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Chronic lymphoid leukemia (CLL) is characterized by the accumulation of functionally defective CD5-positive B lymphocytes. The clinical course of CLL is highly variable, ranging from a long-lasting indolent disease to an unpredictable and rapidly progressing leukemia requiring treatment. It is thus important to identify novel factors that reflect disease progression or contribute to its assessment. Here, we report on a novel STAT3-mediated pathway that characterizes CLL B cells-extended viability and oxidative stress control...

BACKGROUND: The transcription factor STAT3 (signal transducer and activator of transcription 3) is frequently activated in tumor cells. Activated STAT3 forms homodimers, or heterodimers with other TFs such as NF-κB, which becomes activated. Cytoplasmic STAT3 dimers are activated by tyrosine phosphorylation; they interact with importins via a nuclear localization signal (NLS) one of which is located within the DNA-binding domain formed by the dimer. In the nucleus, STAT3 regulates target gene expression by binding a consensus sequence within the promoter...

STAT1 is a key effector of cytokines involved in the resistance to pathogens; its identified transcriptional targets mediate the innate immune response involved in the defense against viruses and bacteria. Little is known about the role of STAT1 in adaptive immunity, including its impact on BCR or surface Ig expression. Analysis of this point is difficult in humans, as STAT1 deficiency is extremely rare. SD patients die early in childhood from a severe immunodeficiency. Herein, a SD B cell line obtained from a SD patient was compared with a B cell line from a STAT1-proficient subject in search of differences in surface Ig expression...

Signal transducer and activator of transcription 1 (STAT1), a transcription factor known to participate in antiviral responses, acts as a tumor suppressor inhibiting cell growth and promoting apoptosis. To study the role of STAT1 in DNA damage-induced apoptosis in B lymphocytes, its active form, STAT1alpha, was specifically inhibited by the overexpression of STAT1beta, the STAT1alpha truncated inhibitory isoform. An episomal vector with a tetracycline-inducible bidirectional promoter was created to induce the expression of 2 proteins, STAT1beta and enhanced green fluorescence protein (EGFP)...

Primary mediastinal large B-cell lymphoma (PMBL), currently recognized as a diffuse large B-cell lymphoma (DLBCL) subtype, shows increased expression of interleukin 4 (IL-4)/IL-13 signaling effectors and targets, suggesting constitutive activation of these pathways. We therefore investigated the functional state of the signal transducer and activator of transcription 6 (STAT6), mediating IL-4/IL-13 transcriptional effects. Constitutive STAT6 phosphorylation and DNA-binding activity were detected in PMBL cell lines but not DLBCL cell lines...

Signal transducer and activator of transcription 5 (STAT5) is activated by numerous cytokines that control blood cell development. STAT5 was also shown to actively participate in leukemogenesis. Among the target genes involved in cell growth, STAT5 had been shown to activate cyclin D1 gene expression. We now show that thrombopoietin-dependent activation of the cyclin D1 promoter depends on the integrity of a new bipartite proximal element that specifically binds STAT5A and -B transcription factors. We demonstrate that the stable recruitment of STAT5 to this element in vitro requires the integrity of an adjacent octamer element that constitutively binds the ubiquitous POU homeodomain protein Oct-1...

The Epstein-Barr virus (EBV) transforms B cells in part by inhibiting the cellular apoptotic programme. This is also observed when Burkitt lymphoma cell lines are infected with EBV. Induction of apoptosis is one of the mechanisms by which fludarabine inhibits the growth of cells with low proliferative capacity. This compound can also inhibit several other mechanisms in the cell, including inhibition of the synthesis of factors such as STAT1. To analyse the relationship between EBV status, fludarabine-induced apoptosis, and transcription factors we studied the EBV-negative Burkitt lymphoma cell line BL2, its EBV-infected counterpart BL2...

Recent experimental data suggest that one of the major effects of BCR-ABL gene expression in hematopoietic cells is the inhibition of apoptosis. Although the exact mechanisms of this phenomenon are not clear, it is thought to be related to the fact that BCR-ABL induces several signalling pathways also activated by growth factors. In order to determine the anti-apoptotic role of BCR-ABL in a hematopoietic cell line and to by-pass the influence of cytokine-dependence, BCR-ABL gene was expressed in the autonomously growing myelomonocytic U937 cell line using retroviral vectors...

Oncostatin M (OSM), a cytokine first identified from activated monocytes and T lymphocytes, is one of the most potent autocrine growth factor for AIDS and Kaposi's sarcoma. Little is known about the effects of OSM on normal vascular cells. We thus exposed human aortic smooth muscle cells (hASMCs) to OSM, examined cell proliferation and morphology, and determined interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2) expression. OSM had a weak antiproliferative effect. After a 4-day incubation with 100 ng/mL OSM, cell count decreased to 69+/-3% of control...

The interleukin-3 dependent murine Ba/F3 cell line has been widely used as an experimental model of cell transformation by BCR-ABL oncogenes as assessed by induction of growth-factor-independence and inhibition of apoptosis in vitro. The signaling pathways used by BCR-ABL oncogenes to exert these effects are unknown. To gain insights into this phenomenon, we have introduced the p190- and p210-encoding BCR-ABL oncogenes as well as the constitutively activated oncogenic murine erythropoietin receptor (cEpoR) into Ba/F3 and compared the behavior of individual clones in response to apoptotic stimuli...

FDCP-1 cells are hematopoietic progenitor cells which require interleukin-3 for survival and proliferation. FDCP-1 cells stably transfected with the murine erythropoietin receptor cDNA survive and proliferate in the presence of erythropoietin. Erythropoietin induces the activation of the short forms (80 kDa) of STAT5 in the cells. Erythropoietin-induced activation of STAT5 was strongly reduced in cells expressing mutated variants of the erythropoietin receptors in which tyrosine residues in their intracellular domain have been eliminated...

A signal transduction pathway activated by many cytokines has recently been elaborated. The JAK kinases and the signal transducers and activators of transcription (STAT) factors have been found to be essential components. In this report, we describe the presence of constitutively activated STAT factors in peripheral blood cells from patients with acute leukemia. We used oligonucleotide probes from the beta-casein and IRF-1 gene promoters and the ISRE probe to detect STAT proteins in nuclear extracts from acute leukemia cells in bandshift assays...

Stimulation of sensitive cells with erythropoietin results in rapid induction of protein tyrosine phosphorylation. Other than tyrosine phosphorylation of one chain of the erythropoietin receptor, the identities of the remaining tyrosine-phosphorylated proteins are undefined. In this report, we demonstrate that the stimulation of the erythropoietin-sensitive human UT7 cells by erythropoietin rapidly resulted in the appearance of phosphatidylinositol 3-kinase activity in anti-phosphotyrosine immunoprecipitates...

The mechanism of action of prolactin (PRL) was studied in murine lymphoid BAF-3 cells transfected with either the long form of the PRL receptor (PRL-R), or a chimeric receptor consisting of the extracellular domain of the PRL-R and the transmembrane and intracellular domain of the erythropoietin receptor (PRL/EPO-R). PRL sustained normal and long-term proliferation of BAF-3 cells expressing either the PRL-R or the hybrid PRL/EPO-R. Upon [125I]PRL cross-linking, both types of BAF-3 transfectants were shown to express two [125I]PRL cross-linked species differing in size by 20 kDa...

Thrombopoietin (TPO) is a newly cloned cytokine which is the major regulator of circulating platelet levels, acting on both proliferation and differentiation of megakaryocytes. We have investigated the ability of TPO to activate the JAK/STAT pathway in megakaryocytic cell lines. We used either the granulocyte-macrophage colony-stimulating factor (GM-CSF)- and/or erythropoietin (EPO)-dependent UT7 cell line in which the murine TPO receptor (mumpl) had been transfected (mumpl-UT7 transfectants) or the MO7E and DAMI cells which express endogenous human TPO receptors...

The molecular components which mediate cytokine signaling from the cell membrane to the nucleus were studied. Upon the interaction of cytokines with their receptors, members of the janus kinase (Jak) family of cytoplasmic protein tyrosine kinases and of the signal transducers and activators of transcription (Stat) family of transcription factors are activated through tyrosine phosphorylation. It has been suggested that the Stat proteins are substrates of the Jak protein tyrosine kinases. MGF-Stat5 is a member of the Stat family which has been found to confer the prolactin response...

Interleukin-3 (IL-3)-, erythropoietin (EPO)-, and prolactin (PRL)-induced signal transduction via the JAK/STAT pathway was studied in the IL-3-dependent BAF-3 lymphoid cell line. Transfected cells expressing either the long form of the PRL receptor or the EPO receptor were used. We demonstrated that IL-3, EPO, and PRL activated a transcription factor related to the mammary transcription factor STAT5 but not to STAT1, -2, -3, or -4 as opposed to interferon gamma (IFN gamma) which activated STAT1 in the same cells...

The B-raf/c-Rmil proto-oncogene belongs to the raf/mil family of serine/threonine protein kinases. It encodes multiple protein isoforms previously shown to be expressed predominantly in neural tissues. We report here that B-Raf proteins of 95 and 72 kDa are also expressed in various human and murine hematopoietic cell lines. Their relative level of expression is variable depending on the cell line examined. The highest level of expression of p95B-raf was found in UT-7 cells, a human pluripotent cell line established from a patient with a megakaryoblastic leukemia...

Surface viscosity (eta S) was measured in the pulmonary lavage fluid obtained from 40 mongrel dogs. Two experimental methods were employed to determine surface viscosity: a) Fourt's "torsion pendulum" procedure; and b) the "viscous traction" viscosimeter. A satisfactory correlation (r = 0.88) between these two methods was obtained. The mean value for surface viscosity of the pulmonary lavage fluid was 3.8 X 10(-2) surface-poise (s.p.) with the torsion pendulum procedure, and 4.3 X 10(-2) s.p. with the viscous traction viscosimeter...

Previous studies have established that antibodies against PRL receptors can mimic PRL effects on casein gene expression and on thymidine incorporation into DNA in the mammary gland. In the present work, bivalent F(ab')2 and monovalent Fab' fragments of the anti-PRL receptor antibodies were prepared. Both inhibited the binding of 125I-labeled PRL to rabbit mammary gland membranes. F(ab')2 as well as the unmodified antibodies were able to enhance casein synthesis and thymidine incorporation into DNA in cultured rabbit mammary gland explants...