Membrane progesterone receptors on the cell membrane: A review highlighting potential export motifs in mPRα regulating its trafficking to the cell surface

Membrane progesterone receptor e (paqr9) is necessary for chorion elevation in zebrafish

Paqr9 is a gene encoding membrane progestin receptor e (mPRe), the fifth subtype of the five mPR subtypes, and is currently classified a member of the progestin and adipoQ receptor (PAQR) family, which consists of 11 genes. To elucidate the physiological functions of the mPR subtypes, we established gene knockout (KO) fish via genome editing of seven paqr genes in zebrafish and analyzed their phenotypes. The null-mutant strain of paqr9 (paqr9-/-) that we established in this study presented reduced chorion elevation and a high percentage of abnormal embryos. Embryos exhibit various kinds of abnormal morphology, which are thought to be caused by insufficient elevation of the chorion. Immunohistochemical staining of ovaries with an anti-Paqr9 antibody revealed that Paqr9 was expressed in the periplasm of oocytes and the surface of chorion in the wild type, whereas signals were absent in paqr9-/- zebrafish. In histological sections, the periplasmic connection between the oocyte plasma membrane and chorion was absent in paqr9-/- oocytes. The number of cortical alveoli (CA) that are responsible for chorion elevation was significantly reduced in paqr9-/- zebrafish. SEM revealed that fiber-supported knob-like structures (KSs) on the chorion were absent in paqr9-/- zebrafish. These results indicate that Paqr9 is required for the preparation of CA during oogenesis. Insufficient formation of the chorion resulted in the abnormal development of embryos.

Establishment of a steroid binding assay for goldfish membrane progesterone receptor (mPR) by coupling with graphene quantum dots (GQDs)

A homogeneous assay was developed to evaluate ligands that target the membrane progesterone receptor alpha (mPRα) of goldfish. This was achieved by employing graphene quantum dots (GQDs), a type of semiconductor nanoparticle conjugated to the goldfish mPRα. When progesterone-BSA-fluorescein isothiocyanate (P4-BSA-FITC) was combined with the other agents, fluorescence was observed through Förster resonance energy transfer (FRET). However, this fluorescence was quenched by binding between the ligand and receptor. This established method demonstrated the ligand selectivity of the mPRα protein. Then, the methylotrophic yeast Pichia pastoris was used to express the goldfish mPRα (GmPRα) protein. The recombinant purified GmPRα protein was coupled with graphene quantum dots (GQDs) to generate GQD-conjugated goldfish mPRα (GQD-GmPRα). Fluorescence at a wavelength of 520 nm was observed through FRET upon the combination of P4-BSA-FITC and subsequent activation by ultraviolet (UV) light. Adding free P4 to the reaction mixture resulted in a decrease in fluorescence intensity at a wavelength of 520 nm. The fluorescence was reduced by the administration of GmPRα ligands but not by steroids that do not interact with GmPRα. The findings indicated that the interaction between the ligand and receptor led to the formation of a complex involving GQD-GmPRα and P4-BSA-FITC. The interaction between the compounds and GQD-GmPRα was additionally validated by a binding experiment that employed the radiolabeled natural ligand [3H]-17α,20β-dihydroxy-4-pregnen-3-one. We established a ligand-binding assay for the fish membrane progesterone receptor that is applicable for screening compounds.

Effects of Endocrine Interventions Targeting ERα or PR on Breast Cancer Risk in the General Population and Carriers of BRCA1/2 Pathogenic Variants

There is evidence suggesting that endocrine interventions such as hormone replacement therapy and hormonal contraception can increase breast cancer (BC) risk. Sexual steroid hormones like estrogens have long been known for their adverse effects on BC development and progression via binding to estrogen receptor (ER) α. Thus, in recent years, endocrine interventions that include estrogens have been discussed more and more critically, and their impact on different BC subgroups has increasingly gained interest. Carriers of pathogenic variants in BRCA1/2 genes are known to have a high risk of developing BC and ovarian cancer. However, there remain open questions to what extent endocrine interventions targeting ERα or the progesterone receptor further increase cancer risk in this subgroup. This review article aims to provide an overview and update on the effects of endocrine interventions on breast cancer risk in the general population in comparison to BRCA1/2 mutation carriers. Finally, future directions of research are addressed, to further improve the understanding of the effects of endocrine interventions on high-risk pathogenic variant carriers.