Interleukin (IL)-3, IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF) regulate proliferation, dierentiation and apoptosis of target cells. Receptors for these cytokines consist of a cytokinespeci®c a subunit and a common shared bc subunit. Tyrosine phosphorylation of the bc is thought to play a critical role in mediating signal transduction events. We have examined the eect of mutation of bc tyrosines on the activation of multiple signal transduction pathways. Activation of protein kinase B (PKB) required JAK2 and was inhibited by dominant-negative phosphatidylinositol 3-kinase (P13K). Overexpression of JAK2 was sucient to activate both protein kinase B (PKB) and extracellular regulated kinase-1 (ERK1). Tyrosine 577 and 612 were found to be critical for the activation of PKB and ERK1, but not activation of STAT transcription factors. Activation of both PKB and ERK have been implicated in the regulation of proliferation and apoptosis. We generated GM-CSFR stable cell lines expressing receptor mutants to evaluate their eect on these processes. Activation of both PKB and ERK was perturbed, while STAT activation remained unaected. Tyrosines 577 and 612 were necessary for optimal proliferation, however, mutation of these tyrosine residues did not aect GM-CSF mediated rescue from apoptosis. These data demonstrate that while phosphorylation of bc tyrosine residues 577 and 612 are important for optimal cell proliferation, rescue from apoptosis can be mediated by alternative signalling routes apparently independent of PKB or ERK activation.

The cytokines granulocyte-macrophage colony-stimulating factor (GM- CSF), interleukin (IL)-3, and IL-5 are important modulators of eosinophilia and eosinophil function. Eosinophil chemotaxis is known to be particularly sensitive for cytokine priming. In the present study, we compared chemotactic responses of eosinophils derived from peripheral blood of allergic asthmatics to responses of eosinophils from peripheral blood of healthy individuals. Eosinophils from allergic asthmatics exhibited a markedly increased sensitivity in their chemotactic response toward platelet-activating factor (PAF) compared with eosinophils from normal donors. In contrast, C5a-induced eosinophil chemotaxis between both groups was similar. This in vivo- primed phenotype could be mimicked in vitro, by preincubating eosinophils from peripheral blood of healthy individuals with picomolar concentrations of either GM-CSF, IL-3, or IL-5. The chemotactic response of eosinophils derived from the circulation of allergic asthmatic patients toward GM-CSF was significantly lower compared with the response of eosinophils of healthy individuals. Our data strongly suggest that release of cytokines may be an important in vivo priming mechanism for eosinophils in the circulation of allergic asthmatic patients. Such an in vivo priming can subsequently result in selective upregulation and downregulation of chemotactic responses toward various chemoattractants release in the lung tissue.

Chromosome condensation by condensin is essential for faithful chromosome segregation. Metazoans have two complexes, named condensin I and II. Both are thought to act by creating looped structures in DNA, but how they do so is unknown. Condensin's SMC subunits together form a composite ATPase with two pseudo-symmetric ATPase sites. We reveal that these sites have opposite functions in the condensation process. One site drives condensation, while the other site rather has a dampening function. Mutation of this dampener site hyperactivates both condensin I and II complexes. We find that hyperactive condensin I efficiently shortens chromosomes in the total absence of condensin II. The two complexes form loops with different lengths, and specifically condensin II is key to the decatenation of sister chromatids and the formation of a straight chromosomal axis.

We report that responses of normal human eosinophils toward the chemokines RANTES and interleukin-8 (IL-8) are modulated and upregulated by priming with IL-5. In a modified Boyden chamber assay, we studied migratory responses toward the members of the chemokine family RANTES, monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1 alpha (MIP-1 alpha) (C-C subfamily), and IL-8, platelet factor-4 (PF-4), and neutrophil-activating peptide-2 (NAP-2) (C-x-C subfamily). These chemokines were also studied in terms of actin polymerization and ([Ca2+]i)-mobilizing properties, intracellular signals that are thought to play a role during migratory responses. We found that eosinophils showed significant migratory responses toward RANTES and IL-8 at concentrations of 10(-9) to 10(-7) mol/L only after priming with IL-5 (10 pmol/L). At these concentrations, PF-4, NAP-2, MCP-1, and MIP-1 alpha induced no significant migratory responses after priming. Unprimed eosinophils only showed a significant migratory response toward RANTES (10(-6) mol/L). Changes in [Ca2+]i were found after addition of RANTES, MIP-1 alpha, and NAP-2 (10 nmol/L) to unprimed eosinophils. RANTES (10(-9) to 10(-7) mol/L) significantly induced actin polymerization both in primed and unprimed eosinophils, whereas IL-8 (10(-9) to 10(-8) mol/L) and MIP-1 alpha (10(-8) mol/L) only induced actin polymerization after priming with IL-5. NAP-2, PF-4, and MCP-1 did not affect actin polymerization. These findings are further evidence for the hypothesis that cytokines like IL-5 and locally secreted chemokines like RANTES and IL-8 are both at the basis of specific eosinophil influx into the allergic inflammatory locus.

The Fc receptor for IgA (Fc alpha R, CD89) is a transmembrane glycoprotein found on monocytes, macrophages, neutrophils, and eosinophils. Here we describe the characterization of a novel isoform of the Fc alpha R cloned from a human eosinophil cDNA library. This clone, Fc alpha Rb, lacks the exon encoding the transmembrane/intracellular region of wild type Fc alpha R, which is replaced by 23 new amino acids. Expression of Fc alpha Rb mRNA could be detected in eosinophils and neutrophils. IIA1.6 murine pro-B cells transfected with Fc alpha Rb cDNA secrete high levels of the protein, but also a substantial amount of Fc alpha Rb is expressed at the cell membrane. Membrane-bound Fc alpha Rb binds IgA-coated beads equally well as wild type Fc alpha R. Surface expression is not affected by phosphatidyl inositol phospholipase C, indicating that glycosyl phosphatidyl inositol-linkage of Fc alpha Rb is not likely. In IIA1.6 cells expressing Fc alpha Rb and FcR gamma, which is necessary for signal transduction by wild type Fc alpha R, no tyrosine phosphorylation or Ca(2+)-mobilization could be observed after receptor cross-linking. These results indicate that Fc alpha Rb is likely to have a different function than wild-type Fc alpha R receptor.