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)

The E2F-1 transcription factor is a critical downstream target of the tumor suppressor, RB. When activated, E2F-1 induces cell proliferation. In addition, deregulation of E2F-1 constitutes an oncogenic stress that can induce apoptosis. The protein kinase ATM is a pivotal mediator of the response to another type of stress, genotoxic stress. In response to ionizing radiation, ATM activates the tumor suppressor p53, a key player in the control of cell growth and viability. We show here that E2F-1 elevates ATM promoter activity and induces an increase in ATM mRNA and protein levels. This is accompanied by an E2F-induced increase in p53 phosphorylation. Expression of the E7 protein of HPV16, which dissociates RB/E2F complexes, also induces the elevation of ATM levels and p53 phosphorylation, implicating endogenous E2F in these phenomena. These data demonstrate that ATM is transcriptionally regulated by E2F-1 and suggest that ATM serves as a novel, ARF-independent functional link between the RB/E2F pathway and p53.
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PMID:ATM is a target for positive regulation by E2F-1. 1252 85

We have analyzed how single-strand DNA gaps affect DNA replication in Xenopus egg extracts. DNA lesions generated by etoposide, a DNA topoisomerase II inhibitor, or by exonuclease treatment activate a DNA damage checkpoint that blocks initiation of plasmid and chromosomal DNA replication. The checkpoint is abrogated by caffeine and requires ATR, but not ATM, protein kinase. The block to DNA synthesis is due to inhibition of Cdc7/Dbf4 protein kinase activity and the subsequent failure of Cdc45 to bind to chromatin. The checkpoint does not require pre-RC assembly but requires loading of the single-strand binding protein, RPA, on chromatin. This is the biochemical demonstration of a DNA damage checkpoint that targets Cdc7/Dbf4 protein kinase.
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PMID:An ATR- and Cdc7-dependent DNA damage checkpoint that inhibits initiation of DNA replication. 1253 33

Ataxia telangiectasia is one of a group of recessive hereditary genomic instability disorders and is characterized by progressive neurodegeneration, immunodeficiency and cancer susceptibility. Heterozygotes for the mutated gene are more susceptible to cancer and to ischaemic heart disease. The affected gene, ATM (ataxia telangiectasia mutated), has been cloned and codes for a protein kinase (ATM), which orchestrates the cellular response to DNA double-strand breaks after ionising radiation. An underlying feature of ataxia telangiectasia is oxidative stress and there is chronic activation of stress response pathways in tissues showing pathology such as the cerebellum, but not in the cerebrum or liver. ATM has also been shown to be activated by insulin and to have a wider role in signal transduction and cell growth. Many, but not all, aspects of the phenotype can be attributed to a defective DNA damage response. The oxidative stress may result directly from accumulated DNA damage in affected tissues or ATM may have an additional role in sensing/modulating redox homeostasis. The basis for the observed tissue specificity of the oxidative damage in ataxia telangiectasia is not clear.
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PMID:Oxidative stress in ataxia telangiectasia. 1263 40

The heterotrimeric DNA-binding protein, replication protein A (RPA), consists of 70-, 34-, and 14-kDa subunits and is involved in maintaining genomic stability by playing key roles in DNA replication, repair, and recombination. RPA participates in these processes through its interaction with other proteins and its strong affinity for single-stranded DNA (ssDNA). RPA-p34 is phosphorylated in a cell-cycle-dependent fashion primarily at Ser-29 and Ser-23, which are consensus sites for Cdc2 cyclin-dependent kinase. By systematically examining RPA-p34 phosphorylation throughout the cell cycle, we have found there are distinct phosphorylated forms of RPA-p34 in different cell-cycle stages. We have isolated and purified a unique phosphorylated form of RPA that is specifically associated with the mitotic phase of the cell cycle. The mitotic form of RPA (m-hRPA) shows no difference in ssDNA binding activity as compared with recombinant RPA (r-hRPA), yet binds less efficiently to double-stranded DNA (dsDNA). These data suggest that mitotic phosphorylation of RPA-p34 inhibits the destabilization of dsDNA by RPA complex, thereby decreasing the binding affinity for dsDNA. The m-hRPA also exhibits altered interactions with certain DNA replication and repair proteins. Using highly purified proteins, m-hRPA exhibited decreased binding to ATM, DNA pol alpha, and DNA-PK as compared to unphosphorylated recombinant RPA (r-hRPA). Dephosphorylation of m-hRPA was able to restore the interaction with each of these proteins. Interestingly, the interaction of RPA with XPA was not altered by RPA phosphorylation. These data suggest that phosphorylation of RPA-p34 plays an important role in regulating RPA functions in DNA metabolism by altering specific protein-protein interactions.
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PMID:RPA phosphorylation in mitosis alters DNA binding and protein-protein interactions. 1264 57

Silencing ATM gene gave rise to enhanced apoptotic response to irradiation and irradiation-like chemotherapy agents, this paper explored the crucial identities of the molecular elements responsible for the enhanced apoptotic response in U937 cells mediated by silencing ATM gene. Two U937 cell mutants named U937-ASPI3K (ATM, negative) and U937-pZeosv2(+) (ATM, wild-type) were used as a cell model system to identify the critical molecule(s) responsible for the varied apoptotic response in the absence or presence of ATM gene. Apoptosis was examined by measuring concentrations of free nucleosome in U937 cells. Western blot was employed to measure nuclear protein abundance of CDC25A, CDC25B, CDC25C, total p34cdc2, p34cdc2, (Thr 161) or p34cdc2 (Thr 14, Tyr 15). RT-PCR was used to estimate CDC25 transcript levels. U937-ASPI3K exhibited an enhanced apoptotic response to lower dosage of irradiation, which could not be blocked by protein synthesis inhibitor. Protein serine-threonine phosphatase inhibitor or cyclin-dependent kinase (CDK) inhibitors, on the other hand, abolished the enhancement indicated that protein phosphorylation/dephosphorylation modification and CDK activity are required for the enhanced apoptotic response in the absence of ATM gene. Upon irradiation, p34cdc2 in U937-pZeosv2(+) was maintained in an inactive state by phosphorylation on threonine 14 (Thr 14) and tyrosine 15 (Tyr 15), which was associated with a dramatic decrease of nuclear CDC25A, CDC25B and CDC25C proteins. In contrast, p34cdc2 in U937-ASPI3K maintained in an active state by dephosphorylation on threonine 14 (Thr 14) and tyrosine 15 (Tyr 15), which was associated with constant nuclear CDC25A, CDC25B and CDC25C protein abundance before and after irradiation. The responsive decrease of nuclear CDC25 proteins occurred at the post-transcription level. Silencing ATM gene blocks the responsive decrease of nuclear CDC25 proteins, which is responsible for failure to inactivate p34cdc2 after irradiation. Active p34cdc2 and CDK2, in turn, acts as the death executors to trigger apoptosis. In summary, aberrantly activated CDK activity is the critical molecular mechanism central to enhanced apoptotic responses in the absence of ATM gene.
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PMID:Failure to inactivate CDK activity is responsible for the enhanced apoptotic response in U937 cells mediated by silencing ATM gene. 1265 1

The impact of disruption of the PI3K (phosphatidylinositol 3-kinase) pathway on the response of human leukemia cells to pharmacological cyclin-dependent kinase (CDK) inhibitors has been examined. Exposure of U937 monocytic leukemia cells to minimally toxic concentrations of flavopiridol (FP), roscovitine, or CGP74514A for 3 h in conjunction with the PI3K inhibitor LY294002 (abbreviated LY in the article) resulted in a marked decrease in Akt phosphorylation. Coexposure of cells to LY and CDK inhibitors also resulted in an early (i.e., within 3 h) and striking increase in mitochondrial damage [e.g., cytochrome c, second mitochondria-derived activator of caspases/direct inhibitor of apoptosis (IAP)-binding protein with low isoelectric point (Smac/DIABLO), and apoptosis-initiating factor (AIF) release], caspase activation, and apoptosis. Similar interactions were observed in a variety of other leukemia cell types (e.g., HL-60, Jurkat, Raji, and NB4). Apoptosis, induced by FP/LY, was substantially blocked by ectopic expression of Bcl-2, but to a considerably lesser extent by dominant-negative caspase-8. FP-induced apoptosis was not enhanced by agents that inhibited protein kinase (PK) A (H89), PKC (GFX), mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK1/2; U0126), p38 MAP kinase (MAPK; SB202190), m-target of rapamycin (TOR; rapamycin), or ataxia-telangiectasia mutation (ATM; caffeine), whereas the PI3K inhibitor wortmannin exerted effects similar to those of LY. The dramatic potentiation of CDK inhibitor-induced apoptosis by LY was accompanied by diminished Bad phosphorylation, induction of Bcl-2 cleavage, and down-regulation of X-linked IAP (XIAP) and Mcl-1. Cells exposed to CDK inhibitors + LY also exhibited reduced phosphorylation of glycogen synthase kinase (GSK)-3, forkhead transcription factor (FKHR), p70(S6K), and ERK, but increased activation of p34(cdc2) and p38 MAPK. LY/CDK inhibitor-treated cells also displayed diminished pRb dephosphorylation on CDK2- and CDK4-specific sites, retinoblastoma protein cleavage, and down-regulation of cyclin D(1). Inducible expression of constitutively active (myristolated) Akt significantly, albeit partially, attenuated apoptosis in Jurkat leukemia cells treated with either FP alone or the combination of FP and LY. Finally, cotreatment with LY and FP resulted in a dramatic increase in apoptosis in primary leukemic blasts obtained from a patient with acute myeloblastic leukemia. Together, these findings suggest that the PI3K/Akt pathway plays a major role in regulating the apoptotic response of human leukemia cells to pharmacological CDK inhibitors and raise the possibility that combined interruption of CDK- and PI3K-related pathways may represent a novel therapeutic strategy in hematological malignancies.
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PMID:The lethal effects of pharmacological cyclin-dependent kinase inhibitors in human leukemia cells proceed through a phosphatidylinositol 3-kinase/Akt-dependent process. 1270 69

Chk2 is a serine/threonine protein kinase found mutated in certain hereditary and sporadic cancers. Ionizing radiation (IR) activates the kinase activity of Chk2 in a phosphorylation-dependent manner. ATM phosphorylates Chk2 on threonine 68, which promotes oligomerization and phosphorylation on threonines 383 and 387 within the activation loop of the catalytic domain. In this study, threonines 68, 383, and 387 were confirmed as sites of Chk2 phosphorylation both in vitro and in vivo. In addition, serine 516 was identified as a novel IR-inducible phosphorylation site in vivo and as a site of autophosphorylation in vitro. Interestingly, Chk2 was capable of autoactivation in the absence of IR when overproduced in bacteria, in 293 cells, and in murine embryonic fibroblasts lacking Chk2. A kinase-inactive mutant of Chk2 was phosphorylated on T68 and T383/T387 but not on S516 in cells containing Chk2 and on T68 but not T383/T387 or S516 in cells lacking Chk2. This establishes a dependency on Chk2 kinase activity for phosphorylation of T383/T387 and S516 but not for T68 in vivo. We demonstrate that T68 phosphorylation is regulated by kinases in addition to ATM and Chk2. Taken together, our data indicate that autophosphorylation of Chk2 can occur both in cis and in trans and suggest that oligomerization may regulate Chk2 activation by promoting these cis- and trans-phosphorylation events. The importance of oligomerization is underscored by the observation that substitution of isoleucine for threonine at position 157, a mutation found in a subset of patients with Li-Fraumeni syndrome, impairs both Chk2 oligomerization and autophosphorylation.
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PMID:Regulation of the Chk2 protein kinase by oligomerization-mediated cis- and trans-phosphorylation. 1280 7

The BRCA1 gene was isolated in 1994; germline mutations of this gene are known to confer susceptibility to breast and ovarian cancer in high-risk families. Since its discovery, several mutations have been identified in this gene; these are scattered throughout the gene, and include insertion and deletion frameshifts, base substitutions, and inferred regulatory mutations. It role in the pathogenesis of breast cancer, which accounts for almost 95%, although unproven to date, cannot be ruled out. The functional inactivation of both copies of this gene in sporadic tumor cells does not follow the traditional mode: the loss of function in BRCA1 is not accompanied by underlying mutation of the gene in tumor cells with loss of heterozygosity for the BRCA1 gene. Several studies now suggest that an alternate mechanism of inactivation, involving promoter hypermethylation that results in reduced expression of the gene, may be common to a significant proportion of sporadic breast and ovarian cancers. BRCA1 as a tumor suppressor plays an important role in maintaining genomic stability. BRCA1 has the ability to interact with numerous proteins and to form complexes that are involved in recognizing and subsequently repairing DNA. BRCA1 contains several functional domains that directly or indirectly interact with a variety of proteins via protein-protein interaction; these include tumor suppressors (BRCA2, p53, Rb and ATM), oncogenes (c-Myc, casein kinase II and E2F), DNA damage repair proteins (RAD50 and RAD51), cell cycle regulators (cyclins and cyclin dependent kinases), transcriptional activators and repressors (RNA polymerase II, RHA, histone deacetylase complex and CtIP), DNA damage-sensing complex and mismatch repair proteins (BRCA1- Associated Surveillance Complex; BASC) and signal transducer and activator of transcription (STAT) among others Formation of foci containing BRCA1 by inherited mutations, or epigenetic mechanisms (promoter methylation) in sporadic cancers leads to a loss of DNA repair ability, disrupts the potential to form complexes with other proteins that are crucial for DNA repair pathways. Thus, BRCA1 plays a significant role in maintaining genomic stability and serves as a tumor suppressor in breast cancer tumorigenesis.
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PMID:BRCA1 in cancer, cell cycle and genomic stability. 1295 14

In eukaryotes, mutations in a number of genes that affect DNA damage checkpoints or DNA replication also affect telomere length [Curr. Opin. Cell Biol. 13 (2001) 281]. Saccharomyces cerevisae strains with mutations in the TEL1 gene (encoding an ATM-like protein kinase) have very short telomeres, as do strains with mutations in XRS2, RAD50, or MRE11 (encoding members of a trimeric complex). Xrs2p and Mre11p are phosphorylated in a Tel1p-dependent manner in response to DNA damage [Genes Dev. 15 (2001) 2238; Mol. Cell 7 (2001) 1255]. We found that Xrs2p, but not Mre11p or Rad50p, is efficiently phosphorylated in vitro by immunopreciptated Tel1p. Strains with mutations eliminating all SQ and TQ motifs in Xrs2p (preferred targets of the ATM kinase family) had wild-type length telomeres and wild-type sensitivity to DNA damaging agents. We also showed that Rfa2p (a subunit of RPA) and the Dun1p checkpoint kinase, which are required for DNA damage repair and which are phosphorylated in response to DNA damage in vivo, are in vitro substrates of the Tel1p and Mec1p kinases. In addition, Dun1p substrates with no SQ or TQ motifs are phosphorylated by Mec1p in vitro very inefficiently, but retain most of their ability to be phosphorylated by Tel1p. We demonstrated that null alleles of DUN1 and certain mutant alleles of RFA2 result in short telomeres. As observed with Xrs2p, however, strains with mutations of DUN1 or RFA2 that eliminate SQ motifs have no effect on telomere length or DNA damage sensitivity.
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PMID:Amino acid changes in Xrs2p, Dun1p, and Rfa2p that remove the preferred targets of the ATM family of protein kinases do not affect DNA repair or telomere length in Saccharomyces cerevisiae. 1296 60

Non-homologous DNA end-joining (NHEJ) is a major pathway of double strand break (DSB) repair in human cells. Here we show that vanillin (3-methoxy-4-hydroxybenzaldehyde)--a naturally occurring food component and an acknowledged antimutagen, anticlastogen and anticarcinogen--is an inhibitor of NHEJ. Vanillin blocked DNA end-joining by human cell extracts by directly inhibiting the activity of DNA-PK, a crucial NHEJ component. Inhibition was selective and vanillin had no detectable effect on other steps of the NHEJ process, on an unrelated protein kinase or on DNA mismatch repair by cell extracts. Subtoxic concentrations of vanillin did not affect the ATM/ATR-dependent phosphorylation of Chk2 or the S-phase checkpoint response after ionising radiation. They significantly potentiated the cytotoxicity of cisplatin, but did not affect sensitivity to UVC. A limited screen of structurally related compounds identified two substituted vanillin derivatives that were 100- and 50-fold more potent than vanillin as DNA-PK inhibitors. These compounds also sensitised cells to cisplatin. The inhibition of NHEJ is consistent with the antimutagenic and other biological properties of vanillin, possibly altering the balance between DSB repair by NHEJ and homologous recombination.
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PMID:Vanillins--a novel family of DNA-PK inhibitors. 1450 Aug 12


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