Characterization, Neurosteroid Binding and Brain Distribution of Human Membrane Progesterone Receptors δ and ϵ (mPRδ and mPRϵ) and mPRδ Involvement in Neurosteroid Inhibition of Apoptosis

Abstract

Three members of the progestin and adipoQ receptor (PAQR) family, PAQR-7, PAQR-8, and PAQR-5 [membrane progesterone (P4) receptor (PR) (mPR)α, mPRβ, and mPRγ], function as plasma mPRs coupled to G proteins in mammalian cells, but the characteristics of two other members, PAQR6 and PAQR9 (mPRδ and mPRε), remain unclear, because they have only been investigated in yeast expression systems. Here, we show that recombinant human mPRδ and mPRε expressed in MDA-MB-231 breast cancer cells display specific, saturable, high-affinity [(3)H]-P4 binding on the plasma membranes of transfected cells with equilibrium dissociation constants (K(d)s) of 2.71 and 2.85 nm, respectively, and low affinity for R5020, characteristics typical of mPRs. P4 treatment increased cAMP production as well as [(35)S]-guanosine 5'-triphosphate (GTP)γS binding to transfected cell membranes, which was immunoprecipitated with a stimulatory G protein antibody, suggesting both mPRδ and mPRε activate a stimulatory G protein (Gs), unlike other mPRs, which activate an inhibitory G protein (Gi). All five mPR mRNAs were detected in different regions of the human brain, but mPRδ showed greatest expression in many regions, including the forebrain, hypothalamus, amygdala, corpus callosum, and spinal cord, whereas mPRε was abundant in the pituitary gland and hypothalamus. Allopregnanolone and other neurosteroids bound to mPRδ and other mPRs and acted as agonists, activating second messengers and decreased starvation-induced cell death and apoptosis in mPRδ-transfected cells and in hippocampal neuronal cells at low nanomolar concentrations. The results suggest that mPRδ and mPRε function as mPRs coupled to G proteins and are potential intermediaries of nonclassical antiapoptotic actions of neurosteroids in the central nervous system.

Purification of the goldfish membrane progestin receptor α (mPRα) expressedin yeast Pichia pastoris

“…Other, recent data suggest that, as part of the cellular response to the binding of progesterone to mPRα, apoptosis is inhibited in breast cancer cells (8)(9)(10). In the membranes of neuroendocrine cells, mPRs appear to interact with G proteins and have a role in the release of hormones and maintain oocyte maturation by regulating gonadotropin releasing hormone (GnRH) secretion (24). Progesterone is known to have neuroprotective effects, which possibly is mediated by mPRα.…”

“…Recently, based on the analyses of proteins expressed in yeast, mPRδ and ε (PAQR6 and 9) were proposed to form novel mPR subtypes (31). Also human orthologs of them, when expressed in human breast cancer cells, were found to have progestin binding activity (24). Therefore, five mPR subtypes have been described at present.…”

Recent advances in structure of progestins and their binding to progesterone receptors

“…Furthermore, a family of membrane progesterone receptors (mPRs) has been found that mediates rapid actions of P ( Figure 1). This non-genomic mechanism has been described in some cellular functions in females such as: oocyte meiotic maturation, GnRH secretion, reproductive behavior, apoptosis of granulose, breast cancer and neuronal cells [14][15][16][17] . These mPRs are G-protein-coupled and function following the cAMP cascade ( Figure 1).…”

The other side of progestins: effects in the brain

“…PROG-induced nongenomic activity is mainly mediated by two different membrane-bound PROG receptor types: the seven-transmembrane progesterone adiponectin Q receptors (PAQR) and the single-transmembrane PGRs (Thomas 2008. The former are G protein-coupled membrane receptors and include three subtypes of receptors: PROG membrane receptors (mPGR) α, β, and γ, also referred to as transmembrane PGRs α, β, or γ (7TMPRα,β,γ) and the two more recently identified subtypes mPGRδ and mPGRε (Pang et al 2013, Hossain et al 2015. When bound to its ligand, these receptors block adenylate cyclase activity to reduce excitation in the CNS , Thomas 2008, Do Rego et al 2009, King 2013.…”