多功能的蛋白:糖原合成酶激酶-3

糖原合成酶激酶-3(GSK-3)是一个多功能的丝氨酸／苏氨酸类激酶,在真核生物中普遍存在。在哺乳动物中包括两个亚型,即GSK-3a和GSK-3β。GSK-3至少在三条细胞通路上有作用：Wnt/wingless,P13-kinase以及Hedgehog信号通路,该酶的作用主要包括调节糖原的合成代谢,参与细胞的分化与增殖等。研究发现,GSK-3在某些疾病,如阿尔茨海默病和非胰岛素依赖型糖尿病(NIDDM)中,其活性会异常升高。现已发现了几种针对该酶的抑制剂,如aloisine,paullones和马来酰胺类化合物等。这些抑制剂的确在分子水平特异性地抑制GSK-3的活性,而对其他激酶几乎没有作用。关于这些抑制剂的研究工作也已经在细胞水平和动物模型上开展起来,为开发以GSK-3为靶点的新的治疗药物创造了良好的基础。     

糖原合成酶激酶-3β与肾脏疾病

糖原合成酶激酶-3β(glycogen synthase kinase-3β,GSK-3β)GSK-3β是一种在真核生物体内广泛存在的丝/苏氨酸蛋白激酶.GSK-3β是Wnt/β-catenin、PI3K/Akt、胰岛素等多种信号通路的关键调节因子,并与多种疾病有关.最近人们发现,GSK-3β是通过使多种底物发生磷酸化来发挥生物学功能.主要就GSK-3β在肾脏疾病研究中的新进展作一综述,希望为探索各种肾脏疾病的发病机制以及寻找有效的治疗手段提供新视角.     

GSK-3与精神障碍的关系

糖原合成酶激酶3(GSK-3)是一种丝/苏氨酸蛋白激酶,通过Wnt/β-catenin等多条信号通路来调节机体的代谢、生长发育和凋亡等过程,是机体生存必不可少的物质。大量研究表明,GSK-3调节异常可以激活特定细胞、通路和环路,从而诱发精神障碍,如双向情感障碍、抑郁症、孤独症和精神分裂症等。抑制GSK-3活性是精神疾病治疗方法的一个重要组分。本文对近年来国内外有关GSK-3在精神疾病中的作用机制予以综述,以期为临床治疗提供依据。     

mTOR信号转导通路抑制剂及其与肿瘤耐药的研究进展

哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin, mTOR)是一种特异性的蛋白激酶,在调控细胞生长、增殖、代谢等多项生命活动中都具有重要意义。mTOR调控功能的失活与异常激活,会导致相关肿瘤和疾病的发生。近年来已有多种mTOR抑制剂用于治疗该信号转导通路异常引起的肿瘤。该文探究多种调控mTOR的信号通路和mTOR抑制剂用于肿瘤治疗的最新进展,还探讨肿瘤细胞对mTOR抑制剂产生耐药性的潜在机制和应对策略。因此,对mTOR信号通路及其调控机制的探索有助于研发全新的肿瘤治疗技术。     

PI3K/Akt/mTOR信号通路及临床相关肿瘤抑制剂

哺乳动物雷帕霉素靶（mTOR）和蛋白激酶B（Akt/PKB）与肿瘤发生的密切关系已被广泛地认可.mTOR是一种丝/苏氨酸激酶,可以通过影响mRNA转录、代谢、自噬等方式调控细胞的生长.它既是PI3K的效应分子,也可以是PI3K的反馈调控因子.mTORC1 和mTORC2是mTOR的两种不同复合物. 对雷帕霉素敏感的mTORC1受到营养、生长因子、能量和应激4种因素的影响.生长因子通过PI3K/Akt信号通路调控mTORC1是最具特征性调节路径.而mTORC2最为人熟知的是作为Akt473磷酸化位点的上游激酶. 同样,Akt/PKB在细胞增殖分化、迁移生长过程中发挥着重要作用. 随着Thr308和Ser473两个位点激活,Akt/PKB也得以全面活化.因此,mTORC2-Akt-mTORC1的信号通路在肿瘤形成和生长中是可以存在的.目前临床肿瘤治疗中,PI3K/Akt/mTOR是重要的靶向治疗信号通路.然而,仅抑制mTORC1活性,不是所有的肿瘤都能得到预期控制.雷帕霉素虽然能抑制mTORC1,但也能反馈性地增加PI3K信号活跃度,从而影响治疗预后.近来发现的第二代抑制剂可以同时抑制mTORC1/2和PI3K活性,这种抑制剂被认为在肿瘤治疗上颇具前景.本综述着重阐述了PI3K/Akt/mTOR信号通路的传导、各因子之间的相互调控以及相关抑制剂的发展.     

糖原合酶激酶-3β在肿瘤细胞中的分子作用机制

糖原合酶激酶-3β(glycogen synthase kinase-3β,GSK-3β)是一种多功能丝氨酸/苏氨酸激酶,通过磷酸化酪氨酸、丝氨酸和苏氨酸位点介导Wnt、Hedgehog、NF-κB和PI3K/Akt等信号通路,参与各类细胞功能的调节。GSK-3β在不同信号通路和细胞类型中扮演不同的角色,导致其在不同的恶性肿瘤中发挥促癌或抑癌的双重作用,与癌细胞的迁移和侵袭有直接关系。在胰腺癌和结肠癌研究中,GSK-3β的高表达调控通过相关信号通路,增强细胞增殖调控因子表达,抑制负性调控因子的活性,促进癌细胞的增殖。GSK-3β能激活上皮细胞间质转型过程中相关因子的表达,增强癌细胞扩散能力;相反,在胃癌和肺癌中,GSK-3β具有积极的抑癌作用。GSK-3β通过阻滞细胞周期和诱导细胞凋亡发挥抑癌作用,通过调节Wnt和PI3K/Akt信号通路,负向调控癌细胞的生长与侵袭,并且GSK-3β磷酸化相关因子以减弱其对癌细胞转移能力的刺激。本文总结了GSK-3β在不同恶性肿瘤中的作用及机制,并针对研究中存在的问题进行分析与展望,为相关领域的研究提供一定的理论基础。     

靶向Ras信号通路抑制剂在肿瘤治疗中的研究进展

Ras信号通路在肿瘤的发生发展中有着重要作用,该通路与肿瘤细胞的增殖、转移、凋亡等关系密切,但目前没有确定的靶向药物在临床上使用。近年来,靶向Ras信号通路的抑制剂研究火热,并且在临床试验中取得了很好疗效。该文围绕着Ras信号通路,重点介绍了Ras信号通路与肿瘤的关系、靶向Ras信号上下游的抑制剂、针对Ras蛋白的共价抑制剂研发进展以及联合用药策略,总结了相关抑制剂的最新进展。该文指出了靶向Ras信号通路面临的诸多挑战,改进抑制剂的结构、明确具体机制以及联合治疗策略将是未来研究大方向。     

肿瘤细胞Hedgehog信号通路及其抑制剂

越来越多的证据显示, 肿瘤的发生、生长、转移、复发以及耐药等均与肿瘤干细胞密切相关.Hedgehog (Hh)信号通路调节胚胎发育和成体许多组织器官干细胞的自我更新与增殖.然而, 那些在正常发育过程中受到Hh信号通路调节的组织器官, 在该信号通路异常时常常发生肿瘤.这些肿瘤包括肝癌、神经胶质瘤、基底细胞癌、横纹肌肉瘤、胰腺癌、小细胞肺癌、胃癌、结肠癌、前列腺癌、黑色素瘤和多发性骨髓瘤等.介绍了近年来Hh信号通路在肿瘤发生和发展过程中的机制、在维持肿瘤干细胞自我更新方面的作用, 以及该通路的特异性抑制剂, 以显示其在肿瘤治疗中潜在的重要意义.最后, 提出了今后肿瘤干细胞Hh通路研究的重点和新思路.     

mTOR信号通路与肾上腺肿瘤发生发展的关系进展

哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin,m TOR)是一种丝/苏氨酸蛋白激酶,是细胞内调控生长、增殖的中心信号分子,与肿瘤发生、发展关系密切.近年发现,m TOR信号通路在肾上腺肿瘤的发生发展中扮演重要角色.许多研究证实,PI3K/Akt/m TOR信号通路的关键蛋白Akt、m TOR、S6K1、4EB-P1的磷酸化水平在肾上腺皮质癌(adrenocortical carcinoma,ACC)和嗜铬细胞瘤(pheochromocytomas,PCC)中均明显高于正常肾上腺组织,且可能与肾上腺肿瘤的恶性转化相关.胰岛素样生长因子2基因的杂合性缺失、PTEN的生殖系突变、微小RNA表达异常均可激活PI3K/Akt/m TOR信号通路,使得血管内皮生长因子、细胞周期蛋白等分子过表达,从而产生抑凋亡、促增殖、促血管形成等效应,使组织呈现出肿瘤特征,并促进肿瘤的侵袭和转移.目前,细胞和动物模型研究已证实m TOR抑制剂对ACC与PCC有良好的疗效,且联合其他抗癌药物治疗效果更佳,这给肾上腺肿瘤患者的治疗带来了新的希望.本文总结了近年来m TOR信号通路与肾上腺肿瘤发生、发展的关系进展,希望为肾上腺肿瘤的机制研究及临床治疗提供实验室依据.     

MEK激酶及其抑制剂的研究进展

丝裂原活化的细胞外信号调节激酶(mitogen-activated extracellular signal-regulated kinase,MEK)是一种可磷酸化靶蛋白上丝氨酸/苏氨酸和酪氨酸残基的双特异性激酶,也是RASRAF-MEK-ERK信号转导通路的主要组分。该信号通路参与了细胞凋亡,细胞周期进行,细胞迁移、分化、代谢和细胞增殖等众多过程的调节。大量研究表明,MEK结构及其表达水平的改变与肿瘤等多种疾病的发生密切相关。因此,对MEK特异性抑制剂的筛选成了当前国际上关于肿瘤治疗研究的热点。目前,已有多种MEK抑制剂被发现,部分已用于肿瘤等疾病的治疗,并显示出较好的临床疗效。该文将对MEK的结构、功能及MEK抑制剂的临床应用等方面的研究进展作一综述。     

The Nuclear Localization of Glycogen Synthase Kinase 3β Is Required Its Putative PY-Nuclear Localization Sequences

Glycogen synthase kinase-3β (GSK-3β), which is a member of the serine/threonine kinase family, has been shown to be crucial for cellular survival, differentiation, and metabolism. Here, we present evidence that GSK-3β is associated with the karyopherin β2 (Kap β2) (102-kDa), which functions as a substrate for transportation into the nucleus. A potential PY-NLS motif (¹⁰⁹IVRLRYFFY¹¹⁷) was observed, which is similar with the consensus PY NLS motif (R/K/H)X_2–5PY in the GSK-3β catalytic domain. Using a pull down approach, we observed that GSK-3β physically interacts with Kap β2 both in vivo and in vitro. Secondly, GSK-3β and Kap β2 were shown to be co-localized by confocal microscopy. The localization of GSK-3β to the nuclear region was disrupted by putative Kap β2 binding site mutation. Furthermore, in transient transfection assays, the Kap β2 binding site mutant induced a substantial reduction in the in vivo serine/threonine phosphorylation of GSK-3β, where- as the GSK-3β wild type did not. Thus, our observations indicated that Kap β2 imports GSK-3β through its putative PY NLS motif from the cytoplasm to the nucleus and increases its kinase activity.     

Glycogen synthase kinase 3: an emerging therapeutic target

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine protein kinase that has recently emerged as a key target in drug discovery. It has been implicated in multiple cellular processes and linked with the pathogenesis of several diseases. GSK-3 inhibitors might prove useful as therapeutic compounds in the treatment of conditions associated with elevated levels of enzyme activity, such as type 2 diabetes and Alzheimer's disease. The pro-apoptotic feature of GSK-3 activity suggests a potential role for its inhibitors in protection against neuronal cell death, and in the treatment of traumatic head injury and stroke. Finally, selective inhibitors of GSK-3 could mimic the action of mood stabilizers such as lithium and valproic acid and be used in the treatment of bipolar mood disorders.     

Substrate Competitive GSK-3 Inhibitors strategy and Implications

Glycogen synthase kinase-3 (GSK-3) is a highly conserved protein serine/threonine kinase ubiquitously distributed in eukaryotes as a constitutively active enzyme. Abnormally high GSK-3 activity has been implicated in several pathological disorders, including diabetes and neuron degenerative and affective disorders. This led to the hypothesis that inhibition of GSK-3 may have therapeutic benefit. Most GSK-3 inhibitors developed so far compete with ATP and often show limited specificity. Our goal is to develop inhibitors that compete with GSK-3 substrates, as this type of inhibitor is more specific and may be useful for clinical applications. We have employed computational, biochemical, and molecular analyses to gain in-depth understanding of GSK-3's substrate recognition. Here we argue that GSK-3 is a promising drug discovery target and describe the strategy and practice for developing specific substrate-competitive inhibitors of GSK-3.     

Regulation and function of glycogen synthase kinase-3 isoforms in neuronal survival

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase consisting of two isoforms, alpha and beta. The activities of GSK-3 are regulated negatively by serine phosphorylation but positively by tyrosine phosphorylation. GSK-3 inactivation has been proposed as a mechanism to promote neuronal survival. We used GSK-3 isoform-specific small interfering RNAs, dominant-negative mutants, or pharmacological inhibitors to search for functions of the two GSK-3 isoforms in regulating neuronal survival in cultured cortical neurons in response to glutamate insult or during neuronal maturation/aging. Surprisingly, RNA interference-induced depletion of either isoform was sufficient to block glutamate-induced excitotoxicity, and the resulting neuroprotection was associated with enhanced N-terminal serine phosphorylation in both GSK-3 isoforms. However, GSK-3beta depletion was more effective than GSK-3alpha depletion in suppressing spontaneous neuronal death in extended culture. This phenomenon is likely due to selective and robust inhibition of GSK-3beta activation resulting from GSK-3beta Ser9 dephosphorylation during the course of spontaneous neuronal death. GSK-3alpha silencing resulted in reduced tyrosine phosphorylation of GSK-3beta, suggesting that tyrosine phosphorylation is also a critical autoregulatory event. Interestingly, GSK-3 inhibitors caused a rapid and long-lasting increase in GSK-3alpha Ser21 phosphorylation levels, followed by a delayed increase in GSK-3beta Ser9 phosphorylation and a decrease in GSK-3alpha Tyr279 and GSK-3beta Tyr216 phosphorylation, thus implying additional levels of GSK-3 autoregulation. Taken together, our results underscore important similarities and dissimilarities of GSK-3alpha and GSK-3beta in the roles of cell survival as well as their distinct modes of regulation. The development of GSK-3 isoform-specific inhibitors seems to be warranted for treating GSK-3-mediated pathology.     

Selective small-molecule inhibitors of glycogen synthase kinase-3 activity protect primary neurones from death

The phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (PKB; also known as Akt) signalling pathway is recognized as playing a central role in the survival of diverse cell types. Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed serine/threonine protein kinase that is one of several known substrates of PKB. PKB phosphorylates GSK-3 in response to insulin and growth factors, which inhibits GSK-3 activity and leads to the modulation of multiple GSK-3 regulated cellular processes. We show that the novel potent and selective small-molecule inhibitors of GSK-3; SB-415286 and SB-216763, protect both central and peripheral nervous system neurones in culture from death induced by reduced PI 3-kinase pathway activity. The inhibition of neuronal death mediated by these compounds correlated with inhibition of GSK-3 activity and modulation of GSK-3 substrates tau and beta-catenin. Thus, in addition to the previously assigned roles of GSK-3, our data provide clear pharmacological and biochemical evidence that selective inhibition of the endogenous pool of GSK-3 activity in primary neurones is sufficient to prevent death, implicating GSK-3 as a physiologically relevant principal regulatory target of the PI 3-kinase/PKB neuronal survival pathway.     

Emerging roles of GSK-3α in pathophysiology: Emphasis on cardio-metabolic disorders

Glycogen synthase kinase-3 (GSK-3) is a widely expressed serine/threonine kinase regulates a variety of cellular processes including proliferation, differentiation and death. Mammals harbor two structurally similar isoforms GSK-3α and β that have overlapping as well as unique functions. Of the two, GSK-3β has been studied (and reviewed) in far greater detail with analysis of GSK-3α often as an afterthought. It is now evident that systemic, chronic inhibition of either GSK-3β or both GSK-3α/β is not clinically feasible and if achieved would likely lead to adverse clinical conditions. Emerging evidence suggests important and specific roles for GSK-3α in fatty acid accumulation, insulin resistance, amyloid-β-protein precursor metabolism, atherosclerosis, cardiomyopathy, fibrosis, aging, fertility, and in a variety of cancers. Selective targeting of GSK-3α may present a novel therapeutic opportunity to alleviate a number of pathological conditions. In this review, we assess the evidence for roles of GSK-3α in a variety of pathophysiological settings.