Liver cytochrome P450 3A endoplasmic reticulum-associated degradation: a major role for the p97 AAA ATPase in cytochrome P450 3A extraction into the cytosol

J Biol Chem. 2011 Feb 4;286(5):3815-28. doi: 10.1074/jbc.M110.186981. Epub 2010 Nov 24.

Abstract

The CYP3A subfamily of hepatic cytochromes P450, being engaged in the metabolism and clearance of >50% of clinically relevant drugs, can significantly influence therapeutics and drug-drug interactions. Our characterization of CYP3A degradation has indicated that CYPs 3A incur ubiquitin-dependent proteasomal degradation (UPD) in an endoplasmic reticulum (ER)-associated degradation (ERAD) process. Cytochromes P450 are monotopic hemoproteins N-terminally anchored to the ER membrane with their protein bulk readily accessible to the cytosolic proteasome. Given this topology, it was unclear whether they would require the AAA-ATPase p97 chaperone complex that retrotranslocates/dislocates ubiquitinated ER-integral and luminal proteins into the cytosol for proteasomal delivery. To assess the in vivo relevance of this p97-CYP3A association, we used lentiviral shRNAs to silence p97 (80% mRNA and 90% protein knockdown relative to controls) in sandwich-cultured rat hepatocytes. This extensive hepatic p97 knockdown remarkably had no effect on cellular morphology, ER stress, and/or apoptosis, despite the well recognized strategic p97 roles in multiple important cellular processes. However, such hepatic p97 knockdown almost completely abrogated CYP3A extraction into the cytosol, resulting in a significant accumulation of parent and ubiquitinated CYP3A species that were firmly ER-tethered. Little detectable CYP3A accumulated in the cytosol, even after concomitant inhibition of proteasomal degradation, thereby documenting a major role of p97 in CYP3A extraction and delivery to the 26 S proteasome during its UPD/ERAD. Intriguingly, the accumulated parent CYP3A was functionally active, indicating that p97 can regulate physiological CYP3A content and thus influence its clinically relevant function.

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / physiology*
  • Animals
  • Cells, Cultured
  • Cytochrome P-450 CYP3A / analysis
  • Cytochrome P-450 CYP3A / metabolism*
  • Cytosol / metabolism*
  • Endoplasmic Reticulum / metabolism*
  • Hepatocytes / enzymology
  • Hepatocytes / metabolism*
  • Male
  • Nuclear Proteins / genetics
  • Nuclear Proteins / physiology*
  • Proteasome Endopeptidase Complex
  • Protein Transport
  • RNA, Small Interfering / pharmacology
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Nuclear Proteins
  • RNA, Small Interfering
  • Cytochrome P-450 CYP3A
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease
  • Adenosine Triphosphatases
  • p97 ATPase