14-3-3 蛋白

介绍了14－3－3蛋白的基本结构和功能,并简要概述了14－3－3蛋白在信号转导,细胞周期调控以及前体蛋白的折叠与运输过程中的作用机理。     

14-3-3 proteins--an update

14-3-3 is a highly conserved acidic protein family, composed of seven isoforms in mammals. 14-3-3 protein can interact with over 200 target proteins by phosphoserine-dependent and phosphoserine-independent manners. Little is known about the consequences of these interactions, and thus are the subjects of ongoing studies. 14-3-3 controls cell cycle, cell growth, differentiation, survival, apoptosis, migration and spreading. Recent studies have revealed new mechanisms and new functions of 14-3-3, giving us more insights on this fascinating and complex family of proteins. Of all the seven isoforms, 14-3-3σ seems to be directly involved in human cancer. 14-3-3σ itself is subject to regulation by p53 upon DNA damage and by epigenetic deregulation. Gene silencing of 14-3-3σ by CpG methylation has been found in many human cancer types. This suggests that therapy-targeting 14-3-3σ may be beneficial for future cancer treatment.     

The 14-3-3s

Multiple members of the 14-3-3 protein family have been found in all eukaryotes so far investigated, yet they are apparently absent from prokaryotes. The major native forms of 14-3-3s are homo- and hetero-dimers, the biological functions of which are to interact physically with specific client proteins and thereby effect a change in the client. As a result, 14-3-3s are involved in a vast array of processes such as the response to stress, cell-cycle control, and apoptosis, serving as adapters, activators, and repressors. There are currently 133 full-length sequences available in GenBank for this highly conserved protein family. A phylogenetic tree based on the conserved middle core region of the protein sequences shows that, in plants, the 14-3-3 family can be divided into two clearly defined groups. The core region encodes an amphipathic groove that binds the multitude of client proteins that have conserved 14-3-3-recognition sequences. The amino and carboxyl termini of 14-3-3 proteins are much more divergent than the core region and may interact with isoform-specific client proteins and/or confer specialized subcellular and tissue localization.     

14-3-3 proteins in neurodegeneration

Among the first reported functions of 14-3-3 proteins was the regulation of tyrosine hydroxylase (TH) activity suggesting a possible involvement of 14-3-3 proteins in Parkinson's disease. Since then the relevance of 14-3-3 proteins in the pathogenesis of chronic as well as acute neurodegenerative diseases, including Alzheimer's disease, polyglutamine diseases, amyotrophic lateral sclerosis and stroke has been recognized. The reported function of 14-3-3 proteins in this context are as diverse as the mechanism involved in neurodegeneration, reaching from basal cellular processes like apoptosis, over involvement in features common to many neurodegenerative diseases, like protein stabilization and aggregation, to very specific processes responsible for the selective vulnerability of cellular populations in single neurodegenerative diseases.Here, we review what is currently known of the function of 14-3-3 proteins in nervous tissue focussing on the properties of 14-3-3 proteins important in neurodegenerative disease pathogenesis.     

14-3-3蛋白研究进展

14-3-3蛋白是高度保守的、所有真核生物细胞中都普遍存在的、在大多数生物物种中由一个基因家族编码的一类蛋白调控家族。它几乎参与生命体所有的生理反应过程,人们在各种组织细胞中发现了各种不同的14-3-3蛋白。作为与磷酸丝氨酸／苏氨酸结合的第一信号分子,14-3-3蛋白在细胞的信号转导中起着至关重要的作用,尤其是它直接参与调节蛋白激酶和蛋白磷酸化酶的活性,被称为蛋白质与蛋白质相互作用的”桥梁蛋白”;它可以与转录因子结合形成复合体,调节相关基因的表达。一些研究表明,14-3-3蛋白调控机制的紊乱可以直接导致疾病的发生,在临床上14-3-3蛋白常常可以作为诊断的标志物。     

Calyculin A-induced vimentin phosphorylation sequesters 14-3-3 and displaces other 14-3-3 partners in vivo

14-3-3 proteins bind their targets through a specific serine/threonine-phosphorylated motif present on the target protein. This binding is a crucial step in the phosphorylation-dependent regulation of various key proteins involved in signal transduction and cell cycle control. We report that treatment of COS-7 cells with the phosphatase inhibitor calyculin A induces association of 14-3-3 with a 55-kDa protein, identified as the intermediate filament protein vimentin. Association of vimentin with 14-3-3 depends on vimentin phosphorylation and requires the phosphopeptide-binding domain of 14-3-3. The region necessary for binding to 14-3-3 is confined to the vimentin amino-terminal head domain (amino acids 1-96). Monomeric forms of 14-3-3 do not bind vimentin in vivo or in vitro, indicating that a stable complex requires the binding of a 14-3-3 dimer to two sites on a single vimentin polypeptide. The calyculin A-induced association of vimentin with 14-3-3 in vivo results in the displacement of most other 14-3-3 partners, including the protooncogene Raf, which nevertheless remain capable of binding 14-3-3 in vitro. Concomitant with 14-3-3 displacement, calyculin A treatment blocks Raf activation by EGF; however, this inhibition is completely overcome by 14-3-3 overexpression in vivo or by the addition of prokaryotic recombinant 14-3-3 in vitro. Thus, phosphovimentin, by sequestering 14-3-3 and limiting its availability to other target proteins can affect intracellular signaling processes that require 14-3-3.     

Cloning of Schistosoma japonicum 14-3-3 epsilon (Sj14-3-3 epsilon), a new member of the 14-3-3 family of proteins from schistosomes

A new member of the 14-3-3 protein family from Schistosoma japonicum has been identified. Phylogenetic analysis showed that this member belongs to the epsilon subfamily of the 14-3-3 proteins, and it is therefore named Sj14-3-3 epsilon. Consistent with the findings for the previously reported S. japonicum 14-3-3 protein (Sj14-3-3), Southern analysis suggested the presence of more than one gene, and/or introns or allelic polymorphism in this epsilon isoform. By RT-PCR, Sj14-3-3 epsilon was shown to be stage-specifically transcribed, being abundant in adults, present in sporocysts but absent in cercariae. Furthermore, mRNA of the epsilon isoform seemed to be much less abundant in the sporocyst stage, compared with Sj14-3-3. This suggests varying requirements of the different 14-3-3 isoforms at different stages of the life cycle.     

14-3-3 Protects against stress-induced apoptosis

Expression of human Bax, a cardinal regulator of mitochondrial membrane permeabilization, causes death in yeast. We screened a human cDNA library for suppressors of Bax-mediated yeast death and identified human 14-3-3β/α, a protein whose paralogs have numerous chaperone-like functions. Here, we show that, yeast cells expressing human 14-3-3β/α are able to complement deletion of the endogenous yeast 14-3-3 and confer resistance to a variety of different stresses including cadmium and cycloheximide. The expression of 14-3-3β/α also conferred resistance to death induced by the target of rapamycin inhibitor rapamycin and by starvation for the amino acid leucine, conditions that induce autophagy. Cell death in response to these autophagic stimuli was also observed in the macroautophagic-deficient atg1Δ and atg7Δ mutants. Furthermore, 14-3-3β/α retained its ability to protect against the autophagic stimuli in these autophagic-deficient mutants arguing against so called ‘autophagic death''. In line, analysis of cell death markers including the accumulation of reactive oxygen species, membrane integrity and cell surface exposure of phosphatidylserine indicated that 14-3-3β/α serves as a specific inhibitor of apoptosis. Finally, we demonstrate functional conservation of these phenotypes using the yeast homolog of 14-3-3: Bmh1. In sum, cell death in response to multiple stresses can be counteracted by 14-3-3 proteins.     

ER export: call 14-3-3

Forward transport of proteins from the ER to the plasma membrane requires escape from the ER's retention machinery. Recent studies suggest that 14-3-3 proteins may mediate ER export of potassium channels destined for the plasma membrane by interfering with dibasic-motif-mediated retention.     

14-3-3蛋白和神经退行性疾病

14-3-3蛋白以二聚体形式存在,识别磷酸丝氨酸／苏氨酸连接的信号分子,通过与其配体蛋白质相互作用,参与细胞信号转导、细胞周期调控和细胞问运输。14-3-3蛋自在脑组织中含量丰富,所有神经元、星形胶质细胞、少突肢质细胞、小胶质细胞的胞液与胞核中都有表述。14-3-3蛋白与神经退行性疾病阿尔茨海默病和帕金森病的发生过程关系密切。     

Survival-promoting functions of 14-3-3 proteins

The 14-3-3 proteins are a family of phosphoserine/phosphothreonine-binding molecules that control the function of a wide array of cellular proteins. We suggest that one function of 14-3-3 is to support cell survival. 14-3-3 proteins promote survival in part by antagonizing the activity of associated proapoptotic proteins, including Bad and apoptosis signal-regulating kinase 1 (ASK1). Indeed, expression of 14-3-3 inhibitor peptides in cells is sufficient to induce apoptosis. Interestingly, these 14-3-3 antagonist peptides can sensitize cells for effective killing by anticancer agents such as cisplatin. Thus, 14-3-3 may be part of the cellular machinery that maintains cell survival, and targeting 14-3-3-ligand interactions may be a useful strategy to enhance the efficacy of conventional anticancer agents.     

14-3-3s are DNA-replication proteins

14-3-3 proteins are conserved multifunctional molecules, involved in many biological processes. Several 14-3-3 isoforms were recently shown to be cruciform DNA-binding proteins, which is a new activity ascribed to the 14-3-3 family. As cruciform-binding proteins, 14-3-3 proteins are putatively involved in the regulation of DNA replication. Inverted repeat sequences that are able to extrude into cruciform structures are a common feature of replication origins in both prokaryotes and eukaryotes. The involvement of cruciform structures in the initiation of DNA replication has been demonstrated. A leading model of 14-3-3 function proposes that they facilitate critical protein-protein interactions, thus serving as a central component of a wide variety of cellular processes.     

14-3-3 proteins in neurological disorders

14-3-3 proteins were originally discovered as a family of proteins that are highly expressed in the brain. Through interactions with a multitude of binding partners, 14-3-3 proteins impact many aspects of brain function including neural signaling, neuronal development and neuroprotection. Although much remains to be learned and understood, 14-3-3 proteins have been implicated in a variety of neurological disorders based on evidence from both clinical and laboratory studies. Here we will review previous and more recent research that has helped us understand the roles of 14-3-3 proteins in both neurodegenerative and neuropsychiatric diseases.     

14-3-3蛋白家族及其临床应用研究进展

14-3-3蛋白家族是一组高度保守的可溶性酸性蛋白质,分子量在28～33kD之间,广泛分布于各种真核生物之中。该蛋白能够特异地结合含有磷酸化丝氨酸或苏氨酸的肽段,参与多种信号转导途径。14-3-3蛋白调节着许多重要细胞生命活动,如：新陈代谢、细胞周期、细胞生长发育、细胞的存活和凋亡以及基因转录,该蛋白家族异常与疾病的发生密切相关,尤其是14-3-3蛋白在脑脊液中的分布与一些神经系统疾病密切相关。14-3-3蛋白已成为一些疾病的临床诊断指标,其作为疾病治疗的靶点也在研究之中。主要阐述了14-3-3蛋白的结构、功能、及其在疾病治疗中的应用。     

14-3-3蛋白家族及其临床应用研究进展

14-3-3蛋白家族是一组高度保守的可溶性酸性蛋白质,分子量在28～33kD之间,广泛分布于各种真核生物之中。该蛋白能够特异地结合含有磷酸化丝氨酸或苏氨酸的肽段,参与多种信号转导途径。14-3-3蛋白调节着许多重要细胞生命活动,如:新陈代谢、细胞周期、细胞生长发育、细胞的存活和凋亡以及基因转录,该蛋白家族异常与疾病的发生密切相关,尤其是14-3-3蛋白在脑脊液中的分布与一些神经系统疾病密切相关。14-3-3蛋白已成为一些疾病的临床诊断指标,其作为疾病治疗的靶点也在研究之中。主要阐述了14-3-3蛋白的结构、功能、及其在疾病治疗中的应用。     

14-3-3 Proteins and regulation of cytoskeleton

The proteins of the 14-3-3 family are universal adapters participating in multiple processes running in the cell. We describe the structure, isoform composition, and distribution of 14-3-3 proteins in different tissues. Different elements of 14-3-3 structure important for dimer formation and recognition of protein targets are analyzed in detail. Special attention is paid to analysis of posttranslational modifications playing important roles in regulation of 14-3-3 function. The data of the literature concerning participation of 14-3-3 in regulation of intercellular contacts and different elements of cytoskeleton formed by microfilaments are analyzed. We also describe participation of 14-3-3 in regulation of small G-proteins and protein kinases important for proper functioning of cytoskeleton. The data on the interaction of 14-3-3 with different components of microtubules are presented, and the probable role of 14-3-3 in developing of certain neurodegenerative diseases is discussed. The data of the literature concerning the role of 14-3-3 in formation and normal functioning of intermediate filaments are also reviewed. It is concluded that due to its adapter properties 14-3-3 plays an important role in cytoskeleton regulation. The cytoskeletal proteins that are abundant in the cell might compete with the other protein targets of 14-3-3 and therefore can indirectly regulate many intracellular processes that are dependent on 14-3-3.