Monoclonal antibodies to ethanol-induced rat liver cytochrome P-450 that metabolizes aniline and nitrosamines

Hybridomas were prepared from mouse myeloma cells and spleen cells derived from female BALB/c mice that had been immunized with a partially purified ethanol-induced rat liver cytochrome P-450 (P-450et). Monoclonal antibodies (MAbs) produced by the hybridomas were screened for binding to P-450et with a radioimmunoassay. Thirty-one independent hybrid clones produced MAbs that had a high affinity for P-450et. Each clone produced MAbs of a single subclass of the mouse immunoglobulins IgG1, IgG2a, IgM, or IgA. Ten of the 31 MAbs also immunoprecipitated P-450et as determined by Ouchterlony double-immunodiffusion analyses. One of the MAbs was tested for cross-reactivity with other rabbit and rat liver cytochromes P-450 and was found not to cross-react with rat liver P-450 induced by either phenobarbital, beta-naphthoflavone, or rabbit liver P-450LM2 or P-450LM4. Nine of the MAbs were tested for cross-reactivity with rat liver clofibrate-induced P-450, rat liver pregnenolone-16-alpha-carbonitrile-induced P-450, and a human liver P-450. All the MAbs showed no cross-reactivity except for one MAb which cross-reacted with both pregnenolone-16-alpha-carbonitrile and human P-450 and three MAbs which cross-reacted with human P-450. Three antigen-precipitating MAbs and four nonprecipitating MAbs were tested for their effects on the aniline p-hydroxylase activity of liver microsomes of untreated rats and from rats treated with acetone, pyrazole, methylpyrazole, or imidazole. One of the seven MAbs tested, 1-91-3, inhibited enzyme activity of acetone-, pyrazole-, or methylpyrazole-induced microsomes by 54, 47, and 48%, respectively. This indicates that at least 50% of microsomal cytochrome P-450 aniline p-hydroxylase activity in the latter is a function of a P-450 enzyme that contained the epitope to which the MAb 1-91-3 is directed. With untreated and imidazole-induced microsomes, 32 and 21% inhibition of the enzyme activity was observed. In reconstituted systems containing phospholipid and NADPH-cytochrome P-450 reductase, MAb 1-91-3 inhibited aniline p-hydroxylase activity of purified ethanol-induced P-450et and acetone-induced P-450 by more than 90%. Nitrosodimethylamine demethylase activity of acetone-induced rat microsomes was inhibited by the various MAbs up to 77% and the activity of the purified acetone-induced P-450 was inhibited up to 92%.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation, complementary DNA sequence, and regulation of rat hepatic lauric acid omega-hydroxylase (cytochrome P-450LA omega). Identification of a new cytochrome P-450 gene family

Lauric acid omega-hydroxylase (cytochrome P-450LA omega) was purified from livers of rats that had been given the hypolipidemic drug clofibrate. Immunoblot analysis with anti-cytochrome P-450LA omega antibody revealed the presence of two clofibrate-induced cytochrome P-450 proteins in both liver and kidney. This antibody was used to screen a lambda gt11 expression library constructed from liver mRNA isolated from rats given clofibrate. The clone, pP-450LA omega, was isolated and found to contain 2062 base pairs with an open reading frame of 509 amino acids (Mr 58,222). The pP-450LA omega cDNA insert was placed in the yeast expression vector pAAH5, and the resultant plasmid expressed a protein of the same size and activity as cytochrome P-450LA omega. The mechanism of the regulation of the cytochrome P-450LA omega gene by hypolipidemic agents was examined. The rate of cytochrome P-450LA omega gene transcription was increased as early as 1 h after administration of clofibrate, and this increase was followed by an elevation of cytochrome P-450LA omega mRNA, immunochemically detectable protein, and cytochrome P-450LA omega activity. In contrast, no increase in transcriptional activity was detected after clofibrate administration for the cytochrome P-450PCN or P-450b/e genes. The cytochrome P-450LA omega has several structural features in common with other cytochrome P-450s, including a conserved cysteine-containing heme-binding fifth ligand fragment and a hydrophobic amino terminus. Overall, cytochrome P-450LA omega shared less than 35% cDNA nucleotide and amino acid similarity with cytochromes P-450c, P-450d, P-450e, and P-450PCN, indicating that it is a member of a new cytochrome P-450 gene family. Southern blot analysis indicates that this family contains two or three genes.

Complementary DNA and protein sequences of ethanol-inducible rat and human cytochrome P-450s. Transcriptional and post-transcriptional regulation of the rat enzyme

The cDNAs encoding ethanol-inducible forms of rat and human cytochrome P-450s have been isolated, sequenced, and used to study the expression of this cytochrome P-450 during development and by various inducing agents. Polyclonal antibody against ethanol-inducible cytochrome P-450 was used to screen rat and human lambda gt11 cDNA expression libraries. The longest cDNAs obtained from each library were completely sequenced, and the deduced amino acid sequence of the rat cDNA was found to correspond to P450j based on the published amino-terminal sequence. The rat and human cytochrome P-450s both contained 493 amino acids and calculated molecular masses of 56,634 and 56,916 daltons, respectively. Human P450j shared 75% nucleotide and 78% amino acid similarities to the respective orthologous rat cDNA and deduced amino acid sequences. Amino acid alignment also revealed that P450j was 48% similar to P450b and P450e, the major phenobarbital-inducible forms, and 54% similar to P450PB1 and P450f, two developmentally regulated forms. Southern blot analyses of rat and human genomic DNAs verified that only a single gene shared extensive homology with P450j. The expression of P450j was found to be developmentally regulated. No immunodetectable protein or P450j mRNA was present in newborn rats; however, rapid increases in P450j mRNA and protein occurred within 1 week after birth in both male and female rats. The levels of P450j and its mRNA thereafter remained elevated up to 12 weeks of age in both sexes. The increases in both P450j and its mRNA paralleled the change in aniline hydroxylase activity during development. Run-on transcriptional analysis confirmed that these increases were due to transcriptional activation of the P450j gene. In contrast to transcriptional activation during development, induction of P450j by various agents such as pyrazole, 4-methylpyrazole, and acetone might be due to post-transcriptional events. A 4-fold elevation in both enzymatic activity and immunodetectable P450j was not accompanied by an increase in P450j mRNA level.

Sequence of two related P-450 mRNAs transcriptionally increased during rat development. An R.dre.1 sequence occupies the complete 3' untranslated region of a liver mRNA

Polyclonal antibody against a cytochrome P-450 expressed in adult male rats was utilized to screen a lambda gt-11 library. Two cDNAs were isolated and sequenced. The cDNA and deduced protein sequence revealed that these P-450s correspond to previously isolated P-450 PB1 (Waxman D. T., Ko, A., and Walsh, C., (1983) J. Biol. Chem. 258, 11937-11947) and P-450f (Ryan, D. E., Iida, S., Wood, A. W., Thomas, P. E., Lieber, C. S., and Levin, W., (1984) J. Biol. Chem. 259, 1239-1250). Both P-450s contain 490 amino acids and share 75% similarity with each other and 50% similarity with P-450b and P-450e. Southern blot analysis indicates that these enzymes are part of a small P-450 gene subfamily composed of two or three members. An unusual feature of P-450 PB1 is the presence of a rat brain identifier-type repetitive sequence (R.dre.1) that encompasses the complete 3' untranslated region of the mRNA. This sequence is absent from P-450f mRNA. A cDNA from an apparent allelic form of P-450 PB1 mRNA was isolated and sequenced. This cDNA was identical to the other P-450 PB1 cDNA except for a single base substitution in the R.dre.1 repeat and the presence of a repeat (AAATAAA)13 at the 3' end of the mRNA. By use of a 3' specific probe for P-450f mRNA and a probe common to P-450 PB1 and P-450f mRNAs, the mechanism by which these P-450s are elevated during rat development was studied. Both RNAs are virtually absent in newborn rats and become elevated between 1 and 4 weeks after birth. Maximal levels of P-450f mRNA levels continue to increase up to 12 weeks after birth, and 2-fold higher levels of P-450f mRNA are reached in 12-week-old female rats compared with male rats. P-450 PB1 mRNA reached maximal levels at 4 weeks and no sex difference in mRNA level was detected for P-450 PB1. Nuclear run-on transcription assays confirmed that the increase in these mRNAs is due to transcriptional activation.

Pregnenolone 16 alpha-carbonitrile-inducible P-450 gene family: gene conversion and differential regulation

A cytochrome P-450 cDNA clone, designated pP450PCN2, homologous to the previously characterized pregnenolone 16 alpha-carbonitrile (PCN)-induced P-450 cDNA (pP450PCN1; F. J. Gonzalez, D. W. Nebert, J. P. Hardwick, and C. B. Kasper, J. Biol. Chem. 260:7435-7441), was isolated from a rat liver cDNA expression library by use of a polyclonal anti-P450PCN1 antibody. This P-450 cDNA contains 2,014 base pairs and yields an open reading frame of a protein consisting of 504 amino acids (Mr = 57,760). P450PCN2 cDNA and protein shared 90% nucleotide and 89% amino acid similarity with P450PCN1 cDNA and protein, respectively. The 5' untranslated, coding, and 3' untranslated regions between the two cDNAs share 94, 93, and 79% similarities, respectively. Nucleotide differences in the coding regions, however, are not evenly distributed. Complete homology exists between the two mRNAs for 425 nucleotides (positions 346 through 771). Other regions of 93 nucleotides containing only one difference and 147 nucleotides containing two differences exist toward the 3' end of the coding regions. These data suggest the possibility that a gene conversion event(s) have occurred subsequent to duplication of the ancestral P450PCN gene. Oligonucleotide probes unique for P450PCN1 and P450PCN2 cDNAs were used to examine the levels of their respective mRNAs in noninduced and PCN-induced liver cells and in male and female rats of various ages. P450PCN1 mRNA was not detectable in either male or female rats at any ages. In contrast, P450PCN2 mRNA was present at a low level in newborn rats and became elevated in both males and females at 1 week of age. Levels of p450PCN2 mRNA continued to increase in males until 12 weeks, whereas the mRNA in females reached peak levels at 2 weeks of age but declined continuously at the onset of puberty (between 4 and 12 weeks). These levels of P45PCN2 mRNA closely parallel the increases in testosterone 6 beta-hydroxylase activity and P450PCN2 protein level, as analyzed by Western blots. P450PCN1 mRNA was induced by PCN, dexamethasone, and phenobarbital in both male and female rats. P450PCN2 mRNA was not significantly induced by PCN or dexamethasone but was readily induced by phenobarbital. Testosterone 6 beta-hydroxylase activity was also induced severalfold by PCN, dexamethasone, and phenobarbital. These data demonstrate that P450PCN1 and P450PCN2 genes are differentially regulated during development and after administration of inducing compounds and furthermore suggest that both enzymes possess testosterone 6 beta-hydroxylase activity.

Preparation of catalytically active cytochromes P-450 by antigen exchange on monoclonal antibody based immunoadsorbents

Catalytically active cytochromes P-450 have been prepared by monoclonal antibody (MAb) directed immunopurification using an antigen-exchange technique. Immunoaffinity-purified cytochromes P-450 that require denaturants for efficient desorption from the immunoaffinity matrix, although significantly lacking in catalytic activity, were found to retain epitopic structural integrity as probed by radioimmunoassay using MAbs to 3-methylcholanthrene and phenobarbital-induced rat liver cytochromes P-450. These denatured cytochromes P-450 were capable of displacing from the immunoaffinity matrices epitopically related cytochromes P-450 that retained aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase activities. Such epitope-specific exchange of denatured for native antigen on a solid-phase matrix containing a MAb may be generally applicable to preparation of proteins with the retention of activity.

Monoclonal antibody-directed determination of cytochrome P-450 types expressed in a human lymphoblastoid cell line

Cytochrome P-450-dependent aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase activities of a cloned line of human lymphoblastoid AHH-1 cells are inhibited by a monoclonal antibody (MAb 1-7-1) prepared to a 3-methylcholanthrene-induced rat liver cytochrome P-450. The monoclonal antibody inhibition determined that a single MAb 1-7-1-sensitive type of cytochrome P-450 is responsible for all of AHH expression in both the basal and benz[a]anthracene-induced cells. Partial inhibition by the MAb 1-7-1, however, indicates that at least two forms of cytochrome P-450 catalyze 7-ethoxycoumarin O-deethylase in both the basal and the induced cells, one form of which is identical to the MAb-sensitive cytochrome P-450 responsible for all of the AHH. Thus, a single cloned cell line is capable of expressing two classes of cytochromes P-450, and the observed multiplicity of cytochrome P-450 in animal tissues does not necessarily depend on cell heterogeneity. A sensitive MAb 1-7-1-based radioimmunoassay also directly demonstrates the presence in these cells of a MAb 1-7-1-specific type of cytochrome P-450 as well as its elevation in the induced cells. These MAb-based methods thus can determine the contribution of specific MAb-defined types of cytochromes P-450 to the cellular metabolism of specific xenobiotics.

Monoclonal antibody-directed radioimmunoassay detects cytochrome P-450 in human placenta and lymphocytes

A multiplicity of cytochromes P-450 is responsible for the detoxification and activation of xenobiotics such as drugs and carcinogens. Individual differences in sensitivity to these agents may reside in the cytochrome P-450 phenotype. A monoclonal antibody-directed radioimmunoassay was developed that detects epitope-specific cytochromes P-450 in human placentas and peripheral lymphocytes. Placentas from women who smoked cigarettes contained greater amounts of cytochrome P-450 with the monoclonal antibody-specific epitope than placentas from nonsmokers. The amount of this cytochrome P-450 in human peripheral lymphocytes increased after treatment of the mitogenized lymphocytes with the cytochrome P-450 inducer benz[a]anthracene.

Detection and purification of cytochromes P-450 in animal tissues with monoclonal antibodies

Monoclonal antibody (MAb)-based radioimmunoassay (RIA) and immunopurification procedures were used to probe the immunochemical relatedness of cytochromes P-450 in tissues from different species. RIAs based on MAb 1-7-1 and MAb 1-31-2, both to the major 3-methylcholanthrene (MC)-induced rat liver microsomal cytochrome P-450, detected antigenically related forms of cytochrome P-450 in liver microsomes from MC-induced rats, C57BL/6 and DBA/2 mice, hamsters, and guinea pigs, and in lung and kidney microsomes of MC-induced rats. Individual cytochromes P-450 were also isolated from these microsomes by MAb-directed immunopurification. When bound to Sepharose, MAb 1-7-1 adsorbed two species of Mr 56,000 and 57,000 from liver microsomes from rats and C57BL/6 mice, while MAb 1-31-2 adsorbed only the Mr 57,000 polypeptide. These results reveal that livers from both rats and C57BL/6 mice contain a cytochrome P-450 (Mr 56,000) with the epitope for 1-7-1 and a cytochrome P-450 (Mr 57,000) with epitopes for both 1-31-2 and 1-7-1. Additional immunochemical relatedness between the cytochromes P-450 in different tissues was demonstrated by MAb-directed immunopurification of cytochromes P-450 from DBA/2 mouse liver (Mr 56,000), guinea pig liver (Mr 53,000), hamster liver (Mr 57,000), and rat lung (Mr 57,000). These results demonstrate the efficacy of MAb-based RIA and immunopurification procedures for simple and rapid detection and purification of cytochromes P-450 from a variety of tissues.

Monoclonal antibody-directed radioimmunoassay of specific cytochromes P-450

A rapid solid phase radioimmunoassay (RIA) for cytochromes P-450 has been developed utilizing specific monoclonal antibodies to major forms of rat liver cytochrome P-450 that are induced by 3-methylcholanthrene (MC-P-450) and phenobarbital (PB-P-450). Monoclonal antibodies (MAbs) that were endogenously labeled with [35S]methionine were used to detect MAb-specific cytochromes P-450 in liver microsomes from untreated rats and rats pretreated with 3-methylcholanthrene (MC) or phenobarbital. The competitive binding assays are rapid and can detect cytochrome P-450 in less than 100 ng of microsomal protein. The RIA was used to examine the distribution of MAb-specific cytochromes P-450 in extrahepatic tissues of MC-treated rats; an approximately 30- to 50-fold greater amount of MC-P-450 in liver relative to lung and kidney was observed, which corresponds well with aryl hydrocarbon hydroxylase activity in these tissues. The inducibility of MAb-specific cytochromes P-450 in several species was also examined by competitive RIA. Significant increases in the MAb-specific P-450 were observed in MC-treated rats, guinea pigs, and C57BL/6 mice, all highly inducible for aryl hydrocarbon hydroxylase; little increase was observed for the relatively noninducible DBA/2 mouse strain.