Membrane progesterone receptor

Membrane progesterone receptors (mPRs) are a group of cell surface receptors and membrane steroid receptors belonging to the progestin and adipoQ receptor (PAQR) family which bind the endogenous progestogen and neurosteroid progesterone, as well as the neurosteroid allopregnanolone. Unlike the progesterone receptor (PR), a nuclear receptor which mediates its effects via genomic mechanisms, mPRs are cell surface receptors which rapidly alter cell signaling via modulation of intracellular signaling cascades. The mPRs mediate important physiological functions in male and female reproductive tracts, liver, neuroendocrine tissues, and the immune system as well as in breast and ovarian cancer. The mPRs appear to be involved in the neuroprotective and antigonadotropic effects of progesterone and allopregnanolone. The progesterone active metabolites 5α-dihydroprogesterone, also a progestogen, and allopregnanolone, which are positive allosteric modulators of the GABAA receptor, have been found to rapidly influence sexual receptivity and behavior in mice, actions that are GABAA receptor-dependent. These proteins are classified into three groups known as mPRα (PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6), and mPRε (PAQR9). Membrane progesterone receptor alpha (mPRα) is a protein that in humans is encoded by the PAQR7 gene. It is a steroid receptor which binds progesterone in vitro. Recent studies suggest the mPRα has important physiological functions in a variety of reproductive tissues. The mPRα is an intermediary in progestin induction of oocyte maturation and stimulation of sperm hyper motility in fish. In mammals, the mPRα has been implied in progesterone regulation of uterine functions in humans and GnRH secretion in rodents. Membrane progesterone receptor beta (mPRβ) is a protein that in humans is encoded by the PAQR8 gene. A recent study has investigated the role of mPRβ in regulating in vitro maturation (IVM) of pig cumulus-oocyte complexes (COCs). This study suggests that the mPRβ is a molecule related to cumulus expansion and it might function by regulation of exocytosis.