Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been known for over a decade that inhibition of protein phosphatase 1 (PP1) activity prevents entry into M phase, but the relevant substrate has not been identified. We report here that PP1 is required for dephosphorylation of the Cdc2-directed phosphatase Cdc25 at Ser287 (of Xenopus Cdc25; Ser216 of human Cdc25C), a site that suppresses Cdc25 during interphase. Moreover, PP1 recognizes Cdc25 directly by interacting with a PP1-binding motif in the Cdc25 N-terminus. We have also found that 14-3-3 binding to phospho-Ser287 protects Cdc25 from premature dephosphorylation. Upon entry into M phase, 14-3-3 removal from Cdc25 precedes Ser287 dephosphorylation, suggesting the existence of a phosphatase- independent pathway for 14-3-3 removal from Cdc25. We show here that this dissociation of 14-3-3 from Cdc25 requires the activity of the cyclin-dependent kinase Cdk2, providing a molecular explanation for the previously reported requirement for Cdk2 in promoting mitotic entry. Collectively, our data clarify several steps important for Cdc25 activation and provide new insight into the role of PP1 in Cdc2 activation and mitotic entry.
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PMID:PP1 control of M phase entry exerted through 14-3-3-regulated Cdc25 dephosphorylation. 1459 72

To explore the molecular mechanisms underlying the actions of Taxol and the functionally related molecule epothilone B (EpoB), we have analyzed the gene expression profiles in A549 cells in response to increasing concentrations of these microtubule-stabilizing drugs. An almost identical expression pattern was observed in cells treated with either Taxol or EpoB. Low concentrations of the drugs induced aberrant mitosis including asymmetric and multipolar cell divisions. At drug concentrations that triggered G(2)-M arrest, cells escaped from a prolonged mitotic arrest without cell division, resulting in tetraploid G(1) cells. This mitotic slippage is correlated with diminished expression of cdc2 kinase, topoisomerase IIalpha, BUB3, and BUB2-like protein 1, as well as with an increased expression of 14-3-3-sigma. Poly(ADP-ribose) polymerase cleavage, an early indicator of apoptosis, occurred in cells undergoing mitotic slippage and in aneuploid cells resulting from aberrant mitosis. In contrast, cells arrested in mitosis demonstrated no signal for apoptosis but had an increased expression of survivin, an inhibitor of apoptosis. Induction of aneuploid or tetraploid G(1) cells was accompanied by increased expression of CD95, p21, and BTG2 that may contribute to cell death because their expression was diminished in an EpoB-resistant cell line. In contrast, expression of GADD45 and PTGF-beta could promote cell survival. We conclude that abnormal mitotic exit is required for apoptotic cell death induced by microtubule-stabilizing drugs.
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PMID:Gene expression and mitotic exit induced by microtubule-stabilizing drugs. 1463 18

DNA-responsive checkpoints operate at the G(2)/M transition to prevent premature mitosis in the presence of incompletely replicated or damaged DNA. These pathways prevent mitotic entry, at least in part, by suppressing Cdc25, the phosphatase that activates Cdc2/Cyclin B. To gain insight into how checkpoint signaling controls Cdc25 function, we have carefully examined the individual steps in Cdc25 activation. We found that removal of the regulatory protein, 14-3-3, that binds to phosphorylated Cdc25 during interphase is one of the early steps in mitotic activation. Moreover, our studies unexpectedly implicated the phosphatase PP1 and the G(1)/S kinase Cdk2 in the process of Cdc25 activation. Here we integrate our findings and those of others to propose a model for Cdc25 activation in an effort to provide insight into novel loci of DNA-responsive checkpoint control of mitotic entry.
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PMID:When the checkpoints have gone: insights into Cdc25 functional activation. 1502 Aug 39

p27(Kip1) (p27), a CDK inhibitor, migrates into the nucleus, where it controls cyclin-CDK complex activity for proper cell cycle progression. We report here that the classical bipartite-type basic amino-acid cluster and the two downstream amino acids of the C-terminal region of p27 function as a nuclear localization signal (NLS) for its full nuclear import activity. Importin alpha3 and alpha5, but not alpha1, transported p27 into the nucleus in conjunction with importin beta, as evidenced by an in vitro transport assay. It is known that Akt phosphorylates Thr 157 of p27 and this reduces the nuclear import activity of p27. Using a pull-down experiment, 14-3-3 was identified as the Thr157-phosphorylated p27NLS-binding protein. Although importin alpha5 bound to Thr157-phosphorylated p27NLS, 14-3-3 competed with importin alpha5 for binding to it. Thus, 14-3-3 sequestered phosphorylated p27NLS from importin alpha binding, resulting in cytoplasmic localization of NLS-phosphorylated p27. These findings indicate that 14-3-3 suppresses importin alpha/beta-dependent nuclear localization of Thr157-phosphorylated p27, suggesting implications for cell cycle disorder in Akt-activated cancer cells.
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PMID:14-3-3 suppresses the nuclear localization of threonine 157-phosphorylated p27(Kip1). 1505 70

14-3-3sigma belongs to the 14-3-3 family of proteins, which are involved in the modulation of diverse signal transduction pathways. Loss of 14-3-3sigma expression has been observed in a number of human cancers, suggesting that it may have a role as a tumor suppressor gene. The aim of the study was to investigate the expression and the functional role of 14-3-3sigma in pancreatic ductal adenocarcinoma (PDAC). Expression of 14-3-3sigma was analyzed using laser capture microdissection (LCM), quantitative real-time-PCR (QRT-PCR), DNA arrays, immunohistochemistry and western blot analysis. The role of 14-3-3sigma in apoptosis and cell cycle regulation was evaluated by western blotting, immunoprecipitation and FACS analysis. By QRT-PCR, 14-3-3sigma mRNA levels were 54-fold increased in pancreatic adenocarcinoma in comparison with normal pancreatic samples and localized in pancreatic cancer cells as determined by LCM. In pancreatic cancer cells, the degree of 14-3-3sigma expression was not decisive for the maintenance of G(2)/M cell cycle checkpoint or induction of apoptosis. Responses to radiation or apoptosis-inducing agents were neither accompanied by a significant 14-3-3sigma accumulation nor by a change in association of 14-3-3sigma with cdc2, bad and bax. In conclusion, the marked over-expression of 14-3-3sigma in PADC together with multiple known genetic and epigenetic alterations of potential 14-3-3sigma interacting partners suggests an important role of aberrant 14-3-3sigma downstream signaling in pancreatic cancer.
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PMID:Enhanced expression of 14-3-3sigma in pancreatic cancer and its role in cell cycle regulation and apoptosis. 1507 49

Cdc25 phosphatases activate cyclin-dependent kinases (Cdks) and thereby promote cell cycle progression. In vertebrates, Chk1 and Chk2 phosphorylate Cdc25A at multiple N-terminal sites and target it for rapid degradation in response to genotoxic stress. Here we show that Chk1, but not Chk2, phosphorylates Xenopus Cdc25A at a novel C-terminal site (Thr504) and inhibits it from C-terminally interacting with various Cdk-cyclin complexes, including Cdk1-cyclin A, Cdk1-cyclin B, and Cdk2-cyclin E. Strikingly, this inhibition, rather than degradation itself, of Cdc25A is essential for the Chk1-induced cell cycle arrest and the DNA replication checkpoint in early embryos. 14-3-3 proteins bind to Chk1-phosphorylated Thr504, but this binding is not required for the inhibitory effect of Thr504 phosphorylation. A C-terminal site presumably equivalent to Thr504 exists in all known Cdc25 family members from yeast to humans, and its phosphorylation by Chk1 (but not Chk2) can also inhibit all examined Cdc25 family members from C-terminally interacting with their Cdk-cyclin substrates. Thus, Chk1 but not Chk2 seems to inhibit virtually all Cdc25 phosphatases by a novel common mechanism.
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PMID:Chk1, but not Chk2, inhibits Cdc25 phosphatases by a novel common mechanism. 1527 8

Cyclin-dependent kinase 11 isoforms (CDK11) are members of the p34(cdc2) superfamily. They have been shown to play a role in RNA processing and apoptosis. In the present study, we investigate whether CDK11 interacts with 14-3-3 proteins. Our study shows that the putative 14-3-3 binding site (113-RHRSHS-118) within the N-terminal domain of CDK11(p110) is functional. Endogenous CDK11(p110) binds directly to 14-3-3 proteins and phosphorylation of the serine 118 within the RHRSHS motif seems to be required for the binding. Besides, CDK11(p110) is capable of interacting with several different isoforms of 14-3-3 proteins both in vitro and in vivo. The interaction of 14-3-3 gamma with CDK11(p110) occurs throughout the entire cell cycle and reaches maximum at the G2/M phase. Interestingly, 14-3-3 gamma shows strong interaction with N-terminal portion of caspase-cleaved CDK11(p110) (CDK11(p60)) product at 48 h after Fas treatment, which correlates with the maximal cleavage level of CDK11(p110) and the maximum activation level of CDK11 kinase activity during apoptosis. Collectively, these results suggest that CDK11 kinases could be regulated by interaction with 14-3-3 proteins during cell cycle and apoptosis.
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PMID:The cyclin-dependent kinase 11 interacts with 14-3-3 proteins. 1588 43

Hyperphosphorylation and aggregation of protein tau are typical for neurodegenerative tauopathies, including Alzheimer's disease (AD). We demonstrate here that human tau expressed in yeast acquired pathological phosphoepitopes, assumed a pathological conformation, and formed aggregates. These processes were modulated by yeast kinases Mds1 and Pho85, orthologues of GSK-3beta and cdk5, respectively. Surprisingly, inactivation of Pho85 increased phosphorylation of tau-4R, concomitant with increased conformational change defined by antibody MC1 and a 40-fold increase in aggregation. Soluble protein tau, purified from yeast lacking PHO85, spontaneously and rapidly formed tau filaments in vitro. Further fractionation of tau by anion-exchange chromatography yielded a hyperphosphorylated monomeric subfraction, termed hP-tau/MC1, with slow electrophoretic mobility and enriched with all major epitopes, including MC1. Isolated hP-tau/MC1 vastly accelerated in vitro aggregation of wild-type tau-4R, demonstrating its functional capacity to initiate aggregation, as well as its structural stability. Combined, this novel yeast model recapitulates hyperphosphorylation, conformation, and aggregation of protein tau, provides insight in molecular changes crucial in tauopathies, offers a source for isolation of modified protein tau, and has potential for identification of modulating compounds and genes.
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PMID:Identification and isolation of a hyperphosphorylated, conformationally changed intermediate of human protein tau expressed in yeast. 1611 83

Co-ordinated progression through the cell cycle is essential for the maintenance of genomic integrity. Several checkpoint mechanisms guarantee that the next step in cell cycle progression is only entered after error-free completion of the previous phase. Cell cycle deregulation caused by changes in 14-3-3 expression has been implicated in cancer formation. 14-3-3 proteins function at several key points in G(1)/S- and G(2)/M-transition by binding to regulatory proteins and modulating their function. In most cases, the association with 14-3-3 proteins requires a specific phosphorylation of the protein ligand and mediates cell cycle arrest. 14-3-3 binding may lead to cytoplasmic sequestration of the protein ligand but may also have other functional consequences. The 14-3-3sigma gene is induced by p53 and its product inhibits G(2)/M progression by cytoplasmatic sequestration of CDC2-cyclin B complexes. In addition, 14-3-3 proteins have been implicated in the transcriptional regulation of CDK-inhibitors as they modulate the transcription factors p53, FOXO and MIZ1. Effects of 14-3-3 proteins on cell cycle progression and the regulation of 14-3-3 activity during the cell cycle are reviewed in this chapter.
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PMID:14-3-3 proteins in cell cycle regulation. 1669 62

Microtubule associated protein tau, which is expressed in six alternatively spliced molecular isoforms in human brain, is abnormally hyperphosphorylated in Alzheimer disease and related tauopathies. Here, we show (i) that GSK-3alpha and neither GSK-3beta nor cdk5 can phosphorylate tau at Ser262 and phosphorylation at Ser235 by cdk5 primes phosphorylation at Thr231 by GSK-3alpha/beta; (ii) that tau isoforms with two N-terminal inserts (tau4L, tau3L) are phosphorylated by cdk5 plus GSK-3 at Thr231 markedly more than isoforms lacking these inserts (tau4, tau3); and (iii) that Thr231 is phosphorylated approximately 50% more in free tau than in microtubule-bound tau, and the phosphorylation at this site results in the dissociation of tau from microtubules. These findings suggest that the phosphorylation of tau at Thr231 and Ser262 by cdk5 plus GSK-3, which inhibits its normal biological activity, is regulated both by its amino terminal inserts and its physical state.
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PMID:Regulation of phosphorylation of tau by cyclin-dependent kinase 5 and glycogen synthase kinase-3 at substrate level. 1704 92


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