent microarray screen on normal breast fibroblasts treated with MCF-7 cancer cell-conditioned-medium, depicting a malignant microenvironment, showed upregulation of prostaglandin E2 synthase (PGES) which is the terminal enzyme responsible for synthesis of Prostaglandin E2 (PGE2). PGE2 is known to be a potent inducer of aromatase, a key enzyme for biosynthesis of estrogens. Since IL-1beta is known to upregulate PGES in other cell types, we hypothesized that IL-1beta, present in a malignant microenvironment, stimulates PGES and thus PGE2 synthesis in stromal fibroblasts, in a paracrine fashion. We herein report the effects of IL-1beta on proliferation and adipogenic program of benign fibroblasts, and on PGE2 levels in a malignant microenvironment. Inhibition of adipogenesis is one mechanism by which malignant epithelial cell-derived factors act in a paracrine fashion to maintain the stromal fibroblasts in an undifferentiated state and hence in an estrogen-synthesizing (aromatase positive) state. We provide evidence that IL-1beta inhibited the differentiation of primary breast fibroblasts in the presence of an adipogenic cocktail. It also had a proliferative effect on these fibroblasts as determined by cell counts over a period of 12 days. Moreover, IL-1beta, but not IL-6, IL-11 and LIF (Leukemia Inhibitory Factor), induced the expression of PGES in these fibroblasts in a time- and dose-dependent fashion. This induction correlated with increased PGE2 secretion as determined by ELISA. Moreover, we determined substantial differences in IL-1beta mRNA levels in normal human mammary epithelial cells (HMEC), MCF-7 breast carcinoma cell line (ERα and PR +), and MDA-MB-231 breast carcinoma cell line (ERα and PR -), with the highest levels detected in MDA-MB-231 and lowest levels detected in normal HMEC. Also, the conditioned media from these cell lines showed various degrees of PGES induction in primary fibroblasts, which were directly proportional to the IL-1beta levels in these cell lines. In conclusion, our findings are suggestive of an epithelial-stromal crosstalk in which IL-1beta plays an important role in proliferation and inhibition of adipogenesis of stromal fibroblasts which would explain the desmoplastic reaction frequently observed in breast tumors. We also uncovered a role of IL-1beta in increased production of PGE2, via increased synthesis of PGES, and hence of increased estrogen production, via PGE2, in the malignant microenvironment. (NCI grant CA67167)

[Proc Amer Assoc Cancer Res, Volume 46, 2005]