Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytochrome P450IIE1 (IIE1) is a microsomal xenobiotic-activating enzyme that is inducible not only by various chemical agents but also by fasting and diabetes. Using a rat model that mimics human obesity, we have found that hepatic IIE1 levels are also increased by this common clinical disorder. Liver microsomes from rats made obese by feeding with an energy-dense diet displayed elevated aggregate P450 content (+28%) and enhanced catalytic activities associated with IIE1, including low-Km N-nitrosodimethylamine demethylation (+66%), aniline hydroxylation (+52%), p-nitrophenol hydroxylation (+170%), and acetaminophen-cysteine conjugate formation (+28%). In contrast, obesity had no significant effect on cytochrome b5 content, P450 reductase activity, benzphetamine demethylation, or erythromycin demethylation, with the latter two reactions being linked with rat IIC11 and IIIA1, respectively. The enhancement of IIE1-dependent drug-metabolizing activities noted in liver microsomes from obese rats was paralleled by a similar increase (111%) in hepatic IIE1 protein content in these animals, as assessed on immunoblots developed with anti-hamster IIE1 IgG. Anti-IIE1-inhibitable rates of microsomal p-nitrophenol metabolism, a reaction highly correlated with IIE1 content (r = 0.88, p less than 0.01), were over 3-fold higher in obese rats than in nonobese controls, providing additional evidence for the obesity-related increase of hepatic IIE1. The induction of IIE1 by the pathophysiological condition of obesity may provide a biochemical basis for the increased incidence of occult liver disease and certain cancers noted in obese individuals.
Mol Pharmacol 1991 Mar
PMID:Induction of cytochrome P450IIE1 in the obese overfed rat. 200 76

Studies carried out in hypophysectomized adult rats have demonstrated that both thyroid hormone and GH can suppress hepatic expression of the steroid 6 beta-hydroxylase P450 2a (IIIA2). The present study further characterizes the influence of thyroid hormone on the expression of P450 2a and two other male-specific hepatic P450s, a steroid 2 alpha/16 alpha-hydroxylase, designated P450 2c (IIC11), and a steroid 15 alpha-hydroxylase, designated P450 RLM2 (IIA2). These studies were carried out in rats rendered hypothyroid by treatment with methimazole, which allows for the nonsurgical depletion of circulating T4, and in hypophysectomized rats. Hypothyroidism led to an increase in hepatic P450 2a (IIIA2) protein and mRNA in both male and female rats that was fully reversed by T4 replacement. In contrast, hypothyroidism decreased by 70-80% the expression of P450 2c (IIC11) activity and mRNA, but did not significantly alter the expression of P450 RLM2 (IIA2). The decrease in P450 2c (IIC11) was not reversed by T4 replacement, suggesting that it is a consequence of the loss of plasma GH pulses that occurs secondary to hypothyroidism. In agreement with these findings, T4 given to hypophysectomized rats partially suppressed the expression of P450 2a (IIIA2) mRNA, but not P450 2c (IIC11) or P450 RLM2 (IIA2) mRNA. A more complete suppression of P450 2a (IIIA2) mRNA as well as P450 2c (IIC11) mRNA was achieved when the hypophysectomized rats were treated with T3 at a supraphysiological, receptor-saturating dose. Although GH administered to intact male rats by continuous infusion fully suppressed all three male-specific P450 proteins and their mRNAs, the same treatment given to hypothyroid rats was only partially suppressive in the case of P450 2a (IIIA2) and P450 RLM2 (IIA2), unless combined with T4. In the case of P450 2c (IIC11), substantial suppression of the residual P450 present in hypothyroid rats was achieved by treatment with GH alone, despite persistent thyroid hormone deficiency. These studies demonstrate that while thyroid hormone is a negative regulator of P450 2a (IIIA2) expression and is required for the full suppression of that P450 and P450 RLM2 (IIA2) by the continuous plasma GH profiles associated with adult female rats, the suppression of P450 2c (IIC11) by continuous plasma GH is largely independent of the presence of thyroid hormone.
Mol Endocrinol 1991 Jan
PMID:Hepatic P450 expression in hypothyroid rats: differential responsiveness of male-specific P450 forms 2a (IIIA2), 2c (IIC11), and RLM2 (IIA2) to thyroid hormone. 201 88

The metabolism of testosterone (TEST), androstenedione (AD) and progesterone (PROG) was assessed in hepatic microsomal fractions from male sheep. Rates of total hydroxylation of each steroid were lower in sheep liver than in microsomes isolated from untreated male rat, guinea pig or human liver, 6 beta-Hydroxylation was the most important pathway of biotransformation of each of the three steroids (0.80, 0.89 and 0.43 nmol/min/mg protein for TEST, AD and PROG, respectively). Significant minor metabolites from TEST were the 2 beta-, 15 beta- and 15 alpha-alcohols (0.19, 0.22 and 0.17 nmol/min/mg microsomal protein, respectively). Apart from the 6 beta-hydroxysteroid, only the 21-hydroxy derivative was formed from PROG at a significant rate (0.27 nmol/min/mg protein). The 6 beta-alcohol was the only metabolite formed from AD at a rate greater than 0.1 nmol/min/mg protein. Antisera raised in rabbits to several rat hepatic microsomal P450s were assessed for their capacity to modulate sheep microsomal TEST hydroxylation. Anti-P450 IIIA isolated from phenobarbital-induced rat liver effectively inhibited TEST hydroxylation at the 2 beta-, 6 beta-, 15 alpha- and 15 beta-positions (by 31-56% when incubated with microsomes at a ratio of 5 mg IgG/mg protein). IgG raised against rat P450 IIC11 and IIB1 inhibited the formation of some of the minor hydroxysteroid metabolites but did not decrease the rate of TEST 6 beta-hydroxylation. Western immunoblot analysis confirmed the cross-reactivity of anti-rat P450 IIIA with an antigen in sheep hepatic microsomes; anti-IIC11 and anti-IIB1 exhibited only weak immunoreactivity with proteins in these fractions. Considered together, the present findings indicate that, as is the case in many mammalian species, 6 beta-hydroxylation is the principal steroid biotransformation pathway of male sheep liver. Evidence from immunoinhibition and Western immunoblot experiments strongly implicate the involvement of a P450 from the IIIA subfamily in ovine steroid 6 beta-hydroxylation.
J Steroid Biochem Mol Biol 1991 May
PMID:Microsomal cytochrome P450-dependent steroid metabolism in male sheep liver. Quantitative importance of 6 beta-hydroxylation and evidence for the involvement of a P450 from the IIIA subfamily in the pathway. 203 54

Genomic clones of a rat testosterone 6 beta-hydroxylase have been isolated and characterized as the first gene (P450/6 beta A) among P450IIIA subfamily. This gene spans about 25Kb and consists of 13 exons, which is the largest number of exons among cytochrome P-450 genes reported previously. The nucleotide sequence of the exon region showed high similarity to those of P450PCN2 and P450PCN1 cDNA (Gonzalez, F.J. et al. (1987) Mol. Cell. Biol. 2969-2974), but several replacements and deletions of nucleotide were found between the P450/6 beta A gene and both cDNAs, indicating the existence of multiple P450IIIA genes in rats.
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PMID:A gene structure of testosterone 6 beta-hydroxylase (P450IIIA). 204 44

Cytochrome P450 is known to cause carcinogen activation and correspondingly increased cancer risk in animal models. In order to determine whether P450 in the colon may be involved in cancer development in the human, the human colon cell line LS174T was examined for the presence of various cytochromes P450. Two isozymes of P450 were identified in the human cell line. Expression of P450IA1 or IA2 was increased by treatment of the cell line with benzanthracene; the induction was demonstrated by an increase in RNA hybridizing to a probe for P450IA1 and by ethoxyresorufin deethylation activity. Western analysis of microsomes isolated from human colon tissue also demonstrated the presence of P450IA1, as well as a form which cross-reacted to an antibody to human P450IIC9. Another isozyme, P450IIE1, was identified by polymerase chain reaction amplification of RNA from LS174T cells. These results underscore the presence of cytochromes P450 in colonic tissue and provide a basis for the involvement of isozyme-specific P450 mediated reactions in carcinogenesis of the colon.
Mol Cell Biochem 1991 Mar 27
PMID:Expression of two cytochromes P450 involved in carcinogen activation in a human colon cell line. 205

The mild nonclassic form of steroid 21-hydroxylase deficiency is one of the most common autosomal recessive disorders in humans, occurring in almost 1% of caucasians and about 3% of Ashkenazi Jews. Many patients with this disorder carry a Val-281----Leu missense mutation in the CYP21 gene. This and most other mutations causing 21-hydroxylase deficiency are normally present in the CYP21P pseudogene and have presumably been transferred to CYP21 by gene conversion. To identify other potential nonclassic alleles, we used recombinant vaccinia virus to express two mutant enzymes carrying the mutations Pro-30----Leu (normally present in CYP21P) and Ser-268----Thr (considered a normal polymorphism of CYP21). Whereas the activity of the protein carrying the Ser----Thr mutation was indeed indistinguishable from the wild type, the enzyme with the Pro----Leu substitution had 60% of wild-type activity for 17-hydroxyprogesterone and about 30% of normal activity for progesterone when assayed in intact cells. When kinetic analysis of the latter mutant enzyme was performed in cellular lysates, the first order rate constants (maximum velocity/dissociation constant) for both substrates were reduced 10- to 20-fold compared with those for the wild-type enzyme. Pro-30 is conserved in many microsomal P450 enzymes and may be important for proper orientation of the enzyme with respect to the aminoterminal transmembrane segment. The Pro----Leu mutation was present in 5 of 18 patients with nonclassic 21-hydroxylase deficiency, suggesting that this mutation indeed acts as a nonclassic deficiency allele.
Mol Endocrinol 1991 May
PMID:A mutation (Pro-30 to Leu) in CYP21 represents a potential nonclassic steroid 21-hydroxylase deficiency allele. 207 28

All nucleated animal cells synthesize heme to provide the prosthetic group of respiratory cytochromes. Large amounts of heme are synthesized by erythroid cells for hemoglobin production and by liver cells for drug-induced cytochromes P450. This review focuses on the first enzyme of the heme biosynthetic pathway, 5-aminolevulinate synthase (ALAS), which catalyzes the rate-controlling step in liver and possibly other tissues. We report that there are two distinct human genes for ALAS: one, a housekeeping gene, is probably ubiquitously expressed while the other is active only in erythroid tissue. By contrast it has been reported that, for porphobilinogen deaminase, the third enzyme of the heme pathway, there is a single human gene with two promoters; one functional in all tissues, the other erythroid specific. In liver, transcription of the housekeeping ALAS gene is induced by drugs and repressed by heme. Heme also acts in a novel way to prevent transport of ALAS into mitochondria, its site of function. Porphyrias result from inherited defects in enzymes of the heme pathway subsequent to ALAS and the molecular abnormality is now known for the most common subtype of acute intermittent porphyria. In developing red cells, levels of ALAS are regulated by increased gene transcription and by a post-transcriptional mechanism, in which iron most probably controls translation of erythroid ALAS mRNA through an iron-responsive element identified in the 5' untranslated region of the mRNA. The human erythroid ALAS gene is located on the X-chromosome, suggesting that a defect in this gene may be responsible for X-linked sideroblastic anemias.
Mol Biol Med 1990 Oct
PMID:Molecular regulation of 5-aminolevulinate synthase. Diseases related to heme biosynthesis. 209 58

The profile of hepatic microsomal cytochrome P450 expressed in the male and female rat was dramatically altered by streptozotocin-induced diabetes. In the diabetic male, P450 forms IIC11, IIC13, IIA2, and IIIA2 were suppressed and forms IIA1 and IIC12 were induced to the levels observed in the immature male rat. A 6- to 8-fold induction of P450 IIE1 was detected in both male and female diabetic rats. A member of the P450 IIIA family was also induced in the diabetic female rat. Accompanying the change in P450 profile in the diabetic male rat was reduction in circulating testosterone and tetraiodothyronine concentrations and a sharp diminution of the normally pulsatile pattern of growth hormone secretion. In contrast to the male rat, the growth hormone secretion pattern in the diabetic female rat was unchanged from control. The hormone and P450 profiles detected in the diabetic male rat suggest a reversion to an immature physiological state. Testosterone replacement treatments carried out for 2 weeks slightly but significantly affected the suppression of P450 IIC11 and reversed the changes in P450 IIA2, IIIA2, and IIC12 in the diabetic male, without altering the suppressed state of growth hormone secretion. However, 1 week of human growth hormone, administered intravenously every 4 hr to diabetic male rats, failed to significantly reverse the diabetes-induced changes in hepatic cytochromes P450, in particular forms IIC11 and IIE1, despite the presence of an episodic plasma hGH profile. An induction of P450 IIE1 in diabetic female rats, without a reduction in growth hormone secretion, suggests that its induction in diabetes in both sexes is not related to changes in growth hormone. In addition, the results of testosterone treatment on the expression of IIC12, IIA2, and IIIA2 in the diabetic male rat suggest a regulatory role for this hormone that does not involve the pituitary secretion of growth hormone. However, the lack of effect of human growth hormone treatment in the diabetic male on levels of individual P450 forms indicates that in diabetes there may be a change in the ability of the male rat hepatocyte to respond to a somatic signal, possibly as a result of the changes in other hormone factors.
Mol Pharmacol 1990 Jan
PMID:Effects of testosterone and growth hormone treatment on hepatic microsomal P450 expression in the diabetic rat. 210 52

Four genes in the P450 IID gene subfamily were isolated from Sprague-Dawley rat lambda EMBL 3 and Charon 4A genomic libraries and completely sequenced. Their transcription start sites were determined by primer extension analysis. The four genes designated IID2, IID3, IID4, and IID5 span 4036, 4371, 4678, and 4567 bp, respectively, and are closely linked head to tail on a 60-kb segment of DNA. All IID genes contained nine exons, and interestingly, the IID2, IID3, and IID4 genes possessed an atypical GC5' splice junction in intron 2. All four genes are transcribed, however, IID4 mRNA is produced at a level of less than one-tenth of those of IID2, IID3, and IID5. The exonic regions of these genes displayed from 79 to 84% sequence similarties. Several regions of extremely high nucleotide similarity were found within the introns, exons, and in the flanking regions of the four genes. These localized areas of high nucleotide similarities are the result of former gene conversion events. Of interest was the finding that the most highly similar region of all IID genes that was maintained by gene conversion covers portions of the eighth and ninth exons and the eighth intron. The ninth exon codes for a region of the P450 protein that is well conserved among all P450 gene families and in all species and that is associated with the noncovalently bound heme iron at the enzyme's active site. These data indicate that gene conversions have maintained sequence homogeneity within a critical region of the four P450 IID proteins.
J Mol Evol 1990 Feb
PMID:The rat P450 IID subfamily: complete sequences of four closely linked genes and evidence that gene conversions maintained sequence homogeneity at the heme-binding region of the cytochrome P450 active site. 210 30

The nucleotide sequence of a cDNA that codes for the major phenobarbital (PB)-inducible male beagle dog hepatic cytochrome P450 has been determined. Using a rabbit P450IIB cDNA probe (R. Gasser, M. Negishi, and R. M. Philpot, 1988, Mol. Pharmacol, 32, 22-30), a cDNA clone with a 2.6-kilobase pair insert was isolated from a lambda gt11 library prepared from hepatic mRNA from a PB-treated dog. The cloned insert was sequenced and found to contain an open reading frame coding for a polypeptide of 494 amino acids (Mr 56,183). The encoded protein can be assigned to the P450IIB subfamily on the basis of homology to cytochromes P450 from other species. The deduced amino acid sequence is 79% identical to that reported for rabbit P450 BO (P450IIB4) and 75% identical to that for rat P450b (P450IIB1). The sequence identity decreases to less than 52% when the dog sequence is compared with other P450II subfamilies. The deduced NH2-terminal 30 amino acids encoded by the dog cDNA are identical to those determined by sequence analysis of purified dog cytochrome P450 PBD-2, and the amino acid composition concurs with that determined for the PBD-2 protein (D. B. Duignan, I. G. Sipes, T. B. Leonard, and J. R. Halpert, 1987, Arch. Biochem. Biophys. 255, 290-303). Northern blots revealed two mRNA species of approximately 1.9 and 2.9 kilobases in length, which hybridized to the coding region of the dog P450IIB cDNA. The level of total hybridizable mRNA was increased approximately sixfold in livers from PB-treated dogs compared with that in untreated animals. This increase correlates well with the reported nearly sixfold increase in the level of PBD-2 protein and the fivefold increase in the rate of hepatic metabolism of 2,2',4,4',5,5'-hexachlorobiphenyl following PB treatment. The two mRNA species may result from the use of different polyadenylation signals located in the 3'-noncoding region or from transcription of more than one gene for PBD-2. Southern blot analysis indicated that the dog P450IIB subfamily contains at least two closely related genes.
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PMID:cDNA and deduced amino acid sequences of a dog hepatic cytochrome P450IIB responsible for the metabolism of 2,2',4,4',5,5'-hexachlorobiphenyl. 211 65


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