Retinoid-induced differentiation of acute promyelocytic leukemia involves PML-RARalpha-mediated increase of type II transglutaminase

Abstract All-trans retinoic acid (t-RA) administration leads to complete remission in acute promyelocytic leukemia (APL) patients by inducing growth arrest and differentiation of the leukemic clone. In the present study, we show that t-RA treatment dramatically induced type II transglutaminase (type II TGase) expression in cells carrying the t(15;17) translocation and expressing the PML-RARalpha product such as the APL-derived NB4 cell line and fresh leukemic cells from APL patients. This induction correlated with t-RA-induced growth arrest, granulocytic differentiation, and upregulation of the leukocyte adherence receptor beta subunit (CD18) gene expression. The increase in type II TGase was not abolished by cycloheximide treatment, suggesting that synthesis of a protein intermediate was not required for the induction. t-RA did not significantly alter the rate of growth arrest and did not stimulate differentiation and type II TGase activity in NB4.306 cells, a t-RA-resistant subclone of the NB4 cell line, or in leukemic cells derived from two patients morphologically defined as APL but lacking the t(15;17). However, in NB4.306 cells, t-RA treatment was able to increase CD18 mRNA expression in a manner similar to NB4 cells. The molecular mechanisms involved in the induction of these genes were investigated. In NB4 cells, using novel receptor-selective ligands such as 9-cis-RA, TTNPB, AM580, and SR11217, we found that RAR- and RARalpha- selective retinoids were able to induce growth arrest, granulocytic differentiation, and type II TGase, whereas the RXR-selective retinoid SR11217 was inactive. Moreover, an RAR alpha-antagonist completely inhibited the expression of type II TGase and CD18 induced by these selective retinoids in NB4 cells. In NB4.306 cells, an RARalpha- dependent signaling pathway was found involved in the modulation of CD18 expression. In addition, expression of the PML-RARalpha gene in myeloid U937 precursor cells resulted in the ability of these cells to induce type II TGase in response to t-RA. On the basis of these results we hypothesize a specific involvement of a signaling pathway involving PML-RAR alpha for the induction of growth arrest, granulocytic differentiation, and type II TGase by retinoids in APL cells.

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Retinoid-induced differentiation of acute promyelocytic leukemia involves PML-RARalpha-mediated increase of type II transglutaminase

Blood ◽

10.1182/blood.v87.5.1939.bloodjournal8751939 ◽

1996 ◽

Vol 87 (5) ◽

pp. 1939-1950 ◽

Cited By ~ 7

Author(s):

L Benedetti ◽

F Grignani ◽

BM Scicchitano ◽

AM Jetten ◽

D Diverio ◽

...

Keyword(s):

Cell Line ◽

Signaling Pathway ◽

Acute Promyelocytic Leukemia ◽

Molecular Mechanisms ◽

Growth Arrest ◽

Promyelocytic Leukemia ◽

Leukemic Cells ◽

Type Ii ◽

Granulocytic Differentiation ◽

Nb4 Cells

All-trans retinoic acid (t-RA) administration leads to complete remission in acute promyelocytic leukemia (APL) patients by inducing growth arrest and differentiation of the leukemic clone. In the present study, we show that t-RA treatment dramatically induced type II transglutaminase (type II TGase) expression in cells carrying the t(15;17) translocation and expressing the PML-RARalpha product such as the APL-derived NB4 cell line and fresh leukemic cells from APL patients. This induction correlated with t-RA-induced growth arrest, granulocytic differentiation, and upregulation of the leukocyte adherence receptor beta subunit (CD18) gene expression. The increase in type II TGase was not abolished by cycloheximide treatment, suggesting that synthesis of a protein intermediate was not required for the induction. t-RA did not significantly alter the rate of growth arrest and did not stimulate differentiation and type II TGase activity in NB4.306 cells, a t-RA-resistant subclone of the NB4 cell line, or in leukemic cells derived from two patients morphologically defined as APL but lacking the t(15;17). However, in NB4.306 cells, t-RA treatment was able to increase CD18 mRNA expression in a manner similar to NB4 cells. The molecular mechanisms involved in the induction of these genes were investigated. In NB4 cells, using novel receptor-selective ligands such as 9-cis-RA, TTNPB, AM580, and SR11217, we found that RAR- and RARalpha- selective retinoids were able to induce growth arrest, granulocytic differentiation, and type II TGase, whereas the RXR-selective retinoid SR11217 was inactive. Moreover, an RAR alpha-antagonist completely inhibited the expression of type II TGase and CD18 induced by these selective retinoids in NB4 cells. In NB4.306 cells, an RARalpha- dependent signaling pathway was found involved in the modulation of CD18 expression. In addition, expression of the PML-RARalpha gene in myeloid U937 precursor cells resulted in the ability of these cells to induce type II TGase in response to t-RA. On the basis of these results we hypothesize a specific involvement of a signaling pathway involving PML-RAR alpha for the induction of growth arrest, granulocytic differentiation, and type II TGase by retinoids in APL cells.

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Retinoic acid is required for and potentiates differentiation of acute promyelocytic leukemia cells by nonretinoid agents

Blood ◽

10.1182/blood.v84.7.2122.2122 ◽

1994 ◽

Vol 84 (7) ◽

pp. 2122-2129 ◽

Cited By ~ 33

Author(s):

A Chen ◽

JD Licht ◽

Y Wu ◽

N Hellinger ◽

W Scher ◽

...

Keyword(s):

Retinoic Acid ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Drug Exposure ◽

Primary Cultures ◽

Leukemia Cell ◽

Promyelocytic Leukemia ◽

Leukemia Cell Line ◽

Granulocytic Differentiation ◽

Nb4 Cells

Abstract Patients with acute promyelocytic leukemia (APL) associated with the t(15;17) translocation and fusion of the promyelocytic leukemia (PML) and retinoic acid receptor-alpha (RAR-alpha) genes achieve complete remission but not cure with all-trans retinoic acid (RA), NB4, a cell line derived from a patient with t(15;17) APL that undergoes granulocytic differentiation when treated with pharmacologic doses of RA, was used as a model for differentiation therapy of APL. We found that NB4 cells are resistant to differentiation by nonretinoid inducers such as hexamethylene bisacetamide (HMBA), butyrates, vitamin D3, or hypoxanthine, all of which can induce differentiation in the commonly used HL60 leukemia cell line. Preexposure of NB4 cells to low concentrations of RA for a period as short as 30 minutes abolished resistance to nonretinoids and potentiated differentiation. Sequential RA and HMBA treatment yielded maximal differentiation by 3 days of drug exposure, whereas the effect of RA alone peaked after 6 days and yielded a smaller percentage of differentiated cells. RA also reversed NB4 cell resistance to butyrates and allowed for synergistic differentiation by these agents. Pretreatment with HMBA before exposure to RA failed to stimulate differentiation. Sequential RA/HMBA treatment also markedly increased the extent of differentiation of primary cultures of bone marrow and peripheral blood mononuclear cells from three APL patients. In one case RA/HMBA treatment overcame resistance to RA in vitro. Together, these results suggest that intermittent low doses of RA followed by either HMBA or butyrates may be a useful combination in the treatment of APL. This clinical strategy may help prevent or overcome RA resistance in APL.

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Retinoic acid is required for and potentiates differentiation of acute promyelocytic leukemia cells by nonretinoid agents

Blood ◽

10.1182/blood.v84.7.2122.bloodjournal8472122 ◽

1994 ◽

Vol 84 (7) ◽

pp. 2122-2129 ◽

Cited By ~ 3

Author(s):

A Chen ◽

JD Licht ◽

Y Wu ◽

N Hellinger ◽

W Scher ◽

...

Keyword(s):

Retinoic Acid ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Drug Exposure ◽

Primary Cultures ◽

Leukemia Cell ◽

Promyelocytic Leukemia ◽

Leukemia Cell Line ◽

Granulocytic Differentiation ◽

Nb4 Cells

Patients with acute promyelocytic leukemia (APL) associated with the t(15;17) translocation and fusion of the promyelocytic leukemia (PML) and retinoic acid receptor-alpha (RAR-alpha) genes achieve complete remission but not cure with all-trans retinoic acid (RA), NB4, a cell line derived from a patient with t(15;17) APL that undergoes granulocytic differentiation when treated with pharmacologic doses of RA, was used as a model for differentiation therapy of APL. We found that NB4 cells are resistant to differentiation by nonretinoid inducers such as hexamethylene bisacetamide (HMBA), butyrates, vitamin D3, or hypoxanthine, all of which can induce differentiation in the commonly used HL60 leukemia cell line. Preexposure of NB4 cells to low concentrations of RA for a period as short as 30 minutes abolished resistance to nonretinoids and potentiated differentiation. Sequential RA and HMBA treatment yielded maximal differentiation by 3 days of drug exposure, whereas the effect of RA alone peaked after 6 days and yielded a smaller percentage of differentiated cells. RA also reversed NB4 cell resistance to butyrates and allowed for synergistic differentiation by these agents. Pretreatment with HMBA before exposure to RA failed to stimulate differentiation. Sequential RA/HMBA treatment also markedly increased the extent of differentiation of primary cultures of bone marrow and peripheral blood mononuclear cells from three APL patients. In one case RA/HMBA treatment overcame resistance to RA in vitro. Together, these results suggest that intermittent low doses of RA followed by either HMBA or butyrates may be a useful combination in the treatment of APL. This clinical strategy may help prevent or overcome RA resistance in APL.

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Valproic Acid Induces Cell Cycle Arrest and Differentiation of t(15;17) Positive Leukemic Cells Independent from ATRA Sensitivity and Has No Effect on CD34pos Cells.

Blood ◽

10.1182/blood.v106.11.2834.2834 ◽

2005 ◽

Vol 106 (11) ◽

pp. 2834-2834 ◽

Cited By ~ 1

Author(s):

Bettina Drescher ◽

Kerstin Goerlich ◽

Dagmar Reile ◽

Axel Doehring ◽

Arnold Ganser ◽

...

Keyword(s):

Valproic Acid ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Hdac Inhibitor ◽

Anticonvulsant Drug ◽

Promyelocytic Leukemia ◽

Leukemic Cells ◽

Inhibition Of Proliferation ◽

Nb4 Cells ◽

Clonogenic Growth

Abstract The translocation t(15;17) in acute promyelocytic leukemia results in the PML/RARα fusion protein. PML/RARα recruits histone deacetylases (HDAC) and represses target genes of wild-type RARα. Recently, the anticonvulsant drug valproic acid (VPA) has been described as an HDAC inhibitor. In order to evaluate the role of VPA in the treatment of acute promyelocytic leukemia, the effect of VPA on the t(15;17) positive cell line NB4 was examined. To exclude toxicity on non malignant stem cells, CD34pos cells were analyzed. In NB4 cells, VPA led to an increase of acetylated histone H4. Histone acetylation was associated with a dose dependent inhibition of proliferation. Furthermore, inhibition of NB4 clonogenic growth was observed. In contrast, clonogenic growth of CD34pos cells was not affected by the presence of VPA. The VPA induced inhibition of cell growth in malignant cells was not caused by altered apoptosis. Rather an arrest at the G1/G0 phase was observed in the presence of VPA. In agreement with p21 expression of leukemic cell lines not harboring the t(15;17) translocation, VPA induced p21 mRNA expression also in t(15;17) positive cells. However, no induction of p21 was observed in normal CD34pos cells. VPA triggered the differentiation of NB4 cells measured by NBT test and surface expression of CD11b and CD11c. Flow cytometry of colonies from CD34pos cells showed an increased fraction of CD34pos cells in the presence of VPA. Thus, VPA does not induce differentiation in non malignant hematopoiesis. To study whether VPA and ATRA induced differentiation are mediated via identical pathways, the process of differentiation was studied in NB4 cells and ATRA resistant NB4-R2 cells. While differentiation in the presence of ATRA led to induction of C/EBPβ and C/EBPε, no change in the expression of these transcription factors was observed after VPA treatment. Downregulation of c-myc was detected upon ATRA as well as VPA treatment, an additive effect was seen after the combination. Resistance to ATRA did not interfere with effects of VPA on cell differentiation. However, upon ATRA treatment no c-myc downregulation was observed in the NB4-R2 cell line. Taken together, VPA acts as an HDAC inhibitor in t(15;17) positive cells and induces myeloid differentiation by mechanisms distinct from ATRA and independent of ATRA-resistance. Moreover, VPA does not interfere with normal hematopoiesis. Therefore, this substance might be helpful in patients with APL - especially in ATRA-resistant disease.

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Transcriptional and Metabolic Dissection of ATRA-Induced Granulocytic Differentiation in NB4 Acute Promyelocytic Leukemia Cells

Cells ◽

10.3390/cells9112423 ◽

2020 ◽

Vol 9 (11) ◽

pp. 2423

Author(s):

Jacopo Albanesi ◽

Nelida Ines Noguera ◽

Cristina Banella ◽

Tommaso Colangelo ◽

Elisabetta De Marinis ◽

...

Keyword(s):

Acute Promyelocytic Leukemia ◽

Molecular Mechanisms ◽

Immune Cell ◽

Aerobic Glycolysis ◽

Therapy Resistance ◽

Therapeutic Strategies ◽

Promyelocytic Leukemia ◽

Metabolic Reprogramming ◽

Granulocytic Differentiation ◽

Nb4 Cells

Acute promyelocytic leukemia (APL) is a hematological disease characterized by a balanced reciprocal translocation that leads to the synthesis of the oncogenic fusion protein PML-RARα. APL is mainly managed by a differentiation therapy based on the administration of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). However, therapy resistance, differentiation syndrome, and relapses require the development of new low-toxicity therapies based on the induction of blasts differentiation. In keeping with this, we reasoned that a better understanding of the molecular mechanisms pivotal for ATRA-driven differentiation could definitely bolster the identification of new therapeutic strategies in APL patients. We thus performed an in-depth high-throughput transcriptional profile analysis and metabolic characterization of a well-established APL experimental model based on NB4 cells that represent an unevaluable tool to dissect the complex mechanism associated with ATRA-induced granulocytic differentiation. Pathway-reconstruction analysis using genome-wide transcriptional data has allowed us to identify the activation/inhibition of several cancer signaling pathways (e.g., inflammation, immune cell response, DNA repair, and cell proliferation) and master regulators (e.g., transcription factors, epigenetic regulators, and ligand-dependent nuclear receptors). Furthermore, we provide evidence of the regulation of a considerable set of metabolic genes involved in cancer metabolic reprogramming. Consistently, we found that ATRA treatment of NB4 cells drives the activation of aerobic glycolysis pathway and the reduction of OXPHOS-dependent ATP production. Overall, this study represents an important resource in understanding the molecular “portfolio” pivotal for APL differentiation, which can be explored for developing new therapeutic strategies.

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Id1 and Id2 Are Retinoic Acid Responsive Genes and Induce a G0/G1 Arrest in Acute Promyelocytic Leukemia Cells.

Blood ◽

10.1182/blood.v104.11.2029.2029 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2029-2029

Author(s):

Jeannet Nigten ◽

Gorica Nikoloski ◽

Theo De Witte ◽

Bert A. Van der Reijden ◽

Joop H. Jansen

Keyword(s):

Retinoic Acid ◽

Dna Binding ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Promyelocytic Leukemia ◽

Leukemic Cells ◽

Bhlh Transcription Factor ◽

G1 Arrest ◽

Granulocytic Differentiation ◽

Bhlh Proteins

Abstract Acute promyelocytic leukemia (APL) is uniquely sensitive to treatment with all-trans retinoic acid (ATRA), which overcomes the differentiation arrest and induces terminal granulocytic differentiation of the leukemic blasts. In 98% of the cases of APL, the leukemic cells express a promyelocytic leukemia (PML)- retinoic acid receptor a (RARa) fusion protein as a result of a t(15;17) chromosome translocation. Previously, we have identified Id1 and Id2 as direct retinoic acid target genes being upregulated after ATRA stimulation in the APL cell line NB4 as well as in primary leukemic cells from APL patients. Id (inhibitor of DNA-binding) proteins act as antagonists of basic helix-loop-helix (bHLH) transcription factors by trapping them in heterodimeric complexes, thereby inhibiting DNA-binding and gene transactivation. Various bHLH proteins are pivotal in the control of differentiation and proliferation in various tissues (like muscle and nerve). We have studied the expression pattern of E2A, an ubiquitously expressed bHLH protein, which is generally considered as a promiscuous heterodimerization partner of other, more tissue restricted bHLH proteins. The expression of E2A was high in untreated APL cells and strongly downregulated upon ATRA stimulation. The simultaneous upregulation of Id1 and Id2, and the downregulation of E2A suggest a role for bHLH proteins in the induction of differentiation of APL cells upon treatment with ATRA. To assess the importance of Id1 and Id2 induction for the neutrophilic differentiation of the cells, we have overexpressed both proteins in the APL cell line NB4 using amphotropic retroviral transduction. Ectopic expression of Id1 and Id2 resulted in respectively 27% (n=3, SD= 9%) and 48% (n=3, SD=25%) inhibition of clonogenic growth in semi-solid medium, compared to vector-transduced control cells. Apart from the reduction in the number of colonies, overexpression of Id1 and Id2 did not alter the ATRA sensitivity of APL cells. NB4 liquid cultures revealed that Id1 and Id2 overexpression resulted in inhibition of proliferation and an increase of the percentage of cells in G0/G1, without having an effect on differentiation or apoptosis. These results indicate that Id1 and Id2 are important retinoic acid responsive genes in APL, and suggest that the inhibition of specific bHLH transcription factor complexes may play a role in the therapeutic effect of ATRA in APL.

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AM580, a stable benzoic derivative of retinoic acid, has powerful and selective cyto-differentiating effects on acute promyelocytic leukemia cells

Blood ◽

10.1182/blood.v87.4.1520.bloodjournal8741520 ◽

1996 ◽

Vol 87 (4) ◽

pp. 1520-1531 ◽

Cited By ~ 54

Author(s):

M Gianni ◽

M Li Calzi ◽

M Terao ◽

G Guiso ◽

S Caccia ◽

...

Keyword(s):

Retinoic Acid ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Retinoic Acid Receptor ◽

Chromosomal Translocation ◽

Promyelocytic Leukemia ◽

Myelogenous Leukemia ◽

Leukemic Cells ◽

Stable Phase ◽

Differentiation Markers

All-trans retinoic acid (ATRA) is successfully used in the cyto- differentiating treatment of acute promyelocytic leukemia (APL). Paradoxically, APL cells express PML-RAR, an aberrant form of the retinoic acid receptor type alpha (RAR alpha) derived from the leukemia- specific t(15;17) chromosomal translocation. We show here that AM580, a stable retinobenzoic derivative originally synthesized as a RAR alpha agonist, is a powerful inducer of granulocytic maturation in NB4, an APL-derived cell line, and in freshly isolated APL blasts. After treatment of APL cells with AM580 either alone or in combination with granulocyte colony-stimulating factor (G-CSF), the compound induces granulocytic maturation, as assessed by determination of the levels of leukocyte alkaline phosphatase, CD11b, CD33, and G-CSF receptor mRNA, at concentrations that are 10- to 100-fold lower than those of ATRA necessary to produce similar effects. By contrast, AM580 is not effective as ATRA in modulating the expression of these differentiation markers in the HL-60 cell line and in freshly isolated granulocytes obtained from the peripheral blood of chronic myelogenous leukemia patients during the stable phase of the disease. In NB4 cells, two other synthetic nonselective RAR ligands are capable of inducing LAP as much as AM580, whereas RAR beta- or RAR gamma-specific ligands are totally ineffective. These results show that AM580 is more powerful than ATRA in modulating the expression of differentiation antigens only in cells in which PML-RAR is present. Binding experiments, using COS-7 cells transiently transfected with PML-RAR and the normal RAR alpha, show that AM580 has a lower affinity than ATRA for both receptors. However, in the presence of PML-RAR, the synthetic retinoid is a much better transactivator of retinoic acid-responsive element-containing promoters than the natural retinoid, whereas, in the presence of RAR alpha, AM580 and ATRA have similar activity. This may explain the strong cyto-differentiating potential of AM580 in PML-RAR-containing leukemic cells.

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Arsenic Trioxide Promotes Histone H3 Phosphoacetylation at the Chromatin ofCASPASE-10in Acute Promyelocytic Leukemia Cells

Journal of Biological Chemistry ◽

10.1074/jbc.m207836200 ◽

2002 ◽

Vol 277 (51) ◽

pp. 49504-49510 ◽

Cited By ~ 73

Author(s):

Ji Li ◽

Peili Chen ◽

Natasha Sinogeeva ◽

Myriam Gorospe ◽

Robert P. Wersto ◽

...

Keyword(s):

Arsenic Trioxide ◽

Acute Promyelocytic Leukemia ◽

Molecular Mechanisms ◽

Expression Profiles ◽

Histone H3 ◽

Gene Expression Profiles ◽

Promyelocytic Leukemia ◽

Therapeutic Effects ◽

Acid Therapy ◽

Nb4 Cells

Arsenic trioxide (As2O3) is highly effective for the treatment of acute promyelocytic leukemia, even in patients who are unresponsive to all-trans-retinoic acid therapy. As2O3is believed to function primarily by promoting apoptosis, but the underlying molecular mechanisms remain largely unknown. In this report, using cDNA arrays, we have examined the changes in gene expression profiles triggered by clinically achievable doses of As2O3in acute promyelocytic leukemia NB4 cells.CASPASE-10expression was found to be potently induced by As2O3. Accordingly, caspase-10 activity also substantially increased in response to As2O3treatment. A selective inhibitor of caspase-10, Z-AEVD-FMK, effectively blocked caspase-3 activation and significantly attenuated As2O3-triggered apoptosis. Interestingly, the treatment of NB4 cells with As2O3markedly increased histone H3 phosphorylation at serine 10, an event that is associated with acetylation of the lysine 14 residue. Chromatin immunoprecipitation assays revealed that As2O3potently enhances histone H3 phosphoacetylation at theCASPASE-10locus. These results suggest that the effect of As2O3on histone H3 phosphoacetylation at theCASPASE-10gene may play an important role in the induction of apoptosis and thus contribute to its therapeutic effects on acute promyelocytic leukemia.

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The Acute Promyelocytic Leukemia-Associated Fusion Protein PML/RAR Blocks t-RA-Induced Differentiation in a Subset of Cells with Stem Cell Potential.

Blood ◽

10.1182/blood.v104.11.1175.1175 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1175-1175

Author(s):

Xiaomin Zheng ◽

Anita Seshire ◽

Elena Puccetti ◽

Hilal Gul ◽

Tim Beissert ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Fusion Protein ◽

Cell Line ◽

Acute Promyelocytic Leukemia ◽

Fusion Proteins ◽

Side Population ◽

Promyelocytic Leukemia ◽

Molecular Remission ◽

Nb4 Cells

Abstract Acute promyelocytic leukemia (APL) is distinguished from other AMLs by cytogenetic, clinical, as well as biological characteristics. The hallmark of APL is the t(15;17) which leads to the expression of the PML/RAR fusion protein. PML/RAR is the central leukemia-inducing lesion in APL and is directly targeted by all trans retinoic acid (t-RA). Patients suffering from APL undergo complete hematologic but not molecular remission upon treatment with t-RA. Virtually all patients treated with t-RA-monotherapy had a rapid relapse within few months. But in the combination with an anthracycline, such as doxorubicin or idarubicin, t-RA improved the long term outcome of APL-patients dramatically. Nothing is known about why t-RA-monotherapy is unable to eradicate completely the leukemic population and how it increases the response to chemotherapy. In vitro, the exposure of early hemopoietic stem cells (HSCs) to t-RA does not induce differentiation but selects immature progenitors. Moreover, mice lacking the t-RA-specific receptor RARalpha do not exhibit an impairment of granulopoiesis or hemopoiesis. The indication, that t-RA may be involved in the hemopoietic differentiation, is given by the HL-60 cell line which undergoes granulocytic differentiation at the pharmacological dosages (10−6M) of t-RA. Furthermore vitamin A-deficient mice or mice treated with a antagonist of t-RA accumulate more immature granulocytes in the bone marrow. PML/RAR mediates the response of APL blasts to t-RA, but it is completely unclear, which effect t-RA exerts on the PML/RAR-positive leukemic stem cells which maintains the blast population and represents the source of relapse. Therefore we investigated the effect of t-RA on a cell population with stem cell capacity expressing PML/RAR isolated from the APL cell line NB4 as well as from CD34+/CD38- KG-1 cells transfected with PML/RAR. Here we report that i) the NB4 cells engrafted in NOD/SCID mice indicating the presence of a subpopulation with stem cell capacity in NB4 cells; ii) NB4 had a Hoechst 3342 excluding side population (SP) representing about 1% of the whole cell population; iii) t-RA reduced but did not deplete the side population in NB4 cells; iv) the expression of PML/RAR increased CD34+/CD38- population in KG-1 cells from 75% to over 95%; v) t-RA reduced the CD34+/CD38- population from 75% to 3,5% in mock transfected KG-1 confirming its capacity to induce differentiation, whereas in PML/RAR-positive KG-1 cells it led only to a reduction from 98% to a 25%, which still maintain the capacity to engraft in NOD-SCID mice; vi) also the expression of other fusion proteins, such as AML-1/ETO or PLZF/RAR, associated with t-RA-resistant AML-subtypes, increased the percentage of CD34+/CD38- KG-1 cells over 90%, which was reduced by t-RA only to 35% and 19%, respectively. Taken together these data suggest that a subset of early HSC expressing PML/RAR exhibit the same t-RA-resistant phenotype as HSC expressing fusion proteins associated with AML-subtypes which, in contrast to APL, do not respond to t-RA. These data may give an explanation, why APL-patients do not achieve complete molecular remission upon t-RA monotherapy and undergo early relapse.

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NCoA4 Containing Transcriptional Complexes Modulates Response of Myelomonocytic Leukemic Cell Line to Retinoids and VD3.

Blood ◽

10.1182/blood.v106.11.4238.4238 ◽

2005 ◽

Vol 106 (11) ◽

pp. 4238-4238

Author(s):

Aurelie Baudet ◽

Laurent Delva ◽

Patrick Balaguer ◽

David Piquemal ◽

Jacques Marti ◽

...

Keyword(s):

Transcription Factors ◽

Cell Line ◽

Real Time ◽

Nuclear Receptors ◽

Growth Arrest ◽

Leukemic Cells ◽

U937 Cells ◽

Monocytic Differentiation ◽

Granulocytic Differentiation ◽

Transcriptional Complexes

Abstract Large scale analyses of transcriptome improve comprehension of complex processes such as differentiation or cell proliferation. SAGE libraries construction of the AML model U937 allowed the identification of new markers of myelomonocytic differentiation induced by retinoids and vitamin D3 (VD3) (Piquemal et al., 2002). Those molecules act through ligand-dependent transcription factors of the nuclear receptors family: RAR, RXR and VDR. Among differentially expressed members of transcriptional complexes, the most relevant was the co-regulator NCoA4 (Nuclear receptor Coactivator 4). This protein that modulates interactions between transcription factors, RNA polymerase II and chromatin remodeling factors, was initially described as a co-activator of the androgen receptor (AR). Its activity has been extended to receptors of estrogens (ER), peroxisome-proliferating activators (PPAR), retinoid X (RXR) and recently to VD3 receptor (VDR). Using real-time semi-quantitative PCR, we found that NCoA4 is specifically expressed during the monocytic differentiation of U937 but not during the granulocytic differentiation of NB4 cell lines. These results were confirmed by analysis on normal and in vitro-differentiated leukemia primary cells. Moreover, its early induction, within 6 hours of retinoids and VD3 treatment on U937 cells, suggests that its expression may be controlled by one or several nuclear receptors. Because of cross-talks between retinoids and VD3 pathways, we used NB4-LR2 cells in which RAR is knock-down. In this cell line, NCoA4 is expressed in a VDR-dependent fashion reinforcing the hypothesis that the coregulator is specifically involved in the VD3-monocytic differentiation of leukemic cells. Next, to explore the role of NCoA4, U937 cells were stably transfected to constitutively over-express the protein. The doubling time of this cell line (U-NCoA4) reaches to 48 hours against 24 hours in U937 cells. Concerning ligand-induced growth arrest, these cells are particularly sensitive to the RXR and VDR agonists while no significative difference was observed after treatment by the RAR agonist or by any combination. In addition, over-expression of NCoA4 induces a slow down of differentiation, as shown by expression of CD11b and CD14 myelomonocytic markers. Thus, in U-NCoA4, except for the RAR agonist, treatment for 72 hours corresponds to treatment for 48 hours levels of U937 cells. To conclude, in term of growth arrest, NCoA4 over-expressing cells are particularly sensitive to RXR and VDR agonists. Thus, natural ligands present in the culture medium might reduce or delay proliferation, inducing the same effect on differentiation. In order to have a large view of networks, transcriptome of U-NCoA4 was analyzed by real time PCR on Low Density Array composed of a hundred messengers extracted from U937 SAGE libraries. Analysis is currently in progress.

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