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Cytochrome P450j, an enzyme involved in nitrosamine metabolism, is expressed in hepatic, pulmonary, and renal tissues and its level is elevated in ethanol- and acetone-treated rats as well as in diabetic rats induced by either streptozotocin or alloxan. Although P450j protein is substantially elevated by all inducing regimens, only in diabetic rats is P450j mRNA increased 10-fold. Nuclear run-on transcription analysis showed that this mRNA increase is not due to transcriptional activation but is due to specific stabilization of the P450j mRNA.

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A specific member of the cytochrome P450 superfamily of enzymes, designated P450IA (including 2 isozymes, P450IA1 and P450IA2), which is involved in the metabolic activation of polycyclic aromatic hydrocarbons and aromatic amines, was studied in lung tissue from 25 lung cancer patients by immunohistochemistry. The pulmonary activity of a P450IA1-dependent enzyme, aryl hydrocarbon hydroxylase (AHH), from the same patients was also measured. Cytochrome P450IA was localized principally in the peripheral airways in alveolar epithelium of types I and II and in ciliated columnar and cuboidal bronchiolar epithelium. The amount of P450IA in the bronchial wall was minimal and was localized mainly in the capillary endothelium and the epithelium of the bronchial glands. Smoking was the most important factor related to the presence of P450IA and the AHH activity in lung tissue. None of the 10 ex-smokers, but all except I of the current smokers had detectable level of P450IA. The localization of the cancer was also correlated with the presence of cytochrome P450IA. Peripheral lung tissue stained positively in all patients with a peripheral adenocarcinoma who currently smoked (8/8) but in less than half of those with a bronchial cancer who were smokers (3/7). Our data suggest that the smokers who have an inducible cytochrome P450IA are especially at increased risk of developing lung cancer of the peripheral adenocarcinomatous type.

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In the present study, we demonstrate that ethanol induces CYP2E1 by protein stabilization in vivo. The control half-life of CYP2E1 was determined to be 6-7 h followed by a slower secondary phase. The half-life of ethanol-stabilized CYP2E1 was calculated to be 38 h. The mechanism underlying the rapid degradation of CYP2E1 was also investigated and appears to involve the ubiquitin-proteasome proteolytic pathway. An in vitro assay using the cytosolic fraction was developed to further characterize CYP2E1 degradation. Using this assay, 40-50% loss of CYP2E1 was observed in 1 h, coincident with the formation of high M r ubiquitin-CYP2E1 conjugates. At concentrations approximating those found in vivo, ethanol protects CYP2E1 from cytosolic degradation. No loss of CYP2B1/2 was observed under identical conditions, suggesting that this reaction is specific for certain P-450s which are rapidly turned over.A member of the microsomal P-450 family of proteins, P-450 2E1 (CYP2E1), 1 is induced by a variety of chemicals and physiological states, some of which have been linked to the development of liver disease and carcinogenesis via oxidative stress (1). The most significant chemical inducer of CYP2E1 is ethanol, a compound which is also a substrate for the protein. Debate still exists as to the precise mechanism of CYP2E1 induction by ethanol, with some reports indicating that ethanol stabilizes CYP2E1 in vitro (2) and another group suggesting that ethanol induces CYP2E1 by increasing protein synthesis (3). In the present study, we have attempted to define the nature of CYP2E1 regulation by ethanol in vivo using controls, chronic ethanol-treated, and ethanol-withdrawing animals. Results from CYP2E1 pulse-labeling show that ethanol induces CYP2E1 predominantly by protein stabilization, with the administration of ethanol attenuating the rapid phase of CYP2E1 degradation. We have also characterized the pathway responsible for this degradation, and present data in vivo and in vitro that suggest ubiquitin conjugation may target CYP2E1 for rapid proteolysis.