Chromosomal translocation t(15;17) in human acute promyelocytic leukemia fuses RAR alpha with a novel putative transcription factor, PML

Induced lineage promiscuity undermines the efficiency of all-trans-retinoid-acid-induced differentiation of acute myeloid leukemia

All-trans retinoid acid (ATRA) can induce terminal differentiation of acute promyelocytic leukemia (APL), also known as the M3 subtype of acute myeloid leukemia (AML). However, non-APL types of AML respond poorly to ATRA-induced differentiation, and the mechanism underlying cell-type-specific resistance against ATRA remains unclear. Here, we use single-cell transcriptome analysis to compare the differentiation trajectories of two AML cell types during ATRA treatment. We show that in NB4 (APL/AML-M3) cells, ATRA activates canonical myeloid lineage factors—including SPI1, CEBPE, and STAT1—to direct near-normal differentiation toward mature granulocytes. By contrast, in HL60 (AML-M2) cells, ATRA-induced differentiation is incomplete and promiscuous, which is characterized by coinduction of both myelopoiesis and lymphopoiesis gene expression programs, as well as transient activation of cis-regulatory elements associated with myeloid differentiation. Our study suggests that the differentiation inducing capacity of ATRA in certain subtypes of AML may be compromised by therapy-induced lineage promiscuity.

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Single-cell analysis of ATRA-induced differentiation in two AML cell types

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In AML-M3/APL cells, ATRA induces a near normal trajectory of granulopoiesis

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In AML-M2 cells, ATRA induces incomplete differentiation and lineage promiscuity

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ATRA-induced lineage promiscuity involves transient cis-regulatory reprogramming

Jiyuan Oridonin A Overcomes Differentiation Blockade in Acute Myeloid Leukemia Cells With MLL Rearrangements via Multiple Signaling Pathways

Differentiation therapy with all-trans-retinoic acid (ATRA) in acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia (AML), has been extremely successful in inducing clinical remission in APL patients. However, the differentiation therapy of ATRA-based treatment has not been effective in other subtypes of AML. In this study, we evaluated a small molecule of ent-kaurene diterpenoid, Jiyuan oridonin A (JOA), on the differentiation blockade in AML cells with the mixed lineage leukemia (MLL) gene rearrangements (MLLr) in MV4-11, MOLM-13 and THP-1 cells. We found that JOA could significantly inhibit the proliferation of MOLM-13, MV4-11 and THP-1 cells. Moreover, JOA promoted cell differentiation coupled with cell-cycle exit at G0/G1 and inhibited the colony- forming capacity of these cells. We showed that the anti-proliferative effect of JOA attributed to cell differentiation is most likely through the martens tretinoin response up pathway in the MOLM-13 cell line, and the hematopoietic cell lineage pathway by the inhibition of c-KIT expression and cell adhesion pathway in the THP-1 cell line. Our findings suggest that JOA could be a novel therapeutic agent against human MLLr acute myeloid leukemia.

OGP46 Induces Differentiation of Acute Myeloid Leukemia Cells via Different Optimal Signaling Pathways

Acute myelogenous leukemia (AML) is characterized by blockage of cell differentiation leading to the accumulation of immature cells, which is the most prevalent form of acute leukemia in adults. It is well known that all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) are the preferred drugs for acute promyelocytic leukemia (APL). However, they can lead to irreversible resistance which may be responsible for clinical failure after complete remission (CR). Moreover, the differentiation therapy of ATRA-based treatment has not been effective against AML with t(8;21) translocation. Here we aimed to identify the differentiation effect of OGP46 on AML cell lines (HL-60, NB4, and Kasumi-1) and explore its possible mechanisms. We found that OGP46 has significant inhibitory activity against these cells by triggering cell differentiation with cell-cycle exit at G1/G0 and inhibited the colony-formation capacity of the AML cells. It was shown that OGP46 induced the differentiation of NB4 cells via the transcriptional misregulation in cancer signaling pathway by PML-RARα depletion, while it was attributed to the hematopoietic cell lineage and phagosome pathway in Kasumi-1 cells, which are all critical pathways in cell differentiation. These results highlight that OGP46 is an active agent not only in the APL cell line NB4 but also in AML-M2 cell lines, especially Kasumi-1 with t(8;21) translocation. Therefore, OGP46 may be a potential compound for surmounting the differentiation blockage in AML.

Inhibition of mitochondrial complex III induces differentiation in acute myeloid leukemia

Although acute myeloid leukemia (AML) is a highly heterogeneous disease with diverse genetic subsets, one hallmark of AML blasts is myeloid differentiation blockade. Extensive evidence has indicated that differentiation induction therapy represents a promising treatment strategy. Here, we identified that the pharmacological inhibition of the mitochondrial electron transport chain (ETC) complex III by antimycin A inhibits proliferation and promotes cellular differentiation of AML cells. Mechanistically, we showed that the inhibition of dihydroorotate dehydrogenase (DHODH), a rate-limiting enzyme in de novo pyrimidine biosynthesis, is involved in antimycin A-induced differentiation. The activity of antimycin A could be reversed by supplement of excessive amounts of exogenous uridine as well as orotic acid, the product of DHODH. Furthermore, we also found that complex III inhibition exerts a synergistic effect in differentiation induction combined with DHODH inhibitor brequinar as well as with the pyrimidine salvage pathway inhibitor dipyridamole. Collectively, our study uncovered the link between mitochondrial complex III and AML differentiation and may provide further insight into the potential application of mitochondrial complex III inhibitor as a mono or combination treatment in differentiation therapy of AML.

Aberrant phase separation and cancer

Eukaryotic cells are intracellularly divided into numerous compartments or organelles, which coordinate specific molecules and biological reactions. Membrane-bound organelles are physically separated by lipid bilayers from the surrounding environment. Biomolecular condensates, also referred to membraneless organelles, are micron-scale cellular compartments that lack membranous enclosures but function to concentrate proteins and RNA molecules, and these are involved in diverse processes. Liquid-liquid phase separation (LLPS) driven by multivalent weak macromolecular interactions is a critical principle for the formation of biomolecular condensates, and a multitude of combinations among multivalent interactions may drive liquid-liquid phase transition (LLPT). Dysregulation of LLPS and LLPT leads to aberrant condensate and amyloid formation, which causes many human diseases, including neurodegeneration and cancer. Here, we describe recent findings regarding abnormal forms of biomolecular condensates and aggregation via aberrant LLPS and LLPT of cancer-related proteins in cancer development driven by mutation and fusion of genes. Moreover, we discuss the regulatory mechanisms by which aberrant LLPS and LLPT occur in cancer and the drug candidates targeting these mechanisms. Further understanding of the molecular events regulating how biomolecular condensates and aggregation form in cancer tissue is critical for the development of therapeutic strategies against tumorigenesis.

Fusion Genes and RNAs in Cancer Development

Fusion RNAs are a hallmark of some cancers. They result either from chromosomal rearrangements or from splicing mechanisms that are non-chromosomal rearrangements. Chromosomal rearrangements that result in gene fusions are particularly prevalent in sarcomas and hematopoietic malignancies; they are also common in solid tumors. The splicing process can also give rise to more complex RNA patterns in cells. Gene fusions frequently affect tyrosine kinases, chromatin regulators, or transcription factors, and can cause constitutive activation, enhancement of downstream signaling, and tumor development, as major drivers of oncogenesis. In addition, some fusion RNAs have been shown to function as noncoding RNAs and to affect cancer progression. Fusion genes and RNAs will therefore become increasingly important as diagnostic and therapeutic targets for cancer development. Here, we discuss the function, biogenesis, detection, clinical relevance, and therapeutic implications of oncogenic fusion genes and RNAs in cancer development. Further understanding the molecular mechanisms that regulate how fusion RNAs form in cancers is critical to the development of therapeutic strategies against tumorigenesis.

IGFBP7 activates retinoid acid-induced responses in acute myeloid leukemia stem and progenitor cells

Treatment of acute promyelocytic leukemia (APL) with all-trans retinoic acid (ATRA) in combination with low doses of arsenic trioxide or chemotherapy leads to exceptionally high cure rates (>90%). ATRA forces APL cells into differentiation and cell death. Unfortunately, ATRA-based therapy has not been effective among any other acute myeloid leukemia (AML) subtype, and long-term survival rates remain unacceptably low; only 30% of AML patients survive 5 years after diagnosis. Here, we identified insulin-like growth factor binding protein 7 (IGFBP7) as part of ATRA-induced responses in APL cells. Most importantly, we observed that addition of recombinant human IGFBP7 (rhIGFBP7) increased ATRA-driven responses in a subset of non-APL AML samples: those with high RARA expression. In nonpromyelocytic AML, rhIGFBP7 treatment induced a transcriptional program that sensitized AML cells for ATRA-induced differentiation, cell death, and inhibition of leukemic stem/progenitor cell survival. Furthermore, the engraftment of primary AML in mice was significantly reduced following treatment with the combination of rhIGFBP7 and ATRA. Mechanistically, we showed that the synergism of ATRA and rhIGFBP7 is due, at least in part, to reduction of the transcription factor GFI1. Together, these results suggest a potential clinical utility of IGFBP7 and ATRA combination treatment to eliminate primary AML (leukemic stem/progenitor) cells and reduce relapse in AML patients.

Emerging role of tumor cell plasticity in modifying therapeutic response

Resistance to cancer therapy is a major barrier to cancer management. Conventional views have proposed that acquisition of resistance may result from genetic mutations. However, accumulating evidence implicates a key role of non-mutational resistance mechanisms underlying drug tolerance, the latter of which is the focus that will be discussed here. Such non-mutational processes are largely driven by tumor cell plasticity, which renders tumor cells insusceptible to the drug-targeted pathway, thereby facilitating the tumor cell survival and growth. The concept of tumor cell plasticity highlights the significance of re-activation of developmental programs that are closely correlated with epithelial-mesenchymal transition, acquisition properties of cancer stem cells, and trans-differentiation potential during drug exposure. From observations in various cancers, this concept provides an opportunity for investigating the nature of anticancer drug resistance. Over the years, our understanding of the emerging role of phenotype switching in modifying therapeutic response has considerably increased. This expanded knowledge of tumor cell plasticity contributes to developing novel therapeutic strategies or combination therapy regimens using available anticancer drugs, which are likely to improve patient outcomes in clinical practice.

TRIM proteins in neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid tumor in childhood. Outcome for children with high-risk NB remains unsatisfactory. Accumulating evidence suggests that tripartite motif (TRIM) family proteins express diversely in various human cancers and act as regulators of oncoproteins or tumor suppressor proteins. This review summarizes the TRIM proteins involving in NB and the underlying molecular mechanisms. We expect these new insights will provide important implications for the treatment of NB by targeting TRIM proteins.

The diagnostic power of CD117, CD13, CD56, CD64, and MPO in rapid screening acute promyelocytic leukemia

Objective

The same immuno-phenotype between HLA-DR-negative acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL) causes APL rapid screening to become difficult. This study aimed to identify the associated antigens for APL and the best model in clinical uses.

Results

A total of 36 APL (PML–RARA+) and 29 HLA-DR-negative non-APL patients enrolled in this study. When a cut-off point of 20% events was applied to define positive or negative status, APL and non-APL patients share a similar immuno-phenotype of CD117, CD34, CD11b, CD13, CD33, and MPO (P > 0.05). However, expression intensity of CD117 (P = 0.002), CD13 (P < 0.001), CD35 (P < 0.001), CD64 (P < 0.001), and MPO (P < 0.001) in APL are significantly higher while CD56 (P = 0.049) is lower than in non-APL subjects. The Bayesian Model Averaging (BMA) analysis identified CD117 (≥ 49% events), CD13 (≥ 88% events), CD56 (≤ 25% events), CD64 (≥ 42% events), and MPO (≥ 97% events) antigens as an optimal model for APL diagnosis. A combination of these factors resulted in an area under curve (AUC) value of 0.98 together with 91.7% sensitivity and 93.1% specificity, which is better than individual markers (AUC were 0.76, 0.84, 0.65, 0.82, and 0.85, respectively) (P = 0.001).

Emerging Cancer Epigenetic Mechanisms Regulated by All-Trans Retinoic Acid

All-trans retinoic acid (RA), which is the dietary bioactive derivative obtained from animal (retinol) and plant sources (beta-carotene), is a physiological lipid signal of both embryonic and postembryonic development. During pregnancy, either RA deficiency or an excessive RA intake is teratogenic. Too low or too high RA affects not only prenatal, but also postnatal, developmental processes such as myelopoiesis and mammary gland morphogenesis. In this review, we mostly focus on emerging RA-regulated epigenetic mechanisms involving RA receptor alpha (RARA) and Annexin A8 (ANXA8), which is a member of the Annexin family, as well as ANXA8 regulatory microRNAs (miRNAs). The first cancer showing ANXA8 upregulation was reported in acute promyelocytic leukemia (APL), which induces the differentiation arrest of promyelocytes due to defective RA signaling caused by RARA fusion genes as the PML-RARA gene. Over the years, ANXA8 has also been found to be upregulated in other cancers, even in the absence of RARA fusion genes. Mechanistic studies on human mammary cells and mammary glands of mice showed that ANXA8 upregulation is caused by genetic mutations affecting RARA functions. Although not all of the underlying mechanisms of ANXA8 upregulation have been elucidated, the interdependence of RA-RARA and ANXA8 seems to play a relevant role in some normal and tumorigenic settings.

The HECT E3 Ligase E6AP/UBE3A as a Therapeutic Target in Cancer and Neurological Disorders

The HECT (Homologous to the E6-AP Carboxyl Terminus)-family protein E6AP (E6-associated protein), encoded by the UBE3A gene, is a multifaceted ubiquitin ligase that controls diverse signaling pathways involved in cancer and neurological disorders. The oncogenic role of E6AP in papillomavirus-induced cancers is well known, with its action to trigger p53 degradation in complex with the E6 viral oncoprotein. However, the roles of E6AP in non-viral cancers remain poorly defined. It is well established that loss-of-function alterations of the UBE3A gene cause Angelman syndrome, a severe neurodevelopmental disorder with autosomal dominant inheritance modified by genomic imprinting on chromosome 15q. Moreover, excess dosage of the UBE3A gene markedly increases the penetrance of autism spectrum disorders, suggesting that the expression level of UBE3A must be regulated tightly within a physiologically tolerated range during brain development. In this review, current the knowledge about the substrates of E6AP-mediated ubiquitination and their functions in cancer and neurological disorders is discussed, alongside with the ongoing efforts to pharmacologically modulate this ubiquitin ligase as a promising therapeutic target.

Current Trends in ATRA Delivery for Cancer Therapy

All-Trans Retinoic Acid (ATRA) is the most active metabolite of vitamin A. It is critically involved in the regulation of multiple processes, such as cell differentiation and apoptosis, by activating specific genomic pathways or by influencing key signaling proteins. Furthermore, mounting evidence highlights the anti-tumor activity of this compound. Notably, oral administration of ATRA is the first choice treatment in Acute Promyelocytic Leukemia (APL) in adults and NeuroBlastoma (NB) in children. Regrettably, the promising results obtained for these diseases have not been translated yet into the clinics for solid tumors. This is mainly due to ATRA-resistance developed by cancer cells and to ineffective delivery and targeting. This up-to-date review deals with recent studies on different ATRA-loaded Drug Delivery Systems (DDSs) development and application on several tumor models. Moreover, patents, pre-clinical, and clinical studies are also reviewed. To sum up, the main aim of this in-depth review is to provide a detailed overview of the several attempts which have been made in the recent years to ameliorate ATRA delivery and targeting in cancer.

Biotransformation of arsenic and toxicological implication of arsenic metabolites

Arsenic is a well-known environmental carcinogen and chronic exposure to arsenic through drinking water has been reported to cause skin, bladder and lung cancers, with arsenic metabolites being implicated in the pathogenesis. In contrast, arsenic trioxide (As₂O₃) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, in which the binding of arsenite (iAs^III) to promyelocytic leukemia (PML) protein is the proposed initial step. These findings on the two-edged sword characteristics of arsenic suggest that after entry into cells, arsenic reaches the nucleus and triggers various nuclear events. Arsenic is reduced, conjugated with glutathione, and methylated in the cytosol. These biotransformations, including the production of reactive metabolic intermediates, appear to determine the intracellular dynamics, target organs, and biological functions of arsenic.

ATO (Arsenic Trioxide) Effects on Promyelocytic Leukemia Nuclear Bodies Reveals Antiviral Intervention Capacity

Human adenoviruses (HAdV) are associated with clinical symptoms such as gastroenteritis, keratoconjunctivitis, pneumonia, hepatitis, and encephalitis. In the absence of protective immunity, as in allogeneic bone marrow transplant patients, HAdV infections can become lethal. Alarmingly, various outbreaks of highly pathogenic, pneumotropic HAdV types have been recently reported, causing severe and lethal respiratory diseases. Effective drugs for treatment of HAdV infections are still lacking. The repurposing of drugs approved for other indications is a valuable alternative for the development of new antiviral therapies and is less risky and costly than de novo development. Arsenic trioxide (ATO) is approved for treatment of acute promyelocytic leukemia. Here, it is shown that ATO is a potent inhibitor of HAdV. ATO treatment blocks virus expression and replication by reducing the number and integrity of promyelocytic leukemia (PML) nuclear bodies, important subnuclear structures for HAdV replication. Modification of HAdV proteins with small ubiquitin-like modifiers (SUMO) is also key to HAdV replication. ATO reduces levels of viral SUMO-E2A protein, while increasing SUMO-PML, suggesting that ATO interferes with SUMOylation of proteins crucial for HAdV replication. It is concluded that ATO targets cellular processes key to HAdV replication and is relevant for the development of antiviral intervention strategies.

Acute promyelocytic leukemia (APL): a review of the literature

Acute Promyelocytic Leukemia (APL) is characterized by a block in differentiation where leukemic cells are halted at the promyelocyte stage. A characteristic balanced chromosomal translocation between chromosomes 15 and 17 t (15;17) (q24; q21) is seen in 95% of cases — the translocation results in the formation of the PML-RARA fusion protein. The introduction of retinoic acid (RA) and arsenic trioxide (ATO) has been responsible for initially remarkable cure rates. However, relapsed APL, particularly in the high-risk subset of patients, remains an important clinical problem. In addition, despite the success of ATRA & ATO, many clinicians still elect to use cytotoxic chemotherapy in the treatment of APL. Patients who become resistant to ATO have an increased risk of mortality. The probability of relapse is significantly higher in the high-risk subset of patients undergoing treatment for APL; overall approximately 10-20% of APL patients relapse regardless of their risk stratification. Furthermore, 20-25% of patients undergoing treatment will develop differentiation syndrome, a common side effect of differentiation agents. Recent evidence using in vitro models has shown that mutations in the B2 domain of the PML protein, mediate arsenic resistance. Alternative agents and approaches considering these clinical outcomes are needed to address ATO resistance as well as the relapse rate in high risk APL.

Roscovitine enhances All-trans retinoic acid (ATRA)-induced leukemia cell differentiation: Novel effects on signaling molecules for a putative Cdk2 inhibitor

All-trans retinoic acid (ATRA)-based differentiation therapy has been unsuccessful in treating t(15;17) negative acute myeloid leukemia (AML) patients, motivating interest in combination therapies using ATRA plus other agents. Using the t (15, 17) negative HL-60 human myeloblastic leukemia model, we find that the cyclin-dependent kinase (CDK) inhibitor, roscovitine, augments signaling by an ATRA-induced macromolecular signalsome that propels differentiation and enhances ATRA-induced differentiation. Roscovitine co-treatment enhanced ATRA-induced expression of pS259- pS289/296/301- pS621-c-Raf, pS217/221-Mek, Src Family Kinases (SFKs) Lyn and Fgr and SFK Y416 phosphorylation, adaptor proteins c-Cbl and SLP-76, Vav, and acetylated 14-3-3 in the signalsome. Roscovitine enhanced ATRA-induced c-Raf interaction with Lyn, Vav, and c-Cbl. Consistent with signalsome hyper-activation, roscovitine co-treatment enhanced ATRA-induced G1/0 arrest and expression of differentiation markers, CD11b, ROS and p47 Phox. Because roscovitine regulated Lyn expression, activation and partnering, a stably transfected Lyn knockdown was generated from wt-parental cells to investigate its function in ATRA-induced differentiation. Lyn-knockdown enhanced ATRA-induced up-regulation of key signalsome molecules, c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, Vav1, SLP-76, and Fgr, but with essentially total loss of pY416-SFK. Compared to ATRA-treated wt-parental cells, differentiation markers p47 phox, CD11b, G1/G0 arrest and ROS production were enhanced in ATRA-treated Lyn-knockdown stable transfectants, and addition of roscovitine further enhanced these ATRA-inducible markers. The Lyn-knockdown cells expressed slightly higher c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, and SLP-76 than wt-parental cells, and this was associated with enhanced ATRA-induced upregulation of Fgr and cell differentiation, consistent with heightened signaling, suggesting that enhanced Fgr may have compensated for loss of Lyn to enhance differentiation in the Lyn-knockdown cells.

Advances in Pediatric Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is a rare disease accounting for only 5%-10% of pediatric acute myeloid leukemia (AML) and fewer than 1000 cases occur annually in the United States across all age groups. Characterized by t (15; 17), with a resultant PML-RARA gene fusion driving leukemia development, advances in therapy have improved outcomes for APL significantly in the past several decades, now making APL the most curable form of AML in both children and adults. Cure rates in APL are now comparable to pediatric B-lymphoid leukemias. The success of APL treatment is due, in part, to the breadth of understanding of the driver PML-RARA mutation as well as collaborative efforts to quickly introduce and maximize the benefit of new therapies. Here, we review the presentation, clinical features, pathogenesis, and treatment advances in pediatric APL.

A two-pronged anti-leukemic agent based on a hyaluronic acid–green tea catechin conjugate for inducing targeted cell death and terminal differentiation

A two-pronged anti-leukemic approach for leukemic cell elimination and differentiation is demonstrated using a hyaluronic acid–green tea catechin conjugate.

RARG Gene Dysregulation in Acute Myeloid Leukemia

Retinoic acid receptor γ (RARγ) belongs to the nuclear receptor superfamily and shares 90% homology with retinoic acid receptor α (RARα) and retinoic acid receptor β (RARβ). RARA rearrangements are well-known to be involved in acute promyelocytic leukemia (APL), but RARG rearrangements can also resemble this kind of leukemia. In this review we trace the role of RARγ, considering both its physiological and oncogenic contribution; from 2011 to date, nine cases of patients harboring RARG fusions have been reported. These patients showed typical APL features, including the clinical presentation, coagulation abnormalities and morphological features of bone marrow (BM), but are not responsive to APL standard therapy. We stress the urgent need for a better comprehension of the critical role of RARG dysregulation in the leukemogenesis process, since optimum therapy strategies have not yet been established.

A dual functional ruthenium arene complex induces differentiation and apoptosis of acute promyelocytic leukemia cells

A dual functional ruthenium arene complex induces differentiation and apoptosis of acute promyelocytic leukemia cells through degradation of PML–RARα and DNA damage.

Human acute promyelocytic leukemia (APL) is the most malignant form of acute leukemia. The fusion of PML and RARα genes is responsible for over 98% of cases of APL. In this work, we found that a Ru(ii) arene complex, [(η⁶-p-bip)Ru(en)Cl][PF₆] (Ru-1), can selectively react with PML, leading to zinc-release and protein unfolding. Consequently, the degradation of the fusion protein PML–RARα occurs, which causes the differentiation of APL cells. In addition, Ru-1 can also bind to DNA and trigger apoptosis of APL cells. Therefore, Ru-1 acts as a dual functional agent that inhibits the growth of APL cells and induces cell differentiation. In contrast, the other non-selective Ru(ii) compound, though also highly reactive to PML, does not exhibit anti-APL activity. The selectivity of Ru-1 to PML suggests a new strategy for the development of anti-APL drugs using ruthenium agents.

PML Bodies in Mitosis

Promyelocytic leukemia (PML) bodies are dynamic intracellular structures that recruit and release a variety of different proteins in response to stress, virus infection, DNA damage and cell cycle progression. While PML bodies primarily are regarded as nuclear compartments, they are forced to travel to the cytoplasm each time a cell divides, due to breakdown of the nuclear membrane at entry into mitosis and subsequent nuclear exclusion of nuclear material at exit from mitosis. Here we review the biochemical and biophysical transitions that occur in PML bodies during mitosis and discuss this in light of post-mitotic nuclear import, cell fate decision and acute promyelocytic leukemia therapy.

A Critical Review of Animal Models Used in Acute Myeloid Leukemia Pathophysiology

Acute myeloid leukemia (AML) is one of the most frequent, complex, and heterogeneous hematological malignancies. AML prognosis largely depends on acquired cytogenetic, epigenetic, and molecular abnormalities. Despite the improvement in understanding the biology of AML, survival rates remain quite low. Animal models offer a valuable tool to recapitulate different AML subtypes, and to assess the potential role of novel and known mutations in disease progression. This review provides a comprehensive and critical overview of select available AML animal models. These include the non-mammalian Zebrafish and Drosophila models as well as the mammalian rodent systems, comprising rats and mice. The suitability of each animal model, its contribution to the advancement of knowledge in AML pathophysiology and treatment, as well as its advantages and limitations are discussed. Despite some limitations, animal models represent a powerful approach to assess toxicity, and permit the design of new therapeutic strategies.

t(15; 17) associated with primary myelofibrosis: a case report of an unusual clinical presentation and diagnostic dilemma

Background

primary myelofibrosis (PMF) is a myeloproliferative neoplasm which is associated with clonal molecular and cytogenetic abnormalities (CA) and varied clinical manifestations. While various CA have been previously described, t(15; 17) has not been reported in association with this condition.

Case presentation

A 69-year-old male presented with constitutional symptoms, cytopenias and bone marrow biopsy revealed immature blasts with fibrosis. Cytogenetic analysis showed a t(15;17) which initially suggested a diagnosis of acute promyelocytic leukemia (APL). However, flourescence in situ hybridization (FISH) and reverse transcriptase polymerase chain reaction (RT-PCR) studies were negative for transcripts promyelocytic leukemia (PML) gene and retinoic acid receptor alpha (RARA) or PML-RARA fusion. Along with these results, a second review of bone marrow histology, flowcytometry and the detection of a calreticulin gene (CALR) mutation helped with the correct diagnosis of PMF. Patient was then treated with ruxolitinib, a JAK (Janus kinase) 1 and 2 inhibitor, and eventually proceeded to receive a matched unrelated reduced intensity conditioning (RIC) allogeneic stem cell transplantation (ASCT) and has been doing well at the 6-month follow up.

Conclusions

Our case highlights two points, that the t(15;17) is diagnostic of Acute Promyelocytic Leukemia (APL) in most cases, there are exceptions and it can be associated with other malignancies without causing any APL like features, as noted in this case. Also, that t(15; 17) by itself is never sufficient to diagnose APL without confirmation by other methods and relying solely on cytogenetics without timely confirmatory tests can lead to risks of delay in diagnosis and appropriate management.

HDAC and HMT Inhibitors in Combination with Conventional Therapy: A Novel Treatment Option for Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is characterized by PML-RARA translocation, which causes the blockage of promyelocyte differentiation. Conventional treatment with Retinoic acid and chemotherapeutics is quite satisfactory. However, there are still patients who relapse or develop resistance to conventional treatment. To propose new possibilities for acute leukemia treatment, we studied the potential of histone deacetylase (HDAC) inhibitor and histone methyl transferase (HMT) inhibitor to enhance conventional therapy in vitro and ex vivo. NB4 and HL60 cell lines were used as an in vitro model; APL patient bone marrow mononuclear cells were used as an ex vivo model. Cell samples were treated with Belinostat (HDAC inhibitor) and 3-Deazaneplanocin A (HMT inhibitor) in combination with conventional treatment (Retinoic acid and Idarubicin). We demonstrated that the combined treatment used in the study had slightly higher effect on cell proliferation inhibition than conventional treatment. Also, enhanced treatment showed stronger effect on induction of apoptosis and on suppression of metabolism. Moreover, the treatment accelerated granulocytic cell differentiation and caused chromatin remodelling (increased H3K14 and H4 acetylation levels). In vitro and ex vivo models showed similar response to the treatment with different combinations of 3-Deazaneplanocin A, Belinostat, Retinoic acid, and Idarubicin. In conclusion, we suggest that 3-Deazaneplanocin A and Belinostat enhanced conventional acute promyelocytic leukemia treatment and could be considered for further investigations for clinical use.

Improved detection of gene fusions by applying statistical methods reveals oncogenic RNA cancer drivers

The extent to which gene fusions function as drivers of cancer remains a critical open question. Current algorithms do not sufficiently identify false-positive fusions arising during library preparation, sequencing, and alignment. Here, we introduce Data-Enriched Efficient PrEcise STatistical fusion detection (DEEPEST), an algorithm that uses statistical modeling to minimize false-positives while increasing the sensitivity of fusion detection. In 9,946 tumor RNA-sequencing datasets from The Cancer Genome Atlas (TCGA) across 33 tumor types, DEEPEST identifies 31,007 fusions, 30% more than identified by other methods, while calling 10-fold fewer false-positive fusions in nontransformed human tissues. We leverage the increased precision of DEEPEST to discover fundamental cancer biology. Namely, 888 candidate oncogenes are identified based on overrepresentation in DEEPEST calls, and 1,078 previously unreported fusions involving long intergenic noncoding RNAs, demonstrating a previously unappreciated prevalence and potential for function. DEEPEST also reveals a high enrichment for fusions involving oncogenes in cancers, including ovarian cancer, which has had minimal treatment advances in recent decades, finding that more than 50% of tumors harbor gene fusions predicted to be oncogenic. Specific protein domains are enriched in DEEPEST calls, indicating a global selection for fusion functionality: kinase domains are nearly 2-fold more enriched in DEEPEST calls than expected by chance, as are domains involved in (anaerobic) metabolism and DNA binding. The statistical algorithms, population-level analytic framework, and the biological conclusions of DEEPEST call for increased attention to gene fusions as drivers of cancer and for future research into using fusions for targeted therapy.

Retinoic acid and arsenic trioxide induce lasting differentiation and demethylation of target genes in APL cells

Acute promyelocytic leukemia (APL) is characterized by arrested differentiation of promyelocytes. Patients treated with all-trans retinoic acid (ATRA) alone experience relapse, while patients treated with ATRA and arsenic trioxide (ATO) are often relapse-free. This suggests sustained changes have been elicited by the combination therapy. To understand the lasting effects of the combination therapy, we compared the effects of ATRA and ATO on NB4 and ATRA-resistant NB4-MR2 APL cells during treatment versus post treatment termination. After treatment termination, NB4 cells treated with ATRA or ATO reverted to non-differentiated cells, while combination-treated cells remained terminally differentiated. This effect was diminished in NB4-MR2 cells. This suggests combination treatment induced more permanent changes. Combination treatment induced higher expression of target genes (e.g., transglutaminase 2 and retinoic acid receptor beta), which in NB4 cells was sustained post treatment termination. To determine whether sustained epigenetic changes were responsible, we quantified the enrichment of histone modifications by chromatin immunoprecipitation, and CpG methylation by bisulfite-pyrosequencing. While ATRA and combination treatment induced similar histone acetylation enrichment, combination treatment induced greater demethylation of target genes, which was sustained. Therefore, sustained demethylation of target genes by ATRA and ATO combination treatment is associated with lasting differentiation and gene expression changes.

Acute Promyelocytic Leukemia: A History over 60 Years-From the Most Malignant to the most Curable Form of Acute Leukemia

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) that is cytogenetically characterized by a balanced reciprocal translocation between chromosomes 15 and 17, which results in the fusion of the promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARα) genes. Because patients with APL present a tendency for severe bleeding, often resulting in an early fatal course, APL was historically considered to be one of the most fatal forms of acute leukemia. However, therapeutic advances, including anthracycline- and cytarabine-based chemotherapy, have significantly improved the outcomes of APL patients. Due to the further introduction of all-trans retinoic acid (ATRA) and-more recently-the development of arsenic trioxide (ATO)-containing regimens, APL is currently the most curable form of AML in adults. Treatment with these new agents has introduced the concept of cure through targeted therapy. With the advent of revolutionary ATRA-ATO combination therapies, chemotherapy can now be safely omitted from the treatment of low-risk APL patients. In this article, we review the six-decade history of APL, from its initial characterization to the era of chemotherapy-free ATRA-ATO, a model of cancer-targeted therapy.

PML-RARα induces all-trans retinoic acid-dependent transcriptional activation through interaction with MED1

Transcriptional activation by PML-RARα, an acute promyelocytic leukemia-related oncofusion protein, requires pharmacological concentrations of all-trans retinoic acid (ATRA). However, the mechanism by which the liganded PML-RARα complex leads to the formation of the preinitiation complex has been unidentified. Here we demonstrate that the Mediator subunit MED1 plays an important role in the ATRA-dependent activation of the PML-RARα-bound promoter. Luciferase reporter assays showed that PML-RARα induced significant transcription at pharmacological doses (1 μM) of ATRA; however, this was submaximal and equivalent to the level of transcription driven by intact RARα at physiological doses (1 nM) of ATRA. Transcription depended upon the interaction of PML-RARα with the two LxxLL nuclear receptor recognition motifs of MED1, and LxxLL→LxxAA mutations led to minimal transcription. Mechanistically, MED1 interacted ATRA-dependently with the RARα portion of PML-RARα through the two LxxLL motifs of MED1. These results suggest that PML-RARα initiates ATRA-induced transcription through its interaction with MED1.

miR-155 expression in antitumor immunity: The higher the better?

MicroRNAs are small noncoding RNAs that modulate gene expression either directly, by impairing the stability and/or translation of transcripts that contain their specific target sequence, or indirectly through the targeting of transcripts that encode transcription factors, factors implicated in signal transduction pathways, or epigenetic regulators. Abnormal expression of micro-RNAs has been found in nearly all types of pathologies, including cancers. MiR-155 has been the first microRNA to be implicated in the regulation of the innate and adaptative immune responses, and its expression is either increased or decreased in a variety of liquid and solid malignancies. In this review, we examine the oncogenic and antitumor potentials of miR-155, with special emphasize on its dose-dependent effects. We describe the impact of miR-155 levels on antitumor activity of lymphocytes and myeloid cells. We discuss miR-155 dose-dependent effects in leukemias and analyze results showing that miR-155 intermediate levels tend to be detrimental, whereas high levels of miR-155 expression usually prove beneficial. We also examine the beneficial effects of high levels of miR-155 expression in solid tumors. We discuss the possible causal involvement of miR-155 in leukemias and dementia in individuals with Down's syndrome. We finally propose that increasing miR-155 levels in immune cells might increase the efficiency of newly developed cancer immunotherapies, due to miR-155 ability to target transcripts encoding immune checkpoints such as cytotoxic T lymphocyte antigen-4 or programmed death-ligand 1.

MiR-15b regulates cell differentiation and survival by targeting CCNE1 in APL cell lines

MicroRNAs have been shown to be involved in various cell processes, including proliferation, apoptosis and differentiation. However, little is known about their function in granulopoiesis. In the present study, overexpression and knockdown experiments revealed that miR-15b was required to block the proliferation of NB4 and HL60 cells and induce them differentiated to granulocyte lineage. Moreover, we identified CCNE1 as a direct target of miR-15b, and demonstrated that CCNE1 was involved in cell differentiation and proliferation in acute promyelocytic leukemia cells. In addition, we demonstrated a novel pathway in which miR-15b regulated cells arrested in the G0/G1 phase and promoted terminal differentiation of cells by targeting CCNE1, which could modulate the cell cycle effort pRb in APL cells. These events blocked cell proliferation and promoted granulocyte differentiation. In conclusion, our data highlighted, for the first time, the important role of miR-15b in myeloid differentiation and suggested the potential role of miR-15b in cancer therapy.

Identification of a point mutation PMLS214L-RARα that alters PML body organization, dynamics and SUMOylation

Genetic mutations on PML-RARα in acute promyelocytic leukemia (APL) are reported to associate with arsenic trioxide (ATO) or all-trans retinoic acid (ATRA) resistance. Here we performed a retrospective analysis of APL patients and identified that the patient with S214L mutation on the PML moiety of PML-RARα showed resistance to both ATO and ATRA. Super-resolution microcopy was used to examine the structural response of PML bodies in wild-type or the S214L mutant cells upon drug treatment. Different protein density and fluidity were identified with the S214L mutant PML bodies by single particle quantification and FRAP analysis. We discovered that altered SUMOylation and ubiquitination might contribute to the drug resistance. Taken together, we have revealed that the S214L mutation on PML-RARα disrupted the organization of PML body and dynamics changes, perturbing structural responses to ATRA and subsequent oncoprotein degradation. Our findings shed new light on the structural alterations of PML bodies and mechanisms of APL drug resistance.

Mad1 destabilizes p53 by preventing PML from sequestering MDM2

Mitotic arrest deficient 1 (Mad1) plays a well-characterized role in the mitotic checkpoint. However, interphase roles of Mad1 that do not impact mitotic checkpoint function remain largely uncharacterized. Here we show that upregulation of Mad1, which is common in human breast cancer, prevents stress-induced stabilization of the tumor suppressor p53 in multiple cell types. Upregulated Mad1 localizes to ProMyelocytic Leukemia (PML) nuclear bodies in breast cancer and cultured cells. The C-terminus of Mad1 directly interacts with PML, and this interaction is enhanced by sumoylation. PML stabilizes p53 by sequestering MDM2, an E3 ubiquitin ligase that targets p53 for degradation, to the nucleolus. Upregulated Mad1 displaces MDM2 from PML, freeing it to ubiquitinate p53. Upregulation of Mad1 accelerates growth of orthotopic mammary tumors, which show decreased levels of p53 and its downstream effector p21. These results demonstrate an unexpected interphase role for Mad1 in tumor promotion via p53 destabilization.

Functional interactions between scaffold proteins, noncoding RNAs, and genome loci induce liquid-liquid phase separation as organizing principle for 3-dimensional nuclear architecture: implications in cancer

The eukaryotic cell nucleus consists of functionally specialized subcompartments. These nuclear subcompartments are biomolecular aggregates built of proteins, transcripts, and specific genome loci. The structure and function of each nuclear subcompartment are defined by the composition and dynamic interaction between these 3 components. The spatio-temporal localization of biochemical reactions into membraneless nuclear subcompartments can be achieved through liquid-liquid phase separation. Based on this organizing principle, nuclear subcompartments are droplet-like structures that adopt spherical shapes, flow, and fuse like liquids or gels. In the present review, we bring into the spotlight seminal works elucidating the functional interactions between scaffold proteins, noncoding RNAs, and genomic loci, thereby inducing liquid-liquid phase separation as an organizing principle for 3-dimensional nuclear architecture. We also discuss the implications in different cancer types as well as the potential use of this knowledge to develop novel therapeutic strategies against cancer.-Rubio, K., Dobersch, S., Barreto, G. Functional interactions between scaffold proteins, noncoding RNAs, and genome loci induce liquid-liquid phase separation as organizing principle for 3-dimensional nuclear architecture: implications in cancer.

PML/RARa blocks the differentiation and promotes the proliferation of acute promyelocytic leukemia through activating MYB expression by transcriptional and epigenetic regulation mechanisms

The promyelocytic leukemia (PML)/retinoic acid receptor-alpha (RARα) onco-fusion protein that is generated from t(15;17) chromosome translocation is crucial for the leukemogenesis of acute promyelocytic leukemia (APL) and is well documented as a transcriptional repressor. To understand the relationship between PML/RARα and the oncogene in the development of APL, we investigate the regulation mechanism of PML/RARα to MYB proto-oncogene and the role of this regulation on the proliferation and differentiation of APL cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assays show that MYB expression was significantly higher in PML/RARα positive cell lines. Microarray data verify that the MYB expression was significantly higher in APL patient samples than in normal promyelocyte samples. Further expression analysis from RT-qPCR and microarray data verifies that the expression of MYB is upregulated by PML/RARα. Transcriptional factor binding analysis shows that MYB is directly bound by PML/RARα and its cofactors. Luciferase assays show that PML/RARα transactivated MYB promoter activity through the RARα binding site and the coexistence of CCAAT enhancer binding protein ε. We also find that PML/RARα increases the acetylation level of the promoter region of MYB. Further evidence demonstrates that PML/RARα regulates MYB expression through long-range interaction. Functionally, PML/RARα increases the cell proliferation and blocks the differentiation through activating MYB expression. Collectively, this study uncovers a novel mechanism of PML/RARα-mediated transcriptional activation and enriches our knowledge of the onco-fusion protein-mediated transcription activation.

c-MYB and DMTF1 in Cancer

The c-Myb gene encodes a transcription factor that regulates cell proliferation, differentiation, and apoptosis through protein-protein interaction and transcriptional regulation of signaling pathways. The protein is frequently overexpressed in human leukemias, breast cancers, and other solid tumors suggesting that it is a bona fide oncogene. c-MYB is often overexpressed by translocation in human tumors with t(6;7)(q23;q34) resulting in c-MYB-TCRβ in T cell ALL, t(X;6)(p11;q23) with c-MYB-GATA1 in acute basophilic leukemia, and t(6;9)(q22-23;p23-24) with c-MYB-NF1B in adenoid cystic carcinoma. Antisense oligonucleotides to c-MYB were developed to purge bone marrow cells to eliminate tumor cells in leukemias. Recently, small molecules that inhibit c-MYB activity have been developed to disrupt its interaction with p300. The Dmp1 (cyclin D binding myb-like protein 1; Dmtf1) gene was isolated through its virtue for binding to cyclin D2. It is a transcription factor that has a Myb-like repeat for DNA binding. The Dmtf1 protein directly binds to the Arf promoter for transactivation and physically interacts with p53 to activate the p53 pathway. The gene is hemizygously deleted in 35-42% of human cancers and is associated with longer survival. The significances of aberrant expression of c-MYB and DMTF1 proteins in human cancers and their clinical significances are discussed.

miR-382-5p modulates the ATRA-induced differentiation of acute promyelocytic leukemia by targeting tumor suppressor PTEN

In acute promyelocytic leukemia (APL), all-trans retinoic acid (ATRA) treatment induces granulocytic differentiation and maturation. MicroRNAs play pivotal roles in formation of the leukemic phenotype. Previously, microRNA-382-5p (miR-382-5p) was upregulated in acute myeloid leukemia (AML) with t(15;17). In the present study, we found that miR-382-5p expression was elevated with ATRA-induced differentiation of APL. To investigate the potential functional role of miR-382-5p in APL differentiation, an APL cell line was transfected with miR-382-5p mimics, inhibitors, or negative control (NC). The results showed in APL cell line NB4 that miR-382-5p downregulation upon ATRA treatment was a key event in the drug response. Mechanistic investigations revealed that miR-382-5p targeted the ATRA-regulated tumor suppressor gene PTEN through direct binding to its 3' UTR. Enforced expression of miR-382-5p or specific PTEN inhibitors inhibited ATRA-induced granulocytic differentiation via regulation of the cell cycle regulator cyclinD1. Conversely, PTEN overexpression promoted differentiation and enhanced sensitivity of NB4 cell line to physiological levels of ATRA. Finally, we found that PTEN overexpression restored PML nuclear bodies (NBs). Taken together, these results demonstrated that up-regulated miR-382-5p in NB4 cell line inhibited granulocytic differentiation through the miR-382-5p/PTEN axis, uncovering PTEN as a critical element in the granulocytic differentiation program induced by ATRA in APL.

Expression of Human Cytomegalovirus IE1 Leads to Accumulation of Mono-SUMOylated PML That Is Protected from Degradation by Herpes Simplex Virus 1 ICP0

To countermeasure the host cellular intrinsic defense, cytomegalovirus (CMV) and herpes simplex viruses (HSV) have evolved the ability to disperse nuclear domain 10 (ND10, aka PML body). However, mechanisms underlying their action on ND10 differ. HSV infection produces ICP0, which degrades the ND10-forming protein PML. Human CMV (HCMV) infection expresses IE1 that deSUMOylates PML to result in dispersion of ND10. It has been demonstrated that HSV ICP0 degraded only the SUMOylated PML, so we hypothesized that HCMV IE1 can protect PML from degradation by ICP0. HCMV IE1-expressing cell lines (U-251 MG-IE1 and HELF-IE1) were used for infection of HSV-1 or transfection of ICP0-expressing plasmid. Multilabeling by immunocytochemistry assay and protein examination by Western blot assay were performed to determine the resultant fate of PML caused by ICP0 in the presence or absence of HCMV IE1. Here, we report that deSUMOylation of human PML (hPML) by HCMV IE1 was incomplete, as mono-SUMOylated PML remained in the IE1-expressing cells, which is consistent with the report by E. M. Schilling, M. Scherer, N. Reuter, J. Schweininger, et al. (J Virol 91:e02049-16, 2017, https://doi.org/10.1128/JVI.02049-16). As expected, we found that IE1 protected PML from degradation by ICP0 or HSV-1 infection. An in vitro study found that IE1 with mutation of L174P failed to deSUMOylate PML and did not protect PML from degradation by ICP0; hence, we conclude that the deSUMOylation of PML is important for IE1 to protect PML from degradation by ICP0. In addition, we revealed that murine CMV failed to deSUMOylate and to protect the HSV-mediated degradation of hPML, and that HCMV failed to deSUMOylate and protect the HSV-mediated degradation of mouse PML. However, IE1-expressing cells did not enhance wild-type HSV-1 replication but significantly increased ICP0-defective HSV-1 replication at a low multiplicity of infection. Therefore, our results uncovered a host-virus functional interaction at the posttranslational level.IMPORTANCE Our finding that HCMV IE1 protected hPML from degradation by HSV ICP0 is important, because the PML body (aka ND10) is believed to be the first line of host intrinsic defense against herpesviral infection. How the infected viruses overcome the nuclear defensive structure (PML body) has not been fully understood. Herpesviral proteins, ICP0 of HSV and IE1 of CMV, have been identified to interact with PML. Here, we report that HCMV IE1 incompletely deSUMOylated PML, resulting in the mono-SUMOylated PML, which is consistent with the report of Schilling et al. (J Virol 91:e02049-16, 2017, https://doi.org/10.1128/JVI.02049-16). The mono-SUMOylated PML was subjected to degradation by HSV ICP0. However, it was protected by IE1 from degradation by ICP0 or HSV-1 infection. In contrast, IE1 with L174P mutation lost the function of deSUMOylating PML and failed to protect the degradation of the mono-SUMOylated PML. Whether the mono-SUMOylated PML has any defensive function against viral infection will be further investigated.

Identification of the novel deletion-type PML-RARA mutation associated with the retinoic acid resistance in acute promyelocytic leukemia

All-trans retinoic acid (ATRA) and arsenic trioxide (ATO) are essential for acute promyelocytic leukemia (APL) treatment. It has been reported that mutations in PML-RARA confer resistance to ATRA and ATO, and are associated with poor prognosis. Although most PML-RARA mutations were point mutations, we identified a novel seven amino acid deletion mutation (p.K227_T233del) in the RARA region of PML-RARA in a refractory APL patient. Here, we analyzed the evolution of the mutated clone and demonstrated the resistance of the mutated clone to retinoic acid (RA). Mutation analysis of PML-RARA was performed using samples from a chemotherapy- and ATRA-resistant APL patient, and the frequencies of mutated PML-RARA transcript were analyzed by targeted deep sequencing. To clarify the biological significance of the identified PML-RARA mutations, we analyzed the ATRA-induced differentiation and PML nuclear body formation in mutant PML-RARA-transduced HL-60 cells. At molecular relapse, the p.K227_T233del deletion and the p.R217S point-mutation in the RARA region of PML-RARA were identified, and their frequencies increased after re-induction therapy with another type of retinoiec acid (RA), tamibarotene. In deletion PML-RARA-transduced cells, the CD11b expression levels and NBT reducing ability were significantly decreased compared with control cells and the formation of PML nuclear bodies was rarely observed after RA treatment. These results indicate that this deletion mutation was closely associated with the disease progression during RA treatment.

Detecting genome-wide directional effects of transcription factor binding on polygenic disease risk

Biological interpretation of genome-wide association study data frequently involves assessing whether SNPs linked to a biological process, for example, binding of a transcription factor, show unsigned enrichment for disease signal. However, signed annotations quantifying whether each SNP allele promotes or hinders the biological process can enable stronger statements about disease mechanism. We introduce a method, signed linkage disequilibrium profile regression, for detecting genome-wide directional effects of signed functional annotations on disease risk. We validate the method via simulations and application to molecular quantitative trait loci in blood, recovering known transcriptional regulators. We apply the method to expression quantitative trait loci in 48 Genotype-Tissue Expression tissues, identifying 651 transcription factor-tissue associations including 30 with robust evidence of tissue specificity. We apply the method to 46 diseases and complex traits (average n = 290 K), identifying 77 annotation-trait associations representing 12 independent transcription factor-trait associations, and characterize the underlying transcriptional programs using gene-set enrichment analyses. Our results implicate new causal disease genes and new disease mechanisms.

Regulation of PKCβ levels and autophagy by PML is essential for high-glucose-dependent mesenchymal stem cell adipogenesis

BACKGROUND/OBJECTIVES

Obesity is a complex disease characterized by the accumulation of excess body fat, which is caused by an increase in adipose cell size and number. The major source of adipocytes comes from mesenchymal stem cells (MSCs), although their roles in obesity remain unclear. An understanding of the mechanisms, regulation, and outcomes of adipogenesis is crucial for the development of new treatments for obesity-related diseases. Recently an unexpected role for the tumor suppressor promyelocytic leukemia protein (PML) in hematopoietic stem cell biology and metabolism regulation has come to light, but its role in MSC biology remains unknown. Here, we investigated the molecular pathway underlying the role of PML in the control of adipogenic MSC differentiation.

SUBJECTS/METHODS

Muscle-derived stem cells (MDSCs) and adipose-derived stem cells (ADSCs) obtained from mice and voluntary patients (as a source of MSCs) were cultured in the presence of high glucose (HG) concentration, a nutrient stress condition known to promote MSCs differentiation into mature adipocytes and the adipogenic potential of PML was assessed.

RESULTS

PML is essential for a correct HG-dependent adipogenic differentiation, and the enhancement of PML levels is fundamental during adipogenesis. Increased PML expression enables the upregulation of protein kinase Cβ (PKCβ), which, in turn, by controlling autophagy levels permits an increase in peroxisome proliferator-activated receptor γ (PPARγ) that leads the adipogenic differentiation. Therefore, genetic and pharmacological depletion of PML prevents PKCβ expression, and by increasing autophagy levels, impairs the MSCs adipogenic differentiation. Human ADSCs isolated from overweight patients displayed increased PML and PKCβ levels compared to those found in normal weight individuals, indicating that the PML-PKCβ pathway is directly involved in the enhancement of adipogenesis and human metabolism.

CONCLUSIONS

The new link found among PML, PKCβ, and autophagy opens new therapeutic avenues for diseases characterized by an imbalance in the MSCs differentiation process, such as metabolic syndromes and cancer.

Generation of In Vitro Model of Epithelial Mesenchymal Transition (EMT) Via the Expression of a Cytoplasmic Mutant Form of Promylocytic Leukemia Protein (PML)

Epithelial Mesenchymal Transition (EMT) is a key event in cancer progression. During this event, epithelial cancer cells undergo molecular and cellular changes leading to their trans-differentiation into mesenchymal cancer cells that are capable of migration, invasion, and metastasis to other tissues and organs. Here, we present a method for in vitro induction of EMT in prostate cancer cell lines using lentiviral expression of a PMLI isoform mutant construct.