Constitutively active STAT5 variants induce growth and survival of hematopoietic cells through a PI 3-kinase/Akt dependent pathway.

Signal Transducer and Activator of Transcription (STATs) are important mediators of cytokine and growth factor-induced signal transduction. STAT5A and STAT5B have been shown to play a role in survival and proliferation of hematopoietic cells both in vitro and in vivo and to contribute to the growth and viability of cells transformed by the TEL-JAK2 oncoprotein. In this study, we investigated the molecular mechanisms by which constitutively active STAT5 proteins induce cell proliferation and survival of Ba/F3 cell lines expressing either dominant positive STAT5A or STAT5B variants or TEL-JAK2 or TEL-ABL fusion proteins.

Characterization of a novel ETS gene, TELB, encoding a protein structurally and functionally related to TEL.

The TEL/ETV6 gene is located at 12p13 and is frequently involved in chromosomal translocations in human malignancies usually resulting in the expression of fusion proteins between the amino terminal part of TEL, and either unrelated transcription factors or protein tyrosine kinases. We report here a novel gene named TELB which is located on human chromosomal band 6p21 and encodes a protein highly related to TEL. TELB is widely expressed in different tissues and, similarly to TEL encodes a sequence-specific transcriptional repressor.

TEL-JAK2 transgenic mice develop T-cell leukemia.

We previously reported a fusion between TEL and JAK2 in a t(9;12)(p24;p13) chromosomal translocation in childhood acute T-cell leukemia. This fusion gene encodes a TEL-JAK2 chimeric protein in which the 336 amino-terminal residues of TEL, including its specific self-association domain, are fused to the kinase domain of JAK2. TEL-JAK2 exhibits constitutive activation of its tyrosine kinase activity which, in turn, confers growth factor-independent proliferation to the interleukin-3-dependent Ba/F3 hematopoietic cell line.

Transforming properties of chimeric TEL-JAK proteins in Ba/F3 cells.

The involvement of the cytokine signaling pathway in oncogenesis has long been postulated. Recently, rearrangements of the gene encoding the tyrosine Janus kinase 2 (JAK2) have been reported in human leukemias indicating a direct JAK-signal transduction and activator of transcription (STAT)-mediated leukemic process. The leukemia-associated TEL-JAK2 fusion protein is formed by the oligomerization domain of the translocated ets leukemia (TEL) protein fused to the catalytic domain of JAK2.

Analysis of TEL proteins in human leukemias.

Chromosomal translocations involving the human 12p13 band frequently affect the TEL gene, usually resulting in gene fusion between TEL and genes encoding proteins of various types. The most frequent 12p13 translocation is the t(12;21)(p13;q22), which recombines TEL with the AML1 gene on chromosome 21 and is frequently associated with deletion of the untranslocated TEL allele. Using antisera against different parts of TEL and against the AML1 proteins, we undertook Western blot and immunofluorescence analyses of leukemic samples with and without 12p13 abnormalities.

Bcl-2 prevents apoptotic mitochondrial dysfunction by regulating proton flux.

We and others have recently shown that loss of the mitochondrial membrane potential (Deltapsi) precedes apoptosis and chemical-hypoxia-induced necrosis and is prevented by Bcl-2. In this report, we examine the biochemical mechanism used by Bcl-2 to prevent Deltapsi loss, as determined with mitochondria isolated from a cell line overexpressing human Bcl-2 or from livers of Bcl-2 transgenic mice. Although Bcl-2 had no effect on the respiration rate of isolated mitochondria, it prevented both Deltapsi loss and the permeability transition (PT) induced by various reagents, including Ca2+, H2O2, and tert-butyl hydroperoxide.

Regulation of the specific DNA binding activity of Xenopus laevis p53: evidence for conserved regulation through the carboxy-terminus of the protein.

Recombinant human p53 isolated either from E. coli or from insect cells is poorly active for binding to DNA but it can be dramatically stimulated by phosphorylation, antibody binding to the carboxy-terminal negative regulatory domain, short peptides derived from this negative regulatory domain or short single strands of DNA. We report here that Xenopus p53 has a very similar behavior.

A TEL-JAK2 fusion protein with constitutive kinase activity in human leukemia.

The Janus family of tyrosine kinases (JAK) plays an essential role in development and in coupling cytokine receptors to downstream intracellular signaling events. A t(9;12)(p24;p13) chromosomal translocation in a T cell childhood acute lymphoblastic leukemia patient was characterized and shown to fuse the 3' portion of JAK2 to the 5' region of TEL, a gene encoding a member of the ETS transcription factor family. The TEL-JAK2 fusion protein includes the catalytic domain of JAK2 and the TEL-specific oligomerization domain.

Bcl-2 targeted overexpression into the erythroid lineage of transgenic mice delays but does not prevent the apoptosis of erythropoietin-deprived erythroid progenitors.

Erythropoietin (Epo) is known to control the erythroid developmental program through various biologic activities including maintenance of viability, cell proliferation, and/or cell maturation. In vitro experiments showed massive apoptosis in cultures of Epo-deprived colony-forming unit-erythroid (CFU-E) progenitors, demonstrating the Epo requirement of late-stage erythroid progenitors for survival. Based on these data, a model has been proposed whereby from CFU-E to proerythroblast stages, Epo acts rather as a survival factor than a proliferating factor.

Chromosome abnormalities of the short arm of chromosome 12 in hematopoietic malignancies: a report including three novel translocations involving the TEL/ETV6 gene.

A wide variety of abnormalities of the short arm of chromosome 12 has been reported in hematologic malignancies. The most frequent rearrangements result from t(12;21)(p13;q22) of childhood acute lymphoblastic leukemia, a translocation cryptic when leukemic cells are analyzed with chromosome banding techniques. This translocation results in a fusion of the TEL/ETV6 and AML1 genes.

Bcl-2 protects from lethal hepatic apoptosis induced by an anti-Fas antibody in mice.

Fas is an apoptosis-signalling cell surface antigen that has been shown to trigger cell death upon specific ligand or antibody binding. Treatment of mice with an anti-Fas antibody causes fulminant hepatic failure due to massive apoptosis. To test a putative protective effect of the anti-apoptotic Bcl-2 protein, transgenic mice were generated to express the human bcl-2 gene product in hepatocytes.

Identification and functional characterization of an erythroid-specific enhancer in the L-type pyruvate kinase gene.

The rat L-type pyruvate kinase gene is transcribed either from promoter L in the liver or promoter L' in erythroid cells. We have now cloned and functionally characterized an erythroid-specific enhancer, mapped in the fetal liver as hypersensitive site B (HSSB) at 3.7 kilobases upstream from the promoter L'.

Three novel sequence variations in the 5' upstream region of the cystic fibrosis transmembrane conductance regulator (CFTR) gene: two polymorphisms and one putative molecular defect.

More than 400 sequence alterations have been identified in the whole coding sequence of the cystic fibrosis transmembrane conductance regulator (CFTR) gene corresponding to the 27 exons and their exon-intron boundaries. However, in some CF chromosomes, no mutation has yet been detected. In such cases, we have explored the promoter and the sequence up to position -1000 from the cap site, by using denaturing gradient gel electrophoresis.

In vitro and in vivo protein--DNA interactions on the rat erythroid-specific L' pyruvate kinase gene promoter.

The rat L-type pyruvate kinase gene possesses two alternative tissue-specific promoters, located 472 bp apart; the upstream L' promoter is erythroid-specific and the downstream L promoter is hepatocyte-specific. The erythroid-specific L' promoter is strongly active in fetal liver at day 17 of gestation, while its activity rapidly decreases thereafter. A L' promoter fragment spanning from nucleotide -320 to +10 with respect to the cap site is able to direct a weak but erythroid-specific transcription in a cell-free system.