Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two previously unidentified human cdc25 genes have been isolated, cdc25A and cdc25B. Both genes rescue a cdc25ts mutant of fission yeast. Microinjection of anti-cdc25A antibodies into HeLa cells causes their arrest in mitosis. cdc25A and cdc25B display endogenous tyrosine phosphatase activity that is stimulated several-fold, in the absence of cdc2, by stoichiometric addition of either cyclin B1 or B2 but not A or D1. Association between cdc25A and cyclin B1/cdc2 was detected in the HeLa cells. These findings indicate that B-type cyclins are multifunctional proteins that not only act as M phase regulatory subunits of the cdc2 protein kinase, but also activate the cdc25 tyrosine phosphatase, of which cdc2 is the physiological substrate. A region of amino acid similarity between cyclins and tyrosine PTPases has been detected. This region is absent in cdc25 phosphatases. The motif may represent an activating domain that has to be provided to cdc25 by intermolecular interaction with cyclin B.
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PMID:Specific activation of cdc25 tyrosine phosphatases by B-type cyclins: evidence for multiple roles of mitotic cyclins. 183 78

The cdc2 protein kinase, first identified as a cell cycle gene required for transition into the S- and M-phases of budding and fission yeast, has been shown to act as a key component in the regulation of the eukaryotic cell cycle. The periodic activation of cdc2 kinase, which is required for entry into M-phase, is regulated by subunit association with cyclin B, the cdc25, wee1, mik1 gene products and differential phosphorylation of the cdc2 protein. Phosphorylation at Tyr 15 inhibits activation of the cdc2/cdc13 complex whereas phosphorylation of Thr 167 is required for kinase activity.
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PMID:Regulation of cdc2 activity in Schizosaccharomyces pombe: the role of phosphorylation. 184 38

Two families of cyclin-like proteins have been found in S. cerevisiae. The clb proteins are the mitotic cyclins. The cln proteins provide an essential function, are required for the G1/S transition, and appear to be rate-limiting for START, but have no obvious role elsewhere in the cycle. The cln proteins are unstable; they form complexes with cdc28; the complexes have protein kinase activity; and at least one of the clns oscillates in abundance through the cell cycle. The action of the cln cyclins at START suggests that they may be 'G1 cyclins'.
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PMID:Saccharomyces cerevisiae cell cycle: cdc28 and the G1 cyclins. 184 39

The cyclins comprise a family of proteins which combine with protein kinase subunits encoded by members of the cdc2 family. The active protein kinase thus formed phosphorylates target proteins in the cell and promotes certain cell cycle transitions. Cyclins A and B show the unusual property of sudden and specific proteolysis shortly before the metaphase-anaphase transition during mitosis. The destruction of the cyclins leads to rapid loss of activity of their kinase companions. The 'simple idea' referred to in the title of this article was that accumulation of cyclin formed maturation promoting factor (MPF), the enzyme that promotes the G2-M transition, and cyclin destruction turned off MPF. The complexity refers to additional controls of cdc2 activity, such as its reversible phosphorylation. Furthermore, many new members of the cyclin family have recently been discovered that may play a role in the regulation of the G1-S transition, and in higher organisms, the cdc2 family is also more numerous than was at first appreciated. Cyclins make important contributions both to subcellular localization and the substrate specificity of their companion kinase subunits. It is too early to say if the entire range of cyclin-like and cdc2-like protein kinases are involved in the control of the cell cycle.
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PMID:Cyclins and their partners: from a simple idea to complicated reality. 184 40

In the fission yeast Schizosaccharomyces pombe, mitosis is initiated following the activation of the cdc2+/cyclin B kinase. The cdc2+/cyclin B kinase is positively regulated by cdc25+ tyrosine phosphatase and negatively regulated by wee1+/mik1+ tyrosine kinases. This regulatory system is evolutionarily conserved throughout higher eukaryotes. Drosophila and humans contain a cdc25+ gene homolog called String and CDC25Hs (hereafter referred to as CDC25Hul), respectively. We recently cloned a wee1+ homolog (WEE1Hu) and two additional cdc25+ homologs (CDC25Hu2 and CDC25Hu3) from human cells. Consequently, human cells contain at least one wee1+ and three cdc25+ homologs. Both CDC25Hu1 and CDC25Hu2 resemble the cdc25+ gene not only in structure and function but also in the mode of expression. They are expressed mostly in G2. On the other hand, CDC25Hu3 is expressed mostly in early S, indicating that it has some novel function in the early phase of the cell cycle. In all the cell lines examined, CDC25Hu2 is expressed to a greater extent than CDC25Hu1 or CDC25Hu3. The expression of CDC25Hu2 is particularly high in various cancer cells including those transformed by SV40 or human papilloma virus type 16 E6, E7, both of which are well known for their ability to induce genomic instability. In addition, there is a noticeable correlation between the extent of aneuploidy and the level of CDC25Hu2 expression in the cancer cells examined. In view of the fact that overexpression of cdc25+ under certain conditions induces genomic instability in the fission yeast, overexpression of CDC25Hu2 associated with many cancer cells might play at least a role in the induction of their chromosomal abnormalities.
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PMID:Mammalian G2 regulatory genes and their possible involvement in genetic instability in cancer cells. 184 45

MPF, a protein kinase complex consisting of cyclin and p34cdc2 subunits, promotes the G2 to M phase transition in eukaryotic cells. The pathway of activation and inactivation of MPF is not well understood, although there is strong evidence that removal of phosphate from a tyrosine residue on p34cdc2 is part of the activation process. INH was originally identified as an activity that could inhibit the posttranslational activation of a latent form of MPF, called pre-MPF, in immature (G2 phase-arrested) Xenopus oocytes. We have purified INH and demonstrated that it is a form of protein phosphatase 2A. Both INH and the catalytic subunit of protein phosphatase 2A can directly inactivate an isolated p34cdc2-cyclin complex. Both cyclin and p34cdc2 become dephosphorylated; the rate of inactivation closely parallels the removal of phosphate from a specific site on p34cdc2. We propose that INH opposes MPF activation by reversing this critical phosphorylation.
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PMID:INH, a negative regulator of MPF, is a form of protein phosphatase 2A. 184 21

A cyclin B homolog was identified in Saccharomyces cerevisiae using degenerate oligonucleotides and the polymerase chain reaction. The protein, designated Scb1, has a high degree of similarity with B-type cyclins from organisms ranging from fission yeast to human. Levels of SCB1 mRNA and protein were found to be periodic through the cell cycle, with maximum accumulation late, most likely in the G2 interval. Deletion of the gene was found not to be lethal, and subsequently other B-type cyclins have been found in yeast functionally redundant with Scb1. A mutant allele of SCB1 that removes an amino-terminal fragment of the encoded protein thought to be required for efficient degradation during mitosis confers a mitotic arrest phenotype. This arrest can be reversed by inactivation of the Cdc28 protein kinase, suggesting that cyclin-mediated arrest results from persistent protein kinase activation.
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PMID:A cyclin B homolog in S. cerevisiae: chronic activation of the Cdc28 protein kinase by cyclin prevents exit from mitosis. 184 58

FUS3 is functionally redundant with KSS1, a homologous yeast protein kinase, for a step(s) in signal transduction between the beta subunit of the guanine nucleotide binding protein (G protein), STE4, and the mating type-specific transcriptional activator, STE12. Either FUS3 or KSS1 can execute this function; when neither gene encoding these protein kinases is present, signal transduction is blocked, causing sterility. This functional redundancy is strain dependent; some standard laboratory strains (S288C) are kss1-. FUS3 has additional functions required for cell cycle arrest and vegetative growth that do not overlap with KSS1 functions. FUS3 mediates cell cycle arrest during mating through transcriptional repression of two G1 cyclins (CLN1 and CLN2) and through posttranscriptional inhibition of a third G1 cyclin (CLN3). FUS3 is also required for vegetative growth in haploid strains dependent upon CLN3 for cell cycle progression but is not required in strains dependent upon either CLN1 or CLN2, suggesting a functional divergence among the three G1 cyclins. The diverse roles for FUS3 suggest that the FUS3 protein kinase has multiple substrates, some of which may be shared with KSS1.
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PMID:FUS3 represses CLN1 and CLN2 and in concert with KSS1 promotes signal transduction. 194 50

Entry into M phase in the eukaryotic cell cycle is controlled by the oscillating activity of MPF. The active component of MPF is now known to be the p34cdc2 protein kinase originally found in yeast. The p34cdc2 protein kinase displays a characteristic M-phase-specific histone H1 kinase activity when it interacts with cyclins, which are proteins that oscillate through the cell cycle and are thought to regulate p34cdc2 activity. Cyclins can induce M phase when introduced into fully grown Xenopus oocytes and cyclin may play a role in normal oocyte maturation. Small Xenopus oocytes do not mature in response to the hormonal triggers which act on stage 6 oocytes. We introduced cyclin into stage 4 (small) Xenopus oocytes and showed that it activates MPF in these cells, probably by interacting with endogenous p34cdc2 kinase. We made labelled extracts from cyclin-mRNA-injected stage 4 oocytes and used them to show differential stability of clam cyclins A and B at oocyte maturation. The relative stability of the two forms of cyclin related directly to their ability to stabilize crude MPF preparations from injected stage 6 oocytes.
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PMID:In vivo regulation of MPF in Xenopus oocytes. 197 3

Preservation of the shape and the integrity of multicellular eukaryotes needs rigorous cell proliferation monitoring. During the prereplicative G1 phase, a finely adjusted and specific control supervises the proliferant/non proliferant states of the cells. Some molecular mechanisms of growth regulation have been identified in recent years. Changes in normal cell attachment on extracellular matrix and intercellular chemical signalling (secretion of informative molecules) activate intracellular signals for division. The transduction mechanisms of the extracellular signalling to the nucleus have been partially elucidated for steroid hormones and growth factors. Molecular biology research and proto-oncogene discoveries have led to considerable progress in understanding the role of these normal genes in the control of cellular proliferation. The initiation of the response to extracellular factors requires: i), direct transducers (specific binding of the steroid hormone on its cytoplasmic or nuclear receptor and high affinity binding of this activated complex to specific DNA sequences); and ii) indirect transducers (binding of growth factors on extracellular domains of specific receptor proteins which convert this extracellular event into several intracellular signals, secondary messengers, protein kinases and specific nuclear regulatory factors). Whatever the transduction system, nuclear events control transcription of growth regulatory genes. The series of enzymatic reactions set in motion by indirect transduction systems require strict regulation systems, the diversity and the complexity of which has been perceived in studies on jun and fos gene families. Each proliferation step is governed by growth stimulators and growth inhibitors, the transformation of normal cells to cancer cells resulting from alterations of these regulatory process. Independent of extracellular stimuli and of their transfer to the nucleus, intracellular controls coordinate cell cycle phases (G1, S, G2 and M) to produce daughter cells identical to the original cell. Two control points are particularly critical: one in G1 (the "start" point) and the other in G2 just before mitosis. Although intermediate steps between extracellular and intracellular controls are still unknown, yeast gene analyses have allowed determination of molecular regulatory mechanisms implicated in the passage of these critical points. A considerable advance was made by the discovery that some of the involved components presented strong sequence and function homologies in organisms from yeast to man, suggesting a phyllogenetically conserved mechanism. It seems likely that the phosphorylation state of protein p34, its association with a G1-phase specific cyclin or a M-phase specific cyclin, and its protein kinase activity regulate the proliferation state of higher eukaryotic cells. In spite of significant advances, much research is still necessary to elucidate all the mechanisms involved in cell cycle control.
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PMID:[Different regulation systems of cell cycle events (dysregulation of these events in the tumoral cell)]. 202 83


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