124,979 research outputs found
Physical interaction between CDK9 and B-Myb results in suppression of B-myb gene autoregulation
No full textB-Myb is a transcription factor belonging to the myb family, whose activity has been associated with augmented DNA synthesis and cell cycle progression. We showed recently that B-Myb autoregulates its own expression through promoter transactivation. We report in this study that CDK9, the cyclin T associated kinase, which phosphorylates and activates RNA-Polymerase II, suppresses B-Myb autoregulation through direct interaction with the carboxyl-terminus of the B-Myb protein. Downregulation of the transactivating ability of B-Myb is independent of the kinase activity of CDK9, because a kinase deficient mutant (dn-CDK9) also represses B-myb gene autoregulation. Overexpression of CDK9 did not result in suppression of p53-dependent transactivation or inhibition of the basal activity of the promoters tested so far, demonstrating that CDK9 is a B-Myb-specific repressor. Rather, transfection of the dominant negative dn-CDK9 construct inhibited the basal activity of the reporter genes, confirming an essential role for CDK9 in gene transcription. In addition, Cyclin T1 restores B-Myb transactivating activity when co-transfected along with CDK9, suggesting that the down-regulatory effect observed on B-Myb is specifically due to CDK9 alone. Thus, our data suggest that CDK9 is involved in the negative regulation of activated transcription mediated by certain transcription factors, such as B-Myb. This may indicate the existence of a feedback loop, mediated by the different activities of CDK9, which links basal with activated transcription
Phenotypic and morphological characterization of neuroblastoma cells costitutively expressing B-myb
No full textB-myb gene is expressed in neuroblastoma cells and down-regulated during differentiation. We used B-myb-transfected LAN-5 cells, which constitutively express high level of B-myb, to detect changes at phenotypic and morphological levels in basal and differentiation conditions. Our results demonstrate that the overexpression of B-myb markedly affects the cytoskeletal composition, the pattern of neurotransmitter enzymes and the extracellular matrix expression. In general, B-myb transfected neuroblastoma cells show a broad potentiality without a direction toward a specific neuroectodermal differentiation pathway. On the other hand, we confirm inhibition of the neuronal differentiation upon retinoic acid (RA) treatment of B-myb transfected cells. Furthermore, the ultrastructural analyses are supportive of a change in the metabolism in B-myb transfected cell treated with RA. Our data suggest that B-myb expression is compatible with an early phase of differentiation of neuroectodermal cells, but must be down-regulated for the completion of the differentiative programm
Regulation of Balb/c3T3 fibroblast proliferation by B-myb is accompanied by selective activation of cdc2 and cyclin D1 expression.
No full textThe B-myb gene is expressed in many cell types at the G1/S transition of the cell cycle. Inhibition of B-myb expression in BALB/c 3T3 fibroblasts by introduction of a B-myb antisense construct greatly diminished cell proliferation, whereas constitutive expression of a human B-myb cDNA in these cells reduced their growth factor requirements and induced a transformed phenotype. Constitutive expression of B-myb cDNA was accompanied by activation of cyclin D1 and cdc2 expression but not of cyclin A and cyclin B. Transfection of BALB/B-myb cells (a cell line expressing high levels of exogenous human B-myb) with a cyclin D1 antisense construct drastically reduced cloning efficiency of these cells. These results suggest that the B-myb-encoded product regulates fibroblast proliferation by activating cdc2 and cyclin D1 gene expression and that abnormal expression of cyclin D1 might be a step in the process of transformation
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cyclin D1-dependent regulation of B-myb activity in early stages of neuroblastoma differentiation.
No full textLevels of the transcription factor B-myb must be down-regulated to allow terminal differentiation of neuroectodermal cells and yet its constitutive expression induces early markers of neural differentiation. Thus, we investigated potential mechanisms of enhanced B-myb activity in early stages of neural differentiation. We report here that B-myb expression does not decrease, cyclin A and Sp1 levels remain constant while p21 levels increase continuously upon retinoic acid-induced differentiation of the LAN-5 neuroblastoma cell line. In contrast, cyclin D1 expression is down-regulated at the onset of the differentiative process by protein destabilization. Luciferase assays of promoter activity indicate that B-myb-dependent transactivation is enhanced in LAN-5 cells treated with retinoic acid (RA) for 24 h. The enhancement is independent from cyclin A but is suppressed by a degradation-resistant mutant form of cyclin D1. The importance of cyclin D1 in controlling B-myb activity is further suggested by co-immunoprecipitation experiments, showing that the amount of cyclin D1 co-immunoprecipitated with B-myb decreased after RA treatment. Thus, B-myb may play an active role in the early stages of differentiation when its transactivation activity is enhanced as a consequence of cyclin D1 down-modulation
B-myb alters the response to myeloid precurson cells to G-CSF
No full textThe human B-myb gene encodes a cell cycle-regulated DNA-binding phosphoprotein which functions as a transcription factor with an important role in cell cycle progression, survival, and differentiation. Recently, it has been demonstrated that ectopic murine B-myb expression blocked the ability of 32Dcl3 cells to proliferate in response to granulocyte colony-stimulating factor (G-CSF) and accelerated the induction of terminal differentiation. In contrast, we report that while 32Dcl3 cells overexpressing human B-myb do display some markers of myeloid differentiation earlier than parental cells, including the expression of myeloperoxidase mRNA and the appearance of band myelocytes in G-CSF-induced cultures, the induction of late markers of differentiation is inhibited. The expression of lactoferrin mRNA is absent and the appearance of terminally differentiated polymorphonuclear cells is severely impaired in B-myb-expressing 32Dcl3 cells. Furthermore, continuous exposure to G-CSF results in the outgrowth of a culture which expresses increased levels of B-myb RNA and is dependent on G-CSF for proliferation while retaining responsiveness to interleukin-3. These data suggest that the B-myb gene is involved in early transcriptional events during myeloid differentiation, but that its expression prevents terminal differentiation
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Resistance to apoptosis in CTLL-2 cells overexpressing B-Myb is associated with B-Myb-dependent bcl-2 induction
No full textTranscriptional regulators of the Myb family play important roles in cell proliferation, differentiation, and survival. To investigate the role of Myb proteins in the regulation of apoptosis, we studied the apoptotic response of interleukin 2-dependent CTLL-2 cells stably transfected with B-Myb. B-Myb-overexpressing cells showed a diminished cytokine dependence and were resistant to apoptosis induced by doxorubicin, ceramide, and dexamethasone, Overexpression of B-Myb was associated with enhanced expression of bcl-2, which was dependent, at least in part, on increased transcription. In transient transfection assays in T-lymphoblastic cells, B-Myb was able to stimulate the promoter activity of the bcl-2 5' flanking region linked to the chloramphenicol acetyltransferase reporter gene. A segment of the bcl-2 promoter (nucleotides +34 to +58 relative to the transcription initiation site) contained a putative Myb-binding site and was shown to specifically interact with B-Myb and to confer B-Myb responsiveness to a bcl-2/chloramphenicol acetyltransferase reporter construct. These results indicate that B-Myb promotes T cells survival by enhancing the expression of bcl-2 and identify bcl-2 as a B-Myb target gene regulated in a DNA binding-dependent manner
The RB-related gene Rb2/p130 in neuroblastoma differentiation and in B-myb promoter down-regulation
No full textThe retinoblastoma family of nuclear factors is composed of RE, the prototype of the tumour suppressor genes and of the strictly related genes p107 and Rb2/p130. The three genes code for proteins, namely pRb, p107 and pRb2/p130, that share similar structures and functions. These proteins are expressed, often simultaneously, in many cell types and are involved in the regulation of proliferation and differentiation. We determined the expression and the phosphorylation of the RE family gene products during the DMSO-induced differentiation of the N1E-115 murine neuroblastoma cells. In this system, pRb2/p130 was strongly up-regulated during mid-late differentiation stages, white, on the contrary, pRb and p107 resulted markedly decreased at late stages. Differentiating N1E-115 cells also showed a progressive decrease in B-myb levels, a proliferation-related protein whose constitutive expression inhibits neuronal differentiation. Transfection of each of the RE family genes in these cells was able, at different degrees, to induce neuronal differentiation, to inhibit [H-3]thymidine incorporation and to down-regulate the activity of the B-myb promoter
Direct transactivation of the anti-apoptotic gene Apolipoprotein J (Clusterin) by B-MYB.
No full textB-MYB is a ubiquitously expressed transcription factor involved in the regulation of cell survival, proliferation, and differentiation. In an attempt to isolate B-MYB-regulated genes that may explain the role of B-MYB in cellular processes, representational difference analysis was performed in neuroblastoma cell lines with different levels of B-MYB expression. One of the genes, the mRNA levels of which were enhanced in B-MYB expressing cells, was ApoJ/ClusterinSGP-2/TRMP-2 (ApoJ/Clusterin), previously implicated in regulation of apoptosis and tumor progression. Here we show that the human ApoJ/Clusterin gene contains a Myb binding site in its 5′ flanking region, which interacts with bacterially synthesized B-MYB protein and mediates B-MYB-dependent transactivation of the ApoJ/Clusterin promoter in transient transfection assays. Endogenous ApoJ/Clusterin expression is induced in mammalian cell lines following transient transfection of a B-MYB cDNA. Blockage of secreted clusterin by a monoclonal antibody results in increased apoptosis of neuroblastoma cells exposed to the chemotherapeutic drug doxorubicin. Thus, activation of ApoJ/Clusterin by B-MYB may be an important step in the regulation of apoptosis in normal and diseased cells
- …
