Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cdk-interacting protein 1 (Cip1) is a p53-regulated 21-kDa protein that inhibits several members of the cyclin-dependent kinase (CDK) family. It was initially observed in complexes containing CDK4, cyclin D, and proliferating cell nuclear antigen (PCNA). PCNA, in conjunction with activator 1, acts as a processivity factor for eukaryotic DNA polymerase (pol) delta, and these three proteins constitute the pol delta holoenzyme. In this report, we demonstrate that Cip1 can also directly inhibit DNA synthesis in vitro by binding to PCNA. Cip1 efficiently inhibits simian virus 40 replication dependent upon pol alpha, activator 1, PCNA, and pol delta, and this inhibition can be overcome by additional PCNA. Simian virus 40 DNA replication, catalyzed solely by high levels of pol alpha-primase complex, is unaffected by Cip1. Using the surface plasmon resonance technique, a direct physical interaction of PCNA and Cip1 was detected. We have observed that Cip1 efficiently inhibits synthesis of long (7.2 kb) but not short (10 nt) templates, suggesting that its association with PCNA is likely to impair the processive movement of pol delta during DNA chain elongation, as opposed to blocking assembly of the pol delta holoenzyme. The implications of the Cip1-PCNA interaction with respect to regulation of DNA synthesis, cell cycle checkpoint control, and DNA repair are discussed.
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PMID:Cdk-interacting protein 1 directly binds with proliferating cell nuclear antigen and inhibits DNA replication catalyzed by the DNA polymerase delta holoenzyme. 791 43

Wild-type p53 functions in the G1 DNA damage checkpoint pathway by activating gene transcription and preventing cell cycle progression. Others reported that mutation of the serine 386 codon in mouse p53 abolished its ability to suppress growth. Serine 386 of murine p53 and the homologous residue of human p53, serine 392, are phosphorylated in vivo and can be phosphorylated in vitro by casein kinase II (CKII). We constructed mutants that changed serine 392 of human p53 to alanine (p53-S392A) or aspartic acid (p53-S392D); cotransfection of both these mutants with a reporter gene carrying a p53-responsive element into the p53-null Saos-2 cell line activated transcription as well as did wild-type p53. Furthermore, both mutants blocked cell cycle progression after transient transfection in these cells. A stable derivative of the T98G human glioblastoma cell line was established that expressed p53-S392A in response to dexamethasone. Overexpression of this mutant activated transcription of the endogenous waf1 (also called cip1) and mdm2 genes to the same extent as wild-type p53 and also produced growth arrest. Finally, p53-S392A and p53-S392D suppressed foci formation by activated ras and adenovirus E1A oncogenes as efficiently as did wild-type p53. Thus, unlike mutants that altered the serine 15 phosphorylation site, elimination of the serine 392 phosphorylation site had no discernible effect on p53 function. We conclude that neither phosphorylation nor RNA attachment to serine 392 are required for human p53's ability to suppress cell growth or to activate transcription in vivo.
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PMID:The carboxy-terminal serine 392 phosphorylation site of human p53 is not required for wild-type activities. 793 49

Overexpression of wild-type p53 protein has been shown to induce arrest in the G1 stage of the cell cycle and to transactivate expression of the gene that encodes the 21-kDa Waf1/Cip1 protein, a potent inhibitor of cyclin-dependent kinase activity. p53-dependent G1 arrest is accompanied by decreased expression of the B-myb gene, a relative of the c-myb cellular oncogene. In this study we show that B-myb expression is required for cells to progress from G1 into S phase and that high levels of ectopic B-myb expression uncoupled from cell cycle regulation rescues cells from p53-induced G1 arrest even in the presence of Waf1/Cip1 transactivation and inhibition of cyclin E/Cdk2 kinase activity. Cotransfection experiments with p53 expression plasmids and expression plasmids encoding in-frame deletion mutations in B-myb coding sequences indicate that the DNA-binding domain of the B-Myb protein is required for this activity. These results provide evidence of a bypass of p53-induced Waf1/Cip1-mediated cell cycle regulatory pathways by a member of the myb oncogene family.
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PMID:Constitutive expression of B-myb can bypass p53-induced Waf1/Cip1-mediated G1 arrest. 793 41

DNA damage inducing treatment of cultured mammalian cells triggers the activation of transcription factors and the prolongation of the half life of p53. As the earliest event detectable in the nucleus (5 min), AP-1 (c-Jun/c-Fos) is post-translationally modified. Triggering this early event and triggering subsequent transcription factor dependent processes requires extra-nuclear components of signal transduction such as Src, Ras, Raf-1 and MAP-2 kinase. Recent efforts have concentrated on examining whether DNA damage or other secondary effects of the damaging agent generate the signal then passed on to transcription factors. Further, it has been studied whether a pathway of reverse signalling exists that originates in the nucleus and reaches the cell surface. At the cell surface the UV induced signalling chain can be interrupted experimentally. Beyond this step DNA damage and signal transduction induced by phorbol esters and growth factors merge and reach the nuclear proteins through common components.
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PMID:The mammalian UV response: mechanism of DNA damage induced gene expression. 794 83

The tumor suppressor p53 is a cell cycle checkpoint protein that contributes to the preservation of genetic stability by mediating either a G1 arrest or apoptosis in response to DNA damage. Recent reports suggest that p53 causes growth arrest through transcriptional activation of the cyclin-dependent kinase (Cdk)-inhibitor Cip1. Here, we characterize the p53-dependent G1 arrest in several normal human diploid fibroblast (NDF) strains and p53-deficient cell lines treated with 0.1-6 Gy gamma radiation. DNA damage and cell cycle progression analyses showed that NDF entered a prolonged arrest state resembling senescence, even at low doses of radiation. This contrasts with the view that p53 ensures genetic stability by inducing a transient arrest to enable repair of DNA damage, as reported for some myeloid leukemia lines. Gamma radiation administered in early to mid-, but not late, G1 induced the arrest, suggesting that the p53 checkpoint is only active in G1 until cells commit to enter S phase at the G1 restriction point. A log-linear plot of the fraction of irradiated G0 cells able to enter S phase as a function of dose is consistent with single-hit kinetics. Cytogenetic analyses combined with radiation dosage data indicate that only one or a small number of unrepaired DNA breaks may be sufficient to cause arrest. The arrest also correlated with long-term elevations of p53 protein, Cip1 mRNA, and Cip1 protein. We propose that p53 helps maintain genetic stability in NDF by mediating a permanent cell cycle arrest through long-term induction of Cip1 when low amounts of unrepaired DNA damage are present in G1 before the restriction point.
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PMID:DNA damage triggers a prolonged p53-dependent G1 arrest and long-term induction of Cip1 in normal human fibroblasts. 795 16

Cell cycle arrest at the G1 checkpoint allows completion of critical macromolecular events prior to S phase. Regulators of the G1 checkpoint include an inhibitor of cyclin-dependent kinase, p16INK4; two tumor-suppressor proteins, p53 and RB (the product of the retinoblastoma-susceptibility gene); and cyclin D1. Neither p16INK4 nor the RB protein was detected in 28 of 29 tumor cell lines from human lung, esophagus, liver, colon, and pancreas. The presence of p16INK4 protein is inversely correlated with detectable RB or cyclin D1 proteins and is not correlated with p53 mutations. Homozygous deletions of p16INK4 were detected in several cell lines, but intragenic mutations of this gene were unusual in either cell lines or primary tumors. Transfection of the p16INK4 cDNA expression vector into carcinoma cells inhibits their colony-forming efficiency and the p16INK4 expressing cells are selected against with continued passage in vitro. These results are consistent with the hypothesis that p16INK4 is a tumor-suppressor protein and that genetic and epigenetic abnormalities in genes controlling the G1 checkpoint can lead to both escape from senescence and cancer formation.
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PMID:Mutations and altered expression of p16INK4 in human cancer. 797 6

Exposure of a wide variety of cells to ionizing (X- or gamma-) irradiation results in a division delay which may have several components including a G1 block, a G2 arrest or an S phase delay. The G1 arrest is absent in many cell lines, and the S phase delay is typically seen following relatively high doses (> 5 Gy). In contrast, the G2 arrest is seen in virtually all eukaryotic cells and occurs following high and low doses, even under 1 Gy. The mechanism underlying the G2 arrest may involve suppression of cyclin B1 mRNA and/or protein in some cell lines and tyrosine phosphorylation of p34cdc2 in others. Similar mechanisms are likely to be operative in the G2 arrest induced by various chemotherapeutic agents including nitrogen mustard and etoposide. The upstream signal transduction pathways involved in the G2 arrest following ionizing radiation remain obscure in mammalian cells; however, in the budding yeast the rad9 gene and in the fission yeast the chk1/rad27 gene are involved. There is evidence indicating that shortening of the G2 arrest results in decreased survival which has led to the hypothesis that during this block, cells repair damaged DNA following exposure to genotoxic agents. In cell lines examined to date, wildtype p53 is required for the G1 arrest following ionizing radiation. The gadd45 gene may also have a role in this arrest. Elimination of the G1 arrest leads to no change in survival following radiation in some cell lines and increased radioresistance in others. It has been suggested that this induction of radioresistance in certain cell lines is due to loss of the ability to undergo apoptosis. Relatively little is known about the mechanism underlying the S phase delay. This delay is due to a depression in the rate of DNA synthesis and has both a slow and a fast component. In some cells the S phase delay can be abolished by staurosporine, suggesting involvement of a protein kinase. Understanding the molecular mechanisms behind these delays may lead to improvement in the efficacy of radiotherapy and/or chemotherapy if they can be exploited to decrease repair or increase apoptosis following exposure to those agents.
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PMID:The molecular basis for cell cycle delays following ionizing radiation: a review. 804 94

Using a new series of p53 mutants targeting the conserved regions we have analysed the relationship of various activities of the protein. Mdm-2 and human papillomavirus (HPV) E6, two proteins which interact with and abrogate p53 function, were shown to bind independently. Deletion of the conserved regions of the protein in which most of the naturally occurring mutations are found (boxes II-V) abrogated transcriptional activity and the ability to interact with E6, supporting the importance of this DNA binding domain to these activities. Nevertheless, these mutants retained the ability to interact with mdm2. One mutant, deleted of all the C-terminal sequences, showed loss of mdm2 binding, E6 binding and transcriptional activity. More subtle mutations within the C-terminus of the protein, including alterations of the cdc2 and CKII phosphorylation sites, had no effect on the transcriptional trans-activation, mdm-2 or E6 binding functions, indicating that phosphorylation of these sites is not essential for these activities. Deletion of conserved box I sequences abolished the interaction with mdm-2 without loss of transcriptional activation or transformation suppressor activity, suggesting that mdm-2 is not a downstream effector of p53 function.
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PMID:Interaction of p53 with MDM2 is independent of E6 and does not mediate wild type transformation suppressor function. 805 35

Xenopus p53 cDNA, homologous to the human tumour suppressor p53, has previously been cloned from oocyte and gastrula libraries. In this report, we describe a polyclonal antibody 2674 raised against Xenopus p53 (Xp53) expressed in bacteria, that recognises proteins of approximately 52, 46 and 35 kDa present in Xenopus oocytes, parthenogenically activated eggs and in somatic tissue culture cells. We report here purification of Xp53 from insect cells infected with Xp53-baculovirus, and this protein is shown to be phosphorylated by casein kinase II but has low sequence-specific DNA binding activity. Using similar purification conditions, we have isolated endogenous Xp53, showing that Xenopus eggs contain high levels of p53 protein. Xp53 from eggs binds to the p53-specific DNA-binding consensus sequence. Two dimensional gel analysis indicates that Xp53 from eggs may exist in various states of phosphorylation. u.v.-induced DNA damage of somatic Xenopus cells results in accumulation of Xp53. We suggest that the high levels of putative Xp53 detected in eggs may represent maternal stockpiles of a protein necessary to protect rapidly dividing cells from the effects of DNA damage.
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PMID:Xenopus p53 is biochemically similar to the human tumour suppressor protein p53 and is induced upon DNA damage in somatic cells. 808 98

The best understood function of p53 is that of cell growth suppression and this is likely to involve sequence-specific DNA binding and modulation of gene expression. Casein kinase II phosphorylates the C-terminal serine of p53 (residue 389 for murine p53) and mutation of this site abolishes p53 growth suppressor function. DNA binding by purified p53 is 'activated' by casein kinase II, suggesting that the carboxyl terminus of p53 represents a critical regulatory domain for sequence-specific DNA binding and hence for growth suppressor function. In the present study we have substituted serine 389 with either aspartic acid (mimics phosphoserine and partially conserves p53 suppressor function) or with alanine, a non-phosphorylable residue which abolishes suppressor function (Milne et al., 1992; Nucleic Acids Research 20, 5565-5570). When expressed in vitro p53ala389 and p53asp389 were both indistinguishable from wild type p53 on the basis of size fractionation and immunoreactivity with PAb421, PAb246 and PAb1620. Both mutants also exhibited specific binding for the DNA consensus p53-CON. Since p53ala389 retains the ability to bind DNA and yet is known to lack growth suppressor function we conclude that phosphorylation by casein kinase II is important for p53 growth suppressor function via a mechanism which is ancillary to p53 sequence-specific DNA binding.
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PMID:Specific DNA binding by p53 is independent of mutation at serine 389, the casein kinase II site. 808 15


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