The intrinsic antiviral defense is based on cellular restriction factors that are constitutively expressed and, thus, active even before a pathogen enters the cell. The promyelocytic leukemia (PML) nuclear bodies (NBs) are discrete nuclear foci that contain several cellular proteins involved in intrinsic antiviral responses against a number of viruses. Accumulating reports have shown the importance of PML as a DNA virus restriction factor and how these pathogens evade this antiviral activity. However, very little information is available regarding the antiviral role of PML against RNA viruses. Dengue virus (DENV) is an RNA emerging mosquito-borne human pathogen affecting millions of individuals each year by causing severe and potentially fatal syndromes. Since no licensed antiviral drug against DENV infection is currently available, it is of great importance to understand the factors mediating intrinsic immunity that may lead to the development of new pharmacological agents that can boost their potency and thereby lead to treatments for this viral disease. In the present study, we investigated the in vitro antiviral role of PML in DENV-2 A549 infected cells.

Overwhelming lines of epidemiological evidence have indicated that persistent infection with hepatitis C virus (HCV) is a major risk for the development of hepatocellular carcinoma (HCC). We have recently shown that HCV core protein mediates functional inactivation of the promyelocytic leukemia (PML) tumor suppressor pathway. However, the role of PML in HCC development yet remains unclear. To clarify the function of PML in liver carcinogenesis and HCV-associated pathogenesis we crossed PML-deficient mice with HCV transgene (HCV-Tg) expressing mice and treated the resulting animals with DEN/Phenobarbital, an established protocol for liver carcinogenesis. Seven months after treatment, livers were examined macroscopically and histologically. Genetic depletion of the tumor suppressor PML coincided with an increase in hepatocyte proliferation, resulting in development of multiple dysplastic nodules in 100% of the PML-deficient livers and of HCCs in 53%, establishing a tumor suppressive function of PML in the liver. In animals expressing the HCV-transgene in PML-deficient background, HCC development occurred even in 73%, while only 7% of their wildtype littermates developed HCC. The neoplastic nature of the tumors was confirmed by histology and expression of the HCC marker glutamine synthetase. Several pro- and antiapoptotic factors were tested for differential expression and liver carcinogenesis was associated with impaired expression of the proapoptotic molecule TRAIL in PML-deficient mice. In conclusion, this study provides first in vivo evidence that the tumor suppressor PML acts as an important barrier in liver carcinogenesis and HCV-dependent liver pathology.

Cardiac glycosides (CGs), inhibitors of Na+/K+-ATPase (NKA), used clinically to treat heart failure, have garnered recent attention as potential anti-cancer and anti-viral agents. A high-throughput phenotypic screen designed to identify modulators of promyelocytic leukemia protein (PML) nuclear body (NB) formation revealed the CG gitoxigenin as a potent activator of PML. We demonstrate that multiple structurally distinct CGs activate the formation of PML NBs and induce PML protein SUMOylation in an NKA-dependent fashion. CG effects on PML occur at the post-transcriptional level, mechanistically distinct from previously described PML activators and are mediated through signaling events downstream of NKA. Curiously, genomic deletion of PML in human cancer cells failed to abrogate the cytotoxic effects of CGs and other apoptotic stimuli such as ceramide and arsenic trioxide that were previously shown to function through PML in mice. These findings suggest that alternative pathways can compensate for PML loss to mediate apoptosis in response to CGs and other apoptotic stimuli.

PML protein plays important roles in regulating cellular homeostasis. It forms PML nuclear bodies (PML-NBs) that act like nuclear relay stations and participate in many cellular functions. In this study, we have examined the proteome of mouse embryonic fibroblasts (MEFs) derived from normal (PML(+/+)) and PML knockout (PML(-/-)) mice. The aim was to identify proteins that were differentially expressed when MEFs were incapable of producing PML. Using comparative proteomics, total protein were extracted from PML(-/-) and PML(+/+) MEFs, resolved by two dimensional electrophoresis (2-DE) gels and the differentially expressed proteins identified by LC-ESI-MS/MS. Nine proteins (PML, NDRG1, CACYBP, CFL1, RSU1, TRIO, CTRO, ANXA4 and UBE2M) were determined to be down-regulated in PML(-/-) MEFs. In contrast, ten proteins (CIAPIN1, FAM50A, SUMO2 HSPB1 NSFL1C, PCBP2, YWHAG, STMN1, TPD52L2 and PDAP1) were found up-regulated. Many of these differentially expressed proteins play crucial roles in cell adhesion, migration, morphology and cytokinesis. The protein profiles explain why PML(-/-) and PML(+/+) MEFs were morphologically different. In addition, we demonstrated PML(-/-) MEFs were less adhesive, proliferated more extensively and migrated significantly slower than PML(+/+) MEFs. NDRG1, a protein that was down-regulated in PML(-/-) MEFs, was selected for further investigation. We determined that silencing NDRG1expression in PML(+/+) MEFs increased cell proliferation and inhibited PML expression. Since NDRG expression was suppressed in PML(-/-) MEFs, this may explain why these cells proliferate more extensively than PML(+/+) MEFs. Furthermore, silencing NDRG1expression also impaired TGF-β1 signaling by inhibiting SMAD3 phosphorylation.

Pressure overload and prolonged angiotensin II (Ang II) infusion elicit cardiac hypertrophy in Ang II receptor 1 (AT(1)) null mouse, whereas Ang II receptor 2 (AT(2)) gene deletion abolishes the hypertrophic response. The roles and signals of the cardiac AT(2) receptor still remain unsettled. Promyelocytic leukemia zinc finger protein (PLZF) was shown to bind to the AT(2) receptor and transmit the hypertrophic signal. Using PLZF knockout mice we directed our studies on the function of PLZF concerning the cardiac specific transcription factor GATA4, and GATA4 targets.

Gastric cancer is one of the most common causes of cancer-related mortality worldwide. Expression of the tumor suppressor, promyelocytic leukemia (PML) protein, is reduced or abolished in gastric carcinomas, in association with an increased level of lymphatic invasion, development of higher pTNM staging, and unfavorable prognosis. Herein, we investigated the relationship between the extent of tumor-infiltrating lymphocytes and the status of PML protein expression in advanced gastric carcinoma. We observed higher numbers of infiltrating T-cells in gastric carcinoma tissues in which PML expression was reduced or abolished, compared to tissues positive for PML. The extent of T-cell migration toward culture supernatants obtained from interferon-gamma (IFN-γ-stimulated gastric carcinoma cell lines was additionally affected by expression of PML in vitro. Interferon-gamma-inducible protein 10 (IP-10/CXCL10) expression was increased in gastric carcinoma tissues displaying reduced PML levels. Moreover, both Pml knockout and knockdown cells displayed enhanced IP-10 mRNA and protein expression in the presence of IFN-γ. PML knockdown increased IFN-γ-mediated Signal Transducer and Activator of Transcription-1 (STAT-1) binding to the IP-10 promoter, resulting in elevated transcription of the IP-10 gene. Conversely, PML IV protein expression suppressed IP-10 promoter activation. Based on these results, we propose that loss of PML protein expression in gastric cancer cells contributes to increased IP-10 transcription via enhancement of STAT-1 activity, which, in turn, promotes lymphocyte trafficking within tumor regions.

A determining role has been assigned to cAMP in the signaling pathways that relieve resistance to anti-leukemia differentiation therapy. However, the underlying mechanisms have not been elucidated yet. Here, we identify cFos as a critical cAMP effector, able to regulate the re-expression and splicing of epigenetically silenced genes associated with maturation (CD44) in retinoid-resistant NB4-LR1 leukemia cells. Furthermore, using RNA interference approach, we show that cFos mediates cAMP-induced ROS generation, a critical mediator of neutrophil maturation, and in fine differentiation. This study highlights some of the mechanisms by which cAMP acts to overcome resistance, and reveals a new alternative cFos-dependent pathway which, though nonexistent in retinoid-sensitive NB4 cells, is essential to rescue the maturation program of resistant cells.

Tetra-arsenic tetra-sulfide (As4S4) is an arsenic compound with anti-tumor activity, especially in acute promyelocytic leukemia (APL) that are resistant to retinoic acid (RA). Although recent studies revealed that the therapeutic action of As4S4 is closely associated with the induction of cellular apoptosis, the exact molecular mechanism of action of As4S4 in RA-resistant APL remains to be clarified. In this study, we found that As4S4-induced apoptosis was accompanied by reduced mRNA and protein expression of SET gene in RA-resistant NB4-R1 cells. Moreover, RNAi knockdown of SET gene further promoted As4S4-induced apoptosis, while SET over-expression inhibited it, suggesting that As4S4 induces apoptosis through the reduction of SET protein in NB4-R1 cells. We also demonstrated that the knockdown of SET gene resulted in the upregulation of protein phosphatase 2 (PP2A) expression and the downregulation of promyelocytic leukemia and retinoic acid receptor α fusion gene (PML-RARα) expression, which were enhanced by As4S4 treatments. By contrast, over-expression of SET gene resulted in PP2A downregulation and PML-RARα upregulation, which were abolished by As4S4 pretreatment. Since PP2A is a pro-apoptotic factor and PMLRARα is an anti-apoptotic factor, our results suggest that As4S4-induced apoptosis in NB4-R1 cells is through the downregulation of SET protein expression, which in turn increases PP2A and reduces PML-RARα expressions to lead to cell apoptosis.

Sirtuins, NAD-dependent protein deacetylases, play important roles in cellular functions such as metabolism and differentiation. Whether sirtuins function in tumorigenesis is still controversial, but sirtuins are aberrantly expressed in tumors, which may keep cancerous cells undifferentiated. Therefore, we investigated whether the inhibition of sirtuin family proteins induces cellular differentiation in leukemic cells. The sirtuin inhibitors tenovin-6 and BML-266 induce granulocytic differentiation in the acute promyelocytic leukemia (APL) cell line NB4. This differentiation is likely caused by an inhibition of SIRT2 deacetylase activity, judging from the accumulation of acetylated α-tubulin, a major SIRT2 substrate. Unlike the clinically used differentiation inducer all-trans retinoic acid, tenovin-6 shows limited effects on promyelocytic leukemia-retinoic acid receptor α (PML-RAR-α) stability and promyelocytic leukemia nuclear body formation in NB4 cells, suggesting that tenovin-6 does not directly target PML-RAR-α activity. In agreement with this, tenovin-6 induces cellular differentiation in the non-APL cell line HL-60, where PML-RAR-α does not exist. Knocking down SIRT2 by shRNA induces granulocytic differentiation in NB4 cells, which demonstrates that the inhibition of SIRT2 activity is sufficient to induce cell differentiation in NB4 cells. The overexpression of SIRT2 in NB4 cells decreases the level of granulocytic differentiation induced by tenovin-6, which indicates that tenovin-6 induces granulocytic differentiation by inhibiting SIRT2 activity. Taken together, our data suggest that targeting SIRT2 is a viable strategy to induce leukemic cell differentiation.

Inactivation of the p53 pathway is a universal event in human cancers and promotes tumorigenesis and resistance to chemotherapy. Inactivating p53 mutations are uncommon in non-complex karyotype leukemias, thus the p53-pathway must be inactivated by other mechanisms. The Apoptosis Stimulating Protein of p53-2 (ASPP2) is a damage-inducible p53-binding protein that enhances apoptosis at least in part through a p53-mediated pathway. We have previously shown, that ASPP2 is an independent haploinsufficient tumor suppressor in vivo. Now, we reveal that ASPP2 expression is significantly attenuated in acute myeloid and lymphoid leukemia - especially in patients with an unfavorable prognostic risk profile and patients who fail induction chemotherapy. In line, knock down of ASPP2 in expressing leukemia cell lines and native leukemic blasts attenuates damage-induced apoptosis. Furthermore, cultured blasts derived from high-risk leukemias fail to induce ASPP2 expression upon anthracycline treatment. The mechanisms of ASPP2 dysregulation are unknown. We provide evidence that attenuation of ASPP2 is caused by hypermethylation of the promoter and 5'UTR regions in native leukemia blasts. Together, our results suggest that ASPP2 contributes to the biology of leukemia and expression should be further explored as a potential prognostic and/or predictive biomarker to monitor therapy responses in acute leukemia.

Fatty acid synthesis and oxidation are frequently exacerbated in leukemia cells, and may therefore represent a target for therapeutic intervention. In this work we analyzed the apoptotic and chemo-sensitizing action of the fatty acid oxidation inhibitor etomoxir in human acute myeloid leukemia cells. Etomoxir caused negligible lethality at concentrations up to 100 µM, but efficaciously cooperated to cause apoptosis with the anti-leukemic agent arsenic trioxide (ATO, Trisenox), and with lower efficacy with other anti-tumour drugs (etoposide, cisplatin), in HL60 cells. Etomoxir-ATO cooperation was also observed in NB4 human acute promyelocytic cells, but not in normal (non-tumour) mitogen-stimulated human peripheral blood lymphocytes. Biochemical determinations in HL60 cells indicated that etomoxir (25-200 µM) dose-dependently inhibited mitochondrial respiration while slightly stimulating glycolysis, and only caused marginal alterations in total ATP content and adenine nucleotide pool distribution. In addition, etomoxir caused oxidative stress (increase in intracellular reactive oxygen species accumulation, decrease in reduced glutathione content), as well as pro-apoptotic LKB-1/AMPK pathway activation, all of which may in part explain the chemo-sensitizing capacity of the drug. Etomoxir also cooperated with glycolytic inhibitors (2-deoxy-D-glucose, lonidamine) to induce apoptosis in HL60 cells, but not in NB4 cells. The combined etomoxir plus 2-deoxy-D-glucose treatment did not increase oxidative stress, caused moderate decrease in net ATP content, increased the AMP/ATP ratio with concomitant drop in energy charge, and caused defensive Akt and ERK kinase activation. Apoptosis generation by etomoxir plus 2-deoxy-D-glucose was further increased by co-incubation with ATO, which is apparently explained by the capacity of ATO to attenuate Akt and ERK activation. In summary, co-treatment with etomoxir may represent an interesting strategy to increase the apoptotic efficacy of ATO and (with some limitations) 2-deoxy-D-glucose which, although clinically important anti-tumour agents, exhibit low efficacy in monotherapy.

Acute myeloid leukemia (AML) is the most common malignant myeloid disorder of progenitor cells in myeloid hematopoiesis and exemplifies a genetically heterogeneous disease. The patients with AML also show a heterogeneous response to therapy. Although all-trans retinoic acid (ATRA) has been successfully introduced to treat acute promyelocytic leukemia (APL), it is rather ineffective in non-APL AML. In our present study, 1200 off-patent marketed drugs and natural compounds that have been approved by the Food and Drug Administration (FDA) were screened for anti-leukemia activity using the retrovirus transduction/transformation assay (RTTA). Furazolidone (FZD) was shown to inhibit bone marrow transformation mediated by several leukemia fusion proteins, including AML1-ETO. Furazolidone has been used in the treatment of certain bacterial and protozoan infections in human and animals for more than sixty years. We investigated the anti-leukemic activity of FZD in a series of AML cells. FZD displayed potent antiproliferative properties at submicromolar concentrations and induced apoptosis in AML cell lines. Importantly, FZD treatment of certain AML cells induced myeloid cell differentiation by morphology and flow cytometry for CD11b expression. Furthermore, FZD treatment resulted in increased stability of tumor suppressor p53 protein in AML cells. Our in vitro results suggest furazolidone as a novel therapeutic strategy in AML patients.

Recent studies show the importance of interactions between CD47 expressed on acute myeloid leukemia (AML) cells and the inhibitory immunoreceptor, signal regulatory protein-alpha (SIRPα) on macrophages. Although AML cells express SIRPα, its function has not been investigated in these cells. In this study we aimed to determine the role of the SIRPα in acute myeloid leukemia.

The adapter protein metastasis suppressor 1 (MTSS1) is implicated as a tumor suppressor or tumor promoter, depending on the type of solid cancer. Here, we identified Mtss1 expression to be increased in AML subsets with favorable outcome, while suppressed in high risk AML patients. High expression of MTSS1 predicted better clinical outcome of patients with normal-karyotype AML. Mechanistically, MTSS1 expression was negatively regulated by FLT3-ITD signaling but enhanced by the AML1-ETO fusion protein. DNMT3B, a negative regulator of MTSS1, showed strong binding to the MTSS1 promoter in PML-RARA positive but not AML1-ETO positive cells, suggesting that AML1-ETO leads to derepression of MTSS1. Pharmacological treatment of AML cell lines carrying the FLT3-ITD mutation with the specific FLT3 inhibitor PKC-412 caused upregulation of MTSS1. Moreover, treatment of acute promyelocytic cells (APL) with all-trans retinoic acid (ATRA) increased MTSS1 mRNA levels. Taken together, our findings suggest that MTSS1 might have a context-dependent function and could act as a tumor suppressor, which is pharmacologically targetable in AML patients.

Chemo- and radiotherapeutic responses of leukemia cells are modified by integrin-mediated adhesion to extracellular matrix. To further characterize the molecular mechanisms by which beta1 integrins confer radiation and chemoresistance, HL60 human acute promyelocytic leukemia cells stably transfected with beta1 integrin and A3 Jurkat T-lymphoma cells deficient for Fas-associated death domain protein or procaspase-8 were examined.

Phagocytotic cells play a fundamental role in the defense against bacterial pathogens. One mechanism whereby bacteria evade phagocytosis is to produce factors that trigger apoptosis. Here we identify for the first time a meningococcal protein capable of inducing macrophage apoptosis. The conserved meningococcal outer membrane protein NhhA (Neisseria hia/hsf homologue A, also known as Hsf) mediates bacterial adhesion and interacts with extracellular matrix components heparan sulphate and laminin. Meningococci lacking NhhA fail to colonise nasal mucosa in a mouse model of meningococcal disease. We found that exposure of macrophages to NhhA resulted in a highly increased rate of apoptosis that proceeded through caspase activation. Exposure of macrophages to NhhA also led to iNOS induction and nitric oxide production. However, neither nitric oxide production nor TNF-α signaling was found to be a prerequisite for NhhA-induced apoptosis. Macrophages exposed to wildtype NhhA-expressing meningococci were also found to undergo apoptosis whereas NhhA-deficient meningococci had a markedly decreased capacity to induce macrophage apoptosis. These data provide new insights on the role of NhhA in meningococcal disease. NhhA-induced macrophage apoptosis could be a mechanism whereby meningococci evade immunoregulatory and phagocytotic actions of macrophages.

The bacterial adenylyl cyclase toxins CyaA from Bordetella pertussis and edema factor from Bacillus anthracis as well as soluble guanylyl cyclase α(1)β(1) synthesize the cyclic pyrimidine nucleotide cCMP. These data raise the question to which effector proteins cCMP binds. Recently, we reported that cCMP activates the regulatory subunits RIα and RIIα of cAMP-dependent protein kinase. In this study, we used two cCMP agarose matrices as novel tools in combination with immunoblotting and mass spectrometry to identify cCMP-binding proteins. In agreement with our functional data, RIα and RIIα were identified as cCMP-binding proteins. These data corroborate the notion that cAMP-dependent protein kinase may serve as a cCMP target.

Previously we reported that the expression of promyelocytic leukemia (PML)-retinoic acid receptor alpha (RARα) fusion gene, which is caused by specific translocation (15;17) in acute promyelocytic leukemia, can enhance constitutive autophagic activity in leukemic and nonleukemic cells, and PML overexpression can sequestrate part of microtubule-associated protein light chain 3 (LC3) protein in PML nuclear bodies, suggesting that LC3 protein also distributes into nuclei although it is currently thought to function primarily in the cytoplasm, the site of autophagosomal formation. However, its potential significance of nucleoplasmic localizations remains greatly elusive. Here we demonstrate that PML interacts with LC3 in a cell type-independent manner as assessed by Co-IP assay and co-localization observation. Overexpressed PML significantly coprecipitates with endogenous and nuclear LC3 protein. Furthermore, a fraction of endogenous PML protein is found to be co-localized with LC3 protein under steady state condition, which is further enhanced by IFNα induction, indicating that PML up-regulation potentiates this interaction. Additionally, DsRed-PML associates with EGFP-LC3 during telophase and G1 phase but not in metaphase and anaphase. Two potential LC3-interacting region (LIR) motifs in PML are required for interaction of PML with LC3 while this association is independent of autophagic activity. Finally, we show that interaction between PML and LC3 contributes to cell growth inhibition function of PML. Considering that PML is an important tumor suppressor, we propose that nuclear portion of LC3 protein may associate with PML to control cell growth for prevention and inhibition of cancer occurrence and development.

Western blotting has been widely used for investigation of protein expression, posttranslational modifications, and interactions. Because western blotting usually involves heat-denaturation of samples prior to gel loading, clarification of detailed procedures for sample preparation have been omitted or neglected in many publications. We show here the case that even excellent primary antibodies failed to detect a specific protein of interest due to a routine heating practice of protein samples. We performed western blotting for transmembrane iron transporter proteins; SLC11A2 (divalent metal transporter 1, DMT1), SLC40A1 (ferroportin 1, Fpn1), and transferrin receptor-1 (TfR1), along with cytoplasmic iron storage protein ferritin H. Our results in 12 human culture cell lysates indicated that only unheated samples prior to gel loading gave rise to clear resolution of DMT1 protein, while heated samples (95°C, 5min) caused the loss of resolution due to DMT1 protein aggregates. Unheated samples also resulted in better resolution for Fpn1 and TfR1 western blots. Conversely, only heated samples allowed to detect ferritin H, otherwise ferritin polymers failed to get into the gel. Neither different lysis/sample loading buffers nor sonication improved the resolution of DMT1 and Fpn1 western blots. Thus, heating samples most critically affected the outcome of western blotting, suggesting the similar cases for thousands of other transmembrane and heat-sensitive proteins.

Replication timing of metazoan DNA during S-phase may be determined by many factors including chromosome structures, nuclear positioning, patterns of histone modifications, and transcriptional activity. It may be determined by Mb-domain structures, termed as "replication domains", and recent findings indicate that replication timing is under developmental and cell type-specific regulation.