PGRMC1 Stabilizes Cytochromes P450 And Is Required for Activity In Vivo

Abstract

Progesterone receptor membrane component 1 (PGRMC1) is a membrane‐bound hemoprotein with many ascribed functions that binds cytochromes P450 in yeast and human cells. In this study, we generated a whole‐body Pgrmc1 KO mouse to examine the function of PGRMC1 in cytochrome P450 biology. Here, we report that Pgrmc1 is a novel post‐translational stabilizer of cytochromes P450 required for cytochrome P450 activity in vivo. In mouse liver, Pgrmc1 bound 13 cytochromes P450 of diverse families (Cyp1, 2, 3, 8, and 51) and functioned to maintain liver cytochrome P450 levels post‐transcriptionally. In the absence of Pgrmc1, cytochrome P450 protein levels were 22–70% of wild‐type. These reductions in P450 enzymes were shown to be physiologically important. Pgrmc1 promoted Cyp1a2 activity in vitro as the Vmax for the Cyp1a2‐dependent O‐deethylation of 7‐ethoxycoumarin was 40% lower in the absence of Pgrmc1 in liver membranes. Mechanistically, PGRMC1 stabilized CYP1A2 post‐translationally, doubling the half‐life of the cytochrome P450 in transfected human cells. The stabilization of cytochromes P450 and promotion of cytochrome P450 activity by Pgrmc1 were the result of a protein‐protein interaction between Pgrmc1 and the cytochrome P450 that did not require Pgrmc1 to bind heme. Reductions in Cyp2e1 protein in Pgrmc1 KO mice protected animals against hepatotoxicity during Cyp2e1‐dependent acetaminophen overdose, the leading cause of acute liver failure in the U.S. This study establishes PGRMC1 as a central component controlling cytochrome P450 activity thus making PGRMC1 the first new player in the liver cytochrome P450 system in 50 years as it joins cytochrome P450 oxidoreductase and cytochrome b5. This study also establishes PGRMC1 as a clinically relevant effector of cytochrome P450 activity, which has direct clinical implications related to the efficacy of pharmacotherapies and will be of interest to pharmacologists, clinicians, and the pharmaceutical industry.Support or Funding InformationM.M. was supported by NIH 5T32GM007445, NIH F31HL131185, and American Heart Association 15PRE25250008. P.E. was supported by NIH R01HL077588 and NIH R21HL094774.