Context: Progesterone (P4) influences ovarian cancer cells by an unknown mechanism.

Objective: The objective was to determine whether P4 acts through progesterone receptor membrane component -1 (PGRMC1) in ovarian cancers.

Design, Setting and Patients: Archival tissue and cDNA provided by OriGene were used for expression studies. In vitro experiments were conducted with Ovcar-3 cells.

Main Outcome Measures: PCR, western blot, immunohistochemistry were used to measure expression of PGRMC1 and nuclear progesterone receptor (PGR). PGRMC1's role in regulating the viability of ovarian cancers was assessed by over expressing PGRMC1, depleting PGRMC1 using siRNA and attenuating PGRMC1's action with a blocking antibody. Apoptosis was determined by DAPI staining.

Results: PGRMC1 mRNA increased while PGR mRNA decreased in advanced stages of ovarian cancer. Unlike PGR, PGRMC1 was expressed in virtually every cancer cell within the tumor. A similar relationship between PGRMC1 and PGR was observed in Ovcar-3 cells. In these cells P4 suppressed apoptosis induced by either serum withdrawal or cisplatin (CDDP). Moreover, in the presence of P4 1) over expression of PGRMC1 reduces the effectiveness of CDDP, 2) depletion of PGRMC1 with siRNA enhances the effects of CDDP and 3) PGRMC1 antibody treatment increases the apoptotic response to CDDP.

Conclusions: These findings indicate that PGRMC1 plays an important role in promoting ovarian cancer cell viability and that attenuating PGRMC1's action makes the ovarian cancer cells more sensitive to CDDP. These data suggests that targeted depletion of PGRMC1could be useful as an adjunct to CDDP therapy.