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J Neuwirt

Publications and source records attributed to J Neuwirt.

At least 37 records · Page 2Linked to original sources
PubMed1987

Iron uptake and transferrin endocytosis in undifferentiated and differentiated erythroid cells.

Iron uptake from transferrin (Tf) by Friend erythroleukemia cells was studied before and after induction of the cells by dimethyl sulfoxide (DMSO) in culture. The increase in iron uptake after 5 days of induction was not accompanied by a proportional increase in the number of transferrin receptors detected by 125I-labeled Tf binding, resulting in DMSO induced cells taking up iron with the rate of about 26 iron atoms per receptor per hour, compared to 15 atoms in uninduced cells. In agreement with this finding are results of the study of cellular 125I or 59Fe-labeled Tf kinetics. In the induced cells Tf endocytosis and release proceeded with identical rates and all the endocytosed iron was retained inside the cell. Tf release by uninduced cells was slower and a part of internalized 59Fe was released. Hemin inhibits Tf-bound iron uptake by DMSO induced cells but not by the uninduced cells. Correspondingly, addition of hemin had little effect on Tf kinetics in the uninduced cells, while the release of Tf was slower in hemin-treated DMSO induced cells. Different efficiency of iron release from internalized Tf, accompanied by changes in cellular Tf kinetics is therefore proposed as a factor determining the rate of iron uptake by developing erythroid cells.

Animals↗
PubMed1986

Identification of leukemia cell-derived inhibitory activity (LIA) in conditioned media from human myeloid leukemic cell line ML-2.

Conditioned media from the human myeloid leukemic cell line ML-2 contain a factor that inhibits the entry of normal CFU-GM into S phase of mitotic cycle as measured by the 3H-TdR suicide technique. This factor was detected in conditioned media prepared by incubating 5 X 10(6) ML-2 cells/ml or 1 X 10(6) ML-2 cells/ml in serum-free RPMI for 5 or 24 hours respectively, and was isolated by ultrafiltration through an XM 300 Diaflo membrane followed by chromatography on Sepharose 6 B. Ferritin, prepared from human placenta, had the same inhibitory effect on CFU-GM. Antibodies against human placental ferritin completely inactivated the inhibitory effect of both human placental ferritin and the factor released from ML-2 cells. The inhibitory activity produced by the cell-line ML-2 was considered as LIA (leukemia cell-derived inhibitory activity) earlier found in HL-60 cell line and AML and CML cells.

Animals↗
PubMed1986

Iron uptake by MOLT 3 cells from transferrin/monoclonal antitransferrin antibody complexes.

The ability of seven monoclonal antibodies (MAbs) reactive with human transferrin (Tf) to inhibit iron uptake from Tf by cells of the human lymphoid line MOLT 3 was compared with the effect of these MAbs on Tf binding to MOLT 3 surface Tf receptors. MAbs HTF-01, HTF-06, HTF-07, HTF-11 and HTF-14 inhibited both iron uptake and Tf binding. Complexing Tf with MAbs HTF-04 or HTF-05 resulted in an increased association of Tf with the cells but iron uptake was diminished. Following the intracellular kinetics of Tf/HTF-04 complex has shown that the whole complex is endocytosed and Tf iron is retained inside the cell, but Tf release from both the cell surface and the intracellular compartment is slower when compared to Tf alone. Iron uptake inhibition was therefore attributed to lengthening of the Tf cell cycle after complexing of Tf with HTF-04 and it is suggested that the rate of cellular Tf turnover might, together with the number of functioning Tf receptors, determine the rate of iron uptake by cells.

Antibodies, Monoclonal↗
PubMed1984

Effect of hemin and heme synthesis inhibitors on cellular protein synthesis.

Inhibitors of heme synthesis, 2,2'-bipyridyl, isonicotinic acid hydrazide (INH), and D,L-penicillamine markedly inhibited only the synthesis of hemoglobin and had no effect on the synthesis of the bulk of nonhemoglobin proteins in spleen cells of anemic mice. Exogenous hemin stimulated the synthesis of hemoglobin as well as the synthesis of the bulk of nonhemoglobin proteins. However, by further analysis of nonhemoglobin proteins it was possible to detect intermediates of hemoglobin synthesis, globin chains with highly specific radioactivity of L-[4,5-3H]leucine which were eluted together with nonhemoglobin proteins during the chromatography on CM-Sephadex C-50. Protein synthesis in Friend erythroleukemia cells of the Fw line which have the genetic defect of heme synthesis was resistant to D,L-penicillamine and Desferal; 2,2'-bipyridyl had an inhibitory effect. Hemin was without effect on protein synthesis in these neoplastic cells.

2,2'-Dipyridyl↗
PubMed1984

Effect of hemin on poly (A)-containing RNA synthesis and transport from nucleus into cytoplasm in Friend cells of the Fw line.

The effect of hemin on the transcription and post-transcriptional events (processing and transport of globin mRNA and other poly(A)-containing RNAs to the cytoplasm) was investigated in murine erythroleukemia Friend cells (MELC) of the Fw line. Uninduced Fw cells or Fw cells induced to differentiation by butyric acid were incubated in vitro without or with exogenous hemin. Short labelling periods (5-20 min) with (3H) uridine were used. The synthesis of globin mRNA and other poly(A)-containing RNAs at the level of their precursors in the nucleus and at the level of mature forms in the cytoplasm was measured. Our results indicate that hemin mainly affects the processing or transport of globin mRNA and other poly(A)-containing RNAs from the nucleus to the cytoplasm. The effect of exogenous hemin is quite different in uninduced and induced Fw cells. Exogenous hemin stimulates accumulation of poly(A)-containing RNA in nuclei of uninduced Fw cells. On the other hand exogenous hemin causes an increase in cytoplasmic globin mRNA and other cytoplasmic poly(A)-containing RNA in Fw cells induced by sodium butyrate.

Animals↗
PubMed1983

Effect of beta adrenergic blocking agents on erythropoiesis in rats.

The purpose of the present study was to analyze the effect of two different beta blocking agents, metipranolol (Trimepranol) and dl-propranolol (Inderal), upon erythropoietin production, erythropoietin responsive cell compartment and erythrocyte production. The effect on erythropoietin production: in rats metipranolol or dl-propranolol was injected daily in a single dose of 10 mg/kg b.wt. On the 5th day, the rats were exposed to an atmospheric pressure of 353.7 torr (47.1 kPa, 6000 m) to stimulate erythropoietin production. The onset of hypoxic exposure was started 1, 4, 12 or 24 hr after the last injection of beta blocking drugs. After the termination of hypoxia, erythropoietin plasma levels were determined in polycythemic mice. The rats treated with metipranolol 1 and 4 hr before hypoxia produced significantly less erythropoietin in response to hypoxia than saline-treated control animals. The effect on erythropoietin responsive cell compartment: polycythemic mice were treated with metipranolol or dl-propranolol in doses of 10 to 40 mg/kg b.wt. and with an erythropoietin standard. Radioiron incorporation into red blood cells in control mice and in mice pretreated with beta blocking agents was not significantly different. The effect on erythrocyte production: in rats treated daily with metipranolol in a single dose of 10 mg/kg b.wt., for a period of 10 days, the rate of erythropoiesis measured by the incorporation of 59Fe into red blood cells was decreased, dl-propranolol (10 mg/kg b.wt.) did not reduce the rate of erythropoiesis. Our results demonstrate that the changes in erythropoiesis after administration of metipranolol may be caused by reduction of erythropoietin production with a consequent reduction of the erythrocyte production rate.

Adrenergic beta-Antagonists↗
PubMed1982

Regulation of erythropoiesis in fetus and mother during normal pregnancy.

The activity of the hormone erythropoietin was assayed (1) in the amniotic fluid of healthy women in the tenth to 16th weeks of pregnancy who had artificial interruption of pregnancy and (2) in the urinary output of healthy pregnant and nonpregnant women. Erythropoietin activity in concentrated urine increased significantly between the 24th and 31st weeks of pregnancy. No erythropoietin activity was demonstrated in amniotic fluid at the tenth week of pregnancy, even when the fluid was concentrated, but it was demonstrated in concentrated amniotic fluid from the 11th to 16th weeks. The assay results prove, indirectly, the hypothesis that increased production of erythrocytes in pregnancy is mediated by the erythropoietin humoral mechanism in both fetus and mother. Erythropoiesis in the fetus probably is regulated by erythropoietin as early as the 11th week of pregnancy.

Adult↗
PubMed1981

The effect of heme on intracellular iron pools during differentiation of Friend erythroleukemia cells.

The inhibition of cellular iron uptake by hemin described previously in reticulocytes was studied in murine erythroleukemia (Friend) cells that can be induced to differentiate in culture by dimethyl sulfoxide (DMSO). Hemin had no effect on iron uptake into noninduced cells. After the induction by DMSO, hemin inhibited iron uptake into Friend cells and this effect of hemin became more pronounced with the further progress of differentiation. The reduction of cellular iron accumulation was caused mainly by inhibition of iron incorporation into heme, iron uptake into the non-heme pool was little influenced by hemin treatment. Inhibition of heme synthesis by isonicotinic acid hydrazide (INH) caused an accumulation of iron in mitochondria in DMSO-induced cells, but not in uninduced cells. On the basis of these results, a specific system transporting iron to mitochondria induced by DMSO treatment is suggested as a target for the inhibitory action of hemin. In Friend cells of the Fw line which are deficient in ferrochelatase, heme has no effect on iron uptake. The addition of INH to the Fw cells does not enhance the iron accumulation in mitochondria.

Animals↗
PubMed1981

Effect of heme on globin messenger RNA synthesis in spleen erythroid cells.

Synthesis of globin mRNA in erythroid spleen cells from anemic mice was measured after in vitro incubation under conditions in which the level of intracellular heme was manipulated. This newly synthesized globin mRNA was isolated by hybridization with globin cDNA covalently bound to cellulose. Isonicotinic acid hydrazide (INH) and penicillamine were used as specific inhibitors of heme synthesis. It has been found that a 120-min incubation of spleen erythroid cells with 5mM INH or 5mM penicillamine reduced [3H] uridine incorporation into globin mRNA by 24% or 36%, respectively. The addition of heme to INH- or penicillamine-treated cells almost completely restored [3H] uridine incorporation into globin mRNA. These results indicate that heme stimulates transcription of processing of globin mRNA.

Animals↗