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D Cortez

Publications and source records attributed to D Cortez.

18 recordsLinked to original sources
PubMed2001

ATR and ATRIP: partners in checkpoint signaling.

The checkpoint kinases ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3 related) transduce genomic stress signals to halt cell cycle progression and promote DNA repair. We report the identification of an ATR-interacting protein (ATRIP) that is phosphorylated by ATR, regulates ATR expression, and is an essential component of the DNA damage checkpoint pathway. ATR and ATRIP both localize to intranuclear foci after DNA damage or inhibition of replication. Deletion of ATR mediated by the Cre recombinase caused the loss of ATR and ATRIP expression, loss of DNA damage checkpoint responses, and cell death. Therefore, ATR is essential for the viability of human somatic cells. Small interfering RNA directed against ATRIP caused the loss of both ATRIP and ATR expression and the loss of checkpoint responses to DNA damage. Thus, ATRIP and ATR are mutually dependent partners in cell cycle checkpoint signaling pathways.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Direct DNA binding by Brca1.

The tumor suppressor Brca1 plays an important role in protecting mammalian cells against genomic instability, but little is known about its modes of action. In this work we demonstrate that recombinant human Brca1 protein binds strongly to DNA, an activity conferred by a domain in the center of the Brca1 polypeptide. As a result of this binding, Brca1 inhibits the nucleolytic activities of the Mre11/Rad50/Nbs1 complex, an enzyme implicated in numerous aspects of double-strand break repair. Brca1 displays a preference for branched DNA structures and forms protein-DNA complexes cooperatively between multiple DNA strands, but without DNA sequence specificity. This fundamental property of Brca1 may be an important part of its role in DNA repair and transcription.

Animals↗
PubMed2000

Functional interactions between BRCA1 and the checkpoint kinase ATR during genotoxic stress.

The BRCA1 gene encodes a tumor suppressor that is mutated in 50% of familial breast cancers. The BRCA1 protein has been implicated in the DNA damage response, as DNA damage induces the phosphorylation of BRCA1 and causes its recruitment into nuclear foci that contain DNA repair proteins. The ataxia-telangiectasia-mutated (ATM) gene product controls overall BRCA1 phosphorylation in response to gamma-irradiation (IR). In this study, we show that BRCA1 phosphorylation is only partially ATM dependent in response to IR and ATM independent in response to treatment with UV light, or the DNA replication inhibitors hydroxyurea (HU) and aphidicolin (APH). We provide evidence that the kinase responsible for this phosphorylation is the ATM-related kinase, ATR. ATR phosphorylates BRCA1 on six Ser/Thr residues, including Ser 1423, in vitro. Increased expression of ATR enhanced the phosphorylation of BRCA1 on Ser 1423 following cellular exposure to HU or UV light, whereas doxycycline-induced expression of a kinase-inactive ATR mutant protein inhibited HU- or UV light-induced Ser 1423 phosphorylation in GM847 fibroblasts, and partially suppressed the phosphorylation of this site in response to IR. Thus, ATR, like ATM, controls BRCA1 phosphorylation in vivo. Although ATR isolated from DNA-damaged cells does not show enhanced kinase activity in vitro, we found that ATR responds to DNA damage and replication blocks by forming distinct nuclear foci at the sites of stalled replication forks. Furthermore, ATR nuclear foci overlap with the nuclear foci formed by BRCA1. The dramatic relocalization of ATR in response to DNA damage points to a possible mechanism for its ability to enhance the phosphorylation of substrates in response to DNA damage. Together, these results demonstrate that ATR and BRCA1 are components of the same genotoxic stress-responsive pathway, and that ATR directly phosphorylates BRCA1 in response to damaged DNA or stalled DNA replication.

Animals↗
PubMed2000

Chk1 is an essential kinase that is regulated by Atr and required for the G(2)/M DNA damage checkpoint.

Chk1, an evolutionarily conserved protein kinase, has been implicated in cell cycle checkpoint control in lower eukaryotes. By gene disruption, we show that CHK1 deficiency results in a severe proliferation defect and death in embryonic stem (ES) cells, and peri-implantation embryonic lethality in mice. Through analysis of a conditional CHK1-deficient cell line, we demonstrate that ES cells lacking Chk1 have a defective G(2)/M DNA damage checkpoint in response to gamma-irradiation (IR). CHK1 heterozygosity modestly enhances the tumorigenesis phenotype of WNT-1 transgenic mice. We show that in human cells, Chk1 is phosphorylated on serine 345 (S345) in response to UV, IR, and hydroxyurea (HU). Overexpression of wild-type Atr enhances, whereas overexpression of the kinase-defective mutant Atr inhibits S345 phosphorylation of Chk1 induced by UV treatment. Taken together, these data indicate that Chk1 plays an essential role in the mammalian DNA damage checkpoint, embryonic development, and tumor suppression, and that Atr regulates Chk1.

Alleles↗
PubMed2000

Induction of nuclear factor kappaB but not kappaB-responsive cytokine expression during myocardial reperfusion injury after neutropenia.

Neutrophils may contribute to myocardial ischemia/reperfusion (I/R) injury by generating reactive oxygen intermediates (ROIs). ROIs activate nuclear factor (NF)-kappaB, which regulates genes for cytokines with negative inotropic effects (interleukin [IL]-1beta, IL-6, and tumor necrosis factor [TNF]-alpha). We investigated the impact of neutrophil depletion on NF-kappaB DNA binding activity, and expression of these cytokines during myocardial I/R injury. Male WKY rats (n = 28) received a single dose of antineutrophil antiserum (i/v). Twenty two hours later, when the peripheral blood neutrophil counts were profoundly decreased (94% reduction), the animals underwent 15 min of left anterior descending coronary artery ligation followed by reperfusion for 0.25, 0.5, 1, 2, 3, and 6 h (n = 4/group). Saline-treated animals underwent a similar protocol, and served as controls (n = 28, 4/group). Neutrophil accumulation, defined by myeloperoxidase activity, was present in controls, but not in anti-PMN antisera-treated animals (at least p <0.05 at 1, 2, 3, and 6 h R). Despite this difference, in both saline- and antiserum-treated animals, the GSH levels were very similar and fell significantly (p < 0.0001) at 15 min R; the levels increased gradually over time. In contrast, GSSG levels rose at 15 and 30 min R (p < 0.05), and declined thereafter. NF-kappaB DNA binding activity increased in both groups at 15 min and again at 3 h of R. Both NF-kappaBp50 and p65 subunits were detected by supershift assay. In saline-injected controls both mRNA and protein for IL-1beta, IL-6, and TNF-alpha were detected at 1 h R; levels remained high until 3 h, then fell (except IL-6, which was elevated at 6 h). In neutropenic animals, however, a significant decrease in mRNA (at least 1.7-fold, p < 0.05) as well as protein levels (at least 2. 3-fold, p < 0.01) for all three cytokines was observed. Thus, while neutrophils had minimal effects on oxidative stress (GSH/GSSG) and oxidative stress-responsive NF-kappaB activity, they contributed significantly to myocardial cytokine expression.

Animals↗
PubMed2000

BASC, a super complex of BRCA1-associated proteins involved in the recognition and repair of aberrant DNA structures.

We report the identities of the members of a group of proteins that associate with BRCA1 to form a large complex that we have named BASC (BRCA1-associated genome surveillance complex). This complex includes tumor suppressors and DNA damage repair proteins MSH2, MSH6, MLH1, ATM, BLM, and the RAD50-MRE11-NBS1 protein complex. In addition, DNA replication factor C (RFC), a protein complex that facilitates the loading of PCNA onto DNA, is also part of BASC. We find that BRCA1, the BLM helicase, and the RAD50-MRE11-NBS1 complex colocalize to large nuclear foci that contain PCNA when cells are treated with agents that interfere with DNA synthesis. The association of BRCA1 with MSH2 and MSH6, which are required for transcription-coupled repair, provides a possible explanation for the role of BRCA1 in this pathway. Strikingly, all members of this complex have roles in recognition of abnormal DNA structures or damaged DNA, suggesting that BASC may serve as a sensor for DNA damage. Several of these proteins also have roles in DNA replication-associated repair. Collectively, these results suggest that BRCA1 may function as a coordinator of multiple activities required for maintenance of genomic integrity during the process of DNA replication and point to a central role for BRCA1 in DNA repair.

Adenosine Triphosphatases↗
PubMed1999

Requirement of ATM-dependent phosphorylation of brca1 in the DNA damage response to double-strand breaks.

The Brca1 (breast cancer gene 1) tumor suppressor protein is phosphorylated in response to DNA damage. Results from this study indicate that the checkpoint protein kinase ATM (mutated in ataxia telangiectasia) was required for phosphorylation of Brca1 in response to ionizing radiation. ATM resides in a complex with Brca1 and phosphorylated Brca1 in vivo and in vitro in a region that contains clusters of serine-glutamine residues. Phosphorylation of this domain appears to be functionally important because a mutated Brca1 protein lacking two phosphorylation sites failed to rescue the radiation hypersensitivity of a Brca1-deficient cell line. Thus, phosphorylation of Brca1 by the checkpoint kinase ATM may be critical for proper responses to DNA double-strand breaks and may provide a molecular explanation for the role of ATM in breast cancer.

Amino Acid Sequence↗
PubMed1998

The univector plasmid-fusion system, a method for rapid construction of recombinant DNA without restriction enzymes.

BACKGROUND: . Modern biological research is highly dependent upon recombinant DNA technology. Conventional cloning methods are time-consuming and lack uniformity. Thus, biological research is in great need of new techniques to rapidly, systematically and uniformly manipulate the large sets of genes currently available from genome projects. RESULTS: . We describe a series of new cloning methods that facilitate the rapid and systematic construction of recombinant DNA molecules. The central cloning method is named the univector plasmid-fusion system (UPS). The UPS uses Cre-lox site-specific recombination to catalyze plasmid fusion between the univector - a plasmid containing the gene of interest - and host vectors containing regulatory information. Fusion events are genetically selected and place the gene under the control of new regulatory elements. A second UPS-related method allows for the precise transfer of coding sequences only from the univector into a host vector. The UPS eliminates the need for restriction enzymes, DNA ligases and many in vitro manipulations required for subcloning, and allows for the rapid construction of multiple constructs for expression in multiple organisms. We demonstrate that UPS can also be used to transfer whole libraries into new vectors. Additional adaptations are described, including directional PCR cloning and the generation of 3' end gene fusions using homologous recombination in Escherichia coli. CONCLUSIONS: . Together, these recombination-based cloning methods constitute a new comprehensive approach for the rapid and efficient generation of recombinant DNA that can be used for parallel processing of large gene sets, a feature that will facilitate future genomic analysis.

Amino Acid Sequence↗
PubMed1998

Oncogenic Abl and Src tyrosine kinases elicit the ubiquitin-dependent degradation of target proteins through a Ras-independent pathway.

Oncogenic forms of the Abl and Src tyrosine kinases trigger the destruction of the Abi proteins, a family of Abl-interacting proteins that antagonize the oncogenic potential of Abl after overexpression in fibroblasts. The destruction of the Abi proteins requires tyrosine kinase activity and is dependent on the ubiquitin-proteasome pathway. We show that degradation of the Abi proteins occurs through a Ras-independent pathway. Significantly, expression of the Abi proteins is lost in cell lines and bone marrow cells isolated from patients with aggressive Bcr-Abl-positive leukemias. These findings suggest that loss of Abi proteins may be a component in the progression of Bcr-Abl-positive leukemias and identify a novel pathway linking activated nonreceptor protein tyrosine kinases to the destruction of specific target proteins through the ubiquitin-proteasome pathway.

Adaptor Proteins, Signal Transducing↗
PubMed1998

A requirement for NF-kappaB activation in Bcr-Abl-mediated transformation.

Bcr-Abl is a chimeric oncoprotein that is strongly implicated in acute lymphoblastic (ALL) and chronic myelogenous leukemias (CML). This deregulated tyrosine kinase selectively causes hematopoietic disorders resembling human leukemias in animal models and transforms fibroblasts and hematopoietic cells in culture. Bcr-Abl also protects cells from death induced on cytokine deprivation or exposure to DNA damaging agents. In addition, the antiapoptotic function of Bcr-Abl is thought to play a necessary role in hematopoietic transformation and potentially in leukemogenesis. The transcription factor NF-kappaB has been identified recently as an inhibitor of apoptosis and as a potential regulator of cellular transformation. This study shows that expression of Bcr-Abl leads to activation of NF-kappaB-dependent transcription by causing nuclear translocation of NF-kappaB as well as by increasing the transactivation function of the RelA/p65 subunit of NF-kappaB. Importantly, this activation is dependent on the tyrosine kinase activity of Bcr-Abl and partially requires Ras. The ability of Bcr-Abl to protect cytokine-dependent 32D myeloid cells from death induced by cytokine deprivation or DNA damage does not, however, require functional NF-kappaB. However, using a super-repressor form of IkappaBalpha, we show that NF-kappaB is required for Bcr-Abl-mediated tumorigenicity in nude mice and for transformation of primary bone marrow cells. This study implicates NF-kappaB as an important component of Bcr-Abl signaling. NF-kappaB-regulated genes, therefore, likely play a role in transformation by Bcr-Abl and thus in Bcr-Abl-associated human leukemias.

Animals↗
PubMed1997

The Bcr-Abl tyrosine kinase activates mitogenic signaling pathways and stimulates G1-to-S phase transition in hematopoietic cells.

Bcr-Abl is a constitutively active tyrosine kinase that is expressed in Philadelphia chromosome (Ph1)-positive human leukemias. Bcr-Abl has been shown to inhibit apoptosis and cause anchorage independent growth. However, its ability to activate mitogenic signaling pathways is controversial. Here we show that Bcr-Abl signaling prevents down-regulation of cyclin-dependent kinase activity and cell cycle arrest after growth factor deprivation of hematopoietic progenitor cells. Using an inducible system to regulate Bcr-Abl expression, we also demonstrate that Bcr-Abl expression is sufficient to induce G1-to-S phase transition, DNA synthesis, and activation of cyclin-dependent kinases in cells that were arrested in G0 by growth factor deprivation. Furthermore, Bcr-Abl activates Ras, Erk, and Jnk pathways as a primary consequence of expression. These data show that Bcr-Abl is one of a select group of oncogenes that is capable of both inhibiting apoptosis and deregulating cell proliferation. The combination of these activities is likely to be important for the progression of CML.

Apoptosis↗
PubMed1996

The BCR-ABL tyrosine kinase inhibits apoptosis by activating a Ras-dependent signaling pathway.

BCR-ABL is a deregulated tyrosine kinase that is expressed in Philadelphia chromosome (Ph1) positive human leukemias. When expressed in hematopoietic cells, BCR-ABL causes cytokine independent proliferation, induces tumorigenic growth and prevents apoptosis in response to cytokine deprivation or DNA damage. One mechanism by which BCR-ABL signals in cells is by activating the small guanine nucleotide binding protein Ras. BCR-ABL-transformed cells have constitutively high levels of active, GTP-bound Ras. Here we use 32D cells that inducibly express a dominant negative Ras protein to define the Ras requirements in BCR-ABL-transformed cells. Dominant negative Ras inhibits BCR-ABL-mediated Ras activation, and induces cell death by an apoptotic mechanism. Therefore, BCR-ABL inhibits apoptosis through activation of a Ras-dependent signaling pathway.

Antineoplastic Agents, Hormonal↗
PubMed1995

Mutant forms of growth factor-binding protein-2 reverse BCR-ABL-induced transformation.

Growth factor-binding protein 2 (Grb2) is an adaptor protein that links tyrosine kinases to Ras. BCR-ABL is a tyrosine kinase oncoprotein that is implicated in the pathogenesis of Philadelphia chromosome (Ph1)-positive leukemias. Grb2 forms a complex with BCR-ABL and the nucleotide exchange factor Sos that leads to the activation of the Ras protooncogene. In this report we demonstrate that Grb2 mutant proteins lacking amino- or carboxyl-terminal src homology SH3 domains suppress BCR-ABL-induced Ras activation and reverse the oncogenic phenotype. The Grb2 SH3-deletion mutant proteins bind to BCR-ABL and do not impair tyrosine kinase activity. Expression of the Grb2 SH3-deletion mutant proteins in BCR-ABL-transformed Rat-1 fibroblasts and in the human Ph1-positive leukemic cell line K562 inhibits their ability to grow as foci in soft agar and form tumors in nude mice. Furthermore, expression of the Grb2 SH3-deletion mutants in K562 cells induced their differentiation. Because Ras plays an important role in signaling by receptor and nonreceptor tyrosine kinases, the use of interfering mutant Grb2 proteins may be applied to block the proliferation of other cancers that depend in part on activated tyrosine kinases for growth.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Structural and signaling requirements for BCR-ABL-mediated transformation and inhibition of apoptosis.

BCR-ABL is a deregulated tyrosine kinase expressed in Philadelphia chromosome-positive human leukemias. Prolongation of hematopoietic cell survival by inhibition of apoptosis has been proposed to be an integral component of BCR-ABL-induced chronic myelogenous leukemia. BCR-ABL elicits transformation of both fibroblast and hematopoietic cells and blocks apoptosis following cytokine deprivation in various factor-dependent cells. To elucidate the mechanisms whereby BCR-ABL induces transformation and blocks apoptosis in hematopoietic cells, we examined the biological effects of expression of a series of BCR-ABL mutants. Single amino acid substitutions in the GRB2 binding site (Y177F), Src homology 2 domain (R552L), or an autophosphorylation site in the tyrosine kinase domain (Y793F) do not diminish the antiapoptotic and transforming properties of BCR-ABL in hematopoietic cells, although these mutations were previously shown to drastically reduce the transforming activity of BCR-ABL in fibroblasts. A BCR-ABL molecule containing all three mutations (Y177F/R552L/Y793F) exhibits a severe decrease in transforming and antiapoptotic activities compared with the wild-type BCR-ABL protein in 32D myeloid progenitor cells. Ras is activated, the SHC adapter protein is tyrosine phosphorylated and binds GRB2, and myc mRNA levels are increased following expression of all kinase active BCR-ABL proteins with the exception of the Y177F/R552L/Y793F BCR-ABL mutant in 32D cells. We propose that BCR-ABL uses multiple pathways to activate Ras in hematopoietic cells and that this activation is necessary for the transforming and antiapoptotic activities of BCR-ABL. However, Ras activation is not sufficient for BCR-ABL-mediated transformation. A BCR-ABL deletion mutant (delta 176-427) that activates Ras and blocks apoptosis but has severely impaired transforming ability in 32D cells has been identified. These data suggest that BCR-ABL requires additional signaling components to elicit tumorigenic growth which are distinct from those required to block apoptosis.

Adaptor Proteins, Signal Transducing↗
PubMed1993

Characterization of stable high molecular weight mutagenic product(s) of plant-activated m-phenylenediamine.

Monocyclic aromatic amines are environmental contaminants and many are promutagens and procarcinogens. Cultured tobacco cells, strain TX1, activated m-phenylenediamine into a frameshift mutagen that reverted the hisD3052 allele in Salmonella typhimurium strains TA98 and YG1024. However, the plant-activated products were refractory in strain TA98/1,8-DNP6. This indicated that these plant-activated products were substrates for bacterial acetyl-CoA: N-hydroxyarylamine O-acetyltransferase. A stable, high molecular weight (> 300 kDa) proximal mutagen was isolated by molecular ultrafiltration membranes. No parent compound was associated with the isolated mutagenic fraction. The high molecular weight fraction induced mutation in S. typhimurium strains TA98, YG1021 and YG1024. From these data we propose a model for the plant-activation of aromatic amine promutagens.

Acetyltransferases↗
PubMedDate not supplied

Retrospective study on dengue in Fortaleza, state of Ceará, Brazil.

A retrospective serologic study was carried out in Fortaleza, State of Ceará, Brazil, in order to detect the dengue virus activity before recognizing the epidemic of 1994. Mac-Elisa was performed by using a mixture of specific DEN-1 and DEN-2 antigens on serum samples from the Emilio Ribas Laboratory collection. Samples were obtained from 1,224 patients with exanthematic febrile disease and negative serological results for rubella. All specimens were taken during November 1993 to May 1994. The results confirmed dengue infections in Fortaleza by November 1993, approximately six months before the beginning of the epidemic, proving how misleading diagnosis of dengue infection are still troublesome, in spite of the strong dengue activity in Ceará. The authors stress the urgent necessity to implement the active surveillance system in order to prevent another extensive dengue fever epidemics in the state. Epidemiological background of the dengue activity in the State of Ceará is described.

Brazil↗