周期蛋白和周期蛋白依赖性激酶及相关激酶抑制剂在细胞周期进程中的调控机制研究进展

在细胞发育过程中,细胞周期起着至关重要的作用。细胞周期进程主要受细胞周期蛋白依赖性激酶(cyclin dependent kinase, CDK)、周期蛋白和内源性CDK抑制剂(cyclin-dependent kinase inhibitors,CKI)调控。其中,CDK是主要的细胞周期调节因子,可与周期蛋白结合形成周期蛋白-CDK复合物,从而使数百种底物磷酸化,调控分裂间期和有丝分裂进程。各类细胞周期蛋白的活性异常,可引起不受控制的癌细胞增殖,导致癌症的发生与发展。因此,了解CDK的活性变化情况、周期蛋白-CDK的组装以及CKI的作用,将有助于了解细胞周期进程中潜在的调控过程,为癌症与疾病的治疗和CKI治疗药物的研发提供基础。本文关注了CDK激活和灭活的关键事件,并总结了周期蛋白-CDK在特定时期及位置的调控过程,以及相关CKI治疗药物在癌症及疾病中的研究进展,最后简单阐述了细胞周期进程研究面临的问题和存在的挑战,以期为后续细胞周期进程的深入研究提供参考和思路。     

CDK16在人类癌症中的作用与机制

细胞周期蛋白依赖性激酶16(cyclin-dependent kinase 16,CDK16)是细胞周期蛋白依赖性激酶(cyclin-dependent kinase,CDK)家族中重要的成员之一,参与了一系列生物学过程,包括调控细胞的周期进程、肿瘤转移、凋亡、代谢和自噬等。CDK16在肿瘤的发生发展中起到重要的调控作用,包括肝癌、乳腺癌、肺癌、肠癌等。因此,CDK16在肿瘤早期诊断、预后、靶向治疗等方面具有巨大的临床应用潜力。本文就CDK16在人类癌症中的作用及机制进行综述,并对靶向CDK16在临床的应用展开讨论。     

WEE1 激酶及其抑制剂在抗肿瘤治疗中的应用进展

WEE1激酶是一种细胞周期调节蛋白,能调控细胞周期蛋白依赖性激酶1(cyclin-dependent kinase 1,CDK1)的磷酸化状态,从而调节CDK1与细胞周期蛋白B(cyclin B)复合物的活性从而实现对细胞周期的调控,且对DNA损伤检查点具有重要的调节作用。WEE1是G2/M期阻滞的关键基因,起着重要的监测作用,在一些癌症中过表达,抑制或下调WEE1激酶均能引发有丝分裂灾难,因此WEE1激酶抑制剂可能在抗癌治疗中有关键作用。在癌症的治疗过程中,WEE1抑制剂与DNA损伤剂、化学药物等联合使用会得到比单独使用更为有效,且在p53缺失的癌细胞中能发挥更好的效果。目前WEE1已成为许多癌症治疗的关键靶点之一,其抑制剂MK-1775已处于临床研究阶段,且能增强一些DNA损伤剂对p53缺失的癌细胞的杀伤能力。本文就WEE1激酶及其抑制剂在抗癌治疗中的应用作一综述。     

细胞周期蛋白依赖性激酶2的功能及其抑制剂的研究

细胞周期蛋白依赖性激酶2(cyclin-dependent kinase 2,CDK2)是CDK家族中的重要成员之一。CDK2的表达或功能异常与多种疾病(如肿瘤、病毒复制与感染、免疫缺陷性疾病和雄性不育等)发生机制密切相关。CDK2抑制剂已成为抗肿瘤药物研发中的一个重要靶点。该文对CDK2在细胞周期调控、细胞增殖、细胞分化、细胞凋亡中的作用机制以及CDK2抑制剂的研发进行综述。     

Polo样激酶1抑制剂Rigosertib对细胞放射损伤的防护作用

DNA双链断裂是电离辐射诱发最严重DNA损伤,能启动细胞周期阻滞、修复和死亡系列信号反应,其中周期阻滞是DNA损伤应答的重要过程,为DNA损伤修复提供了充足的时间。周期蛋白依赖性激酶4/6(cyclin-dependent kinase 4/6,CDK4/6)、周期蛋白依赖性激酶1(cyclin-dependent kinase1,CDK1)和Polo样激酶1(Polo-like kinase 1,PLK1)等是细胞周期调控关键激酶,其抑制剂可以阻滞细胞周期进程,是否具有细胞放射防护作用有待进一步探究。本文选择人宫颈癌细胞HeLa、人正常乳腺细胞MCF-10A以及人脐静脉上皮细胞HUVEC为研究对象,研究比较了PLK1抑制剂Rigosertib、Volasertib, CDK4/6抑制剂Palbocilib, CDK1抑制剂Ro-3306的辐射防护作用。流式细胞术检测表明,Rigosertib、Volasertib、Ro-3306将细胞阻滞于G₂期(P<0.05,P<0.01或P<0.001),Palbocilib将细胞阻滞于G₁     

植物细胞周期调控因子及其功能的研究进展

细胞周期调控因子能通过影响细胞周期对植物细胞的生长、分裂和分化产生作用,进而调节植物的生长发育。本文综述了近几年来植物细胞周期调控因子中细胞周期蛋白（cyclin,CYC）、周期蛋白依赖激酶（cyclin-dependent kinase,CDK）等的作用机理及研究进展,阐述了各调控因子在植物生长发育过程中的作用。     

细胞周期负调控

调控细胞周期的关键是调节细胞周期蛋白依赖性蛋白激酶(CDK)的活性。细胞周期蛋白可结合并激活CDK,CDK活性还可通过磷酸化作用调节。因此细胞周期负调控包括以下3点:①细胞周期蛋白降解速度;②CDK磷酸化状态;③CDK抑制蛋白(CKI)。酵母中CKI包括FAR1,p40、PHO81,哺乳动物CKI有p21家族(包括p21、p27)及p16家族(包括p16、p15)。细胞周期负调控与抑癌基因密切相关,是不同抗肿瘤因子作用的共同途径。     

p21亚细胞定位与肿瘤

p21是一种重要的周期蛋白依赖性激酶抑制因子(cyclin-dependent-kinase inhibitor, CKI),主要通过调控细胞周期维持细胞的生长和增殖。此外, p21还参与调控细胞凋亡、细胞衰老以及细胞运动等过程。近年来越来越多的研究表明, p21的功能具有双重性。当p21定位在细胞核时,其主要通过抑制周期蛋白依赖性激酶(cyclin-dependent kinases, CDKs)的活性介导细胞周期停滞,抑制细胞增殖;当定位在细胞质时, p21能够促进细胞增殖。本文主要对p21的生物学功能、亚细胞定位调控机制及其在肿瘤研究中的最新进展予以综述。     

CDK2-AP1改变与高频微卫星不稳定肠癌发生的关系

细胞周期素依赖激酶2-相关蛋白1（cyclin—dependent kinase 2-associated protein 1,CDK2-AP1）基因是一个重要的生长抑制基因,主要通过抑制细胞周期素依赖激酶2（cyclin—dependent kinase 2,CDK2）的活性发挥其生长抑制作用。新的研究发现,在结直肠癌患者中,CDK2-AP1的差异表达与微卫星状态相关,其表达缺陷是高频微卫星不稳定（microsatellite instability—high,MSI—H）结直肠癌（colorectal cancer,CRC）恶性转化的一个显著特点,并且参与疾病的发生发展。     

细胞周期依赖性激酶4(Cdk4)在肿瘤发生发展中的作用

细胞周期依赖性激酶4(cdk4)是丝氨酸/苏氨酸激酶家族的成员,调控细胞周期G1期的进程.Cdk4与周期蛋白D(cyclin D)结合形成复合物,在G1期的演进中起重要作用,一旦出现失调就可能导致癌症的发生,并且也有一系列的内在和外在的信号调控着这个复合物.Cdk4以及它的调控因子在肿瘤的发生和转移中都显示了重要的作用.     

Cdk-counteracting phosphatases unlock mitotic exit

Entry into mitosis of the eukaryotic cell cycle is driven by rising cyclin-dependent kinase (Cdk) activity. During exit from mitosis, Cdk activity must again decline. Cdk downregulation by itself, however, is not able to guide mitotic exit, if not a phosphatase reverses mitotic Cdk phosphorylation events. In budding yeast, this role is played by the Cdc14 phosphatase. We are gaining an increasingly detailed picture of its regulation during anaphase, and of the way it orchestrates ordered progression through mitosis. Much less is known about protein dephosphorylation during mitotic exit in organisms other than budding yeast, but evidence is now mounting for crucial contributions of regulated phosphatases also in metazoan cells.     

A Novel Member of the Cyclin-Dependent Kinase Family in Paramecium tetraurelia

Passage through the cell cycle in eukaryotes requires the successive activation of different cyclin-dependent protein kinases. Here, we describe the identification and characterization of a novel class of cyclin-dependent protein kinase, termed Cdk2, in the ciliate Paramecium tetraurelia. It is 301 amino acids long, 7 amino acids shorter than Cdk1, the CDK that is associated with macronuclear DNA synthesis. All the catalytic domains typical of protein kinases can be located within the sequence and putative regulatory phosphorylation sites equivalent to Thr14, Tyr15, and Thr161 in human CDK1 are also conserved. The 'PSTAIRE' region characteristic of most CDKs is perfectly conserved. Cdk2 shares only 48% homology to Cdk1 at the amino acid level, suggesting that the evolutionary separation of Cdk1 and Cdk2 is ancient, and implying that they have different roles in cell cycle regulation. Like Cdk1, Cdk2 does not bind to yeast p13suc1, even though it has better conservation of p13suc1 binding sites than Cdk1 does. The Cdk2 protein level is relatively constant throughout the vegetative cell cycle. Cdk2 exhibits kinase activity towards bovine histone H1 in vitro with the maximal level late in the cell cycle, suggesting it may be involved in the regulation of cytokinesis. Our results further support the view that an analogue of the cyclin-dependent kinase cell cycle regulatory system like that of yeast and higher eukaryotic cells operates in Paramecium and that a family of cyclin-dependent kinases may control different aspects of the Paramecium cell cycle.     

Cyclin Proteolysis and CDK Inhibitors: Two Redundant Pathways to Maintain Genome Stability in Mammalian Cells

Cyclin-dependent kinases (CDKs) are regulated by cyclin proteolysis and CDK inhibitors (CKIs) during mitotic exit and G1 phase in yeast and Drosophila, and disruption of both regulatory pathways leads to genomic instability. Our study using mouse cell lines that constitutively express a stabilized mutant of cyclin A revealed that three CKIs, p21, p27, and Rb-related p107, are responsible for cyclin proteolysis-independent inactivation of CDK during mitotic exit and G1. Enforced expression of cyclin A in the cells lacking all three CKIs induced rapid tetraploidization. Thus, the redundant pathways consisting of cyclin proteolysis and CKIs control CDK activity during mitotic exit and contribute to maintenance of genome stability in mammalian cells.     

A new pathway for mitogen-dependent cdk2 regulation uncovered in p27(Kip1)-deficient cells

BACKGROUND: The ability of cyclin-dependent kinases (CDKs) to promote cell proliferation is opposed by cyclin-dependent kinase inhibitors (CKIs), proteins that bind tightly to cyclin-CDK complexes and block the phosphorylation of exogenous substrates. Mice with targeted CKI gene deletions have only subtle proliferative abnormalities, however, and cells prepared from these mice seem remarkably normal when grown in vitro. One explanation may be the operation of compensatory pathways that control CDK activity and cell proliferation when normal pathways are inactivated. We have used mice lacking the CKIs p21(Cip1) and p27(Kip1) to investigate this issue, specifically with respect to CDK regulation by mitogens. RESULTS: We show that p27 is the major inhibitor of Cdk2 activity in mitogen-starved wild-type murine embryonic fibroblasts (MEFs). Nevertheless, inactivation of the cyclin E-Cdk2 complex in response to mitogen starvation occurs normally in MEFs that have a homozygous deletion of the p27 gene. Moreover, CDK regulation by mitogens is also not affected by the absence of both p27 and p21. A titratable Cdk2 inhibitor compensates for the absence of both CKIs, and we identify this inhibitor as p130, a protein related to the retinoblastoma gene product Rb. Thus, cyclin E-Cdk2 kinase activity cannot be inhibited by mitogen starvation of MEFs that lack both p27 and p130. In addition, cell types that naturally express low amounts of p130, such as T lymphocytes, are completely dependent on p27 for regulation of the cyclin E-Cdk2 complex by mitogens. CONCLUSIONS: Inhibition of Cdk2 activity in mitogen-starved fibroblasts is usually performed by the CKI p27, and to a minor extent by p21. Remarkably p130, a protein in the Rb family that is not related to either p21 or p27, will directly substitute for the CKIs and restore normal CDK regulation by mitogens in cells lacking both p27 and p21. This compensatory pathway may be important in settings in which CKIs are not expressed at standard levels, as is the case in many human tumors.     

The Cyclin-Dependent Kinase (CDK) Family Member PNQALRE/CCRK Supports Cell Proliferation but has no Intrinsic CDK-Activating Kinase (CAK) Activity

The cyclin-dependent kinases (CDKs) that drive the eukaryotic cell cycle must be phosphorylated within the activation segment (T-loop) by a CDK-activating kinase (CAK) to achieve full activity. Although a requirement for CDK-activating phosphorylation is conserved throughout eukaryotic evolution, CAK itself has diverged between metazoans and budding yeast, and fission yeast has two CAKs, raising the possibility that additional mammalian enzymes remain to be identified. We report here the characterization of PNQALRE (also known as CCRK or p42), a member of the mammalian CDK family most similar to the cell-cycle effectors Cdk1 and Cdk2 and to the CAK, Cdk7. Although PNQALRE/CCRK was recently proposed to activate Cdk2, we show that the monomeric protein has no intrinsic CAK activity. Depletion of PNQALRE by >80% due to RNA interference (RNAi) impairs cell proliferation, but fails to arrest the cell cycle at a discrete point. Instead, both the fraction of cells with a sub-G1 DNA content and cleavage of poly(ADP-ribose) polymerase (PARP) increase. PNQALRE knockdown did not diminish Cdk2 T-loop phosphorylation in vivo or decrease CAK activity of a cell extract. In contrast, depletion of Cdk7 by RNAi causes a proportional decrease in the ability of an extract to activate recombinant Cdk2. Our data do not support the proposed function of PNQALRE/CCRK in activating CDKs, butinstead reinforce the notion of Cdk7 as the major, and to date the only, CAK in mammalian cells.