Expression profile of heptahelical putative membrane progesterone receptors in epithelial ovarian tumors

Abstract

A novel class of putative progestin binding proteins has been recently identified as potential mediators of rapid nongenomic hormone actions. The proteins designated membrane progestin receptor (mPR) alpha, beta, and gamma were initially discovered in fish and shown to have a role in oocyte maturation. The predicted multiple membrane spanning domain structure of the mPRs resembles that of heptahelical G-protein-coupled receptors. Phylogenetic analysis indicated that the mPRs belong to the large progestin and adiponectin Q receptor (PAQR) gene family. Based on the reported expression of the 3 mPRs in hormone-responsive tissues of the female reproductive tract and on the role of steroid hormones in cancer, we investigated the expression of these novel progestin receptors in epithelial tumors of the ovary. The transcript levels of the 3 human mPR/PAQRs were assessed by semiquantitative reverse transcriptase polymerase chain reaction in 28 ovarian samples, including normal tissues, cystadenomas, borderline tumors, and common types of ovarian carcinomas. Two of the 3 transcripts for the mPR/PAQRs proteins appeared differentially expressed in the tumors examined. Expression of mPR alpha and beta was demonstrated in ovarian tumors at both messenger RNA and protein level, and their expression appeared to be independent of the expression of the classic nuclear progestin receptors. Expression of mPR gamma (PAQR V) was elevated in endometrioid and clear cell carcinomas, 2 related neoplastic counterparts of hormonally responsive tissues, suggesting a potential role of the mPR/PAQRs in the pathogenesis of epithelial ovarian tumors.