Abstract
Progesterone receptor membrane component 1 (PGRMC1) has been recently shown to interact with several cytochromes P450 (CYPs) and to activate enzymatic activity of CYPs involved in sterol biosynthesis. We analyzed the interactions of PGRMC1 with the drug-metabolizing CYPs, 2C2, 2C8 and 3A4, in transfected cells. Based on co-immunoprecipitation assays, PGRMC1 bound efficiently to all three CYPs and binding to the catalytic cytoplasmic domain of CYP2C2 was much more efficient than to a chimera containing only the N-terminal transmembrane domain. Downregulation of PGRMC1 expression levels in HEK 293 and HepG2 cell lines stably expressing PGRMC1-specific siRNA, had no effect on the ER localization and expression levels of CYPs, whereas enzymatic activities of CYPs 2C2, 2C8 and 3A4 were slightly higher in PGRMC1-deficient cells. Co-transfection of cells with CYPs and PGRMC1 resulted in PGRMC1 concentration-dependent inhibition of the CYP activities and this inhibition was partially reversed by increased expression of the CYP reductase (CPR). In contrast, CYP51 activity was decreased by downregulation of PGRMC1 and expression of PGRMC1 in the PGRMC1-deficient cells increased CYP51 activity. In cells co-transfected with CPR and PGRMC1, strong binding of CPR to PGRMC1 was observed, however, in the presence of CYP2C2, interaction of PGRMC1 with CPR was significantly reduced suggesting that CYP2C2 competes with CPR for binding to PGRMC1. These data show that in contrast to sterol synthesizing CYPs, PGRMC1 is not required for the activities of several drug-metabolizing CYPs and its overexpression inhibits those CYPs' activities. Further, PGRMC1 binds to CPR which may influence CYP activity.
- Received August 27, 2010.
- Revision received November 16, 2010.
- Accepted November 16, 2010.
- The American Society for Pharmacology and Experimental Therapeutics