Stat5及JAK-Stat5通路

信号转导与转录因子（Stats）家族是一个由7个成员组成的转录调控家族,其中Stat5由于在多种细胞因子刺激时均可起到重要作用而引起了广泛的关注。Stat5具有两种不同类型,即Stat5a和Stat5b,它们均可被多种细胞因子所激活,启动JAK-Stat5信号通路,从而调节相应基因的表达。在两种Stat5的激活中,特殊位点的丝氨酸和酪氨酸的磷酸化对Stat5的激活起重要的作用。对信号通路严格的控制对于生物体来说具有重要的意义,在JAK-Stat5信号通路中,以SOCS3为代表的SOCS家族对JAK-Stat5的负反馈调节具有重要作用。     

5'-deoxy-5'-thioanalogs of adenosine and inosine 5'-monophosphate: studies with 5'-nucleotidase and alkaline phosphatase

The interaction of 5'-deoxy-5'-thioadenosine 5'-monophosphate (A(S)MP) and 5'-deoxy-5'-thioinosine 5'-monophosphate (I(S)MP) with snake venom, 5'nucleotidase, and calf intestinal mucosa alkaline phosphatase has been characterized. The substrates, A(S)MP and I(S)MP, are analogs of adenosine 5'-monophosphate and inosine 5'-monophosphate in which sulfur replaces oxygen as the bridge between the 5'-carbon of the ribose and the phosphorous. The P-S bond of both A(S)MP and I(S)MP was hydrolyzed by alkaline phosphatase producing the corresponding thionucleoside as a reaction product. The Km for A(S)MP was 270 microM and the V for alkaline phosphatase was 110 nmol/min/mg (8% of the V for AMP), whereas the corresponding values for I(S)MP were 300 microM and 530 nmol/min/mg protein, respectively. In contrast, 5'-nucleotidase did not catalyze hydrolysis of either A(S)MP or I(S)MP. A(S)MP and I(S)MP were competitive inhibitors of the 5'-nucleotidase hydrolysis of AMP and IMP, respectively, with Ki values of 975 and 13 microM. Decreasing the pH of the reaction from 8.1 to 7.1 lowered the Ki for I(S)MP by 100-fold, to a value of 0.15 microM.     

Mechanism of inactivation of S-adenosyl-L-homocysteine hydrolase by 5'-deoxy-5'-S-allenylthioadenosine and 5'-deoxy-5'-S-propynylthioadenosine

5'-Deoxy-5'-S-allenylthioadenosine 1 and 5'-deoxy-5'-S-propnylthioadenosine 2, derived from adenosine, were prepared. 1 and 2 caused irreversible inactivation of AdoHcy hydrolase. ESI mass spectra analysis of the inactivated enzyme demonstrated that 1 and 2 were type II "mechanism-based" inhibitors.     

Preparation, characterization, and chemical properties of the flavin coenzyme analogues 5-deazariboflavin, 5-deazariboflavin 5'-phosphate, and 5-deazariboflavin 5'-diphosphate, 5'leads to5'-adenosine ester.

In order to facilitate interpretation of the deazaisoalloxazine system as a valid mechanistic probe of flavoenzyme catalysis, we have examined some of the fundamental chemical properties of this system. The enzymatic synthesis, on a micromole scale, of the flavin coenzyme analogues 5-deazariboflavin 5'-phosphate (deazaFMN) and 5-deazariboflavin 5'-diphosphate, 5' leads to 5'adenosine ester (deazaFAD) has been achieved. This latter synthesis is accomplished with a partially purified FAD synthetase complex (from Brevibacterium ammoniagenes), containing both phosphorylating and adenylylating activities, allowing direct conversion of the riboflavin analogue to the flavin adenine dinucleotide level. The structure of the reduced deazaflavin resulting from enzymatic and chemical reduction is established as the 1,5-dihydrodeazaflavin by proton magnetic resonance. Similarly, the C-5 position of the deazaflavins is demonstrated to be the locus for hydrogen transfer in deazaflavin redox reactions. Preparation of 1,5-dihydrodeazaflavins by sodium borohydride reduction stabilized them to autoxidation (t 1/2 approximately 40 h, 22 degrees C) although dihydrodeazaflavins are rapidly oxidized by other electron acceptors, including riboflavin, phenazine methosulfate, methylene blue, and dichlorophenolindophenol. Mixtures of oxidized and reduced deazaflavins undergo a rapid two-electron disproportionation (k = 22 M-1 S-1 0 degrees C), and oxidized deazaflavins form transient covalent adducts with nitroalkane anions at pH less than 5. Generalized methods for the synthesis of isotopically labeled flavin and deazaflavin coenzymes and their purification by adsorptive chromatography are given.     

Enzyme-catalyzed redox reactions with the flavin analogues 5-deazariboflavin, 5-deazariboflavin 5'-phosphte, and 5-deazariboflavin 5'-diphosphate, 5' leads to 5'-adenosine ester.

The ability of 5-deazaisoalloxazines to substitute for the isoalloxazine (flavin) coenzyme has been examined with several flavoenzymes. Without exception, the deazaflavin is recognized at the active site and undergoes a redox change in the presence of the specific enzyme substrate. Thus, deazariboflavin is reduced catalytically by NADH in the presence of the Beneckea harveyi NAD(P)H:(flavin) oxidoreductase, the reaction proceeding to an equilibrium with an equilibrium constant near unity. This implies an E0 of -0.310 V for the deazariboflavindihydrodeazariboflavin couple, much lower than that for isoalloxazines. With this enzyme, both riboflavin and deazariboflavin show the same stereospecificity with respect to the pyridine nucleotide, and despite a large difference in Vmax for the two, both have the same rate-determining step (hydrogen transfer). Direct transfer of the hydrogen is seen between the nicotinamide and deazariboflavin in both reaction directions. DeazaFMN reconstituted yeast NADPH: (acceptor) oxidoreductase (Old Yellow Enzyme), and deazaFAD reconstituted D-amino acid:O2 oxidoreductase and Aspergillus niger D-glucose O2 oxidoreductase are all reduced by substrate at approximately 10(-5) the rate of holoenzyme; none are reoxidized by oxygen or any of the tested artificial electron acceptors, though deazaFADH-bound to D-amino acid:O2 oxidoreductase is rapidly oxidized by the imino acid product. Direct hydrogen transfer from substrate to deazaflavin has been demonstrated for both deazaFAD-reconstituted oxidases. These data implicate deazaflavins as a unique probe of flavin catalysis, in that any mechanism for the flavin catalysis must account for the deazaflavin reactivity as well.     

Evidence that intracellular synthesis of 5-fluorouridine-5'-phosphate from 5-fluorouracil and 5-fluorouridine is compartmentalized

L1210 cells were exposed to equitoxic concentrations of [14C]5-fluorouracil and [3H]5-fluorouridine for 4 hours. The RNA from these cells was separated into cytosolic and nuclear fractions, and then further fractionated by chromatography on poly-U Sepharose, Sephadex G-200 and DEAE-cellulose. The ratio of tritium to carbon-14 incorporated into various species of RNA differed by as much as 6-fold, indicating that the respective 5-fluorouridine-5'-monophosphates synthesized from the two precursors are localized in separate pools that do not mix rapidly.     

5'-Amino-5'-deoxyaristeromycin and its antiviral properties

An efficient, three-step synthesis of 5'-amino-5'-deoxyaristeromycin (5), from a protected form of aristeromycin (6), is described. Compound 5 was evaluated against a large number of viruses. It showed weak activity towards vaccinia, herpes simplex virus 2, and cytomegalovirus. No other activity was observed. Compound 5 displayed some cytotoxicity towards the host cell lines human foreskin fibroblast, Daudi, and human T-lymphocyte (CEM).     

Analogues of ribose 5-phosphate and 5-phosphoribosyl pyrophosphate. The preparation and properties of ribose 5-phosphorothioate and 5-phosphoribosyl 1-methylenediphosphonate

1. 5-Phosphoribosyl 1-methylenediphosphonate was isolated after reaction of ribose 5-phosphate and O-adenylyl methylenediphosphonate with 5-phosphoribosyl pyrophosphate synthetase from Ehrlich ascites-tumour cells. 2. The analogue reacted with adenine phosphoribosyltransferase, hypoxanthine phosphoribosyltransferase and nicotinamide phosphoribosyltransferase [K(m) (analogue)/K(m) (5-phosphoribosyl pyrophosphate) 0.17, 0.19 and 6.3 respectively; V(max.) (analogue)/V(max.) (5-phosphoribosyl pyrophosphate) 0.011, 0.26 and 1.1 respectively]. 3. The analogue was not a substrate for 5-phosphoribosyl pyrophosphate amidotransferase or orotate phosphoribosyltransferase. 4. Ribose 5-phosphorothioate was synthesized by allowing ribose to react with thiophosphoryl chloride in triethyl phosphate. The analogue was a substrate for 5-phosphoribosyl pyrophosphate synthetase from Ehrlich ascites-tumour cells. When this reaction was coupled to either adenine phosphoribosyltransferase or hypoxanthine phosphoribosyltransferase, adenosine 5'-phosphorothioate or inosine 5'-phosphorothioate was formed respectively.     

Tissue-Specific Differences in DNA Modifications (5-Hydroxymethylcytosine, 5-Formylcytosine, 5-Carboxylcytosine and 5-Hydroxymethyluracil) and Their Interrelationships

Background

Replication-independent active/enzymatic demethylation may be an important process in the functioning of somatic cells. The most plausible mechanisms of active 5-methylcytosine demethylation, leading to activation of previously silenced genes, involve ten-eleven translocation (TET) proteins that participate in oxidation of 5-methylcytosine to 5-hydroxymethylcytosine which can be further oxidized to 5-formylcytosine and 5-carboxylcytosine. Recently, 5-hydroxymethylcytosine was demonstrated to be a relatively stable modification, and the previously observed substantial differences in the level of this modification in various murine tissues were shown to depend mostly on cell proliferation rate. Some experimental evidence supports the hypothesis that 5-hydroxymethyluracil may be also generated by TET enzymes and has epigenetic functions.

Results

Using an isotope-dilution automated online two-dimensional ultra-performance liquid chromatography with tandem mass spectrometry, we have analyzed, for the first time, all the products of active DNA demethylation pathway: 5-methyl-2′-deoxycytidine, 5-hydroxymethyl-2′-deoxycytidine, 5-formyl-2′-deoxycytidine and 5-carboxyl-2′-deoxycytidine, as well as 5-hydroxymethyl-2′-deoxyuridine, in DNA isolated from various rat and porcine tissues. A strong significant inverse linear correlation was found between the proliferation rate of cells and the global level of 5-hydroxymethyl-2′-deoxycytidine in both porcine (R² = 0.88) and rat tissues (R² = 0.83); no such relationship was observed for 5-formyl-2′-deoxycytidine and 5-carboxyl-2′-deoxycytidine. Moreover, a substrate-product correlation was demonstrated for the two consecutive steps of iterative oxidation pathway: between 5-hydroxymethyl-2′-deoxycytidine and its product 5-formyl-2′-deoxycytidine, as well as between 5-formyl-2′-deoxycytidine and 5-carboxyl-2′-deoxycytidine (R² = 0.60 and R² = 0.71, respectively).

Conclusions

Good correlations within the substrate-product sets of iterative oxidation pathway may suggest that a part of 5-formyl-2′-deoxycytidine and/or 5-carboxyl-2′-deoxycytidine can be directly linked to a small portion of 5-hydroxymethyl-2′-deoxycytidine which defines the active demethylation process.     

The presence of guanosine 5'-diphospho-5'-guanosine and guanosine 5'-triphospho-5'-adenosine in brine shrimp embryos

Acid-soluble extracts of dormant embryos of the brine shrimp, Artemia salina, contain small amounts of two previously undescribed dinucleotides which we have identified to be guanosine 5'-diphospho-5'-guanosine and guanosine 5'-triphospho-5'-adenosine. These compounds each comprise about 0.03% of the dry weight of the encysted embryos and are related chemically to guanosine 5'-triphospho-5'-guanosine and guanosine 5'-tetraphospho-5'-guanosine which have been shown previously to be major constituents of the nucleotide pool of Artemia cysts. These new dinucleotides were purified from perchloric acid extracts of dormant cysts by ion exchange column chromatography and identified by means of chemical, spectrophotometric, and enzymatic analyses compared to commercially available compounds. The possible role of these new compounds in nucleotide and nucleic acid metabolism in Artemia embryos is discussed.     

Synthesis and biological activity of the new 5-fluorocytosine derivatives, 5'-deoxy-N-alkyloxycarbonyl-5-fluorocytosine-5'-carboxylic acid

A series of 5-fluorocytosine derivatives, 5'-deoxy-N-alkyloxycarbonyl-5-fluorocytosine-5'-carboxylic acid 6, were synthesized and evaluated for their antitumor activity.     

Interaction of thymidylate synthase with the 5'-thiophosphates, 5'-dithiophosphates, 5'-H-phosphonates and 5'-S-thiosulfates of 2'-deoxyuridine, thymidine and 5-fluoro-2'-deoxyuridine.

New analogs of dUMP, dTMP and 5-fluoro-dUMP, including the corresponding 5'-thiophosphates (dUMPS, dTMPS and FdUMPS), 5'-dithiophosphates (dUMPS2, dTMPS2 and FdUMPS2), 5'-H-phosphonates (dUMP-H, dTMP-H and FdUMP-H) and 5'-S-thiosulfates (dUSSO3, dTSSO3 and FdUSSO3), have been synthesized and their interactions studied with highly purified mammalian thymidylate synthase. dUMPS and dUMPS2 proved to be good substrates, and dTMPS and dTMPS2 classic competitive inhibitors, only slightly weaker than dTMP. Their 5-fluoro congeners behaved as potent, slow-binding inhibitors. By contrast, the corresponding 5'-H-phosphonates and 5'-S-thiosulfates displayed weak activities, only FdUMP-H and FdUSSO3 exhibiting significant interactions with the enzyme, as weak competitive slow-binding inhibitors versus dUMR The pH-dependence of enzyme time-independent inhibition by FdUMP and FdUMPS was found to correlate with the difference in pKa values of the phosphate and thiophosphate groups, the profile of FdUMPS being shifted (approximately 1 pH unit) toward lower pH values, so that binding of dUMP and its analogs is limited by the phosphate secondary hydroxyl ionization. Hence, together with the effects of 5'-H-phosphonate and 5'-S-thiosulfate substituents, the much weaker interactions of the nucleotide analogs (3-5 orders of magnitude lower than for the parent 5'-phosphates) with the enzyme is further evidence that the enzyme's active center prefers the dianionic phosphate group for optimum binding.