MARIA ALMIRA CORREIA, PH.D., Professor of Pharmacology

The research work is focused on the elucidation of the regulation and the structure and function relationships of hepatic cytochromes P450 and tryptophan 2,3-dioxygenase (TDO), and the mechanisms of P450 suicide inactivation by several clinically relevant agents. We have specifically examined the secobarbital (SB)-mediated inactivation of cytochrome P450 2B1. We have isolated the relevant ¹⁴C-SB-alkylated peptide and by mass spectrometric/sequencing analyses identified it to be an active site peptide, distal to the heme moiety of P450 2B1. The influence of the apoproteins on the heterolytic and homolytic O-O cleavage of individual P450s was examined. We have also structurally characterized the drug-induced heme modification of the proteins of cytochromes P450 using CuOOH-inactivated P450s as models. This inactivation process brands P450s for proteolytic removal. We have shown that CuOOH-inactivated P450 2B1 inactivated in this fashion is rapidly ubiquitinated and proteolysed when incubated with the rat liver cytosol, supplemented with ATP, MgCl₂ and ubiquitin. Immunoprecipitation studies using a polyclonal antibody raised to bovine pituitary multicatalytic protease (MCP), revealed that this enzyme was indeed involved in the liver cytosolic degradation of CuOOH-inactivated 2B1, thereby identifying the hepatic 26S ATP/ubiquitin-dependent proteolytic system as a major participant in this process. Studies with 26S proteasome inhibitors confirm that the 26S proteasome species plays a major role in the degradation of heme-modified P450s. In parallel, we have examined the role of hepatic heme in the regulation of hepatic TDO turnover (synthesis and degradation) and its structure-function relationships after expression of this enzyme, in high yields and a functionally active form in E. Coli.

SELECTED PUBLICATIONS:

1. Correia MA, Sadeghi S, Mundo-Paredes E. CYTOCHROME P450 UBIQUITINATION: Branding for the Proteolytic Slaughter? Annu Rev Pharmacol Toxicol, 45:439-464, 2005.
2. Han X, Lee G, Hefner C, Maher JJ, Correia MA. HEME-REVERSIBLE IMPAIRMENT OF CYP2B1/2 INDUCTION IN HEME DEPLETED RAT HEPATOCYTES IN PRIMARY CULTURE : TRANSLATIONAL CONTROL BY A HEPATIC eIF2{alpha} KINASE? J Pharmacol Exp Ther, 2005.
3. Liao M, Zgoda VA, Murray BP, Correia MA. Vacuolar Degradation of Rat Liver Cyp2b1 in Saccharomyces Cerevisiae: Further Validation of the Yeast Model and Structural Implications for the Degradation of Mammalian Endoplasmic Reticulum P450 Proteins. Mol Pharmacol, 2005.