The mechanisms by which AML1/ETO (A/E) fusion protein induces leukemogenesis in acute myeloid leukemia (AML) without mutagenic events remain elusive. Here we show that interactions between A/E and hypoxia-inducible factor 1α (HIF1α) are sufficient to prime leukemia cells for subsequent aggressive growth. In agreement with this, HIF1α is highly expressed in A/E-positive AML patients and strongly predicts inferior outcomes, regardless of gene mutations. Co-expression of A/E and HIF1α in leukemia cells causes a higher cell proliferation rate in vitro and more serious leukemic status in mice. Mechanistically, A/E and HIF1α form a positive regulatory circuit and cooperate to transactivate DNMT3a gene leading to DNA hypermethylation. Pharmacological or genetic interventions in the A/E-HIF1α loop results in DNA hypomethylation, a re-expression of hypermethylated tumor-suppressor p15(INK4b) and the blockage of leukemia growth. Thus high HIF1α expression serves as a reliable marker, which identifies patients with a poor prognosis in an otherwise prognostically favorable AML group and represents an innovative therapeutic target in high-risk A/E-driven leukemia.
AML1-ETO fusion protein (AE) is generated by t(8;21)(q22;q22) chromosomal translocation, which is one of the most frequently observed structural abnormalities in acute myeloid leukemia (AML) and displays a pivotal role in leukemogenesis. The histone acetyltransferase p300 promotes self-renewal of leukemia cells by acetylating AE and facilitating its downstream gene expression as a transcriptional coactivator, suggesting that p300 may be a potential therapeutic target for AE-positive AML. However, the effects of p300 inhibitors on leukemia cells and the underlying mechanisms have not been extensively investigated. In the current study, we analyzed the anti-leukemia effects of C646, a selective and competitive p300 inhibitor, on AML cells. Results showed that C646 inhibited cellular proliferation, reduced colony formation, evoked partial cell cycle arrest in G1 phase, and induced apoptosis in AE-positive AML cell lines and primary blasts isolated from leukemic mice and AML patients. Nevertheless, no significant inhibitory effects were observed in granulocyte colony-stimulating factor-mobilized normal peripheral blood stem cells. Notably, AE-positive AML cells were more sensitive to lower C646 doses than AE-negative ones. And C646-induced growth inhibition on AE-positive AML cells was associated with reduced global histone H3 acetylation and declined c-kit and bcl-2 levels. Therefore, C646 may be a potential candidate for treating AE-positive AML.
As one of the best known cancer testis antigens, PRAME is overexpressed exclusively in germ line tissues such as the testis as well as in a variety of solid and hematological malignant cells including acute myeloid leukemia. Therefore, PRAME has been recognized as a promising target for both active and adoptive anti-leukemia immunotherapy. However, in most patients with PRAME-expressing acute myeloid leukemia, PRAME antigen-specific CD8+ CTL response are either undetectable or too weak to exert immune surveillance presumably due to the inadequate PRAME antigen expression and PRAME-specific antigen presentation by leukemia cells. In this study, we observed remarkably increased PRAME mRNA expression in human acute myeloid leukemia cell lines and primary acute myeloid leukemia cells after treatment with a novel subtype-selective histone deacetylase inhibitor chidamide in vitro. PRAME expression was further enhanced in acute myeloid leukemia cell lines after combined treatment with chidamide and DNA demethylating agent decitabine. Pre-treatment of an HLA-A0201+ acute myeloid leukemia cell line THP-1 with chidamide and/or decitabine increased sensitivity to purified CTLs that recognize PRAME100–108 or PRAME300–309 peptide presented by HLA-A0201. Chidamide-induced epigenetic upregulation of CD86 also contributed to increased cytotoxicity of PRAME antigen-specific CTLs. Our data thus provide a new line of evidence that epigenetic upregulation of cancer testis antigens by a subtype-selective HDAC inhibitor or in combination with hypomethylating agent increases CTL cytotoxicity and may represent a new opportunity in future design of treatment strategy targeting specifically PRAME-expressing acute myeloid leukemia.
We retrospectively analyzed a large study to investigate the association of hepatitis B virus (HBV) with aggressive B cell non-Hodgkin's lymphoma (aggressive B-NHL) in China, where HBV is endemic. HBV was present in 39 aggressive B-NHL patients (10.46%), 13 indolent B-NHL patients (5.09%), 12 multiple myeloma (MM) patients (3.67%), and 5 solitary plasmacytoma (SP) patients (6.67%). HBV infection was significantly associated with increased risks for aggressive B-NHL (P < 0.01). HBV seems to have a very important role in the pathogenesis of aggressive B-NHL in China.
The t(8;21)(q22;q22) translocation, resulting in a chimeric protein AML1/ETO (A/E), is one of the most common chromosomal abnormalities in acute myeloid leukemia (AML). It has been reported that additional mutagenic “hits” are required for A/E to be a leukemic driver, but it is unclear why most A/E-positive patients don’t carry such gene mutations. We hypothesized that unconventional and more universal events might cooperate with A/E to drive leukemogenesis. Hypoxia inducible factor 1a (HIF1a) is a transcription factor mediating the cellular response to hypoxia in malignant cells. To identify the key molecule responsible for A/E-driven leukemia, we focused on HIF1a signaling, as it is selectively activated in AML stem cells in a hypoxia-independent fashion. Using qPCR analysis, we measured HIF1a mRNA levels in bone marrow mononuclear cells from 73 A/E-positive and 59 A/E-negative patients with newly diagnosed AML and 15 healthy donors. HIF1a was highly expressed in A/E-positive patients, as compared to A/E-negative patients and healthy controls. The expression of HIF1a was positively correlated with the expression of A/E, independent of KIT mutation. Patients were grouped into quartiles according to HIF1a expression levels (Q1-Q4, each quartile containing 25% of patients) and divided into high HIF1a (HIF1a high, Q4; n = 33) and low HIF1a (HIF1a low, Q1-Q3; n = 99). AE-positive patients with high HIF1a expression had a significantly shorter OS (median = 19.0 months vs. not reached, P = 0.015) and EFS (median = 9.0 months vs. 24.0 months, P = 0.001) compared to those with low HIF1a expression. Notably, HIF1a-associated inferior prognosis in A/E-positive patients was KIT mutation-independent. In patients carrying wild-type KIT [n = 53, about 73% (53/73) of the entire A/E-patients], those with high HIF1a levels had a shorter OS (median = 23.1 months vs. not reached, P = 0.008) and EFS (median = 9.4 months vs. not reached, P = 0.001) than those with low HIF1a levels. Multivariate analysis revealed that high HIF1a levels were independent prognostic indicators for both OS and EFS (P = 0.014, HR = 3.574 and P = 0.004, HR = 4.304, respectively) in AE-positive patients. Mechanistic studies revealed that A/E and HIF1a formed a positive regulatory circuit, in which A/E bound to HIF1a gene promoter and transactivated HIF1a or vice versa. Co-expression of AE and HIF1a in leukemia cells caused a higher cell proliferation rate in vitro and more serious leukemic status in mice. To gain insight into the molecular basis of A/E-HIF1a functional cooperation in leukemogenesis, we examined the mRNA levels of DNMT1, DNMT3a and DNMT3b expression in bone marrow samples from above-mentioned AML patients and healthy donors using qPCR. The result showed that DNMT3a, but not DNMT1 and DNMT3b, was significantly overexpressed in A/E-positive patients, as compared to A/E-negative patients and healthy donors. DNMT3a levels were positively correlated with both A/E and HIF1a levels. We therefore focused on evaluating the role of DNMT3a in A/E-positive AML. We found that DNMT3a expression was positively correlated with both A/E and HIF1a levels. As an individual event, A/E or HIF1a was enriched on DNMT3a gene promoter and synergistically increased DNMT3a transcription and enhanced global DNA methylation. Pharmacological or genetic interventions in the AE-HIF1a loop resulted in DNA hypomethylation, a reexpression of hypermethylated tumor suppressor p15INK4band the blockage of leukemia growth. In summary, we showed that A/E and HIF1a form a regulatory circuit and cooperatively control aggressive leukemia growth through DNMT3a transactivation and subsequent DNA hypermethylation. Thus, the HIF1a-DNMT3a nexus serves as a reliable marker, which identifies patients with a poor prognosis in an otherwise prognostically favorable AML group, and represents an innovative therapeutic target in high-risk AE-positive leukemia. Disclosures No relevant conflicts of interest to declare.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.