The ektacytometric elongation Index (EI) of erythrocytes, validation of a prognostic, rheological biomarker for patients with sickle cell disease.

OBJECTIVES: Validation of the measurement of erythrocyte deformability as a useful prognostic, rheological biomarker for patients with sickle cell disease (SCD). METHODS: The degree of reduced deformability was based on the value of the maximum elongation index (EImax ) of the deformability curve of an osmotic gradient ektacytometer. The performance of this technique was analytically and clinically validated by analysing 200 normal subjects and 100 patients with well-documented thalassemia's and Hb variants in relation to their clinical condition. RESULTS: In this study, we show that EImax is a reproducible parameter with a small inter-individual coefficient of (Biological) variation (CV)=1.6% and a small intra-individual CV=3.5%. We demonstrate that loss of deformability correlates with the clinical condition and the various mutations underlying sickle cell disease and thalassemia. For SCD patients, a strongly reduced EImax with a cut-off =0.360 is a signal for future vaso-occlusive (VOC) events requiring hospitalisation with a specificity=85%, sensitivity=80%, PPV=81% and NPV=84% based on a ROC curve (AUC=0.89). CONCLUSION: This study validated the clinical utility of EImax as a prognostic marker for future clinical problems in individual high-risk SCD patients. In addition, EImax may help to achieve an adequate personal transfusion policy for an optimal blood flow in anaemic patients with SCD.

MiR-17/20/93/106 promote hematopoietic cell expansion by targeting sequestosome 1-regulated pathways in mice.

MicroRNAs (miRNAs) are pivotal for regulation of hematopoiesis but their critical targets remain largely unknown. Here, we show that ectopic expression of miR-17, -20,-93 and -106, all AAAGUGC seed-containing miRNAs, increases proliferation, colony outgrowth and replating capacity of myeloid progenitors and results in enhanced P-ERK levels. We found that these miRNAs are endogenously and abundantly expressed in myeloid progenitors and down-regulated in mature neutrophils. Quantitative proteomics identified sequestosome 1 (SQSTM1), an ubiquitin-binding protein and regulator of autophagy-mediated protein degradation, as a major target for these miRNAs in myeloid progenitors. In addition, we found increased expression of Sqstm1 transcripts during CSF3-induced neutrophil differentiation of 32D-CSF3R cells and an inverse correlation of SQSTM1 protein levels and miR-106 expression in AML samples. ShRNA-mediated silencing of Sqstm1 phenocopied the effects of ectopic miR-17/20/93/106 expression in hematopoietic progenitors in vitro and in mice. Further, SQSTM1 binds to the ligand-activated colony-stimulating factor 3 receptor (CSF3R) mainly in the late endosomal compartment, but not in LC3 positive autophagosomes. SQSTM1 regulates CSF3R stability and ligand-induced mitogen-activated protein kinase signaling. We demonstrate that AAAGUGC seed-containing miRNAs promote cell expansion, replating capacity and signaling in hematopoietic cells by interference with SQSTM1-regulated pathways.

The deubiquitinating enzyme DUB2A enhances CSF3 signalling by attenuating lysosomal routing of the CSF3 receptor.

Ubiquitination of the CSF3R [CSF3 (colony-stimulating factor 3) receptor] occurs after activated CSF3Rs are internalized and reside in early endosomes. CSF3R ubiquitination is crucial for lysosomal routing and degradation. The E3 ligase SOCS3 (suppressor of cytokine signalling 3) has been shown to play a major role in this process. Deubiquitinating enzymes remove ubiquitin moieties from target proteins by proteolytic cleavage. Two of these enzymes, AMSH [associated molecule with the SH3 domain of STAM (signal transducing adaptor molecule)] and UBPY (ubiquitin isopeptidase Y), interact with the general endosomal sorting machinery. Whether deubiquitinating enzymes control CSF3R trafficking from early towards late endosomes is unknown. In the present study, we asked whether AMSH, UBPY or a murine family of deubiquitinating enzymes could fulfil such a role. This DUB family (deubiquitin enzyme family) comprises four members (DUB1, DUB1A, DUB2 and DUB2A), which were originally described as being haematopoietic-specific and cytokine-inducible, but their function in cytokine receptor routing and signalling has remained largely unknown. We show that DUB2A expression is induced by CSF3 in myeloid 32D cells and that DUB2 decreases ubiquitination and lysosomal degradation of the CSF3R, leading to prolonged signalling. These results support a model in which CSF3R ubiquitination is dynamically controlled at the early endosome by feedback mechanisms involving CSF3-induced E3 ligase (SOCS3) and deubiquitinase (DUB2A) activities.

Site-specific ubiquitination determines lysosomal sorting and signal attenuation of the granulocyte colony-stimulating factor receptor.

Ubiquitination of cytokine receptors controls intracellular receptor routing and signal duration, but the underlying molecular determinants are unclear. The suppressor of cytokine signaling protein SOCS3 drives lysosomal degradation of the granulocyte colony-stimulating factor receptor (G-CSFR), depending on SOCS3-mediated ubiquitination of a specific lysine located in a conserved juxtamembrane motif. Here, we show that, despite ubiquitination of other lysines, positioning of a lysine within the membrane-proximal region is indispensable for this process. Neither reallocation of the motif nor fusion of ubiquitin to the C-terminus of the G-CSFR could drive lysosomal routing. However, within this region, the lysine could be shifted 12 amino acids toward the C-terminus without losing its function, arguing against the existence of a linear sorting motif and demonstrating that positioning of the lysine relative to the SOCS3 docking site is flexible. G-CSFR ubiquitination peaked after endocytosis, was inhibited by methyl-beta-cyclodextrin as well as hyperosmotic sucrose and severely reduced in internalization-defective G-CSFR mutants, indicating that ubiquitination mainly occurs at endosomes. Apart from elucidating structural and spatio-temporal aspects of SOCS3-mediated ubiquitination, these findings have implications for the abnormal signaling function of G-CSFR mutants found in severe congenital neutropenia, a hematopoietic disorder with a high leukemia risk.

Janus kinases promote cell-surface expression and provoke autonomous signalling from routing-defective G-CSF receptors.

CSF3R [G-CSF (granulocyte colony-stimulating factor) receptor] controls survival, proliferation and differentiation of myeloid progenitor cells via activation of multiple JAKs (Janus kinases). In addition to their role in phosphorylation of receptor tyrosine residues and downstream signalling substrates, JAKs have recently been implicated in controlling expression of cytokine receptors, predominantly by masking critical motifs involved in endocytosis and lysosomal targeting. In the present study, we show that increasing the levels of JAK1, JAK2 and TYK2 (tyrosine kinase 2) elevated steady-state CSF3R cell-surface expression and enhanced CSF3R protein stability in haematopoietic cells. This effect was not due to inhibition of endocytotic routing, since JAKs did not functionally interfere with the dileucine-based internalization motif or lysine-mediated lysosomal degradation of CSF3R. Rather, JAKs appeared to act on CSF3R in the biosynthetic pathway at the level of the ER (endoplasmic reticulum). Strikingly, increased JAK levels synergized with internalization- or lysosomal-routing-defective CSF3R mutants to confer growth-factor independent STAT3 (signal transducer and activator of transcription 3) activation and cell survival, providing a model for how increased JAK expression and disturbed intracellular routing of CSF3R synergize in the transformation of haematopoietic cells.

Successful treatment of a noninhibitory antibody-mediated acquired factor X deficiency in a patient with marginal-zone lymphoma.

Prolonged clotting times were observed in a patient with spontaneous hemorrhage. Analysis showed severe factor X deficiency due to clearance by a noninhibitory antibody. Lymphadenopathy identified on imaging led to diagnosis of marginal B-cell lymphoma. Treatment of lymphoma with rituximab and chlorambucil resulted in complete disappearance of the bleeding disorder.

Scratching the surface: signaling and routing dynamics of the CSF3 receptor.

Following activation by their cognate ligands, cytokine receptors undergo intracellular routing towards lysosomes where they are degraded. Cytokine receptor signaling does not terminate at the plasma membrane, but continues throughout the endocytotic pathway. The modes of internalization and intracellular trafficking of specific receptors, the level of recycling towards the plasma membrane, the type of protein modifications (phosphorylation, ubiquitination) and the enzymes involved in these processes are remarkably diverse. This heterogeneity may contribute to the fine-tuning of signal amplitudes and duration from different receptors. The colony-stimulating factor 3 receptor (CSF3R) is unique for its balanced signaling output, first leading to proliferation of myeloid progenitors, followed by a cell cycle arrest and granulocytic differentiation. The mechanisms associated with CSF3R signal modulation, involving receptor lysine ubiquitination and redox-controlled phosphatase activities, are to a large extent confined to the signaling endosome. Interactions between signaling endosomes and the endoplasmic reticulum play a key role in this process. Here, we review the mechanisms of intracellular routing of CSF3R, their consequences for myeloid blood cell development and their implications for myeloid diseases.

Cdc37p is involved in osmoadaptation and controls high osmolarity-induced cross-talk via the MAP kinase Kss1p.

Cdc37p, the p50 homolog of Saccharomyces cerevisiae, is an Hsp90 cochaperone involved in the targeting of protein kinases to Hsp90. Here we report a role for Cdc37p in osmoadaptive signalling in this yeast. The osmosensitive phenotype that is displayed by the cdc37-34 mutant strain appears not to be the consequence of deficient signalling through the high osmolarity glycerol (HOG) MAP kinase pathway. Rather, Cdc37p appears to play a role in the filamentous growth (FG) pathway, which mediates adaptation to high osmolarity parallel to the HOG pathway. The osmosensitive phenotype of the cdc37-34 mutant strain is aggravated upon the deletion of the HOG gene. We report that the hyper-osmosensitive phenotype of the cdc37-34, hog1 mutant correlates to a reduced of activity of the FG pathway. We utilized this phenotype to isolate suppressor genes such as KSS1 that encodes a MAP kinase that functions in the FG pathway. We report that Kss1p interacts physically with Cdc37p. Like Kss1p, the second suppressor that we isolated, Dse1p, is involved in cell wall biogenesis or maintenance, suggesting that Cdc37p controls osmoadapation by regulating mitogen-activated protein kinase signalling aimed at adaptive changes in cell wall organization.