Activation of a positive feedback loop involving IL-6 and aromatase promotes intratumoral 17β-estradiol biosynthesis in endometrial carcinoma microenvironment

Tumor-stroma interactions contribute greatly to intratumoral estrogen biosynthesis in endometrial carcinoma, but the mechanisms involved remain largely unknown. Previous study demonstrated that intratumoral aromatase upregulation in stromal cells participated in this process, but the specific aromatase-regulators have not been reported. In the present study, we found that aromatase expression in intratumoral stroma, but not in tumor epithelium, correlated positively with interleukin 6 (IL-6) expression in cancer epithelial cells by immunohistochemistry, which was confirmed using laser capture microdissection/real-time reverse transcription-PCR. With stimulation by exogenous IL-6, aromarase expression was increased in stromal cells not but not in cancer cells. Aromatase mRNA levels in endometrial cancer cells were not influenced by cocultivation with intratumoral stromal cells. When cocultured with 17-estradiol (E-2)-treated cancer cells, aromatase mRNA in stromal cells was significantly elevated and increased IL-6 protein levels were detected in E-2-treated culture medium. Next, we demonstrated that E-2-induced IL-6 production was through cooperation between estrogen receptor and nuclear factor-kappa B. Furthermore, an IL-6 receptor blocking antibody could attenuate the upregulation of aromatase expression in stromal cells and the E-2 concentration in coculture systems of cancer and stromal cells. The results were confirmed by an orthotopic nude endometrial carcinoma model in vivo. These studies elucidated the activation of a positive feedback loop, that is, IL-6 stimulated by E-2 in endometrial cancer cells induced aromatase expression in stromal cells, promoting enhanced intratumoral E-2 synthesis. Blocking of this tumor-stroma interaction may be a therapeutic strategy to overcome in situ estrogen biosynthesis in endometrial carcinoma. What's new? Aromatase expression and activity may contribute to malignancy and poor survival in endometrial carcinoma, but specific aromatase regulators in the endometrial tumor microenvironment are unknown. According to this study, an important aromatase regulator may be IL-6, owing to a positive feedback loop in which IL-6 is induced by estrogen in cancer cells and stimulates aromatase expression in intratumoral stromal cells, thereby promoting estrogen biosynthesis in situ. Inhibition of IL-6 with an anti-IL-6 receptor antibody attenuated both aromatase expression in stromal cells and estrogen concentration in coculture systems of cancer cells and stromal cells. The results were confirmed in an orthotopic endometrial carcinoma mouse model.