一组多功能的错配修复蛋白

错配修复蛋白是DNA错配修复系统中主要功能蛋白质,主要参与DNA复制过程中对错配碱基的识别和修复.近年来研究表明错配修复蛋白还参与DNA损伤信号的传递、细胞周期的调控、减数分裂和有丝分裂等.错配修复蛋白缺陷会增加患肿瘤的危险性或者直接导致肿瘤;由于错配修复蛋白参与了DNA损伤信号传递、周期调控,错配修复蛋白缺陷还会导致细胞对相关抗癌药物产生耐受.     

miR-9的研究进展

microRNAs(miRNAs)是真核生物中一类长度约为21²5 nt的非编码小分子RNA,在转录后水平调控基因的表达。作为microRNA中的一员——miR-9广泛存在于不同物种中。近年来的研究表明,它在体内发挥重要的生物学作用,参与调控生物体的生长发育及细胞的自我更新和多向分化等多种生理活动,而且其表达紊乱与多种肿瘤密切相关,在肿瘤的发生、侵袭及转移中起着举足轻重的作用。因此,miR-9的研究对于揭示基因表达的调控机理与疾病防治等具有重要意义。     

热休克蛋白（HSPs）在胚胎发育中作用的研究进展

在胚胎发育,特别是早期胚胎发育时期,基因转录活跃、蛋白质大量合成,细胞的增殖和分化非常剧烈,细胞的环境在不断变化,细胞对外界刺激十分敏感。这个时期的HSPs变化和作用表现得非常突出。本文简要总结了近十年有关热休克蛋白在胚胎发育中作用的研究成果。根据胚胎发育地HSPs的依赖性、HSPs基因表达的发育阶段特异性和组织特异性、干扰胚胎发育中HSPs表达程序以后导致胚胎异常发育等现象推测：（1）热休克基因与和／功调控体形形成、肌肉及神经分化,而在胚胎发育中具有看家基因的功能;（2）热休克蛋白作为伴侣分子,通过介导新合成的和／或可逆变性的蛋白质正确折叠、装配、转动及促进不需要的和／或不可逆变性的蛋白质降解,参与胚胎的正常发育和保护胚胎不受不良刺激的影响。这方面的深入研究,必将有助于阐明胚胎发育、细胞增殖、细胞分化和去分化、细胞转化、生物适应性等的分子机理。     

上皮剪接调节蛋白1的研究进展

上皮剪接调节蛋白1(Epithelial splicing regulatory protein 1,ESRP1)是近年来发现的一种上皮细胞特异性剪接因子,主要通过选择性剪接在转录后水平调节基因的表达,继而影响细胞的功能。研究表明,ESRP1通过调控上皮间质转化、细胞周期进展、氧化还原反应以及脂肪酸代谢等过程,多方面参与肿瘤的发生、发展和对治疗药物的反应。小鼠实验研究表明,ESRP1基因敲除可以导致多种器官发育异常,包括颅面部畸形、皮肤屏障功能受损、肾脏以及耳蜗发育不良等。此外,ESRP1还可以通过调控转录因子的活性以及非编码RNA的生成,提高小鼠成纤维细胞重编程为多能干细胞的效率并维持人胚胎干细胞的多能性。鉴于ESRP1在多个研究领域的重要性,本文对ESRP1常见的下游靶分子、信号通路、以及在生理病理环境下所发挥的功能进行阐述,以期进一步指导基础研究和临床应用。     

新型多功能蛋白家族DABB类蛋白研究进展

DABB类蛋白含有1～2个二聚化α+β桶状结构域(dimericα+β barrel domain, DABB)。DABB结构域最早在嗜氢菌的果糖1,6二磷酸醛缩酶的C端和盐胁迫下胡杨的热休克蛋白(Hsp90)、羟脯氨酸糖蛋白(HRGP)中发现。目前报道的该类蛋白主要存在于植物、细菌和真菌中,在动物中尚无报道。在植物中,DABB类蛋白与植物抵御多种病原真菌入侵和非生物胁迫相关。在微生物中,DABB类蛋白主要参与氧化还原相关的代谢过程。目前,关于DABB结构域的具体功能仍不清楚,尚无关于DABB类蛋白的综述文献,本综述从含有此结构域的DABB类蛋白的物种来源、DABB结构域的特点及其保守氨基酸、DABB类蛋白的系统进化等方面,对植物和细菌DABB类蛋白的研究现状进行了总结,并对该类蛋白的研究与应用前景进行了展望。     

γ疱疹病毒亚科肿瘤形成相关蛋白的研究进展

疱疹病毒普遍存在于动物中,分为α、β、γ 3个亚科.γ亚科的多种病毒都具有诱导宿主形成肿瘤的能力.本文讨论了EB病毒、卡波西肉瘤相关疱疹病毒和鼠猴疱疹病毒等3种病毒中参与细胞转化、信号转导、病毒基因组复制和细胞增殖相关基因的结构和功能.     

多功能的胞内衔接蛋白syntenin

Syntenin蛋白是在原核生物及真核生物中广泛存在的一类胞内衔接蛋白（adaptor proteins）. Syntenin由N端结构域（N-terminal domain,NTD）、两个串联的PDZ结构域(postsynaptic density protein, disc large and zonula occludens, PDZ)和C端结构域（C-terminal domain,CTD）组成,在生物进化过程中相对保守. Syntenin蛋白的PDZ结构域可与不同膜受体C端的PDZ结合基序（PDZ-binding motif,PBM）特异性结合, PDZ结构域结合受体的多样性导致了syntenin功能的多样性. 本文综述了syntenin蛋白的发现与分布及其结构特征,对syntenin在肿瘤转移、细胞质膜蛋白组装、参与动物免疫等领域的研究成果进行了较为详细的综述,同时介绍了syntenin在参与动物胚胎发育调控、血管生成和轴突生长等方面的研究进展.     

多功能蛋白ASPP2在肿瘤发生发展中的作用

恶性肿瘤的发生发展是一个多因素、多步骤参与的复杂过程,临床上肿瘤治疗存在复发率高且易耐药等现象,寻找肿瘤易转移、易复发及耐药的干预靶点对恶性肿瘤的诊断和治疗意义重大。多功能蛋白p53促凋亡刺激蛋白2 (ASPP2)是一种单倍体不足肿瘤抑制因子,自被发现以来其在肿瘤中的作用备受关注。ASPP2在多种恶性肿瘤中的表达均明显下调,且其下调水平与肿瘤晚期及不良预后相关,表明其在肿瘤发生发展中扮演重要角色。本文主要综述ASPP2在肿瘤转移、耐药和代谢等方面的研究进展,为以ASPP2为治疗靶点的研究提供理论依据。     

热休克蛋白(HSPs)在胚胎发育中的作用研究进展

本文总结了近十年有关热休克蛋白在动物胚胎发育中动态变化的研究成果,并讨论了热休克蛋白在歪胎发育中可能作用。     

Protein kinase CK2 phosphorylates the cell cycle regulatory protein Geminin

Geminin contributes to cell cycle regulation by a timely inhibition of Cdt1p, the loading factor required for the assembly of pre-replication complexes. Geminin is expressed during S and G2 phase of the HeLa cell cycle and phosphorylated soon after its synthesis. We show here that Geminin is an excellent substrate for protein kinase CK2 in vitro; and that the highly specific CK2 inhibitor tetrabromobenzotriazole (TBB) blocks the phosphorylation of Geminin in HeLa protein extracts and HeLa cells in vivo. The sites of CK2 phosphorylation are located in the carboxyterminal region of Geminin, which carries several consensus sequence motifs for CK2. We also show that a minor phosphorylating activity in protein extracts can be attributed to glycogen synthase kinase 3 (GSK3), which most likely targets a central peptide in Geminin. Treatment of HeLa cells with TBB does not interfere with the ability of Geminin to interact with the loading factor Cdt1.     

Peptide binding to Geminin and inhibitory for DNA replication

Geminin binds to Cdt1 to ensure that DNA replication occurs only once during the cell cycle. To identify the peptide that binds to Geminin and thereby modifies the latter's ability to alter the DNA replication activity in human cancer cells, we screened a phage display library of random peptides in successive cycles of phage library panning and found one peptide sequence that bound to the 31-111 amino acid residues of Geminin. Delivery of this peptide sequence into the nucleus of HCT116 human colon cancer cells resulted in the suppression of BrdU incorporation. These results provide new insights into the function of Geminin and further validate Geminin as a potential therapeutic target in tumors.     

Two Geminin homologs regulate DNA replication in silkworm,Bombyx mori

DNA replication is rigorously controlled in cells to ensure that the genome duplicates exactly once per cell cycle. Geminin is a small nucleoprotein, which prevents DNA rereplication by directly binding to and inhibiting the DNA replication licensing factor, Cdt1. In this study, we have identified 2 Geminin genes, BmGeminin1 and BmGeminn2, in silkworm, Bombyx mori. These genes contain the Geminin conserved coiled-coil domain and are periodically localized in the nucleus during the S-G2 phase but are degraded at anaphase in mitosis. Both BmGeminin1 and BmGeminin2 are able to homodimerize and interact with BmCdt1 in cells. In addition, BmGeminin1 and BmGeminin2 can interact with each other. Overexpression of BmGeminin1 affects cell cycle progression: cell cycle is arrested in S phase, and RNA interference of BmGeminin1 leads to rereplication. In contrast, overexpression or knockdown of BmGeminin2 with RNAi did not significantly affect cell cycle, while more rereplication occurred when BmGeminin1 and BmGeminin2 together were knocked down in cells than when only BmGeminin1 was knocked down. These data suggest that both BmGeminin1 and BmGeminin2 are involved in the regulation of DNA replication. These findings provide insight into the function of Geminin and contribute to our understanding of the regulation mechanism of cell cycle in silkworm.     

Geminin and Brahma act antagonistically to regulate EGFR-Ras-MAPK signaling in Drosophila

Geminin was identified in Xenopus as a dual function protein involved in the regulation of DNA replication and neural differentiation. In Xenopus, Geminin acts to antagonize the Brahma (Brm) chromatin-remodeling protein, Brg1, during neural differentiation. Here, we investigate the interaction of Geminin with the Brm complex during Drosophila development. We demonstrate that Drosophila Geminin (Gem) interacts antagonistically with the Brm-BAP complex during wing development. Moreover, we show in vivo during wing development and biochemically that Brm acts to promote EGFR-Ras-MAPK signaling, as indicated by its effects on pERK levels, while Gem opposes this. Furthermore, gem and brm alleles modulate the wing phenotype of a Raf gain-of-function mutant and the eye phenotype of a EGFR gain-of-function mutant. Western analysis revealed that Gem over-expression in a background compromised for Brm function reduces Mek (MAPKK/Sor) protein levels, consistent with the decrease in ERK activation observed. Taken together, our results show that Gem and Brm act antagonistically to modulate the EGFR-Ras-MAPK signaling pathway, by affecting Mek levels during Drosophila development.     

Loss of Geminin induces rereplication in the presence of functional p53

Strict regulation of DNA replication is essential to ensure proper duplication and segregation of chromosomes during the cell cycle, as its deregulation can lead to genomic instability and cancer. Thus, eukaryotic organisms have evolved multiple mechanisms to restrict DNA replication to once per cell cycle. Here, we show that inactivation of Geminin, an inhibitor of origin licensing, leads to rereplication in human normal and tumor cells within the same cell cycle. We found a CHK1-dependent checkpoint to be activated in rereplicating cells accompanied by formation of gammaH2AX and RAD51 nuclear foci. Abrogation of the checkpoint leads to abortive mitosis and death of rereplicated cells. In addition, we demonstrate that the induction of rereplication is dependent on the replication initiation factors CDT1 and CDC6, and independent of the functional status of p53. These data show that Geminin is required for maintaining genomic stability in human cells.     

Subcellular translocation signals regulate Geminin activity during embryonic development

BACKGROUND INFORMATION: Geminin (Gem) is a protein with roles in regulating both the fidelity of DNA replication and cell fate during embryonic development. The distribution of Gem is predominantly nuclear in cells undergoing the cell cycle. Previous studies have demonstrated that Gem performs multiple activities in the nucleus and that regulation of Gem activation requires nuclear import in at least one context. In the present study, we defined structural and mechanistic features underlying subcellular localization of Gem and tested whether regulation of the subcellular localization of Gem has an impact on its activity in cell fate specification during embryonic development. RESULTS: We determined that nuclear localization of Gem is dependent on a bipartite NLS (nuclear localization signal) in the N-terminus of Xenopus Gem protein. This bipartite motif mapped to a Gem N-terminal region previously shown to regulate neural cell fate acquisition. Microinjection into Xenopus embryos demonstrated that import-deficient Gem was incapable of modulating ectodermal cell fate, but that this activity was rescued by fusion to a heterologous NLS. Cross-species comparison of Gem protein sequences revealed that the Xenopus bipartite signal is conserved in many non-mammalian vertebrates, but not in mammalian species assessed. Instead, we found that human Gem employs an alternative N-terminal motif to regulate the protein's nuclear localization. Finally, we found that additional mechanisms contributed to regulating the subcellular localization of Gem. These included a link to Crm1-dependent nuclear export and the observation that Cdt1, a protein in the pre-replication complex, could also mediate nuclear import of Gem. CONCLUSIONS: We have defined new structural and regulatory features of Gem, and showed that the activity of Gem in regulating cell fate, in addition to its cell-cycle-regulatory activity, requires control of its subcellular localization. Our data suggest that rather than being constitutively nuclear, Gem may undergo nucleocytoplasmic shuttling through several mechanisms involving distinct protein motifs. The use of multiple mechanisms for modulating Gem subcellular localization is congruent with observations that Gem levels and activity must be stringently controlled during cell-cycle progression and embryonic development.     

Geminin Inhibits a Late Step in the Formation of Human Pre-replicative Complexes

The initial step in initiation of eukaryotic DNA replication involves the assembly of pre-replicative complexes (pre-RCs) at origins of replication during the G₁ phase of the cell cycle. In metazoans initiation is inhibited by the regulatory factor Geminin. We have purified the human pre-RC proteins, studied their interactions in vitro with each other and with origin DNA, and analyzed the effects of HsGeminin on formation of DNA-protein complexes. The formation of an initial complex containing the human origin recognition complex (HsORC), HsCdt1, HsCdc6, and origin DNA is cooperative, involving all possible binary interactions among the components. Maximal association of HsMCM2–7, a component of the replicative helicase, requires HsORC, HsCdc6, HsCdt1, and ATP, and is driven by interactions of HsCdt1 and HsCdc6 with multiple HsMCM2–7 subunits. Formation of stable complexes, resistant to high salt, requires ATP hydrolysis. In the absence of HsMCM proteins, HsGeminin inhibits the association of HsCdt1 with DNA or with HsORC-HsCdc6-DNA complexes. However, HsGeminin does not inhibit recruitment of HsMCM2–7 to DNA to form complexes containing all of the pre-RC proteins. In fact, HsGeminin itself is a component of such complexes, and interacts directly with the HsMcm3 and HsMcm5 subunits of HsMCM2–7, as well as with HsCdt1. Although HsGeminin does not prevent the initial formation of DNA-protein complexes containing the pre-RC proteins, it strongly inhibits the formation of stable pre-RCs that are resistant to high salt. We suggest that bound HsGeminin prevents transition of the pre-RC to a state that is competent for initiation of DNA replication.