Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.10.3.1 (tyrosinase)
9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The tyrosinase promoter has been used to target expression of the mutated human T24 Ha-ras oncogene in pigment-producing cells of transgenic mice. Two independent founder mice carrying the transgene survived and showed the same distinct phenotype of mutated coat color, deeply pigmented skin with multiple nevi, and twirling behavior. The offspring of one of these founders were developed into a line that stably expressed the same phenotype. Histopathological analysis of the tissues revealed hyperpigmentation and/or melanocytic hyperplasia in the skin, eyes, inner ear, and meningeal membranes in the brain. Reverse transcriptase-polymerase chain reaction analysis revealed expression of the transgene in skin, brain, and spleen. We propose that these transgenic mice will be a model for studying the process of multistage melanoma carcinogenesis and a system for evaluating potential chemopreventive agents.
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PMID:Hyperpigmentation and melanocytic hyperplasia in transgenic mice expressing the human T24 Ha-ras gene regulated by a mouse tyrosinase promoter. 766 20

Basic investigation into the nature of melanin monomer and polymer synthesis in pigment cells has revealed many of the new underlying factors involved in its regulation and control by three melanogenesis-related genes, tyrosinase, TRP-1 and TRP-2, and other non-tyrosinase glycoproteins. Pigment cells can undergo clinically and biologically recognizable progressive multi-step carcinogenesis. Generally parallel to this progressive cancerization is accentuated melanogenesis. Using this accentuated melanogenesis to develop a specific diagnosis and cure for melanoma (Mm) has long been a challenge. However, until recently, no success was achieved. As an example, attempting to utilize the fact that dopa accumulates as a melanin substrate within Mm cells, hybrid compounds of dopa and cytotoxic drugs were developed. However, these compounds were found to have severe systemic side effects and were therefore unusable. Another newer Mm treatment involves high energy radiation such as fast neutrons. But this is quite non-selective, killing both the target cancer and the normal surrounding tissue. Since 1972, I have developed the idea of coupling the high energy releasing system of thermal neutron irradiation with the non-toxic 10B-dopa analogue, 10B1-L-p-boronophenylalanine (10B1-L-BPA). Thermal neutrons are essentially harmless, but, after specific absorption by 10B, release high LET alpha-particles and 7Li-atoms with an energy of 2.33 MeV up to a distance of 14 mu, the diameter of Mm cells, thus selectively killing them without damaging surrounding normal tissue. After the synthesis of 10B1-L-BPA, exhaustive in vitro and in vivo radiological studies on its enhanced killing effect were done to develop optimal Mm Boron Neutron Capture Therapy (NCT).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Melanogenesis investigation leading to selective melanoma neutron capture therapy and diagnosis. 785 54

Some studies have shown the potential relevance of the oxidation products of 4-hydroxytamoxifen (4OHTAM) in carcinogenesis. Other studies show 4OHTAM has antioxidant properties. We characterized the one-electron oxidative activation reactions of 4OHTAM and three other phenolics, 3-hydroxytamoxifen (3OHTAM), 1-(4-hydroxyphenyl)-1, 2-diphenylethene, and phenol (PhOH), catalyzed by myeloperoxidase (MPx), horseradish peroxidase (HRP), lactoperoxidase, mushroom tyrosinase, and nonenzymatic initiators in vitro under a variety of conditions and in cells. Differences in activation of the phenolics by the enzymes were directly compared using cis-parinaric acid (PnA)-loaded human serum albumin. All phenolics were substrates for the enzymes, but MPx only weakly activated 4OHTAM to its phenoxyl radical. In HL60 cells loaded metabolically with PnA so that effects on phospholipids could be monitored by HPLC with fluorescence detection, PhOH plus H2O2 caused massive oxidation across all phospholipid classes. 4OHTAM dose-dependently protected phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholine against both H2O2-induced and normal metabolic oxidation. This suggested 4OHTAM is a poor substrate for intracellular MPx. In rat aorta smooth muscle cells loaded with PnA, 4OHTAM also protected against AMVN-induced peroxidation of those three phospholipids and sphingomyelin, whereas 3OHTAM did not. Spin trapping of glutathionyl radicals (GS*) with DMPO and quantifying the ESR-silent nitrone form of the GS-DMPO adduct by HPLC showed that neither 3OHTAM plus H2O2 nor 4OHTAM plus H2O2 caused a significant level of GSH oxidation with isolated MPx, nor did the latter in HL60 cells, whereas PhOH plus H2O2 was a potent source of GS* in both systems. Both 4OHTAM and 3OHTAM formed the nitrone adduct under cell-free conditions when activated with HRP. The data show that the substrate specificity of a given (myelo)peroxidase determines if a phenolic exerts pro- (through generation of reactive phenoxyl radicals) or antioxidant (through radical scavenging) properties in intracellular environments.
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PMID:Peroxidase-catalyzed pro- versus antioxidant effects of 4-hydroxytamoxifen: enzyme specificity and biochemical sequelae. 989 15

Although tamoxifen is approved for the treatment of hormone-dependent breast cancer as well as for the prevention of breast cancer in high-risk women, several studies in animal models have shown that tamoxifen is heptocarcinogenic, and in humans, tamoxifen has been associated with an increased risk of endometrial cancer. One potential mechanism of tamoxifen carcinogenesis could involve metabolism of tamoxifen to 3,4-dihydroxytamoxifen followed by oxidation to a highly reactive o-quinone which has the potential to alkylate and/or oxidize cellular macromolecules in vivo. In the study presented here, we synthesized the 3,4-dihydroxytamoxifen, prepared its o-quinone chemically and enzymatically, and studied the reactivity of the o-quinone with GSH and deoxynucleosides. The E (trans) and Z (cis) isomers of 3,4-dihydroxytamoxifen were synthesized using a concise synthetic pathway (four steps). This approach is based on the McMurry reaction between the key 4-(2-chloroethoxy)-3,4-methylenedioxybenzophenone and propiophenone, followed by selective removal of the methylenedioxy ring of (E, Z)-1-[4-[2-(N,N-dimethylamino)ethoxy]phenyl]-1-(3, 4-methylenedioxyphenyl)-2-phenyl-1-butene with BCl(3). Oxidation of 3,4-dihydroxytamoxifen by activated silver oxide or tyrosinase gave 3,4-dihydroxytamoxifen-o-quinone as a mixture of E and Z isomers. The resulting o-quinone has a half-life of approximately 80 min under physiological conditions. Reaction of the o-quinone with GSH gave two di-GSH conjugates and three mono GSH conjugates. Incubation of 3,4-dihydroxytamoxifen with GSH in the presence of microsomal P450 gave the same GSH conjugates which were also detected in incubations with human breast cancer cells (MCF-7). Reaction of 3, 4-dihydroxytamoxifen-o-quinone with deoxynucleosides gave only thymidine and deoxyguanosine adducts; neither deoxyadenosine nor deoxycytosine adducts were detected. Preliminary studies conducted with human breast cancer cell lines showed that 3, 4-dihydroxytamoxifen exhibited cytotoxic potency similar to that of 4-hydroxytamoxifen and tamoxifen in an estrogen receptor negative (ER(-)) cell line (MDA-MB-231); however, in the ER(+) cell line (MCF-7), the catechol metabolite was about half as toxic as the other two compounds. Finally, in the presence of microsomes and GSH, 4-hydroxytamoxifen gave predominantly quinone methide GSH conjugates as reported in the previous paper in this issue [Fan, P. W., et al. (2000) Chem. Res. Toxicol. 13, XX-XX]. However, in the presence of tyrosinase and GSH, 4-hydroxytamoxifen was primarily converted to o-quinone GSH conjugates. These results suggest that the catechol metabolite of tamoxifen has the potential to cause cytotoxicity in vivo through formation of 3,4-dihydroxytamoxifen-o-quinone.
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PMID:Synthesis and reactivity of a potential carcinogenic metabolite of tamoxifen: 3,4-dihydroxytamoxifen-o-quinone. 1064 67

The modifying effects of topical application of the phenolic antioxidant protocatechuic acid (PA) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse skin tumor promotion were investigated. Dimethylbenz[a]anthracene-initiated female ICR mice were treated with TPA (1.6 nmol) twice weekly for 20 weeks to promote papilloma formation. Pre-treatment with 16nmol PA 30 min prior to each TPA treatment significantly inhibited the number of papillomas per mouse by 52% (P < 0.05). On the other hand, PA pre-treatment at a high dose (1600 nmol) significantly enhanced tumor numbers by 38% (P < 0.05). Interestingly, in the group treated with a quite high dose (20000 nmol) of PA 5 min prior to each TPA application, the average number of tumors per mouse was reduced by 38%, whereas the same PA dose 3 h before TPA treatment significantly enhanced tumor numbers by 84% (P < 0.01). These results suggested that topically applied PA was converted to compound(s) lacking antioxidative properties and/or rather possessing the potential to enhance tumor development. A similar tendency was also observed in the short-term experiment of TPA-induced inflammation and oxidative stress; i.e. two groups pre-treated with PA at 20000 nmol, 30min and 3h before TPA treatment, did not show suppression or even significantly enhanced TPA-induced leukocyte infiltration, H(2)O(2) generation, thiobarbituric acid-reacting substances level and proliferating cell nuclear antigen index, while PA treatment together with TPA significantly suppressed these parameters. Treatment with a high dose (20000 nmol) of PA alone for 3h enhanced oxidative stress by reducing glutathione levels in mouse skin, which was counteracted by the tyrosinase inhibitor arbutin. Oxidative stress responses such as leukocyte infiltration and H(2)O(2) generation were also counteracted by arbutin. These results suggested that tyrosinase-dependent oxidative metabolism of PA was at least partially involved in the enhanced effects of PA on TPA-induced inflammatory responses and thus tumor promotion.
Carcinogenesis 2000 Oct
PMID:A simple phenolic antioxidant protocatechuic acid enhances tumor promotion and oxidative stress in female ICR mouse skin: dose-and timing-dependent enhancement and involvement of bioactivation by tyrosinase. 1102 49

Human papillomavirus type 16 (HPV16) has been known to be the major factor for the development of uterine cervical carcinomas. We have developed a line of transgenic mice that express the HPV16 E6 and E7 genes in certain organs using a fusion gene which consists of the tyrosinase promoter and E6/E7 of HPV16, and have chosen the tyrosinase minigene as a co-injected visual marker for the identification of transgenic mice. Our transgenic mice (1) expressed E6/E7 transgene mainly in skin and heart, and (2) showed skin and eye pigmentation profiles, and (3) raised incidence of hyperplastic skin lesions. We had performed two-stage skin carcinogenesis experiment to detect the susceptibility of skin papilloma development in our transgenic mice, using dimethylbenz-anthracene (DMBA) as a initiating agent and 12-O-tetradecanoyl-phorbol-13-acetate (TPA). After 1 week of DMBA treatment (25 microg dissolved in 0.2 ml acetone) and 15 consecutive weeks of TPA treatment (2.5 microg dissolved in 0.2 ml acetone) on the back of transgenic and non-transgenic control mice (Fv-1(b) strain mice which are Friend virus B-type susceptible (FVB)/N), papilloma incidence was increased in our transgenic mice approximately 2-fold higher than in control (in female mice, 69.2 vs. 30%, respectively). Thus our transgenic mice may be useful for the development of immunological or other therapies for HPV-associated cancers.
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PMID:Development of spontaneous hyperplastic skin lesions and chemically induced skin papillomas in transgenic mice expressing human papillomavirus type 16 E6/E7 genes. 1105 47

Catechol estrogens and catecholamines are metabolized to quinones, and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogenic benzene can also be oxidized to its quinone. We report here that quinones obtained by enzymatic oxidation of catechol and dopamine with horseradish peroxidase, tyrosinase or phenobarbital-induced rat liver microsomes react with DNA by 1,4-Michael addition to form predominantly depurinating adducts at the N-7 of guanine and the N-3 of adenine. These adducts are analogous to the ones formed with DNA by enzymatically oxidized 4-catechol estrogens (Cavalieri,E.L., et al. (1997) PROC: Natl Acad. Sci., 94, 10937). The adducts were identified by comparison with standard adducts synthesized by reaction of catechol quinone or dopamine quinone with deoxyguanosine or adenine. We hypothesize that mutations induced by apurinic sites, generated by the depurinating adducts, may initiate cancer by benzene and estrogens, and some neurodegenerative diseases (e.g. Parkinson's disease) by dopamine. These data suggest that there is a unifying molecular mechanism, namely, formation of specific depurinating DNA adducts at the N-7 of guanine and N-3 of adenine, that could initiate many cancers and neurodegenerative diseases.
Carcinogenesis 2002 Jun
PMID:Catechol ortho-quinones: the electrophilic compounds that form depurinating DNA adducts and could initiate cancer and other diseases. 1208 31

Data on the biologic activity of protocatechuic acid are contradictory; some studies have shown that it acts as an antioxidant and suppresses chemical-induced carcinogenesis and others that it induces oxidative stress and promotes tumour formation. The anticarcinogenicity of protocatechuic acid was postulated to be related, in part, to its specific suppression of neoplastic hyperproliferation. To determine whether protocatechuic acid was preferentially antiproliferative to malignant cells, non-malignant and carcinoma cells were exposed for 24 hr to protocatechuic acid (2.5 to 25 mM) and viability was assessed with the neutral red assay. The cell lines were derived from tissues of the human oral cavity, the initial site of exposure upon ingestion of dietary protocatechuic acid, and included normal GN61 gingival fibroblasts, immortalized, non-tumorigenic S-G gingival epithelial cells, and malignant HSG1 cells derived from the salivary gland, HSC-2 cells from the floor of the oral cavity, and CAL27 cells from the tongue. Selective toxicity of protocatechuic acid to malignant cells was not observed. Furthermore, using a total cellular protein determination to quantitate cell growth, no differences in comparative sensitivities of S-G epithelial cells and HSG1 carcinoma cells were noted in a 3 day continuous exposure to 2.5 to 12.5 mM protocatechuic acid and in recovery from a 24 hr exposure to 3 to 15 mM protocatechuic acid. The S-G and HSG1 cells were then used to study the effects of elevated concentrations of protocatechuic acid on oxidative stress. For both cell types, protocatechuic acid induced oxidative stress, presumably through its bioactivation by a tyrosinase pathway. A brief exposure to 25 mM protocatechuic acid lowered the levels of intracellular glutathione and potentiated Fe2+-induced lipid peroxidation of the cells. As determined with the neutral red assay, S-G and HSG1 cells exposed briefly to a non-toxic level (0.5 mM) of the glutathione depleter, 1,3-bis(2-chloroethyl)-N-nitrosourea, were hypersensitive to a subsequent challenge with 10 mM protocatechuic acid and preexposure of the S-G and HSG1 cells to a nontoxic level of protocatechuic acid (2.5 mM) enhanced their sensitivity to a subsequent exposure to tert-butyl hydroperoxide. These findings were consistent with protocatechuic acid, at high levels (> or = 10 mM), acting as an inducer of oxidative stress.
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PMID:In vitro cytotoxicity of protocatechuic acid to cultured human cells from oral tissue: involvement in oxidative stress. 1257 31

Estrogen replacement therapy has been correlated with an increased risk for developing breast and endometrial cancers. One potential mechanism of estrogen carcinogenesis involves metabolism of estrogens to 2- and 4-hydroxylated catechols, which are further oxidized to electrophilic/redox active o-quinones that have the potential to both initiate and promote the carcinogenic process. Previously, we showed that the equine estrogens, equilin and equilenin, which are major components of the estrogen replacement formulation Premarin (Wyeth-Ayerst), are primarily metabolized to the catechol, 4-hydroxyequilenin. This catechol was found to autoxidize to an o-quinone causing oxidation and alkylation of DNA in vitro and in vivo. To block catechol formation from equilenin, 4-halogenated equilenin derivatives were synthesized. These derivatives were tested for their ability to bind to the estrogen receptor, induce estrogen sensitive genes, and their potential to form catechol metabolites. We found that the 4-fluoro derivatives were more estrogenic than the 4-chloro and 4-bromo derivatives as demonstrated by a higher binding affinity for estrogen receptors alpha and beta, an enhanced induction of alkaline phosphatase activity in Ishikawa cells, pS2 expression in S30 cells, and PR expression in Ishikawa cells. Incubation of these compounds with tyrosinase in the presence of GSH showed that the halogenated equilenin compounds formed less catechol GSH conjugates than the parent compounds, equilenin and 17beta-hydroxyequilenin. In addition, these halogenated compounds showed less cytotoxicity in the presence of tyrosinase than the parent compounds in S30 cells. Also, as stated above, the 4-fluoro derivatives showed similar estrogenic effects as compared with parent compounds; however, they were less toxic in S30 cells as compared to equilenin and 17beta-equilenin. Because 17beta-hydroxy-4-halogenated equilenin derivatives showed higher estrogenic effects than the halogenated equilenin derivatives in vitro, we studied the relative ability of the 17beta-hydroxy-4-halogenated equilenin derivatives to induce estrogenic effects in the ovariectomized rat model. The 4-fluoro derivative showed higher activity than 4-chloro and 4-bromo derivatives as demonstrated by inducing higher vaginal cellular differentiation, uterine growth, and mammary gland branching. However, 17beta-hydroxy-4-fluoroequilenin showed a lower estrogenic activity than 17beta-hydroxyequilenin and estradiol, which could be due to alternative pharmacokinetic properties for these compounds. These data suggest that the 4-fluoroequilenin derivatives have promise as alternatives to traditional estrogen replacement therapy due to their similar estrogenic properties with less overall toxicity.
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PMID:Effect of halogenated substituents on the metabolism and estrogenic effects of the equine estrogen, equilenin. 1280 57

Studies of estrogen metabolism, formation of DNA adducts, carcinogenicity, cell transformation and mutagenicity have led to the hypothesis that reaction of certain estrogen metabolites, predominantly catechol estrogen-3,4-quinones, with DNA can generate the critical mutations initiating breast, prostate and other cancers. The endogenous estrogens estrone (E1) and estradiol (E2) are oxidized to catechol estrogens (CE), 2- and 4-hydroxylated estrogens, which can be further oxidized to CE quinones. To determine possible DNA adducts of E1(E2)-3,4-quinones [E1(E2)-3,4-Q], we reported previously that the reaction of E1(E2)-3,4-Q with dG produces the depurinating adduct 4-hydroxyE1(E2)-1-N7Gua [4-OHE1(E2)-1-N7Gua] by 1,4-Michael addition (Stack et al., Chem. Res. Toxicol., 1996, 9, 851). We report here that reaction of E1(E2)-3,4-Q with Ade results in the formation of 4-OHE1(E2)-1-N3Ade by 1,4-Michael addition. The N7Gua and N3Ade depurinating adducts formed both in vitro and in rat mammary gland in vivo were analyzed by HPLC with electrochemical detection and, for some samples, by LC/MS/MS. When E2-3,4-Q was reacted with DNA in vitro, the depurinating adducts 4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua, which are rapidly lost from DNA by cleavage of the glycosyl bond, were formed (>99% of the total adducts), as well as traces of stable adducts, which remain in DNA unless removed by repair. Similar results were obtained when 4-OHE2 was oxidized by horseradish peroxidase, lactoperoxidase, tyrosinase or phenobarbital-induced rat liver microsomes in the presence of DNA. When 4-OHE2 or E2-3,4-Q was injected into the mammary glands of female ACI rats in vivo and the mammary tissue was excised 1 h later, the depurinating adducts 4-OHE2-1-N3Ade and 4-OHE2-1-N7Gua constituted >99% of the total adducts formed. In addition, 4-OHE2 conjugates formed by reaction of E2-3,4-Q with glutathione were also detected. These results demonstrate that the 4-CE are metabolized to CE-3,4-Q, which react with DNA to form primarily depurinating adducts. These adducts can generate the critical mutations that initiate cancer (Chakravarti et al., Oncogene, 2001, 20, 7945; Chakravarti et al., Proc. Am. Assoc. Cancer Res., 2003, 44, 180).
Carcinogenesis 2004 Feb
PMID:Metabolism and DNA binding studies of 4-hydroxyestradiol and estradiol-3,4-quinone in vitro and in female ACI rat mammary gland in vivo. 1457 56


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