Heterologous expression of equine CYP3A94 and investigation of a tunable system to regulate co-expressed NADPH P450 oxidoreductase levels

PLoS One. 2014 Nov 21;9(11):e113540. doi: 10.1371/journal.pone.0113540. eCollection 2014.

Abstract

The activity of cytochrome P450 enzymes depends on the enzyme NADPH P450 oxidoreductase (POR). The aim of this study was to investigate the activity of the equine CYP3A94 using a system that allows to regulate the POR protein levels in mammalian cells. CYP3A94 and the equine POR were heterologously expressed in V79 cells. In the system used, the POR protein regulation is based on a destabilizing domain (DD) that transfers its instability to a fused protein. The resulting fusion protein is therefore degraded by the ubiquitin-proteasome system (UPS). Addition of "Shield-1" prevents the DD fusion protein from degradation. The change of POR levels at different Shield-1 concentrations was demonstrated by cytochrome c reduction, Western immunoblot analysis, and immunocytochemistry. The alteration of CYP3A94 activity was investigated using a substrate (BFC) known to detect CYP3A4 activity. Equine CYP3A94 was demonstrated to be metabolically active and its activity could be significantly elevated by co-expression of POR. Cytochrome c reduction was significantly increased in V79-CYP3A94/DD-POR cells compared to V79-CYP3A94 cells. Surprisingly, incubation with different Shield-1 concentrations resulted in a decrease in POR protein shown by Western immunoblot analysis. Cytochrome c reduction did not change significantly, but the CYP3A94 activity decreased more than 4-fold after incubation with 500 nM and 1 µM Shield-1 for 24 hours. No differences were obtained when V79-CYP3A94 POR cells with and without Shield-1 were compared. The basal activity levels of V79-CYP3A94/DD-POR cells were unexpectedly high, indicating that DD/POR is not degraded without Shield-1. Shield-1 decreased POR protein levels and CYP3A94 activity suggesting that Shield-1 might impair POR activity by an unknown mechanism. Although regulation of POR with the pPTuner system could not be obtained, the cell line V79-CYP3A94/DD-POR system can be used for further experiments to characterize the equine CYP3A94 since the CYP activity was significantly enhanced with co-expressed POR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cloning, Molecular / methods*
  • Cricetinae
  • Cytochrome P-450 Enzyme System / genetics*
  • Cytochrome P-450 Enzyme System / metabolism*
  • Cytochromes c / metabolism
  • Female
  • Gene Expression Regulation*
  • HEK293 Cells
  • Horses
  • Humans
  • Male
  • Morpholines / pharmacology
  • NADPH-Ferrihemoprotein Reductase / genetics*
  • NADPH-Ferrihemoprotein Reductase / metabolism

Substances

  • Morpholines
  • Shield-1 compound
  • Cytochromes c
  • Cytochrome P-450 Enzyme System
  • NADPH-Ferrihemoprotein Reductase

Grants and funding

This work was supported by Swiss National Science Foundation (SNSF), http://www.snf.ch/en/Pages/default.aspx: #310030_149954, #310030_119911; and Berne University Research Foundation: #10/2013, #46/2012. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.