糖原合酶激酶-3，一个信号通路的重要调控因子

糖原合酶激酶-3 (glycogen synthase kinase-3,GSK-3) 是一种多功能的丝氨酸／苏氨酸蛋白激酶,在蛋白质合成、信号传递、细胞增殖、细胞分化、神经功能、肿瘤形成及胚胎发育等众多细胞进程中均扮演重要的角色.GSK-3 能够使多种底物发生磷酸化,并参与胰岛素、Wnt及Hedgehog 等多个信号通路的调控. GSK-3抑制剂在信号通路中能有效地抑制病理情况下GSK-3活性的异常增高,达到治疗的目的.GSK-3的抑制剂将作为一种潜在的药物对治疗糖尿病、阿尔海默茨症、肿瘤等疾病发挥效用.     

Glycation exacerbates the neuronal toxicity of β-amyloid

Accumulation evidence shows that β-amyloid (Aβ) is a neurotoxic and accumulation of Aβ is responsible for the pathology of Alzheimer''s disease (AD). However, it is currently not fully understood what makes Aβ toxic and accumulated. Previous studies demonstrate that Aβ is a suitable substrate for glycation, producing one form of the advanced glycation endproducts (AGEs). We speculated that Aβ-AGE formation may exacerbate the neurotoxicity. To explore whether the Aβ-AGE is more toxic than the authentic Aβ and to understand the molecular mechanisms, we synthesized glycated Aβ by incubating Aβ with methylglyoxal (MG) in vitro and identified the formation of glycated Aβ by fluorescence spectrophotometer. Then, we treated the primary hippocampal neurons cultured 8 days in vitro with Aβ-AGE or Aβ for 24 h. We observed that glycation exacerbated neurotoxicity of Aβ with upregulation of receptor for AGE (RAGE) and activation of glycogen synthase kinase-3 (GSK-3), whereas simultaneous application of RAGE antibody or GSK-3 inhibitor reversed the neuronal damages aggravated by glycated Aβ. Thereafter, we found that Aβ is also glycated with an age-dependent elevation of AGEs in Tg2576 mice, whereas inhibition of Aβ-AGE formation by subcutaneously infusion of aminoguanidine for 3 months significantly rescued the early cognitive deficit in mice. Our data reveal for the first time that the glycated Aβ is more toxic. We propose that the glycated Aβ with the altered secondary structure may be a more suitable ligand than Aβ for RAGE and subsequent activation of GSK-3 that can lead to cascade pathologies of AD, therefore glycated Aβ may be a new therapeutic target for AD.     

相容溶质四氢嘧啶与羟基四氢嘧啶的代谢调控研究进展

四氢嘧啶(Ectoine)及其衍生物羟基四氢嘧啶(5-hydroxyectoine,5-HE)是嗜盐微生物胞内合成的一类能够抵抗外界高盐胁迫的相容溶质,具有细胞、细胞膜、蛋白质和核酸的保护作用,可抵抗高盐、高温、冷冻和干燥等极端环境因素的刺激,从而倍受关注。本文对不同类型微生物Ectoine/5-HE(Ects)生物合成代谢、分解代谢以及吸收/转运系统涉及的调控机制进行综述,以期为Ects合成产量的提升与高效积聚策略的优化,提供一定的理论参考依据。     

Insulin-Driven PI3K-AKT Signaling in the Hepatocyte Is Mediated by Redundant PI3Kα and PI3Kβ Activities and Is Promoted by RAS

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Respirometric evaluation and modeling of glucose utilization by Escherichia coli under aerobic and mesophilic cultivation conditions

The study presents a mechanistic model for the evaluation of glucose utilization by Escherichia coli under aerobic and mesophilic growth conditions. In the first step, the experimental data was derived from batch respirometric experiments conducted at 37 degrees C, using two different initial substrate to microorganism (S(0)/X(0)) ratios of 15.0 and 1.3 mgCOD/mgSS. Acetate generation, glycogen formation and oxygen uptake rate profile were monitored together with glucose uptake and biomass increase throughout the experiments. The oxygen uptake rate (OUR) exhibited a typical profile accounting for growth on glucose, acetate and glycogen. No acetate formation (overflow) was detected at low initial S(0)/X(0) ratio. In the second step, the effect of culture history developed under long-term growth limiting conditions on the kinetics of glucose utilization by the same culture was evaluated in a sequencing batch reactor (SBR). The system was operated at cyclic steady state with a constant mean cell residence time of 5 days. The kinetic response of E.coli culture was followed by similar measurements within a complete cycle. Model calibration for the SBR system showed that E. coli culture regulated its growth metabolism by decreasing the maximum growth rate (lower microH) together with an increase of substrate affinity (lower K(S)) as compared to uncontrolled growth conditions. The continuous low rate operation of SBR system induced a significant biochemical substrate storage capability as glycogen in parallel to growth, which persisted throughout the operation. The acetate overflow was observed again as an important mechanism to be accounted for in the evaluation of process kinetics.     

The hepatic PP1 glycogen-targeting subunit interaction with phosphorylase a can be blocked by C-terminal tyrosine deletion or an indole drug

The inhibition of hepatic glycogen-associated protein phosphatase-1 (PP1-G(L)) by glycogen phosphorylase a prevents the dephosphorylation and activation of glycogen synthase, suppressing glycogen synthesis when glycogenolysis is activated. Here, we show that a peptide ((280)LGPYY(284)) comprising the last five amino acids of G(L) retains high-affinity interaction with phosphorylase a and that the two tyrosines play crucial roles. Tyr284 deletion abolishes binding of phosphorylase a to G(L) and replacement by phenylalanine is insufficient to restore high-affinity binding. We show that a phosphorylase inhibitor blocks the interaction of phosphorylase a with the G(L) C-terminus, suggesting that the latter interaction could be targeted to develop an anti-diabetic drug.     

An Escherichia coli mutant producing a truncated inactive form of GlgC synthesizes glycogen: further evidences for the occurrence of various important sources of ADPglucose in enterobacteria

AC70R1-504 Escherichia coli mutants possess a glgC* gene with a nucleotide change resulting in a premature stop codon that renders a truncated, inactive form of GlgC. Cells over-expressing the wild type glgC, but not those over-expressing the AC70R1-504 glgC*, accumulated high ADPglucose and glycogen levels. AC70R1-504 mutants accumulated glycogen, whereas DeltaglgCAP deletion mutants lacking the whole glycogen biosynthetic machinery displayed a glycogen-less phenotype. AC70R1-504 cells with enhanced glycogen synthase activity accumulated high glycogen levels. By contrast, AC70R1-504 cells with high ADPG hydrolase activity accumulated low glycogen. These data further confirm that enterobacteria possess various sources of ADPglucose linked to glycogen biosynthesis.     

Escherichia coli AspP activity is enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars

Escherichia coli ADP-sugar pyrophosphatase (AspP) is a "Nudix" hydrolase that catalyzes the hydrolytic breakdown of ADP-glucose linked to glycogen biosynthesis. Moderate increases of AspP activity in the cell are accompanied by significant reductions of the glycogen content. In vitro analyses showed that AspP activity is strongly enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars, providing a first set of indicative evidences that AspP is a highly regulated enzyme. To our knowledge, AspP is the sole bacterial enzyme described to date which is activated by both G1,6P(2) and nucleotide-sugars.     

Long noncoding RNA OIP5-AS1 acts as a competing endogenous RNA to promote glutamine catabolism and malignant melanoma growth by sponging miR-217

The long noncoding RNA (lncRNA) OIP5-AS1 has been considered to promote the growth and metastasis of many human tumors. However, the role of OIP5-AS1 in melanoma has not been reported. In this study, we found that OIP5-AS1 levels were significantly elevated in melanoma tissue and that high OIP5-AS1 expression was an independent risk factor for the poor survival of patients with melanoma. miR-217 suppressed glutamine catabolism in melanoma cells by targeting glutaminase (GLS), the rate-limiting enzyme of glutamine catabolism. We also demonstrated that OIP5-AS1 acted as a sponge of miR-217 to upregulate GLS expression, thus promoting glutamine catabolism and melanoma growth. Overall, this result elucidates a new mechanism for OIP5-AS1 in metabolism in melanoma and provides a potential therapeutic target for patients with melanoma.