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W Vainchenker

Publications and source records attributed to W Vainchenker.

At least 163 records · Page 9Linked to original sources
PubMed1990

Interleukin 6 dependence of spontaneous in vitro differentiation of B cells from patients with IgM gammapathy.

Blood B cells from eight patients with clonal lymphoid disorders characterized by monoclonal IgM secretion (four with malignant plasmacytic proliferation typical of Waldenström macroglobulinemia and four without overt lymphoid neoplasia) were found to spontaneously differentiate in vitro into plasma cells. In all instances, monoclonal plasma cells (8-45% of the cells) were generated from extensively purified B cells or T-cell-depleted peripheral blood mononuclear cells after a 7-day culture period, with a corresponding high rate of IgM secretion into the culture medium. This differentiation occurred in the absence of any cell proliferation process as measured by [3H]thymidine uptake at day 2 or 4. Normal B cells did not differentiate under the same experimental conditions. Detection of interleukin 6 (IL-6) bioactivity in all patients' B-cell culture supernatants as well as of IL-6 mRNA in freshly prepared, uncultured B cells in the two cases studied by in situ hybridization suggested that IL-6 secretion by B cells may play a role in this process. Moreover, in the four patients without overt lymphoid proliferation, B-cell differentiation was significantly inhibited (60-80%) in the presence of anti-IL-6 antibodies. In contrast, anti-IL-6 antibodies did not preclude the differentiation into plasma cells of B cells from the four patients with bona fide Waldenström macroglobulinemia. These results suggest a two-step pathogenesis for such human lymphoplasmacytic clonal proliferations, the initial stage being characterized by an IL-6-dependent autocrine differentiation pathway.

Antibodies, Monoclonal↗
PubMed1989

Structure of the promoter region and tissue specificity of the human glycophorin C gene.

Glycophorin C (GPC) is an integral membrane protein of human erythrocytes which plays an important role in regulating the deformability and mechanical stability of red cells. Recently, the structural gene for this glycoprotein has been cloned (Colin, Y., Le Van Kim, C., Tsapis, A., Clerget, M., d'Auriol, L., London, J., Galibert, F., and Cartron, J. P. (1989) J. Biol. Chem. 264, 3773-3780), and we have now determined the sequence of the 1050 base pairs of DNA preceding the transcription initiation site mapped in erythroid cells. This region contains different potential regulatory cis-acting elements found in a variety of eukaryotic promoters (TATA box, CAAT box, Sp1-binding site) as well as sequences present in the promoter and enhancer regions of genes specific for the erythroid lineage (CACCC box and NF-E1-binding site). Northern blot analysis and immunological studies indicate that the GPC gene is expressed in a large number of cells and tissues. However, the level of transcription as well as the glycosylation of the mature GPC differ in erythroid and nonerythroid cells. Primer extension analysis and mapping of the 5' end GPC mRNA by the polymerase chain reaction indicate that different transcription sites are utilized for the expression of the GPC gene in erythroid and nonerythroid tissues and cell lines.

Base Sequence↗
PubMed1989

Developmentally regulated expression of a 78 kDa erythroblast membrane glycoprotein immunologically related to the platelet thrombospondin receptor.

We have previously described a monoclonal antibody (FA6-152), obtained by immunizing mice with fetal human erythrocytes [Edelman, Vinci, Villeval, Vainchenker, Henri, Miglierina, Rouger, Reviron, Breton-Gorius, Sureau & Edelman (1986) Blood 67, 56-63]. The antibody labelled fetal, but not adult, erythrocytes and bound to both fetal and adult platelets and monocytes. In the present study we have characterized the antigen recognized by FA6-152 on human platelets and on cells of the erythroid lineage at different stages of maturation. FA6-152 precipitated a chymotrypsin-resistant 88 kDa sialoglycoprotein from both iodinated and periodate/NaB3H4-surface-labelled platelets which corresponds to glycoprotein IV, the platelet thrombospondin (TSP) receptor. After neuraminidase treatment, a shift of the apparent molecular mass from 88 kDa to 85 kDa was observed. Scatchard analysis revealed that 125I-FA6-152 bound saturably with high affinity to a single class of platelet binding sites (Kd 6.4 +/- 0.6 nM). The number of FA6-152 IgG molecules bound per platelet was 25,400 +/- 8,800 (n = 4) and did not change upon thrombin activation of platelets. At low doses of alpha-thrombin (0.025 unit), FA6-152 inhibited platelet aggregation as well as endogenous TSP binding to the platelet surface. Immunofluorescence labelling of bone-marrow cells and of cultures in vitro of burst-forming units-erythroid (BFU-E) and colony-forming units-erythroid (CFU-E) revealed that that FA6-152 antigen is a very early marker of erythroid differentiation and that its expression declines during maturation. Immunochemical identification of the FA6-152 antigen on fetal erythroblasts and fetal mature erythrocytes revealed a 78 kDa glycoprotein migrating just in front of the glycophorin A dimer. The antigen, which was absent from adult mature erythrocytes, was also detected in human erythroleukaemic (HEL) cells where FA6-152 precipitated two bands of molecular mass 85 and 88 kDa. Our data establish the existence of a previously unidentified 78 kDa erythroblast cell-surface glycoprotein whose expression is developmentally regulated during erythroid differentiation and which is immunologically related to the 88 kDa platelet TSP receptor.

Antibodies, Monoclonal↗
PubMed1989

Expression of the c-fos protooncogene by human and murine erythroblasts.

The expression of the c-fos protooncogene was investigated by in situ hybridization in normal murine bone marrow cells. A strong signal was found in murine marrow cells having the morphologic features of erythroblasts. This result was confirmed in human marrow cells using a double labeling technique (in situ hybridization and immunocytochemistry). A majority (70%) of the cells expressing c-fos mRNA were glycophorin A-positive. In contrast, granulocytic precursors (CD 15-positive) or monocytes and their precursors (CD 14-positive cells) did not significantly hybridize with the c-fos probe. In addition, c-fos mRNA (2.2Kb) was detected by Northern blotting in RNA extracted from homogeneous populations of erythroblasts obtained by immune panning from fetal liver and from adult blood BFU-E-derived colonies. Fos protein was also detected in erythroblasts by immunofluorescence. The high level of c-fos mRNA previously found in hematopoietic tissue should therefore be related to the transcription of the c-fos gene during terminal erythroid differentiation.

Animals↗
PubMed1989

Regulation of the expression of IL-6 in human monocytes.

IL-6 is a cellular regulatory molecule with various cell-dependent functions. We have studied the control of IL-6 expression in human monocytes because they play a key role in the production of this molecule. The effects of adherence and different cytokines including CSF-1, IFN-gamma, IL-1 alpha, and granulocyte-macrophage-CSF were tested on IL-6 expression. IL-6 mRNA was usually not detected in the starting population of PBMC. Adherence induced IL-6 gene expression in monocytes in less than 2 h and subsequently IL-6 secretion. Priming of monocytes by adherence was more efficient for IL-6 overinduction by CSF-1. In contrast, high level induction of IL-6 by IFN-gamma in unfractionated PBMC did not require adherence and in situ hybridization revealed that IL-6 mRNA was present in monocytes but not in lymphocytes. A similar phenomenon was observed for IL-1 alpha and granulocyte-macrophage-CSF. Two cell lines, HL-60 and U937, in which monocytic differentiation occurs after induction by PMA, were subsequently investigated. IL-6 was not constitutively detectable in these two cell lines, whereas PMA treatment induced IL-6 expression. This effect was rapid (30 min) and transitory in HL-60, whereas IL-6 mRNA was still detected after 72 h of induction in U937. Addition of human rIL-6 on U937 and HL-60 cells inhibited their proliferation and enhanced expression of HLA class I Ag.

Cell Adhesion↗
PubMed1989

Early expression of glycophorin C during normal and leukemic human erythroid differentiation.

Glycophorins C and D (GPC and GPD) are two erythrocyte glycoproteins which originate from the same gene but differ in their NH2-terminal residues. The cell surface expression of these glycoproteins during normal and erythroid differentiation has been investigated with monoclonal and polyclonal antibodies and has been compared to the expression of glycophorin A (GPA), the major sialoglycoprotein of human red cells. Using glycosylation-independent antibodies (monoclonal or polyclonal), GPC or GPD was detected in erythroid and nonerythroid cell lineages. However, a glycosylation-dependent monoclonal antibody (MR4-130) detected an epitope on GPC which appears to be erythroid specific, suggesting that lineage specificity of this glycoprotein is related to some carbohydrate structures. During normal erythroid differentiation, GPC was expressed early at the level of erythroid progenitors (part of erythroid burst-forming unit and erythroid colony-forming unit) as detected with a glycosylation-independent monoclonal antibody (APO 3), whereas GPA is only present during terminal erythroid differentiation. The MR4-130 epitope was not coordinately expressed on the cell surface with the GPC molecule in the erythroid differentiation, since it was detected at the level of the more mature erythroid colony-forming unit slightly later than the GPC polypeptide. In four erythroleukemic patients, blast cells blocked at discrete stages of the erythroid differentiation were also investigated with antibodies and complementary DNA probes for GPA and GPC. GPA was immunologically detected in three of four cases, and its cell surface expression was correlated with the amount of specific mRNA in the cells, as seen by Northern blot analysis. GPC was immunologically detected on the blast cells of all four patients. However, in two cases including one with positive expression of GPA, the MR4-130 epitope was absent from the GPC molecule. By Northern blot analysis, we found that the GPC/GPD mRNA was present at a high level in all four patient samples. Western blot analysis of GPC and GPD in two of these patients revealed that these mRNAs were mostly translated into the GPD molecule, suggesting that these glycoproteins might be differently processed in certain cases of erythroleukemia.

Antibodies, Monoclonal↗
PubMed1989

Effects of five recombinant hematopoietic growth factors on enriched human erythroid progenitors in serum-replaced cultures.

Erythroid progenitors from normal human marrow were purified by a two-step immune panning method permitting both the enrichment of erythroid progenitors (plating efficiency up to 10%) and the separation of CFU-E from BFU-E. The purified erythroid progenitors were grown in serum-replaced conditions; in some experiments at an average of one cell per well. Human recombinant granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin 3 (IL3), erythroid potentiating activity (EPA), and human erythropoietin (Epo) either recombinant or homogenous native were tested for their effect on CFU-E growth. Epo was an absolute requirement for CFU-E growth and was sufficient to obtain colony formation at the unicellular level whereas GM-CSF and IL3 did not further increase the plating efficiency. EPA potentiated the effect of Epo on this progenitor only in experiments performed at unicellular level. Human recombinant GM-CSF, IL3, Interleukin 1 alpha (IL1 alpha), and Epo were subsequently tested for their ability to promote BFU-E growth. GM-CSF and IL3 supported the growth of erythroid bursts in the presence of Epo, even at the unicellular level. However, IL3 promoted a higher number of bursts than GM-CSF under all conditions tested. These two growth factors have no or very small additive effects when tested in combination. IL1 alpha added to Epo alone had no effect on the growth of BFU-E whereas it potentiated the combined action of IL3 and GM-CSF on the primitive BFU-E. In conclusion, this study confirms at the unicellular level and under serum-free conditions that erythroid progenitors are regulated by multipotential growth factors in early phases of erythropoiesis and become sensitive only to Epo in later phases of differentiation.

Bone Marrow Cells↗
PubMed1989

Uptake of plasma fibrinogen into the alpha granules of human megakaryocytes and platelets.

The origin of platelet alpha-granule fibrinogen (Fg), whether from endogeneous synthesis or exogeneous derivation, remains unknown. Although Fg biosynthesis by megakaryocytes (MK) has been suggested, recent studies have demonstrated that certain alpha-granular proteins originate primarily from plasma. To study the origin of alpha-granule Fg, platelet-associated Fg was measured by ELISA and Western blotting, and localized by immunofluorescence and immunoelectron microscopy in a patient with symptomatic congenital afibrinogenemia before and after replacement therapy with cryoprecipitate. alpha-Granule Fg was detected in the majority of platelets as early as 24 h postinfusion, suggesting that direct platelet uptake was occurring. Platelet Fg reached a maximum value of 42.5% of normal values at 3 d postinfusion and was localized in the alpha-granules, while plasma levels followed a typical half-life profile. Significant alpha-granule Fg was still detectable at 13 d postinfusion, with plasma Fg virtually absent. Studies on cultured CFU-MKs from the patient also confirmed that MKs can incorporate exogeneous Fg into alpha-granules. These results indicate that platelet alpha-granule Fg can be derived from the circulating plasma pool and that Fg uptake can occur in both platelets and MKs.

Adult↗
PubMed1989

Expression of platelet glycoproteins by erythroid blasts in four cases of trisomy 21.

In four patients with trisomy 21 (three constitutional, one acquired) with a morphological undifferentiated leukemia, diagnosis of erythroid leukemia was established by both immunophenotyping and ultrastructural studies. Indeed, a majority of blasts from three patients expressed several erythroid markers such as carbonic anhydrase 1, spectrin beta chain, and glycophorin A. In addition, band 3 and hemoglobin were immunologically detected in a fraction of the blast cells from two cases. At ultrastructural level, a majority or all blast cells exhibited erythroid differentiation features such as theta granules and ferritin molecules. However, platelet glycoproteins GP Ib, GP IIb, and GP IIIa were also immunologically detected in a fraction (from 14-82%) of the blasts. Since the ultrastructural study indicated that some promegakaryoblasts were also present in three patients, double labeling between erythroid markers (glycophorin A or carbonic anhydrase I) and platelet glycoprotein (Ib or IIIa) was performed and showed a clear overlap between the two kinds of markers. A similar approach was performed at ultrastructural level and indicated that blast cells with ultrastructural erythroid features of differentiation may have three distinct phenotypes, i.e., presence of glycophorin A without platelet glycoproteins or, conversely, the presence of platelet glycoproteins without glycophorin A and coexpression of glycophorin A and platelet glycoproteins. Expression of glycophorin A correlated directly with the differentiation level of the erythroid blasts, whereas platelet glycoproteins were essentially expressed in the more primitive leukemic erythroid cells. The GP Ib synthesized by these blasts was subsequently studied. The GP Ib alpha mRNA analyzed by Northern blot from these erythroid cells was identical in size with that from megakaryocytic cells as was the molecular weight of the GP Ib molecule from both after immunoprecipitation by a monoclonal antibody. Therefore, "in vivo" erythroid leukemic cells may express the main platelet glycoproteins including GP Ib.

Antibodies, Monoclonal↗
PubMed1989

Uncoordinated expression of fibrinogen compared with thrombospondin and von Willebrand factor in maturing human megakaryocytes.

The localization of three known alpha-granule proteins, thrombospondin (TSP), von Willebrand factor (vWF), and fibrinogen (Fg) has been studied in human megakaryocytes (MK) by immunofluorescence and immunoelectron microscopy. For this study, highly purified populations of MK were prepared from human bone marrow either by counterflow centrifugal elutriation or by cell culture from normal subjects and from two patients with megakaryoblastic leukemia. In normal bone marrow immature MK, TSP, and vWF were observed in the Golgi-associated vesicles and in small immature alpha-granules; in mature MK, they were found in the matrix of the mature large alpha-granules. Surprisingly, Fg was detected neither in the Golgi area, nor in the small precursors of alpha-granules; it was only found in the mature alpha-granules but this labeling was generally weaker than in blood platelets. In order to confirm these differences between the expression of Fg and vWF or TSP additional studies were performed on cultured maturing MK: immunofluorescent and ultrastructural immunogold labeling confirmed that vWF appeared early in the maturation while the same immature MK were negative for Fg. In the late maturation stage, the three proteins were detected in the alpha-granules. In order to know whether Fg was lately synthesized or endocytosed from the outside medium, normal MK were grown in the presence of either normal or afibrinogenemic plasma, and normal serum. Fg was detected only in the alpha-granules of MK grown in normal plasma. Similar results were observed with malignant MK, whose maturation was independent of the culture conditions. In conclusion, this study brings immunocytochemical evidence that vWF and TSP are synthesized by immature MK, whereas Fg appears later in the MK alpha-granules and its expression is dependent of the presence of an exogenous Fg source.

Adult↗
PubMed1989

Limits of phenotypic markers for the diagnosis of megakaryoblastic leukemia.

Diagnosis of megakaryoblastic and early erythroid leukemia requires the use of differentiation markers that in most cases permit their precise diagnosis. In some cases, their use can be misleading. Here we report and discuss some examples. A platelet peroxidase (PPO) activity is detected in most cases of early erythroid leukemias as well as in the CFU-E-like cells of normal marrow, thus providing evidence that PPO activity must be studied along with other (immunologic or ultrastructural) markers to permit a reliable diagnosis of megakaryoblastic leukemia. Ferritin molecules an erythroid marker, could be detected as a cluster at ultrastructural level in leukemic platelets and in micromegakaryocytes of one patient. However, in blasts of the erythroid lineage, ferritin molecules are also either dispersed in the cytoplasm or localized in theta granules. Immunologic markers have also their own limit. Indeed, in one patient, GB IIb and IIIa were detected on erythroid blasts, resulting in a phenotype very similar to HEL cells. Carbonic anhydrase (CA) I, an early erythroid marker, was detected in the platelets of four leukemic patients and was present along with an increased expression of CA II. This study emphasizes the fact that precise diagnosis of leukemia cannot be performed with a single marker of differentiation, but requires the simultaneous use of several lineage restricted markers.

Antibodies↗
PubMed1988

New hematopoietic differentiation antigens detected by anti-K562 monoclonal antibodies.

Following immunizations of BALB/c mice with K562 cells, we have obtained seven original monoclonal antibodies (MoAbs): (a) One MoAb, GA3, defines an antigen essentially restricted to the red cell series. This antigen is expressed on immature erythroblasts but is not detectable on the surface of early and late erythroid progenitors. GA3 MoAb immunoprecipitates a Mr 105,000 glycoprotein on K562 cells. (b) Two MoAbs, 14B6 and 12B1, react with cells of the monocytic series. MoAb 14B6, which also faintly stains platelets, is reactive with immature myeloid cells and the majority of hematopoietic progenitors. The 14B6 antigen has been immunoprecipitated from 12-O-tetradecanoylphorbol-13-acetate treated K562 cells as a Mr 130,000-100,000 protein. Antigen 12B1 is expressed only on cultured monocyte/macrophages and is restricted to a subpopulation of monocytes and to follicular dendritic cells. It is not detected on hematopoietic progenitors. Immunoprecipitation experiments performed on 12-O-tetradecanoylphorbol-13-acetate treated K562 cells revealed a glycoprotein with a molecular weight of 93,000-86,000. (c) Two anti-K562 MoAbs, CF4 and HE10, recognize a myeloid differentiation antigen expressed from the granulomonocytic colony forming unit stage to polymorphonuclear neutrophils. These MoAbs detect an apparently original glycolipid moiety distinct from LeX. (d) Two MoAbs recognize antigens expressed on the granulomonocytic series. 2E1 recognizes the monocyte low affinity Fc receptor (Mr 40,000) and defines a new cluster of myeloid differentiation (CDw32). The antigen is expressed on a small portion of immature hematopoietic progenitors. 8F5 identifies a Mr 95,000 protein which is also present on plasma cells. In some experiments, it is detected on erythroid colony forming unit analysis. Immunizations with K562 cells thus resulted in the production of antibodies recognizing antigens of the monocytic, granulocytic, as well as erythroid series. However, three of them are also detected on hematopoietic progenitors.

Animals↗
PubMed1988

Human platelet alpha granules contain a nonspecific inhibitor of megakaryocyte colony formation: its relationship to type beta transforming growth factor (TGF-beta).

Whole blood serum (WBS) and platelet-poor plasma-derived serum (PDS) from the same normal subject were compared for their abilities to support human megakaryocyte (MK) colony formation. In all cases, PDS promoted the growth of a higher number (20-50%) of MK colonies than did WBS. Increasing amounts of WBS decreased the number of colonies, whereas increasing concentration of PDS had no marked effects. Crude platelet extracts or platelet secretory products from thrombin-activated platelets also elicited an inhibition of MK colony formation in a dose-dependent manner. A complete inhibition was found for a dose equivalent to 1.10(9) platelets/ml and a 50% inhibition in a range of 1.10(7)-1.10(8) platelets/ml. These platelet products were also inhibitory for erythroid progenitor growth. Platelets from two patients with gray platelet syndrome elicited only a minor inhibition of MK growth, suggesting that the platelet alpha granule is the origin of this inhibition. When platelet extracts were acid-treated, the biological activity of the inhibitor on CFU-MK and CFU-E growth was 20-50-fold higher. In addition, a potent stimulatory activity on the growth of day 7 CFU-GM was observed. The enhancement of biological activities by acid treatment suggests that type beta transforming growth factor (TGF-beta) could be involved in this platelet inhibitory activity. The homogeneous native TGF-beta (from 1 pg to 1 ng/ml) produced the same effects previously induced by platelet products. It totally inhibited CFU-MK growth (at a 500 pg/ml), it inhibited CFU-E growth, and it stimulated growth of day 7 CFU-GM in the presence of a colony-stimulating factor. The inhibition of CFU-MK growth was also observed on purified progenitors. In conclusion, these results suggest that TGF-beta may be implicated in negative autocrine regulation of megakaryopoiesis. However, since this molecule has ubiquitous biological activities, its physiologic relevance as a normal regulator of megakaryopoiesis requires further investigation.

Blood Physiological Phenomena↗
PubMed1988

Human megakaryocytopoiesis: in vitro regulation and characterization of megakaryocytic precursor cells by differentiation markers.

Understanding of human megakaryopoiesis has been improved by in vitro culture techniques, characterization of platelet proteins as differentiation markers and megakaryocyte purification. A continuum of megakaryocytic cells ranging from the CFU-MK (cell capable of proliferation) to the platelet has been demonstrated. CFU-MK is a heterogeneous population of cells which do not express platelet proteins other than platelet GP IIb and IIIa which may be present in low concentration. The main platelet proteins are synthesized later during differentiation of a 2N cell, just before the polyploidization process. Several homogeneous growth factors GM-CSF, interleukin 3 and erythropoietin are able to sustain human megakaryocyte colony formation. However, no specific MK-CSF has yet been purified. Purification of factors active on late stages of differentiation has proved difficult when using in vivo techniques to test their activity. However, recently such a factor has been purified to homogeneity by testing its action on the biosynthesis of PF4 by megakaryocytes. A negative regulation of megakaryopoiesis has been suggested by the inhibition of MK-colony formation by platelet products especially TGF-beta. A better understanding of human megakaryopoiesis may be of importance as it may allow modifications of platelet production in a clinical setting.

Hematopoiesis↗
PubMed1988

Use of a monoclonal antibody (GA3) to demonstrate lineage restricted O-glycosylation on leukosialin during terminal erythroid differentiation.

A murine monoclonal antibody (GA3) obtained by immunizing mice with cells of the human erythroleukemic cell line K562 is shown to define a 105 kilodalton (kd) membrane antigen on K562 cells that is restricted within the hematopoietic system to the erythroid lineage and to a minor population of CD3, CD4 positive T lymphocytes. Cocapping studies and immunoprecipitation experiments performed with GA3 and L10, an anti-sialophorin monoclonal antibody reacting with leukosialin (Gp 105) on K562 cells, demonstrate that the antigen detected by GA3 on K562 cells is identical to leukosialin. Neuraminidase treatment but not tunicamycin treatment of K562 cells abolishes the expression of the GA3-epitope without affecting the L10-epitope thus providing evidence that terminal sialic acid present on O-linked oligosaccharide chains on Gp 105 is essential for the expression of the GA3-epitope. Further analysis by flow cytometry and immune panning experiments performed on bone marrow cells with GA3 or L10 demonstrate that, in contrast to L10, which reacts with all types of hematopoietic progenitors, the epitope recognized by GA3 is restricted to the erythroid lineage, and appears during erythroid differentiation before glycophorin A on the earliest morphologically recognizable erythroid precursor, the proerythroblast. Our results therefore suggest that O-linked oligosaccharides on leukosialin express lineage restricted and even maturation restricted antigenic structures that might serve as cell lineage specific markers.

Animals↗
PubMed1988

Pyruvate kinase synthesis and degradation by normal and pathologic cells during erythroid maturation.

Mature erythrocytes contain a specific isozyme of pyruvate kinase (R-PK) while immature erythroblasts coexpress R-PK and another isozyme, M2-PK. To determine what roles degradation and decreasing of synthesis played in the disappearance of M2-PK during erythroid maturation, M2-PK and R-PK synthesis and degradation were studied in erythroblasts from fetal liver and blood BFU-E-derived erythroblasts from healthy subjects, an erythroleukemic patient, and a patient with an erythrocyte PK hyperactivity associated with M2-PK persistence in mature erythrocytes. In normal erythroblasts, R-PK synthesis was constant throughout erythroid maturation, whereas M2-PK synthesis decreased to the point of becoming undetectable. R-PK degradation was very low, while M2-PK degradation was more pronounced and steady during erythroid maturation. In leukemic erythroblasts, total protein turnover was higher than in normal cells, but the M2-PK degradation rate was lower. In erythroblasts from the patient with M2-PK persistence in mature erythrocytes, M2-PK synthesis did not decline with cell maturation. In conclusion, our results emphasize the importance of the decrease of M2-PK synthesis in the disappearance of M2-PK during erythroid maturation. Further studies of patients with pathologic persistence of M2-PK synthesis will help in the understanding of this event involved in erythroid maturation.

Adult↗