ALBERT

Description: All-trans retinoic acid (RA) is an important morphogen in vertebrate development, a normal constituent in human adult blood and is also involved in the control of cell growth and differentiation in acute promyelocytic leukemia. We have examined the effects of RA on normal hematopoiesis by using early hematopoietic progenitor cells (HPC) stringently purified from adult peripheral blood. In clonogenetic fetal calf serum-supplemented (FCS+) or -nonsupplemented (FCS-) culture treated with saturating levels of interleukin-3 (IL-3) granulocyte- macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Ep) (combined with c-kit ligand in FCS(-)-culture conditions), RA induces a dramatic dose-dependent shift from erythroid to granulomonocytic colony formation, the latter colonies being essentially represented by granulocytic clones. This shift is apparently not caused by a recruitment phenomenon, because in FCS+ culture, the total number of colonies is not significantly modified by RA addition. In FCS- liquid- suspension culture supplemented with saturating Ep level and low-dose IL-3/GM-CSF, adult HPC undergo unilineage erythropoietic differentiation: Here again, treatment with high-dose RA induces a shift from the erythroid to granulocytic differentiation pathway. Studies on RA time-response or pulse treatment in semisolid or liquid culture show that early RA addition is most effective, thus indicating that early but not late HPC are sensitive to its action. We then analyzed the expression of the master GATA1 gene, which encodes a finger transcription factor required for normal erythroid development; addition of RA to HPC stimulated into unilineage erythropoietic differentiation in liquid culture caused a virtually complete inhibition of GATA1 mRNA induction. These results indicate that RA directly inhibits the erythroid differentiation program at the level of early adult HPC, and may lead to a shift from the erythroid to granulocytic differentiation pathway. This phenomenon is correlated with inhibition of GATA1 induction in the early stages of erythropoietic differentiation.

Description: The effect of succinylacetone (SA), a highly specific inhibitor of ALA- dehydratase and heme synthesis, on hemoglobin (Hb) production, transferrin receptor (TfR), and ferritin expression was analyzed in differentiating Friend leukemia cells (FLC). This compound exerted a pronounced inhibitory effect not only on heme and Hb synthesis, but also on all the remaining above-mentioned parameters. In particular, SA induced: (1) a reduction of the level of alpha-globin mRNA; (2) a decreased number of exposed TfR molecules, without modification of their affinity for the ligand; (3) a reduced level of TfR RNA, without significant change of TfR gene transcription rate; and (4) a lower ferritin content. The addition of exogenous hemin to differentiating FLC exerted opposite effects, and particularly induced an increase of both the number of TfRs and ferritin content. These findings suggest that in erythroid cells optimal heme synthesis is required to coordinately sustain globin chains synthesis and TfR/ferritin production; thus, the intracellular heme level may represent a key regulatory factor in the Hb synthesis pathway.

Description: Uni- or multi-lineage suppression of hematopoiesis is observed in the majority of acquired immunodeficiency syndrome (AIDS) patients. The mechanism(s) underlying these abnormalities is not understood: particularly, the human immunodeficiency virus (HIV) infection of hematopoietic progenitor and stem cells (HPCs/HSCs) is highly controversial. We report that CD34+ HPCs from adult peripheral blood (PB) are in part CD4+ and susceptible to in vitro HIV infection. Primitive CD34+ HPCs were approximately 80% purified from PB. Double labeling for CD34 and CD4 membrane antigens was shown for 5% to 20% of the purified cells, thus suggesting their potential susceptibility to HIV-1 infection. The enriched HPC population, challenged with purified or unpurified HIV-1 strains, was cloned in unicellular methylcellulose culture. The single colonies generated by erythroid burst-forming units (BFU-E), granulocyte-macrophage colony-forming units (CFU-GM), and granulocyte-erythroid-macrophage-megakaryocyte colony-forming units (CFU-GEMM) were analyzed for the presence of HIV, ie, for gag DNA, tat mRNA, and p24 protein by PCR, reverse transcription PCR (RT-PCR), and enzyme-linked immunosorbent assay, respectively. In the first series of experiments incubation of HPCs with HIV-1 at multiplicities of infection (MOI) ranging from 0.01 to 10 TCID50/cell consistently yielded an 11% to 17% infection efficiency of BFU-E-generated colonies, thus indicating the sensitivity of HPCs to in vitro HIV infection. An extensive series of experiments was then performed on HPCs challenged with HIV at 0.1 MOI level. In the initial studies proviral gag sequences were detected in 9.2% of 121 analyzed CFU-GM colonies. In further experiments tat mRNA was monitored in 17% and 23% of BFU-E and CFU-GM colonies, respectively, but never in CFU-GEMM clones. Finally, 12% of CFU-GM clones and rare erythroid bursts were shown to be positive for the p24 viral protein. In control studies, purified HPCs grown in liquid suspension culture were induced to terminal unilineage erythroid, monocytic, or granulocytic differentiation: monocytes were consistently HIV-infected, whereas mature-terminal erythroblasts and granulocytes were not. Our observations indicate that a minority of primitive HPCs, but not of the multipotent type, is susceptible to in vitro HIV infection. These observations may reflect on the in vivo hematopoietic impairment in AIDS patients; more important, they provide an experimental model for studies on HIV hematopoietic infection and in vitro tests for anti-HIV HSC gene therapy.

Description: All-trans retinoic acid (RA) is an important morphogen in vertebrate development, a normal constituent in human adult blood and is also involved in the control of cell growth and differentiation in acute promyelocytic leukemia. We have examined the effects of RA on normal hematopoiesis by using early hematopoietic progenitor cells (HPC) stringently purified from adult peripheral blood. In clonogenetic fetal calf serum-supplemented (FCS+) or -nonsupplemented (FCS-) culture treated with saturating levels of interleukin-3 (IL-3) granulocyte- macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Ep) (combined with c-kit ligand in FCS(-)-culture conditions), RA induces a dramatic dose-dependent shift from erythroid to granulomonocytic colony formation, the latter colonies being essentially represented by granulocytic clones. This shift is apparently not caused by a recruitment phenomenon, because in FCS+ culture, the total number of colonies is not significantly modified by RA addition. In FCS- liquid- suspension culture supplemented with saturating Ep level and low-dose IL-3/GM-CSF, adult HPC undergo unilineage erythropoietic differentiation: Here again, treatment with high-dose RA induces a shift from the erythroid to granulocytic differentiation pathway. Studies on RA time-response or pulse treatment in semisolid or liquid culture show that early RA addition is most effective, thus indicating that early but not late HPC are sensitive to its action. We then analyzed the expression of the master GATA1 gene, which encodes a finger transcription factor required for normal erythroid development; addition of RA to HPC stimulated into unilineage erythropoietic differentiation in liquid culture caused a virtually complete inhibition of GATA1 mRNA induction. These results indicate that RA directly inhibits the erythroid differentiation program at the level of early adult HPC, and may lead to a shift from the erythroid to granulocytic differentiation pathway. This phenomenon is correlated with inhibition of GATA1 induction in the early stages of erythropoietic differentiation.

Description: Although it is well established that homeobox (HOX) genes play a key role in normal human embryogenesis, the expression and function of HOX genes in normal hematopoiesis is largely unknown. We have investigated by reverse transcriptase-polymerase chain reaction the mRNA expression of HOXB cluster genes (32 to 52 position in the cluster: from HOXB2 through B9) in 72% to 88% purified hematopoietic progenitor cells (HPCs) from adult peripheral blood induced in liquid suspension culture to gradual erythroid or granulopoietic (largely eosinophilic) differentiation and maturation by differential growth factor (GF) stimulus (ie, low-dose interleukin-3 [IL-3] and granulocyte-macrophage colony-stimulating factor [GM-CSF] and high-dose erythropoietin, or saturating amounts of IL-3/GM-CSF, respectively). Only B3 is expressed in quiescent HPCs. After GF treatment B3 expression is enhanced in the initial 24 hours and then through differentiation and maturation in erythroid and granulopoietic cultures. HOXB4 and B5 are induced at slightly later times and expressed through maturation in both lineages, whereas B6 is selectively induced in granulocytic differentiation. B2 is transiently expressed at low level in the granulopoietic pathway, whereas it is detected only in advanced stages of erythropoiesis: B7, B8, and B9 are essentially not detected. Functional studies were performed with antisense phosphorothioate oligomers to HOX mRNAs and included control analysis of the targeted mRNA. The results are strictly coherent with the HOX mRNA expression pattern: (1) anti-B3 oligomer (alpha-B3) treatment of purified HPCs induces a striking blockade of both erythroid and granulomonocytic colony formation (similarly, alpha-B3 treatment of K562 cell line causes a significant dose-related inhibition of cell proliferation); (2) alpha-B6 selectively and markedly inhibits granulomonocytic colony formation; (3) alpha-B4 and alpha-B5 cause a significant, less pronounced decrease of both colony types; (4) finally, alpha-B2 and alpha-B7, -B9 exert little and no effect, respectively. These studies provide novel evidence on the coordinate expression of selected HOXB cluster genes in erythropoiesis and granulopoiesis, particularly in the early stages of differentiation: B3 apparently functions as a master gene in early hematopoiesis, whereas B6 exerts a key selective function in the granulopoietic pathway.

Description: The effect of succinylacetone (SA), a highly specific inhibitor of ALA- dehydratase and heme synthesis, on hemoglobin (Hb) production, transferrin receptor (TfR), and ferritin expression was analyzed in differentiating Friend leukemia cells (FLC). This compound exerted a pronounced inhibitory effect not only on heme and Hb synthesis, but also on all the remaining above-mentioned parameters. In particular, SA induced: (1) a reduction of the level of alpha-globin mRNA; (2) a decreased number of exposed TfR molecules, without modification of their affinity for the ligand; (3) a reduced level of TfR RNA, without significant change of TfR gene transcription rate; and (4) a lower ferritin content. The addition of exogenous hemin to differentiating FLC exerted opposite effects, and particularly induced an increase of both the number of TfRs and ferritin content. These findings suggest that in erythroid cells optimal heme synthesis is required to coordinately sustain globin chains synthesis and TfR/ferritin production; thus, the intracellular heme level may represent a key regulatory factor in the Hb synthesis pathway.