Altered regulation of the cytochrome P4501A1 gene: novel inducer-independent gene expression in pulmonary carcinoma cell lines

NOX5-L can stimulate proliferation and apoptosis depending on its levels and cellular context, determining cancer cell susceptibility to cisplatin

The NADPH oxidase, NOX5, is known to stimulate cell proliferation in some cancers by generating reactive oxygen species (ROS). We show here that the long form of NOX5 (NOX5-L) also promotes cell death, and thus determines the balance of proliferation and death, in skin, breast and lung cancer cells. Moderate expression of NOX5-L induced cell proliferation accompanied by AKT and ERK phosphorylation, whereas an increase in NOX5-L above a certain threshold promoted cancer cell death accompanied by caspase-3 activation. Notably, cisplatin treatment increased NOX5-L levels through CREB activation and enhanced NOX5-L activity through augmentation of Ca²⁺ release and c-Abl expression, ultimately triggering ROS-mediated cancer cell death—a distinct pathway absent in normal cells. These results indicate that NOX5-L determines cellular responses in a concentration- and context-dependent manner.

The human lung adenocarcinoma cell line EKVX produces an infectious xenotropic murine leukemia virus

The cell lines of the NCI-60 panel represent different cancer types and have been widely utilized for drug screening and molecular target identification. Screening these cell lines for envelope proteins or gene sequences related to xenotropic murine leukemia viruses (X-MLVs) revealed that one cell line, EKVX, was a candidate for production of an infectious gammaretrovirus. The presence of a retrovirus infectious to human cells was confirmed by the cell-free transmission of infection to the human prostate cancer cell line LNCaP. Amplification and sequencing of additional proviral sequences from EKVX confirmed a high degree of similarity to X-MLV. The cell line EKVX was established following passage of the original tumor cells through nude mice, providing a possible source of the X-MLV found in the EKVX cells.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

Expression and regulation of xenobiotic-metabolizing cytochrome P450 (CYP) enzymes in human lung

Pathogenesis of lung diseases, such as lung cancer and chronic obstructive pulmonary disease, is tightly linked to exposure to environmental chemicals, most notably tobacco smoke. Many of the compounds associated with these diseases require an enzymatic activation to exert their deleterious effects on pulmonary cells. These activation reactions are mostly catalyzed by cytochrome P450 (CYP) enzymes. Interindividual differences in the in situ activation and inactivation of chemical toxicants may contribute to the risk of developing lung diseases associated with these compounds. This review summarizes in detail the expression of individual CYP forms in human pulmonary tissue and gives a view on the significance of the pulmonary expression of CYP enzymes. The localization of individual CYP enzymes in various cell types of human lung and the emerging field of regulation of human pulmonary CYP enzymes are discussed. At least CYP1A1 (in smokers), CYP1B1, CYP2B6, CYP2E1, CYP2J2, and CYP3A5 proteins are expressed in human lung, and also other CYP forms are likely to be expressed. Xenobiotic-metabolizing CYP enzymes are mostly expressed in bronchial and bronchiolar epithelium, Clara cells, type II pneumocytes, and alveolar macrophages in human lung, although individual CYP forms have different patterns of localization in pulmonary tissues. Problems in animal to human lung toxicity extrapolation and several specific aspects requiring more detailed assessment are identified.

Cancer chemopreventive activity of resveratrol

Cancer chemopreventive agents are designed to reduce the incidence of tumorigenesis by intervening at one or more stages of carcinogenesis. Recently, resveratrol, a natural product found in the diet of humans, has been shown to function as a cancer chemopreventive agent. Resveratrol was first shown to act as an antioxidant and antimutagenic agent, thus acting as an anti-initiation agent. Further evidence indicated that resveratrol selectively suppresses the transcriptional activation of cytochrome P-450 1A1 and inhibits the formation of carcinogen-induced preneoplastic lesions in a mouse mammary organ culture model. Resveratrol also inhibits the formation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted mouse skin tumors in the two-stage model. The enzymatic activities of COX-1 and -2 are inhibited by resveratrol in cell-free models, and COX-2 mRNA and TPA-induced activation of protein kinase C and AP-1-mediated gene expression are suppressed by resveratrol in mammary epithelial cells. In addition, resveratrol strongly inhibits nitric oxide generation and inducible nitric oxide synthase protein expression. NF kappa B is strongly linked to inflammatory and immune responses and is associated with oncogenesis in certain models of cancer, and resveratrol suppresses the induction of this transcription factor by a number of agents. The mechanism may involve decreasing the phosphorylation and degradation of I kappa B alpha. At the cellular level, resveratrol also induces apoptosis, cell cycle delay or a block in the G(1) --> S transition phase in a number of cell lines. Thus, resveratrol holds great promise for future development as a chemopreventive agent that may be useful for several disorders. Preclinical toxicity studies are underway that should be followed by human clinical trials.

Induction and regulation of xenobiotic-metabolizing cytochrome P450s in the human A549 lung adenocarcinoma cell line

Several cytochrome P450 (CYP) enzymes are expressed in the human lung, where they participate in metabolic inactivation and activation of numerous exogenous and endogenous compounds. In this study, the expression pattern of all known xenobiotic-metabolizing CYP genes was characterized in the human alveolar type II cell-derived A549 adenocarcinoma cell line using qualitative reverse transcriptase/polymerase chain reaction (RT-PCR). In addition, the mechanisms of induction by chemicals of members in the CYP1 and CYP3A subfamilies were assessed by quantitative RT-PCR. The expression of messenger RNAs (mRNAs) of CYPs 1A1, 1B1, 2B6, 2C, 2E1, 3A5, and 3A7 was detected in the A549 cells. The amounts of mRNAs of CYPs 1A2, 2A6, 2A7, 2A13, 2F1, 3A4, and 4B1 were below the limit of detection. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CYP1A1 and CYP1B1 mRNAs 56-fold and 2.5-fold, respectively. CYP3A5 was induced 8-fold by dexamethasone and 11-fold by phenobarbital. CYP3A4 was not induced by any of the typical CYP3A4 inducers used. The tyrosine kinase inhibitor genistein and the protein kinase C inhibitor staurosporine blocked TCDD-elicited induction of CYP1A1, but they did not affect CYP1B1 induction. Protein phosphatase inhibitors okadaic acid and calyculin A enhanced TCDD-induction of CYP1B1 slightly, but had negligible effects on CYP1A1 induction. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in human pulmonary epithelial cells and give the first indication of the induction of CYP3A5 by glucocorticoids in human lung cells. These results establish that having retained several characteristics of human lung epithelial cell CYP expression, the A549 lung cell line is a valuable model for mechanistic studies on induction of the pulmonary CYP system.

Induction of cytochrome P-450 1A1 by omeprazole in human HepG2 cells is protein tyrosine kinase-dependent and is not inhibited by alpha-naphthoflavone

Benzimidazole compounds, such as omeprazole and thiabendazole, are a different type of CYP1A1 inducer from Ah receptor-ligands, such as TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) and 3-methylcholanthrene. In HepG2 cells, the commonly used tyrosine kinase inhibitors, herbimycin-A and a series of tyrphostins, inhibited the induction of CYP1A1 produced by treatment with TCDD. Genistein, another type of tyrosine kinase inhibitor, inhibited the induction of CYP1A1 whether it was produced by omeprazole or TCDD; however, this inhibition was caused by a dual effect of genistein, that is an anti-tyrosine kinase and an anti-topoisomerase I effect. An antagonist of Ah receptor, alpha-naphthoflavone (0.1-10 microM), and 3'-methoxy-4'-aminoflavone (1 microM), did not inhibit the induction of CYP1A1 produced in HepG2 cells by omeprazole, but both of them did inhibit that produced by TCDD. In one of a number of human lung tumor cell lines, S6T, the inducibility of CYP1A1 was high by TCDD, whereas the inducibility by omeprazole was low. Thus, omeprazole appears to induce CYP1A1 by initiating a protein tyrosine kinase-mediated signal transduction pathway, a different pathway from that inhibited by TCDD.

Human liver S-9 metabolic activation: proficiency in cytogenetic assays and comparison with phenobarbital/beta-naphthoflavone or aroclor 1254 induced rat S-9

Induced rat liver S-9 is routinely used for metabolic activation in cytogenetic assays. When a compound gives a positive test result only with rat S-9, the significance for humans should be assessed. To evaluate the use of human S-9, we used sister-chromatid exchanges (SCEs) and chromosome aberrations (Abs) in Chinese hamster ovary cells to test five pro-mutagens, each preferentially activated by a different family of P-450: benzo(a)pyrene (BP), dimethylnitrosamine (DMN), diethylnitrosamine (DEN), aflatoxin B1 (AFB), and 2-acetylaminofluorene (2-AAF). We tested two human S-9 preparations, one from a single liver and a second pooled from two livers known to have good activity for several P-450s. Concentrations and ratios of NADP and isocitrate were adjusted to optimize NADPH generation by the S-9. Abs were scored 20 hr, and SCEs 29-45 hr, after the beginning of a 3 hr treatment. P-450 enzyme activities were generally higher in rat than human S-9. With the single-liver human S-9, increase in SCEs were seen with all chemicals; with both human S-9s, increases in Abs were seen with all chemicals except BP. (The level of P-450 1A1, required for BP activation, is very low in human liver.) Compared with rat S-9, generally higher concentrations of human S-9 and of promutagens were required to see positive results. However, human S-9 effectively activated 2-AAF, whereas neither of the two types of rat S-9 produced Abs with 2-AAF. We also compared rat S-9s induced with Aroclor 1254 or phenobarbital/ beta-naphthoflavone (PB/beta NF). Although there were some differences in P-450 enzyme activities, these did not translate into differences in Abs induction. At low doses of AFB and of BP, PB/beta NF induced S-9 appeared more effective than Aroclor 1254 induced S-9.

Partial characterization of the human CYP1A1 negatively acting transcription factor and mutational analysis of its cognate DNA recognition sequence

Previous studies in our laboratory identified a negative regulatory domain in the 5'-flanking region of the human CYP1A1 gene containing two negative regulatory elements (NRE). Characterization of one of these elements revealed three nuclear protein binding regions: a 21-bp palindrome with a point of symmetry at -784 and two guanine- and cytosine-rich elements that flank the palindrome. Functional studies suggested the palindrome is critical for transcriptional repression, whereas the guanine- and cytosine-rich sequences play a secondary role. In this study, the interaction between nuclear proteins and the CYP1A1 NRE was further defined. Electrophoretic mobility shift assays (EMSA) indicated that the NRE -784 palindrome alone, but not the guanine- and cytosine-rich sequences minus the palindrome, was capable of specific nuclear protein binding. Competitive cotransfection experiments confirmed this observation in intact cells. Specific residues important for DNA-protein interactions were identified by site-directed mutagenesis and competitive EMSA. The loss of specific protein binding was also correlated with the loss of negative regulatory activity in a transient-expression assay. Finally, competitive EMSA was performed with consensus oligonucleotides for known transcription factors. An NF-Y consensus sequence efficiently competed with the NRE probe for specific nuclear protein binding. EMSA supershift analyses indicate that a protein immunologically related to NF-YB is part of the specific nuclear protein complex binding the human CYP1A1 NRE. These studies have refined our understanding of the sequences critical for the transcriptional repression of human CYP1A1. To our knowledge, this is also the first report implicating a member of the NF-Y transcription factor family in negative gene regulation.

Initial characterization of the major mouse cytochrome P450 enzymes involved in the reductive metabolism of the hypoxic cytotoxin 3-amino-1,2,4-benzotriazine-1,4-di-N-oxide (tirapazamine, SR 4233, WIN 59075)

The benzotriazine di-N-oxide SR 4233 (tirapazamine, WIN 59075) is currently in phase I clinical trials as the lead compound in a series of novel and highly selective antitumour hypoxic cytotoxins. Reductive bioactivation is thought to proceed via a one-electron reduced, oxidizing nitroxide radical and also forms the inactive single N-oxide SR 4317 via radical disproportionation or a second one-electron reduction. In mouse liver microsomes reductive metabolism is catalysed predominantly by cytochrome P450 (70%) and cytochrome P450 reductase (30%). The aim of the present study was to examine which cytochrome P450 isozymes may be involved. Reduction of SR 4233 to SR 4317 was monitored by HPLC analysis. Metabolism by microsomes from both control and dexamethasone-induced BALB/c male mice was 70% inhibited by carbon monoxide. The cytochrome P450 inhibitor SKF 525A, following aerobic preincubation, also inhibited SR 4233 reduction by 58%. Reduction was induced 2-3-fold by dexamethasone and was not accountable by increases in cytochrome P450 reductase or DT-diaphorase. The induction data and the greater degree of inhibition of SR 4233 reduction by metyrapone compared to alpha-naphthoflavone suggested a possible involvement of Cyp2b, Cyp2c and Cyp3a cytochrome P450 subfamilies. Both Cyp3a (7.4-fold) and Cyp2b (1.8-fold) type enzymes were shown by western immunoblot analysis to be induced by dexamethasone, the latter correlating more closely with increased SR 4233 reductase activity and also with the 2-fold induction of benzphetamine N-demethylase, a Cyp2b-type enzyme. No inhibition of SR 4233 reduction was seen with erythromycin or cyclosporin A which act as substrates/inhibitors for Cyp3a-type enzymes, but inhibition was seen with p-nitrophenol and tolbutamide which are substrates for Cyp2el- and Cyp2c-type enzymes, respectively (11% and 25% inhibition in induced microsomes). SR 4233 itself inhibited benzphetamine N-demethylase, which is catalysed by Cyp2b-type enzymes but not erythromycin N-demethylase which is catalysed by Cyp3a-type isoforms. Immunoinhibition studies with epitope specific monoclonal antibodies were consistent with the major involvement of phenobarbitone- and steroid-inducible products of the Cyp2b and Cyp2c subfamilies. These forms contributed at least 53% and 26%, respectively, of the cytochrome P450-associated SR 4233 reductase activity in the induced microsomes. The findings support our earlier conclusion that cytochrome P450 is the major SR 4233 reductase in mouse liver and provides leads as to the possible involvement of specific isoforms in human tumours and normal tissues.

Validation of a novel molecular orbital approach (COMPACT) for the prospective safety evaluation of chemicals, by comparison with rodent carcinogenicity and Salmonella mutagenicity data evaluated by the U.S. NCI/NTP

The molecular dimensions and electronic structures of 100 chemicals of structural diversity have been determined from molecular orbital calculations and molecular mechanics. From these parameters of molecular structure, those chemicals that are likely substrates of cytochromes P4501 and P4502E have been identified by the computer-optimized molecular parametric analysis of chemical toxicity (COMPACT) programme, and their potential toxicity, mutagenicity and carcinogenicity evaluated. The degree of correlation between COMPACT prediction of toxicity and rodent two species life-span carcinogenicity data is estimated to be 92%, and between COMPACT and Salmonella mutagenicity (Ames test) data is 64%. Anomalous rodent carcinogens are rationalized on the basis of biochemical mechanisms of metabolism, genotoxicity and carcinogenicity. Correlation of the Ames test data with rodent carcinogenicity data was 64%, but correlation of COMPACT plus Ames data versus rodent carcinogenicity data provided the highest correlation of 94%.

Cytochrome P-450 induction in human lung tumor-derived cell lines. Characterisation and effects of inflammatory mediators

Cytochrome P-450 species (P-450) comprise a polymorphic multigene family of heme-containing enzymes which are essential to the phase-I metabolism of xenobiotics. Induction of P-450 species by drugs and carcinogens has been extensively studied; endogenous regulation of P-450 also occurs during normal development and disease. The aim of this project was to study the in-vitro induction of P-450 and its modulation by inflammatory mediators in the human lung tumor-derived cell lines NCI H322 and NCI H358. The cell lines expressed detectable levels of 7-ethoxyresorufin O-deethylase which could be induced by benzanthracene. After benzanthracene treatment, a protein tentatively identified as isozyme CYP1A1 was detected by Western-blot analysis and a concommitant increase in CYP1A mRNA expression was observed. Optimal induction was observed at a benzanthracene concentration of 5 micrograms/ml with cells grown in RPMI medium containing 10% fetal calf serum. The effects of endotoxin, dexamethasone and five recombinant DNA-derived cytokines, interleukin-1 beta, tumor necrosis factor, and interferons alpha, beta and gamma, on constitutive and benzanthracene-induced ethoxyresorufin O-deethylase activity were examined in NCI H322 cells. Of all the lymphokines studied, only interferon gamma had any marked effect. Administration of this lymphokine strongly suppressed ethoxyresorufin O-deethylase activity in both control and benzanthracene-treated cells.

Molecular markers for the diagnosis and prognosis of lung cancer

Molecular probes for lung cancer have greatly increased the understanding of the biology of this disease and the preneoplastic changes that precede it. They have confirmed and extended the clinical, pathologic, and biologic reasons for the primary division of lung cancers into small cell and non-small cell lung cancer types. Many molecular changes are present in lung cancers and involve dominant oncogenes and recessive growth regulatory genes. Clinical application of these markers will aid diagnosis, classification, and clinical management.

Differences in 2,3,7,8-tetrachlorodibenzo-p-dioxin-inducible CYP1A1 expression in human breast carcinoma cell lines involve altered trans-acting factors

Differences in expression of the CYP1A1 gene have previously been observed in human breast carcinoma cell lines exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using an expression vector containing the functional 5'-regulatory region of human CYP1A1 (up to -1140) fused to the reporter gene CAT (for chloramphenicol acetyltransferase), the breast carcinoma cell lines, MCF-7, T47-D and ZR-75-1, classified as highly responsive to TCDD, were highly responsive to TCDD in the chloramphenicol acetyltransferase assay as well. Gel mobility shift assays have shown that these cell lines express a nuclear protein that binds the aryl hydrocarbon (Ah) receptor responsive element. The low or non-responsive cell lines, AL-1, BT-20 and CAMA-1, were low or non-responsive to TCDD in the chloramphenicol acetyltransferase assay, suggesting that the low-responsive phenotype is caused by altered trans-acting factors. However, the mechanism appears to differ among the cell lines. Whereas no induction was observed in AL-1, a fivefold induction in activity was observed in BT-20 and CAMA-1. The TCDD concentration giving half-maximum induction differed greatly between CAMA-1 and BT-20. The gel mobility shift assay showed the presence of a protein that bound specifically to the Ah responsive element in the non-responsive cell line AL-1, as well as the low-responsive cell lines, BT-20 and CAMA-1. The high basal activity but low induction observed in CAMA-1 may be due to an Ah receptor constitutively bound to the Ah responsive element.

Constitutive and inducible expression of human cytochrome P450IA1 in yeast Saccharomyces cerevisiae: an alternative enzyme source for in vitro studies

A cDNA of human cytochrome P450IA1 was expressed in yeast Saccharomyces cerevisiae on a multicopy plasmid under the control of the constitutive GAPFL or the inducible PHO5 promoter. Microsomes of transformed yeast contained substantial amounts of the heterologous enzyme as determined by reduced CO-difference spectra (156-68 pmol/mg). Enzyme kinetics with 7-ethoxyresorufin as substrate resulted in a Km value of 92 nM and a Vmax value of 223 pmol/mg/min, which is comparable to data obtained with human liver microsomes. The antimycotic drug ketoconazole (Ki = 22nM) as well as the isozyme specific P450 inhibitor alpha-naphthoflavone (Ki = 1.2 nM) were shown to be strong inhibitors of human P450IA1. Taken together, these data show that heterologous P450 gene expression in yeast is a potent instrument for the study of enzyme specific parameters and might be used to answer further questions with regard to substrate specificity as well as drug interaction in a background with no interfering activities.