scholarly journals Id2 expression increases with differentiation of human myeloid cells

Blood ◽  
1996 ◽  
Vol 87 (12) ◽  
pp. 5225-5231 ◽  
Author(s):  
A Ishiguro ◽  
KS Spirin ◽  
M Shiohara ◽  
A Tobler ◽  
AF Gombart ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
Cell Lines ◽  
Myeloid Leukemia ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Leukemic Cells ◽  
Myeloid Differentiation ◽  
Northern Hybridization ◽  
Id Proteins ◽  
Normal Human

Id proteins are helix-loop-helix (HLH) transcriptional factors that lack the basic DNA binding domain. The Id proteins have been reported generally to function as inhibitors of cell differentiation, and their gene expression is often downregulated during cell differentiation. We examined the expression of human Id mRNAs by Northern hybridization in 11 human myeloid cell lines, several myeloid cell lines induced to differentiate, fresh myeloid leukemia samples, and normal human myeloid cells. Id2 mRNA was expressed in myelomonoblastic and monoblastic leukemic cells (PLB-985, THP-1, and U-937) but was weakly expressed in myeloblastic leukemic cells (KG-1 and HL-60). Id2 mRNA levels markedly increased with induction of differentiation of myeloid blasts (HL-60, PLB-985, THP-1, and U-937) toward either granulocytes or macrophages. Examination of fresh acute myeloid leukemic samples from 22 individuals also showed prominent Id2 mRNA expression in those samples having more differentiated blasts. Using the French-American-British classification, only 2 of 8 M0/M1 samples expressed Id2 mRNA; however, 10 of 13 M2/M3/M4 samples expressed it. In normal human myeloid cells, Id2 mRNA was expressed in cultured macrophages from bone marrow and in mature granulocytes and monocytes from peripheral blood. The half-life of Id2 mRNA was short (1 hour), and its expression was inducible by cessation of protein synthesis. Id3 mRNA was moderately expressed in monoblastic cell lines (THP-1 and U-937), and levels decreased with their differentiation. Almost no Id3 expression was detectable in either other myeloid leukemia lines, fresh leukemic samples, or normal human myeloid cells by Northern analyses. Id1 mRNA was not detected by polymerase chain reaction in either leukemic or normal myeloid cells except in K562 myeloid/erythroid cells. These results showed that Id2 mRNA was constitutively expressed in more mature myeloid blast cells and level markedly increased with terminal myeloid differentiation, suggesting that Id2 protein may inhibit an HLH transcriptional complex that normally represses myeloid differentiation.

Inhibition of Cellular Aminopeptidases as Novel Therapy for AML.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2588-2588
Author(s):  
Christopher Jenkins ◽  
Chris Pepper ◽  
Ken Mills ◽  
Alan Burnett
Keyword(s):  
Acute Myeloid Leukemia ◽  
Cell Lines ◽  
Myeloid Leukemia ◽  
Human Cancer ◽  
Myeloid Cells ◽  
Chemotherapeutic Agents ◽  
Molecular Therapy ◽  
Leukemic Cells ◽  
Therapeutic Window ◽  
Acute Myeloid

Abstract CHR 2797 is one of a new class of enzyme inhibitors with a pleiotropic effect against a number of human cancer cells. It is thought to inhibit the M1 family of metalloenzymes that include aminopeptidases, and is under investigation for the treatment of acute myeloid leukemia. Aminopeptidases catalyse the hydrolysis of the terminal amino acids from short chain polypeptides and they are involved in the continuous cycle of protein formation and degradation in cells. As malignant cells are thought to be more highly dependant on this protein cycling, interrupting this pathway is therefore a potential therapeutic target for novel agents. The effects of the aminopeptidase inhibitor CHR 2797 were investigated in AML cells in-vitro. Leukemic cells and cell lines were treated with CHR 2797 at a range of 0.0002 – 20μM and IC50 values were calculated from the WST-1 proliferation experiments. The AML cell lines HL60, KG1, K562 and U937 had an average IC50 of 1μM with a range between 0.01 and 10μM. Primary diagnostic AML samples (n=40) were analysed and an IC50 range of between 0.01 and >40μM were detected, with a median of 0.8μM. The effects of CHR 2797 were also analysed on normal bone marrow samples (n=10). The IC50 range was between 6.2 and >40μM with a median of 15μM, demonstrating a potential therapeutic window between the treatment of the leukemic cells and toxicity to the normal samples. The level of synergy or antagonism with conventional therapeutic agents was calculated using a combination index. Synergy was demonstrated in 70% of cell samples in combination with ARA-C, and 80% with Velcade. Synergy was also shown in 60% of cells samples with ATRA, even in non-promyelocytic leukemia types. Annexin V and cell cycle analysis confirmed apoptosis after treatment with CHR 2797 in many cases. A degree of differentiation of acute promyelocytic cells to mature myeloid cells was also stimulated with the treatment. The effects of CHR 2797 on cellular aminopeptidases were also measured. CD13 is a cell surface protein which is expressed selectively on myeloid cells and is also classified as an aminopeptidase N. Its activity can be measured by the conversion of the substrate ala-MCA to the protein MCA that can be detected on a fluorometric plate reader. CHR 2797 was demonstrated to reduce CD13 activity in a time and dose responsive manner. The reduction in activity was demonstrated immediately following addition of the drug, and a persistent effect was shown over four days of cell culture. A reduction in CD13 activity was also shown with a concentration of CHR 2797 of under 0.5μM; and with a 10μM dose the activity in many AML samples was reduced by >90%. New treatments are needed for acute myeloid leukemia to improve survival and reduce the toxicity of conventional therapy. This study demonstrates that CHR 2797 might be an effective molecular therapy for AML, either alone or in combination with other chemotherapeutic agents.

scholarly journals Styryl Quinazolinones as Potential Inducers of Myeloid Differentiation via Upregulation of C/EBPα

Molecules ◽  
2018 ◽  
Vol 23 (8) ◽  
pp. 1938 ◽  
Author(s):  
Radhakrishnan Sridhar ◽  
Hisashi Takei ◽  
Riyaz Syed ◽  
Ikei Kobayashi ◽  
Liu Hui ◽  
...  
Keyword(s):  
Myeloid Leukemia ◽  
Leukemia Cell ◽  
Myeloid Cell ◽  
Leukemic Cells ◽  
Myeloid Differentiation ◽  
Granulocytic Differentiation ◽  
Leukemia Cell Lines ◽  
Expression Activity ◽  
Differentiation Marker ◽  
Neutrophil Differentiation

The CCAAT enhancer-binding protein α (C/EBPα) plays an important role in myeloid cell differentiation and in the enhancement of C/EBPα expression/activity, which can lead to granulocytic differentiation in acute myeloid leukemia (AML) cells. We found that styryl quinazolinones induce upregulation of C/EBPα expression, and thereby induce myeloid differentiation in human myeloid leukemia cell lines. We screened a series of active styryl quinazolinones and evaluated the structure–activity relationship (SAR) of these small molecules in inducing C/EBPα expression—thereby prompting the leukemic cells to differentiate. We observed that compound 78 causes differentiation at 3 μM concentration, while 1 induces differentiation at 10 μM concentration. We also observed an increase in the expression of neutrophil differentiation marker CD11b upon treatment with 78. Both the C/EBPα and C/EBPε levels were found to be upregulated by treatment with 78. These SAR findings are inspiration to develop further modified styryl quinazolinones, in the path of this novel differentiation therapy, which can contribute to the care of patients with AML.

CD38 ligation inhibits normal and leukemic myelopoiesis

Blood ◽  
2000 ◽  
Vol 95 (2) ◽  
pp. 535-542 ◽  
Author(s):  
Elisabetta Todisco ◽  
Toshio Suzuki ◽  
Kleebsabai Srivannaboon ◽  
Elaine Coustan-Smith ◽  
Susana C. Raimondi ◽  
...  
Keyword(s):  
Myeloid Leukemia ◽  
Kinase Activity ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Cell Aggregation ◽  
Suppressive Effect ◽  
Myeloid Differentiation ◽  
Cell Recovery ◽  
Growth And Survival ◽  
Cd34 Cells

CD38 is a transmembrane molecule whose expression varies during hematopoietic cell differentiation. We used stroma-supported cultures of human myeloid cells to assess the effects of CD38 ligation on myeloid differentiation. In 8 experiments with CD34+cells purified from normal bone marrow or cord blood, flow cytometry used with antibodies to CD34 and myeloperoxidase (MPO) identified 4 cell populations after 7 days of culture. Addition of anti-CD38 (T16) to the cultures induced a profound reduction of the most mature (CD34−MPO++) cell population, which includes promyelocytes, myelocytes and metamyelocytes; mean (± SD) cell recovery was 12.8% ± 9.8% of that in parallel cultures with an isotype-matched control antibody. The suppressive effect of CD38 ligation on phenotypically more immature normal cells was inconsistent but generally less pronounced. Recovery of CD34++MPO− cells was 63.3% ± 24.4%, recovery of CD34[+/−]MPO− cells was 95.3% ± 35.1%, and recovery of CD34−MPO+cells was 42.0% ± 18.7% of that in control cultures. However, anti-CD38 suppressed recovery of cells obtained from 6 patients with CD38+ acute myeloid leukemia; after 7-day cultures, cell recovery was 25.2% ± 21.7% of that in control cultures. Cell recovery was also reduced by F(ab′)2 or Fab fragments of anti-CD38. CD38 ligation dramatically suppressed recovery of murine 32D myeloid cells transfected with human CD38 and cocultured with stroma (3.8% ± 7.3%; n = 7). CD38 ligation of CD38 + 32D cells also induced cell aggregation, tyrosine kinase activity, and Ca++ influx. We conclude that CD38 mediates signals that culminate in suppression of myeloid cell growth and survival.

scholarly journals Novel Evidence That Pituitary Gonadotropins Directly Stimulate Human Leukemic cells—studies on Myeloid Cell Lines and Primary Patient AML and CML Cells

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2204-2204
Author(s):  
Ahmed Ismail ◽  
Katarzyna Anna Mierzejewska ◽  
Anna Janowska-Wieczorek ◽  
A. Robert Turner ◽  
Mariusz Z Ratajczak ◽  
...  
Keyword(s):  
Cell Lines ◽  
Sex Hormones ◽  
Myeloid Leukemia ◽  
Hormone Receptors ◽  
Leukemia Cell ◽  
Myeloid Cell ◽  
Gonadal Hormones ◽  
Leukemic Cells ◽  
Gonadal Hormone ◽  
Human Leukemic Cells

Abstract Background . It has been postulated that hematopoietic stem/progenitor cells (HSPCs) can become specified from a population of migrating primordial germ cells (PGCs) isolated from embryos. In support of this intriguing possibility, HSPCs and PGCs are both highly migratory populations of stem cells, and evidence has accumulated for the sharing of several mutated genes (e.g., Sall4) as well as chromosomal aberrations between germline tumors and leukemias or lymphomas, which suggests their common clonal origin. In fact, we recently observed that normal murine HSPCs express several functional receptors for pituitary gonadal hormones, such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL), in addition to gonadal hormones including estrogens, androgen, and progesterone. Of note, the plasma levels of FSH and LH are elevated in older patients, which correlate with an increase in the incidence of myeloid leukemia. Hypothesis . Based on this, we have hypothesized that gonadotropic hormones play a yet underappreciated role in human malignant hematopoiesis. Materials and Methods . To address this issue, we performed a complex series of experiments employing human myeloid hematopoietic cell lines (KG-1a, K-562, U937, THP-1, HEL) and primary patient cells (AML, CML) to address the influence of pituitary sex hormones (FSH, LH, PRL) as well as gonadal sex hormones (androgen, estrogen, progesterone) on proliferation, migration, and adhesion of malignant cells. In addition, expression of the corresponding receptors was evaluated at the mRNA level by PCR, and their functionality was confirmed by signaling studies based on phosphorylation of major signal transduction pathways (AKT, MAPKp42/44, STAT). Results. We demonstrate for the first time that human myeloid leukemia cell lines express all pituitary gonadotropin and several gonadal hormone receptors and that FSH and LH receptors are functional on these cells, as evaluated by chemotaxis and adhesion assays. Moreover, FSH and LH receptors were expressed and functional on patient leukemic blasts in bone marrow (BM) and peripheral blood (PB). Human leukemic cells from cell lines and primary patient-derived cells also expressed some other gonadal hormone receptors (PRL-R, estrogen, progesterone, and androgen receptors), albeit at lower levels. Moreover, we observed that several human myeloid cell lines as well as primary patient leukemic cells responded to sex hormones by proliferation. Conclusions . Our data are the first to indicate that pituitary-secreted gonadotropins stimulate migration, adhesion, and proliferation of leukemic cells. This latter effect seems to be direct, as the receptors for these hormones respond to stimulation by phosphorylation of intracellular pathways involved in cell proliferation. Established human myeloid leukemia cell lines and primary patient blasts also responded to stimulation by gonadal sex hormones. Finally, our studies provide further evidence supporting a developmental link between hematopoiesis and the germline. Disclosures No relevant conflicts of interest to declare.

Identification and Characterization of 6-Benzylthioinosine as a Novel Myeloid Differentiation-Inducing Compound.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 905-905
Author(s):  
David N. Wald ◽  
Hanna Vermaat ◽  
Zizhen Kang ◽  
Stanton L. Gerson ◽  
Kevin D. Bunting ◽  
...  
Keyword(s):  
Cell Lines ◽  
Myeloid Leukemia ◽  
Nucleoside Transporters ◽  
Leukemic Cells ◽  
Myeloid Differentiation ◽  
Great Promise ◽  
Established Tumor ◽  
Low Toxicity

Abstract Acute myeloid leukemia (AML) is the most common form of leukemia in adults and despite advances in treatment the 5 year survival is less than 20–50% in adults and significantly lower in the elderly. The remarkable success in treating one relatively uncommon subset of AML, APL, with all trans-retinoic acid (ATRA) illustrates the great promise for agents with greater efficacy and less toxicity. Utilizing ATRA, the presumed cure of 75–85% of patients is possible. ATRA’s remarkable success stems from the fact that AML is a disease characterized by the arrest of differentiation of immature myeloid cells. ATRA overcomes this block in differentiation by forcing leukemic cells to mature. Unfortunately, ATRA is not clinically useful for patients with AML that do not have the APL subtype. Through a compound library screen, we have recently identified several novel leukemia differentiation-inducing compounds structurally unrelated to previously described differentiation-inducers including a particularly promising compound, 6-benzylthioinosine (6BT). 6BT is a nucleoside analogue that induces monocytic differentiation of multiple AML cell lines as well as primary leukemic patient samples as measured by immunophenotyping, morphology, and NBT reduction. 6BT can induce terminal differentiation of leukemic cells as evidenced by complete prevention of colony formation in soft agar assays after pretreatment with low doses of 6BT (5μM) for 72 hours. In addition 6BT has potent in vivo activity. 6BT completely prevents subcutaneous tumor formation in myeloid leukemia mouse xenograft models in nude mice using HL-60 or MV4-11 leukemic cell lines (n=5) and significantly inhibits myeloid leukemia tumor growth in an HL-60 established tumor xenograft model (n=5). In the established tumor model at the end of the 4 week study period, tumors were significantly smaller after 6BT treatment as compared to vehicle treated mice (0.16g +/− 0.05g vs 0.73g +/− 0.28g). Evidence of 6BT-mediated in vivo differentiation exists as 92% of the tumor cells expressed the mature myeloid cell surface marker CD11b as compared to only 16% in the vehicle control after 4 weeks. Early studies suggest 6BT partially depletes purine nucleotide stores leading to growth inhibition and subsequent myeloid differentiation. Treatment of HL-60 cells with 6BT (5μM) leads to rapid depletion of approximately 75% of ATP stores within 24 hours. The depletion of ATP is not due to the differentiation process itself as after 6BT treatment HL-60 cells contain 24.6% +/− 2.8 of the ATP levels of vehicle treated cells compared to 91.2% +/− 7.2 in ATRA (1μM) treated cells. Preliminary studies also indicate that 6BT exhibits relatively low toxicity with an LD50 at 5 days greater than 100μM in human umbilical vein endothelial cells, mouse embryonic fibroblasts, and primary human lymphocytes. The low toxicity is likely related to its unique chemical structure that prevents its uptake into most mammalian cells as it acts as an inhibitor of one of the main nucleoside transporters, ent1. It is known that leukemic cells can express nucleoside transporters that are not widely expressed by other cell types. As differentiation therapy has already been demonstrated in the case of ATRA to significantly improve the prognosis of patients with AML, further characterization of 6BT could lead to a novel AML therapy that is more efficacious, less toxic, and better tolerated especially for elderly patients.

scholarly journals Whole-genome fingerprint of the DNA methylome during chemically induced differentiation of the human AML cell line HL-60/S4

2019 ◽  
Author(s):  
Enoch Boasiako Antwi ◽  
Ada Olins ◽  
Vladimir B Teif ◽  
Matthias Bieg ◽  
Tobias Bauer ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
Cell Line ◽  
Differential Expression ◽  
Differential Methylation ◽  
Cpg Methylation ◽  
Leukemic Cells ◽  
Ctcf Binding ◽  
Myeloid Differentiation ◽  
Whole Genome

AbstractBackgroundMyeloid differentiation gives rise to a plethora of immune cells in the human body. This differentiation leaves strong signatures in the epigenome through each differentiated state of genetically identical cells. The leukemic HL-60/S4 promyelocytic cell can be easily differentiated from its undifferentiated promyelocyte state into neutrophil-and macrophage-like cell states, making it an excellent system for studying myeloid differentiation. In this study, we present the underlying genome and epigenome architecture of HL-60/S4 through its undifferentiated and differentiated cell states.ResultsWe performed whole genome bisulphite sequencing of HL-60/S4 cells and their differentiated counterparts. With the support of karyotyping, we show that HL-60/S4 maintains a stable genome throughout differentiation. Analysis of differential CpG methylation reveals that most methylation changes occur in the macrophage-like state. Differential methylation of promoters was associated with immune related terms. Key immune genes, CEBPA, GFI1, MAFB and GATA1 showed differential expression and methylation. However, we observed strongest enrichment of methylation changes in enhancers and CTCF binding sites, implying that methylation plays a major role in large scale transcriptional reprogramming and chromatin reorganisation during differentiation. Correlation of differential expression and distal methylation with support from chromatin capture experiments allowed us to identify putative proximal and long-range enhancers for a number of immune cell differentiation genes, including CEBPA and CCNF. Integrating expression data, we present a model of HL-60/S4 differentiation in relation to the wider scope of myeloid differentiation.ConclusionsFor the first time, we elucidate the genome and CpG methylation landscape of HL-60/S4 during differentiation. We identify all differentially methylated regions and positions. We link these to immune function and to important factors in myeloid differentiation. We demonstrate that methylation plays a more significant role in modulating transcription via enhancer reprogramming, rather than by promoter regulation. We identify novel regulatory regions of key components in myeloid differentiation that are regulated by differential methylation. This study contributes another layer of “omics” characterisation of the HL-60/S4 cell line, making it an excellent model system for studying rapid in vitro cell differentiation.Summary statementEpigenomics plays a major role in cell identity and differentiation. We present the DNA methylation landscape of leukemic cells during in-vitro differentiation, to add another ‘omics layer to better understand the mechanisms behind differentiation.

scholarly journals E4F1 deficiency results in oxidative stress–mediated cell death of leukemic cells

2011 ◽  
Vol 208 (7) ◽  
pp. 1403-1417 ◽  
Author(s):  
Elodie Hatchi ◽  
Genevieve Rodier ◽  
Matthieu Lacroix ◽  
Julie Caramel ◽  
Olivier Kirsh ◽  
...  
Keyword(s):  
Cell Death ◽  
Cell Lines ◽  
Myeloid Leukemia ◽  
Tumor Regression ◽  
Fetal Liver ◽  
Leukemia Cell ◽  
Leukemic Cells ◽  
Viral Oncoprotein ◽  
Mitochondrial Defects

The multifunctional E4F1 protein was originally discovered as a target of the E1A viral oncoprotein. Growing evidence indicates that E4F1 is involved in key signaling pathways commonly deregulated during cell transformation. In this study, we investigate the influence of E4F1 on tumorigenesis. Wild-type mice injected with fetal liver cells from mice lacking CDKN2A, the gene encoding Ink4a/Arf, developed histiocytic sarcomas (HSs), a tumor originating from the monocytic/macrophagic lineage. Cre-mediated deletion of E4F1 resulted in the death of HS cells and tumor regression in vivo and extended the lifespan of recipient animals. In murine and human HS cell lines, E4F1 inactivation resulted in mitochondrial defects and increased production of reactive oxygen species (ROS) that triggered massive cell death. Notably, these defects of E4F1 depletion were observed in HS cells but not healthy primary macrophages. Short hairpin RNA–mediated depletion of E4F1 induced mitochondrial defects and ROS-mediated death in several human myeloid leukemia cell lines. E4F1 protein is overexpressed in a large subset of human acute myeloid leukemia samples. Together, these data reveal a role for E4F1 in the survival of myeloid leukemic cells and support the notion that targeting E4F1 activities might have therapeutic interest.

Cell membrane-associated proteoglycans mediate extramedullar myeloid proliferation in granulomatous inflammatory reactions to schistosome eggs

1993 ◽  
Vol 104 (2) ◽  
pp. 477-484
Author(s):  
M. Alvarez-Silva ◽  
L.C. da Silva ◽  
R. Borojevic
Keyword(s):  
Growth Factors ◽  
Growth Factor ◽  
Connective Tissue ◽  
Endogenous Growth ◽  
Cell Lines ◽  
Cell Layer ◽  
Heparan Sulphate ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Gm Csf

In chronic murine schistosomiasis, extramedullar myelopoiesis was observed, with proliferation of myeloid cells in liver parenchyma and in periovular granulomas. We have studied the question of whether cells obtained from granulomatous connective tissue may act as myelopoietic stroma, supporting long-term myeloid proliferation. Primary cell lines (GR) were obtained in vitro from periovular granulomas, induced in mouse livers by Schistosoma mansoni infection. These cells were characterized as myofibroblasts, and represent liver connective tissue cells involved in fibro-granulomatous reactions. They were able to sustain survival and proliferation of the multipotent myeloid cell lines FDC-P1 and DA-1 (dependent on interleukin-3 and/or granulocyte-macrophage colony stimulating factor, GM-CSF) without the addition of exogenous growth factors. This stimulation was dependent upon myeloid cell attachment to the GR cell layer; GR cell-conditioned medium had no activity. Primary murine skin fibroblasts could not sustain myelopoiesis. The endogenous growth-factor was identified as GM-CSF by neutralization assays with monoclonal antibodies. The stimulation of myelopoiesis occurred also when GR cells had been fixed with glutardialdehyde. The observed stimulatory activity was dependent upon heparan sulphate proteoglycans (HSPGs) associated with GR cell membranes. It could be dislodged from the cell layer with heparin or a high salt buffer. Our results indicate a molecular interaction between endogenous growth-factor and HSPGs; this interaction may be responsible for the stabilization and presentation of growth factors in myelopoietic stromas, mediating extramedullar proliferation of myeloid cells in periovular granulomas.

scholarly journals Nonhistone protein antigen profiles of five leukemic cell lines reflect the extent of myeloid differentiation

Blood ◽  
1984 ◽  
Vol 63 (3) ◽  
pp. 701-710 ◽  
Author(s):  
A Goldberger ◽  
G Brewer ◽  
LS Hnilica ◽  
RC Briggs
Keyword(s):  
Cell Lines ◽  
Myeloid Cell ◽  
Leukemic Cell ◽  
Nuclear Extract ◽  
Myeloid Differentiation ◽  
Chromosomal Protein ◽  
Protein Antigens ◽  
Nonhistone Protein ◽  
Leukemic Cell Lines ◽  
Chromatin Proteins

Abstract The human leukemic cell lines, K562, KG-1, and HL-60, and the blast subclones, KG-1a and HL-60 blast, were utilized to relate differences in nonhistone protein antigens to stages of myeloid cell differentiation. Chromatin proteins were separated on SDS- polyacrylamide gels, transferred electrophoretically to nitrocellulose sheets, and visualized by the peroxidase-antiperoxidase method of Sternberger. Screening with antisera raised against total and dehistonized chromatin and a nuclear extract from these cells revealed quantitative as well as qualitative differences between the cell lines. A decrease in antigen content seemed to parallel progressive stages of myeloid cell development. The results indicate that a number of chromosomal protein antigens are lost or modified during differentiation. An antigen(s) of approximately 55,000 molecular weight was found in HL-60 chromatin, but was not present in its less differentiated subclone or in the other lines representative of earlier stage cells. Upon the induction of HL-60 cells to mature to end stages with 4 microM retinoic acid, a significant increase in the mol wt 55,000 activity was seen. This antigen was detected only with antisera against HL-60 total chromatin and granulocyte nuclei, and it was found only in normal mature granulocytes and in the later stage cells of the HL-60 culture. Thus, the antigen appears to be associated with a differentiated myeloid function.

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