scholarly journals Effects of Fifty-Hertz Electromagnetic Fields on Granulocytic Differentiation of ATRA-Treated Acute Promyelocytic Leukemia NB4 Cells

2018 ◽  
Vol 46 (1) ◽  
pp. 389-400 ◽  
Author(s):  
Alfredo Errico Provenzano ◽  
Stefano Amatori ◽  
Maria Gemma Nasoni ◽  
Giuseppe Persico ◽  
Sergio Russo ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Acute Promyelocytic Leukemia ◽  
Electromagnetic Fields ◽  
Cellular Proliferation ◽  
Biological Effects ◽  
Promyelocytic Leukemia ◽  
Ros Generation ◽  
Granulocytic Differentiation ◽  
Nb4 Cells ◽  
Oxidative Balance

Background/Aims: Life on Earth is constantly exposed to electromagnetic fields (EMFs) and the effects induced by EMFs on biological systems have been extensively studied producing different and sometimes contradictory results. Extremely low-frequency electromagnetic fields (ELF-EMFs) have shown to play a role in regulating cell proliferation and differentiation, although how EMFs influence these processes remains unclear. Human acute promyelocytic leukemia (APL) cells are characterized by the arrest of differentiation at the promyelocytic stage due to epigenetic perturbations induced by PML/RARα fusion protein (Promyelocytic Leukemia protein - PML/Retinoic Acid Receptor alpha - RARα). Therapeutic administration of all-trans retinoic acid (ATRA) re-establishes the leukemogenic mechanism re-inducing the normal differentiation processes. Methods: We studied the effects of ELF-EMFs (50 Hz, 2 mT) on the ATRA-mediated granulocytic differentiation process of APL NB4 cells (a cell line established from the bone marrow of a patient affected by the acute promyelocytic leukemia) by monitoring cellular proliferation and morphology, nitrob lue tetrazolium (NBT) reduction and the expression of differentiation surface markers. Finally, we investigated mechanisms focusing on reactive oxygen species (ROS) generation and related molecular pathways. Results: ELF-EMF exposure decreases cellular proliferation potential and helps ATRA-treated NB4 cells to mature. Furthermore, the analysis of ROS production and the consequent extracellular signal regulated kinases (ERK1/2) phosphorylation suggest that a changed intracellular oxidative balance may influence the biological effects of ELF-EMFs. Conclusions: These results indicate that the exposure to ELF-EMF promotes ATRA-induced granulocytic differentiation of APL cells.

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

Blood ◽  
1994 ◽  
Vol 84 (7) ◽  
pp. 2122-2129 ◽  
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.

Death Associated Protein 5 (DAP5/p97/NAT1) Contributes to Retinoic Acid-Induced Granulocytic Differentiation and Arsenic Trioxide Induced Apotosis through Inhibition of PI3K/Akt/mTOR Pathway in Acute Promyelocytic Leukemia Cells: A Novel Mechanism.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 2836-2836
Author(s):  
Bulent Ozpolat ◽  
Ugur Akar ◽  
Isabel Zorilla-Calancha ◽  
Pablo Vivas-Mejia ◽  
Gabriel Lopez-Berestein
Keyword(s):  
Retinoic Acid ◽  
Arsenic Trioxide ◽  
Acute Promyelocytic Leukemia ◽  
Translation Initiation ◽  
Promyelocytic Leukemia ◽  
Mtor Pathway ◽  
Granulocytic Differentiation ◽  
Induced Expression ◽  
Nb4 Cells ◽  
Induced Apoptosis

Abstract All-trans Retinoic Acid (ATRA) is a naturally occurring metabolite of retinol (vitamin A)and acts as a potent inducer of cellular differentiation and growth arrest in acute promyelocytic leukemia (APL), a type of acute myeloid leukemia (M3-AML). APL is characterized by translocation t(15;17), fusing PML (promyelocytic leukemia) and RARα (retinoic acid receptor) genes, leding to expression of PML/RARα receptor protein and differentiation block. Arsenic trioxide (ATO) induces (<0.5 μM) differentiation at low doses and apoptosis at high doses (>1 μM) in APL cells. Currently, both ATRA and ATO are successfully used in the treatment of APL in the clinic. However, the molecular mechanisms of myeloid differentiation and apoptosis induced by these agents are not fully understood. We previously reported that ATRA inhibits the translation initiation through multiple mechanisms, including upregulation of translation initiation inhibitors, DAP5/p97 and PDCD4 tumor suppressor protein. Here we investigated the role and regulation of death associated protein-5 (DAP5/p97/NAT1), a novel inhibitor of translational initiation, in myeloid (granulocytic and monocytic) cell differentiation and apoptosis. We found that ATRA (1 μM) induced a marked DAP5/p97 protein and mRNA expression during granulocytic differentiation of NB4 and HL60 cells but not in differentiation-resistant cells, which express very low levels of DAP5/p97. DAP5/p97 was translocated into nucleus during the differentiation of NB4 cells induced ATRA. At differentiation inducing doses, ATO, dimethysulfoxide, 1,25-dihydroxy-vitamin-D3, and phorbol-12-myristate-13-acetate also induced a significant DAP5/p97 expression in NB4 cells. However, ATO at apoptotic doses, but not ATRA, induced DAP5/p86, a proapoptotic form of DAP5/p97. ATRA and ATO -induced expression of DAP5/p97 was associated with inhibition of phosphaditylinositol 3-kinase (PI3K)/Akt pathway, which is known to stimulate cap-dependent translation of mRNAs. To show direct link between PI3K/Akt/mTOR pathway and DAP5 expression, we treated cell with PI3K and mTOR inhibitors LY294002 and by rapamycin, respectively. We found that inhibition of PI3K/Akt/mTOR pathway upregulated DAP5/p97 expression in NB4 cells. Finally, knockdown of DAP5/p97 expression by small interfering RNA significantly inhibited ATRA-induced granulocytic differentiation detected by expression of CD11b and ATO-induced apoptosis in NB4 cells detected by Annexin V assay (p<0.05). In conclusion, our data suggest that DAP5/p97 plays a role in ATRA-induced differentiation and ATO-induced apoptosis in APL cells. Our data demonstrated for the first time that DAP5/p97 is constitutively suppressed by of PI3K/Akt/mTOR pathway, and ATRA and ATO-induced expression of DAP5 is mediated by the inhibition of this survival pathway, suggesting a novel mechanism of DAP5 regulation and a role of translational control in induction of differentiation and apoptosis. Figure Figure

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

Blood ◽  
1994 ◽  
Vol 84 (7) ◽  
pp. 2122-2129 ◽  
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.

FOXO3A as a key molecule for all-trans retinoic acid–induced granulocytic differentiation and apoptosis in acute promyelocytic leukemia

Blood ◽  
2010 ◽  
Vol 115 (18) ◽  
pp. 3787-3795 ◽  
Author(s):  
Yasuhiko Sakoe ◽  
Kumi Sakoe ◽  
Keita Kirito ◽  
Keiya Ozawa ◽  
Norio Komatsu
Keyword(s):  
Retinoic Acid ◽  
Acute Promyelocytic Leukemia ◽  
Cellular Responses ◽  
Promyelocytic Leukemia ◽  
Granulocytic Differentiation ◽  
Nb4 Cells ◽  
Protein Levels ◽  
Trans Retinoic Acid ◽  
All Trans Retinoic Acid ◽  
Promising Target

Abstract All-trans retinoic acid (ATRA) induces granulocytic differentiation and apoptosis in acute promyelocytic leukemia (APL) cells, although the detailed mechanisms are not fully understood. We investigated ATRA-induced cellular responses mediated by the transcription factor FOXO3A in APL cells. FOXO3A was constitutively phosphorylated and localized in the cytoplasm in both APL-derived NB4 cells and primary APL cells. Upon treating the cells with ATRA, FOXO3A phosphorylation was reduced and FOXO3A translocated into the nucleus. In addition, the expression of tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), a target molecule for FOXO3A, was increased at the transcriptional and protein levels. As expected, transfection of a short hairpin RNA (shRNA) oligonucleotide specific for FOXO3A significantly inhibited ATRA-induced granulocytic differentiation and apoptosis in NB4 cells. In NB4-derived ATRA-resistant NB4/RA cells, neither FOXO3A nuclear localization nor subsequent TRAIL induction was observed after ATRA treatment. Furthermore, forced expression of active FOXO3A in the nucleus induced TRAIL production and apoptosis in NB4/RA cells. We conclude that activation of FOXO3A is an essential event for ATRA-induced cellular responses in NB4 cells. FOXO3A is a promising target for therapeutic approaches to overcome ATRA resistance in APL.

Proteome Analysis of the Proteins Associated with All-Trans Retinoic Acid Resistance in Acute Promyelocytic Leukemia Cells

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 5042-5042
Author(s):  
Pengcheng He ◽  
Mei Zhang ◽  
Jun Qi ◽  
Xiaoning Wang ◽  
Jieying Xi ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Protein Expression ◽  
Cell Line ◽  
Acute Promyelocytic Leukemia ◽  
Comparative Proteomics ◽  
Promyelocytic Leukemia ◽  
Differentially Expressed ◽  
Nb4 Cells ◽  
Trans Retinoic Acid ◽  
All Trans Retinoic Acid

Abstract Although 90% patients with untreated acute promyelocytic leukemia(APL) obtain complete remission because of the usage of all-trans retinoic acid(ATRA), patients with ATRA-resistance are increased gradually. ATRA-resistance has become one of the main causes which affect the long-term therapeutic efficacy of APL. The mechanisms of ATRA-resistance are complex, which probably involve the metabolism of ATRA, abnormal expression of cellular retinoic acid binding protein(CRABP) and P-glycoprotein(P-gp), mutation of RARα and aberration translocation of APL. However, in these previous researches, it was one or a few proteins but not the entirety proteins that were emphasized on the mechanisms of ATRA-resistance. Comparative proteomics can analyze the entire protein expression in cells in whole and has the superiority in screening the drug-resistance proteins differentially expressed. In order to investigate the mechanisms of ATRA-resistance in APL in whole, we compared and analyzed the protein expression profiles between MR2 cells(APL cell line with ATRA-resistance) and NB4 cells(APL cell line with ATRA-sensitiveness) by comparative proteomics. After the total proteins of MR2 cells and NB4 cells were extracted respectively, they were separated by two-dimensional electrophoresis(2-DE). The differences in proteome profile between MR2 cells and NB4 cells analyzed by ImageMaster™ 2D Platinum software. The average protein spots in 2-DE maps of MR2 and NB4 cells were 1160±51 and 1068±33 respectively. 8 protein spots were selected to be identified by Matrix-assisted laser desorption/ionization time of flight-mass spectrometry (MALDI-TOF-MS), in which the quantity of the protein differentially expressed was more than two times(≥2 or ≤0.5) between MR2 and NB4 cells’ 2-DE map. They were all successfully identified and their definite information was obtained. Among them, 6 proteins were probably involved in the mechanisms of ATRA-resistance in APL and they were Cofilin-1, Elongation factor 1-beta (EF-1β), Tropomyosin isoform(TM), High mobility group protein B1(HMGB1), Ran-specific GTPase-activating protein (RanGAP1) and Galectin-1. Moreover, so far there was no related report on the roles of HMGB1, RanGAP1 and Galectin-1 in the mechanisms of ATRA-resistance in APL. These differential proteins identified provide the new clues for us to further elucidate the mechanisms of ATRA-resistance from multiple factor.

PML/RARa Represses Transactivation of PSMB10 Via a PU.1-Dependent Manner In Acute Promyelocytic Leukemia

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3866-3866
Author(s):  
Xianwen Yang ◽  
Ping Wang ◽  
Xujie Zhao ◽  
Huahua Zhu ◽  
Sai-Juan Chen ◽  
...  
Keyword(s):  
Transcriptional Regulation ◽  
Retinoic Acid ◽  
Immune System ◽  
Acute Promyelocytic Leukemia ◽  
Target Genes ◽  
Promyelocytic Leukemia ◽  
Class I ◽  
Luciferase Reporter ◽  
Atra Treatment ◽  
Nb4 Cells

Abstract Abstract 3866 Immunoproteasome is a special form of proteasome which contains three unique interferonγ (IFNγ) induced catalytic subunits, i.e. PSMB8, PSMB9 and PSMB10. Immunoproteasome plays a pivotal role in generating certain peptide antigens for MHC class I presentation. Dysregulation of the immunoproteasome system may contribute to the pathogenesis of certain types of malignancies, including leukemia. Our previous study has identified the target genes of PML/RARa, the initiating factor of acute promyelocytic leukemia (APL) on the genome-wide scale, and demonstrated that PML/RARa could selectively target PU.1-regulated genes, which is a critical mechanism for the pathogenesis of APL. PSMB10, encoding an important composition of immunoproteasome, is one of the identified target genes which are regulated by PML/RARa in this manner. Here we revealed the detailed transcriptional regulation mechanism of PSMB10 in APL. Chromatin immunoprecipitation (ChIP)-PCR assay showed that PML/RARa and PU.1 could bind to the PSMB10 promoter in APL cells, including patient derived NB4 cells and Zn-treated PR9 cells. Re-ChIP assay further demonstrated that PML/RARa and PU.1 co-existed on the same DNA fragment of the PSMB10 promoter, which provided the possibility that PML/RARa and PU.1 could co-regulate the PSMB10 promoter. Using a transient luciferase reporter system, we found that PU.1 transactivated the PSMB10 promoter and PML/RARa repressed the PU.1-dependent transactivation. All-trans retinoic acid (ATRA) could relief the repression caused by PML/RARa. To further demonstrate that the PU.1 site (-37bp∼-29bp) and related retinoic acid response elements (RAREs) (-555bp∼-549bp, -258bp∼-252bp) were essential for PML/RARa to function as an effective repressor, we prepared a series of mutant constructs, including the PU.1-site mutant, the construct mutated on both RARE half (RAREh) sites and two constructs respectively mutated on one of the two RAREh sites, and then transfected them into myeloid U937 cells. From the results of luciferase reporter assays, we found that both PU.1 site and RAREh sites played important roles in PML/RARa-mediated transcriptional repression, moreover, the second RAREh site (-258bp∼-252bp) contributed more than the first one (-555bp∼-549bp). Through electrophoretic mobility shift assay (EMSA), we further determined that PML/RARa could interact with PU.1 through protein-protein interaction, and then bind to the PU.1 site on the PSMB10 promoter. Recent study has shown that ATRA treatment could induce the production of anti-PML/RARa in APL mouse, which implicates that ATRA plays an important role in activating immune system. As the essential elements for immune response, HLA class I antigens (A, B & C) present peptides, which are produced from digested proteins degraded by immunoproteasome, to the surface of antigen-presenting cells. We thus utilized real time RT-PCR to measure the expression of PSMB10 and HLA-A/B/C during ATRA-induced NB4 cells differentiation. We found the levels of PSMB10 and HLA-A/B/C expression were up-regulated in ATRA-treated NB4 cells. These results suggested that the enhanced expression of PSMB10 availed immunoproteasome restoration, which benefited the reactivation of immune system during ATRA treatment therapy. Our results not only demonstrate the detailed transcriptional regulation of PSMB10 in APL but imply the potential function of PSMB10 during ATRA treatment as well. Disclosures: No relevant conflicts of interest to declare.

scholarly journals PML-RAR Binds to the +7kb Enhancer of CEBPE and Inhibits Its Expression

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 43-43
Author(s):  
Pavithra Shyamsunder ◽  
Shree Pooja Sridharan ◽  
Pushkar Dakle ◽  
Zeya Cao ◽  
Vikas Madan ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Regulatory Element ◽  
Promyelocytic Leukemia ◽  
Luciferase Reporter ◽  
Myeloid Differentiation ◽  
Atra Treatment ◽  
Granulocytic Differentiation ◽  
Nb4 Cells ◽  
Acute Myeloid

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML). The disease is identified by distinctive morphology and is distinguished by a balanced reciprocal translocation between chromosomes 15 and 17. This aberration leads to the fusion between promyelocytic leukemia (PML) gene located on chromosome 15q21, and retinoic acid receptor α (RARA) gene from chromosome 17q21, leading to the resultant chimeric onco-fusion protein PML-RARA, which is detectable in more than 95% patients and disturbs proper promyelocytic differentiation. All-trans retinoic acid (ATRA) can induce granulocytic differentiation in APL and is used to treat APL patients. Genes containing PML-RARA-targeted promoters are transcriptionally suppressed in APL and most likely constitute a major mechanism of transcriptional repression occurring in APL. A growing body of evidence points to the role of distal regulatory elements, including enhancers, in the control of gene expression. In order to understand the unique sets of enhancers that might be under the control of PML-RAR and crucial for granulocytic differentiation of NB4 cells, we analysed the enhancer landscape of control and ATRA treated NB4 cells. H3K9Ac mapping identified a repertoire of enhancers that were gained in NB4 cells treated with ATRA. Closer investigation of these enhancer elements revealed enrichment of H3K9Ac signals around major drivers of myeloid differentiation. Of note, we identified a gain in enhancer signature for a region about 7kb downstream of the CEBPE gene. Our previous studies identified a novel enhancer for CEBPE in murine hematopoietic cells, which was 6 downstream of CEBPE core promoter. It appears that the +7kb region we identified in human APL cells may be analogous to the murine enhancer. We also observed that PML-RAR binds this +7kb region and ATRA treatment of NB4 cells displaced binding of PML-RAR from the + 7kb region, suggestive of a transcriptional repressive effect of PML-RAR at such enhancer elements. To test the transcription regulating potential of this +7kb region, we used catalytically inactive Cas9 fused to Krüppel associated box (KRAB) domain (dCas9-KRAB). We designed three guide RNAs covering this regulatory region. The sgRNAs effectively repressed expression of CEBPE accompanied by lowered granulocytic differentiation of these guide RNA targeted NB4 cells after ATRA treatment. To explore transcription factor (TF) occupancy at this +7 kb region, we analysed public available ChIP-seq datasets for hematopoiesis-specific factors. Analysis revealed that the +7kb region was marked by an open chromatin signature, accompanied by binding of a majority of hematopoietic TFs around this putative regulatory element with concurrent binding of EP300. Strikingly we noticed binding of CEBPA, CEBPB and CEBPE at this regulatory element. To assess whether binding of these members of the CEBP family of TFs is functionally relevant, luciferase reporter and electrophoretic mobility shift assays (EMSA) were performed. Co expression of the CEBP TFs led to significant induction of luciferase expression, and this data was further confirmed using EMSA assays. Based on these observations, we propose that PML-RAR blocks granulocytic differentiation by occupying this +7kb enhancer of CEBPE, hinders binding of other cell type/lineage specific TFs, and blocks CEBPE expression. When cells are stimulated with ATRA, PML-RAR is displaced from the CEBPE enhancer, allowing for efficient binding of myeloid-specific TFs. This results in increased CEBPE expression, which in turn promotes efficient granulocytic differentiation. The findings from our study expands our current understanding of the mechanism of differentiation therapy, the role of onco-fusion proteins in inhibiting myeloid differentiation, and may provide new therapeutic approaches to many acute myeloid leukemias. Disclosures Ong: National University of Singapore: Other: Royalties.

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

Blood ◽  
1996 ◽  
Vol 87 (5) ◽  
pp. 1939-1950 ◽  
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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