bluuebunny/crossref_metadata_2025_split huggingface dataset:
TLR Activation By MSC Derived Extracellular Vesicles Drives Myeloid Commitment
Authors: Yoon Young Me , Goloviznina Natalya A , Butler John , Verghese Santhosh Chakkaramakkil , Kurre Peter 
Published: October 2019

Abstract
Hematopoietic stem and progenitor cells (HSPC) are responsive to paracrine signaling in the bone marrow microenvironment. We recently showed that leukemia derived extracellular vesicles (EVs) directly regulate HSPC in the leukemic niche and confer a net loss of progenitor function in part through direct action of a highly abundant miRNA on the hematopoietic transcription factor c-Myb. These observations motivated us to explore the potential regulation of HSPC by EVs present during steady state hematopoiesis in the unperturbed bone marrow. Mesenchymal stromal cells (MSC) comprise a diverse set of cells secreting supportive factors central to the maintenance of HSPC. We systematically characterized EVs released by murine MSCs as a candidate population and demonstrated that EVs themselves carry cytokines, predominantly interleukin (IL) -1, -2, -4,-6 and -17A, as well as G-CSF and Interferon g. As a functional corollary, we found that MSC EVs led to preferential granulocyte and monocyte differentiation in co-culture with C-kit enriched HSPCs, when compared to vesicle free condition (termed S100). These observations were further supported by the expansion of KSL (c-kit+,Sca-1+,lin-) and MPP2-4 (CD48+, CD150+/-) progenitor populations. To determine the in vivo relevance of these findings we performed a series of competitive transplantation experiments, that demonstrated that MSC-EV exposed HSPCs outperformed HSPCs cultured with EV depleted media, with striking advantage in early, but a significant deficit in later (week 16) myeloid recovery, compared to the S100 condition. These observations were broadly consistent with recent evidence for HSPC regulation by toll like receptors (TLRs) and we confirmed that the observed deficit in progenitor phenotypes was partially reversed in MSC-EV co-cultures with HSPCs from animals with genetic disruption of TLR4 or MyD88. EV-TLR engagement further induced a NF-kB response with downstream transcriptional activation of canonical transcriptional targets (STAT1, IRF1, -9) and significantly upregulated the release of IL-3, -6, IFNg, and G-CSF in exposed WT HSPC, compared with S100. Finally, we performed deconvolution microscopy studies of co-cultured HSPC and demonstrated the Pearson's spatial correlation between fluorescently tagged MSC-EV and TLR4 as well as the early and late endosomal marker proteins, Rab5 and Rab7, respectively. We conclude that MSC-derived EV trafficking of TLR contributes to the homeostatic regulation of HSPCs in the bone marrow microenvironment as a mechanism of tonic regulation of hematopoiesis.

Disclosures
No relevant conflicts of interest to declare.
SF3B1 Interactions with Chromatin Are Dynamic and Regulated in a Cell Cycle-Dependent Manner
Authors: Murthy Tushar , Bluemn Theresa , Pillai Manoj M. , Minella Alex C 
Published: October 2019

Abstract
Splicing factor 3B1 (SF3B1) is a member of the U2 snRNP complex that is a key regulator of RNA splicing. RNA splicing begins with the recognition of splice sites (ss) at the 5' and 3' ends of introns and ends with the removal of introns and joining of exons flanking them. SF3B1 plays an important role in this process by facilitating the recognition of the 3'ss. SF3B1 is frequently mutated in numerous cancers as well as the myelodysplastic syndromes (MDS). Mutations within the HEAT domain of the protein potentially contribute to disease pathogenesis. In addition to influencing splicing by binding to pre-mRNA, SF3B1 has been shown to affect splicing of exons by associating with them directly on chromatin via histone/nucleosome interactions. However, it is not understood if or how SF3B1 association with chromatin is regulated. Given that N-terminal serine and threonine residues on SF3B1 are known substrates of cyclin E-Cdk2, which phosphorylates histone subunits and other chromatin associated proteins, we hypothesized that CDK2 activity regulates SF3B1-nucleosome interactions. Although SF3B1 is phosphorylated during splicing catalysis, the function of this phosphorylation has remained unknown. We have now discovered, using nucleosome preparations and histone subunit co-immunoprecipitation assays in synchronized cells, that endogenous SF3B1 interacts with nucleosomes in a highly cell-cycle dependent manner, while total cellular abundance of SF3B1 remains invariant during cell cycle progression. In human and mouse cells, including hematopoietic cell lines, SF3B1 is excluded from chromatin during both G0 (quiescence) and G2/M phases of cell cycle. Notably, SF3B1 is enriched within chromatin maximally during S-phase. Unexpectedly, we found that the inhibition of Cdc2 (Cdk1) during G2/M enforces the SF3B1-chromatin interaction, pointing to a direct role for Cdc2 in restraining this interaction during mitosis. Further, SF3B1 loading onto chromatin during early cell cycle progression from G0 to S-phase is inhibited by Cdk2 inhibition. Thus, Cdk2 and Cdc2 appear to have antagonistic roles in controlling SF3B1-chromatin interactions during the cell cycle. Our findings suggest that Cdk activity may regulate the recruitment of the spliceosome machinery in order to coordinate splicing of particular transcripts with cell cycle progression. Current studies are focusing on how disease-associated mutations in the HEAT domain of SF3B1 affect the dynamics of its cell cycle-dependent interaction with nucleosomes and corresponding alterations to splicing outcomes.

Disclosures
No relevant conflicts of interest to declare.
TAFII250 Is Critical in AML1-ETO Mediated Leukemogenesis
Authors: Xu Ye , Man Na , Martinez Concepcion , Martinez Camilo , Beckedorf Felipe , Cheng Guoyan , Greenblatt Sarah Merin , Wang Lan , Shiekhattar Ramin , Nimer Stephen D. 
Published: October 2019

Abstract
Background: Rearrangement between chromosome 8 and 21 is the most frequently observed chromosomal translocation. In AML patients, it leads to the formation of a novel fusion protein AML1-ETO. AML1-ETO functions as a transcriptional regulator to suppress myeloid differentiation and to promote self-renewal of hematopoiesis stem cells, which are of importance in leukemia development. However, AML1-ETO has no enzymatic function, thus targeting AML1-ETO directly is technically difficult. TAFII250, a largest subunit of the transcription factor IID complex (TFIID) serves to bring other components of basal transcription machinery to the preinitiation complex during the transcription initiation. And TAFII250 also plays a crucial role in the expression of genes involved in cell cycle and apoptosis. Yet despite the importance of these processes, there is no direct evidence implicating TAFII250 in cancer development. We have reported that acetylation of AML1-ETO on lysine 43 is critical for AML1-ETO mediated leukemogenesis and used a peptide pulldown strategy to identify proteins that preferring interact with acetylated AML1-ETO and identified TAFII250. Here, we are going to report the functions of TAFII250 in AML1-ETO induced leukemogenesis.
Methods: We used Kasumi-1 and SKNO-1 cell lines derived from t(8; 21)AML patients, and a mouse AML1-ETO exon 9a (AE9a) expressing cell line developed from bone marrow cells of mice injected with bone marrow cells infected with AE9a to perform in vitro and in vivo studies.
Results: We demonstrate that TAFII250 associates with AML1-ETO in AML cells through its bromodomain recognizing acetylated lysine 43 on AML1-ETO. The knockdown of TAFII250 completely abolished the proliferation of AML1-ETO expressing cells and has little influence on cell growth of non AML1-ETO expressing cells K562 and CD34+ cells. In addition, when we examined cleaved caspase 3 and PARP by western and measured annexin-V through flow cytometry, we found that the deficiency of TAFII250 induces apoptosis in AML1-ETO expressing cells. Further, the co-immunoprecipitation assay revealed that the deficiency of TAFII250 blocks the binding of AML1-ETO to CBFb (core binding factor beta subunit) and the recruitment of AML1-ETO at the promoter regions of a subset of its target genes. Consequently, loss of TAFII250 interferes with the expression of these genes. The depletion of TAFII250 also has negative effect on the self-renewal of leukemic cells, promoting their differentiation. Most importantly, the loss of TAFII250 severely impairs leukemia development in AE9a expressing cells.
Conclusions: Together, these results reveal an essential role of TAFII250 in AML1-ETO mediated leukemogenesis and imply that TAFII250 might be a therapeutic target for AML1-ETO expressing AMLs.

Disclosures
No relevant conflicts of interest to declare.
Tyrosine 842 Residue in the Activation Loop of FLT3-ITD Is Indespensible for Oncogenic Transformation
Authors: Kazi Julhash U. , Rönnstrand Lars 
Published: October 2019

Abstract
The receptor tyrosine kinase FLT3 is mutated in around 30% of acute myeloid leukemia patients. The so-called internal tandem duplication (ITD) mutation in the juxtamembrane domain is the most common type of mutation in FLT3. Other oncogenic mutations include point mutations in the kinase domain. One of the hallmark of receptor activation is phosphorylation on several tyrosine residues in the receptor. Oncogenic FLT3 mutants display constitutive activity leading to aberrant cell proliferation and survival. Phosphorylation on several critical tyrosine residues is known to be essential for FLT3 signaling. The tyrosine residue Y842, which is located in the activation loop of FLT3, and is well conserved in all receptor tyrosine kinases. It has been demonstrated that tyrosine phosphorylation of the activation loop is essential for the activity of some but not all receptor tyrosine kinases. In this report we show that phosphorylation on Y842 residue is dispensable for receptor activity and stability. However, Y842 plays critical roles in oncogenic FLT3-ITD mediated transformation. We have shown that a Y-to-F mutation (Y842F) results in reduced cell viability and proliferation. This mutation also led to dramatic decrease in in vitro colony formation in semi-solid medium. Furthermore, cells carrying the Y842F mutant of FLT3-ITD displayed significant delay in tumor formation in nude mice. Gene expression analysis, using microarrays, showed that mutation of Y842 causes suppression of anti-apoptotic genes. Finally, we showed that phosphorylated Y842 is a binding site for SHP2 and mutation of this site results in impaired activation of signaling through the RAS/ERK pathway. Collectively, our data suggest that Y842 in FLT3 plays an important role in FLT3-mediated RAS/ERK signaling and cellular transformation.

Disclosures
No relevant conflicts of interest to declare.
Clinical Features and Outcomes of Isolated Myeloid Sarcoma in the United States: Analysis Using a National Dataset
Authors: Goyal Gaurav , Bartley Adam C , Al-Kali Aref , Hogan William J , Litzow Mark , Go Ronald S. 
Published: October 2019

Abstract
Introduction
Isolated myeloid sarcoma is a rare form (<1%) of acute myeloid leukemia presenting as extramedullary tumor. Contemporary clinical data are mostly limited to institutional case series. Using the National Cancer Database, the largest public cancer registry covering >70% of all newly diagnosed cancers in the United States, we determined the patterns of anatomical presentation and clinical outcome of myeloid sarcoma.
Methods
We identified patients with a histologically confirmed diagnosis of isolated myeloid sarcoma from 2004-2013 using International Classification of Diseases for Oncology version 3 (ICD-O-3) code: 9930. To allow at least 1 year of follow-up, only patients diagnosed from 2004-2012 were included in the survival analysis using Kaplan-Meier estimates.
Results
A total of 746 patients were included in the study. The median age of patients was 59 years (range, 41 to 73) and 56% were males. The anatomical distribution and median overall survival of patients are depicted in the Table. The top 3 most common sites of presentation were connective/soft tissues (31.3%), skin/breast (12.3%), and digestive system (10.3%). Compared to other races, Blacks were more likely to have presentation in bones/joints (11.8% vs 6.3% in others), lymph nodes/spleen (22.1% vs. 9%), and less likely in skin/breast (4.4% vs. 13.8%). Asians were more likely to present with cardiopulmonary/mediastinal disease as compared to other races (13.6% vs. 4.2%). According to outcomes, we can categorize the patients into 3 groups: good (median overall survival >30 months: reproductive and digestive systems), intermediate (median overall survival 15-30 months: head/neck and kidney/bladder/retroperitoneum/adrenal), and poor (median overall survival <15 months: nervous system, connective/soft tissue, and bones/joints). There was no significant difference in overall survival between males and females (P =0.06). Among the races, Blacks had the worst overall survival (P =0.02; Figure).
Conclusions
This is the largest registry-based study on isolated myeloid sarcoma in the United States. Isolated myeloid sarcoma has a diverse anatomic clinical presentation and the overall survival varied significantly according to sites of presentation and racial subgroups. The results of our study may aid the prognostication of patients for treatment decision making and in the understanding of the biological differences by anatomic sites of presentation.
Table Anatomical distribution and median overall survival of isolated myeloid sarcoma Table. Anatomical distribution and median overall survival of isolated myeloid sarcoma Figure Overall survival by sex and race in isolated myeloid sarcoma Figure. Overall survival by sex and race in isolated myeloid sarcoma

Disclosures
Al-Kali: Onconova Therapeutics, Inc.: Research Funding; Celgene: Research Funding.
Genome-Wide Genotype-Based Risk Model for Survival in Core Binding Factor Acute Myeloid Leukemia Patients
Authors: Park Silvia , Hangseok Choi , Kim Hee-Je , Ahn Jae-Sook , Kim Hyeoung Joon , Kim Sung-Hyun , Mun Yeung-Chul , Jung Chul Won , Kim Dong Hwan 
Published: October 2019

Abstract
Introduction: The present study attempted to build a single nucleotide polymorphism (SNP)-based risk model for predicting overall survival (OS) and event free survival (EFS) in patients with core binding factor acute myeloid leukemia (CBF-AML).
Methods: Adopting genome-wide SNP array using Affymetrix SNP array 6.0, we analyzed 868,157 SNPs with respect to OS and EFS in 104 patients with CBF-AML. Significant SNPs were identified from single SNP analysis. The risk model was constructed with incorporation of six SNPs and three clinical factors (age, c-kit exon 17 mutation, and LDH) for OS, and six SNPs and three clinical factors (age, WBC, and LDH) for EFS. The model was further defined into low and high risk groups based on risk scores.
Results: The median age was 39 years, and the subgroup of t(8;21) and inv(16) or t(16;16) was assessed in 68 (65.4%) and 36 patients (34.6%). Finally 6 SNPs per each OS (rs4353685, rs4908185, rs7709207, rs12034, rs1554844, and rs17241868) and EFS (rs13385610, rs11210617, rs11169282, rs7709207, rs4438401 and rs16894846) were incorporated into the risk model. OS was significantly different in favor of the low risk group (80.4%) compared to the high risk group (22.0% at 3 years; p= 8.75 x 10-13; HR 8.67). For EFS, there was also a significant difference between the low (75.0%) versus high risk group (17.1% at 3 years; p=5.95 x 10-13; HR 7.67).
Conclusion: A genome-wide SNP based risk model can stratify CBF-AML patients according to their OS and EFS in 104 patients.
Figure 1 Overall survival and event free survival by risk model composed of SNPs and clinical risk factors Figure 1. Overall survival and event free survival by risk model composed of SNPs and clinical risk factors Figure 2 Figure 2.

Disclosures
No relevant conflicts of interest to declare.
The Macrophage-Specific CD163 Is an Endocytic Receptor for Von Willebrand Factor (VWF) Cleaving Protease ADAMTS13
Authors: Verbij Fabian , Sorvillo Nicoletta , Kaijen Paul , Hrdinova Johana , Fijnheer Rob , ten Brinke Anja , Meijer Alexander B. , van Alphen Floris P. , van der Berg Timo K. , Graversen Jonas H. , Moestrup Soren K. , Voorberg Jan 
Published: October 2019

Abstract
Von Willebrand Factor (VWF) cleaving protease ADAMTS13 is responsible for proteolysis of ultra large VWF multimers in the circulation. ADAMTS13 is synthesized by hepatic stellate cells in the liver. Also endothelial cells have been suggested to contribute to the synthesis of ADAMTS13. In patients with acquired thrombotic thrombocytopenic purpura auto-reactive antibodies are formed primarily against the spacer domain of ADAMTS13. Previously we have shown that monocyte-derived dendritic cells were able to endocytose ADAMTS13 via the macrophage mannose receptor and subsequently process it into peptides and present it on MHC class II. However, it is currently unclear which receptor contributes to the clearance of ADAMTS13 from the circulation. The half-life of ADAMTS13 was measured following plasma infusion in patients with congenital TTP and was found to vary between 2.1 and 3.3 days.
Internalization of ADAMTS13 by tissue-resident macrophages may contribute to its clearance from the circulation. Here we investigated endocytic mechanisms contributing to the uptake of ADAMTS13 by macrophages. Human monocyte-derived macrophages (MDMs) were used to monitor the uptake of fluorescently labelled recombinant ADAMTS13 by flow cytometry. Internalization of ADAMTS13 was blocked upon addition of the cell-permeable dynamin-inhibitor dynasore. Partial blockage of ADAMTS13 internalization was observed employing mannan; uptake however was not affected by a blocking antibody directed towards the macrophage mannose receptor CD206. A pull-down with ADAMTS13 and subsequent mass spectrometric analysis identified the hemoglobin scavenger receptor CD163 as a candidate receptor for ADAMTS13. CD163 is primarily expressed by the monocyte-macrophage lineage and is highly expressed on type-2 macrophages present in the bone marrow, the red pulp of the spleen and in the liver on Kupffer cells. Blocking experiments with a monoclonal anti-CD163 antibody EDHu-1 resulted in a decreased ADAMTS13 internalization by macrophages. Pronounced inhibition of ADAMTS13 uptake by EDHu-1 was observed in macrophages in which the expression of CD163 was boosted upon incubation with IL-10. In agreement with these findings CD163-expressing CHO cells but not CHO CD163-/- cells were capable of rapidly internalizing ADAMTS13. Surface plasmon resonance revealed high affinity binding of ADAMTS13 to soluble CD163 containing scavenger receptor cysteine-rich (SRCR) domain 1-9. Our results position CD163 as a novel binding partner for ADAMTS13 and suggest that binding of ADAMTS13 to CD163 promotes its internalization by macrophages.

Disclosures
No relevant conflicts of interest to declare.
Cyclin D2 Overexpression Recapitulates Mantle Cell Lymphoma in Mice
Authors: Pieters Tim , Goossens Steven , T'Sas Sara , Berx Geert , Haigh Jody J. , Vlierberghe Pieter Van 
Published: October 2019

Abstract
Mantle cell lymphoma (MCL) is a highly aggressive subtype of B-cell lymphoma that is characterized by a poor response to current treatment regimens. Most MCLs carry a prototypical translocation, t(11;14), which juxtaposes the CCND1 gene towards the immunoglobulin heavy chain (IGH) locus, resulting in cyclin D1 overexpression. Strikingly, MCL has not been recapitulated in transgenic mouse models of Ccnd1 overexpression alone. Notably, a subset of MCL patients are cyclin D1 negative but instead overexpress cyclin D2 (encoded by CCND2)as a consequence of recurrent genomic rearrangements involving the CCND2 locus.
Here, we developed a novel conditional ROSA26-driven Ccnd2 overexpression mouse model and showed that hematopoietic-specific Ccnd2 activation is sufficient to drive MCL formation in mice. Starting from 36 weeks, these mice develop huge B-cell lymphomas and these tumor cells have the typical MCL morphology, are Sox11 positive and disseminate into other organs, all typical features of MCL. In addition, preliminary shallow sequencing analysis revealed a somatic Crlf2 deletion as a cooperative genetic event in one of the murine Ccnd2-driven MCL tumors.
In this study, we want to further validate and characterize this novel Ccnd2-driven mouse model for MCL and test putative synergisms between Ccnd2 overexpression and other recurrent cooperating genetic lesions that occur in human MCL, such as loss of p53 or SOX11 activation. Noteworthy, the MCL cells from this mouse model also contain a luciferase reporter, allowing accurate in vivo tracing of tumor cells in xenograft experiments. These xenograft experiments can be used as preclinical models, in which bioluminescence is used to asses the tumor burden and to monitor tumor regression upon drug treatment. In conclusion, we have developed a novel mouse model in which Ccnd2 overexpression faithfully recapitulates MCL and this model will allow us to understand the molecular mechanisms that drive MCL and identify and test novel drugs to treat this aggressive and until now incurable disease.

Disclosures
No relevant conflicts of interest to declare.