A vicious loop of fatty acid-binding protein 4 and DNA methyltransferase 1 promotes acute myeloid leukemia and acts as a therapeutic target.

Aberrant DNA methylation mediated by deregulation of DNA methyltransferases (DNMT) is a key hallmark of acute myeloid leukemia (AML), yet efforts to target DNMT deregulation for drug development have lagged. We previously demonstrated that upregulation of fatty acid-binding protein 4 (FABP4) promotes AML aggressiveness through enhanced DNMT1-dependent DNA methylation. Here, we demonstrate that FABP4 upregulation in AML cells occurs through vascular endothelial growth factor (VEGF) signaling, thus elucidating a crucial FABP4-DNMT1 regulatory feedback loop in AML biology. We show that FABP4 dysfunction by its selective inhibitor BMS309403 leads to downregulation of DNMT1, decrease of global DNA methylation and re-expression of p15INK4B tumor suppressor gene by promoter DNA hypomethylation in vitro, ex vivo and in vivo. Functionally, BMS309403 suppresses cell colony formation, induces cell differentiation, and, importantly, impairs leukemic disease progression in mouse models of leukemia. Our findings highlight AML-promoting properties of the FABP4-DNMT1 vicious loop, and identify an attractive class of therapeutic agents with a high potential for clinical use in AML patients. The results will also assist in establishing the FABP4-DNMT1 loop as a target for therapeutic discovery to enhance the index of current epigenetic therapies.

Fatty acid-binding protein FABP4 mechanistically links obesity with aggressive AML by enhancing aberrant DNA methylation in AML cells.

Obesity is becoming more prevalent worldwide and is a major risk factor for cancer development. Acute myeloid leukemia (AML), the most common acute leukemia in adults, remains a frequently fatal disease. Here we investigated the molecular mechanisms by which obesity favors AML growth and uncovered the fatty acid-binding protein 4 (FABP4) and DNA methyltransferase 1 (DNMT1) regulatory axis that mediates aggressive AML in obesity. We showed that leukemia burden was much higher in high-fat diet-induced obese mice, which had higher levels of FABP4 and interleukin (IL)-6 in the sera. Upregulation of environmental and cellular FABP4 accelerated AML cell growth in both a cell-autonomous and cell-non-autonomous manner. Genetic disruption of FABP4 in AML cells or in mice blocked cell proliferation in vitro and induced leukemia regression in vivo. Mechanistic investigations showed that FABP4 upregulation increased IL-6 expression and signal transducer and activator of transcription factor 3 phosphorylation leading to DNMT1 overexpression and further silencing of the p15INK4B tumor-suppressor gene in AML cells. Conversely, FABP4 ablation reduced DNMT1-dependent DNA methylation and restored p15INK4B expression, thus conferring substantial protection against AML growth. Our findings reveal the FABP4/DNMT1 axis in the control of AML cell fate in obesity and suggest that interference with the FABP4/DNMT1 axis might be a new strategy to treat leukemia.

AML1/ETO cooperates with HIF1α to promote leukemogenesis through DNMT3a transactivation.

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.

The incidence of hepatocellular carcinoma is reduced in patients with chronic hepatitis B on long-term nucleos(t)ide analogue therapy.

BACKGROUND: North American data are lacking on the effect of nucleos(t)ide analogues (NA) in preventing chronic hepatitis B (CHB)-related hepatocellular carcinoma (HCC). AIM: To determine the incidence of HCC in NA-treated patients and compare this risk with that predicted without treatment based on the REACH-B model. METHODS: In this retrospective study, the incidence of HCC was determined in CHB patients initiated on NA from 1999 to 2012. Pre-treatment data utilised in the REACH-B model were used to predict the annual HCC risk. The standardised incidence ratio (SIR) for HCC was calculated by comparing the observed to expected number of cases, and HCC risk factors determined by Cox proportional hazards regression. RESULTS: Five hundred and forty nine initiated NA (14% lamivudine, 5% adefovir, 1.5% telbivudine, 39% entecavir, 41% tenofovir). Over a median follow-up of 3.2 years (IQR 1.9-4.6), 11 (3.2%) were diagnosed with HCC. Among 322 with data to calculate the REACH-B model, the median age at treatment initiation was 46 years (IQR 38-55), 65% were male, 32% HBeAg positive and 20% had cirrhosis. The median pre-treatment ALT was 71 U/L (IQR 41-127) and HBV DNA was 6.48 log10 copies/mL (4.95-8.04). The observed annual HCC incidence (0.9%; 95% CI 0.5-1.7) was significantly lower than predicted without treatment by the REACH-B model (SIR 0.46; 95% CI 0.23-0.82); this risk was reduced after 4 years of therapy (SIR 0.49; 95% CI 0.2-1.00). CONCLUSIONS: In this Canadian study of nucleos(t)ide analogues-treated patients with chronic hepatitis B, the incidence of HCC was lower than expected, suggesting that NA reduce the risk of chronic hepatitis B-related HCC.

Core structure of the envelope glycoprotein GP2 from Ebola virus at 1.9-A resolution.

Ebola virions contain a surface transmembrane glycoprotein (GP) that is responsible for binding to target cells and subsequent fusion of the viral and host-cell membranes. GP is expressed as a single-chain precursor that is posttranslationally processed into the disulfide-linked fragments GP1 and GP2. The GP2 subunit is thought to mediate membrane fusion. A soluble fragment of the GP2 ectodomain, lacking the fusion-peptide region and the transmembrane helix, folds into a stable, highly helical structure in aqueous solution. Limited proteolysis studies identify a stable core of the GP2 ectodomain. This 74-residue core, denoted Ebo-74, was crystallized, and its x-ray structure was determined at 1.9-A resolution. Ebo-74 forms a trimer in which a long, central three-stranded coiled coil is surrounded by shorter C-terminal helices that are packed in an antiparallel orientation into hydrophobic grooves on the surface of the coiled coil. Our results confirm the previously anticipated structural similarity between the Ebola GP2 ectodomain and the core of the transmembrane subunit from oncogenic retroviruses. The Ebo-74 structure likely represents the fusion-active conformation of the protein, and its overall architecture resembles several other viral membrane-fusion proteins, including those from HIV and influenza.

Effect of procainamide on pulmonary thromboembolism and platelet malondialdehyde in mice.

AIM: To study the effect of procainamide (PA) on pulmonary thromboembolism, platelet malondialdehyde (MDA) level and platelet aggregation induced by collagen and adrenaline. METHODS: Pulmonary thromboembolism, 2-thiobarbituric acid fluorescence micro-determination, conventional microscopic counting, and platelet aggregation test were used. RESULTS: PA (10-20 mg.kg-1) and mannitol (200 mg.kg-1) reduced thrombosis by 30%-75% and 75%, respectively. Thrombocytopenia followed thrombosis increased after the pretreatment of PA and mannitol. MDA decreased by both of them in vivo. In vitro, PA inhibited platelet aggregation and MDA production induced concentration-dependently by collagen and adrenaline. CONCLUSION: Inhibition of PA on pulmonary thromboembolism is involved in the decrease of platelet aggregation and MDA production.

[Effect of thrombin on cytosolic calcium and membrane potential in single human platelets].

Fluo-3 and di-BA-C4 (3) -loaded human platelets were immobilized on a fibrinogen-coated surface and the cytosolic free [Ca2+]i and the membrane potentials were measured in single thrombin-activated platelets by ACAS-570 (Adherent Cell Analysis and Sorting Cytometer). Fluorescence of fluo-3 and di-BA-C4 (3) was low in rest immobilized platelets without obviously repetitive spiking. When the platelets were activated by thrombin, a rapid rise of cytosolic [Ca2+]i and membrane potential was observed. Subsequently, oscillations in [Ca2+]i to an extent of about 500 fluorescent units were observable, whereas the membrane potential remained at the peak level, i.e., the change of [Ca2+]i in no way of accord with that membrane potential. The above results indicate that the thrombin induced membrane depolarization is not due to influx of Ca2+.

Pathological features of coronary atherosclerotic plaques in nonagenarians.

The atherosclerotic lesions from 4 major epicardial coronary arteries (left main, left anterior descending, left circumflex and right coronary arteries) of 23 nonagenarians patients were compared with that from 23 patients aged 60-69. The arteries were cut into transversely 5 mm long segments and were examined by microscope. The inside circumferences of the lumen were measured by computerized morphometric analysis. The results showed that the numbers of atherosclerotic plaques, percentages of narrowing of the coronary arterial lumen and circumferences of the arterial lumen in both groups were similar. But there were much more fibrous and resting (silent) or regressive plaques in the group aged 90-99 years as well as less lipid and active or progressive plaques than those in the group of 60-69 years. The above morphological findings may be correlated with the fact that there was a similar incidence of coronary heart disease but a less risk of acute myocardial infarction in patients aged 90-99 years than those aged 60-69 years.