Expression of Progesterone Receptor Membrane Component-2 Within the Immature Rat Ovary and Its Role in Regulating Mitosis and Apoptosis of Spontaneously Immortalized Granulosa Cells1

Abstract

Progesterone receptor membrane component 2 (Pgrmc2) mRNA was detected in the immature rat ovary. By 48 h after eCG, Pgrmc2 mRNA levels decreased by 40% and were maintained at 48 h post-hCG. Immunohistochemical studies detected PGRMC2 in oocytes and ovarian surface epithelial, interstitial, thecal, granulosa, and luteal cells. PGRMC2 was also present in spontaneously immortalized granulosa cells, localizing to the cytoplasm of interphase cells and apparently to the mitotic spindle of cells in metaphase. Interestingly, PGRMC2 levels appeared to decrease during the G1 stage of the cell cycle. Moreover, overexpression of PGRMC2 suppressed entry into the cell cycle, possibly by binding the p58 form of cyclin dependent kinase 11b. Conversely, Pgrmc2 small interfering RNA (siRNA) treatment increased the percentage of cells in G1 and M stage but did not increase the number of cells, which was likely due to an increase in apoptosis. Depleting PGRMC2 did not inhibit cellular (3)H-progesterone binding, but attenuated the ability of progesterone to suppress mitosis and apoptosis. Taken together these studies suggest that PGRMC2 affects granulosa cell mitosis by acting at two specific stages of the cell cycle. First, PGRMC2 regulates the progression from the G0 into the G1 stage of the cell cycle. Second, PGRMC2 appears to localize to the mitotic spindle, where it likely promotes the final stages of mitosis. Finally, siRNA knockdown studies indicate that PGRMC2 is required for progesterone to slow the rate of granulosa cell mitosis and apoptosis. These findings support a role for PGRMC2 in ovarian follicle development.

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

“…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.…”

“…The next obvious step will be to determine PGRMC1 mechanism of action and how it might function in concert with PAQR family members to regulate P4 responses in breast cancer. PGRMC1 has been implicated in many cellular processes that may promote tumor cell survival and growth including sterol metabolism, 62,63 chemical detoxification, 31 chemoresistance, 29,64,65 gene transcription, 39,66 cell stress response 67 and survival, 35 mitosis, 44,45,66 and immune regulation. 68 A recent study identified several treatment targets that have been analyzed experimentally and in clinical trials for triple negative breast cancer.…”

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

“…PGRMC2 also seems to be involved in granulosa cells mitosis, as evidenced by initial studies using a granulosa cell line, spontaneously immortalized granulosa cells (SIGCs). In these cells, depleting PGRMC2 using siRNA promotes entry into the cell cycle but does not increase cell number [10]. Rather there is an increased incidence of apoptosis.…”

“…It is known that both MAPR family members are highly expressed in granulosa cells [10][11][12] and may be involved regulating granulosa cell mitosis. For example, there is a 50% reduction in the number of antral follicles present within the immature ovary of conditional knockout mice in which PGRMC1 is depleted from granulosa cells [2,3].…”

“…The function of PGRMC1 and PGRMC2 in the ovary is generally discussed in relationship to progesterone-mediated effects on mitosis and apoptosis, given that depleting either MAPR attenuates the antiapoptotic and/or antimitotic action of progesterone (P4) [2,3,[10][11][12][13][14]. Although PGRMC2 is essential for P4's antimitotic action [10] Pgrmc2 siRNA treatment does not reduce the capacity of SIGCs to bind P4 [10].…”