Context: The enzyme 17beta-hydroxysteroid dehydrogenase type 2 (HSD17B2), exerts a local antiestrogenic effect by metabolizing biologically active estradiol to inactive estrone in endometrial epithelial cells. Retinoic acid (RA) induces HSD17B2 expression, but the underlying mechanism is not known.

Objective: To elucidate the molecular mechanisms responsible for HSD17B2 expression in human endometrial cells.

Method: Human endometrial Ishikawa and RL95–2 cell lines were cultured in the presence or absence of RA to analyze endogenous HSD17B2 expression, transcription factor complex formation, and promoter activity.

Results: RA induced HSD17B2 mRNA levels in a dose- and time-dependent manner in endometrial cells. The RA antagonist ANG11273 abolished RA-induced HSD17B2 expression. siRNA ablation of RAR or RXR completely blocked RA-induced HSD17B2 gene expression. Analysis of serial deletion and site-directed mutants of the HSD17B2 promoter fused to a reporter gene indicated that RA induction requires a cis-regulatory sequence that binds the SP class of transcription factors. Chromatin-immunoprecipitation-PCR and gel-shift assays showed that RAR/RXR and SP1/SP3 interact with this HSD17B2 promoter sequence. siRNA ablation of SP1 and SP3 expression markedly decreased HSD17B2 basal expression and blocked RA-induced expression. Finally, immunoprecipitation-immunoblotting demonstrated RA-induced interactions between RAR/RXR and SP1/SP3 in intact endometrial cells.

Conclusions: In endometrial epithelial cells, RA stimulates formation of a multimeric complex comprised of RAR/RXR tethered to transcription factors SP1 and SP3 on the HSD17B2 promoter. Assembly of this transcriptional complex is necessary for RA induction of HSD17B2 expression and may be an important mechanism for local estradiol inactivation in the endometrium.