Chinese hamster V79 cell lines were constructed for stable expression of human cytochrome P450 1B1 (P450 1B1) in order to study its role in the metabolic activation of chemicals and toxicological consequences. The new V79 cell lines were applied to studies on DNA adduct formation of the polycyclic aromatic hydrocarbon (PAH) dibenzo[a,l]pyrene (DB[a,l]P). This compound has been found to be an environmental pollutant, and in rodent bioassays it is the most carcinogenic PAH yet discovered. Activation of DB[a,l]P in various metabolizing systems occurs via fjord region DB[a,l]P-11, 12-dihydrodiol 13,14-epoxides (DB[a,l]PDE): we found that DB[a,l]P is stereoselectively metabolized in human mammary carcinoma MCF-7 cells to the (-)-anti- and (+)-syn-DB[a,l]PDE which both bind extensively to cellular DNA. To follow up this study and to relate specific DNA adducts to activation by individual P450 isoforms, the newly established V79 cells stably expressing human P450 1B1 were compared with those expressing human P450 1A1. DNA adduct formation in both V79 cell lines differed distinctively after incubation with DB[a,l]P or its enantiomeric 11,12-dihydrodiols. Human P450 1A1 catalyzed the formation of DB[a,l]PDE-DNA adducts as well as several highly polar DNA adducts as yet unidentified. The proportion of these highly polar adducts to DB[a,l]PDE adducts was dependent upon both the concentration of DB[a,l]P and the time of exposure. In contrast, V79 cells stably expressing human P450 1B1 generated exclusively DB[a,l]PDE-DNA adducts. Differences in the total level of DNA binding were also observed. Exposure to 0.1 microM DB[a,l]P for 6 h caused a significantly higher level of DNA adducts in V79 cells stably expressing human P450 1B1 (370 pmol/mg of DNA) compared to those with human P450 1A1 (35 pmol/mg of DNA). A 4-fold higher extent of DNA binding was catalyzed by human P450 1B1 (506 pmol/mg of DNA) compared to human P450 1A1 (130 pmol/mg of DNA) 6 h after treatment with 0.05 microM (-)-(11R,12R)-dihydrodiol. In cells stably expressing human P450 1B1 the DNA adducts were derived exclusively from the (-)-anti-DB[a,l]PDE. These results indicate that human P450 1B1 and P450 1A1 differ in their regio- and stereochemical selectivity of activation of DB[a,l]P with P450 1B1 forming a higher proportion of the highly carcinogenic (-)-anti-(11R, 12S,13S,14R)-DB[a,l]PDE metabolite.

Previously, we identified a novel human cytochrome P450 cDNA that is inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and represents the first member of a new subfamily designated cytochrome P4501B1 (CYP1B1; Sutter, T. R., Tang, Y. M., Hayes, C. L., Wo, Y. P., Jabs, E. W., Li, X., Yin, H., Cody, C. W., and Greenlee, W.

Cytochrome P4501B1 (CYP1B1) is involved in the activation of many carcinogens and in the metabolism of steroid hormones, including 17beta-oestradiol (E2) and testosterone. We report a significant difference in the allele frequencies of two point mutations in the coding region of the CYP1B1 gene among Caucasian (n = 189), African-American (n = 52) and Chinese (Linxian) (n = 109) populations. A (C to G) transversion at position 1666 in exon 3, which results in an amino acid substitution of Leu432 to Val, was present in African-Americans with an allele frequency for Va1432 of 0.75, in Caucasians of 0.43, and in Chinese of 0.17. A (C to T) transition at position 1719 in exon 3, with no amino acid change (Asp449), appeared to be closely linked with the Val432 variant. Results using human lung microsomal preparations from individuals with the CYP1B1Val/Val and CYP1B1Leu/Leu genotypes indicate that Val432 variant may be a high activity allele and thus may contribute to the interindividual differences in CYP1B1 activity. Because CYP1B1 is involved in hormone and carcinogen metabolism, and given the disparate rates of prostate cancer among ethnic groups, we also evaluated the association of the CYP1B1 Leu432Val polymorphism with prostate cancer risk in a pilot case-control study. Among Caucasians, 34% of men with cancer (n = 50) were homozygous for the Val432 polymorphism, while only 12% of matched control subjects (n = 50) had this genotype. These preliminary data indicate that genetic polymorphisms in CYP1B1 might play an important role in human prostate carcinogenesis.

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Chinese contributions to the field of spine have a significant increase during the past 10 years, particularly from Mainland China. Hong Kong had the highest quality research output in terms of mean impact factor and mean citation per article.

We recently found single amino acid substitutions ((213)Arg/His and (223)Met/Val) in polymorphic human phenol-sulfating phenol sulfotransferase (SULT: cDNAs encoding ST1A3, P PST or HAST1/2) among Caucasians and African-Americans. In a Japanese population (n = 143), allele frequencies of (213)Arg and (213)His were 83.2 and 16. 8%, respectively, but the (223)Val allele was not found. (213)His homozygosity was reportedly associated with both very low (>7-fold) sulfating activities of p-nitrophenol (at 4 microM) and low thermostability in platelets. Sulfating-activity determinations using recombinant (213)Arg- and (213)His-forms (ST1A3*1 and ST1A3*2, respectively) did not, however, reveal appreciable deficiency in [(35)S]3'-phosphoadenosine 5'-phosphosulfate (PAPS)-dependent sulfation of p-nitrophenol (4 microM) by ST1A3*2 (7.5 vs. 10.2 nmol/min/nmol SULT for ST1A3). Kinetic parameters for p-nitrophenol for p-nitrophenol sulfation supported the slight decrease in sulfating activities at 4 microM (K(m), 0.82 vs. 1.75 microM; V(max), 13.2 vs. 13.1 nmol/min/nmol SULT, respectively, for ST1A3*1 and *2). p-Nitrophenyl sulfate-dependent 2-naphthol sulfation by ST1A3*2 was 69% of that by ST1A3*1 (p<0.05). However, ST1A3*2 was remarkably unstable at 45 and 37 degrees C as compared to ST1A3*1. The lower p-nitrophenol sulfating activity of ST1A3*2 may explain the lower platelet p-nitrophenol sulfation in ST1A3*2 homozygotes. Protein instability and ST1A3 gene regulation may be both involved in the polymorphism of p-nitrophenol sulfation in human tissues.