Mutagen activation by cDNA-expressed P(1)450, P(3)450, and P450a

Area of Science:

• Biochemistry
• Molecular Biology
• Toxicology

Background:

• Cytochrome P450 (P450) enzymes are crucial for metabolizing xenobiotics and endogenous compounds.
• Understanding the specific activities and carcinogen activation profiles of different P450 isoforms is vital for risk assessment.

Purpose of the Study:

• To express rodent P450 cDNAs (P1450, P3450, P450a) using the vaccinia virus-T7 RNA polymerase system.
• To characterize the enzymatic activities and substrate specificities of the expressed P450 isoforms.
• To evaluate the mutagenic activation potential of various carcinogens by the expressed P450s.

Main Methods:

• cDNA expression of rodent P450 isoforms (P1450, P3450, P450a) via the modified vaccinia virus-T7 RNA polymerase system.
• Assay of specific enzyme activities including aryl hydrocarbon hydroxylase, acetanilide hydroxylase, testosterone 7 alpha-hydroxylase, and ethoxycoumarin deethylase.
• Analysis of mutagen activation of 19 diverse carcinogens using the expressed P450 systems.

Main Results:

• Successful expression of functional P1450, P3450, and P450a with appropriate molecular weights and characteristic enzyme activities.
• P1450 primarily catalyzed aryl hydrocarbon hydroxylase and ethoxycoumarin deethylase.
• P3450 catalyzed acetanilide hydroxylase and ethoxycoumarin deethylase, and notably activated polycyclic aromatic hydrocarbons and heterocyclic amines.
• P450a exhibited testosterone 7 alpha-hydroxylase activity with minimal mutagen activation.

Conclusions:

• The vaccinia virus-T7 RNA polymerase system is a versatile tool for expressing and characterizing diverse cytochrome P450 isoforms.
• Different P450 isoforms display distinct substrate specificities and varying capacities for activating carcinogens to mutagenic forms.
• This expression system facilitates detailed analysis of P450 function in xenobiotic metabolism and chemical carcinogenesis.