Progesterone limits the tumor-promoting effects of the beta-subunit of human chorionic gonadotropin via non-nuclear receptors

Abstract

Background Beta-hCG can be detected in post-menopausal women, who also demonstrate an increased cancer risk. Whether ovarian hormones mediate cytotoxic effects on beta-hCG-responsive tumor cells, whether beta-hCG exerts enhanced pro-tumorigenic effects in the absence of ovarian steroids, and whether steroid administration can have restorative effects on tumor molecular profiles and progression, remain unaddressed. Methods The effect of ovarian steroids on the proliferation, viability and apoptosis of beta-hCG responsive LLC1 tumor cells were assessed. Involvement of nuclear/non-nuclear steroid receptors was evaluated by assessing presence and employing receptor antagonists, by cAMP measurements, and by assessing MAP kinase activation. LLC1 tumor cells were implanted in female non-transgenic mice, in beta-hCG transgenic mice and in ovariectomized beta-hCG transgenic mice; progesterone was additionally administered to the latter two groups. Tumor volumes were measured, and RNA-seq, qPCR and immunohistochemistry were employed to characterize tumor molecular profiles. TCGA databases for lung adenocarcinoma, colon adenocarcinoma and glioblastoma were probed with human orthologs of newly-identified genes to reveal clinically-relevant associations, with a focus on the post-menopausal state. Results Ovarian steroids demonstrated anti-tumor effects in vitro; progesterone caused tumor cell apoptosis via non-nuclear receptors and the phosphorylation of p38. Beta-hCG, particularly in absence of the ovaries (a mimic of the post-menopausal state), constituted an aggravated pro-tumorigenic signal for implanted LLC1 tumor cells. Progesterone dampened aggravated tumor growth in ovariectomized mice. RNA-seq on excised tumors identified genes associated with enhanced beta-hCG-mediated tumor growth in ovariectomized mice, as well as with the anti-tumor effects of progesterone. TCGA analysis revealed correlations between the expression of several newly-identified, progesterone-influenced genes (and of intra-tumoral beta-hCG) and poor patient prognosis, specifically in post-menopausal women. Conclusion This study describes a previously-unidentified interplay between progesterone and beta-hCG in the regulation of tumorigenesis. Murine tumor-associated gene signatures, combined with queries on aggressive human tumors reveal, for the first time, that beta-hCG acts as an additionally potent pro-tumorigenic signal when the ovaries are quiescent. Associations of progesterone-influenced genes (and intra-tumoral beta-hCG) with prognosis were revealed. Intra-tumoral / extra-tumoral beta-hCG may be a useful prognostic indicator in post-menopausal women with cancer, and progesterone may constitute a potential therapeutic in such cases.