Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method is described by which different forms of S-adenosylmethionine synthetase are separated. The method makes use of fast protein liquid chromatography on an anion exchange hydrophilic polyether resin. Different forms of S-adenosylmethionine synthetase from rat and human liver and kidney and rat zajdela hepatoma cells can be separated within 15 min. From a mixture of rat liver and kidney cytosols all three forms alpha, beta and gamma can be separated. The time needed to separate the different forms of S-adenosylmethionine synthetase is reduced from 3 h with conventional gel filtration methods, to 15 min using this HPLC anion-exchange method. Also the amount of tissue needed to detect the different forms is reduced from 125 mg to 12.5 mg of fresh rat liver tissue. These advantages make this newly developed method applicable when large numbers of samples have to be analyzed or when only small amounts of tissue are available.
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PMID:Separation of different forms of S-adenosylmethionine synthetase by fast protein liquid chromatography. 234 65

With 2',3'-O-isopropylideneadenosine or its N6-benzoyl derivative as starting material, synthetic routes to two novel adducts of L-methionine and beta,gamma-imido-ATP have been devised. One adduct, 14 (2:3 mixture of 6' epimers), had a P alpha OCH(R1)CH2 system [R1 = CH2-L-SCH2CH2CH2CH(NH2)CO2H] in place of the P alpha OC(5')H2 system of ATP, while the other, 16 (2:3 mixture of 5' epimers), had a P alpha OCH2CH2CH(R2) system [R2 = L-SCH2CH2CH(NH2)CO2H]. The ribose-P alpha bridge in 14 and 16 contained one more methylene group than in two homologous methionine-ATP adducts studied previously. Adduct 14 was a potent inhibitor of the rat M-2 (normal tissue) and M-T (Novikoff ascitic hepatoma) variants of methionine adenosyltransferase and gave competitive kinetics vs MgATP (Ki = 0.39 and 0.63 microM, respectively) or vs L-methionine (Ki = 2.2 and 2.7 microM). Adduct 16 was likewise a potent inhibitor competitive vs MgATP (Ki = 0.44 and 0.81 microM, respectively) or L-methionine (Ki = 2.1 and 1.5 microM). The kinetic data indicate that 14 and 16 inhibit by binding simultaneously to the MgATP and L-methionine substrate sites and that the extra methylene group facilitates the interaction of their methionine residues with these methionine sites.
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PMID:Toward the synthesis of isozyme-specific enzyme inhibitors. Potent inhibitors of rat methionine adenosyltransferases. Effect of one-atom elongation of the ribose-P alpha bridge in two covalent adducts of L-methionine and beta,gamma-imido-ATP. 325 24

The title compounds (14a,b) were 5' epimers of a derivative of a phosphonate isostere of ATP in which the CH2OP alpha system of ATP was replaced by CH(R)CH2P alpha [R = L-S(CH2)2CH(NH2)CO2H]. They resisted synthesis via attempted S-alkylation of the corresponding epimeric 5'-mercapto derivatives. A practicable route to 14a,b commenced with Michael condensation of L-homocysteine with the diphenyl ester of the 5',6'-vinyl phosphonate analogue of 2',3'-O-isopropylideneadenosine 5'-phosphate. The resulting epimeric 5' thioethers were separated by reverse-phase HPLC. The two phenyl groups were replaced by benzyl groups, after which the alpha-amino acid residue was protected as an N-Boc methyl ester. Both benzyl groups were removed by hydrogenolysis, and the resulting phosphonic acid was converted into its pyrophosphoryl derivative. Blocking groups were then removed under conditions that furnished 14a and 14b without racemization of their L-amino acid residues. Also synthesized were the P beta-NH-P gamma imido analogue (15a) of 14a and the sulfoxide derivative (16a) of 14a. The structures of 14a and 16a were verified by FAB mass spectra, which revealed the protonated molecular ions of their sodium salts. All adducts appeared to function as dual substrate site inhibitors (competitive to ATP and to methionine) of the rat normal tissue (MAT-2) form of methionine adenosyltransferase (MAT); 14a and 15a [KM(ATP)/Ki = 4 and 9, respectively] were the most effective. Adduct 15a was the most effective inhibitor [KM(ATP)/Ki = 13] of the MAT-T form from rat hepatoma tissue; the kinetic data indicated dual-site inhibition by 15a with apparently complete coverage of the ATP site and incomplete coverage of the methionine site. The inhibition properties of the adducts indicated little preference in the order in which the two MAT forms bound ATP and methionine.
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PMID:Isozyme-specific enzyme inhibitors. 11. L-homocysteine-ATP S-C5' covalent adducts as inhibitors of rat methionine adenosyltransferases. 348 76

The title compound is a covalent adduct of L-methionine (Met) and beta,gamma-imido-ATP. In its synthesis the N-Boc derivative of 5'(R)-C-(aminomethyl)-N6-benzoyl-5'-O-tosyl-2',3'-O- isopropylidenadenosine was converted by the successive actions of CF3CO2H and HNO2 into the corresponding 5'(R)-C-hydroxymethyl derivative. Treatment of this with disodium L-homocysteinate led to attack of sulfur at C6', apparently via a 5',6'-epoxide, and to total stereoselective inversion at C5' to furnish, after debenzoylation, 5'(R)-C-(L-homocystein-S-ylmethyl)-2',3'-O-isopropylidene ade nosine. The 5' configuration was established by conversion of this into the known 5'(S)-C-methyl-2',3'-O-isopropylidene adenosine with Raney nickel. The alpha-amino acid residue was protected as an N-Boc methyl ester, after which the 5'-hydroxyl was phosphorylated with benzyl phosphate and dicyclohexylcarbodiimide. The phosphoanhydride bond with inorganic imidodiphosphate was then created by established methods. Finally, blocking groups were removed under conditions that gave the desired adduct with no racemization of its L-methionine residue. It was a potent inhibitor [KM(ATP)/Ki = 1080; KM(Met)/Ki = 7.7] of the M-2 (normal tissue) form of rat methionine adenosyltransferase and of the M-T (hepatoma tissue) form [KM(ATP)/Ki = 670; KM(Met)/Ki = 22]. Inhibitions were competitive with respect to ATP or to L-methionine, indicating a dual substrate site mode of binding to the enzyme forms.
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PMID:Isozyme-specific enzyme inhibitors. 14. 5'(R)-C-[(L-homocystein-S-yl)methyl]adenosine 5'-(beta,gamma-imidotriphosphate), a potent inhibitor of rat methionine adenosyltransferases. 349 43

A synthesis is described of the title compound and its 5'S epimer, which are two-substrate adducts of adenosine 5'-triphosphate (ATP) and L-methionine (Met) in which the C(5')H2OP system in ATP is replaced by CH(R)CH2NHP [R = L-S(CH2)2CH(NH2)CO2H]. The 5'R epimer was a potent nonselective competitive inhibitor [averaged Ki = 0.32 microM; KM(ATP)/Ki = 440] vs. ATP of the rat M-2 (normal tissue) and M-T (Novikoff ascitic hepatoma) variants of methionine adenosyltransferase. It produced simple noncompetitive inhibition (averaged Ki = 2.7 microM) vs. Met with both variants. The 5'S epimer inhibited M-T competitively vs. ATP, but was 74-fold less effective than the 5'R epimer. Replacement of the homocysteine moiety in the 5'R epimer by hydrogen markedly reduced inhibitory potency, as indicated by Ki values of 14 microM for competitive inhibition vs. ATP and 580 microM for noncompetitive inhibition vs. Met with M-2. The data suggest that the 5'R epimer can interact simultaneously with two enzymic sites. Information on the kinetic mechanism of a human counterpart of M-2 and inhibitor properties of a previously studied Met-ATP adduct are consistent with the view that the two sites might resemble those that interact with the initial products of the reaction, S-adenosylmethionine and triphosphate.
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PMID:Isozyme-specific enzyme inhibitors. 13. S-[5'(R)-[(N-triphosphoamino)methyl]adenosyl]-L-homocysteine, a potent inhibitor of rat methionine adenosyltransferases. 357 77

Monosubstituted adenosine 5'-triphosphate (ATP) derivatives with a substituent of up to four atoms at any of eight positions in the adenosine moiety, or with an isosteric group replacement at O5' or in the triphosphate moiety, have been evaluated kinetically as substrates and inhibitors of liver (I), kidney (II), and Novikoff hepatoma (T) variants of rat methionine adenosyltransferase. Inhibitory potencies were expressed as KM(ATP)/Ki (for competitive inhibition vs. ATP) or as KM(ATP)/KM when no Ki value was available. Variant I was inhibited more powerfully than II or T by all of four ATP derivatives for which comparative data were obtained. Among 15 ATP derivatives, four were substrates of II or T and the remainder inhibited II and T competitively with respect to ATP; most derivatives exhibited at least moderate (greater than 0.5) inhibitory potency. Differential inhibition of II and T was shown by 11 of 14 ATP derivatives; relative inhibitory potencies (T:II) ranged from 5.5 with 2-SCH3-ATP [KM(ATP)/Ki = 1.3 with T] to 0.24 with the ATP isostere with a C5'-CH2-P alpha system [KM(ATP)/Ki = 1.9 with II]. The most effective inhibitor was the P beta, P gamma imido isostere of ATP with inhibitory potencies of 25 and 35 for II and T, respectively. The findings provide further evidence that substrate derivatives with single short groups attached at various positions, or with single isosteric group replacements, are frequently useful probes in the design of isozyme-selective inhibitors.
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PMID:Isozyme-specific enzyme inhibitors. 10. Adenosine 5'-triphosphate derivatives as substrates or inhibitors of methionine adenosyltransferases of rat normal and hepatoma tissues. 395 Sep 12

Two isozymes of ATP:L-methionine S-adenosyltransferase (MAT) were fractionated from rat Novikoff solid hepatoma. Their Km values for L-methionine and/or their inhibition constants for various L-methionine analogues were significantly different from the kinetic constants obtained for three isozymes fractionated from normal rat liver. Ki values for cycloleucine and (+/-)-2-aminobicyclo[2.1.1]hexane-2-carboxylic acid, presented for each tumor and liver isozyme, indicate that (+/-)-2-aminobicyclo[2.1.1]hexane-2-carboxylic acid was the more potent inhibitor. Dixon plots were also used to test a series of amino acid analogues [cycloleucine, 1-aminocyclobutanecarboxylic acid, 1-aminocyclohexanecarboxylic acid, (+/-)-2-aminobicyclo[2.1.1]hexane-2-carboxylic acid, L-2-amino-4-hexynoic acid, (Z)-L-2-amino-5-chloro-trans-4-hexenoic acid, L-ethionine, S-n-propyl-DL-homocysteine, S-n-butyl-DL-homocysteine, and seleno-DL-ethionine] of methionine for inhibitory potency. Fixed L-methionine concentrations were used to determine the concentration of inhibitor necessary to inhibit the MAT reaction by 50%. Differential inhibitory activities of the amino acid analogues were noted between the tumor and rat liver isozymes thus supporting the suggestion that tumor-derived MAT isozymes may provide an exploitable target for cancer chemotherapy.
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PMID:Chemotherapeutic potential of methionine analogue inhibitors of tumor-derived methionine adenosyltransferases. 684 99

It is known that a high incidence of hepatocellular carcinoma in rat liver can be induced by such azo dye carcinogens as 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB). Mammalian S-adenosylmethionine (AdoMet) synthetase exists as two isozymes, non-hepatic-type and liver-type enzymes, which are the products of two different genes. We have examined the expression of two AdoMet synthetase isozyme proteins and mRNAs in rat hepatomas induced by 3'-Me-DAB. The levels of non-hepatic-type enzyme protein and mRNA are clearly induced by 3'-Me-DAB feeding. On the other hand, the levels of liver-type enzyme protein and mRNA are nearly the same or slightly decreased during hepatocarcinogenesis. These results indicate that the expression of the non-hepatic-type isozyme gene is obviously influenced with the progression of carcinogenesis and that the non-hepatic-type isozyme is useful as a oncodevelopmental marker in the liver.
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PMID:Expression of non-hepatic-type S-adenosylmethionine synthetase isozyme in rat hepatomas induced by 3'-methyl-4-dimethylaminoazobenzene. 822 30

The sequence of a full-length cDNA coding for human liver S-adenosylmethionine synthetase has been determined. It spans 3217 nucleotides and encodes a protein of 395 amino acid residues, with a calculated molecular mass of 43,647 Da. The structural features deduced from the amino acid sequence show a close similarity to those of the rat liver enzyme. The liver-specific S-adenosylmethionine synthetase gene appears to be present as a single copy in the genome, as revealed by Southern analysis. The occurrence of a single mRNA species for this enzyme has been determined by primer extension and Northern analysis. Among several human tissues examined, this gene is expressed only in the liver. Similar S-adenosylmethionine synthetase mRNA levels have been detected in biopsies from normal human liver and from patients with alcoholic cirrhosis and hepatocellular carcinoma. Based on these results, a possible mechanism of regulation of human liver S-adenosylmethionine synthetase is discussed.
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PMID:Characterization of a full-length cDNA encoding human liver S-adenosylmethionine synthetase: tissue-specific gene expression and mRNA levels in hepatopathies. 839 62

S-adenosylmethionine synthetase (SAMS) catalyzes the formation of S-adenosylmethionine (SAM) and is essential to normal cell function. There are two forms of SAMS, liver-specific and nonliver-specific (often referred to as "kidney"), which are products of two different genes. SAMS isoenzymes differ greatly in kinetic parameters and sensitivity to inhibition by methionine analogs. The current work studied changes in SAMS and their significance in liver cancer. Northern blot analysis showed that while normal liver expresses only liver-specific SAMS, both HepG2 and HuH-7 cells express only nonliver-specific SAMS. Absence of liver-specific SAMS messenger RNA (mRNA) was not because of gene deletion or rearrangement but complete lack of gene transcription. Reverse-transcription polymerase chain reaction (RT-PCR) with liver- and kidney-specific SAMS primers showed that liver-specific SAMS mRNA was absent with only kidney SAMS mRNA present in HepG2, HuH-7, Hep3B, and HuH-1 cells, and four consecutive hepatocellular carcinoma (HCC) specimens. Normal liver tissues from the same patients express both forms of SAMS mRNA. As a result of the change in SAMS expression, SAMS activity was higher in HepG2 and HuH-7 cells at physiologically relevant methionine concentrations but lower at high (mmol/L) methionine concentrations than rat hepatocytes. Treatment with ethionine and seleno-D,L-ethionine, two inhibitors known to have I50 values 50 to 60 times lower against SAMS purified from Novikoff hepatoma cells as compared with SAMS purified from normal rat liver, resulted in increased cell lysis in HepG2 and HuH-7 cells but not cultured rat hepatocytes. These agents did not affect cellular adenosine triphosphate (ATP) levels but inhibited SAMS activity in HepG2 and HuH-7 cells when added to their protein extracts. In summary, expression of SAMS is altered in human liver cancer. This occurrence may provide a potentially exploitable target for cancer chemotherapy.
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PMID:Changes in S-adenosylmethionine synthetase in human liver cancer: molecular characterization and significance. 890 81


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