Detection of a Functional Hybrid Receptor γc/GM-CSFRβ in Human Hematopoietic CD34+ Cells

A functional hybrid receptor associating the common γ chain (γc) with the granulocyte/macrophage colony-stimulating factor receptor β (GM-CSFRβ) chain is found in mobilized human peripheral blood (MPB) CD34+ hematopoietic progenitors, SCF/Flt3-L primed cord blood (CB) precursors (CBPr CD34+/CD56−), and CD34+ myeloid cell lines, but not in normal natural killer (NK) cells, the cytolytic NK-L cell line or nonhematopoietic cells. We demonstrated, using CD34+ TF1β cells, which express an interleukin (IL)-15Rα/β/γc receptor, that within the hybrid receptor, the GM-CSFRβ chain inhibits the IL-15–triggered γc/JAK3-specific signaling controlling TF1β cell proliferation. However, the γc chain is part of a functional GM-CSFR, activating GM-CSF–dependent STAT5 nuclear translocation and the proliferation of TF1β cells. The hybrid receptor is functional in normal hematopoietic progenitors in which both subunits control STAT5 activation. Finally, the parental TF1 cell line, which lacks the IL-15Rβ chain, nevertheless expresses both a functional hybrid receptor that controls JAK3 phosphorylation and a novel IL-15α/γc/TRAF2 complex that triggers nuclear factor κB activation. The lineage-dependent distribution and function of these receptors suggest that they are involved in hematopoiesis because they modify transduction pathways that play a major role in the differentiation of hematopoietic progenitors

Co expression of SCF and KIT in gastrointestinal stromal tumours (GISTs) suggests an autocrine/paracrine mechanism

KIT is a tyrosine kinase receptor expressed by several tumours, which has for specific ligand the stem cell factor (SCF). KIT is the main oncogene in gastrointestinal stromal tumours (GISTs), and gain-of-function KIT mutations are present in 70% of these tumours. The aim of the study was to measure and investigate the mechanisms of KIT activation in 80 KIT-positive GIST patients. KIT activation was quantified by detecting phosphotyrosine residues in Western blotting. SCF production was determined by reverse transcriptase–PCR, ELISA and/or immunohistochemistry. Primary cultures established from three GISTs were also analysed. The results show that KIT activation was detected in all cases, even in absence of KIT mutations. The fraction of activated KIT was not correlated with the mutational status of GISTs. Membrane and soluble isoforms of SCF mRNA were present in all GISTs analysed. Additionally, SCF was also detected in up to 93% of GISTs, and seen to be present within GIST cells. Likewise, the two SCF mRNA isoforms were found to be expressed in GIST-derived primary cultures. Thus, KIT activation in GISTs may in part result from the presence of SCF within the tumours

Evaluation of quantitative variation in gene expression.

We investigate the behaviour of the gene-expression rate as a statistical variable using autoradiographic data for 39 transcripts from a heterogeneous set of 80 breast-tissue cultures. Despite standardization, the data distributions of all transcripts showed intervals of normality and intervals of systematic departure from normality which most frequently resulted in a significant skewness and/or kurtosis. Non-normal shapes are attributed to modulation of gene expression. This statistical particularity creates difficulties in the evaluation of differences among specimens. Using classical parametric and non-parametric procedures for normal and non-normal variation, respectively, we demonstrate that large differences in optical density are neither necessary nor sufficient for associating expression rates with biological factors. The transcripts coding for the metalloprotease stromelysin-3 (ST3) and for the receptor to insulin-like growth factors (IGFR) are used as examples and their variation is presented in detail. ST3 expression appeared to be specifically associated with mammary stroma fibroblasts derived from post-radiation fibrosis lesions. IGFR was expressed at higher rates in mammary gland and skin fibroblasts than in mammary epithelial cells and was subject to frequent and strong modulation

Interferon Inhibits Cardiac Cell Function in Vitro

Abstract Interferon which has been shown to exert important effects on cellular function was utilized to investigate its effect on cardiac cell beating in vitro. When steadily pulsating rat cardiac cultures were continuously exposed to rat interferon for 24 hr, a decrease in the beating rate was observed. Mouse interferon which also exerted antiviral activity on rat heart nonmuscle cells also decreased the beating rate of rat cardiac cultures. Human leukocyte interferon when tested at the same dose at which rat interferon was active, exhibited no antiviral activity in rat heart nonmuscle cells and did not exert beating rate effects. When mouse interferon was incubated with antiserum prepared against mouse interferon both antiviral and beating activity were neutralized to the same extent. None of the interferons used produced morphological effects on the heart cells and with rat interferon the beating rate effect was reversible. This finding, that interferon affects cardiac cell function in vitro, may have relevance to clinical application

Early effect of interferon on mouse leukemia cells cultivated in a chemostat.

Mouse interferon preparations inhibited the multiplication of mouse leukemia L 1210 cells cultivated under steady-state conditions in a chemostat. The use of this sensitive and controlled system led to the detection of a rapid inhibition in the incorporation of (3-H)thymidine into cellular acid-precipitable material 2 hr after the addition of interferon, whereas an effect on cell multiplication was not detected until 22 hr later. Interferon exerted only a transitory effect on the incorporation of (3-H)uridine into acid-precipitable material and no effect on the incorporation of 14-C-amino acids into cellular protein. It is suggested that the chemostat offers many advantages for the investigation of those physiologic factors or chemotherapeutic substances that modify cell division