Publications

• Steroid hormone hydroxylase specificities of eleven cDNA-expressed human cytochrome P450s.

  Waxman D.J., Lapenson D.P., Aoyama T., Gelboin H.V., Gonzalez F.J., Korzekwa K.

  Steroid hydroxylation specificities were determined for 11 forms of human cytochrome P450, representing four gene families and eight subfamilies, that were synthesized in human hepatoma Hep G2 cells by means of cDNA-directed expression using vaccinia virus. Microsomes isolated from the P450-expres ... >> More

  Steroid hydroxylation specificities were determined for 11 forms of human cytochrome P450, representing four gene families and eight subfamilies, that were synthesized in human hepatoma Hep G2 cells by means of cDNA-directed expression using vaccinia virus. Microsomes isolated from the P450-expressing Hep G2 cells were isolated and then assayed for their regioselectivity of hydroxylation toward testosterone, androstenedione, and progesterone. Four of the eleven P450s exhibited high steroid hydroxylase activity (150-900 pmol hydroxysteroid/min/mg Hep G2 microsomal protein), one was moderately active (30-50 pmol/min/mg) and six were inactive. In contrast, 10 of the P450s effectively catalyzed O-deethylation of 7-ethoxycoumarin, a model drug substrate, while only one (P450 2A6) catalyzed significant coumarin 7-hydroxylation. Human P450 4B1, which is expressed in lung but not liver, catalyzed the 6 beta-hydroxylation of all three steroids at similar rates and with only minor formation of other hydroxylated products. Three members of human P450 family 3A, which are expressed in liver and other tissues, also catalyzed steroid 6 beta-hydroxylation as their major activity but, additionally, formed several minor products that include 2 beta-hydroxy and 15 beta-hydroxy derivatives in the case of testosterone. These patterns are similar to those exhibited by rat family 3A P450s. Although several rodent P450s belonging to subfamilies 2A, 2B, 2C, 2D are active steroid hydroxylases, four of five human P450s belonging to these subfamilies exhibited very low activity or were inactive, as were the human 1A and 2E P450s examined in the present study. These studies demonstrate that individual human cytochrome P450 enzymes can hydroxylate endogenous steroid hormones with a high degree of stereospecificity and regioselectivity, and that some, but not all of the human cytochromes exhibit metabolite profiles similar to their rodent counterparts. << Less

  Arch Biochem Biophys 290:160-166(1991) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Catalytic properties of polymorphic human cytochrome P450 1B1 variants.

  Shimada T., Watanabe J., Kawajiri K., Sutter T.R., Guengerich F.P., Gillam E.M.J., Inoue K.

  Four polymorphic human cytochrome P450 (CYP) 1B1 allelic variants, namely Arg48,Ala119,Leu432,Asn453, Arg48,Ser119,Leu432,Asn453, Arg48, Ala119,Val432,Asn-453 and Arg48,Ser119,Val432,Asn453, were expressed in Escherichia coli together with human NADPH-P450 reductase and the recombinant proteins (i ... >> More

  Four polymorphic human cytochrome P450 (CYP) 1B1 allelic variants, namely Arg48,Ala119,Leu432,Asn453, Arg48,Ser119,Leu432,Asn453, Arg48, Ala119,Val432,Asn-453 and Arg48,Ser119,Val432,Asn453, were expressed in Escherichia coli together with human NADPH-P450 reductase and the recombinant proteins (in bacterial membranes) were used to assess whether CYP1B1 polymorphisms affect catalytic activities towards a variety of P450 substrates, including diverse procarcinogens and steroid hormones. Activities for activation of 19 procarcinogens to DNA-damaging products by these four CYP1B1 variants in a Salmonella typhimurium NM2009 umu response system were found to be essentially similar, except that a Arg48, Ser119,Leu432,Asn453 variant was slightly more active (1.2-to 1.5-fold) than the other three CYP1B1 enzymes in catalyzing activation of (+)- and (-)-benzo[a]pyrene-7, 8-diols, 7,12-dimethylbenz[a]anthracene-3,4-diol, benzo[g]chrysene-11,12-diol, benzo[b]fluoranthene-9,10-diol, 2-amino-3,5-dimethylimidazo[4,5-f]quinoline, 2-amino-3-methylimidazo[4,5-f]quinoline and 2-aminofluorene. Kinetic analysis of 17beta-estradiol hydroxylation showed that V(max) values for 4-hydroxylation ranged between 0.9 and 1.5 nmol/min/nmol P450 for 4-hydroxylation and 0.3 and 0.6 nmol/min/nmol P450 for 2-hydroxylation in these CYP1B1 variants, with K(m) values ranging from 1 to 9 microM. Interestingly, the ratio of product formation of 4-hydroxyestradiol to 2-hydroxyestradiol was higher for the Val432 variants of CYP1B1 variants than the Leu432 variants of the enzyme. The same trend was noted in the ratio of estrone 4-hydroxylation to estrone 2-hydroxylation catalyzed by CYP1B1 variants. Mutation in the CYP1B1 genes also affected the K(m) and V(max) values in the 6beta-hydroxylation of testosterone and 6beta- and 16alpha-hydroxylation of progesterone. These results indicate that the polymorphisms in the human CYP1B1 gene cause some alterations in catalytic function towards procarcinogens and steroid hormones and thus may make some contribution to susceptibilities of individuals towards mammary and lung cancers in humans. << Less

  Carcinogenesis 20:1607-1613(1999) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Progesterone and testosterone hydroxylation by cytochromes P450 2C19, 2C9, and 3A4 in human liver microsomes.

  Yamazaki H., Shimada T.

  Roles of human cytochrome P450 (P450 or CYP) 2C9, 2C19, and 3A4 in the oxidation of progesterone and testosterone were studied in recombinant P450 enzymes and in human liver microsomes. In vitro inhibition experiments showed that progesterone and its 17alpha- and 21-hydroxylated metabolites and 11 ... >> More

  Roles of human cytochrome P450 (P450 or CYP) 2C9, 2C19, and 3A4 in the oxidation of progesterone and testosterone were studied in recombinant P450 enzymes and in human liver microsomes. In vitro inhibition experiments showed that progesterone and its 17alpha- and 21-hydroxylated metabolites and 11-deoxycortisol suppressed the CYP2C19-dependent R-warfarin 7-hydroxylation activities, with progesterone being the most active. These steroid chemicals also inhibited CYP2C9-dependent S-warfarin 7-hydroxylation activities though lesser extents seen with those in CYP2C19 enzyme. Progesterone was found to be a competitive inhibitor of CYP2C19 and CYP2C9 in human liver microsomes. Recombinant CYP2C19 catalyzed progesterone to form 21-hydroxyprogesterone as a major product and 16alpha- and 17alpha-hydroxyprogesterone as minor products. CYP2C9 also had progesterone 21-hydroxylation activities, although the activities were lower than those catalyzed by CYP2C19. Vmax/Km ratios for the progesterone 21-hydroxylation activity of CYP2C19 were determined to be 13- and 32-fold higher than those of CYP2C9 and 3A4, respectively. CYP3A4 oxidized progesterone to form 16alpha-, 6beta-, and 2beta-hydroxyprogesterone as major products and 21-hydroxyprogesterone as a minor product, but did not produce detectable levels of 17alpha-hydroxyprogesterone. Immunoinhibition experiments suggested that anti-CYP2C9 (which inhibits both CYP2C9 and CYP2C19 catalytic activities) suppressed the progesterone 21-hydroxylation activities catalyzed by liver microsomes of humans and monkeys and that anti-CYP2C11 inhibited the progesterone 21-hydroxylation activities catalyzed by liver microsomes of male rats. CYP2C19 was also found to oxidize testosterone at 17-position to form androstenedione. Androstenedione formation catalyzed by liver microsomes of humans and monkeys and of male rats was suppressed by anti-CYP2C9 and anti-CYP2C11, respectively. These results suggest that CYP2C19 plays important roles in the oxidation of progesterone and testosterone in human liver microsomes, although the physiological significance of these metabolic pathways remains unclear. CYP2C9 may have some, but lesser extent than those by CYP2C19, of the catalytic roles for the metabolism of progesterone and testosterone by human liver microsomes. << Less

  Arch Biochem Biophys 346:161-169(1997) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Cytochrome P-450 hPCN3, a novel cytochrome P-450 IIIA gene product that is differentially expressed in adult human liver. cDNA and deduced amino acid sequence and distinct specificities of cDNA-expressed hPCN1 and hPCN3 for the metabolism of steroid hormones and cyclosporine.

  Aoyama T., Yamano S., Waxman D.J., Lapenson D.P., Meyer U.A., Fischer V., Tyndale R., Inaba T., Kalow W., Gelboin H.V., Gonzalez F.J. , et al.

  Immunoblotting analysis of human liver microsome preparations revealed that human cytochrome P-450 PCN1 (hPCN1, Mr approximately 52,000) was expressed in each of 40 individual specimens examined. In about 10-20% of the livers, an immunologically related protein having a lower electrophoretic mobil ... >> More

  Immunoblotting analysis of human liver microsome preparations revealed that human cytochrome P-450 PCN1 (hPCN1, Mr approximately 52,000) was expressed in each of 40 individual specimens examined. In about 10-20% of the livers, an immunologically related protein having a lower electrophoretic mobility (Mr approximately 52,500) was also detected. A single liver was found that expressed only the lower mobility protein, designated hPCN3, and RNA isolated from this liver was used to construct a lambda gt11 library. The library was screened with an hPCN1 cDNA probe resulting in the isolation of a unique full-length cDNA that was sequenced and shown to encode hPCN3. The deduced amino acid sequence of this cDNA contained 502 residues, a calculated molecular mass of 57,115 daltons, and displayed 84% similarity with hPCN1. The deduced amino-terminal sequence of hPCN3 was identical to that of HFLa, a major cytochrome P-450 expressed in human fetal liver that is immunologically cross-reactive with several family III cytochrome P-450s. hPCN1 and hPCN3 cDNAs were expressed in Hep G2 cells using a vaccinia virus expression system and shown to encode active enzymes, both characterized by reduced CO-binding spectra with lambda max at 450 nm. Enzymatic analysis revealed that both cytochrome P-450s were similarly active in catalyzing oxidation of the calcium channel blocking drug nifedipine. Both enzymes also catalyzed 6 beta-hydroxylation of the steroid hormones testosterone, progesterone, and androstenedione, although hPCN1 exhibited several-fold higher expressed activity than hPCN3. Several minor oxidation products of these steroids (e.g. 15 beta-hydroxytestosterone), comprising up to approximately 20% of the total metabolites, were formed by hPCN1 but not hPCN3, indicating that hPCN3 is a more highly regiospecific monooxygenase catalyst with steroid substrates. Clear differences were also detected in their catalytic activities toward the immunosuppressive drug cyclosporine, with two hydroxylated metabolites (M1 and M17) and one demethylated metabolite (M21) formed by hPCN1 but only one metabolite (M1) formed by hPCN3. These studies establish that hPCN3 is a newly described cytochrome P-450 that is differentially expressed in the adult human population and that has overlapping substrate specificity compared to hPCN1 for metabolism of steroid and drug substrates. << Less

  J. Biol. Chem. 264:10388-10395(1989) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.