Progesterone Receptor Membrane Component-1 (PGRMC1) and PGRMC-2 Interact to Suppress Entry into the Cell Cycle in Spontaneously Immortalized Rat Granulosa Cells1

Abstract

Progesterone receptor membrane component 1 (PGRMC1) and PGRMC2 are expressed in rat granulosa cells and spontaneously immortalized granulosa cells (SIGCs) but their biological roles are not well defined. The present studies demonstrate that depleting either Pgrmc1 or Pgrmc2 in SIGCs increases entry into the cell cycle but does not increase cell proliferation. Rather, PGRMC1 and/or PGRMC2-deplete cells accumulate in metaphase and undergo apoptosis. Because both PGRMC1 and PGRMC2 localize to the mitotic spindle, their absence likely accounts for cells arresting in metaphase. Moreover, pull-down assays, colocalization studies and in situ proximity ligation assays (PLA) indicate that PGRMC1 binds PGRMC2. Disrupting the PGRMC1:PGRMC2 complex through the use of siRNA or the cytoplasmic delivery of a PGRMC2 antibody increases entry into the cell cycle. Conversely, overexpressing either PGRMC1-GFP or GFP-PGRMC2 fusion protein inhibits entry into the cell cycle. Subsequent studies reveal that depleting PGRMC1 and/or PGRMC2 reduces the percentage of cells in G0 and increases the percentage of cells in G1. These observations indicate that in addition to their role at metaphase, PGRMC1 and PGRMC2 are involved in regulating entry into the G1 stage of the cell cycle. Interestingly, both PGRMC1 and PGRMC2 bind GTPase-activating protein-binding protein 2 (G3BP2) as demonstrated by pull-down assays, colocalization assays, and PLAs. G3bp2 siRNA treatment also promotes entry into the G1 stage. This implies that dynamic changes in the interaction among PGRMC1, PGRMC2, and G3BP2 play an important protein regulating the rate at which SIGCs enter into the cell cycle.

PGRMC1 participates in late events of bovine granulosa cells mitosis and oocyte meiosis

“…This is consistent with effects of depleting PGRMC1 in SIGCs, where cells accumulate in metaphase and then undergo cell death. 12 Another possible outcome of cytokinesis failure is the formation of bior multi-nucleated cells. This is not the case for bGCs since multinucleated granulosa cells were not observed in PGRMC1 RNAi treated cells (data not shown).…”

“…2,9 Accordingly, in vitro studies using different ovarian cell lines have shown that depleting PGRMC1 expression suppresses cell proliferation. [10][11][12] However the mechanism of action by which PGRMC1 controls ovarian cell proliferation is poorly understood.…”

Progesterone receptor membrane component 1 promotes survival of human breast cancer cells and the growth of xenograft tumors

“…41 More recently, PGRMC1 was shown to interact with PGRMC2 to suppress entry of SIGCs into the cell cycle. 42 During early gestation, PGRMC1 localizes to the nuclei of mitotic cells within the uterus at the interface between the undifferentiated and terminally differentiated stroma during decidualization. 43 A role for PGRMC1 in enhancing microtubule stability during mitosis has also been proposed, wherein PGRMC1 was found to directly interact with b-tubulin.…”

“…44 In addition to its role in metaphase, PGRMC1, along with its binding partner PGRMC2, is involved in regulating entry into the G1 stage of the granulosa cell cycle. 42,45 PGRMC1 forms a physical interaction with aurora kinase B on metaphase II chromosomes in bovine oocytes, and failure to do so is suggested to play a role in increased aneuploidy in cows with reduced antral follicle counts. 46 These studies in reproductive tissues provide foundational information about the mitotic/meiotic functions of PGRMC1 as a mediator of the actions of P4 in ovarian somatic and germ cells.…”

Role of Protein-Protein Interactions in Metabolism: Genetics, Structure, Function

“…Interestingly, this difference allows human PGRMC1 to form stable homodimers through hydrophobic heme-heme stacking interactions, explaining earlier observations of dimeric complexes (Min et al, 2004;Kabe et al, 2016). Since the hemebinding residues are conserved among MAPRs, these proteins may all share the ability of heme-dependent homo-and/or heterodimerization (Peluso et al, 2014). Although PGRMC1 had originally been defined as a component of a progesterone-binding protein complex with affinities in the nM range (Meyer et al, 1996), it remained questionable whether progesterone actually binds directly to PGRMC1 itself.…”