PubMed Health⌕ Search

Biomedical subjects

M Titeux

Publications and source records attributed to M Titeux.

At least 55 records · Page 3Linked to original sources
PubMed1983

The number of the Trf receptors on human hematopoietic cell lines is influenced by membrane phospholipids.

The effect of phospholipases and of inhibitors of phospholipases on the binding of 125I-Trf to human hematopoietic cell lines was investigated. The results showed that incubation of the cells with phospholipases or inhibitors of phospholipases elicited a significant reduction of the Trf binding. This phenomenon was related to a reduction of Trf binding sites without affecting the affinity of the receptors for Trf. These results suggest that the phospholipids of the cell membrane may modulate the binding of transferrin to its receptor.

Acetophenones↗
PubMed1983

[Modulation of the expression of transferrin receptors by iron, hemin and protoporphyrin IX].

The expression of transferrin receptors in human leukemic cell lines was investigated. Our results have clearly shown that heme, iron and protoporphyrin-IX may modulate the expression of Trf receptors: iron and heme induce a decrease in the number of Trf receptors; in contrast protoporphyrin-IX elicited a significant increase in the number of Trf receptors. On the basis of these data we suggest that the intracellular concentration of iron, heme and protoporphyrin-IX may represent the main factor involved in the regulation of the expression of Trf receptors.

Animals↗
PubMed1982

Inhibition of insulin receptor binding by phorbol esters.

Phorbol esters inhibit the binding of insulin to its receptors on U-937 monocyte-like and HL-60 promyelocytic leukemia human cell lines. Within 20-30 min, exposure of these cells to 12-O-tetradecanoylphorbol 13-acetate (TPA) at 37 degrees C results in a 50% reduction of the specific binding of 125I-insulin. Half-maximal inhibition occurs at 1 nM TPA. Other tumor-promoting phorbol esters also inhibit 125I-insulin binding in a dose-dependent manner which parallels their known promoting activity in vivo. TPA does not alter the degradation of the hormone nor does it induce any shedding of its receptors in the medium. The effect of phorbol esters is dependent on temperature and cell type. It is less prominent at 22 degrees C than at 37 degrees C. It is reversible within 2 h at 37 degrees C. TPA reduces the binding of insulin predominantly by increasing its dissociation rate. This effect results in an accelerated turnover of the hormone on its receptors.

Animals↗
PubMed1982

Megakaryocyte cultures in the chronic phase and in the blast crisis of chronic myeloid leukaemia: studies on the differentiation of the megakaryocyte progenitors and on the maturation of megakaryocytes in vitro.

Megakaryocyte (MK) colony formation has been studied in the chronic phase and in the blast crisis of chronic myeloid leukaemia (CML). Blood cells were grown in plasma clot for 13 d. MKs were subsequently identified by immunofluorescent techniques using two monoclonal antiplatelet antibodies (AN51 and J15). The maturation process was studied by ultrastructural methods. A marked increase in the number of circulating CFU-MK was observed in all the 10 cases studied prior to chemotherapy (70-fold increase per ml of blood). No significant modification in the regulation of MK colony formation as compared to that of normal subjects was observed. The predominant abnormality in maturation in culture was the occurrence of many hypoploid MKs (microMKs). However, the cytoplasmic maturation of the MKs was identical to that of normal subjects with occasional platelet shedding. Since microMKs predominated in some patients, scoring of MK colonies in CML necessitated immunofluorescent labelling to permit identification of MKs. During the blast crisis, MK colony formation occurred in four out of five patients with an extremely high plating efficiency in the case of promegakaryoblastic transformation. In contrast, MK colonies could not be grown from blood samples of patients with acute leukaemia, including two cases of promegakaryoblastic leukaemia. Maturation of MKs in blast crisis was identical to that of the chronic phase. Furthermore, after short periods of culture in liquid medium, circulating promegakaryoblasts from patients in blast crisis matured with the consequent production of alpha-granules and demarcation membranes. These results confirm the contention that CML represents a pluripotent stem-cell disease, involving the MK lineage, and suggest that the block in maturation during the acute phase can be overcome in vitro.

Cell Differentiation↗
PubMed1982

Hemoglobin expression in clones of K562 cell line.

The K562 cell line was cloned by dilution and the pattern of hemoglobin (Hb) production was analyzed in the clones thus obtained. The pattern of hemoglobin synthesis was different from one clone to another. According to the Hb phenotype the clones were classified in three main groups; group I no detectable Hb; group II Hb Portland; group III Hb Portland + Hb Gower I. The addition of hemin induced a better hemoglobinization and a shift in the pattern of Hb production: clones of group I were induced to produce Hb Portland and clones of group II to synthesize Hb Gower I. A constant order in the sequential expression of the different hemoglobins was observed: no Hb leads to Hb Portland + Hb Gower I. The proportion of the different globin chains varied from one clone to another, but an inverse correlation between the synthesis of G gamma and epsilon chains was observed. The alpha/non-alpha chain ratio was unbalanced in all the clones and the addition of hemin induced only a moderate increase of the synthesis of alpha chains. Recloning of three primary clones increased the homogeneity of the hemoglobin pattern, in particular after hemin induction.

Clone Cells↗
PubMed1982

Clonal expression of the Tn antigen in erythroid and granulocyte colonies and its application to determination of the clonality of the human megakaryocyte colony assay.

To evaluate whether exposure of Tn determinants at the surface of human erythrocytes, platelets, and granulocytes could arise from a somatic mutation in a hemopoietic stem cell, burst-forming unit erythroid (BFU-E) colonies, colony-forming unit granulocyte-macrophage (CFU-GM), and colony-forming unit-eosinophil (CFU-Eo) were grown from a blood group O patient with a typical Tn syndrome displaying two distinct populations (Tn(+) and Tn(-)) of platelets, granulocytes, and erythrocytes. A large number of colonies was observed. Individual colonies were studied with a fluorescent conjugate of Helix pomatia agglutinin (HPA). A sizeable fraction of each of the erythroid and granulocytic colonies appeared to consist exclusively of either HPA-positive or HPA-negative cells, thereby demonstrating the clonal origin of those exhibiting the Tn marker. Similar results were obtained from a second patient. These findings establish that the HPA labeling of Tn cells is an accurate marker permitting assessment of the clonality of the human megakaryocyte (MK) colony assay. For the study of MK cultures a double-staining procedure using the HPA lectin and a monoclonal antiplatelet antibody (J-15) was applied in situ to identify all MK constituting a colony. Our results, obtained in studies of 133 MK colonies, provide definitive evidence that the human MK colony assay is clonal because all MK colonies were exclusively composed of Tn(+) and Tn(-) MK. Furthermore, the distribution of MK within a single colony was shown to be seminormal with a mean at 6 MK, isolated MK typically being absent in culture. Comparison of the proportion of mature Tn(+) cells in blood with their respective Tn(+) progenitors has also shown that no proliferative advantage occurs after the commitment; because Tn polyagglutinability is an acquired disorder, then the expansion of the Tn(+) clone must occur either during the proliferative stage of the pluripotent stem cell or during the commitment itself. This study therefore affords evidence that a blood group antigen plays a role in the differentiation of a pluripotent stem cell.

Adult↗
PubMed1982

Regulation of i- and I-antigen expression in the K562 cell line.

Expression of i- and I-antigen in K562 cultured under different conditions of culture was investigated. Under standard conditions of culture, i-antigen expression was very high (100% of i-labeled cells) in contrast to I-antigen expression of which was very low (2 to 5% of I-labeled cells). The addition of hemin to K562 cells did not modify the mean antigenic density or the proportion of i- and I-labeled cells. In contrast, sodium butyrate elicited an important increase in the proportion of cells exhibiting I-antigen associated to a decrease of i-antigenic density. The effect of butyrate was reversible and dependent upon de novo protein and messenger RNA synthesis since it was abolished in the presence of cycloheximide or actinomycin D. The stimulation of i-antigen conversion to I-antigen elicited by butyrate cannot be directly related to an induction of differentiation since evidence in this sense is lacking; in fact, butyrate did not increase the hemoglobin content of K562 cells. The passage from exponential to stationary phase of growth (cell density inhibition) was associated with an increase in I-antigen expression and a slight decrease in i-antigen density on the surface of K562 cells.

Antigens↗
PubMed1982

Normal human serum contains a factor(s) capable of inhibiting megakaryocyte colony formation.

Growth of megakaryocyte colonies from human bone marrow progenitors has been achieved in plasma clot culture. Megakaryocyte colonies were identified either by cytological examination or by immunofluorescent labelling using a monoclonal antiplatelet antibody (J 15). No significant differences were observed in the quantitation of the colonies by these two methods. In the absence of a stimulating factor, MK colonies were detectable when high cellular concentrations were seeded. Among the numerous conditioned media tested for their ability to stimulate MK colony formation, conditioned medium from leukocytes stimulated by PHA (PHA-LCM) was the most effective. However, under standard conditions of culture corresponding to 20% normal human sera, colony formation was not related linearly to seeding density even when cultures were stimulated by PHA-LCM. Upon reduction of the concentration of serum (2.5-5%) in the culture medium, colony formation displayed a linear relationship seeding density only when PHA-LCM was used as the stimulating factor. At the same time, the size of the colonies increased. Such inhibition was observed with all the human sera tested but it varied in extent from one batch to another. Replacement of serum by albumin, iron-saturated transferrin, alpha-thioglycerol and low density lipoproteins at physiological concentration but in the presence of bovine plasma provided a culture system whose ability to support colony formation equalled that of low concentrations of whole serum; spontaneous MK colony formation still occurred. Our results provide evidence for the presence of an inhibitor(s) of MK colony formation in normal human sera, and demonstrate the role of cellular factors in stimulating MK colony formation.

Blood↗
PubMed1981

Change in i-antigen expression of erythrocytes during in vivo aging.

The expression of i-antigen during the in vivo aging of erythrocytes from normal subjects and beta-thalassemic patients was investigated by immunofluorescence labeling and by immunoagglutination. The results showed that the expression of i-antigenic determinants inversely related to the aging of RBCs. This phenomenon could be either the result of a progressive loss of i-antigenic structures or the consequence of i to I transformation occurring during RBCs aging in vivo.

Anemia, Hemolytic, Autoimmune↗
PubMed1981

Cellular regulation of i and I antigen expressions in human erythroblasts grown in vitro.

In order to study the cellular regulation of i and I antigen expressions n erythroid cells, burst-forming-unit erythroids were grown in methylcellulose from the blood of normal human adults. Erythroid colonies were harvested on days 9, 11 or 14 of culture. Individual colonies or pooled colonies were subsequently cytocentrifuged and then i or I antigens were studied by immunofluorescence using a monoclonal anti-i or I antibody. Labelled cells were firstly located, their erythroid origin and their stage of maturation were subsequently ascertained after May-Grünwald-Giemsa staining. This approach shows that: (1) a marked heterogeneity occurred from one colony to another, most of the colonies being i-negative while the others contained a mixed population composed by a minority of i-positive erythroid cells; (2) the proportion of both i colonies and i cells decreased with the aging of culture; (3) i antigen was preferentially expressed on immature erythroblasts; however, immaturity per se was not sufficient to determine i expression; (4) I antigen expression was also related to the process of erythroid maturation but in an inverse way; its expression was higher in mature erythroblasts than in immature ones.

Adult↗
PubMed1981

Embryonic and fetal hemoglobin synthesis in K562 cell line.

K562 cell line was grown in liquid suspension and in plasma clot cultures. Morphological studies revealed the presence of a minority of cells, which were identified as erythroblasts. However, the majority of the cells remained unidentified. Biochemical studies confirmed the synthesis of hemoglobin by K562 cells. The pattern of hemoglobin (Hb) production was of the embryonic type, with the presence of small amount of fetal Hb. The addition of several inducers, like Epo and butyrate, was unable to modify the pattern of Hb production of K562. In contrast, the addition of hemin increased the synthesis of Hb and stimulated the synthesis of fetal Hb and probably adult Hb.

Butyrates↗
PubMed1981

Heterogeneity in the cellular commitment of a human leukemic cell line: K 562.

The cellular origin of the K 562 cell line, established from a patient in the blast crisis of chronic myeloid leukemia has been investigated. In agreement with previous reports, an erythroid differentiation was observed. A minority of immature, but hemoglobinized erythroblasts were identified both by electron microscopy and by immunofluorescence using an antibody to gamma-globin chains. Embryonic and fetal hemoglobin (Hb) were synthesized. Hemin increased the number of erythroblasts as well as the absolute amount of Hb synthesized: the Hb pattern was also significantly modified. By cytochemical ultrastructural detection of peroxidase activity (PA), a weak PA, distinct from granulocytic peroxidases, was found exclusively in the nuclear envelope and rough endoplasmic reticulum in a small number proportion of cells. In its localization this PA resembled that of normal and leukemic promegakaryoblasts. The addition of sodium butyrate or dimethylformamide markedly increased the number of these cells (up to 30%) but did not modify their cytoplasmic maturation. No modification of Hb synthesis was observed. Cloning of the K 562 line revealed a marked heterogeneity from one clone to another in Hb production, in the phenotype of Hb synthesis, and in the inducibility by butyrate or dimethylformamide. An inverse relationship between the number of cells with PA and Hb production was found in the different clones. Recloning some of these primary clones resulted in secondary clones, which displayed properties similar to those from which they had originated. All attempts to obtain granulocytic differentiation by addition of different inducers failed. These results clearly indicate that the K 562 cell line arises from the proliferation of bipotent stem cells, these cells possessing variable capacities of differentiation toward erythroid and presumably megakaryocytic cell lineages.

Cell Line↗
PubMed1980

[Cellular regulation of the expression of i and I antigens during the in vitro differentiation of BFU-E].

Burst forming units (BFU-E) from the blood of eight normal adults were grown in methylcellulose culture. Follow up of i and I antigens detected by an indirect immunofluorescence technique from the 9th to the 14th day of culture revealed that i antigen expression diminished while maturation proceeded. On the contrary 1 antigen expression increased meanwhile. Nevertheless, in addition to this maturation process, expression of i antigen must be determined by a regulatory mechanism operating during erythroid stem cell differentiation since a large proportion of immature erythroblasts at the 10th day of culture do not express i antigen.

Adult↗
PubMed1980

Disappearance of Hb F and i antigen during the first year of life.

In order to investigate whether a common control mechanism is involved in the diminution of i antigen expression and that of Hb F content in human erythrocytes during the postnatal period, we compared changes in 72 normal infants aged from 0 to 12 months. The proportion of hemoglobins (Hb F, Hb A, Hb A2) and the quantitation of "i" antigen were determined on the total population of red blood cells. In addition, the percentage of individual cells containing Hb F or "i" antigen or both (F cells, "i" cells, and F + "i" cells) were evaluated by using a rhodamine-conjugated anti-Hb F and a fluorescein conjugated anti-system on the same smear preparation. The results provided by the two most sensitive techniques (F cell counting and "i agglutinability) indicated that the curves of disappearance of Hb F and "i" antigen along the 12 first months after birth were identical. A strong correlation (r = 0.97, P < 0.0001) existed between the percentage of F cells and "i" antigen expression. In addition, the progressive increase in Hb A2 concentration was inversely correlated firstly with the proportion of Hb F and second with the expression of the "i" antigen. These results suggest that the switch from fetal to adult hemoglobin and the transformation of "i" antigen expression occurring during the first year following birth are governed by a common control mechanism.

Aging↗