Paroxysmal nocturnal hemoglobinuria and the glycosylphosphatidylinositol anchor

SUMO: From Bench to Bedside

Sentrin/small ubiquitin-like modifier (SUMO) is protein modification pathway that regulates multiple biological processes, including cell division, DNA replication/repair, signal transduction, and cellular metabolism. In this review, we will focus on recent advances in the mechanisms of disease pathogenesis, such as cancer, diabetes, seizure, and heart failure, which have been linked to the SUMO pathway. SUMO is conjugated to lysine residues in target proteins through an isopeptide linkage catalyzed by SUMO-specific activating (E1), conjugating (E2), and ligating (E3) enzymes. In steady state, the quantity of SUMO-modified substrates is usually a small fraction of unmodified substrates due to the deconjugation activity of the family Sentrin/SUMO-specific proteases (SENPs). In contrast to the complexity of the ubiquitination/deubiquitination machinery, the biochemistry of SUMOylation and de-SUMOylation is relatively modest. Specificity of the SUMO pathway is achieved through redox regulation, acetylation, phosphorylation, or other posttranslational protein modification of the SUMOylation and de-SUMOylation enzymes. There are three major SUMOs. SUMO-1 usually modifies a substrate as a monomer; however, SUMO-2/3 can form poly-SUMO chains. The monomeric SUMO-1 or poly-SUMO chains can interact with other proteins through SUMO-interactive motif (SIM). Thus SUMO modification provides a platform to enhance protein-protein interaction. The consequence of SUMOylation includes changes in cellular localization, protein activity, or protein stability. Furthermore, SUMO may join force with ubiquitin to degrade proteins through SUMO-targeted ubiquitin ligases (STUbL). After 20 yr of research, SUMO has been shown to play critical roles in most, if not all, biological pathways. Thus the SUMO enzymes could be targets for drug development to treat human diseases.

Hematopoietic Cell Transplantation for Paroxysmal Nocturnal Hemoglobinuria in the Age of Eculizumab

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired clonal hematopoietic cell disease characterized by the destruction of hematopoietic cells through activation of the complement system with manifestations that can be life-threatening including hemolysis, thrombosis, and marrow failure. Allogeneic hematopoietic cell transplantation (HCT) remains the sole cure for PNH, but eculizumab, a terminal complement inhibitor of C5, has been used to prevent complement-mediated hemolysis in patients with PNH since its approval by the Food and Drug Administration in 2007. We examined outcomes of HCT in patients with PNH to evaluate the effects of disease subtype, conditioning intensity, and eculizumab use either pre-HCT or post-HCT. Fifty-five patients with a diagnosis of PNH underwent at least 1 HCT, with 4 patients requiring a second HCT for graft failure. The median age at the time of first HCT was 30.0 years (range, 4.2 to 66.9 years). Seventeen patients (30.9%) had classical PNH, and the remaining 38 patients had PNH associated with another marrow disorder (aplastic anemia in 26 of the 38). Indications for HCT included pancytopenia in 47.3% of the patients, myeloid malignancy (myelodysplastic syndrome, myeloproliferative neoplasm, or acute myelogenous leukemia) in 21.8%, recurrent hemolysis in 20.0%, and thrombosis in 10.9%. Of the 55 first HCTs, 26 were performed with myeloablative conditioning, 27 were performed with reduced-intensity conditioning, and 2 sets of identical twins underwent HCT without any conditioning. Donor types included HLA-matched related in 38.2%, HLA-matched unrelated in 34.5%, single HLA-allele mismatched unrelated in 16.4%, umbilical cord blood in 5.5%, syngeneic in 3.6%, and HLA-haploidentical in 1.8%. The median duration of follow-up in surviving patients was 6.1 years (range, 2.1 to 46.1 years) after first HCT. The median time to neutrophil and platelet engraftment was 17 days and 19 days, respectively; all but 2 patients (96.3%) had sustained engraftment. Overall survival was 70% at 5 years. Neither the choice of conditioning intensity nor PNH subtype affected survival. Nineteen patients died during follow-up, including 12 patients before day +365. Six patients received treatment with eculizumab before HCT, and 2 were treated after HCT. All patients treated with eculizumab were alive at a median follow-up of 2.3 years (range, .2 to 6.9 years). Both patients treated with eculizumab after HCT had minimal to no acute GVHD (aGVHD), with grade I skin aGVHD in 1 patient and no aGVHD in the other patient, and no chronic GVHD at 2.1 and 4.1 years post-HCT, respectively. With the approval of eculizumab, the indications for HCT include persistent hemolysis, persistent thrombosis, and associated marrow failure. Administration of eculizumab before and after HCT warrants further study, particularly considering our observation of minimal to no GVHD in 2 patients who received eculizumab after HCT.

The platelet function defect of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare, acquired stem cell disorder, characterised by an abnormal susceptibility of red blood cells to complement induced lysis, resulting in repeated episodes of intravascular haemolysis and haemoglobinuria, thromboembolic events at atypical locations and, to a much lesser extent, bleeding complications. Platelet function is assumed to be abnormal, however, a defect has not yet been characterised and underlying mechanisms remain elusive. To explore these issues, we investigated platelet function in PNH patients using assays for clot formation under low and high shear force (thrombelastography and PFA100 device), adhesion to glass beads in native whole blood (Hellem method), aggregometry using various agonists (Born method), and flow cytometric assays for baseline and agonist-induced surface expression density of alpha-granule (CD62P) and lysosomal granule proteins (CD63), ligand binding to surface receptors (thrombospondin), and expression density of activation-induced neoepitopes of the fibrinogen receptor complex (PAC-1). Platelet PNH clone size determined by CD55 and CD59 labelling was compared to the clone sizes of granulocytes, monocytes, erythrocytes, and reticulocytes. A profound reduction of platelet reactivity was observed in PNH patients for all "global function" assays (clot formation, adhesion, aggregation). Platelet hyporeactivity was confirmed using flow cytometric assays. Whereas baseline levels of flow cytometrically determined platelet activation markers did not differ significantly between controls and PNH patients, agonist-induced values of all markers were distinctly reduced in the PNH group. Moreover, significantly reduced white blood cell counts (3.1/nl vs. 5.9/nl), haemoglobin values (9.5 vs. 14.3/g per dl), and platelet counts (136 vs. 219/nl) delineate profound tricytopenia in PNH patients. The fraction of particular cell types lacking the surface expression of GPI-anchored glycoproteins is referred to as the respective PNH clone; median PNH clone sizes of cells with short life spans (reticulocytes, platelets, granulocytes) was 50-80% of total cell populations compared to 20% of red blood cells. The results of our laboratory investigations show, that in PNH, reduced platelet counts coincide with reduced platelet reactivity. The foremost clinical complication in PNH, however, is venous thromboembolism, very probably induced by an activated and dysregulated plasmatic coagulation system. From these seemingly contradictory findings we infer, that part of the platelet hyporeactivity is probably due to reactive downregulation of platelet function in response to chronic hyperstimulation. The overall result is thought to be an unsteady balance, associated with thromboembolism in a larger proportion of patients, and with bleeding in a smaller proportion.

Hematopoietic cell transplantation from related and unrelated donors after minimal conditioning as a curative treatment modality for severe paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal disorder caused by a somatic mutation of the X-linked phosphatidylinositol glycan class A gene. Allogeneic hematopoietic cell transplantation (HCT) after high-dose conditioning is the only curative treatment; however, it is associated with high treatment-related mortality. Here, we report on allogeneic HCT for PNH after minimal conditioning. Seven adult patients with high-risk PNH underwent peripheral blood HCT from HLA-A-, -B-, -C-, -DRB1-, and -DQB1-matched related (n = 2) and unrelated (n = 5) donors. Conditioning included fludarabine 30 mg/m(2)/d on days -4 to -2 and 2 Gy of total body irradiation on day 0. After HCT, patients were given immunosuppressive therapy with oral cyclosporine starting on day -3 and mycophenolate mofetil starting on day 0. All 7 patients attained durable engraftment. After 28 days, a median of 77% (range, 53%-96%) T-cell donor chimerism was found in bone marrow and peripheral blood. T-cell chimerism increased to 91% (range, 76%-100%) on day +180 and to 100% in all surviving patients after 12 months. All 7 patients attained complete remissions of their disease. Four patients are alive 13 to 38 months after HCT. Three patients died of treatment-related mortality, 1 because of complications after acute pancreatitis and multiorgan failure, 1 because of infection related to chronic graft-versus-host disease (GVHD), and 1 because of bleeding after liver biopsy for late subacute/chronic GVHD. Allogeneic HCT from related and unrelated donors after minimal conditioning is a new and potentially curative option for patients with advanced PNH.

Plasmatic coagulation and fibrinolytic system alterations in PNH

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized pathophysiologically by intravascular lysis of blood cells and clinically by thromboembolic events, often atypical in localization. In this study, we examined the plasmatic coagulation system of PNH patients to investigate a potential relation between coagulation alterations and disease intensity (PNH clone size). We found evidence for both an increase in procoagulant and in fibrinolytic activity, resulting in increased fibrin generation and turnover. Whereas a positive association of the procoagulant potential with PNH clone size was notable, fibrinolytic activity showed an inverse association with clone size. As a possible cause, a growing impairment of fibrinolytic activation and/or an increasing displacement of fibrinolytic activity is assumed. These mechanisms are most likely caused by the detachment of the glycosyl-phosphatidyl-inositol-anchored urokinase plasminogen activator receptor from cell surfaces, causing a progressive resistance to fibrinolytic stimuli, together with a probable shift of the fibrinolytic potential from cell surfaces to soluble, circulating complexes, resulting in a cellular fibrinolysis-steal phenomenon. Together, these processes are accused of mediating an increased thrombophilic risk in PNH. As hereditary prothrombogenic defects were found more frequently in patients suffering ischaemic complications, genetic thrombophilia seems to confer an additional thromboembolic risk in PNH, and should therefore be screened for.

Diagnostic significance of measurement of the receptor for urokinase-type plasminogen activator on granulocytes and in plasma from patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired stem cell disorder characterized by the deficiency of all proteins anchored to the membrane by the glycosyl-phosphatidylinositol (GPI) anchor. The receptor for urokinase-type plasminogen activator (uPAR) also is attached to the cell membrane by a GPI anchor, and that soluble uPAR (suPAR) is present in plasma. In the present study, we measured uPAR, CD55, and CD59 on granulocytes by means of flow cytometry and suPAR in plasma by means of immunoradiometric assay. The subjects were 20 patients with PNH, 59 other patients with anemia, and 21 healthy individuals. In patients with PNH, both the mean fluorescence intensity and the positive percentage of fluorescence-activated granulocytes of uPAR, CD55, and CD59 were remarkably decreased, whereas in patients with other forms of anemia, except 2 patients with aplastic anemia, the results were not altered in comparison with those for the healthy individuals. The level of uPAR was reduced to the same extent as were those of CD55 and CD59 on the PNH-affected granulocytes. Some peak shape abnormalities (double peaks, peak tailing, or both) in the histogram of fluorescence intensity were also found in patients with PNH. The suPAR concentration of PNH plasma was 4.04+/-2.47 ng/mL, which was higher than that of the healthy individuals, 1.73+/-0.96 ng/mL (P < .01). The positive percentage of fluorescence-activated granulocytes was inversely associated with the plasma suPAR level in patients with PNH (r = -0.79, P < .01). Our data suggest that measurement of uPAR on granulocytes by means of flow cytometry and of suPAR in plasma by means of immunoradiometric assay are specific techniques for the diagnosis of PNH.

Circulating PIG-A mutant T lymphocytes in healthy adults and patients with bone marrow failure syndromes

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal hematological disorder with acquired PIG-A gene mutations and absent surface expression of proteins utilizing glycosylphosphatidylinositol (GPI) anchors. PNH often follows aplastic anemia, suggesting PIG-A mutant cells have relative dominance over normal hematopoietic cells. Somatic PIG-A mutations could arise after aplasia, or healthy persons could have rare PIG-A mutant cells that expand under selection pressure.

METHODS

We developed an in vitro negative selection method to isolate GPI-deficient T lymphocytes using aerolysin, an Aeromonas toxin that binds GPI anchors and induces cell lysis. Peripheral blood mononuclear cells (PBMC) from normal adults and patients with PNH or other bone marrow failure syndromes were analyzed.

RESULTS

From healthy adults, 166 T lymphocyte clones with deficient GPI-linked surface protein expression (CD55, CD59) were isolated. The mean mutant frequency (M(f)) of aerolysin-resistant clones was 17.8 +/- 13.8 per 10(6) PBMC, range 5.0-59.6 per 10(6) cells. Clones had a Class A complementation defect and distinct PIG-A mutations. Patients with PNH had elevated aerolysin-resistant M(f) values averaging 19 x 10(-2), a 10,000-fold difference. Two patients with Fanconi anemia and two others with mild aplastic anemia had M(f) values less than 15 x 10(-6), but two with recovering aplastic anemia had M(f) values of 20 x 10(-4), representing an intermediate value between normal persons and PNH patients.

CONCLUSION

Identification of PIG-A mutant T lymphocytes in healthy adults suggests PNH could develop following intense negative selection of hematopoiesis, with clonal outgrowth of naturally occurring PIG-A mutant stem cells.

Bone marrow transplants for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare clonal haematological disorder characterized by intravascular haemolysis and increased risk of thrombosis. PNH is associated with bone marrow failure syndromes including aplastic anaemia, myelodysplasia and leukaemia. Bone marrow transplants are sometimes used to treat PNH, but small series and reporting biases make assessment of transplant outcome difficult. The outcome of 57 consecutive allogeneic bone marrow transplants for PNH reported to the International Bone Marrow Transplant Registry (IBMTR) between 1978 and 1995 was analysed. The 2-year probability of survival in 48 recipients of HLA-identical sibling transplants was 56% (95% confidence interval 49-63%). Two recipients of identical twin transplants remain alive 8 and 12 years after treatment. One of seven recipients of alternative donor allogeneic transplants is alive 5 years after transplant. The most common causes of treatment failure were graft failure and infections. Our results indicate that bone marrow transplantation can restore normal bone marrow function in about 50% of PNH patients.

Vitronectin Concentrates Proteolytic Activity on the Cell Surface and Extracellular Matrix by Trapping Soluble Urokinase Receptor-Urokinase Complexes

Urokinase-type-plasminogen activator (uPA) and its receptor are localized in the vessel wall where they are involved in cellular activation and remodelling processes. Besides the cell surface glycolipid (GPI)-anchored urokinase receptor (uPAR), which binds uPA with high affinity, recent evidence points to the existence of soluble uPAR (suPAR), as well. In the present study, the origin, binding mechanism, and cellular effects of suPAR were examined. Under basal conditions human vascular smooth muscle cells (HVSMC), human umbilical vein endothelial cells (HUVEC), and monocytic cells released 0.1 to 2 ng/mL suPAR, which was increased twofold to fivefold after phorbol ester (PMA) stimulation, as measured by a function-dependent enzyme-linked immunosorbent assay (ELISA). suPAR alone did not bind to HVSMC or HUVEC, but reduced cellular uPA binding by 50% to 70%. However, after removal of GPI-uPAR with phosphatidylinositol-specific phospholipase C, suPAR dose-dependently increased uPA binding by fourfold to fivefold. This increase in binding was completely inhibited by vitronectin (VN) and by a monoclonal antibody against VN, but not by other matrix proteins or antibodies. Thus, VN-mediated uPA binding to cells was regulated by the ratio of soluble to surface-associated uPAR. In a uPAR-deficient cell line (LM-TK−), suPAR increased uPA binding up to 10-fold, whereas the truncated receptor lacking the amino-terminal uPA-binding domain was ineffective. The formation of a ternary uPA/suPAR/VN-complex on the cell surface and the free extracellular matrix could be inhibited by a monoclonal antibody against VN, as well as by plasminogen activator inhibitor-1 (PAI-1). Moreover, VN-mediated binding of the uPA/suPAR-complex led to a fivefold increase in plasminogen activator activity. Through this novel pathway, VN concentrates the uPA/suPAR-complex to cell surfaces and extracellular matrix sites, leading to the accumulation of plasminogen activator activity required for cell migration and tissue remodelling processes.

Vitronectin Concentrates Proteolytic Activity on the Cell Surface and Extracellular Matrix by Trapping Soluble Urokinase Receptor-Urokinase Complexes

Urokinase-type-plasminogen activator (uPA) and its receptor are localized in the vessel wall where they are involved in cellular activation and remodelling processes. Besides the cell surface glycolipid (GPI)-anchored urokinase receptor (uPAR), which binds uPA with high affinity, recent evidence points to the existence of soluble uPAR (suPAR), as well. In the present study, the origin, binding mechanism, and cellular effects of suPAR were examined. Under basal conditions human vascular smooth muscle cells (HVSMC), human umbilical vein endothelial cells (HUVEC), and monocytic cells released 0.1 to 2 ng/mL suPAR, which was increased twofold to fivefold after phorbol ester (PMA) stimulation, as measured by a function-dependent enzyme-linked immunosorbent assay (ELISA). suPAR alone did not bind to HVSMC or HUVEC, but reduced cellular uPA binding by 50% to 70%. However, after removal of GPI-uPAR with phosphatidylinositol-specific phospholipase C, suPAR dose-dependently increased uPA binding by fourfold to fivefold. This increase in binding was completely inhibited by vitronectin (VN) and by a monoclonal antibody against VN, but not by other matrix proteins or antibodies. Thus, VN-mediated uPA binding to cells was regulated by the ratio of soluble to surface-associated uPAR. In a uPAR-deficient cell line (LM-TK−), suPAR increased uPA binding up to 10-fold, whereas the truncated receptor lacking the amino-terminal uPA-binding domain was ineffective. The formation of a ternary uPA/suPAR/VN-complex on the cell surface and the free extracellular matrix could be inhibited by a monoclonal antibody against VN, as well as by plasminogen activator inhibitor-1 (PAI-1). Moreover, VN-mediated binding of the uPA/suPAR-complex led to a fivefold increase in plasminogen activator activity. Through this novel pathway, VN concentrates the uPA/suPAR-complex to cell surfaces and extracellular matrix sites, leading to the accumulation of plasminogen activator activity required for cell migration and tissue remodelling processes.

Paroxysmal nocturnal hemoglobinuria as a molecular disease

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired, clonal disorder of hematopoietic cells caused by somatic mutation in the X-linked PIGA gene encoding a protein involved in the synthesis of the glycosylphosphatidylinositol (GPI) anchor by which many proteins are attached to the membrane of cells. About 15 proteins have been found to be lacking or markedly deficient on the abnormal blood cells. These defects result in a clinical syndrome that includes intravascular hemolysis mediated by complement, unusual venous thromboses, deficits of hematopoiesis, and other manifestations. Therapy is presently directed mainly at the consequences of the disorder rather than its basic causes and includes replacement of iron, folic acid, and whole blood; hormonal modulation (prednisone, androgens); anticoagulation; and bone marrow transplantation. PNH is a chronic disease with more than half of adult patients surviving 15 years or more; prognosis is less good in children.

Cell signalling by inositol phosphoglycans from different species

The discovery of glycosyl-phosphatidylinositol (GPI) molecules and their products has given new insight into the field of signal transduction. In the last decade a novel mechanism of protein attachment to membranes has emerged, which involves a covalent linkage of the protein to the glycan moiety of a GPI. The discovery that GPI-anchored proteins are ubiquitous throughout the eukaryotes was followed by the observation that uncomplexed GPI molecules are implicated in signal transduction for a diversity of hormones and growth factors. The hydrolysis of free-GPI generates a novel second messenger: the inositol phosphoglycan (IPG). The aim of this article is to review the role of IPG and IPG-like molecules in signal transduction and to discuss future research directions.

Paroxysmal nocturnal haemoglobinuria: long-term follow-up and prognostic factors. French Society of Haematology

BACKGROUND

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare acquired disorder of haematopoietic stem cells. Although knowledge about the pathophysiology of the disease is increasing, no multivariate analysis of factors influencing survival has been undertaken, mainly because the disease is rare. We undertook such an investigation.

METHODS

Data were collected on 220 patients with PNH diagnosed over a 46-year period (1950-1995) from participating French centres. Diagnosis of the disease required, at least, an unequivocally positive Ham's test.

FINDINGS

The Kaplan-Meier survival estimate was 65% (SE 4) at 10 years and 48% (6) at 15 years after diagnosis. 8-year cumulative incidence rates of the main complications (pancytopenia, thrombosis, and myelodysplastic syndrome) were 15% (3), 28% (4), and 5% (2), respectively. Demographic data, presenting features, initial treatment, complications, and causes of death were similar to those previously reported. In multivariate analysis, seven factors were significantly associated with survival in patients with PNH. Poor survival was associated with the occurrence of thrombosis as a complication (relative risk 10.2 [95% CI 6-17], p < 0.0001), evolution to pancytopenia (5.5 [2.8-11], p < 0.0001), myelodysplastic syndrome or acute leukaemia (19.1 [7.3-50], p < 0.001), age over 55 years at diagnosis (4 [2.4-6.9], p < 0.0001), need for additional treatment (2.1 [1.3-3.6], p < 0.003), and thrombocytopenia at diagnosis (2.2 [1.3-3.8, p < 0.003). Better survival was shown for patients in whom aplastic anaemia antedated PNH (0.32 [0.14-0.72], p < 0.02). Factors associated in multivariate analysis with a high risk of thrombosis during the disease course were thrombosis at diagnosis (5.1 [2.5-10.6], p = 0.0002), age over 54 years (2.6 [1.5-4.6, p = 0.0014), and infection at diagnosis (2.6 [1.3-5.2], p = 0.0099). The risk factors for progression to pancytopenia were absence at diagnosis of anaemia (4.03 [1.3-12.2], p = 0.03) and neutropenia (2.45 [1.1-5.7], p = 0.03). The risk factors for development of myelodysplastic syndrome or acute leukaemia were abdominal pain crisis at presentation (10.5 [2.5-44.0], p = 0.004) and year of diagnosis after 1983 (8.45 [1.8-40.7], p = 0.004).

INTERPRETATION

This large number of cases permitted a detailed analysis of prognostic factors for the first time, in this rare disease. Estimates of PNH prognostic factors may serve as baseline data in the assessment of current and future treatments for this disease.

An uncleaved glycosylphosphatidylinositol signal mediates Ca(2+)-sensitive protein degradation

Inv-gp80 is a chimeric protein which contains a signal for the attachment of a glycosylphosphatidylinositol (GPI) anchor. When expressed in Dictyostelium discoideum, this protein fails to become GPI anchored and is retained within the cell as an integral membrane protein. We have compared the subcellular localization and degradation of Inv-gp80 with that of its intracellular but soluble counterpart, Inv-gp80sc. Inv-gp80sc lacks the hydrophobic C-terminal 22 amino acids of Inv-gp80. The N-linked oligosaccharides of both Inv-gp80 and Inv-gp80sc remained sensitive to endoglycosidase H, and both proteins co-fractionated with endoplasmic reticulum marker enzymes on Percoll gradients. Under normal conditions, Inv-gp80 displayed a half-life (t 1/2) of 90 min, while Inv-gp80sc displayed a t 1/2 of 120 min. The degradation of both proteins required ATP, was inhibited by tosyl phenylalanylchloromethane (Tos-Phe-CH2Cl) and was insensitive to inhibitors of lysosomal function. While depletion of Ca2+ from the endoplasmic reticulum had no effect on the degradation of Inv-gp80sc, it stimulated the degradation of Inv-gp80. When the GPI anchor signal sequence of Inv-gp80 was replaced with the transmembrane domain of the interleukin-2 receptor, the degradation of the protein was no longer influenced by Ca2+ fluxes. The data suggest that while the GPI anchor sequence of Inv-gp80 does not contain determinants regulating the degradation of the protein under basal conditions, it targets Inv-gp80 for rapid degradation under conditions where Ca2+ is depleted from the endoplasmic reticulum.

Role of phosphatidylinositol-linked proteins in paroxysmal nocturnal hemoglobinuria pathogenesis

Patients with paroxysmal nocturnal hemoglobinuria have one or more mutant hematopoietic stem cell clones deficient in glycosylphosphatidylinositol (GPI)-anchor synthesis owing to somatic mutations in the X-linked gene PIG-A. The progeny of mutant stem cells dominates the peripheral blood. The presence of a large number of GPI-anchor deficient, complement-sensitive erythrocytes leads to hemolytic anemia. The somatic mutations in PIG-A are small, various, and widely distributed in the coding regions and splice sites, indicating they occur randomly. Profiles of the mutations vary geographically, suggesting the presence of mutagen-induced mutations. The clonal dominance by the mutants does not seem to be solely due to the PIG-A mutation but may be caused either by autonomous expansion of the mutants due to a combination of the PIG-A mutation and some other genetic change(s) or by selection that preferentially suppresses normal stem cells.

Cell surface-bound urokinase-type plasminogen activator facilitates infiltration of freshly isolated granulocytes into fibrin matrix

Human cell lines of myelo/monocytic origin express the cellular receptor for urokinase-type plasminogen activator (uPA-R). The receptor localizes urokinase-type plasminogen activator (uPA) to the surface of the cell, where it can convert plasminogen to the active serine proteinase plasmin. Plasmin may subsequently account for proteolysis of pericellular proteins. We demonstrated the expression of the uPA-R by freshly isolated neutrophilic granulocytes by using a specific mAb. In freshly isolated granulocytes we detected only a weak occupation of the uPA-R; further uPA binding by granulocytes was saturable and proceeded in a dose-dependent manner. Receptor-bound uPA retained its enzymatic activity. Saturation of isolated granulocytes with exogenous uPA enhanced cellular infiltration into a fibrin matrix in vitro. uPA-dependent infiltration was inhibited by an anti-catalytic monoclonal anti-uPA antibody. The findings show that circulating neutrophilic granulocytes express the cell surface uPA-R and suggest that surface-binding of uPA may facilitate the infiltration of granulocytes into a fibrin clot, a process that might add to thrombolysis in vivo.

Activated platelets in paroxysmal nocturnal haemoglobinuria

One of the major causes of morbidity and mortality in paroxysmal nocturnal haemoglobinuria (PNH) is venous thrombosis. We have studied fibrinolysis, coagulation and platelets in 11 patients with PNH in an attempt to identify the possible mechanism(s) of thrombosis in PNH. In this study we did not identify any fibrinolytic defects, evidence of coagulation activation, nor reduction in coagulation inhibitors. In contrast, in this cohort of 11 PNH patients we have identified varying degrees of platelet activation as defined by the surface expression of activation-dependent proteins and the binding of adhesive proteins to the platelet surface. The thrombotic events in PNH usually occur in the venous system. Our studies and previous experimental studies suggest that anti-platelet therapy may be efficacious in reducing the incidence and severity of venous thrombosis in PNH.

Activation of human endothelial cells by viable or heat-killed gram-negative bacteria requires soluble CD14

In response to bacterial lipopolysaccharides (LPS; endotoxin), endothelial cells are converted to an activation phenotype expressing both proinflammatory and procoagulant properties that include the induction of leukocyte adhesion molecules and tissue factor expression. LPS-induced endothelial cell activation requires a soluble form of the monocyte LPS receptor, sCD14. We evaluated the capacity of multiple strains of gram-negative and gram-positive bacteria to induce endothelial E-selectin and tissue factor expression through sCD14-dependent pathways with cultured human umbilical vein endothelial cells (HUVE). Both viable and heat-killed gram-negative bacteria (Bacteroides fragilis, Enterobacter cloacae, Haemophilus influenzae, and Klebsiella pneumoniae) but not viable or heat-killed gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, and Streptococcus pneumoniae) induced prominent E-selectin surface expression detected by enzyme-linked immunosorbent assay. Tissue factor activity on HUVE, indicated by factor X activation, was induced in response to gram-negative bacteria but not in response to gram-positive bacteria. Gram-negative bacteria induced transcriptional activation in HUVE, indicated by the appearance of E-selectin-specific mRNA and by the demonstration of activation of NF-kappa B, a trans-activating factor necessary for E-selectin and tissue factor gene transcription. In contrast, neither E-selectin mRNA nor activation of NF-kappa B was detected in HUVE treated with gram-positive bacteria. Endothelial cell activation by gram-negative bacteria in each of these assays was inhibited with a monoclonal antibody (60bd) against CD14. Furthermore, CHO-K1 cells, transfected with human recombinant CD14, responded to all strains of gram-negative bacteria (viable or heat killed), indicated by CHO-K1 NF-kappa B activation. We conclude that gram-negative bacteria induce endothelial cell activation through a common sCD14-dependent pathway.

Cholangitis associated with paroxysmal nocturnal hemoglobinuria: another instance of ischemic cholangiopathy?

Ischemia is increasingly recognized as a cause of cholangiopathy. The aim of this study was to report a case of association of paroxysmal nocturnal hemoglobinuria with abrupt-onset cholangiopathy. Anomalies resembling sclerosing cholangitis were documented in a patient suffering from recurrent biliary pain. None of the conditions that have been associated with primary sclerosing cholangitis or other forms of cholangiopathy was present, but shortly thereafter, paroxysmal nocturnal hemoglobinuria occurred. Hepatic vein thrombosis later complicated the course of the disease. Because the fortuitous coincidence of these uncommon conditions is unlikely, this case indicates that paroxysmal nocturnal hemoglobinuria is a cause of ischemic cholangiopathy. Other thrombogenic conditions may also be implicated in some instances of apparently idiopathic cholangiopathy.

Immunohistochemical localization of C9 neoantigen and the terminal complement inhibitory protein CD59 in human endometrium

PROBLEM

Human endometrium expresses complement components, receptors, and regulatory proteins, many of which appear to be expressed in a hormone-dependent manner. Whether terminal complement components are also present in the endometrium is unknown. CD59, a broadly expressed protein that blocks association of C9 with C8 in the membrane attack complex, is localized in reproductive tissue to human spermatozoa, seminal plasma, amniotic fluid, and placenta. The present study examines human endometrium for the presence of CD59 and terminal complement proteins.

METHOD

Endometrial biopsies were obtained from six normal women from various phases of the menstrual cycle and analyzed by immunohistochemistry, using MEM-43 anti-human CD59 and anti-human SC5b-9 murine monoclonal antibodies and the immunoperoxidase technique.

RESULTS

Both CD59 protein and SC5b-9 (C9 neoantigen) were demonstrated to be present in endometrial glandular epithelium throughout the menstrual cycle. No specific staining was demonstrated in the stromal compartment.

CONCLUSION

CD59 protein and terminal complement proteins are expressed in glandular epithelial cells of normal human endometrium, in both proliferative and luteal phases, suggesting that expression is not hormonally dependent. These analyses further support the presence of a functionally active complement system in normal human endometrium.

Urokinase receptor is a multifunctional protein: influence of receptor occupancy on macrophage gene expression

Binding of urokinase to the glycolipid-anchored urokinase receptor (uPAR) has been implicated in macrophage differentiation. However, no biochemical markers of differentiation have yet been directly linked to uPAR occupancy. As extensive changes in proteolytic profile characterize monocytic differentiation, we have examined the role of uPAR occupancy on protease expression by differentiating phagocytes. Antibodies to either urokinase or to uPAR that prevent receptor binding inhibited induction of cathepsin B in cultured monocytes and both cathepsin B and 92-kD gelatinase mRNA and protein in phorbol diester-stimulated myeloid cells. Mannosamine, an inhibitor of glycolipid anchor assembly, also blocked protease expression. Anti-catalytic urokinase antibodies, excess inactive urokinase, or aprotinin had no effect, indicating that receptor occupancy per se regulated protease expression. Antibodies to the integrins CD11a and CD29 or to the glycolipid-anchored proteins CD14 and CD55 also had no effect. Protease induction was independent of matrix attachment. Antibodies to urokinase or uPAR affected neither the decrease in cathepsin G nor the increase in tumor necrosis factor-alpha in phorbol ester-stimulated cells. These data establish that uPAR is a multifunctional receptor, not only promoting pericellular proteolysis and matrix attachment, but also effecting cysteine- and metallo-protease expression during macrophage differentiation.