1,721,041 research outputs found
Post-transcriptional mechanisms in BCR/ABL leukemogenesis: role of shuttling RNA-binding proteins.
No full textShuttling hnRNPs control the fate of eukaryotic mRNAs throughout their journey from the active site of transcription to that of translation; thus, gain or loss of their function in hematopoietic cells might result in altered hematopoiesis and/or be associated with the process of leukemogenesis. In BCR/ABL-expressing cells, there is a marked increase in the protein levels FUS, hnRNP A1 and hnRNP E2, three RNA-binding proteins involved in the regulation of mRNA processing, nucleocytoplasmic export, and translation. Ectopic expression and/or inhibition of the activity of these RNA-binding proteins affects proliferation, survival, and differentiation of normal and BCR/ABL-expressing cells, suggesting that enhanced expression/activity of certain RNA-binding proteins plays an important, but as yet unrecognized, role in BCR/ABL leukemogenesis. The identification of the mRNA subsets associated with RNA-binding proteins upregulated in BCR/ABL-expressing cells should functionally link the process of leukemogenesis with alteration of mRNA metabolism
Translational regulation by the p210 BCR/ABL oncoprotein
No full textThe ability of oncogenic proteins to regulate the rate of translation of specific mRNA subsets may be a rapid and efficient mechanism to modulate the levels and, in many cases, the activity of the corresponding proteins. In the past few years, we have identified several RNA binding proteins with translation regulatory activity whose expression is markedly activated in the blast crisis of chronic myelogenous leukemia, which represents the most malignant disease stage. Perturbation of the activity of some RNA binding proteins suppresses the leukemogenic potential of BCR/ABL-expressing cells. Most importantly, we have identified some of the targets of these RNA binding proteins. Two of these targets, c/ebp alpha and mdm2 mRNAs, are directly relevant for the altered differentiation and survival of leukemic cells. The identification of mRNA targets translationally regulated by RNA binding proteins overexpressed in tumor cells may lead to the development of therapeutic strategies aimed at modulating the translation rate of specific mRNAs
Granulocytic differentiation of normal hematopoietic precursor cells induced by transcriptional factor PU.1 correlates with negative regulation of the c-myb promoter.
No full textNumerous transcription factors allow hematopoietic cells to respond to lineage- and stage-specific cytokines and/or to act as their effectors. The transcription factors PU.1 and c-Myb are essential for hematopoiesis, most likely acting at distinct stages of differentiation, but sharing a common set of target genes. To determine whether PU.1 and c-Myb are functionally interrelated, murine bone marrow (BM) cells and 32Dcl3 murine myeloid precursor cells were infected with a retrovirus carrying a PU.1 cDNA and assessed for myeloid colony formation and for granulocytic differentiation, respectively. Compared with noninfected normal BM cells or to cells infected with an empty virus, hematopoietic precursor cells expressing PU.1 formed an increased number of interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF )–stimulated colonies. Moreover, granulocytic differentiation of 32Dcl3 cells constitutively expressing PU.1 was accelerated, as indicated by morphology and by expression of differentiation markers. Downregulation of c-Myb protein levels by expression of an antisense c-myb construct was also associated with a faster kinetics of 32Dcl3 granulocytic differentiation. Sequence analysis of the 5′ flanking region of the c-myb gene revealed a consensus PU box at position +16 to +21 able to specifically interact in electrophoretic mobility shift assays with either bacterially synthesized PU.1 protein or whole cell extracts from differentiated 32Dcl3 cells. Transient expression of PU.1 in cotransfection assays in different cell lines resulted in inhibition of chloramphenicol acetyl transferase activity driven by different segments of the c-myb promoter. Moreover, such an effect was dependent on an intact PU box. Thus, the ability of PU.1 to potentiate terminal myeloid differentiation appears to involve downregulation of c-myb expression, an essential step during differentiation of hematopoietic precursor cells
The biology of CML blast crisis
No full textChronic myelogenous leukemia (CML) evolves from a chronic phase characterized by the Philadelphia chromosome as the sole genetic abnormality into blast crisis, which is often associated with additional chromosomal and molecular secondary changes. Although the pathogenic effects of most CML blast crisis secondary changes are still poorly understood, ample evidence suggests that the phenotype of CML blast crisis cells (enhanced proliferation and survival, differentiation arrest) depends on cooperation of BCR/ABL with genes dysregulated during disease progression. Most genetic abnormalities of CML blast crisis have a direct or indirect effect on p53 or Rb (or both) gene activity, which are primarily required for cell proliferation and survival, but not differentiation. Thus, the differentiation arrest of CML blast crisis cells is a secondary consequence of these abnormalities or is caused by dysregulation of differentiation-regulatory genes (le, C/EBPalpha). Validation of the critical role of certain secondary changes (le, loss of p53 or C/EBPalpha function) in murine models of CMIL blast crisis and in in vitro assays of BCR/ABL transformation of human hematopoietic progenitors might lead to the development of novel therapies based on targeting BCR/ABL and inhibiting or restoring the gene activity gained or lost during disease progression (ie, p53 or C/EBPalpha)
A cell proliferation-dependent multiprotein complex NC-3A positively regulates the CD34 promoter via a TCATTT-containing element.
No full textThe CD34 cell surface antigen is a glycoprotein expressed by hematopoietic stem and progenitor cells and also by certain nonhematopoietic cell-types. Because CD34 expression is regulated both at the transcriptional and the posttranscriptional level, we attempted to identify factors that, by interacting with the 5' flanking region of the human CD34 gene, may regulate its promoter activity in proliferating hematopoietic cells. By electrophoretic mobility shift assay, UV cross-linking and DNase I footprinting analyses, we identified a multiprotein complex, designated NC-3A, that specifically interacts with the CD34 promoter region from nucleotides -375 to -351. Sequence analysis of this region revealed the presence of a distinct motif, TCATTT. Chloramphenicol acetyl-transferase assays used to assess promoter activity in transiently transfected cells showed that this TCATTT-containing element, which is conserved in both the human and the murine CD34 genes, mediates positive regulatory activity in hematopoietic and nonhematopoietic cells, and acts as an enhancer when placed upstream of a heterologous promoter. Moreover, loss of CD34 promoter activity was caused by mutation of the TCATTT motif. In addition, the interaction of the nuclear multiprotein complex NC-3A with this enhancer element is proliferation-dependent. These data indicate that, although not cell-type specific, the formation of a multiprotein complex NC-3A interacting with the region from nucleotides -375 to 351 plays an important role in controlling CD34 promoter activity in proliferating hematopoietic cells
Altered mRNA translation: possible mechanism for CML disease progression.
No full textChronic myelogenous leukemia (CML) is a clonal disorder arising from neoplastictransformation of the hematopoietic stem cell.1 The typical clinical course of CMLinvolves progression from a protracted chronic phase (CP) to a rapidly fatal blast crisis(BC) characterized by clonal expansion of an immature population of myeloid blast cellswhich exhibit enhanced proliferative potential, reduced susceptibility to apoptosis, anddifferentiation arrest. The latter feature is typical of CML-BC as apparently normalneutrophils and late myeloid precursors accumulate in the bone marrow and peripheralblood of CML-chronic phase patients.1,2 The introduction of the Abl kinase inhibitorGleevec (imatinib mesylate or STI571) as the drug of choice in the treatment of CML islikely to have a profound effect on the course of chronic phase CML. However, in blastcrisis CML, the therapeutic effect of Gleevec is transient and relapse of the disease is themost frequent outcome.3 Thus, it remains critically important to understand the molecularmechanisms underlying progression of CML from chronic phase to blast crisis, as thisadvanced disease stage does not respond to conventional therapy and is associated with ahigh mortality rate.While there is no doubt that expression of the BCR/ABL oncoprotein in hematopoieticstem cells is the initiating event in CML, it is somewhat controversial whether BCR/ABLplays an equally essential role during disease progression or in the blast crisis disease stage.In growth factor-dependent cell lines, ectopic expression of the BCR/ABL oncoproteinis sufficient to induce factor-independent proliferation, increased survival, and differentiationarrest, a phenotype reminiscent of that of CML blast crisis cells.4,5 However, constitutiveexpression of BCR/ABL in normal primary marrow cells leads to a myeloproliferativedisorder which is, instead, reminiscent of chronic phase CML.6 Thus, it is unclear whetherBCR/ABL oncogenic activity per se accounts for CML disease progression or if secondarygenetic alterations are required. In any case, continuous expression/activity of BCR/ABLis necessary for maintaining the leukemic phenotype in mice.7,8There is evidence that genetic inactivation of p53 occurs in blast crisis CML. Althougha p53-deficient background appears to favor blastic transformation in the appropriatemouse models,9,10 mutations in the p53 gene have been detected only in the 25% of blastcrisis.11 Another recurrent mutation in blast crisis CML is the double Philadelphiachromosome, which is detected in 20% of cases.12 In addition, expression of BCR/ABLis higher in mononuclear cells from blast crisis compared to chronic phase CMLpatients,13 and growth factor-independent and differentiation-arrested cell lines expressinghigh doses of BCR/ABL develop from growth factor-dependent cells that express low levelsof the p210 BCR/ABL oncoprotein.14 Thus, high levels of BCR/ABL in the appropriatetarget cells may have a role in blastic transformation. Consistent with this, the increasedexpression of BCR/ABL during disease progression and transformation of growth factor-dependent myeloid precursor cell lines correlates with changes in gene expression, some ofwhich involve regulators of mRNA metabolism like FUS, hnRNP A1, hnRNP E2 andLa.5,14-16In particular, the increased expression of hnRNP E2 and La, two shuttling RNA bindingproteins which function as regulators of mRNA translation,17,18 suggests that BCR/ABLand, perhaps, other oncogenic tyrosine kinases, may modulate gene expression at thetranslational level
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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