Monoclonal antibodies to rat liver cytochrome P-450 2c/RLM5 that regiospecifically inhibit steroid metabolism

Hybridomas were formed from myeloma cells and spleen cells derived from BALB/c female mice immunized with purified liver microsomal cytochrome P-450 2c/RLM5 (P-450 gene IIC11) isolated from untreated adult male rats. Six hybridoma clones produced monoclonal antibodies (MAbs) of the IgM(kappa) type. All the MAbs bound strongly to P-450 2c/RLM5 when measured by radioimmunoassay, and four of the six specifically immunoprecipitated P-450 2c/RLM5 in an Ouchterlony double-immunodiffusion test. These four MAbs also bound but did not immunoprecipitate P-450 RLM3. The MAbs that precipitated P-450 2c/RLM5 neither bound nor precipitated P-450 PB-B (gene IIB1) and P-450 BNF-B (gene IA1) of rats or P-450 LM2 and P-450 LM4 of rabbits. In contrast, mouse polyclonal anti-P-450 2c/RLM5 antibody strongly immunoprecipitated P-450 RLM3 as well as P-450 2c/RLM5 and to a lesser extent P-450 PB-B and P-450 LM2. The MAbs that precipitated P-450 2c/RLM5 also inhibited by more than 90% androstenedione 16 alpha-hydroxylase activity of untreated rat microsomes, but did not inhibit microsomal 6 beta- or 7 alpha-hydroxylation. In addition, complete inhibition of both androstenedione 16 alpha-hydroxylation and testosterone 16 alpha-hydroxylation was observed in a reconstituted system with P-450 2c/RLM5. Androstenedione 6 beta-hydroxylation catalyzed by P-450 2c/RLM5 was also inhibited, whereas P-450 3-catalyzed 7 alpha-hydroxylation was not inhibited by the MAbs. P-450 2c/RLM5 catalyzed 2 alpha-, 16 alpha- and 6 beta-hydroxylation of progesterone in a reconstituted system were also inhibited by the MAb by 60-80%. These MAbs should prove useful for "reaction phenotyping," i.e. for defining the contribution of microsomal P-450 2c/RLM5 to the oxidative metabolism of endogenous steroids and other P-450 substrates in animal and human tissues.

Oncogene expressions detected by in situ hybridization of squamous metaplasia, dysplasia and primary lung cancer in human

In order to elucidate the dynamic changes of oncogene expression in the sequential cascade of squamous metaplasia, dysplasia, and squamous cell carcinoma of the bronchial epithelium, hybridization in situ was employed with a biotinylated oncogene probe. The expression of c-myc was localized exclusively in nuclei. While normal bronchial epithelium revealed no discernible clumps of c-myc grains, except occasional grains less than 3 per cell, squamous metaplasia showed increased number of grains and a few clusters of c-myc grains. In dysplasia, c-myc expression was more intensive than in squamous metaplasia. Approximately, 1/3 to 2/3 of tumor cell populations of squamous cell carcinomas of the lung revealed tremendously increased c-myc expression. In addition clumpy grains of c-myc in squamous cell carcinoma appeared more frequently than in squamous metaplasia or dysplasia. The c-myc expression was found to vary between different samples and within each cancer, and not all cancer cells expressed c-myc. These data indicate that c-myc oncogene plays it's role on reprogramming for growth control of cell populations particularly in multistage carcinogenesis and progression of lung cancer. These dynamic alterations of c-myc expression suggest that neoplastic transformation may occur conceivably at the dysplastic phase eventually resulting in carcinoma in situ. This means, in turn, squamous dysplasia is a putative precancerous lesion of the human lung.

Cytochromes P-450 in murine lung. An immunohistochemical study with monoclonal antibodies

We have used a panel of monoclonal antibodies (Mabs) and immunofluorescence to investigate the distribution of species of cytochrome P-450 inducible by 3-methylcholanthrene (3-MC) and phenobarbital (PB) in the lungs of "responsive" C57BL/6 and "nonresponsive" DBA/2 mice. A Mab (1-7-1) specific for an epitope common to rat cytochromes P-450c (P450IA1) and P-450d (P450IA2) detected the corresponding murine species (P1-450/P3-450) in cells of the alveolar septa, including type II cells, as well as endothelial cells lining blood vessels. Cytochrome P1-450 (Mabs 1-31-2, 1-36-1) is localized in type II cells of the alveolar septa but is not found in endothelial cells. Patterns of immunoreactivity with the 3-MC-specific Mabs indicate that alveolar septal cells possess P1-450 and P3-450, whereas endothelial cells of the vasculature are not the sites of P1-450, but rather of P3-450. Similar immunoreactivities for the 3-MC-defined P-450s are demonstrated in the lungs of C57BL/6 and DBA/2 mice. A Mab (2-66-3) which recognizes P-450b/P-450e (P450IIB1/P450IIB2) is reactive with P-450s localized in type II alveolar and bronchiolar epithelial cells, including nonciliated Clara cells. The epitope for cytochromes P-450b/P-450e is present in constitutive form within the lung and does not appear to be responsive to induction by PB. In contrast, epitopes for P1-450/P3-450 and P1-450 are not expressed constitutively but are only detected when induced by 3-MC.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunochemical characterization of cytochrome P-450 isozymes responsible for benzene oxidation in the rat liver

The contribution of cytochrome P-450 isozymes to benzene metabolism in liver microsomes from fed, fasted, pyrazole-, phenobarbital (PB)- and ethanol-treated rats and in respective isocaloric controls was investigated using monoclonal antibodies (mAbs). Clone 1-7-1 mAb did not inhibit benzene metabolism, whereas clone 2-66-3 inhibited only in PB-induced microsomes at a high concentration of benzene (6.26 mM), and clone 1-91-3 mAb inhibited benzene metabolism in all cases. The degree of inhibition was as follows: fed congruent to isocaloric control congruent to PB less than fasted less than pyrazole congruent to ethanol. The pattern of inhibition was similar with clone 1-91-3 for low (0.23 mM) and high concentrations of benzene, except in PB-induced microsomes. Western blot analysis showed that clone 1-7-1 mAb did not bind any liver microsomal protein in the region of cytochrome P-450s, whereas with clone 2-66-3 a clear-cut band was seen only in liver microsomes from PB-treated rats, with clone 1-98-1, a band was detected in microsomes from all treated groups, in the following order: PB = isocaloric control less than fed less than fasted less than pyrazole less than ethanol. These results indicate that (i) cytochromes P-450b,e and P-450j contribute to benzene metabolism in rat liver; (ii) the former has a low affinity to benzene and is induced by PB; and (iii) P-450j has a high affinity to benzene and is induced by 1-day fasting, pyrazole and ethanol, but decreased by PB treatment.

Measurement of cyclosporine in plasma from patients with various transplants: HPLC radioimmunoassay with a specific monoclonal antibody compared

This study compares cyclosporin A (CsA) concentrations in plasma from patients receiving various transplants, as measured by HPLC and RIA with a monoclonal antibody for CsA and an 125I-labeled ligand. The RIA was restandardized with in-house standards because it overestimated CsA by an average of 23%. The RIA was sensitive to 2 micrograms/L, the standard curve was linear from 20 to 500 micrograms of CsA per liter, analytical recovery was 98%, and CVs were less than 8% for intra- and interassay precision. RIA (y) vs HPLC (x) for 283 plasma samples from 145 patients gave a slope = 1.1256, r = 0.979. When the results were segregated according to transplant type, CsA in liver and heart recipients was overestimated by RIA as compared with HPLC: slope = 1.202, r = 0.973 and slope = 1.1477, r = 0.983, respectively. Adult and pediatric CsA values were acceptable when RIA and HPLC were compared: slope = 1.0755, r = 0.977 and slope = 1.0563, r = 0.980, respectively. For six samples (four heart, two liver recipients) where HPLC and RIA values demonstrated wide discrepancies, repeat HPLC and analysis of eluate fractions gave CsA concentrations nearer values by the initial HPLC assay. We conclude that this RIA cannot be substituted for HPLC in the case of heart and liver recipients. The need for each laboratory to standardize the RIA is obvious.

Measurement of cyclosporine in plasma from patients with various transplants: HPLC radioimmunoassay with a specific monoclonal antibody compared

This study compares cyclosporin A (CsA) concentrations in plasma from patients receiving various transplants, as measured by HPLC and RIA with a monoclonal antibody for CsA and an 125I-labeled ligand. The RIA was restandardized with in-house standards because it overestimated CsA by an average of 23%. The RIA was sensitive to 2 micrograms/L, the standard curve was linear from 20 to 500 micrograms of CsA per liter, analytical recovery was 98%, and CVs were less than 8% for intra- and interassay precision. RIA (y) vs HPLC (x) for 283 plasma samples from 145 patients gave a slope = 1.1256, r = 0.979. When the results were segregated according to transplant type, CsA in liver and heart recipients was overestimated by RIA as compared with HPLC: slope = 1.202, r = 0.973 and slope = 1.1477, r = 0.983, respectively. Adult and pediatric CsA values were acceptable when RIA and HPLC were compared: slope = 1.0755, r = 0.977 and slope = 1.0563, r = 0.980, respectively. For six samples (four heart, two liver recipients) where HPLC and RIA values demonstrated wide discrepancies, repeat HPLC and analysis of eluate fractions gave CsA concentrations nearer values by the initial HPLC assay. We conclude that this RIA cannot be substituted for HPLC in the case of heart and liver recipients. The need for each laboratory to standardize the RIA is obvious.

Monoclonal antibodies directed characterization of epidermal and hepatic cytochrome P-450 isozymes induced by skin application of therapeutic crude coal tar

A single application of crude coal tar (CCT) solution (USP) to the skin of neonatal rats was shown to induce epidermal and hepatic cytochrome P-450(P-450)-dependent monooxygenase activities. To further characterize the induction response, in this study we have utilized highly specific monoclonal antibodies (MoAb) 1-7-1, 2-66-3, and 1-98-1 directed against highly purified rat liver P-450s induced by 3-methyl-cholanthrene, phenobarbital and ethanol, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of hepatic microsomes prepared from CCT-treated animals showed a significant increase in the coomassie blue stainable proteins in the P-450 region; however, this was not evident in epidermal microsomes. Immunoblot analysis of epidermal and hepatic microsomes with MoAb 1-7-1 revealed strong immunoprecipitin bands in both tissues. MoAb 2-66-3 showed significant immunoreactivity only with hepatic microsomes. Interestingly, CCT treatment resulted in suppression of immunoreactivity with MoAb 1-98-1 in hepatic microsomes. MoAb 1-7-1 and 2-66-3 exhibited concentration-dependent inhibitory effects in aryl hydrocarbon hydroxylase and 7-ethoxycoumarin-O-deethylase activities induced by CCT application. MoAb 1-7-1 was substantially more effective in this respect. Epidermal and hepatic microsomes prepared from CCT-treated rats showed significantly greater metabolism of benzo(a)pyrene (BP). MoAb 1-7-1 and MoAb 2-66-3 inhibited BP metabolism in both the tissues. However, MoAb 1-7-1 was more inhibitory in this regard as compared to MoAb 2-66-3. These studies indicate that topical application of therapeutic CCT to the skin of neonatal rats results in induction of P-450 isozyme c in epidermis and isozymes b and c in liver, and that this induction is associated with the suppression of P-450 isozyme j in liver.

Isozyme-specific monoclonal antibody-directed assessment of induction of hepatic cytochrome p-450 by clotrimazole

Clotrimazole, an N-substituted imidazole widely used as an antifungal agent, has been shown to both inhibit and induce hepatic cytochrome P-450 and related monooxygenase activities. In this study the profile of hepatic cytochrome P-450 isozyme(s) induced by clotrimazole treatment of male Sprague-Dawley rats was investigated. Clotrimazole administration (100 mg/kg, daily for 4 days, ig) resulted in 86% induction of spectrally detectable cytochrome P-450 in hepatic microsomes. In these microsomes 7-ethoxycoumarin O-deethylase (126%), aminopyrine N-demethylase (176%), benzphetamine N-demethylase (117%), p-nitrophenol hydroxylase (89%), and 7-ethoxyresorufin O-deethylase (62%) activities were significantly induced, whereas aryl hydrocarbon hydroxylase activity remained unchanged. Characterization of cytochrome P-450 isozyme(s) in hepatic microsomes prepared from clotrimazole-treated animals was based on the immunoreactivity of these microsomes with highly specific monoclonal antibodies (MAbs) raised against 3-methylcholanthrene-specific P-450 (MAb 1-7-1), phenobarbital-specific P-450 (MAb 2-66-3), pregnenolone-16 alpha-carbonitrile-specific P-450 (MAb C2), and ethanol-inducible P-450 (MAb 1-98-1). Western blot analysis of hepatic microsomes prepared from clotrimazole-treated animals with MAb 2-66-3, MAb 1-98-1, and MAb C2 revealed strong immunoreactive bands, whereas moderate reactivity was observed with MAb 1-7-1. MAb 2-66-3 significantly inhibited 7-ethoxycoumarin O-deethylase activity 45%), whereas MAb 1-7-1 moderately inhibited 7-ethoxyresorufin O-deethylase activity (-30%) in clotrimazole-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidermal cytochrome P-450: immunochemical characterization of isoform induced by topical application of 3-methylcholanthrene to neonatal rat

To further define the capacity of skin to metabolize various drugs and carcinogens by the cytochrome P-450 (P-450)-dependent monooxygenase, we studied the profile of P-450 isoform(s) in neonatal rat epidermis after application of 3-methylcholanthrene (3-MC) to skin. Highly specific monoclonal antibodies (MAbs) 2-66-3 and 1-7-1 against purified rat liver P-450 isoforms b and c induced by phenobarbital and 3-MC, respectively, were used. After a single topical application of 3-MC to rats aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin-O-deethylase and 7-ethoxyresorufin-O-deethylase activities in epidermal microsomes were induced significantly. Radioimmunoassay of epidermal microsomes from untreated control animals with 35S-labeled MAb-2-66-3 showed significant binding whereas negligible binding with MAb 1-7-1 was observed. On the other hand significant binding was observed with 35S-labeled MAb 1-7-1 with epidermal microsomes prepared from 3-MC-treated animals. Histochemical staining of epidermis from control animals showed no immunoreactivity with either MAb 1-7-1 or MAb 2-66-3 whereas epidermis obtained from 3-MC-treated rats showed significant immunoreactivity with MAb 1-7-1. Western blot analysis of epidermal microsomes prepared from control animals showed no immunoreactivity with either MAb 1-7-1 or 2-66-3 whereas epidermal microsomes prepared from 3-MC-treated animals showed distinct immunoreactivity with MAb 1-7-1. MAb 2-66-3 inhibited AHH and 7-ethoxycoumarin-O-deethylase activity (40-50%) in microsomes prepared from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen hydroxylation catalysed by a cell line (SD1) that stably expresses rat hepatic cytochrome P-450 PB-4 (IIB1)

Androgen hydroxylation catalysed by Chinese hamster fibroblast SD1 cells, which stably express cytochrome P-450 form PB-4, the rat P450IIB1 gene product, was assessed and compared to that catalysed by purified cytochrome P-450 PB-4 isolated from rat liver. SD1 cell homogenates catalysed the NADPH-dependent hydroxylation of androstenedione and testosterone with a regioselectivity very similar to that purified by P-450 PB-4 (16 beta-hydroxylation/16 alpha-hydroxylation = 6.0-6.8 for androstenedione; 16 beta/16 alpha = 0.9 for testosterone). Homogenates prepared from the parental cell line V79, which does not express detectable levels of P-450 PB-4 or any other cytochrome P-450, exhibited no androgen 16 beta- or 16 alpha-hydroxylase activity. The hydroxylase activities catalysed by the SD1 cell homogenate were selectively and quantitatively inhibited (greater than 90%) by a monoclonal antibody to P-450 PB-4 at a level of antibody (40 pmol of antibody binding sites/mg of SD1 homogenate) that closely corresponds to the P-450 PB-4 content of the cells (48 pmol of PB-4/mg of SD1 homogenate). Fractionation of cell homogenates into cytosol and microsomes revealed that the P-450 PB-4-mediated activities are associated with the membrane fraction. Although the P-450 PB-4-specific content of the SD1 microsomes was 15% of that present in phenobarbital-induced rat liver microsomes, the P-450 PB-4-dependent androstenedione 16 beta-hydroxylase activity of the SD1 membrane fraction was only 2-3% of that present in the liver microsomes. This activity could be stimulated several-fold, however, by supplementation of SD1 microsomes with purified rat NADPH P-450 reductase. These studies establish that a single P-450 gene product (IIB1) can account for the hydroxylation of androgen substrates at multiple sites, and suggest that SD1 cells can be used to assess the catalytic specificity of P-450 PB-4 with other substrates as well.

Evidence for a PCN-P450 enzyme in chickens and comparison of its development with that of other phenobarbital-inducible forms

Of four monoclonal antibodies to purified rat liver cytochrome P450s, including those from 3-methylcholanthrene-, phenobarbital-, ethanol-, and pregnenolone-16-alpha-carbonitrile-treated rats, only the monoclonal antibody against pregnenolone-16-alpha-carbonitrile-inducible P450 immunodetected proteins in chicken liver microsomes after blotting from sodium dodecyl sulfate-polyacrylamide gels. This protein migrated identically with the pregnenolone-16-alpha-carbonitrile-inducible P450 detected in microsomes from dexamethasone-treated rats. It was most predominant in liver microsomes from chickens at 1 day posthatching, whereas much lower levels were observed in the embryo and at 36 days posthatch. Phenobarbital and dexamethasone were both effective inducers of this protein. The developmental profile and induction by phenobarbital and dexamethasone of several cytochrome P450-associated catalytic activities were compared with those of the immunodetected protein. Chicken liver microsomal erythromycin demethylase, a characteristic activity of rat pregnenolone-16-alpha-carbonitrile-inducible P450, was similar in developmental profile and induction to the immunodetected protein, with a high degree of augmentation at 1 day posthatch compared with that in the embryo and at 36 days posthatch; aldrin epoxidase, benzphetamine demethylase, ethylmorphine demethylase, and aminopyrine demethylase were more similar to each other in development and induction and were less well correlated with the immunodetected protein. This evidence suggests the presence in chicken liver of at least two types of P450, one a form related to the pregnenolone-16-alpha-carbonitrile-inducible P450 family. All of the catalytic activities were induced after pretreatment of chickens with phenobarbital but aldrin epoxidase was most effectively induced. Aldrin epoxidase was also detected in microsomes from untreated embryos as early as 7 days of incubation. Erythromycin demethylase was the only catalytic activity induced by dexamethasone. There was a trend of increased specific activity toward all the substances after hatching, indicating a more efficient P450 system, possibly due to a sharp increase in some isozymes, including the form from the pregnenolone-16-alpha-carbonitrile-inducible P450 family. This evidence for a pregnenolone-16-alpha-carbonitrile-inducible P450 in chickens agrees with sequence information that suggests the early evolution of this form and demonstrates the suitability of the chicken for studies of P450 evolution.

Bacillus subtilis subtilisin gene (aprE) is expressed from a sigma A (sigma 43) promoter in vitro and in vivo

In vitro studies demonstrated that the Bacillus subtilis subtilisin gene (aprE) could be transcribed by RNA polymerase holoenzyme reconstituted from core and sigma A factor obtained from vegetative cells. Upstream deletions (from -45) reduced the amount of transcription from the promoter. A deletion downstream of the promoter that overlapped a putative downstream minor promoter did not affect transcription from the sigma A promoter, which indicated that the putative downstream promoter is not utilized in vivo. S1 nuclease mapping studies showed that there was a low level of transcription from the subtilisin promoter during the growth phase and that the site of transcription initiation was the same during log and stationary phases. We conclude from these findings that there is only one promoter for the subtilisin gene and that it can be transcribed by the sigma A form of RNA polymerase in vitro.

Differential induction of fetal mouse liver and lung cytochromes P-450 by beta-naphthoflavone and 3-methylcholanthrene

Previous studies have shown that the incidences of liver and lung tumors in mice exposed transplacentally to 3-methyl-cholanthrene (MC) were significantly influenced by the sensitivity of both mothers and fetuses to induction of cytochrome(s) P-450 by polycyclic aromatic hydrocarbons. In order to delineate further the biochemical and molecular processes underlying the observed biological effects, the inductive effect of MC and beta-naphthoflavone (beta NF) on cytochrome P-450 was determined at the biochemical and molecular levels. C57BL/6 females were mated with DBA/2 males and treated i.p. on day 17 of gestation with olive oil alone, 150 mg/kg of beta NF or different doses of MC. At various times after injection the mothers were sacrificed and the fetuses removed for biochemical and molecular studies. MC caused maximal induction of aryl hydrocarbon hydroxylase (AHH) activity by 8 h in both the liver and lung. beta NF caused nearly maximal induction of AHH activity by 8 h in the lung but had little effect on liver AHH activity at this time. Maximal induction with beta NF occurred by 24 h in both organs. Addition of monoclonal antibody 1-7-1, specific for the MC-inducible forms of cytochrome P-450 (P-450IA1 and A2), to the incubation mixtures resulted in a 55-70% inhibition of AHH activity in both lung and liver assays, regardless of the inducing agent used, while having no effect on AHH activity from oil-treated mice. RNA blot analysis carried out in parallel with enzyme assays demonstrated that the levels of enzyme activity correlated very well with the levels of steady-state RNAs. MC caused maximal induction of P-450IA1 RNA levels 4 h after injection in both organs and a biphasic secondary increase was observed in the lung. Maximal levels of P-450IA1 RNA were seen at 12-16 h following injection of beta NF. However, the ratio of P-450IA1 RNAs present at 16 versus 2 h in the beta NF-treated liver appeared greater than that in the lung. P-450IA2 was also induced in fetal liver and lung, but at low levels relative to P-450IA1. The results indicate that the increase in functional AHH activity was primarily due to induction of cytochrome P-450IA1. The differences in induction kinetics observed for cytochromes P-450IA1 and A2 suggest that these enzymes exhibit both tissue- and inducer-dependent specificity.

Effects of a series of 4-alkyl analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine on the major inducible cytochrome P-450 isozymes of rat liver

Various 4-alkyl analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) cause mechanism-based inactivation of cytochrome P-450 (P-450) by destroying the heme prosthetic group. We have examined the isozyme selectivity of representative DDC analogues with respect to the major inducible P-450 isozymes of rat liver. Hepatic microsomes from untreated, phenobarbital (PB)-treated, beta-naphthoflavone (beta NF)-treated, and dexamethasone (DEX)-treated rats were incubated with a DDC analogue and NADPH and were subsequently analyzed for P-450 and heme content, P-450 isozyme immunoreactivity, and enzyme activity. Compared with the uninduced state, 4-isopropyl-DDC caused slightly less P-450 destruction following beta NF induction and much greater destruction following DEX pretreatment. Also, 4-hexyl-DDC was found to cause less P-450 destruction following PB or DEX pretreatment, compared with results obtained with untreated rats. These results suggest that DDC analogues possess different isozyme selectivity profiles. Monoclonal antibodies (MAbs) directed against the major inducible isozymes of P-450 were used to probe Western blots of microsomal protein following DDC analogue treatment. The formation of lower molecular mass (45-55 kDa) immunoreactive proteins in microsomes from beta NF-treated rats following DDC analogue treatment was revealed by two MAbs (1-31-2 and 1-36-1), suggesting that the apoprotein of the major beta NF-inducible isozyme, P-450c, is subject to alteration by DDC analogues. In microsomes from DEX-treated rats, DDC analogues caused the formation of higher molecular mass (80, 94, and 115 kDa) proteins showing immunoreactivity with MAb 2-13-1, directed against a major DEX-inducible isozyme belonging to the P-450p family. These immunochemical findings are supported by the demonstration that DDC analogues also caused mechanism-based inhibition of the catalytic activity of P-450c (7-ethoxyresorufin O-deethylase) and P-450p (erythromycin N-demethylase) but not that of the major PB-inducible isozyme, P-450b (7-pentoxyresorufin O-dealkylase). The combined immunochemical and enzymic studies indicate that rat liver P-450 c and p are targets for mechanism-based inactivation by DDC analogues.

Monoclonal antibody-directed characterization of rat hepatic P450 catalyzing the omega-1 and omega-2 hydroxylation of prostaglandins

Previous studies have demonstrated that methylcholanthrene (MC) treatment of rats increases 10-fold the omega-2 hydroxylation of prostaglandin E2 (PGE2) by liver microsomes (K. A. Holm, R. J. Engell, and D. Kupfer (1985) Arch. Biochem. Biophys. 237, 477-489). The current study identifies the cytochrome P450 form, which catalyzes a major portion of the omega-2 hydroxylation of prostaglandins in liver microsomes of MC-treated rats (MC-microsomes) and examines whether the same enzyme catalyzes this reaction in microsomes from untreated rats (control microsomes). Three monoclonal antibodies (MAbs), MC 1-7-1, 1-31-2, and 1-36-1, raised against the major liver P450 from MC-treated rats were used. MAb 1-7-1 binds P450(57K) and P450(56K) (P450c and P450d, respectively); MAb 1-31-2 binds primarily P450(57K); and 1-36-1 binds solely P450(57k). MAb 1-7-1 inhibited omega-2 and omega-1 PGE2 hydroxylations in MC-microsomes by 70 and 45%, respectively. By contrast, MAb 1-31-2 and 1-36-1 were not inhibitory. MAb 1-7-1 did not inhibit PGE2 omega-2 hydroxylation in control or in microsomes from phenobarbital-treated rats (PB-microsomes). Since MAb 1-7-1 binds to both P450c and P450d, and 1-31-2 and 1-36-1 bind to P450c but are not inhibitory, these findings did not permit the determination of whether in MC microsomes a single isozyme (P450c or P450d) or both isozymes catalyze the omega-2 hydroxylation. This question was partially resolved by the observation that immunoaffinity-isolated P450c, supplemented with purified NADPH-P450 reductase, catalyzes effectively the omega-2 hydroxylation and to a lesser extent the omega-1 hydroxylation. There was no activity in the absence of reductase. The P450 antibody complex exhibits characteristics similar to those of the omega-2 hydroxylating activity in intact MC-microsomes supported by H2O2, by demonstrating a much higher activity when H2O2 is used instead of reductase and NADPH. Furthermore, a reconstituted monooxygenase composed of rat liver reductase and P450c, purified by conventional means, hydroxylated PGE2 at the omega-2 and omega-1 sites at a ratio of 2.8, similar to that obtained with the P450-antibody complex. These findings demonstrate that a major portion of the omega-2 hydroxylation of PGs in MC-microsomes is catalyzed by P450c; however, the possibility that some omega-2 hydroxylating activity is due to P450d was not ruled out.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of rat hepatic N-nitrosodimethylamine demethylase by acetone is due to protein stabilization

The N-nitrosodimethylamine demethylase (P450I-IE1) is induced severalfold in liver by giving rats ethanol, acetone, pyrazole, and other related small molecular weight compounds. This induction is not the result of an increase in IIE1 mRNA, but could be due to either an increase in translation rate or a decrease in protein degradation. To determine the mechanism of induction, we measured IIE1 synthesis and degradation rates in untreated and acetone-treated rats. This was accomplished by immunopurification of radiolabeled IIE1 protein using a specific monoclonal antibody subsequent to in vivo labeling of total cellular protein with either NaH14CO3 or [3H]leucine. We found that in rats fed acetone, the rate of IIE1 synthesis was not changed; however, IIE1 degradation was markedly altered. In untreated rats, IIE1 protein was degraded via a biphasic pathway consisting of both a rapid and slow component with approximate half-lives of 7 and 37 h, respectively. However, in acetone-treated rats, only a monophasic curve with a half-life of 37 h was observed. The abolition of the rapid degradation component of the IIE1 turnover cycle indicates that induction of IIE1 by acetone is primarily due to specific stabilization of IIE1 protein. Since acetone is also metabolized by IIE1, we believe that this may be a substrate-induced enzyme stabilization.

Human liver cytochrome P-450 related to a rat acetone-inducible, nitrosamine-metabolizing cytochrome P-450: identification and isolation

A monoclonal antibody (MAb) to a rat acetone-inducible and nitrosamine-metabolizing form of microsomal cytochrome P-450, P-450ac, detected a related P-450 in human liver microsomes by both immunoblot and competitive radioimmunoassay. This MAb was also used to immunopurify microsomal cytochromes P-450 from both human liver and acetone-treated rats; these were electrophoretically homogeneous with apparent molecular weights of 56,200 and 53,000 daltons, respectively. The structures of the cytochromes P-450 were compared by peptide mapping and amino-terminal sequence analyses. They differed in their peptide maps but displayed amino-terminal sequence similarity in their first 19 residues. This report thus demonstrates the utility of MAbs to rat cytochromes P-450 for detection, identification and structural characterization of human P-450s.

Comparison of the formation of benzo[a]pyrene diolepoxide-DNA adducts in vitro by rat and human microsomes: evidence for the involvement of P-450IA1 and P-450IA2

The involvement of cytochrome P-450 isozymes in the activation of benzo[a]pyrene (BP) by human placental and liver microsomes was studied in vitro using monoclonal antibodies (Mab) toward the major 3-methylcholanthrene (MC)-inducible and phenobarbital-inductible rat liver P-450 isozymes (Mab 1-7-1 and Mab 2-66-3, respectively). Microsomes from human placenta and liver and rat liver were incubated with BP and DNA, and BP-diolepoxide-DNA (BPDE-DNA) adducts were measured by synchronous fluorescence spectrophotometry (SFS). The only BP metabolite giving the same fluorescence peak as chemically modified BPDE-DNA was BP-7,8-dihydrodiol. Five (smokers) out of 29 human placentas (smokers and nonsmokers), and five out of nine human livers were able to metabolically activate BP to BPDE-DNA adducts in this system. The Mab 1-7-1 totally inhibited the formation of BPDE-DNA adducts in placental microsomal incubations. Inhibition using rat or human liver microsomes was 50-60% and about 90%, respectively. The Mab 2-66-3 had no effect in any of the microsome types. Adduct formation was inhibited more strongly and at lower concentrations of Mab 1-7-1 compared with the inhibition of AHH activity. This study is a clear indication of the major role of P-450IA1 (P-450c) in human placenta and probably P-450IA2 (P-450d) in human liver in BP activation, while other isozymes also take part in the activation in rat liver. Furthermore, this clearly indicates that AHH activity and BP activation are not necessarily associated.

Monoclonal antibody directed detection of cytochrome P-450 (PCN) in human fetal liver

Monoclonal antibodies (MAbs) raised to rat liver cytochrome P-450s induced by phenobarbital, 3-methylcholanthrene, and pregnenolone-16 alpha-carbonitrile were used to detect these epitope specific P-450s in human abortion fetuses 14-24 weeks of age. This was performed using a Western blot technique. In parallel, ECOD was determined in the same tissue specimens. Of seven different MAbs used MAb PCN 2-13-1/C2 was the only one that immunodetected a cytochrome P-450 band with Western blot analyses of human fetal liver microsomes. This band was consistently detected in all fetal liver specimens studied although the intensity varied among samples. No bands were detected in microsomal preparations from adrenal and renal tissues obtained from the same fetuses. The human adult liver microsomal specimens also contained a MAb PCN 2-13-1/C2 identified cytochrome P-450 band. ECOD activity was detected in all but one of the human fetal livers and varied between 0.22 and 47.5 pmol min-1 mg protein-1, as compared to 113 to 489 pmol min-1 mg protein-1 in human adult livers. In all of the fetuses except one the adrenal ECOD activity (0.63-37.0 pmol min-1 mg protein-1) exceeded that in the liver. The renal ECOD activities were, however, low. The hepatic and adrenal ECOD activities correlated with each other (r = 0.95). Although the ECOD activity is a function of several different P-450s there was also a correlation (r = 0.78) between the ECOD activity and the MAb immunodetected protein band intensity in Western blots of human fetal liver microsomes. The presence of a MAb PCN 2-13-1/C2 identified band in fetal liver microsomes may be indicative of a steroid-dependent effect in fetal life.

Pyrazole is different from acetone and ethanol as an inducer of the polysubstrate monooxygenase system in mice: evidence that pyrazole-inducible P450Coh is distinct from acetone-inducible P450ac

The induction of liver microsomal monooxygenase activities elicited by pyrazole, ethanol, and acetone, all shown to be inducers of rat P450j and rabbit P450LM3a, has been compared in inbred strains of DBA/2N, AKR/J, and Balb/c mouse. Pyrazole strongly increases coumarin 7-hydroxylase (COH) activity in DBA/2N but much less in other strains. The effect of pyrazole on aniline p-hydroxylase and ethanol oxidase activities is also strain dependent: an increase was seen only in the DBA/2N strain. Ethanol and acetone were unable to induce COH, whereas aniline p-hydroxylase and ethanol oxidase were elevated about 1.4- to 3.3-fold in all strains. No strain difference could be detected in aniline p-hydroxylase or ethanol oxidase inducibility. There was a strong correlation between aniline p-hydroxylase and ethanol oxidase activities in every strain, whereas no positive correlation could be found between COH and aniline p-hydroxylase activities. Immunoinhibition experiments showed that a polyclonal antibody against purified pyrazole-inducible COH (P450Coh) blocked about 90% of COH activity, but only about 10% of aniline p-hydroxylase or ethanol oxidase in mouse liver microsomes. Monoclonal antibody 1-91-3 (raised against rat acetone-inducible P450ac) did not inhibit COH, whereas aniline p-hydroxylase was blocked 46-76% and ethanol oxidase 25-70%, depending on the source of microsomes. In immunoblots, anti-P450Coh recognized only its own antigen but not the P450ac, whereas monoclonal antibody 1-98-1 against P450ac detected P450ac and a corresponding form in the D2 mouse liver, but not the P450Coh. The purified P450ac and P450Coh had molecular masses of 52 and 50 kDa, respectively, on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These antigens were expressed differentially in response to pyrazole, ethanol, and acetone: P450Coh was increased only after pyrazole treatment, but 1-98-1-detectable protein was elevated in D2 mouse liver microsomes by ethanol and acetone, but not by pyrazole. We conclude that mouse P450Coh and rat P450ac are not corresponding forms of the same isozyme, and that a P450ac-like protein, responsible for most of aniline p-hydroxylation and ethanol oxidation, is present in the D2 mouse liver. These two P450 isozymes are also dissimilarly expressed in the mouse liver in response to inducer administration.

Distribution and induction sites of phenobarbital- and 3-methylcholanthrene-inducible cytochromes P-450 in murine liver: immunohistochemical localization with monoclonal antibodies

Monoclonal antibodies specific for cytochromes P-450 induced by 3-methylcholanthrene (Mab 1-7-1) and phenobarbital (Mab 2-66-3) have been used in an unlabeled peroxidase-antiperoxidase immunohistochemical procedure to investigate the intralobular distribution and induction sites of the hemoproteins within the livers of CD-1, C57BL/6, and DBA/2 mice. 3-Methylcholanthrene-specific cytochromes P-450 were localized predominantly in centrilobular hepatocytes of control mice from all strains and were present at higher levels in CD-1 and C57BL/6 mice than in DBA/2 mice. Treatment with either 3-methylcholanthrene or beta-naphthoflavone produced striking increases of 3-methylcholanthrene-specific cytochromes P-450 in hepatocytes from all regions of the hepatic lobule in CD-1 and C57BL/6 mice, but not in DBA/2 mice. Phenobarbital-specific cytochromes P-450 were localized in hepatocytes throughout all segments of the lobule in control mice, with slightly greater hemoprotein content in centrilobular hepatocytes. Treatment with phenobarbital resulted in enhancement of cytochrome P-450 that was visualized in hepatocytes in all regions of the lobule. Strain-related differences were not observed for phenobarbital-specific cytochromes P-450. These results demonstrate that constitutive levels of 3-methylcholanthrene- and phenobarbital-specific cytochromes P-450 are localized predominantly in centrilobular hepatocytes of murine livers, and induction of the hemoproteins is manifested to the greatest extent in periportal hepatocytes, resulting in a more uniform distribution throughout the hepatic lobule.

Oncogene expression detected by in situ hybridization in human primary lung cancer

By means of in situ hybridization using biotinylated oncogene probes and the immunohistochemical reaction of avidin-biotin complex-alkaline phosphatase with substrate, we investigated expression of c-myc oncogene in the formalin-fixed, paraffin-embedded tissue sections from seven patients with squamous cell carcinoma (six cases) and small cell carcinoma (one case) of primary lung origin. The expression of c-myc oncogene was greatly enhanced in all cases studied, with individual and cell-to-cell variation. In contrast, all of the specimens incubated with deoxyribonuclease after the standard pretreatment with ribonuclease T1 were negative for the expression of c-myc oncogene. The in situ hybridization permits estimation of a heterogeneous amplification of c-myc oncogene that may be related to secondary alterations occurring during the progression of the malignant lung tumors.

Mouse hepatic cytochrome P-450 isozyme induction by 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, pyrazole, and phenobarbital

The effects of 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) and pyrazole on mouse hepatic cytochrome P-450 isozyme expression were compared to the P-450 induction pattern elicited by phenobarbital. TCPOBOP and PB administration caused a similar induction profile by increasing microsomal protein and cytochrome P-450 content and the catalytic activities of several monooxygenases in DBA/2N and AKR/J mice. There were, however, several quantitative and some qualitative differences in the induction profile caused by phenobarbital and TCPOBOP. A few strain-related differences were also observed. Immunoblot analysis with polyclonal anti-coumarin hydroxylase (P-450Coh) antibody and epitope-specific monoclonal antibodies 1-7-1 and 2-66-3 showed that both phenobarbital and TCPOBOP increase the amount of P450IIB and P-450Coh. TCPOBOP caused a more pronounced increase in the amount of P-450IIB than phenobarbital, and TCPOBOP also caused an increase in the amount of P-450IA2. These data suggest that in the mouse, TCPOBOP increases mainly the expression of P-450 isozymes responsive to phenobarbital. The effects of pyrazole differed greatly from those caused by TCPOBOP and phenobarbital. In the DBA/2N mice, pyrazole increased coumarin 7-hydroxylation 9.4-fold, whereas in the AKR/J mice the activity was induced only to a level equivalent to the DBA/2N basal level. In immunoblot experiments with anti-P-450Coh antibody, the amount of P-450Coh was considerably higher in DBA/2N mice treated with phenobarbital, TCPOBOP, or pyrazole in comparison with the AKR/J mice, indicating a strain specificity in the inducibility of coumarin 7-hydroxylase by pyrazole.