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)

An array of tandem heptapeptide repeats at the carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II constitute a highly conserved structure essential for viability. Studies have established that the CTD is phosphorylated at different stages of the transcription cycle, and that it may be involved in transcriptional regulation. The exact role of the CTD remains elusive, as in vitro reconstituted transcription using the adenovirus major late promoter does not require the CTD. Previous studies showed that transcription from the murine dihydrofolate reductase (DHFR) promoter can be only accomplished by the form of RNA polymerase II that contains the hypophosphorylated CTD (RNAPIIA), but not by the form that lacks it (RNAPIIB). Here we show that the CTD, but not its phosphorylation, is required for initiation of transcription. We also show that transcription requires CTD kinase activity provided by the CDK subunit of TFIIH.
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PMID:Requirement for TFIIH kinase activity in transcription by RNA polymerase II. 756 58

Although a number of transfection experiments have suggested potential targets for the action of the E2F1 transcription factor, as is the case for many transcriptional regulatory proteins, the actual targets in their normal chromosomal environment have not been demonstrated. We have made use of a recombinant adenovirus containing the E2F1 cDNA to infect quiescent cells and then measure the activation of endogenous cellular genes as a consequence of E2F1 production. We find that many of the genes encoding S-phase-acting proteins previously suspected to be E2F targets, including DNA polymerase alpha, thymidylate synthase, proliferating cell nuclear antigen, and ribonucleotide reductase, are indeed induced by E2F1. Several other candidates, including the dihydrofolate reductase and thymidine kinase genes, were only minimally induced by E2F1. In addition to the S-phase genes, we also find that several genes believed to play regulatory roles in cell cycle progression, such as the cdc2, cyclin A, and B-myb genes, are also induced by E2F1. Moreover, the cyclin E gene is strongly induced by E2F1, thus defining an autoregulatory circuit since cyclin E-dependent kinase activity can stimulate E2F1 transcription, likely through the phosphorylation and inactivation of Rb and Rb family members. Finally, we also demonstrate that a G1 arrest brought about by gamma irradiation is overcome by the overexpression of E2F1 and that this coincides with the enhanced activation of key target genes, including the cyclin A and cyclin E genes.
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PMID:Cellular targets for activation by the E2F1 transcription factor include DNA synthesis- and G1/S-regulatory genes. 762 16

The transcription factor E2F activates the expression of multiple genes involved in cell proliferation, such as c-myc and the dihydrofolate reductase gene. Regulation of E2F involves its interactions with other cellular proteins, including the retinoblastoma protein (Rb), the Rb-related protein p107, cyclin A, and cdk2. We undertook a detailed analysis of E2F DNA-binding activities and their cell cycle behavior in primary human T cells. Three E2F DNA-binding activities were identified in resting (G0) T cells with mobilities in gel shift assays distinct from those of previously defined E2F complexes. One of these activities was found to be a novel, less abundant, Rb-E2F complex. The most prominent E2F activity in resting T cells (termed complex X) was abundant in both G0 and G1 but disappeared as cells entered S phase, suggesting a possible role in negatively regulating E2F function. Complex X could be dissociated by adenovirus E1A with a requirement for an intact E1A conserved region 2. However, X failed to react with a variety of antibodies against Rb or p107, implicating the involvement of an E1A-binding protein other than Rb or p107. In addition to these novel E2F complexes, three distinct forms of unbound (free) E2F were resolved in gel shift experiments. These species showed different cell cycle kinetics. UV cross-linking experiments suggested that a distinct E2F DNA-binding protein is uniquely associated with the S-phase p107 complex and is not associated with Rb. Together, these results suggest that E2F consists of multiple, biochemically distinct DNA-binding proteins which function at different points in the cell cycle.
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PMID:Cell cycle analysis of E2F in primary human T cells reveals novel E2F complexes and biochemically distinct forms of free E2F. 832 Dec 4

The differential activation of cyclin and cyclin-dependent kinase genes by the adenovirus E1A gene product (E1A) or serum factors was studied with a rat 3Y1 derivative cell line, g12-21, in which the E1A12S cDNA can be expressed in response to dexamethasone (dex). The induction of DNA synthesis in quiescent g12-21 cells occurred within 12 h after serum stimulation, while it occurred within 8 h after treatment with dex. The expression of cyclin D1 and E genes in the serum-stimulated cells was induced in mid G1 and mid to late G1, respectively, while that of the cyclin D1 gene was not induced and the induction of the cyclin E gene was shifted to the G1/S boundary in the dex-treated cells. The cdk2 gene was induced in late G1 and cdc2 and cyclin A genes at the G1/S boundary in both serum-stimulated and dex-treated cells. These results suggest that E1A skips cell cycle events which normally occur in early to mid G1 and may directly activate late-response genes. Analysis of the transcription factor E2F complexes formed in the promoter regions of cdc2 and dihydrofolate reductase genes showed that the amount of complexes formed is maximal at the G1/S boundary, but decreases in S phase when these genes are transcribed extensively.
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PMID:Differential activation of cyclin and cyclin-dependent kinase genes by adenovirus E1A12S cDNA product. 837 70

p21Sdi1/WAF1/Cip1 inhibits cyclin-dependent protein kinases and cell proliferation. p21 is presumed to inhibit growth by preventing the phosphorylation of growth-regulatory proteins, including the retinoblastoma tumor suppressor protein (pRb). The ultimate effector(s) of p21 growth inhibition, however, is largely a matter of conjecture. We show that p21 inhibits the activity of E2F, an essential growth-stimulatory transcription factor that is negatively regulated by unphosphorylated pRb. p21 suppressed the activity of E2F-responsive promoters (dihydrofolate reductase and cdc2), but E2F-unresponsive promoters (c-fos and simian virus 40 early) were unaffected. Moreover, the simian virus 40 early promoter was rendered p21 suppressible by introducing wild-type, but not mutant, E2F binding sites; p21 deletion mutants showed good agreement in their abilities to inhibit E2F transactivation and DNA synthesis; and E2F-1 (which binds pRb), but not E2F-4 (which does not), reversed both inhibitory effects of p21. Despite the central role for pRb in regulating E2F, p21 suppressed growth and E2F activity in cells lacking a functional pRb. Moreover, p21 protein (wild type but not mutant) specifically disrupted an E2F-cyclin-dependent protein kinase 2-p107 DNA binding complex in nuclear extracts of proliferating cells, whether or not they expressed normal pRb. Thus, E2F is a critical target and ultimate effector of p21 action, and pRb is not essential for the inhibition of growth or E2F-dependent transcription.
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PMID:Inhibition of E2F activity by the cyclin-dependent protein kinase inhibitor p21 in cells expressing or lacking a functional retinoblastoma protein. 864 10

Progression of eukaryotic cells through the cell cycle is governed by the sequential formation, activation, and subsequent inactivation of a series of cyclin-dependent kinase (Cdk) complexes. p27(Kip1) (p27) is a Cdk inhibitor that blocks, in vitro, the activity of cyclin D-Cdk4, cyclin D-Cdk6, cyclin E-Cdk2 as well as cyclin A-Cdk2, a complex active during S phase. The level of p27 protein expression, usually high in G0/G1 resting cells, declines as cells progress toward S phase and enforced expression of p27 in fibroblasts causes G1 arrest. This situation prevails in CCL39, a Chinese hamster lung fibroblast cell line (this report). However, in addition to p27, several other Cdk inhibitors known to alter G1 progression coexist in most mammalian cells. To investigate the specific contribution of p27 in the control of the mitogen-sensitive G0/G1 arrest, we specifically reduced its synthesis by expressing a full-length p27 antisense cDNA in CCL39 cells. Interestingly, reduction of up to 90% of p27 protein expression increased both basal and serum-stimulated gene transcription of cyclin D1, cyclin A, dihydrofolate reductase, and DNA synthesis reinitiation. Moreover, overexpression of this antisense allows cells to grow for several generations in a serum-free medium supplemented with insulin and transferrin only, thus suggesting that p27-depleted cells cannot exit the cell cycle. These effects were fully reversed by coexpression of a plasmid encoding p27 sense. We conclude that p27, by setting the level of growth factor requirement, plays a pivotal role in controlling cell cycle exit, a fundamental step in growth control.
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PMID:Abrogation of p27Kip1 by cDNA antisense suppresses quiescence (G0 state) in fibroblasts. 870 74

The molecular karyotype of a murine isolate of Encephalitozoon cuniculi, a microsporidian with a wide range of mammalian hosts, comprises eleven chromosomes ranging in size between 217 and 315 kb. To determine specific chromosomal markers, a partial genomic library was constructed and cloned DNA fragments were hybridized to chromosomal bands separated by pulsed-field gel electrophoresis. Most probes were assigned to single chromosomes, indicating prevalence of low-copy number nucleotide sequences within the very small genome of E. cuniculi (2.9 Mb). A few probes were shown to hybridize to all chromosomes. These repetitive DNA fragments corresponded to either rRNA genes or some non-coding regions whose sequences were characterized by short micro- and minisatellites. The chromosomal locations of beta-tubulin genes and six newly identified protein-encoding genes were determined. Genes encoding dihydrofolate reductase, thymidylate synthase, serine hydroxymethyl transferase, a cdc2 kinase-like protein and helicase ERCC6-like protein were each located on a single chromosome whereas genes for both beta-tubulin and aminopeptidase were on two different chromosomes. The mapping will serve as a reference for further analysis of intraspecific karyotype polymorphism in different isolates from different host species.
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PMID:Mapping of repetitive and non-repetitive DNA probes to chromosomes of the microsporidian Encephalitozoon cuniculi. 921 May 86

Histone acetylation is emerging as a major regulatory mechanism thought to modulate gene expression by altering the accessibility of transcription factors to DNA. In this study, treatment of human tumor cells with the histone deacetylase inhibitor, trapoxin (TPX), resulted in selective changes in genes that control the cell cycle. TPX activated p21(waf1) transcription that led to elevated p21(waf1) protein levels in three human tumor cell lines without altering the protein levels of cdk2, cdk4, or cyclin B. In addition, TPX increased cyclin E transcription without increasing the levels of Rb, E2F, dihydrofolate reductase, or glyceraldehyde-3-phosphate dehydrogenase. The elevated levels of p21(waf1) protein led to decreased Rb phosphorylation and cdk2 activity. These effects resulted in G(1) and G(2) cell cycle arrest in H1299 human lung and MDA-MB-435 breast carcinoma cells and apoptosis in A549 lung carcinoma cells. Chromatin immunoprecipitation assays revealed that TPX increased the level of chromatin acetylation associated with histone H3 in the trapoxin-responsive region of the p21(waf1) promoter. This study demonstrates that inhibition of HDAC by TPX increases acetylation of H3-associated chromatin and alters gene expression with marked selectivity.
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PMID:Histone deacetylase inhibition selectively alters the activity and expression of cell cycle proteins leading to specific chromatin acetylation and antiproliferative effects. 1057 69

Regulation of gene expression in mammals through methylation of cytosine residues at CpG dinucleotides is involved in the development and progression of tumors. Because many genes that are involved in the control of cell proliferation are regulated by members of the E2F family of transcription factors and because some E2F DNA-binding sites are methylated in vivo, we have investigated whether CpG methylation can regulate E2F functions. We show here that methylation of E2F elements derived from the dihydrofolate reductase, E2F1, and cdc2 promoters prevents the binding of all E2F family members tested (E2F1 through E2F5). In contrast, methylation of the E2F elements derived from the c-myc and c-myb promoters minimally affects the binding of E2F2, E2F3, E2F4, and E2F5 but significantly inhibits the binding of E2F1. Consistent with these studies, E2F3, but not E2F1, activates transcription through methylated E2F sites derived from the c-myb and c-myc genes whereas both E2F1 and E2F3 fail to transactivate a reporter gene that is under the control of a methylated dihydrofolate reductase E2F site. Together, these data illustrate a means through which E2F activity can be controlled.
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PMID:CpG methylation as a mechanism for the regulation of E2F activity. 1082 96

The retinoblastoma tumor suppressor protein (pRB) negatively regulates early-G(1) cell cycle progression, in part, by sequestering E2F transcription factors and repressing E2F-responsive genes. Although pRB is phosphorylated on up to 16 cyclin-dependent kinase (Cdk) sites by multiple G(1) cyclin-Cdk complexes, the active form(s) of pRB in vivo remains unknown. pRB is present as an unphosphorylated protein in G(0) quiescent cells and becomes hypophosphorylated (approximately 2 mol of PO(4) to 1 mol of pRB) in early G(1) and hyperphosphorylated (approximately 10 mol of PO(4) to 1 mol of pRB) in late G(1) phase. Here, we report that hypophosphorylated pRB, present in early G(1), represents the biologically active form of pRB in vivo that is assembled with E2Fs and E1A but that both unphosphorylated pRB in G(0) and hyperphosphorylated pRB in late G(1) fail to become assembled with E2Fs and E1A. Furthermore, using transducible dominant-negative TAT fusion proteins that differentially target cyclin D-Cdk4 or cyclin D-Cdk6 (cyclin D-Cdk4/6) and cyclin E-Cdk2 complexes, namely, TAT-p16 and TAT-dominant-negative Cdk2, respectively, we found that, in vivo, cyclin D-Cdk4/6 complexes hypophosphorylate pRB in early G(1) and that cyclin E-Cdk2 complexes inactivate pRB by hyperphosphorylation in late G(1). Moreover, we found that cycling human tumor cells expressing deregulated cyclin D-Cdk4/6 complexes, due to deletion of the p16(INK4a) gene, contained hypophosphorylated pRB that was bound to E2Fs in early G(1) and that E2F-responsive genes, including those for dihydrofolate reductase and cyclin E, were transcriptionally repressed. Thus, we conclude that, physiologically, pRB is differentially regulated by G(1) cyclin-Cdk complexes.
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PMID:Differential regulation of retinoblastoma tumor suppressor protein by G(1) cyclin-dependent kinase complexes in vivo. 1141 52


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