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)

Cyclin E/Cdk2 acts at the G1/S-phase transition to promote the E2F transcriptional program and the initiation of DNA synthesis. To explore further how cyclin E/Cdk2 controls S-phase events, we examined the subcellular localization of the cyclin E/Cdk2 interacting protein p220(NPAT) and its regulation by phosphorylation. p220 is localized to discrete nuclear foci. Diploid fibroblasts in Go and G1 contain two p220 foci, whereas S- and G2-phase cells contain primarily four p220 foci. Cells in metaphase and telophase have no detectable focus. p220 foci contain cyclin E and are coincident with Cajal bodies (CBs), subnuclear organelles that associate with histone gene clusters on chromosomes 1 and 6. Interestingly, p220 foci associate with chromosome 6 throughout the cell cycle and with chromosome 1 during S phase. Five cyclin E/Cdk2 phosphorylation sites in p220 were identified. Phospho-specific antibodies against two of these sites react with p220 within CBs in a cell cycle-specific manner. The timing of p220 phosphorylation correlates with the appearance of cyclin E in CBs at the G1/S boundary, and this phosphorylation is maintained until prophase. Expression of p220 activates transcription of the histone H2B promoter. Importantly, mutation of Cdk2 phosphorylation sites to alanine abrogates the ability of p220 to activate the histone H2B promoter. Collectively, these results strongly suggest that p220(NPAT) links cyclical cyclin E/Cdk2 kinase activity to replication-dependent histone gene transcription.
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PMID:Cell cycle-regulated phosphorylation of p220(NPAT) by cyclin E/Cdk2 in Cajal bodies promotes histone gene transcription. 1099 87

In Xenopus development the mid-blastula transition (MBT) marks a dramatic change in response of the embryo to ionizing radiation. Whereas inhibition of cyclin D1-Cdk4 and cyclin A2-Cdk2 by p27(Xic1) has been linked to cell cycle arrest and prevention of apoptosis in embryos irradiated post-MBT, distinct roles for these complexes during apoptosis are evident in embryos irradiated pre-MBT. Cyclin A2 is cleaved by caspases to generate a truncated complex termed Delta N-cyclin A2-Cdk2, which is kinase active, not inhibited by p27(Xic1), and not sensitive to degradation by the ubiquitin-mediated proteasome pathway. Moreover, Delta N-cyclin A2-Cdk2 has an expanded substrate specificity and can phosphorylate histone H2B at Ser-32, which may facilitate DNA cleavage. Consistent with a role for cyclin A2 in apoptosis, the addition of Delta N-cyclin A2-Cdk2, but not full-length cyclin A2-Cdk2, to Xenopus egg extracts triggers apoptotic DNA fragmentation even when caspases are not activated. Similarly, cyclin D1 is targeted by caspases, and the generated product exhibits higher affinity for p27(Xic1), leading to reduced phosphorylation of the retinoblastoma protein (pRB) during apoptosis. These data suggest that caspase cleavage of both cyclin D1-Cdk4 and cyclin A2-Cdk2 promotes specific apoptotic events in embryos undergoing apoptosis in response to ionizing radiation.
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PMID:A role for G1/S cyclin-dependent protein kinases in the apoptotic response to ionizing radiation. 1217 96

p220(NPAT) is a substrate of cyclin E/Cdk2 that localizes in nuclear organelles called Cajal bodies in a cell cycle-regulated manner. In normal diploid fibroblasts, p220 is concentrated in two Cajal bodies tethered to histone gene clusters at chromosome 6p21 during G(1), S, and G(2) phases and two additional Cajal bodies tethered to histone genes at 1q21 during S, and G(2) phases. Overexpression of p220 in U2OS cells can promote the G(1)/S transition and can also promote transcription from histone H2B and H4 luciferase reporter constructs. How p220 expression induces these activities and whether the two activities are related are unknown. In this study, we developed a "lox-scanning" mutagenesis approach to identify functional domains in p220. We identified two distinct functional regions of p220. The C-terminal half of the protein contains multiple elements that are required for its ability to induce S phase in transfected cells. In contrast, sequences at the N terminus appear to be critical for activation of histone H4 and H2B reporter constructs. We identified an approximately 30-amino-acid motif at the N terminus of p220 that has the characteristics of a LisH motif. LisH motifs are found in a large number of proteins in the database but are of unknown function. Point mutations in conserved residues in the LisH motif of p220 block histone H4 transcriptional activity without affecting localization in Cajal bodies or phosphorylation on Cdk2 phosphorylation sites. These studies indicate that the ability of p220 to promote S phase is independent of its ability to promote histone H4 transcription and suggests that p220 may link cyclin E/Cdk2 to multiple independent downstream functions.
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PMID:The cyclin E/Cdk2 substrate and Cajal body component p220(NPAT) activates histone transcription through a novel LisH-like domain. 1272 24

We have isolated and functionally characterized a multicomponent Oct-1 coactivator, OCA-S which is essential for S phase-dependent histone H2B transcription. The p38 component of OCA-S binds directly to Oct-1, exhibits potent transactivation potential, is selectively recruited to the H2B promoter in S phase, and is essential for S phase-specific H2B transcription in vivo and in vitro. Surprisingly, p38 represents a nuclear form of glyceraldehyde-3-phosphate dehydrogenase, and binding to Oct-1, as well as OCA-S function, is stimulated by NAD(+) but inhibited by NADH. OCA-S also interacts with NPAT, a cyclin E/cdk2 substrate that is broadly involved in histone gene transcription. These studies thus link the H2B transcriptional machinery to cell cycle regulators, and possibly to cellular metabolic state (redox status), and set the stage for studies of the underlying mechanisms and the basis for coordinated histone gene expression and coupling to DNA replication.
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PMID:S phase activation of the histone H2B promoter by OCA-S, a coactivator complex that contains GAPDH as a key component. 1288 15

DNA damage and activation of the cell cycle have been implicated in numerous neurodegenerative diseases, including Alzheimer disease, Parkinson's disease, and amyotrophic lateral sclerosis. To better understand the role of cell cycle proteins in DNA-damage induced neuronal cell death, we examined various cell cycle proteins during camptothecin-induced death of human neuroblastoma cells. We report a rapid induction of p53 and increased expression of p21, concurrent with reduced levels of many cell cycle proteins that regulate G1 to S phase cell cycle progression. However, we found increased levels of cdk2 and cyclin E, and formation of a cyclin E-cdk2-p21 protein complex. DNA damage failed to induce activation and progression of the cell cycle. Finally, camptothecin-induced neuronal cell death occurred concurrent with phosphorylation of histone H2B. Pretreatment of cells with cdk inhibitor olomoucine impeded cdk2-cyclin E accumulation, but not the induction of p53. Olomucine concurrently delayed histone H2B phosphorylation, caspase-3 activation and cell death. These findings suggest that DNA-damage of differentiated neuroblastoma cells induces a rapid p53-mediated inhibition of cell cycle progression and induction of cdk2-cyclin E, followed by caspase-3 activation, phosphorylation of histone and cell death.
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PMID:DNA damage induces cdk2 protein levels and histone H2B phosphorylation in SH-SY5Y neuroblastoma cells. 1615 45

To date, several classes of enzymes have been shown to affect transcription by catalyzing the modifications of nucleosomes via methylation. Employing our global proteomic screen, GPS, we have determined that the loss of Bur2, a component of the Bur1/Bur2 cyclin-dependent protein kinase, results in a decrease in histone H3(K4) methylation catalyzed by COMPASS. Furthermore, Bur1/Bur2 is required for histone H2B monoubiquitination by Rad6/Bre1. The effect on histone monoubiquitination and methylation is the result of defective Bur1/Bur2-mediated phosphorylation of Rad6 on its serine residue 120 and proper recruitment of the Paf1 complex to chromatin. We have also demonstrated that serine 120 of Rad6 is required for histone H2B monoubiquitination and the regulation of gene expression in vivo. Our results identify in vivo substrates for Bur1/Bur2, thus linking its role to transcriptional elongation and demonstrating a potential activation mechanism for histone H2B monoubiquitination by the Rad6/Bre1 complex.
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PMID:The Bur1/Bur2 complex is required for histone H2B monoubiquitination by Rad6/Bre1 and histone methylation by COMPASS. 1630 22

Efficient transcription is linked to modification of chromatin. For instance, tri-methylation of lysine 4 on histone H3 (H3K4) strongly correlates with transcriptional activity and is regulated by the Bur1/2 kinase complex. We found that the evolutionarily conserved Ccr4-Not complex is involved in establishing H3K4 tri-methylation in Saccharomyces cerevisiae. We observed synthetic lethal interactions of Ccr4-Not components with BUR1 and BUR2. Further analysis indicated that the genes encoding the Not-proteins are essential for efficient regulation of H3K4me3, but not H3K4me1/2, H3K36me2 or H3K79me2/3 levels. Moreover, regulation of H3K4me3 levels by NOT4 is independent of defects in RNA polymerase II loading. We found NOT4 to be important for ubiquitylation of histone H2B via recruitment of the PAF complex, but not for recruitment or activation of the Bur1/2 complex. These results suggest a mechanism in which the Ccr4-Not complex functions parallel to or downstream of the Bur1/2 kinase to facilitate H3K4me3 via PAF complex recruitment.
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PMID:Regulation of histone H3K4 tri-methylation and PAF complex recruitment by the Ccr4-Not complex. 1739 37

Elongation by RNA polymerase II (RNAPII) is a finely regulated process in which many elongation factors contribute to gene regulation. Among these factors are the polymerase-associated factor (PAF) complex, which associates with RNAPII, and several cyclin-dependent kinases, including positive transcription elongation factor b (P-TEFb) in humans and BUR kinase (Bur1-Bur2) and C-terminal domain (CTD) kinase 1 (CTDK1) in Saccharomyces cerevisiae. An important target of P-TEFb and CTDK1, but not BUR kinase, is the CTD of the Rpb1 subunit of RNAPII. Although the essential BUR kinase phosphorylates Rad6, which is required for histone H2B ubiquitination on K123, Rad6 is not essential, leaving a critical substrate(s) of BUR kinase unidentified. Here we show that BUR kinase is important for the phosphorylation in vivo of Spt5, a subunit of the essential yeast RNAPII elongation factor Spt4/Spt5, whose human orthologue is DRB sensitivity-inducing factor. BUR kinase can also phosphorylate the C-terminal region (CTR) of Spt5 in vitro. Like BUR kinase, the Spt5 CTR is important for promoting elongation by RNAPII and recruiting the PAF complex to transcribed regions. Also like BUR kinase and the PAF complex, the Spt5 CTR is important for histone H2B K123 monoubiquitination and histone H3 K4 and K36 trimethylation during transcription elongation. Our results suggest that the Spt5 CTR, which contains 15 repeats of a hexapeptide whose consensus sequence is S[T/A]WGG[A/Q], is a substrate of BUR kinase and a platform for the association of proteins that promote both transcription elongation and histone modification in transcribed regions.
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PMID:Control of transcriptional elongation and cotranscriptional histone modification by the yeast BUR kinase substrate Spt5. 1936 74

Cyclin-dependent kinase-9 (CDK9) was originally characterized as a transcription elongation factor which regulates RNA Polymerase II (RNAPII) activity following transcriptional initiation. However, recent evidence from a number of studies have shown that CDK9 plays an important role in regulating not only RNAPII activity but also co-transcriptional histone modification and mRNA processing events such as splicing and 3' end processing. Importantly, our previous work and the work presented here demonstrate that CDK9 functions to guide a complex network of chromatin modifications including histone H2B monoubiquitination (H2Bub1), H3 lysine 4 trimethylation (H3K4me3) and H3K36me3. This function appears to be dependent upon not only the phosphorylation of the RNA Polymerase II C-terminal domain but also upon other CDK9 targets such as the Suppressor of Ty Homolog-5 (SUPT5H), Negative Elongation Factor-E (NELF-E) and probably the human Rad6 homolog UBE2A. We provide a working model by which CDK9 may control co-transcriptional replication-dependent histone mRNA 3' end processing in an H2Bub1 and H3K4me3-dependent manner and uncover new and important differences between the functions of human CDK9 and its yeast counterparts Ctk1 and Bur1.
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PMID:Insights into the function of the human P-TEFb component CDK9 in the regulation of chromatin modifications and co-transcriptional mRNA processing. 1984 66

Cyclin-dependent kinase-9 (CDK9) plays a central role in transcriptional elongation and controls multiple cotranscriptional histone modifications, including histone H2B monoubiquitination (H2Bub1). Like other CDK9-dependent histone modifications, the role of CDK9 in maintaining H2Bub1 was shown to be partially dependent upon the phosphorylation status of Ser2 of the RNA polymerase II (RNAPII) C-terminal domain (CTD). Since mutation of Ser2 within the RNAPII CTD resulted in a milder effect on H2Bub1 compared with CDK9 knockdown, we explored whether another CDK9 target may also influence H2Bub1. Based on its homology to yeast Bur1, we hypothesized that CDK9 may directly phosphorylate and activate the ubiquitin-conjugating enzyme utilized for H2B monoubiquitination. Indeed, we demonstrate that UBE2A specifically interacts with CDK9, but not CDK2. Furthermore, UBE2A is phosphorylated by CDK9 in vitro and increases UBE2A activity. Interestingly, CDK9 knockdown not only decreases UBE2A phosphorylation and H2Bub1, but also significantly impairs the induction of UBE2A-dependent monoubiquitination of proliferating cell nuclear antigen (PCNA). Thus, we provide the first evidence that CDK9 is required for the activity of UBE2A in humans, and that its activity is not only required for maintaining H2Bub1, but also for the monoubiquitination of PCNA. The common involvement of these two ubiquitinations in distinct DNA repair pathways may provide a mechanistic rationale for further exploring CDK9 as a combinatorial target for increasing the efficacy of existing cancer therapies based on the induction of DNA damage and are repaired by mechanisms which require H2Bub1 and/or PCNA ubiquitination.
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PMID:Phosphorylation by cyclin-dependent kinase-9 controls ubiquitin-conjugating enzyme-2A function. 2272 97


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