Epstein-Barr virus activates F-box protein FBXO2 to limit viral infectivity by targeting glycoprotein B for degradation.

Epstein-Barr virus (EBV) is a human cancer-related virus closely associated with lymphoid and epithelial malignancies, and EBV glycoprotein B (gB) plays an essential role in viral entry into both B cells and epithelial cells by promoting cell-cell fusion. EBV gB is exclusively modified with high-mannose-linked N-glycans and primarily localizes to the endoplasmic reticulum (ER) with low levels on the plasma membrane (PM). However, the mechanism through which gB is regulated within host cells is largely unknown. Here, we report the identification of F-box only protein 2 (FBXO2), an SCF ubiquitin ligase substrate adaptor that preferentially binds high-mannose glycans and attenuates EBV infectivity by targeting N-glycosylated gB for degradation. gB possesses seven N-glycosylation sites, and FBXO2 directly binds to these high-mannose moieties through its sugar-binding domain. The interaction promotes the degradation of glycosylated gB via the ubiquitin-proteasome pathway. Depletion of FBXO2 not only stabilizes gB but also promotes its transport from the ER to the PM, resulting in enhanced membrane fusion and viral entry. FBXO2 is expressed in epithelial cells but not B cells, and EBV infection up-regulates FBXO2 levels. In summary, our findings highlight the significance of high-mannose modification of gB and reveal a novel host defense mechanism involving glycoprotein homeostasis regulation.

TAL1 mediates imatinib-induced CML cell apoptosis via the PTEN/PI3K/AKT pathway.

Chronic myeloid leukemia (CML) is associated with chromosomal translocation t(9; 22), which results in formation of the BCR-ABL oncogene. CML is treated with tyrosine kinase inhibitors (TKIs), which target BCR-ABL, to eradicate BCR-ABL + cells. However, the TKI imatinib (IM) fails to eliminate quiescent leukemia stem cells (LSCs) in CML. In this study, we demonstrate that transcription factor TAL1 is down-regulated in CML LSCs by BCR-ABL, and IM triggers TAL1 mRNA expression. In addition, loss of TAL1 abrogates IM-induced CML cell apoptosis. RNA-seq analysis suggests that TAL1 expression may affect PI3K/AKT pathway. Moreover, depletion of TAL1 inhibits the expression of PTEN, which is a negative regulator of the PI3K/AKT pathway. Our results reveal an unexpected involvement of TAL1 in CML etiology and demonstrate that TAL1 may regulate PTEN expression and lead to inhibition of the PI3K/AKT pathway in the response of CML cells to TKI. These results implicate regulation of PTEN expression as a novel mechanism for the transcriptional regulatory networks of TAL1 in CML.

The c-Myc-regulated lncRNA NEAT1 and paraspeckles modulate imatinib-induced apoptosis in CML cells.

Chronic myeloid leukemia (CML) is a clonal disease characterized by the presence of the constitutively active tyrosine kinase BCR-ABL oncoprotein. Although BCR-ABL is crucially important for pathogenesis and treatment response, it is thought that some additional factors might be involved in the regulation of these processes. Aberrant expression of long noncoding RNAs (lncRNAs) has recently been identified to be involved in various diseases including cancer, suggesting that lncRNAs may play a role in BCR-ABL-mediated CML. In this study, we found that nuclear-enriched abundant transcript 1 (NEAT1), a lncRNA essential for the formation of nuclear body paraspeckles, is significantly repressed in primary CML cells. NEAT1 expression could be restored by inhibiting BCR-ABL expression or its kinase activity in K562 cells. We also demonstrated that NEAT1 is regulated by c-Myc. Knockdown of NEAT1 could promote imatinib (IM)-induced apoptosis, and we demonstrated that the NEAT1-binding paraspeckle protein splicing factor proline/glutamine-rich (SFPQ) is required for NEAT1-mediated apoptosis in K562 cells. RNA-seq analysis revealed that SFPQ regulates cell growth and death pathway-related genes, confirming its function in IM-induced apoptosis. Collectively, these results assign a biological function to the NEAT1 lncRNA in CML apoptosis and may lead to fuller understanding of the molecular events leading to CML.

Inhibition of long non-coding RNA NEAT1 impairs myeloid differentiation in acute promyelocytic leukemia cells.

BACKGROUND: Acute promyelocytic leukemia (APL) is characterized by the reciprocal translocation t(15;17), which fuses PML with retinoic acid receptor alpha (RARα). Although PML-RARα is crucially important for pathogenesis and responsiveness to treatment, the molecular and cellular mechanisms by which PML-RARα exerts its oncogenic potential have not been fully elucidated. Recent reports have suggested that long non-coding RNAs (lncRNAs) contribute to the precise control of gene expression and are involved in human diseases. Little is known about the role of lncRNA in APL. METHODS: We analyzed NEAT1 expression in APL samples and cell lines by real-time quantitative reverse transcription-PCR (qRT-PCR). The expression of PML-RARα was measured by Western blot. Cell differentiation was assessed by measuring the surface CD11b antigen expression by flow cytometry analysis. RESULTS: We found that nuclear enriched abundant transcript 1 (NEAT1), a lncRNA essential for the formation of nuclear body paraspeckles, is significantly repressed in de novo APL samples compared with those of healthy donors. We further provide evidence that NEAT1 expression was repressed by PML-RARα. Furthermore, significant NEAT1 upregulation was observed during all-trans retinoic acid (ATRA)-induced NB4 cell differentiation. Finally, we demonstrate the importance of NEAT1 in myeloid differentiation. We show that reduction of NEAT1 by small interfering RNA (siRNA) blocks ATRA-induced differentiation. CONCLUSIONS: Our results indicate that reduced expression of the nuclear long noncoding RNA NEAT1 may play a role in the myeloid differentiation of APL cells.

CD69 is a Promising Immunotherapy and Prognosis Prediction Target in Cancer.

Immunotherapy utilizing T cells that attack tumors is a promising strategy for treatment, but immune suppressive T cell subsets, such as regulatory T cell (Treg), and immune checkpoint molecules, including programmed death-1 (PD-1), can suppress the intensity of a T cell immune reaction and thereby impair tumor clearance. Cluster of differentiation 69 (CD69), known as an early leukocyte activation marker, can be used as a measure or early marker of T cell activation. In recent years, the functions of CD69 in the regulation of Treg/Th17 (T helper cell 17) differentiation and in the tissue retention of T cells have attracted considerable interest. These functions are related to the role of CD69 in immune suppression in tumor environments (TME). In this review, we first summarized current perspectives in the biological function of CD69 and demonstrated that CD69 acts as a regulator of T cell activation, differentiation, retention, and exhaustion. Then, we discussed recent advances in understanding of CD69 deficiency and anti-CD69 antibody administration and shed light on the value of targeting on CD69 for cancer immunotherapy and prognosis prediction.

Inhibition of NRF2 enhances the acute myeloid leukemia cell death induced by venetoclax via the ferroptosis pathway.

Venetoclax, an inhibitor that selectively targets B cell lymphoma-2 (BCL-2) that has been approved for treating adult acute myeloid leukemia (AML) in combination with hypomethylating agents. However, its short duration of response and emergence of resistance are significant issues. In this study, we found that the sensitivity of AML cells to venetoclax was considerably enhanced by ML385, an inhibitor of the ferroptosis factor nuclear transcription factor erythroid 2-related factor 2 (NRF2). Using AML samples, we verified that NRF2 and its target gene ferritin heavy chain 1 (FTH1) were highly expressed in patients with AML and correlated with poor prognosis. Downregulation of NRF2 could inhibit FTH1 expression and significantly enhance the venetoclax-induced labile iron pool and lipid peroxidation. By contrast, NRF2 overexpression or administration of the reactive oxygen species inhibitor N-acetylcysteine and vitamin E could effectively suppress the anti-AML effects of ML385+venetoclax. Furthermore, the ferroptosis inducer erastin increased the anti-AML effects of venetoclax. Our study demonstrated that NRF2 inhibition could enhance the AML cell death induced by venetoclax via the ferroptosis pathway. Thus, the combination of ML385 with venetoclax may offer a favorable strategy for AML treatment.

High percentage of bone marrow CD8+ tissue-resident-like memory T cells predicts inferior survival in patients with acute myeloid leukemia.

Tissue-resident memory T (TRM) cells infiltrating solid tumors could influence tumor progression and the response to immune therapies. However, the proportion and prognostic value of TRM cells in the bone marrow (BM) of patients with acute myeloid leukemia (AML) are unclear. In this study, we used flow cytometry to assay the phenotype of 49 BM samples from patients newly diagnosed with AML (ND-AML). We found that the BM CD8+ effector memory (TEM) cells highly expressed CD69 (CD8+ TRM-like T cells), and their percentage was significantly increased in patients with ND-AML compared with that in healthy individuals (HI). The high percentage of CD8+ TRM-like subset was associated with poor overall survival in our ND-AML cohort. The Kaplan-Meier Plotter database verified a significantly reduced survival rate among patients with high expression of CD8+ TRM-like T cell characteristic genes (CD8A, CD69, and TOX), especially the M4 and M5 subtypes. Phenotypic analysis revealed that the BM CD8+ TRM-like subpopulation exhibited exhausted T cell characteristics, but its high expression of CD27 and CD28 and low expression of CD57 suggested its high proliferative potential. The single-cell proteogenomic dataset confirmed the existence of TRM-like CD8+ T cells in the BM of patients with AML and verified the high expression of immune checkpoints and costimulatory molecules. In conclusion, we found that the accumulation of BM CD8+ TRM-like cells could be an immune-related survival prediction marker for patients with AML.

Spectral-domain optical coherence tomographic assessment of Schlemm's canal in Chinese subjects with primary open-angle glaucoma.

PURPOSE: To evaluate in vivo features of Schlemm's canal (SC) in patients with primary open-angle glaucoma (POAG) with spectral-domain optical coherence tomography (SD-OCT) and to investigate the relationship of SC size with intraocular pressure (IOP) and glaucoma severity. DESIGN: Prospective, comparative study. PARTICIPANTS: Fifty Chinese patients with newly diagnosed POAG who had not undergone surgery and 50 normal Chinese subjects from a population-based, cross-sectional study in Shanghai. METHODS: All participants underwent SD-OCT. The diameter and area of SC were examined in the temporal and nasal sections and measured with customized software. MAIN OUTCOME MEASURES: Patient demographics, repeatability and reproducibility assessed with the coefficient of variation (CV) and the intraclass correlation coefficient (ICC), SC parameters and their correlation with IOP, and the mean deviation (MD) of the visual field were analyzed. RESULTS: The percentage of sections in which SC was observable was similar between eyes with POAG and normal eyes, and ranged from 78% to 86%. For intraobserver repeatability, the CV and ICC values were 7.9% and 0.97 for diameter, and 13.8% and 0.83 for area, respectively. For interobserver repeatability, the CV and ICC values were 13.6% and 0.89 for diameter, and 13.4% and 0.80 for area, respectively. Significant differences between the 2 groups were found for the average SC area (11332 ± 2015 µm(2) vs. 13991 ± 1357 µm(2); P<0.001), but not for the SC diameter (40.2 ± 7.1 µm vs. 45.2 ± 4.0 µm; P = 0.195). In addition, the mean IOP values correlated well only with the SC area (ρ = -0.674, P<0.001), not with the SC diameter (ρ = -0.103, P = 248). No significant correlations were found between the MD values and the SC parameters. CONCLUSIONS: Eyes with POAG have a decreased SC area compared with normal eyes. A correlation between the SC area and the IOP also was observed. However, the degree of glaucoma damage was not consistently associated with the SC area. Spectral-domain OCT could be used for investigating SC changes in patients with glaucoma.

Overexpression of CASP1 triggers acute promyelocytic leukemia cell pyroptosis and differentiation.

Caspase-1 (CASP1)-mediated classical pyroptosis plays a key role in cancer development and management, however, the role of CASP1 and its regulation has not yet been documented for acute promyelocytic leukemia (APL). Here, we found that CASP1/GSDMD had lower expression in patients with APL and most other subtypes of primary de novo acute myeloid leukemia (AML) and was increased in all-trans-retinoic acid (ATRA)-treated APL cells. We showed that ATRA increases and activates CASP1 to trigger the pyroptosis and differentiation of APL cells. Mechanistically, ATRA could induce CASP1 expression via the IFNγ/STAT1 pathway in APL cells. In conclusion, ATRA-induced activation of CASP1 may serve as a suppressor in APL progression, as it triggers pyroptotic cell death and differentiation.

High expression of LOC541471, GDAP1, SOD1, and STK25 is associated with poor overall survival of patients with acute myeloid leukemia.

BACKGROUND: Acute myeloid leukemia (AML) is an aggressive heterogeneous hematological malignancy with remarkably heterogeneous outcomes. This study aimed to identify potential biomarkers for AML risk stratification via analysis of gene expression profiles. METHODS: RNA sequencing data from 167 adult AML patients in the Cancer Genome Atlas (TCGA) database were obtained for overall survival (OS) analysis, and 52 bone marrow (BM) samples from our clinical center were used for validation. Additionally, siRNA was used to investigate the role of prognostic genes in the apoptosis and proliferation of AML cells. RESULTS: Co-expression of 103 long non-coding RNAs (lncRNAs) and mRNAs in the red module that were positively correlated with European Leukemia Network (ELN) risk stratification and age was identified by weighted gene co-expression network analysis (WGCNA). After screening by uni- and multivariate Cox regression, Kaplan-Meier survival, and protein-protein interaction analysis, four genes including the lncRNA LOC541471, GDAP1, SOD1, and STK25 were incorporated into calculating a risk score from coefficients of the multivariate Cox regression model. Notably, GDAP1 expression was the greatest contributor to OS among the four genes. Interestingly, the risk score, ELN risk stratification, and age were independent prognostic factors for AML patients, and a nomogram model constructed with these factors could illustrate and personalize the 1-, 3-, and 5-year OS rates of AML patients. The calibration and time-dependent receiver operating characteristic curves (ROCs) suggested that the nomogram had a good predictive performance. Furthermore, new risk stratification was developed for AML patients based on the nomogram model. Importantly, knockdown of LOC541471, GDPA1, SOD1, or STK25 promoted apoptosis and inhibited the proliferation of THP-1 cells compared to controls. CONCLUSIONS: High expression of LOC541471, GDAP1, SOD1, and STK25 may be biomarkers for risk stratification of AML patients, which may provide novel insight into evaluating prognosis, monitoring progression, and designing combinational targeted therapies.

Current insight into the regulation of PD-L1 in cancer.

The molecular mechanisms underlying cancer immune escape are a core topic in cancer immunology research. Cancer cells can escape T cell-mediated cellular cytotoxicity by exploiting the inhibitory programmed cell-death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1, CD274) immune checkpoint. Studying the PD-L1 regulatory pattern of tumor cells will help elucidate the molecular mechanisms of tumor immune evasion and improve cancer treatment. Recent studies have found that tumor cells regulate PD-L1 at the transcriptional, post-transcriptional, and post-translational levels and influence the anti-tumor immune response by regulating PD-L1. In this review, we focus on the regulation of PD-L1 in cancer cells and summarize the underlying mechanisms.

Correlation of the transcription factors IRF4 and BACH2 with the abnormal NFATC1 expression in T cells from chronic myeloid leukemia patients.

OBJECTIVE: T cell dysfunction is a common characteristic of patients with myeloid leukemia and is closely related to clinical efficacy and prognosis. In order to clarify the mechanisms leading to the T cell dysfunction, we characterized the gene expression profile of T cells from chronic myelogenous leukemia (CML) patients by microarray analysis and investigated the related regulating pathway. METHODS: We employed gene expression profiling, bioinformatics and real-time quantitative reverse transcription PCR (RT-qPCR) to detect genes differentially expressed in CML patients versus healthy donors. RESULTS: There were 1704 genes differentially expressed between CD3+ T cells from CML patients and healthy donors, including 868 up-regulated genes and 836 down-regulated genes, which mostly related to T cell functional pathways. In particular, lower expression of NFATC1, a member of the TCR signaling pathway, was detected in CD3+ T cells from CML patients. We further found that the expression of IRF4 and BACH2, transcription factors that potentially regulate NFATC1, in CD3+ T cells from CML patients was significantly lower than that in healthy donors. CONCLUSION: We for the first time observed the altered gene expression profiles of CD3+ T cells from CML patients, and the results suggested that IRF4, BACH2 and NFATC1 may be involved in regulating T cell dysfunction in CML patients in the form of a transcriptional regulatory network. These findings may provide potential targets for tyrosine kinase inhibitors in combination with other targeted immunotherapies .

Anticancer effects of disulfiram in T-cell malignancies through NPL4-mediated ubiquitin-proteasome pathway.

T-cell malignancies, including T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoma (TCL), are characterized by inferior treatment effects, high heterogeneity, poor prognosis, and a lack of specific therapeutic targets and drugs to improve outcome. Disulfiram (DSF) is a drug used to clinically control alcoholism that has recently been shown to be cytotoxic for multiple cancers. However, the underlying effects and mechanisms of DFS treatment in patients with T-cell malignancies are not well characterized. In this study, we report that DSF promotes apoptosis and inhibits the proliferation of malignant T-cell cell lines and primary T-ALL cells. We provide evidence that DSF exerts anticancer activity in T-cell malignancies by targeting the NPL4-mediated ubiquitin-proteasome pathway. Notably, high expression of NPL4 and 2 ubiquitin-proteasome pathway genes, anaphase-promoting complex subunit 1 (ANAPC1) and proteasome 26S subunit ubiquitin receptor, non-ATPase 2 (PSMD2), was significantly associated with unfavorable overall survival (OS) for patients with TCL and T-ALL (p < 0.05). More importantly, the weighted combination of NPL4, ANAPC1, and PSMD2 could visually display the 1-, 3-, and 5-year OS rates for patients with T-cell malignancies in a nomogram model and facilitate risk stratification. Specifically, risk stratification was an independent predictor of OS for patients with T-cell malignancies. In conclusion, DSF might induce apoptosis and inhibit the proliferation of malignant T-cells via the NPL4-mediated ubiquitin-proteasome pathway and offer a potential therapeutic option for T-cell malignancies.

Physalin B inhibits cell proliferation and induces apoptosis in undifferentiated human gastric cancer HGC-27 cells.

BACKGROUND: Physalin B (PB) from Physalis angulata L. (Solanaceae) is a naturally occurring secosteroid with multiple biological activities, including anti-inflammatory and anticancer activity. However, PB's effects and mechanisms in human gastric cancer (GC) cells are not well characterized. METHODS: The undifferentiated GC cell line HGC-27 and semi-differentiated GC cell line SGC-7901 were treated with PB. Cell counting kit-8 (CCK-8) and colony formation assays were performed to evaluate cell viability. Apoptosis and the cell cycle were assessed by Annexin V/PI and PI/RNase DNA staining assays, respectively, and Western blotting was used to evaluate the expression of a protein. RESULTS: PB significantly inhibited the proliferation of HGC-27 cells in a dose- and time-dependent manner. Moreover, PB induced G0/G1 cycle arrest and caspase-dependent apoptosis of HGC-27 cells. Cleaved caspases 8, 3, and 7, poly(ADP)-ribose polymerase (PARP), and the cyclin-dependent kinase (CDK) inhibitor p-Chk2 was induced by PB in HGC-27 cells, while the cell cycle-related proteins cyclin D1, cyclin D3, CDK4, CDK6, cyclin E, and phosphorylated retinoblastoma tumor suppressor protein (p-Rb) were downregulated in a dose-dependent manner. CONCLUSIONS: PB inhibits proliferation via cyclin-dependent kinase and induces caspase-dependent apoptosis in HGC-27 cells, suggesting that PB might be a novel and effective agent for undifferentiated GC therapy.

BET bromodomain inhibition rescues PD-1-mediated T-cell exhaustion in acute myeloid leukemia.

Sustained expression of programmed cell death receptor-1 (PD-1) is correlated with the exhaustion of T cells, and blockade of the PD-1 pathway is an effective immunotherapeutic strategy for treating various cancers. However, response rates are limited, and many patients do not achieve durable responses. Thus, it is important to seek additional strategies that can improve anticancer immunity. Here, we report that the bromodomain and extraterminal domain (BET) inhibitor JQ1 inhibits PD-1 expression in Jurkat T cells, primary T cells, and T-cell exhaustion models. Furthermore, JQ1 dramatically impaired the expression of PD-1 and T-cell immunoglobulin mucin-domain-containing-3 (Tim-3) and promoted the secretion of cytokines in T cells from patients with acute myeloid leukemia (AML). In line with that, BET inhibitor-treated CD19-CAR T and CD123-CAR T cells have enhanced anti-leukemia potency and resistant to exhaustion. Mechanistically, BRD4 binds to the NFAT2 and PDCD1 (encoding PD-1) promoters, and NFAT2 binds to the PDCD1 and HAVCR2 (encoding Tim-3) promoters. JQ1-treated T cells showed downregulated NFAT2, PD-1, and Tim-3 expression. In addition, BET inhibitor suppressed programmed death-ligand 1 (PD-L1) expression and cell growth in AML cell lines and in primary AML cells. We also demonstrated that JQ1 treatment led to inhibition of leukemia progression, reduced T-cell PD-1/Tim-3 expression, and prolonged survival in MLL-AF9 AML mouse model and Nalm6 (B-cell acute lymphoblastic leukemia cell)-bearing mouse leukemia model. Taken together, BET inhibition improved anti-leukemia immunity by regulating PD-1/PD-L1 expression, and also directly suppressed AML cells, which provides novel insights on the multiple effects of BET inhibition for cancer therapy.

Inhibition of BCL11B induces downregulation of PTK7 and results in growth retardation and apoptosis in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive subtype of leukemia with poor prognosis, and biomarkers and novel therapeutic targets are urgently needed for this disease. Our previous studies have found that inhibition of the B-cell leukemia/lymphoma 11B (BCL11B) gene could significantly promote the apoptosis and growth retardation of T-ALL cells, but the molecular mechanism underlying this effect remains unclear. This study intends to investigate genes downstream of BCL11B and further explore its function in T-ALL cells. We found that PTK7 was a potential downstream target of BCL11B in T-ALL. Compared with the healthy individuals (HIs), PTK7 was overexpressed in T-ALL cells, and BCL11B expression was positively correlated with PTK7 expression. Importantly, BCL11B knockdown reduced PTK7 expression in T-ALL cells. Similar to the effects of BCL11B silencing, downregulation of PTK7 inhibited cell proliferation and induced apoptosis in Molt-4 cells via up-regulating the expression of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and p27. Altogether, our studies suggest that PTK7 is a potential downstream target of BCL11B, and downregulation of PTK7 expression via inhibition of the BCL11B pathway induces growth retardation and apoptosis in T-ALL cells.

Regulation of PD-1 in T cells for cancer immunotherapy.

Study of the molecular mechanisms underlying cancer immune escape is one of the core issues in immuno-oncology research. Cancer cells can evade T cell cytotoxicity by exploiting the upregulation of T cell inhibitory receptors on T cells and their ligands on cancer cells. These upregulated proteins include the inhibitory receptor programmed cell-death protein 1 (PD-1) and its ligand programmed cell death 1 ligand 1 (PD-L1), which can induce T cell exhaustion and reduce T cell activation. Characterizing PD-1 regulation will help to elucidate the molecular mechanisms underlying T cell exhaustion and improve cancer treatment. Recent studies have found that tumor cells regulate PD-1 during gene transcription, post-transcriptional regulation, and post-translational modification and influence the effects of the anticancer immune response by targeting PD-1. In this review,we summarize the mechanisms of PD-1 regulation in T cells.

The c-Myc-regulated miR-17-92 cluster mediates ATRA-induced APL cell differentiation.

BACKGROUND: Despite advances in the treatment of acute promyelocytic leukemia (APL) with all-trans-retinoic acid (ATRA), its underlying mechanism has not been fully elucidated. The oncogenic microRNA cluster miR-17-92 modulates multiple cellular processes, including survival, proliferation, and apoptosis. However, the role of miR-17-92 and its regulation has not yet been documented for APL. METHODS: We analyzed miR-17-92 expression in APL samples and cell lines by qRT-PCR. The expression of c-Myc was measured by western blot. Cell differentiation was assessed by measuring the surface CD11b antigen expression by flow cytometry analysis. RESULTS: We observed that miR-17-92 was upregulated in APL compared with healthy donors. Furthermore, we demonstrated that expressions of c-Myc and miR-17-92 are markedly suppressed during ATRA-induced NB4 cell differentiation. Importantly, we also demonstrated that miR-17-92 is directly regulated by c-Myc during the granulocytic differentiation of APL cells. Finally, the overexpression of miR-17-5p blocks ATRA-induced differentiation. CONCLUSIONS: We report abnormal expression of the miR-17-92 cluster in APL cells, which is responsible for the differentiation block in blast cells in APL. In addition, we identified miR-17-92 as a target gene of c-Myc during ATRA-induced granulocytic differentiation.