Induction of cytochrome P-450b,e-type isozymes by polychlorinated biphenyls in rat liver. Molecular cloning of induced mRNAs

Expression of CYP2B1 in freshly isolated and proliferating cultures of epithelial rat lung cells

Bronchiolar Clara cells and alveolar type 2 cells of the lung are known to express relatively high levels of P450 enzymes compared to other pulmonary cells. Populations of enriched type 2 cells and Clara cells were isolated from rat lung by a procedure including lung perfusion, protease digestion, centrifugal elutriation, and differential attachment. Alveolar macrophages were removed by lavage. The purity of the type 2 cell-enriched population was approximately 90%, and the purity of the Clara cell-enriched population was 40-50%. Both type 2 cells and the cells of the Clara cell-enriched population proliferated in culture. CYP2B1 mRNA was expressed approximately to the same level in type 2 cells and the Clara cell-enriched population. The mRNA levels remained roughly constant for both cell types throughout the culture period, except for an early transient reduction. The apoenzyme level of CYP2B1 was 2-3 times higher in freshly isolated cells of the Clara cell-enriched population than in the type 2 cells. Both epithelial cell types showed decreased level of CYP2B1 apoenzyme in culture. The differences in the CYP2B1 mRNA and apoenzyme expression levels in freshly isolated cells and cultured cells suggest the existence of a post-transcriptional regulatory mechanism for CYP2B1 expression in lung cells. The characterization of specific functions of lung cells in culture, such as P450 gene expression, provides necessary information for the use of the cells in in vitro pulmonary toxicology.

Factors affecting the mitotic stability of high-copy-number integration into the ribosomal DNA of Saccharomyces cerevisiae

Yeast vectors suitable for high-level expression of heterologous proteins should combine a high copy number with high mitotic stability. The pMIRY integrative vector system, based upon targeted integration into the yeast rDNA locus, developed in our laboratory satisfies these criteria. However, insertion of a (foreign) gene drastically reduced its mitotic stability of the resulting vector in comparison to its parent. In this paper we have investigated a number of possible reasons for this reduction in stability. The results demonstrate that plasmid size is an important, but not the only, determinant of mitotic stability. Stable maintenance is only observed when the complete plasmid has a size no larger than that of the rDNA unit (9.1 kb). In addition stability depends upon the nature of the rDNA fragment present in the plasmid, required for targeting its integration. On the other hand, it turned out to be irrelevant for mitotic stability whether the heterologous gene was expressed or not. These findings will be important in the design of a pMIRY vector suitable for industrial production of heterologous proteins.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

Effect of in vivo chromate, acetone and combined treatment on rat liver in vitro microsomal chromium(VI) reductive activity and on cytochrome P450 expression

Cytochrome P450 (P450IIE1) in rat has previously been shown to exhibit high chromate [Cr(VI)] reductase activity (Mikalsen et al. 1991). The present study reports on the effect of chromate treatment in vivo in rats and on the modulating effect of acetone + fasting on chromium(VI) toxicity. No effect of intraperitoneal injection with 5 mg chromate/kg was observed, whereas 15 mg chromate/kg decreased the liver microsomal Cr(VI) reductase activity by about 30% in in vitro microsomal incubations. In addition, the P450 and cytochrome b5 contents were decreased by about 30% and 25% respectively. Acetone + fasting caused increases of total microsomal P450 and cytochrome b5 contents, associated with similar increases in apoproteins P450IIE1 and P450IIB1 + 2, and their corresponding mRNA, and apoprotein NADPH-P450 reductase, as well as NADPH-P450 reductase and microsomal Cr(VI) reductive activities. Related to acetone + fasting alone, when given in combination with chromate (15 mg/kg) the Cr(VI) reductive activity was decreased by about 30%, associated with decreases in the P450 and cytochrome b5 contents, 65% and 35% respectively. This further reduced the apoprotein levels of P450IIB1 + 2, P450IIE1, and NADPH-P450 reductase to 90%, 60%, and 40%, respectively, and the mRNA levels of P450IIB2 and P450IIE1. No effect was observed on NADPH-P450 reductase activity. This dose also caused some macroscopic alterations in the liver. In contrast, the P450IIE1 apoprotein level in the lung was apparently stabilized or even increased by chromate in rats treated with acetone + fasting.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol-, fasting-, and acetone-inducible cytochromes P-450 in rat liver: regulation and characteristics of enzymes belonging to the IIB and IIE gene subfamilies

Two major forms of hepatic microsomal cytochrome P-450 were purified from starved and acetone-treated rats. On the basis of amino acid sequence analysis, they were identified as P-450j and P-450b. Ethanol or acetone treatment of rats caused a 9-fold increase in the amount of P-450j in liver microsomes accompanied by similar increases in the rate of NADPH-dependent metabolism of carbon tetrachloride, acetone, and benzene. Immunological experiments indicated that P-450j constitutes the major catalyst of the microsomal metabolism of the latter agents and contributes by about 50% to microsomal P-450-dependent ethanol oxidation under the conditions used. The P-450j-dependent catalytic activities had a high rate of turnover. In contrast, this was not the case for the immunodetectable P-450j, indicating the occurrence of inactive forms of this protein in microsomes. Starvation or ethanol or acetone treatment caused 10-30-fold increases in the amount of both mRNA and apoprotein of P-450b,e compared to control. Run-on experiments and the concomitant increases of the P-450b,e gene products at the mRNA and protein levels indicated the appearance of mainly a transcriptional activation by acetone, ethanol, or starvation. Fasting exerted, in addition, a pronounced synergistic effect on acetone-dependent induction of P-450b,e mRNA (3-fold), apo-P-450b,e (4.3-fold), P-450j mRNA (2-fold), and apo-P-450j (2-fold). No increase of mRNA coding for P-450j, compared to control, was seen after acetone or ethanol treatment alone. The results indicate that effects of ethanol, acetone, and/or starvation on drug and xenobiotic metabolism are caused by the induction of P-450 forms belonging to at least two gene subfamilies.