Steel factor (SLF) acts synergistically with various hematopoietic growth factors that use the Jak-Stat pathways in vivo and in vitro, although the contribution by SLF to this pathway is unknown. We show here that SLF induces time- and dose-dependent phosphorylation of Stat3 in the human growth factor-dependent cell lines MO7e and TF-1. This phosphorylation occurs exclusively on serine residues. Simultaneous stimulation with SLF plus other cytokines that induce tyrosine phosphorylation of Stat3, such as interleukin-9 (IL-9) in MO7e cells or IL-6 in TF-1 cells, resulted in tyrosine phosphorylation and enhanced serine phosphorylation of Stat3. Serine phosphorylation alone did not promote nuclear translocation or DNA binding activity to the sis- inducible element of Stat3. However, costimulation with SLF plus IL-9 in MO7e cells resulted in the nuclear translocation of serine- hyperphosphorylated Stat3. Serine phosphorylation of Stat3 was also observed by the stimulation of cells with granulocyte-macrophage colony- stimulating factor and IL-3, which do not induce tyrosine phosphorylation of Stat3. These results suggest that SLF might modulate the Jak-Stat3 pathway by serine phosphorylation and that the Jak-Stat pathway may be differentially regulated by the combinational stimulation of two or more cytokines.
A 36-year-old man who had been treated for Evans syndrome (ES) developed an aplastic crisis caused by acute human parvovirus B19 (HPV) infection. Profound thrombocytopenia (8.0 x 10(9)/l) followed with a sudden increase in platelet-associated IgG (PAIgG) (1376.9 ng/10(7) plts). Bone marrow examination revealed a considerable number of haemophagocytic histiocytes without any disturbance of megakaryopoiesis. To our knowledge this is the first case of aplastic crisis with virus-associated haemophagocytosis in a patient with ES, which provides an interesting insight into the mechanisms for thrombocytopenia in HPV infection.
Flt3 Ligand (L), a newly identified stimulating/co-stimulating cytokine for hematopoietic stem and progenitor cells, was assessed for its capacity, in comparison to that of steel factor, to prolong the survival in culture of hematopoietic stem and progenitor cells from CD34++ + human cord blood. The addition of Flt3-L to serum-depleted cultures significantly prolonged the survival of high-proliferative-potential colony-forming cells (HPP-CFC) as well as that of multipotential (CFU-GEMM) and granulocyte-macrophage (CFU-GM) progenitor cells. The concentrations of Flt3-L necessary for these effects were similar to those of SLF, and low concentrations of Flt3-L and SLF which were inactive when used alone were active in these effects when used together. These results may be of practical value for short-term storage, treatment and/or transport of purified populations of cord blood stem and progenitor cells.
Rearrangement of the breakpoint cluster region (bcr) and the chromosomal location of c-abl and 3'-bcr were studied in two patients with Philadelphia chromosome (Ph1)-negative chronic myelocytic leukemia (CML). One patient (patient 1) had a normal karyotype and the other (patient 2), 46,XY,inv(3)(q21q26). Both patients showed the bcr rearrangement by Southern blot analysis with a 1.2kb 3'-bcr probe. In situ hybridization studies demonstrated the location of the homologous sequences of bcr on chromosome 22 in patient 1, and on chromosomes 9 and 22 in patient 2. These findings indicate that the morphologically normal-looking chromosomes 9 and 22 in patient 2 are the result of a retranslocation between chromosomes 9q+ and 22q-, abnormalities which were first formed by a standard Ph1 translocation.
Erythropoietin (EPO) and thrombopoietin (c-MPL ligand; TPO) are structurally similar cytokines and support respectively, the proliferation and differentiation for erythroid and megakaryocytic lineages, as well as more primitive progenitors. We studied the effect of these cytokines on the induction of adhesion of human growth-factor-dependent hematopoietic cells to immobilized fibronectin, which is a main component of the extracellular matrix in the bone marrow. MO7ER cells that are genetically engineered to express human EPO receptor and MO7e cells that express endogenous c-MPL were used. Stimulation with either TPO or EPO induced rapid increases in adhesion of M07ER cells to fibronectin without apparent change of expression of integrins. Experiments with inhibitory monoclonal antibodies (mAbs) demonstrated that CD41, which has been reported to be involved in TPO-induced adhesion of megakaryocytic cells, is not responsible for this enhanced adhesion. Anti-beta 1 integrin mAb inhibited adhesion completely, while inhibition by anti-alpha 4 integrin mAb and anti-alpha 5 integrin mAb was partial. Combination of anti-alpha 4 mAb plus anti-alpha 5 mAb completely abolished adhesion, as did anti-beta 1 mAb, suggesting that the adhesion is mediated by both alpha 4 beta 1 and alpha 5 beta 1 integrins. Experiments using inhibitors suggested that ligand binding followed by activation of intracellular tyrosine kinases along with PI3-kinase activation is required. After stimulation of M07ER cells with either TPO or EPO, fibronectin-attached cells, but not cells in suspension, showed tyrosine phosphorylation of focal adhesion kinase, which plays a central role in integrin-mediated signaling. These data suggest that TPO and EPO might be involved in homing/migration to the bone marrow microenvironment by hematopoietic cells that express corresponding receptors.
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