Acute myelogenous leukemia: a human cell line responsive to colony-stimulating activity

Transforming growth factor beta inhibits growth of more differentiated myeloid leukemia cells and retinoblastoma protein phosphorylation at serine 795

Transforming growth factor beta (TGF-beta) has been shown to be a specific inhibitor of early human myeloid progenitors. We show here that TGF-beta1 potentially inhibited not only the growth of primitive but also more mature myeloid leukemic cells. Surprisingly, those apparently more mature progenitor cells, such as MV4-11 and Mo7e cells, are very sensitive to the action of TGF-beta. The addition of TGF-beta1 to liquid cultures of these cells significantly inhibited their proliferation, with as much as 72% inhibition of growth of MV4-11 cells. The suppressive effect by TGF-beta1 was not reversed or prevented by granulocyte-macrophage colony-stimulating factor or interleukin 3 used to promote cell growth in TF-1a and MV4-11 cells. TGF-beta1 completely abolished the clonal growth of MV4-11 cells in soft agar and inhibited Mo7e, KG-1, K562, TF-1, and TF-1a colony growth by 99%, 90%, 63%, 53%, and 43%, respectively. The cells treated with TGF-beta1 showed progressive accumulation in the G1 phase of cell cycle. Maximal G1 arrest (93%) was observed in MV4-11 cells. Using anti-retinoblastoma protein (pRb) and anti-specific phosphorylated-pRb antibodies, we demonstrated that TGF-beta1 greatly inhibited pRb phosphorylation at serine 795 in MV4-11 and Mo7e cells. Taken together, our data suggest that the sensitivity of myeloid leukemic progenitor cells to growth inhibition by TGF-beta may not be inversely correlated with their maturation stage, and the inhibition of the cells appeared to be linked to the suppression of pRb phosphorylation at serine 795.

Evidence for Distinct Intracellular Signaling Pathways in CD34+ Progenitor to Dendritic Cell Differentiation from a Human Cell Line Model

Intracellular signals that mediate differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have previously shown that protein kinase C (PKC) activation (with phorbol ester (PMA) alone) specifically induces differentiation of primary human CD34+ hemopoietic progenitor cells (HPC) to mature DC. We now find that cytokine-driven (granulocyte-macrophage CSF and TNF-α) CD34+ HPC→DC differentiation is preferentially blocked by inhibitors of PKC activation. To further identify intracellular signals and downstream events important in CD34+ HPC→DC differentiation we have characterized a human leukemic cell line model of this process. The CD34+ myelomonocytic cell line KG1 differentiates into dendritic-like cells in response to granulocyte-macrophage CSF plus TNF-α, or PMA (with or without the calcium ionophore ionomycin, or TNF-α), with different stimuli mediating different aspects of the process. Phenotypic DC characteristics of KG1 dendritic-like cells include morphology (loosely adherent cells with long neurite processes), MHC I+/MHC IIbright/CD83+/CD86+/CD14− surface Ag expression, and RelB and DC-CK1 gene expression. Functional DC characteristics include fluid phase macromolecule uptake (FITC-dextran) and activation of resting T cells. Comparison of KG1 to the PMA-unresponsive subline KG1a reveals differences in expression of TNF receptors 1 and 2; PKC isoforms α, βI, βII, and μ; and RelB, suggesting that these components/pathways are important for DC differentiation. Together, these findings demonstrate that cytokine or phorbol ester stimulation of KG1 is a model of human CD34+ HPC to DC differentiation and suggest that specific intracellular signaling pathways mediate specific events in DC lineage commitment.

Bcr-abl protein detection in peripheral blood mononuclear cells for follow-up of chronic myelogenous leukaemia patients

We have assessed the value of p210 protein detection in peripheral blood cells for follow-up of chronic myelogenous leukaemia (CML) patients. Quantification was achieved by comparing the relative intensities of the p210 bands with those of the normal abl protein (p145). Serial dilution of Ph-positive K562 cells with Ph-negative HL60 or KG1 cells revealed a linear correlation between the p210/p145 ratio and the number of Ph-positive cells (r = 0.998; p < 0.001) with a sensitivity of detecting less than 1% Ph-positive cells in 5 x 10(6) cells. Ninety-six consecutive patients were enrolled in the study and a total of 155 Western blot analyses have been performed and compared to chromosomal analyses of bone marrow. Parallel RT-PCR analyses have been performed on 99 occasions. All patients with positive cytogenetic findings also probed positive for p210. In 23 instances p210 was detectable despite negative chromosomal analysis. In 16 samples these results were confirmed by RT-PCR. In patients with partial cytogenetic remission (n = 26) the results of the p210 assay correlated significantly with the percentage of Ph-positive metaphases (r = 0.69; p < 0.001). In conclusion, monitoring of CML patients by quantification of the bcr-abl protein is a feasible and sensitive alternative to chromosomal analysis of bone marrow.

Novel BTB/POZ domain zinc-finger protein, LRF, is a potential target of the LAZ-3/BCL-6 oncogene

BTB/POZ-domain C2H2 zinc(Zn)-finger proteins are encoded by a subfamily of genes related to the Drosophila gap gene krüppel. To date, two such proteins, PLZF and LAZ-3/BCL-6, have been implicated in oncogenesis. We have now identified a new member of this gene subfamily which encodes a 62 kDa Zn-finger protein, termed LRF, with a BTB/POZ domain highly similar to that of PLZF. Both human and mouse LRF genes, which localized to syntenic chromosomal regions (19p13.3 and 10B5.3, respectively), were widely expressed in adult tissues and cell lines. At approximately 9.5-10.0 days of embryonic development, the mouse LRF gene was expressed in the limb buds, pharyngeal arches, tail bud, placenta and neural tube. The LRF protein associated in vivo with LAZ-3/BCL-6, but not with PLZF to which it was more related. Although the LRF, or LAZ-3/BCL-6, BTB/POZ domain could readily homodimerize, no heterodimerization was detected in vivo between the LRF and LAZ-3/BCL-6 BTB/POZ domains and interaction between full length LRF and LAZ-3/BCL-6 required the presence of both the BTB/POZ domain and Zn-fingers in each partner protein. As expected from the above results, LRF and LAZ-3/BCL-6 also colocalized with each other in the nucleus. Taken together, our findings suggest that BTB/ POZ-domain Zn-finger proteins may function as homo and heterodimeric complexes whose formation, and hence the resultant effect on transcription of their downstream target genes, is determined by the levels and expression domains of a given partner protein.

History and classification of human leukemia-lymphoma cell lines

Continuous human leukemia-lymphoma cell lines have become indispensable tools in hematological research since the establishment of the first human lymphoma cell line Raji in 1963. We summarize here historical landmarks in the establishment of unique leukemia-lymphoma-derived cell lines from the various cell lineages; their special importance in hematopoietic research is emphasized. The first cell lines were derived from African Burkitt lymphomas and were found to integrate the Epstein-Barr virus in their genome leading to the discovery and isolation of this virus. However, it was later recognized that not every cell line derived from a patient with leukemia-lymphoma represents a malignant cell line as residual normal B-lymphocytes can also be immortalized by EBV infection. During the following 20-30 years many other types of hematopoietic cell lines, commonly derived from hematopoietic neoplasms, were established. These panels of cell lines now span almost the whole spectrum of hematopoietic cell lineages (except for dendritric cells) and the various distinct stages of differentiation along the respective cell axes. From early on, cell lines became important tools for basic and clinical hematological research, initially mainly in the field of immunology, but later expanding to other areas also. It became apparent that leukemia-lymphoma cell lines are of monoclonal origin, are arrested at a discrete maturational stage during differentiation in each lineage, and show sustained and growth factor-independent or -dependent unlimited proliferation. Categorization of cell lines might best be based on the physiological stages of hematopoietic differentiation in the various cell lineages. For an adequate classification, detailed characterizations of both the cell lines and the primary cells from which the cell lines originated are absolutely mandatory. In summary, the availability of large numbers of continuous leukemia-lymphoma cell lines has greatly facilitated clinical and immunobiological studies of normal and malignant hematopoiesis. Human leukemia-lymphoma cell lines will continue to provide exquisite model systems for many biomedical disciplines.

Characterization of a unique factor-independent variant derived from human factor-dependent TF-1 cells: a transformed event

A factor-independent variant (TF-1a) has been isolated from the factor-dependent TF-1 cell line. The subline has been grown continuously in culture for > 1.5 years without added cytokines. The cells retain the ability to respond to multicytokines, with a different response pattern from its parental cell line. The TF-1 cells appeared singly in liquid culture. In contrast. TF-1a cells formed aggregates which increased markedly in size and in number upon TGFbeta1 treatment and showed a diminished TGFbeta-mediated growth inhibition. TF-1a, but not TF-1 cells, formed colonies in soft agar culture in the absence of any added growth factors, and developed the capacity to generate an invasive tumor(s) in nude mice. There was a constitutive activation of MAPK and MEK in TF-1a but not in TF-1 cells, which may be one of the mechanisms leading to factor-independent growth of TF-1a cells. Phenotypically, TF-1 cells were CD34+ /CD38+, whereas TF-1a cells were CD34+ /CD38-. This suggests that TF-1a may represent a less mature hematopoietic cell than TF-1. In conclusion, TF-1a is different from TF-1 in many important aspects which are associated with neoplastic transformation. The variant appears to be an excellent model for studying the process of progressive malignant transformation of myeloid cells and for studying signal pathways involved in the spontaneous and factor-induced growth of the cells.

Methylation of the p16INK4A gene in multiple myeloma

The p16INK4A (p16) binds to both cyclin D-CDK4 and cyclin D-CDK6 and inhibits the progression of the cell cycle from G1 to S phase. Loss of expression of this protein can occur by several mechanisms including structural alterations. Recent studies have suggested that the loss of expression of p16 can occur by hypermethylation of the gene. The methylation status of the p16 gene in multiple myeloma was examined in three myeloma cell lines (U266, RPMI8226 and IM9) and 16 primary myeloma samples using methylation-specific polymerase chain reaction (MSP). The U266 and RPMI8226 cell lines contained a completely methylated p16 gene and the IM9 line had a partially methylated p16 gene. Identical results were obtained by another polymerase chain reaction (PCR)-based methylation assay system as well as Southern blotting after using a methylation-sensitive restriction enzyme. The U266 cell line expressed no p16, and the IM9 had weak expression as determined by reverse transcript (RT-)PCR. The U266 cells began to express, and IM9 increased the accumulation of, the p16 RNA after treatment with the demethylating agent 5'-aza-2-deoxycytidine (10(-6)-10(-5) M). This suggested that the levels of methylation of the p16 gene detected by the MSP technique correlated with the regulation of transcription of this gene. Examination of the primary myeloma samples showed that eight of 16 (50%) contained a methylated p16 gene. We have previously found that alterations of the p16 gene, such as deletions and point mutations, are rare in primary multiple myeloma; none of the 16 samples included in this study had p16 gene alterations. Our results suggest that methylation of the p16 gene may contribute to the development and/or progression of multiple myeloma.

Identification of sequence-tagged transcripts differentially expressed within the human hematopoietic hierarchy

Hematopoiesis is regulated by a complex gene expression program. To gain further insight into the molecular mechanisms underlying this process in humans, we sampled the transcriptional activity of the CD34+ hematopoietic progenitor line KG1a by single-pass sequencing the 5' ends of 1018 clones from a unidirectional cDNA library. Searches of public databases with the resulting expressed sequence tags (ESTs) identified 101 clones that showed no sequence similarity to any of the existing entries and that were therefore considered to derive from previously undescribed genes. Of the remaining 917 ESTs, 553 (a total of 485 distinct transcripts) corresponded to known genes. A further 279 KG1a ESTs matched or exhibited sequence similarity to ESTs or genomic sequences from humans and other species. Among the latter were putative human orthologs of developmental and cell cycle control genes from Caenorhabditis elegans, Drosophila, and yeast, as well as genes whose predicted amino acid sequences showed similarity to mammalian transcription factors. Hybridization of selected novel KG1a ESTs to globally amplified cDNAs prepared from single primary human hematopoietic precursors and homogeneous populations of terminally maturing hematopoietic cells revealed transcripts that are expressed preferentially at a specific stage or in a particular lineage within the hematopoietic hierarchy. Thus, included in the KG1a EST dataset are candidates for new human genes that may play roles in hematopoietic differentiative progression and lineage commitment.

Antibody-directed superantigen-mediated T-cell killing of myeloid leukaemic cell line cells

Bacterial superantigens (SAgs) bound to MHC class II molecules on target cells are efficient activators of cytotoxic T cells expressing certain T cell receptor (TCR) Vbeta regions We described earlier that the specificity of the SAg Staphylococcus enterotoxin A (SEA) can be changed by introducing a D227A point mutation in the major MHC class II binding site and by genetically fusing the SEA mutant (SEAm) to protein A (PA). This SEAm-PA fusion protein can then be used to direct cytotoxic T cells to tumour cells coated with monoclonal antibodies (mAbs). In this communication, we tested the PA-SEAm fusion protein together with mAbs against the myeloid cell surface antigens CD13, CD15 and CD33. A SEA-reactive T cell line was used as effector cells against 10 different myeloid leukaemic cell lines. Optimal lysis of antigen positive leukaemic cells was obtained at a PA-SEAm concentration of 1 ng/ml and effector : target cell ratios of 15 : 1. No correlation between target cell sensitivity and the level of surface antigen expression could be seen. The 6 acute myeloid leukaemia (AML) cell lines tested appeared to be more sensitive than the 4 chronic myeloid leukaemia (CML) cell lines. The sensitivity of the AML cell line HL-60 could be improved further by stimulation with TNFalpha. This was accompanied by increased surface ICAM-1 expression whereas specific target molecule expression (CD13, CD33) was unchanged. This suggests that sensitivity to lysis is related to the leukaemic subtype and ICAM-1 expression but not to the tumour antigen density. Our results show that it is possible to direct cytotoxic T cells to myeloid leukaemia cells by using SAgs linked to mAbs, and encourage the construction and testing of a recombinant direct SAg-mAb fusion protein as a candidate drug for therapy of myeloid leukaemias.

Cell separation based on the reversible interaction between calmodulin and a calmodulin-binding peptide

A cell separation system based on the calcium-dependent interaction of calmodulin (CM) with a calmodulin-binding peptide (CBP) has been developed. The prototype of this system utilizes an indirect method to label the target cell population. Cells are first labeled with a primary monoclonal antibody directed to a specific cell surface antigen, then with a secondary affinity reagent, consisting of a polyclonal goat anti-mouse IgG (GAM-IgG) that has been cross-linked to a CBP derived from the sequence of the rabbit skeletal muscle myosin light chain kinase. In the presence of Ca2+, the CBP on the cells labeled with GAM-IgG-CBP binds to biotinylated calmodulin (CM-Biotin) with high affinity. The target cells are then captured with a solid-phase streptavidin. The unbound non-target cells are washed away and the immobilized target cells are released by chelating Ca2+ with EGTA. The specificity of the GAM-IgG-CBP and CM-Biotin and the feasibility of using this system to separate cells was demonstrated using the KG-1 human acute myelogenous leukemia cell line. KG-1 cells were fractionated on the basis of cell surface expression of HLA-DR. The cell selection reagents and the cell separation process did not affect KG-1 cell viability while cells selected by this procedure were 90% pure with a yield of 75%. This cell separation system also was used for rare cell isolation from normal human peripheral blood mononuclear cells. T cells expressing the Vbeta5 T cell receptor, which represent < 5% of the unfractionated cells, were isolated with 89% viability, 72% purity, 80% yield, and retained the ability to respond to activation signals as measured by blast transformation. The results from this study show that a cell selection system based on the reversible interaction between CM and a CBP can be applied to gently and efficiently isolate cells from a heterogeneous starting population that are free of the solid matrix without exposure to the stresses of mechanical or enzymatic release.

Neoexpression of the c-met/Hepatocyte Growth Factor-Scatter Factor Receptor Gene in Activated Monocytes

Hepatocyte growth factor-scatter factor (HGF-SF ) mediates mito-, moto-, and morphogenic effects through the MET receptor, a membrane bound tyrosine kinase. HGF-SF/MET signaling is mitogenic for a large number of epithelial and endothelial cells and activates organ regeneration. HGF-SF transcripts have been detected in various myeloid cell lines. Therefore, the potential role of HGF-SF/MET signaling for circulating cells of the immune system, especially under conditions of inflammation, was evaluated. Several B-lymphoid and myeloid cell lines were found to express HGF-SF or c-met transcripts, while activity of both genes was mutually exclusive with the exception of low level coexpression in two B-cell lines. HGF-SF transcripts were present in low quantities in freshly isolated peripheral blood mononuclear cells (PBMNCs). In contrast, c-met expression was not detected in freshly isolated cells from peripheral blood, but was induced in monocytes by activation of monocytic or T-cell function. HGF-SF incubation led to an increased c-fos steady state transcript level in myeloblastic K562 cells and moderately promoted cell viability of freshly isolated preactivated monocytes. c-met expression is thus established in activated monocytes, in particular under conditions resembling inflammation, making these cells accessible to functional effects of HGF-SF.

Modulation of Idarubicin-Induced Apoptosis in Human Acute Myeloid Leukemia Blasts by All-Trans Retinoic Acid, 1,25(OH)2 Vitamin D3, and Granulocyte-Macrophage Colony-Stimulating Factor

The relationship between differentiation of human myeloid cells and apoptosis remains unclear. Recent studies have shown that terminal differentiation need not necessarily lead to the apoptotic demise of myeloid cells, while other studies have shown that induction of differentiation is associated with increased resistance to apoptosis-inducing agents, such as chemotherapy and γ-irradiation. Such results are pertinent to the treatment of acute myeloid leukemia (AML) and myelodysplastic syndrome, where differentiating agents and hemopoietic growth factors are being combined with chemotherapy to enhance response and limit toxicity. To elucidate the factors governing apoptosis in human AML blasts, we have studied the cytotoxic effect of idarubicin on HL60, U937 and KG1 cells, after incubation with all-trans retinoic acid (ATRA), 1,25(OH)2 D3, and granulocyte-macrophage colony-stimulating factor (GM-CSF ). We show that prior incubation of human myeloid leukemic cells with ATRA or 1,25(OH)2 D3 induced resistance to idarubicin-induced apoptosis, which was modulated by coincubation with GM-CSF. The altered chemosensitivity of cells depended on the degree of G0/G1 cell-cycle arrest induced by incubation with ATRA, 1,25(OH)2 D3, and GM-CSF and was independent of differentiation status or Bcl-2 oncoprotein expression. These findings suggest that cell-cycle arrest in human leukemic cells can be induced by exogenous agents and may promote drug resistance. Determining the mechanisms by which cell-cycle arrest is induced may permit understanding of the processes by which the cells escape cytotoxic drug-mediated apoptosis.

Neoexpression of the c-met/Hepatocyte Growth Factor-Scatter Factor Receptor Gene in Activated Monocytes

Hepatocyte growth factor-scatter factor (HGF-SF ) mediates mito-, moto-, and morphogenic effects through the MET receptor, a membrane bound tyrosine kinase. HGF-SF/MET signaling is mitogenic for a large number of epithelial and endothelial cells and activates organ regeneration. HGF-SF transcripts have been detected in various myeloid cell lines. Therefore, the potential role of HGF-SF/MET signaling for circulating cells of the immune system, especially under conditions of inflammation, was evaluated. Several B-lymphoid and myeloid cell lines were found to express HGF-SF or c-met transcripts, while activity of both genes was mutually exclusive with the exception of low level coexpression in two B-cell lines. HGF-SF transcripts were present in low quantities in freshly isolated peripheral blood mononuclear cells (PBMNCs). In contrast, c-met expression was not detected in freshly isolated cells from peripheral blood, but was induced in monocytes by activation of monocytic or T-cell function. HGF-SF incubation led to an increased c-fos steady state transcript level in myeloblastic K562 cells and moderately promoted cell viability of freshly isolated preactivated monocytes. c-met expression is thus established in activated monocytes, in particular under conditions resembling inflammation, making these cells accessible to functional effects of HGF-SF.

Modulation of Idarubicin-Induced Apoptosis in Human Acute Myeloid Leukemia Blasts by All-Trans Retinoic Acid, 1,25(OH)2 Vitamin D3, and Granulocyte-Macrophage Colony-Stimulating Factor

The relationship between differentiation of human myeloid cells and apoptosis remains unclear. Recent studies have shown that terminal differentiation need not necessarily lead to the apoptotic demise of myeloid cells, while other studies have shown that induction of differentiation is associated with increased resistance to apoptosis-inducing agents, such as chemotherapy and γ-irradiation. Such results are pertinent to the treatment of acute myeloid leukemia (AML) and myelodysplastic syndrome, where differentiating agents and hemopoietic growth factors are being combined with chemotherapy to enhance response and limit toxicity. To elucidate the factors governing apoptosis in human AML blasts, we have studied the cytotoxic effect of idarubicin on HL60, U937 and KG1 cells, after incubation with all-trans retinoic acid (ATRA), 1,25(OH)2 D3, and granulocyte-macrophage colony-stimulating factor (GM-CSF ). We show that prior incubation of human myeloid leukemic cells with ATRA or 1,25(OH)2 D3 induced resistance to idarubicin-induced apoptosis, which was modulated by coincubation with GM-CSF. The altered chemosensitivity of cells depended on the degree of G0/G1 cell-cycle arrest induced by incubation with ATRA, 1,25(OH)2 D3, and GM-CSF and was independent of differentiation status or Bcl-2 oncoprotein expression. These findings suggest that cell-cycle arrest in human leukemic cells can be induced by exogenous agents and may promote drug resistance. Determining the mechanisms by which cell-cycle arrest is induced may permit understanding of the processes by which the cells escape cytotoxic drug-mediated apoptosis.

Modulation of the Apoptotic Response of Human Myeloid Leukemia Cells to a Diphtheria Toxin Granulocyte-Macrophage Colony-Stimulating Factor Fusion Protein

It has previously been shown that human granulocyte-macrophage colony-stimulating factor (GM-CSF) can be fused to a truncated diphtheria toxin (DT) to produce a recombinant fusion toxin that kills GM-CSF receptor–bearing cells. We now report that DT388–GM-CSF induces apoptosis and inhibition of colony formation in semisolid medium in receptor positive cells, and that the induction of apoptosis correlates with GM-CSF–receptor occupancy at low ligand concentrations. Also, the induction of apoptosis correlates with the inhibition of protein synthesis and is inversely related to the amount of intracellular antiapoptotic proteins (Bcl2 and Bc1XL ). Nine myeloid leukemia cells lines and four nonmyeloid leukemia cell lines were incubated with 0.7 nmol/L of 125I–GM-CSF in the presence or absence of excess cold GM-CSF and bound label measured. High affinity receptor numbers varied from 0 to 291 molecules per cell. Cells were incubated with varying concentrations of recombinant fusion toxin for 48 hours and incorporation of 3H-leucine (protein synthesis), segmentation of nuclei after DAPI staining (apoptosis), and colony formation in 0.2% agarose (clonogenicity) were measured. DT388–GM-CSF at 4 × 10−9 mol/L inhibited colony formation 1.5 to 3.0 logs for receptor positive cell lines. Protein synthesis and apoptosis IC50s varied among cell lines from greater than 4 × 10−9 mol/L to 3 × 10−13 mol/L. GM-CSF–receptor occupancy at 0.7 nmol/L GM-CSF–ligand concentration correlated with the protein synthesis IC50 . Similarly, the protein synthesis inhibition and apoptosis induction correlated well, except in cells overexpressing Bcl2 and BclXL , in which 25- to 150-fold inhibition of apoptosis was observed. We conclude that DT388–GM-CSF can kill acute myeloid leukemia blasts but that apoptotic sensitivities will depend on the presence of at least 100 high affinity GM-CSF receptors/cell and the absence of overexpressed antiapoptotic proteins.

A Novel, Myeloid Transcription Factor, C/EBPε, Is Upregulated During Granulocytic, But Not Monocytic, Differentiation

Human C/EBPε is a newly cloned CCAAT/enhancer-binding transcription factor. Initial studies indicated it may be an important regulator of human myelopoiesis. To elucidate the range of expression of C/EBPε, we used reverse transcription-polymerase chain reaction (RT-PCR) analysis and examined its expression in 28 hematopoietic and 14 nonhematopoietic cell lines, 16 fresh myeloid leukemia samples, and normal human hematopoietic stem cells and their mature progeny. Prominent expression of C/EBPε mRNA occurred in the late myeloblastic and promyelocytic cell lines (NB4, HL60, GFD8), the myelomonoblastic cell lines (U937 and THP-1), the early myeloblast cell lines (ML1, KCL22, MDS92), and the T-cell lymphoblastic leukemia cell lines CEM and HSB-2. For the acute promyelocytic leukemia cell line NB4, C/EBPε was the only C/EBP family member that was easily detected by RT-PCR. No C/EBPε mRNA was found in erythroid, megakaryocyte, basophil, B lymphoid, or nonhematopoietic cell lines. Most acute myeloid leukemia samples (11 of 12) from patients expressed C/EBPε. Northern blot and RT-PCR analyses showed that C/EBPε mRNA decreased when the HL60 and KG-1 myeloblast cell lines were induced to differentiate toward macrophages. Similarly, Western blot analysis showed that expression of C/EBPε protein was either unchanged or decreased slightly as the promyelocytic cell line NB4 differentiated down the macrophage-like pathway after treatment with a potent vitamin D3 analog (KH1060). In contrast, C/EBPε protein levels increased dramatically as NB4 cells were induced to differentiate down the granulocytic pathway after exposure to 9-cis retinoic acid. Furthermore, very early, normal hematopoietic stem cells (CD34+/CD38−), purified from humans had very weak expression of C/EBPε mRNA, but levels increased as these cells differentiated towards granulocytes. Likewise, purified granulocytes appeared to express higher levels of C/EBPε mRNA than purified macrophages. Addition of phosphothiolated antisense, but not sense oligonucleotides to C/EBPε, decreased clonal growth of HL-60 and NB4 cells by about 50% compared with control cultures. Taken together, our results indicate that expression of C/EBPε is restricted to hematopoietic tissues, especially myeloid cells as they differentiate towards granulocytes and inhibition of its expression in HL-60 and NB4 myeloblasts and promyelocytes decreased their proliferative capacity. Therefore, this transcriptional factor may play an important role in the process of normal myeloid development.

A Novel, Myeloid Transcription Factor, C/EBPε, Is Upregulated During Granulocytic, But Not Monocytic, Differentiation

Human C/EBPε is a newly cloned CCAAT/enhancer-binding transcription factor. Initial studies indicated it may be an important regulator of human myelopoiesis. To elucidate the range of expression of C/EBPε, we used reverse transcription-polymerase chain reaction (RT-PCR) analysis and examined its expression in 28 hematopoietic and 14 nonhematopoietic cell lines, 16 fresh myeloid leukemia samples, and normal human hematopoietic stem cells and their mature progeny. Prominent expression of C/EBPε mRNA occurred in the late myeloblastic and promyelocytic cell lines (NB4, HL60, GFD8), the myelomonoblastic cell lines (U937 and THP-1), the early myeloblast cell lines (ML1, KCL22, MDS92), and the T-cell lymphoblastic leukemia cell lines CEM and HSB-2. For the acute promyelocytic leukemia cell line NB4, C/EBPε was the only C/EBP family member that was easily detected by RT-PCR. No C/EBPε mRNA was found in erythroid, megakaryocyte, basophil, B lymphoid, or nonhematopoietic cell lines. Most acute myeloid leukemia samples (11 of 12) from patients expressed C/EBPε. Northern blot and RT-PCR analyses showed that C/EBPε mRNA decreased when the HL60 and KG-1 myeloblast cell lines were induced to differentiate toward macrophages. Similarly, Western blot analysis showed that expression of C/EBPε protein was either unchanged or decreased slightly as the promyelocytic cell line NB4 differentiated down the macrophage-like pathway after treatment with a potent vitamin D3 analog (KH1060). In contrast, C/EBPε protein levels increased dramatically as NB4 cells were induced to differentiate down the granulocytic pathway after exposure to 9-cis retinoic acid. Furthermore, very early, normal hematopoietic stem cells (CD34+/CD38−), purified from humans had very weak expression of C/EBPε mRNA, but levels increased as these cells differentiated towards granulocytes. Likewise, purified granulocytes appeared to express higher levels of C/EBPε mRNA than purified macrophages. Addition of phosphothiolated antisense, but not sense oligonucleotides to C/EBPε, decreased clonal growth of HL-60 and NB4 cells by about 50% compared with control cultures. Taken together, our results indicate that expression of C/EBPε is restricted to hematopoietic tissues, especially myeloid cells as they differentiate towards granulocytes and inhibition of its expression in HL-60 and NB4 myeloblasts and promyelocytes decreased their proliferative capacity. Therefore, this transcriptional factor may play an important role in the process of normal myeloid development.

CD34 Expression Patterns During Early Mouse Development Are Related to Modes of Blood Vessel Formation and Reveal Additional Sites of Hematopoiesis

CD34 is a cell surface glycoprotein that is selectively expressed within the human hematopoietic system on stem and progenitor cells, and in early blood vessels. To elucidate its functions during early blood vessel formation and hematopoiesis, we analyzed the expression patterns, in day 8 to day 10 mouse embryos, of CD34 RNA by in situ hybridization and protein by immunohistochemistry using the monclonal antibody RAM 34. Levels of expression in embryonic blood vessels were correlated with the mode of vessel formation, being high in pre-endothelial cells and in vessels forming by vasculogenesis (particularly the dorsal aortae) or angiogenesis, but low in vessels forming by coalescence (the cardinal veins). CD34+ erythroid cells, presumably of yolk sac origin, were present in the liver of day 10 embryos; at the same stage, putative definitive hematopoietic cells, strongly CD34+, were present in the para-aortic mesenchyme. Possible sites of hemangioblastic differentiation were detected in the form of CD34+ endothelium-attached hematopoietic cells in the dorsal aorta and in two previously unreported locations, the proximal umbilical and vitelline arteries. These observations suggest functions for CD34 in relation to specific modes of blood vessel formation, and a hemangioblastic role in both embryonic and extraembryonic sites.

CD34 Expression Patterns During Early Mouse Development Are Related to Modes of Blood Vessel Formation and Reveal Additional Sites of Hematopoiesis

CD34 is a cell surface glycoprotein that is selectively expressed within the human hematopoietic system on stem and progenitor cells, and in early blood vessels. To elucidate its functions during early blood vessel formation and hematopoiesis, we analyzed the expression patterns, in day 8 to day 10 mouse embryos, of CD34 RNA by in situ hybridization and protein by immunohistochemistry using the monclonal antibody RAM 34. Levels of expression in embryonic blood vessels were correlated with the mode of vessel formation, being high in pre-endothelial cells and in vessels forming by vasculogenesis (particularly the dorsal aortae) or angiogenesis, but low in vessels forming by coalescence (the cardinal veins). CD34+ erythroid cells, presumably of yolk sac origin, were present in the liver of day 10 embryos; at the same stage, putative definitive hematopoietic cells, strongly CD34+, were present in the para-aortic mesenchyme. Possible sites of hemangioblastic differentiation were detected in the form of CD34+ endothelium-attached hematopoietic cells in the dorsal aorta and in two previously unreported locations, the proximal umbilical and vitelline arteries. These observations suggest functions for CD34 in relation to specific modes of blood vessel formation, and a hemangioblastic role in both embryonic and extraembryonic sites.

Distribution of active alpha- and beta-subunits of beta-N-acetylhexosaminidase as a function of leukaemic cell types

beta-N-Acetylhexosaminidase isoenzymes, and the distribution of the alpha- and beta-subunits forming the enzyme in a representative series of fresh leukaemic cells and in established leukaemic cell lines, were obtained by using a combination of DEAE-cellulose chromatography and assay with the fluorogenic substrates 4-methylumbelliferyl-beta-N-acetylglucosaminide hydrolyzed by both alpha and beta subunits, and 4-methylumbelliferyl-beta-N-acetylglucosaminide-6-SO4 hydrolyzed only by hexosaminidase isoenzymes containing alpha-subunits. The presence of hexosaminidase S (the alpha alpha dimer), was found in all the leukaemic cell populations we surveyed, but not in normal human cells. The presence of this isoenzyme can therefore be considered as an additional marker of leukaemic cells. A prevalence of hexosaminidase A and A-like intermediate forms (alpha beta structure), characterize leukaemic cells of myeloid origin, whereas greater amounts of hexosaminidase B and B-like intermediate forms (beta beta structure), were consistent attributes of leukaemic cells of lymphoid origin. An over-expression of beta-subunits in blasts might be related to their undifferentiated status. These changes in the isoenzymes of hexosaminidase may prove informative about a variety of changes in the biology of leukaemic cells that could range from chromosomal alterations to changes in the proteolytic processing and glycosylation.

Hydroquinone resistance in a murine myeloblastic leukemia cell line. Involvement of quinone reductase and glutathione-dependent detoxification in nonclassical multidrug resistance

A hydroquinone-resistant derivative of the M1 cell line, designated M1HQ, was generated and used to evaluate the biochemical mechanism responsible for resistance to oxidative stress-inducing agents. The hydroquinone concentrations that were cytotoxic to 50 and 90% of the parental M1 cell line in 48 hr were 25 and 90 microM, respectively, whereas exposure to 500 microM hydroquinone did not decrease M1HQ viability significantly. M1HQ cells grew slower than M1 cells and exhibited significantly higher resistance to colchicine, doxorubicin, hydrogen peroxide, 4-hydroperoxycyclophosphamide, and 1,3-bis (2-chloroethyl)-1-nitrosourea but not to benzoquinone, vinblastine, or gamma-radiation. M1HQ cells possessed significantly higher levels of total thiols, glutathione, glutathione peroxidase, glutathione reductase, quinone reductase, and gamma-glutamyl transpeptidase than the parental M1 cell line. Steady-state gamma-glutamylcysteine synthetase mRNA expression also was 1.6-fold higher in M1HQ cells. P-glycoprotein transcripts were detectable in both M1 and M1HQ cells, but were 2-fold higher in M1HQ. Multidrug resistance-associated protein transcripts were not detectable in either M1 or M1HQ. Hydroquinone resistance in M1HQ cells was partially reversible with a combination of inhibitors of quinone reductase, gamma-glutamylcysteine synthetase, glutathione peroxidase, and the multidrug resistance-associated protein, but not with inhibitors of P-glycoprotein, gamma-glutamyl transpeptidase, or glutathione-S-transferase. When treated with [14C]hydroquinone, M1HQ cells did not generate significant hydroquinone-protein adducts but did release an adduct similar to N-acetylcysteinyl-benzoquinone. In contrast, numerous [14C]hydroquinone-protein adducts were produced in M1 cells, while the N-acetylcysteinyl-benzoquinone-like molecule was undetectable. Thus, hydroquinone resistance in M1HQ cells appeared to result from a glutathione-dependent detoxification and export mechanism.

Ionizing radiation effects on the KG1a primitive hematopoietic cell line

PURPOSE

Better understanding of radiation-induced effects on the hematopoietic system is important in both the context of therapeutic intervention and accidental exposure. However, direct study of these effects on the hematopoietic stem cell pool is hampered by the small number of accessible cells. We, thus, studied radiation-induced effects on the KG1a stem cell line.

METHODS AND MATERIALS

We confirmed and extended the immunophenotype of KG1a with monoclonal antibodies, established a radiation survival curve, and quantified mRNAs by Northern blotting 30 min after 1, 2, and 3 Gy of ionizing radiation (IR) and followed for up to 48 h after a 3 Gy dose. Cell cycle status and apoptosis were assessed by fluorescent-activated cell sorter (FACS) analysis, cell morphology, and DNA fragmentation.

RESULTS

KG1a was found to be CD34+, CD7+, Thy1 low, CD38 low, lineage negative (neg), C-KITneg and HLA-DRneg, a phenotype consistent with a primitive hematopoietic origin. This immunophenotype was not altered by x-ray irradiation. The D0 value was 1.75 Gy. We showed a time-dependent variation of c-jun mRNA expression with an early and transient dose-dependent induction followed by a second increase at 24 and 48 h: a biphasic dose-dependent variation of bcl-2 expression 30 min after irradiation with a reduction of mRNA level at 1 Gy, and a normalization at higher doses and stable levels of mRNA for c-fos, c-myc, G-CSF, GM-CSF, IL-6, TNF-alpha, TGF-beta, and MIP-1 alpha genes. Cell cycle analysis showed the absence of G1/S phase arrest, a point consistent with the absence of detection of P53 mRNA by Northern blot analysis. The dose-dependent G2/M phase arrest was not followed by significant apoptotic cell death.

CONCLUSION

Taken together, this data indicates that radiation-induced cell death of KG1a, a cell line that has a relatively high D0 value, does not seem to be the result of the apoptotic pathway but occurs subsequent to a G2/M phase arrest.

In vitro infection of primary and retrovirus-infected human leukocytes by human foamy virus

The infectivity of human foamy virus (HFV) was examined in primary and cultured human leukocytes. Cell-free infectious viral stocks of HFV were prepared from the human kidney cell line 293 transfected with an infectious molecular clone of HFV. HFV productively infects a variety of human myeloid and lymphoid cell lines. In addition, primary cell cultures enriched for human CD4+, monocytes and brain-derived microglial cells, were readily infected by HFV. Interestingly, while infected primary CD4+ lymphocytes and microglial cells showed marked cytopathology characteristic of foamy virus, HFV-infected monocyte-derived macrophages failed to show any cytopathology. In addition, marked cytotoxicity due to HFV infection was seen in both human T-cell leukemia virus type 1- and human immunodeficiency virus type 1-infected T-cell lines and in human immunodeficiency virus type 1-infected monocytoid cell lines. Thus, HFV infection produces differential cytopathology in a wide host range of primary human leukocytes and hematopoietic cell lines.

A regulatory domain within the virus-response element of the interferon alpha 1 gene acts as a transcriptional repressor sequence and determinant of cell-specific gene expression

Type-I interferons are encoded by a multigene family, the major members of which are at least 13 IFN A subtypes and a single IFN B gene. IFNs A and B are induced in response to similar stimuli, such as virus infection and double-stranded RNA, but in different cell types: the induction of IFN A is almost exclusively restricted to cells of lymphoid origin, while IFN B has been found to be induced in a variety of cell types including fibroblasts. The virus-responsive enhancer element in the promoter region of IFN A family members is largely responsible for the differential expression of individual subtypes in responsive cells. In this paper we describe experiments which address the issue of the differential expression of IFN A and IFN B in different cell types. We show that IFN-beta is induced in a variety of cells of different origin, while not all of these are able to secrete IFN-alpha. By transfection of reporter gene constructs comprising the virus-responsive enhancer from the IFN A1 and IFN B genes, we show that this differential response is mediated at the level of transcription via these control elements. More detailed analysis of the function of these regions identifies specific sequences within the IFN A1 virus response element that has an inhibitory effect on expression in cells that are normally inducible, and is also implicated in the overall suppression of IFN A induction in non-inducible cells.

Characterization of IgG Fc receptors on CD34 antigen-expressing cell lines (KG-1 and KG-1a)

Although Fc gamma receptors (Fc gamma R) on mature blood cells have been extensively studied, there are only limited data on Fc gamma R expression in the early haematopoietic progenitor cells. In this study, we used the stem cell antigen (CD34)-expressing cell line (KG-1) and its less differentiated subline (KG-1a) as a model for the study of Fc gamma R in the early haematopoietic progenitors. Flow cytometry and immunoprecipitation studies on KG-1 and KG-1a cells with anti-Fc gamma R mAb showed that Fc gamma RII is the only Fc gamma R expressed on the cell surface. Analysis of the steady-state levels of Fc gamma R mRNA in KG-1 and KG-1a cells using a quantitative in situ hybridization assay revealed the presence of only Fc gamma RII mRNA. On further analysis Fc gamma RIIA mRNA but no Fc gamma RIIB or Fc gamma RIIC transcripts were found in these cells; Fc gamma RIIA transcripts with and without the transmembrane exon were present in approximately equal amounts. These findings are surprisingly similar to those observed previously with Fc gamma R in platelets and megakaryocytic cells but different from those found with Fc gamma R in cells of other lineages. These data suggest that the Fc gamma R transcript distribution pattern observed in the early haematopoietic progenitors (KG-1 cells) is retained in later stages of haematopoietic differentiation only in cells of megakaryocytic lineage.

Interleukins and colony stimulating factors in human myeloid leukemia cell lines

The present review has summarized the expression, production and effects of the human interleukins (IL) 1-11 and myelopoietic colony stimulating factors (CSF) in the established myeloid leukemia cell lines and in cells from patients with acute myeloid leukemia as well as the oncogene expression reported in these myeloid leukemia cell lines. The genetic dissection of leukemic myelopoiesis may provide new perspectives for the control of myeloid leukemias. Based on their expression of phenotypic markers (e.g., surface antigens, cytochemical staining, etc.), myeloid cell lines can be further subdivided into myelogenous, monocytic, erythroid and megakaryoblastic leukemia cell lines. Due to the close relationship of erythroid and megakaryoblastic progenitor cells and to the existence of a probably common precursor cell giving rise to these two different cell lineages, many megakaryoblastic cell lines express erythroid markers (e.g., expression of hemoglobin or glycophorin A) and conversely cell lines with a predominant erythroid profile might display megakaryoblastic features (e.g., platelets peroxidase or glycoproteins CD41, CD42b or CD61). The recent cloning of the specific cytokine: thrombopoietin (TPO) and its receptor generated a strong interest in these particular myeloid cell lines that are discussed in more detail in the present review. Both normal and leukemic megakaryocytopoiesis are stimulated by granulocyte-macrophage colony stimulating factor (GM-CSF), IL-3, GM-CSF/IL-3 fusion protein, IL-6, IL-11 and TPO but inhibited by IL-4, interferon-alpha (IFN-alpha) and IFN-gamma. Human megakaryoblastic leukemia cell lines have common biological features: high expression of the megakaryocytic specific antigen (CD41); high expression of early myeloid antigens (CD34, CD33 and CD13); constitutive expression of IL-6 and platelet-derived growth factor; a complex karyotype picture; expression of c-kit (the stem cell factor receptor); growth-dependency or -stimulation by IL-3 and/or GM-CSF; and in vivo tumorigenicity in mice associated with marked fibrosis. Whereas numerous chemical and biologic agents induce granulocytic and/or monocytic differentiation of myeloid leukemia cell lines, only a few agents including phorbol myristate acetate, vitamin D3, IFN-alpha, IL-6 and thrombin have been reported to induce megakaryocytic differentiation in the megakaryoblastic leukemia cells.

A human homolog of the mitochondrial protein import receptor Mom19 can assemble with the yeast mitochondrial receptor complex

Import of preproteins into mitochondria requires transport machineries in both mitochondrial membranes that have been characterized in Saccharomyces cerevisiae and Neurospora crassa. By cDNA analysis, we identified a human protein of 16 kDa with significant overall homology to the fungal mitochondrial import receptor Mom19, including the three typical characteristics: a hydrophobic N-terminal segment, a tetratrico peptide motif in the middle and a negatively charged C-terminus. The human Mom19 homolog is expressed in all tissues analyzed. When synthesized in vitro, the human Mom19 homolog is targeted to isolated yeast mitochondria and specifically associates with the outer membrane receptor complex, suggesting that indeed a mitochondrial import receptor was identified.

Short-term stability of HIV provirus levels in the peripheral blood of HIV-infected individuals

Changes in viral load have been reported to reflect disease progression or response to therapy; however, the stability of HIV DNA levels in HIV-infected individuals has not been extensively studied. Cellular HIV DNA levels in infected individuals were evaluated over a short time period to determine degree of variability as well as any correlation with other measurements of virus load or immune status. Peripheral blood mononuclear cells (PBMC) were obtained several times over 1 month from 32 asymptomatic or symptomatic non-AIDS, HIV-infected individuals currently on AZT therapy. PCR amplification of the HIV gag region was performed with DNA from PBMC lysates and the PCR amplified products quantitated by liquid phase hybridization. HIV DNA levels in the majority of the patients were relatively stable, with 26 of 32 persons having less than threefold change. Changes over the study period were both positive and negative, and the median change in HIV DNA levels was 68.6%. These changes were found to positively correlate with fluctuations in plasma p24 levels. In contrast, no correlations were found with other measurements of immune system activity, including changes in CD4 number, CD4 percent, and beta 2-microglobulin when compared with provirus changes. This study shows that levels of HIV DNA can be relatively stable over short periods in most non-AIDS, HIV-infected persons.

Potentiation of tumor necrosis factor-mediated cytotoxicity on human myeloid cell lines: effects of interferons versus dimethylsulphoxide

After prolonged incubation times of 72 h IFN alpha 2a and IFN beta 1 significantly reduced cell growth in the myelomonocytic U937 and THP1 cell lines. IFN gamma showed only slight growth inhibitory activities. IFN activities were potentiated by the highly polar differentiation inducer dimethylsulphoxide, which is similar to our previous study on tumor necrosis factor (TNF). However, in contrast with TNF, none of the interferon types induced cell cytotoxicity or DNA fragmentation. Like DMSO, all interferons potentiated TNF-induced cytotoxicity, IFN beta 1 and IFN gamma being the most potent in this respect. When applied together, DMSO and IFN gamma enhanced TNF-mediated cell lysis in either an additive (in the case of U937, THP1, HL60 cells) or a synergistic (in the case of KG1) manner, suggesting that the mechanisms of the potentiating activity of DMSO and IFN gamma are different. The potential role of the simultaneous use of DMSO-related molecules, and TNF and/or IFN in leukemic cancer chemotherapy is discussed.

A novel intracellular antigen in HL-60 cells that changes in molecular weight after granulocytic and monocytic differentiation

The present study reports the identification and partial characterization of a novel antigen with M(r) 100,000 by a monoclonal antibody (D29A8) that was obtained by immunizing BALB/c mice with nuclei of HL-60 cells. D29A8 detected mainly a nucleolar macromolecule with M(r) 100,000 (p100). On the other hand, when HL-60 cells were induced to differentiate either into a granulocytic or monocytic pathway, the antibody detected mainly a cytoplasmic macromolecule with M(r) 95,000 (p95). Since two subtypes of the antigen (p100 and p95) appear to be present in the same cells that differ in the stage of cell differentiation, the antigen may play an important role in cellular differentiation.

Differential regulation of the expression of interleukin-2 receptor gamma-chain during the in vitro differentiation of human myeloid cells

The common gamma-chain (gamma c) is a shared component of cell-surface receptors for the interleukins- 2, -4 and -7, and possibly others. We studied its expression in cells and cell lines of myeloid origin and found ubiquitous presence of gamma c mRNA in all cells examined. Differential regulation of gamma c expression was observed in myeloid cell lines induced to differentiate in vitro. In K-562 erythromyeloid cells, a sharp rise in the levels of gamma c mRNA and protein accompanied megakaryocytic, but not erythroid, differentiation. Surface binding of interleukin-2, as well as the transcripts for cognate receptor chains, were scarcely detectable in K-562 cells, whereas a significant increase in the binding of granulocyte-macrophage colony-stimulating factor specifically occurred during their megakaryocytic maturation. Our data indicate that expression of gamma c is a common feature of human myeloid cells, and suggest that its expression may be a requirement for human myelopoiesis.

A new monoclonal antibody (A78-G/A7) to the Thomsen-Friedenreich pan-tumor antigen

A new monoclonal antibody to the Thomsen-Friedenreich (TF) antigen (or, more precisely, epitope; Gal beta 1-3GalNAc-) has been developed that is specific for both anomeric forms of this disaccharide (TF alpha and TF beta, including related structures on glycolipids), and not assay restricted. We demonstrate that this avid antibody (A78-G/A7) is well suited for immunohistochemistry on paraffin-embedded and cryosectioned tissues, immunoblotting, ELISA techniques, and hemagglutination. Immunohistochemistry on paraffin sections does not require proteolytic or microwave pretreatment. The binding characteristics of this antibody are largely independent of variations in pH (6.0-8.2) and temperature (4-37 degrees C). Immunoblotting with KG-1 (human acute myelogenous leukemia) cells revealed a series of TF-active glycoproteins with a main band at about 155 kDa. Immunoprecipitation was performed using a new technique applicable to IgM-type antibodies.

Vitamin D3 analogs: effect on leukemic clonal growth and differentiation, and on serum calcium levels

In vitro, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) induces differentiation of HL-60 cells and inhibits their proliferation as well as the proliferation of leukemic cells from patients. In vivo, the survival of mice challenged with syngeneic leukemic cells is enhanced by treatment with 1,25(OH)2D3. Patients treated with 1,25(OH)2D3 develop hypercalcemia at a serum level of 2 x 10(-10) mol/l which is a concentration too low to achieve an antileukemic effect in vitro. Several interesting vitamin D3 analogs have recently been developed. We initially examined the effect of 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3 and 24a,26a,27a-tri-homo-22,24-diene-1-alpha,25-(OH)2-D3 on clonal growth and differentiation of HL-60 cells. Each of the analogs had comparable effects on clonal growth with 50% inhibition (ED50) at concentrations of 0.2-0.5 x 10(-9) M; 1,25(OH)2D3 was about 20- to 50-fold less active in inhibiting growth. Differentiation was determined by induction of superoxide production, as measured by nitroblue tetrazolium (NBT) reduction and by expression of a macrophage-specific enzyme (alpha napthyl acetate esterase (ANAE)). The 24a,26a,27a-tri-homo-22,24-diene-1-alpha,25-(OH)2-D3 and 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3 were about 5- to 14-fold more potent than 1,25(OH)2D3. The hypercalcemia inducing side-effects of these analogs and three other previously identified, extremely potent vitamin D3 compounds, as well as 1,25(OH)2D3, were studied. The analogs were administered intraperitoneally every other day (qod) for 5 weeks; serum was collected weekly and Ca2+ measured by atomic absorption spectrophotometry. The highest tolerated dose of each analog leaving all mice alive was for 1,25(OH)2D3: 0.25 micrograms; 1,25(OH)2-24a,26a,27a-tri-homo-22,24-diene-D3: 0.25 micrograms; and 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3: 0.0625 micrograms. Another hexafluoro compound with potent abilities to induce differentiation (1,25(OH)2-16ene-23yne-26,27-F6-D3) was very toxic, all mice died in the second week while receiving 0.0625 micrograms qod. Prior studies showed that the most potent compound in inducing differentiation of HL-60 was 1,25(OH)2-20-epi-D3; but it is very toxic as only one mouse survived a dose of > or = 0.0125 micrograms qod for 5 weeks. 1,25(OH)2-16ene-23yne-D3 is an extremely active inducer of differentiation but, on the other hand, it has low potential to produce hypercalcemia; mice maintained normal serum calcium levels even while receiving 2 micrograms qod for 5 weeks.(ABSTRACT TRUNCATED AT 400 WORDS)

Amplification of the E2F1 transcription factor gene in the HEL erythroleukemia cell line

The E2F transcription factor plays an important regulatory role in cell proliferation, mediating the expression of genes whose products are essential for inducing resting cells to enter the cell cycle and synthesize DNA. To investigate the possible involvement of E2F in hematopoietic malignancies, we isolated genomic clones encompassing the human E2F1 gene. We then used fluorescence in situ hybridization to localize E2F1 to human chromosome 20q11, telomeric to the p107 locus, a gene whose product is related to the retinoblastoma gene product (pRb). This finding contrasts with the 1p36 and 6q22 chromosomal locations previously assigned E2F2 and E2F3, two additional members of the E2F family. Although deletions or structural rearrangements of E2F1 were not detected in 14 primary acute leukemia or myelodysplasia samples with structural abnormalities of chromosome 20q11, the gene was amplified and overexpressed in HEL erythroleukemia cells and translocated to other chromosomes in several established human leukemia cell lines. This study provides the first evidence of gene amplification involving a member of the E2F family of transcription factors. We propose that E2F1 overexpression in erythroid progenitors may stimulate abnormal cell proliferation by overriding negative regulatory signals mediated by tumor suppressor proteins such as pRb.

Isolation of unknown genes from human bone marrow by differential screening and single-pass cDNA sequence determination

A cDNA sequencing project was initiated to characterize gene expression in human bone marrow and develop strategies to isolate novel genes. Forty-eight random DNAs from total human bone marrow were subjected to single-pass DNA sequence analysis to determine a limited complexity of mRNAs expressed in the bone marrow. Overall, 8 cDNAs (17%) showed no similarity to known sequences. Information from DNA sequence analysis was used to develop a differential prescreen to subtract unwanted cDNAs and to enrich for unknown cDNAs. Forty-eight cDNAs that were negative with a complex probe were subject to single-pass DNA sequence determination. Of these prescreened cDNAs, the number of unknown sequences increased to 23 (48%). Unknown cDNAs were also characterized by RNA expression analysis using 25 different human leukemic cell lines. Of 13 unknown cDNAs tested, 10 were expressed in all cell types tested and 3 revealed a hematopoietic lineage-restricted expression pattern. Interestingly, while a total of only 96 bone marrow cDNAs were sequenced, 31 of these cDNAs represent sequences from unknown genes and 12 showed significant similarities to sequences in the data bases. One cDNA revealed a significant similarity to a serine/threonine-protein kinase at the amino acid level (56% identity for 123 amino acids) and may represent a previously unknown kinase. Differential screening techniques coupled with single-pass cDNA sequence analysis may prove to be a powerful and simple technique to examine developmental gene expression.

A tetrazolium-based colorimetric MTT assay to quantitate human monocyte mediated cytotoxicity against leukemic cells from cell lines and patients with acute myeloid leukemia

The MTT-colorimetric monocyte mediated cytotoxicity assay, based upon the ability of living cells to reduce 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) into formazan, was evaluated using leukemic cells from five representative human leukemic cell lines and from 28 patients with acute myeloid leukemia (AML). An excellent linearity between absorbance and leukemic cell number was observed up to 5 x 10(4) cells/well and 50 x 10(4) cells/well for all cell lines and patients samples tested, respectively, in a 96-wells microtiter culture system. A huge variability in the susceptibility of leukemic cells to purified and IFN-gamma-activated human monocytes could be observed at effector-to-target cell (E:T) ratios of 1. The mean signal-to-noise ratio of the MTT assay for monocyte-leukemic cell mixtures from patients was 2.69 +/- 0.39 at E:T 1. In conclusion, the MTT based monocyte mediated cytotoxicity assay should be useful for studying the susceptibility of a variety of leukemic cells from cell lines and from patients with AML to monocytes in a rapid, sensitive and semi-automated manner.

Human peripheral blood granulocytes and myeloid leukemic cell lines express both transcripts encoding for stem cell factor

Stem cell factor (SCF), the ligand for the c-kit proto-oncogene, has been shown to play a critical role in the migration of melanocytes and germ cells during embryogenesis as well as in the proliferative control of the hematopoietic compartment. In this study we investigated the expression of both the soluble and transmembrane SCF forms in purified peripheral blood populations and in several hematopoietic cell lines. Expression of both transcripts, though in different ratios, was identified in whole bone marrow, in bone marrow stromal cells and in human peripheral blood. In peripheral blood, SCF expression could be ascribable to polymorphonuclear leukocytes (PMN), whereas no SCF expression was detected in isolated lymphocytes, monocytes and in some T lymphoid cell lines. Conversely, some hematopoietic myeloid cell lines, such as HL-60, KG1 and K562, express SCF with similar patterns.

Correlation of heat resistance and HSP-70A mRNA levels in human tumor cells measured by competitive quantitative polymerase chain reaction

PURPOSE

Several HSP-70 genes have been cloned and sequenced in human cells. Among these genes, the HSP-70A mRNA and protein levels correlate best with the development and decay of thermotolerance and intrinsic thermal sensitivity. Leukemic and nonleukemic human tumor cells express low levels of the normally heat inducible HSP-70A mRNA in control nonheated cells. Using a competitive quantitative polymerase chain reaction, we have measured the levels of mRNA for this gene and have correlated it with both transient and intrinsic thermal sensitivity of tumor cells. Such studies were also extended to tumor samples obtained from patients.

METHODS AND MATERIALS

In these studies, the plasmid phHSP-70 which contains the entire human HSP-70A gene was modified by the insertion of the T7 promoter at the 5'-end untranslated region as well as the insertion of a 23 bp synthetic linker at the BamH1 site in the promoter region of the HSP-70A gene. The PCR primers were located such that the amplified fragment contained the linker. Using the T7 polymerase, the HSP-70A mRNA was transcribed from this plasmid (phHSP-70L) in vitro. A known amount of HSP-70A mRNA was then added to the total RNA prepared from the cell samples or from the tumor tissues obtained from patients. Using the components of the PCR reaction plus known amounts of HSP-70A mRNA synthesized from phHSP-70L and unknown amounts of total cellular RNA, the samples were amplified and analysed on a denaturing acrylamide gel. The PCR products obtained from phHSP-70L were 23 bp larger than the PCR products obtained from the cell samples due to the addition of the synthetic linker to the HSP-70A gene in phHSP-70L and therefore, the two products could be easily distinguished from each other and quantitated. The alpha-32P-dCTP incorporated in each sample was quantitated by AMBIS Scanner. When the 32P-counts were equal in the known and the unknown samples, the amount of the HSP-70A mRNA was taken to be equal in the known and the unknown sample.

RESULTS

The results show that HSP-70A mRNA levels can be used to predict the survival levels during the development and decay of thermotolerance. In nonleukemic human tumor cell lines, there are as much as 40-50-fold induction of HSP-70A mRNA levels during the peak of thermotolerance. In leukemic cell lines, however, HSP-70A mRNA levels are induced only by three-fold during the same time period. These differences between the levels of HSP-70A mRNA positively correlate with the amount of tolerance development in leukemic and nonleukemic tumor cells. HSP-70A mRNA levels also vary in different tumor cells under nonheated conditions and there is a positive correlation between HSP-70A mRNA levels in nonleukemic human tumor cells and the level of their intrinsic thermal resistance.

CONCLUSION

HSP-70A mRNA levels can be used to predict the intrinsic thermal sensitivity of nonleukemic human tumor cells.

Inhibition of the differentiation of human myeloid cell lines by redox changes induced through glutathione depletion

We have investigated the effect of redox changes in vivo on the differentiation of two human myeloid cell lines, HL-60 and KG-1. The glutathione-depleting agent diethyl maleate (DEM) prevented the development of differentiated features in response to phorbol esters, including adherence of the cells to plastic surfaces and repression of the myeloperoxidase and CD34 genes. Moreover, DEM abolished phorbol 12-myristate 13-acetate-induced activation of the transcription factors AP-1 and Egr-1, suggesting that inhibition of differentiation may be due, at least in part, to redox modifications of these proteins.

Selective expression of heat shock genes during differentiation of human myeloid leukemic cells

Several studies have indicated a role for heat shock proteins during development and differentiation. In these studies we have examined the patterns of activation of the HSP-70A, HSP-70B, HSP-70B' and HSP-28 mRNAs and proteins during the differentiation of immature human leukemic cells to more mature progenitors by several differentiation-inducing agents. K562 cells activate the mRNA for HSP-70A, HSP-70B' and HSP-28 genes in the presence of hemin or sodium butyrate as cells differentiate into late erythroblasts. K562 cells become progressively more resistant to killing by heat shock during their differentiation to late erythroblasts. Further, selective inhibition of HSP-70A by antisense oligonucleotides to reduce HSP-70 kDa accumulation results in consistent reduction of hemoglobin production by 25-30% in K562 cells exposed to hemin, HL-60 cells differentiate into mature macrophages within 3 days following addition of PMA. HSP-70A mRNA levels increase within the first 2 h of PMA treatment and remain elevated for up to 3 days during the cells' gradual differentiation into mature macrophages. PMA and sodium butyrate treatment also cause elevated levels of HSP-28 mRNA expression; this increase is barely detectable at 24 h but is considerable at 72 h when about 90% of HL-60 cells are differentiated into mature macrophages or monocytes. These studies show that HSP-70A, HSP-70B' and HSP-28 may have specific roles during the differentiation of blood cell progenitors into erythrocytes or macrophages. Further, differentiation alters the thermal sensitivity of leukemic cells.

Sequence analysis and functional studies of interleukin-3 receptor alpha subunit-encoding cDNAs amplified from KG-1 leukemic cells and normal human marrow

Two partial cDNAs encoding the human interleukin-3 receptor alpha subunit (IL-3R alpha) were cloned from KG-1 leukemic cells using the polymerase chain reaction. Sequence analysis of these cDNAs predicted two single-amino-acid (aa) changes as compared with the published TF-1 leukemic cell IL-3R alpha sequence [Kitamura et al., Cell 66 (1991) 1165-1174]. These changes were confirmed by sequence analysis of a second set of independently derived cDNAs. Identical aa changes were found in the IL-3R alpha encoded by cDNAs cloned from normal CD34+ human marrow cells. Ligation of the partial cDNAs derived from KG-1 cells resulted in a full-length functional IL-3R alpha cDNA clone. Deletion of the extracellular 'LSXWS' consensus sequence resulted in complete loss of detectable [125I]IL-3 binding when this mutant receptor was co-expressed in COS-7 cells with the beta subunit of the IL-3 receptor.

Proliferating cell nuclear antigen and Ki-67 antigen expression in human haematopoietic cells during growth stimulation and differentiation

By flow cytometric dual parameter analysis of proliferating cell nuclear antigen (PCNA) and the Ki-67 antigen a detailed cell cycle analysis can be performed. In this study the coordinated expression of these two growth-related antigens was investigated in human haematopoietic cells at entrance into the cell cycle as well as at exit from the cycle. In mitogen-stimulated peripheral blood lymphocytes entering the first cell cycle, the Ki-67 antigen was found to be expressed in S phase cells and not in G1 cells. Thus, the Ki-67 antigen expression in PCNA-positive S phase cells differed between continuously cycling cells and cells entering the cell cycle. Based on this difference, it was possible to visualize and evaluate the recruitment of cells into the first cell cycle from a resting stage. This new cell cycle parameter can give additional information concerning tumour growth. The Ki-67 antigen was also studied during different stages of G1 and was found to be expressed at high levels in early G1 cells compared with other parts of G1.

FLT4 receptor tyrosine kinase gene mapping to chromosome band 5q35 in relation to the t(2;5), t(5;6), and t(3;5) translocations

FLT4 is a recently cloned receptor tyrosine kinase cDNA, which is characterized by seven immunoglobulin-like loops in its extracellular domain. We have previously mapped the FLT4 gene to chromosome segment 5q33-qter using somatic cell hybrids. Here we have refined the localization to band 5q35 by fluorescence in situ hybridization and show that the gene is translocated to chromosomes 2 and 6 in the t(2;5)(p23;q35) and t(5;6)(q35;p21) translocations, respectively, of Ki-I-positive lymphomas, as well as to chromosome 3 in the t(3;5)(q25.1;q34) translocation, which is occasionally found in myelodysplastic syndromes and acute myeloid leukemia. No evidence was obtained for a rearrangement or deregulation of the translocated FLT4 gene. We further show that abundant FLT4 mRNA expression occurs only in erythroid and megakaryoblastoid cell lines among nine leukemia cell lines studied.

HEX: a novel homeobox gene expressed during haematopoiesis and conserved between mouse and human

We describe the cloning of a novel homeodomain-containing gene, which is highly conserved between mouse and human. The human cDNA was initially isolated from human haematopoietic tissue and denoted HEX (haematopoietically expressed homeobox). Sequence analysis of the coding sequences from mouse and the partial cDNA from human shows that the homeodomain is most closely related to those of the HIx and HOX11 proteins. The HEX gene is present as a single copy in the human genome. Analysis of murine genomic DNA shows, in addition to an intron-containing gene homologous to HEX, the presence of a processed copy of the gene which has arisen within the last few million years. Analysis of human and murine haematopoietic cells and cell lines, revealed expression of the HEX gene in multipotential progenitors, as well as cells of the B-lymphocyte and myeloid lineages. However HEX was not expressed in T-lymphocytes or erythroid cells. This pattern of HEX gene expression suggests that it may play a role in haematopoietic differentiation.