Identification of a novel mechanism of NF-kappaB inactivation by progesterone through progesterone receptors in Hec50co poorly differentiated endometrial cancer cells: induction of A20 and ABIN-2

OBJECTIVE: Nuclear factor kappa B (NFkappaB) is a strong anti-apoptotic factor, which is constitutively active in human endometrial cancer cells. Progesterone is the principal growth inhibitory hormone in the endometrial epithelium and promotes apoptosis. To identify the pathways through which progesterone controls NFkappaB function, we explored its genomic and non-genomic effects in endometrial cancer cells. METHODS: PR-negative Hec50co endometrial cancer cells were engineered to express high levels of the A or B isoform of PR (PRA or PRB) by adenoviral infection. Cells were treated with progesterone or vehicle alone, and RNA was isolated. Affymetrix microarrays were performed and transcriptional control of the genes of highest interest was confirmed by semi-quantitative RT-PCR. To assess the non-genomic effects of PR on inflammation associated with NF-kappaB, electromobility shift assays (EMSAs) were performed. RESULTS: Expression analysis demonstrated a significant effect of progesterone after 12- and 24-h treatment on several genes; in particular, A20 and ABIN-2 were induced through PRB. These factors bind in a complex and inhibit NFkappaB transcriptional activity. In addition, EMSAs revealed the complete inhibition of NFkappaB dimer binding to DNA by both PRA and PRB. CONCLUSIONS: Progesterone is the principal differentiating hormone in the endometrium. We have now identified several down-stream pathways of action, one of which is the control of genes involved in NFkappaB activity. The tumorigenic inflammatory and anti-apoptotic effects of NFkappaB are inhibited by progesterone/PRB through the transcriptional control of binding proteins A20 and ABIN-2. This pathway offers interesting targets for future therapeutic development.