Cell. 2017:170(6):1079-1095.e20.DOI: 10.1016/j.cell.2017.07.032

Restoration of TET2 Function Blocks Aberrant Self-Renewal and Leukemia Progression

Cimmino, Luisa; Dolgalev, Igor; Wang, Yubao; Yoshimi, Akihide; Martin, Gaelle H; Wang, Jingjing; Ng, Victor; Xia, Bo; Witkowski, Matthew T; Mitchell-Flack, Marisa; Grillo, Isabella; Bakogianni, Sofia; Ndiaye-Lobry, Delphine; Martin, Miguel Torres; Guillamot, Maria; Banh, Robert S; Xu, Mingjiang; Figueroa, Maria E; Dickins, Ross A; Abdel-Wahab, Omar; Park, Christopher Y; Tsirigos, Aristotelis; Neel, Benjamin G; Aifantis, Iannis

Loss-of-function mutations in TET2 occur frequently in patients with clonal hematopoiesis, myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML) and are associated with a DNA hypermethylation phenotype. To determine the role of TET2 deficiency in leukemia stem cell maintenance, we generated a reversible transgenic RNAi mouse to model restoration of endogenous Tet2 expression. Tet2 restoration reverses aberrant hematopoietic stem and progenitor cell (HSPC) self-renewal in vitro and in vivo. Treatment with vitamin C, a co-factor of Fe2+ and alpha-KG-dependent dioxygenases, mimics TET2 restoration by enhancing 5-hydroxymethylcytosine formation in Tet2-deficient mouse HSPCs and suppresses human leukemic colony formation and leukemia progression of primary human leukemia PDXs. Vitamin C also drives DNA hypomethylation and expression of a TET2-dependent gene signature in human leukemia cell lines. Furthermore, TET-mediated DNA oxidation induced by vitamin C treatment in leukemia cells enhances their sensitivity to PARP inhibition and could provide a safe and effective combination strategy to selectively target TET deficiency in cancer.

PMID: 28823558
ISSN: 1097-4172 

Journal of experimental medicine. 2017.DOI: 10.1084/jem.20161595

miR-99 regulates normal and malignant hematopoietic stem cell self-renewal

Khalaj, Mona; Woolthuis, Carolien M; Hu, Wenhuo; Durham, Benjamin H; Chu, S Haihua; Qamar, Sarah; Armstrong, Scott A; Park, Christopher Y

The microRNA-99 (miR-99) family comprises a group of broadly conserved microRNAs that are highly expressed in hematopoietic stem cells (HSCs) and acute myeloid leukemia stem cells (LSCs) compared with their differentiated progeny. Herein, we show that miR-99 regulates self-renewal in both HSCs and LSCs. miR-99 maintains HSC long-term reconstitution activity by inhibiting differentiation and cell cycle entry. Moreover, miR-99 inhibition induced LSC differentiation and depletion in an MLL-AF9-driven mouse model of AML, leading to reduction in leukemia-initiating activity and improved survival in secondary transplants. Confirming miR-99's role in established AML, miR-99 inhibition induced primary AML patient blasts to undergo differentiation. A forward genetic shRNA library screen revealed Hoxa1 as a critical mediator of miR-99 function in HSC maintenance, and this observation was independently confirmed in both HSCs and LSCs. Together, these studies demonstrate the importance of noncoding RNAs in the regulation of HSC and LSC function and identify miR-99 as a critical regulator of stem cell self-renewal.

PMID: 28733386
ISSN: 1540-9538 

Nature cell biology. 2017:19(7):758-760.DOI: 10.1038/ncb3566

snoRNAs contribute to myeloid leukaemogenesis

Khalaj, Mona; Park, Christopher Y

The mechanism of action of oncogenes in acute myeloid leukaemia is poorly understood. A study now shows that the fusion oncoprotein AML1-ETO regulates leukaemogenesis by increasing the expression of small nucleolar RNAs through post-transcriptional mechanisms, resulting in increased ribosomal RNA methylation, protein translation, and promotion of leukaemic-cell self-renewal and growth.

PMID: 28659642
ISSN: 1476-4679 

Blood. 2017:129(25):3279-3280.DOI: 10.1182/blood-2017-05-780007

EPCR: a novel marker of cultured cord blood HSCs

Martin, Gaelle H; Park, Christopher Y

PMID: 28642358
ISSN: 1528-0020 

Blood. 2017:130(2):176-180.DOI: 10.1182/blood-2016-12-757377

Functional evidence for derivation of systemic histiocytic neoplasms from hematopoietic stem/progenitor cells

Durham, Benjamin H; Roos-Weil, Damien; Baillou, Claude; Cohen-Aubart, Fleur; Yoshimi, Akihide; Miyara, Makoto; Papo, Matthias; Helias-Rodzewicz, Zofia; Terrones, Nathalie; Ozkaya, Neval; Dogan, Ahmet; Rampal, Raajit; Urbain, Fanny; Le Fevre, Lucie; Diamond, Eli L; Park, Christopher Y; Papo, Thomas; Charlotte, Frederic; Gorochov, Guy; Taly, Valerie; Bernard, Olivier A; Amoura, Zahir; Abdel-Wahab, Omar; Lemoine, Francois M; Haroche, Julien; Emile, Jean-Francois

Langerhans Cell Histiocytosis (LCH) and the non-LCH neoplasm Erdheim-Chester Disease (ECD) are heterogeneous neoplastic disorders marked by infiltration of pathologic macrophage-, dendritic cell-, or monocyte-derived cells in tissues driven by recurrent mutations activating MAP kinase signaling. Although recent data indicate that at least a proportion of LCH and ECD patients have detectable activating kinase mutations in circulating hematopoietic cells and bone marrow-based hematopoietic progenitors, functional evidence of the cell-of-origin of histiocytosis from actual patient materials has long been elusive. Here we provide evidence for mutations in MAP kinase signaling intermediates in CD34+ cells from patients with ECD and LCH/ECD, including detection of shared origin of LCH and acute myelomonocytic leukemia driven by TET2-mutant CD34+ cell progenitors in one patient. We also demonstrate functional self-renewal capacity for CD34+ cells to drive the development of histiocytosis in xenotransplantation assays in vivo. These data indicate that the cell-of-origin of at least a proportion of patients with systemic histiocytoses resides in hematopoietic progenitor cells prior to committed monocyte/macrophage or dendritic cell differentiation and provide the first example of a patient-derived xenotransplantation model for a human histiocytic neoplasm.

PMID: 28566492
ISSN: 1528-0020 

Science translational medicine. 2017:9(374).DOI: 10.1126/scitranslmed.aaj2025

CD99 is a therapeutic target on disease stem cells in myeloid malignancies

Chung, Stephen S; Eng, William S; Hu, Wenhuo; Khalaj, Mona; Garrett-Bakelman, Francine E; Tavakkoli, Montreh; Levine, Ross L; Carroll, Martin; Klimek, Virginia M; Melnick, Ari M; Park, Christopher Y

Acute myeloid leukemia (AML) and the myelodysplastic syndromes (MDS) are initiated and sustained by self-renewing malignant stem cells; thus, eradication of AML and MDS stem cells is required for cure. We identified CD99 as a cell surface protein frequently overexpressed on AML and MDS stem cells. Expression of CD99 allows for prospective separation of leukemic stem cells (LSCs) from functionally normal hematopoietic stem cells in AML, and high CD99 expression on AML blasts enriches for functional LSCs as demonstrated by limiting dilution xenotransplant studies. Monoclonal antibodies (mAbs) targeting CD99 induce the death of AML and MDS cells in a SARC family kinase-dependent manner in the absence of immune effector cells or complement, and anti-CD99 mAbs exhibit antileukemic activity in AML xenografts. These data establish CD99 as a marker of AML and MDS stem cells, as well as a promising therapeutic target in these disorders.

PMID: 28123069
ISSN: 1946-6242 

Seminars in hematology. 2017:54(1):1-3.DOI: 10.1053/j.seminhematol.2016.10.007

Hematopoiesis in aging: Current concepts and challenges [Editorial]

Park, Christopher Y

PMID: 28088981
ISSN: 1532-8686 

Seminars in hematology. 2017:54(1):4-11.DOI: 10.1053/j.seminhematol.2016.11.002

Molecular mechanisms underlying lineage bias in aging hematopoiesis

Elias, Harold K; Bryder, David; Park, Christopher Y

Although hematopoietic stem cells (HSCs) have traditionally been thought to possess the ability to give rise to all the mature cell types in the hematopoietic system, this conception of hematopoiesis was based on evaluation of hematopoietic output from large numbers of HSCs using transplantation models. More recent studies evaluating HSCs at the clonal or near-clonal level, both in transplantation studies and during in situ hematopoiesis, have established that individual HSCs can exhibit lineage bias, giving rise to myeloid-biased, lymphoid-biased, or more balanced differentiation, with the proportion of myeloid-biased HSCs increasing with age. This age-associated shift in lineage potential is associated with decreased cellular immunity and increased incidence of diseases with prominent inflammatory components including atherosclerosis, autoimmunity, neurodegenerative disease, and carcinogenesis. Understanding the molecular mechanisms that regulate this shift in linage bias therefore represents an important area of investigation in numerous human diseases. In this review, we summarize our current understanding of the cell-intrinsic (autonomous) and cell-extrinsic factors that regulate HSC lineage fate bias during aging. In addition, we have attempted to bring attention to important caveats and unanswered questions related to the issue of HSC lineage bias to encourage explorations of these important lines of inquiry. Ultimately, we expect a comprehensive understanding of HSC lineage bias during aging to have important implications for human health, since strategies to alter lineage bias in old HSCs not only has the potential to restore immune function in the elderly, but also to reduce the incidence of inflammation-associated diseases, many for which there is a current unmet need for novel and more effective treatments.

PMID: 28088987
ISSN: 1532-8686 

Blood. 2016:127(19):2268-2269.DOI: 10.1182/blood-2016-03-704338

Context matters in MLL-AF9-driven leukemias

Park, Christopher Y

PMID: 27206664
ISSN: 1528-0020 

Blood. 2016:127(10):1242-1248.DOI: 10.1182/blood-2015-07-607945

Hematopoietic stem/progenitor cell commitment to the megakaryocyte lineage

Woolthuis, Carolien M; Park, Christopher Y

The classical model of hematopoiesis has long held that hematopoietic stem cells (HSCs) sit at the apex of a developmental hierarchy in which HSCs undergo long-term self-renewal while giving rise to cells of all the blood lineages. In this model, self-renewing HSCs progressively lose the capacity for self-renewal as they transit into short-term self-renewing and multipotent progenitor states, with the first major lineage commitment occurring in multipotent progenitors, thus giving rise to progenitors that initiate the myeloid and lymphoid branches of hematopoiesis. Subsequently, within the myeloid lineage, bipotent megakaryocyte-erythrocyte and granulocyte-macrophage progenitors give rise to unipotent progenitors that ultimately give rise to all mature progeny. However, over the past several years, this developmental scheme has been challenged, with the origin of megakaryocyte precursors being one of the most debated subjects. Recent studies have suggested that megakaryocytes can be generated from multiple pathways and that some differentiation pathways do not require transit through a requisite multipotent or bipotent megakaryocyte-erythrocyte progenitor stage. Indeed, some investigators have argued that HSCs contain a subset of cells with biased megakaryocyte potential, with megakaryocytes directly arising from HSCs under steady-state and stress conditions. In this review, we discuss the evidence supporting these nonclassical megakaryocytic differentiation pathways and consider their relative strengths and weaknesses as well as the technical limitations and potential pitfalls in interpreting these studies. Ultimately, such pitfalls will need to be overcome to provide a comprehensive and definitive understanding of megakaryopoiesis.

PMID: 26787736
ISSN: 1528-0020

eLife. 2016:5.DOI: 10.7554/eLife.10421

Regulatory consequences of neuronal ELAV-like protein binding to coding and non-coding RNAs in human brain

Scheckel, Claudia; Drapeau, Elodie; Frias, Maria A; Park, Christopher Y; Fak, John; Zucker-Scharff, Ilana; Kou, Yan; Haroutunian, Vahram; Ma'ayan, Avi; Buxbaum, Joseph D; Darnell, Robert B

Neuronal ELAV-like (nELAVL) RNA binding proteins have been linked to numerous neurological disorders. We performed crosslinking-immunoprecipitation and RNAseq on human brain, and identified nELAVL binding sites on 8681 transcripts. Using knockout mice and RNAi in human neuroblastoma cells, we showed that nELAVL intronic and 3' UTR binding regulates human RNA splicing and abundance. We validated hundreds of nELAVL targets among which were important neuronal and disease-associated transcripts, including Alzheimer's disease (AD) transcripts. We therefore investigated RNA regulation in AD brain, and observed differential splicing of 150 transcripts, which in some cases correlated with differential nELAVL binding. Unexpectedly, the most significant change of nELAVL binding was evident on non-coding Y RNAs. nELAVL/Y RNA complexes were specifically remodeled in AD and after acute UV stress in neuroblastoma cells. We propose that the increased nELAVL/Y RNA association during stress may lead to nELAVL sequestration, redistribution of nELAVL target binding, and altered neuronal RNA splicing.

PMID: 26894958
ISSN: 2050-084x 

Cancer discovery. 2016:6(2):154-165.DOI: 10.1158/2159-8290.CD-15-0913

Diverse and Targetable Kinase Alterations Drive Histiocytic Neoplasms

Diamond, Eli L; Durham, Benjamin H; Haroche, Julien; Yao, Zhan; Ma, Jing; Parikh, Sameer A; Wang, Zhaoming; Choi, John; Kim, Eunhee; Cohen-Aubart, Fleur; Lee, Stanley Chun-Wei; Gao, Yijun; Micol, Jean-Baptiste; Campbell, Patrick; Walsh, Michael P; Sylvester, Brooke; Dolgalev, Igor; Aminova, Olga; Heguy, Adriana; Zappile, Paul; Nakitandwe, Joy; Ganzel, Chezi; Dalton, James D; Ellison, David W; Estrada-Veras, Juvianee; Lacouture, Mario; Gahl, William A; Stephens, Philip J; Miller, Vincent A; Ross, Jeffrey S; Ali, Siraj M; Briggs, Samuel R; Fasan, Omotayo; Block, Jared; Heritier, Sebastien; Donadieu, Jean; Solit, David B; Hyman, David M; Baselga, Jose; Janku, Filip; Taylor, Barry S; Park, Christopher Y; Amoura, Zahir; Dogan, Ahmet; Emile, Jean-Francois; Rosen, Neal; Gruber, Tanja A; Abdel-Wahab, Omar

Histiocytic neoplasms are clonal, hematopoietic disorders characterized by an accumulation of abnormal, monocyte-derived dendritic cells or macrophages in Langerhans Cell (LCH) and non-Langerhans (non-LCH) histiocytoses, respectively. The discovery of BRAFV600E mutations in ~50% of these patients provided the first molecular therapeutic target in histiocytosis. However, recurrent driving mutations in the majority of BRAFV600E-wildtype, non-LCH patients are unknown, and recurrent cooperating mutations in non-MAP kinase pathways are undefined for the histiocytic neoplasms. Through combined whole exome and transcriptome sequencing, we identified recurrent kinase fusions involving BRAF, ALK, and NTRK1, as well as recurrent, activating MAP2K1 and ARAF mutations in BRAFV600E-wildtype, non-LCH patients. In addition to MAP kinase pathway lesions, recurrently altered genes involving diverse cellular pathways were identified. Treatment of MAP2K1- and ARAF-mutated, non-LCH patients using MEK and RAF inhibitors, respectively, resulted in clinical efficacy demonstrating the importance of detecting and targeting diverse kinase alterations in these disorders.

PMID: 26566875
ISSN: 2159-8290 

New England journal of medicine. 2015:373(18):1733-1747.DOI: 10.1056/NEJMoa1506583

Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia

Tiacci, Enrico; Park, Jae H; De Carolis, Luca; Chung, Stephen S; Broccoli, Alessandro; Scott, Sasinya; Zaja, Francesco; Devlin, Sean; Pulsoni, Alessandro; Chung, Young R; Cimminiello, Michele; Kim, Eunhee; Rossi, Davide; Stone, Richard M; Motta, Giovanna; Saven, Alan; Varettoni, Marzia; Altman, Jessica K; Anastasia, Antonella; Grever, Michael R; Ambrosetti, Achille; Rai, Kanti R; Fraticelli, Vincenzo; Lacouture, Mario E; Carella, Angelo M; Levine, Ross L; Leoni, Pietro; Rambaldi, Alessandro; Falzetti, Franca; Ascani, Stefano; Capponi, Monia; Martelli, Maria P; Park, Christopher Y; Pileri, Stefano A; Rosen, Neal; Foa, Robin; Berger, Michael F; Zinzani, Pier L; Abdel-Wahab, Omar; Falini, Brunangelo; Tallman, Martin S

BACKGROUND: BRAF V600E is the genetic lesion underlying hairy-cell leukemia. We assessed the safety and activity of the oral BRAF inhibitor vemurafenib in patients with hairy-cell leukemia that had relapsed after treatment with a purine analogue or who had disease that was refractory to purine analogues. METHODS: We conducted two phase 2, single-group, multicenter studies of vemurafenib (at a dose of 960 mg twice daily)--one in Italy and one in the United States. The therapy was administered for a median of 16 weeks in the Italian study and 18 weeks in the U.S. study. Primary end points were the complete response rate (in the Italian trial) and the overall response rate (in the U.S. trial). Enrollment was completed (28 patients) in the Italian trial in April 2013 and is still open (26 of 36 planned patients) in the U.S. trial. RESULTS: The overall response rates were 96% (25 of 26 patients who could be evaluated) after a median of 8 weeks in the Italian study and 100% (24 of 24) after a median of 12 weeks in the U.S. study. The rates of complete response were 35% (9 of 26 patients) and 42% (10 of 24) in the two trials, respectively. In the Italian trial, after a median follow-up of 23 months, the median relapse-free survival was 19 months among patients with a complete response and 6 months among those with a partial response; the median treatment-free survival was 25 months and 18 months, respectively. In the U.S. trial, at 1 year, the progression-free survival rate was 73% and the overall survival rate was 91%. Drug-related adverse events were usually of grade 1 or 2, and the events most frequently leading to dose reductions were rash and arthralgia or arthritis. Secondary cutaneous tumors (treated with simple excision) developed in 7 of 50 patients. The frequent persistence of phosphorylated ERK-positive leukemic cells in bone marrow at the end of treatment suggests bypass reactivation of MEK and ERK as a resistance mechanism. CONCLUSIONS: A short oral course of vemurafenib was highly effective in patients with relapsed or refractory hairy-cell leukemia. (Funded by the Associazione Italiana per la Ricerca sul Cancro and others; EudraCT number, 2011-005487-13; ClinicalTrials.gov number NCT01711632.).

PMID: 26352686
ISSN: 1533-4406 

Cell reports. 2015:13(3):504-515.DOI: 10.1016/j.celrep.2015.09.019

Myeloid Dysregulation in a Human Induced Pluripotent Stem Cell Model of PTPN11-Associated Juvenile Myelomonocytic Leukemia

Mulero-Navarro, Sonia; Sevilla, Ana; Roman, Angel C; Lee, Dung-Fang; D'Souza, Sunita L; Pardo, Sherly; Riess, Ilan; Su, Jie; Cohen, Ninette; Schaniel, Christoph; Rodriguez, Nelson A; Baccarini, Alessia; Brown, Brian D; Cave, Helene; Caye, Aurelie; Strullu, Marion; Yalcin, Safak; Park, Christopher Y; Dhandapany, Perundurai S; Yongchao, Ge; Edelmann, Lisa; Bahieg, Sawsan; Raynal, Patrick; Flex, Elisabetta; Tartaglia, Marco; Moore, Kateri A; Lemischka, Ihor R; Gelb, Bruce D

Somatic PTPN11 mutations cause juvenile myelomonocytic leukemia (JMML). Germline PTPN11 defects cause Noonan syndrome (NS), and specific inherited mutations cause NS/JMML. Here, we report that hematopoietic cells differentiated from human induced pluripotent stem cells (hiPSCs) harboring NS/JMML-causing PTPN11 mutations recapitulated JMML features. hiPSC-derived NS/JMML myeloid cells exhibited increased signaling through STAT5 and upregulation of miR-223 and miR-15a. Similarly, miR-223 and miR-15a were upregulated in 11/19 JMML bone marrow mononuclear cells harboring PTPN11 mutations, but not those without PTPN11 defects. Reducing miR-223's function in NS/JMML hiPSCs normalized myelogenesis. MicroRNA target gene expression levels were reduced in hiPSC-derived myeloid cells as well as in JMML cells with PTPN11 mutations. Thus, studying an inherited human cancer syndrome with hiPSCs illuminated early oncogenesis prior to the accumulation of secondary genomic alterations, enabling us to discover microRNA dysregulation, establishing a genotype-phenotype association for JMML and providing therapeutic targets.

PMID: 26456833
ISSN: 2211-1247 

Genes & development. 2015:29(19):2037-2053.DOI: 10.1101/gad.269415.115

A majority of m6A residues are in the last exons, allowing the potential for 3' UTR regulation

Ke, Shengdong; Alemu, Endalkachew A; Mertens, Claudia; Gantman, Emily Conn; Fak, John J; Mele, Aldo; Haripal, Bhagwattie; Zucker-Scharff, Ilana; Moore, Michael J; Park, Christopher Y; Vagbo, Cathrine Broberg; Kussnierczyk, Anna; Klungland, Arne; Darnell, James E Jr; Darnell, Robert B

We adapted UV CLIP (cross-linking immunoprecipitation) to accurately locate tens of thousands of m(6)A residues in mammalian mRNA with single-nucleotide resolution. More than 70% of these residues are present in the 3'-most (last) exons, with a very sharp rise (sixfold) within 150-400 nucleotides of the start of the last exon. Two-thirds of last exon m(6)A and >40% of all m(6)A in mRNA are present in 3' untranslated regions (UTRs); contrary to earlier suggestions, there is no preference for location of m(6)A sites around stop codons. Moreover, m(6)A is significantly higher in noncoding last exons than in next-to-last exons harboring stop codons. We found that m(6)A density peaks early in the 3' UTR and that, among transcripts with alternative polyA (APA) usage in both the brain and the liver, brain transcripts preferentially use distal polyA sites, as reported, and also show higher proximal m(6)A density in the last exons. Furthermore, when we reduced m6A methylation by knocking down components of the methylase complex and then examined 661 transcripts with proximal m6A peaks in last exons, we identified a set of 111 transcripts with altered (approximately two-thirds increased proximal) APA use. Taken together, these observations suggest a role of m(6)A modification in regulating proximal alternative polyA choice.

PMID: 26404942
ISSN: 1549-5477 

Cancer cell. 2015:27(5):617-630.DOI: 10.1016/j.ccell.2015.04.006

SRSF2 Mutations Contribute to Myelodysplasia by Mutant-Specific Effects on Exon Recognition

Kim, Eunhee; Ilagan, Janine O; Liang, Yang; Daubner, Gerrit M; Lee, Stanley C-W; Ramakrishnan, Aravind; Li, Yue; Chung, Young Rock; Micol, Jean-Baptiste; Murphy, Michele E; Cho, Hana; Kim, Min-Kyung; Zebari, Ahmad S; Aumann, Shlomzion; Park, Christopher Y; Buonamici, Silvia; Smith, Peter G; Deeg, H Joachim; Lobry, Camille; Aifantis, Iannis; Modis, Yorgo; Allain, Frederic H-T; Halene, Stephanie; Bradley, Robert K; Abdel-Wahab, Omar

Mutations affecting spliceosomal proteins are the most common mutations in patients with myelodysplastic syndromes (MDS), but their role in MDS pathogenesis has not been delineated. Here we report that mutations affecting the splicing factor SRSF2 directly impair hematopoietic differentiation in vivo, which is not due to SRSF2 loss of function. By contrast, SRSF2 mutations alter SRSF2's normal sequence-specific RNA binding activity, thereby altering the recognition of specific exonic splicing enhancer motifs to drive recurrent mis-splicing of key hematopoietic regulators. This includes SRSF2 mutation-dependent splicing of EZH2, which triggers nonsense-mediated decay, which, in turn, results in impaired hematopoietic differentiation. These data provide a mechanistic link between a mutant spliceosomal protein, alterations in the splicing of key regulators, and impaired hematopoiesis.

PMID: 25965569
ISSN: 1878-3686 

Nano letters. 2015:15(4):2358-2364.DOI: 10.1021/nl504610d

Mesoscale nanoparticles selectively target the renal proximal tubule epithelium

Williams, Ryan M; Shah, Janki; Ng, Brandon D; Minton, Denise R; Gudas, Lorraine J; Park, Christopher Y; Heller, Daniel A

We synthesized "mesoscale" nanoparticles, approximately 400 nm in diameter, which unexpectedly localized selectively in renal proximal tubules and up to 7 times more efficiently in the kidney than other organs. Although nanoparticles typically localize in the liver and spleen, modulating their size and opsonization potential allowed for stable targeting of the kidneys through a new proposed uptake mechanism. Applying this kidney targeting strategy, we anticipate use in the treatment of renal disease and the study of renal physiology.

PMID: 25811353
ISSN: 1530-6992 

Blood. 2015:125(14):2206-2216.DOI: 10.1182/blood-2014-06-585273

MiR-29a maintains mouse hematopoietic stem cell self-renewal by regulating Dnmt3a

Hu, Wenhuo; Dooley, James; Chung, Stephen S; Chandramohan, Dhruva; Cimmino, Luisa; Mukherjee, Siddhartha; Mason, Christopher E; Strooper, Bart de; Liston, Adrian; Park, Christopher Y

Hematopoietic stem cells (HSCs) possess the ability to generate all hematopoietic cell types as well as to self-renew over long periods, but the mechanisms that regulate their unique properties are incompletely understood. Herein, we show that homozygous deletion of the miR-29a/b-1 bicistron results in decreased numbers of hematopoietic stem and progenitor cells (HSPCs), decreased HSC self-renewal, and increased HSC cell cycling and apoptosis. The HSPC phenotype is specifically due to loss of miR-29a, since miR-29b expression is unaltered in miR-29a/b-1 null HSCs, and only ectopic expression of miR-29a restores HSPC function both in vitro and in vivo. HSCs lacking miR-29a/b-1 exhibit widespread transcriptional dysregulation and adopt gene expression patterns similar to normal committed progenitors. A number of predicted miR-29 target genes, including Dnmt3a, are significantly upregulated in miR-29a/b-1 null HSCs. The loss of negative regulation of Dnmt3a by miR-29a is a major contributor to the miR-29a/b-1 null HSPC phenotype, as both in vitro Dnmt3a shRNA knockdown assays and a genetic haploinsufficiency model of Dnmt3a restored the frequency and long-term reconstitution capacity of HSCs from miR-29a/b-1 deficient mice. Overall, these data demonstrate that miR-29a is critical for maintaining HSC function through its negative regulation of Dnmt3a.

PMID: 25634742
ISSN: 0006-4971 

Blood. 2015:126(23).DOI: 

Diverse and Targetable Kinase Alterations Drive Histiocytic Neoplasms [Meeting Abstract]

Durham, Benjamin Heath; Diamond, Eli L; Haroche, Julien; Yao, Zhan; Ma, Jing; Parikh, Sameer A; Choi, John; Kim, Eunhee; Cohen-Aubart, Fleur; Lee, Stanley Chun-Wei; Gao, Yijun; Micol, Jean-Baptiste; Campbell, Patrick; Walsh, Michael P; Sylvester, Brooke; Dolgalev, Igor; Olga, Aminova; Heguy, Adriana; Zappile, Paul; Nakitandwe, Joy; Dalton, James; Ellison, David W; Estrada-Veras, Juvianee; Lacouture, Mario; Gahl, William A; Stephens, Phil; Miller, Vincent A; Ross, Jeffrey; Ali, Siraj; Heritier, Sebastien; Donadieu, Jean; Solit, David; Hyman, David M; Baselga, Jose; Janku, Filip; Taylor, Barry S; Park, Christopher Y; Dogan, Ahmet; Amoura, Zahir; Emile, Jean-Francois; Rampal, Raajit K; Rosen, Neal; Gruber, Tanja A; Abdel-Wahab, Omar

ISSN: 1528-0020 

PLoS one. 2015:10(7):e0131722-e0131722.DOI: 10.1371/journal.pone.0131722

Reversibility of Defective Hematopoiesis Caused by Telomere Shortening in Telomerase Knockout Mice

Raval, Aparna; Behbehani, Gregory K; Nguyen, Le Xuan Truong; Thomas, Daniel; Kusler, Brenda; Garbuzov, Alina; Ramunas, John; Holbrook, Colin; Park, Christopher Y; Blau, Helen; Nolan, Garry P; Artandi, Steven E; Mitchell, Beverly S

Telomere shortening is common in bone marrow failure syndromes such as dyskeratosis congenita (DC), aplastic anemia (AA) and myelodysplastic syndromes (MDS). However, improved knowledge of the lineage-specific consequences of telomere erosion and restoration of telomere length in hematopoietic progenitors is required to advance therapeutic approaches. We have employed a reversible murine model of telomerase deficiency to compare the dependence of erythroid and myeloid lineage differentiation on telomerase activity. Fifth generation Tert-/- (G5 Tert-/-) mice with shortened telomeres have significant anemia, decreased erythroblasts and reduced hematopoietic stem cell (HSC) populations associated with neutrophilia and increased myelopoiesis. Intracellular multiparameter analysis by mass cytometry showed significantly reduced cell proliferation and increased sensitivity to activation of DNA damage checkpoints in erythroid progenitors and in erythroid-biased CD150hi HSC, but not in myeloid progenitors. Strikingly, Cre-inducible reactivation of telomerase activity restored hematopoietic stem and progenitor cell (HSPC) proliferation, normalized the DNA damage response, and improved red cell production and hemoglobin levels. These data establish a direct link between the loss of TERT activity, telomere shortening and defective erythropoiesis and suggest that novel strategies to restore telomerase function may have an important role in the treatment of the resulting anemia.

PMID: 26133370
ISSN: 1932-6203

Experimental hematology. 2015:43(9):S88-S88.DOI: 


Park, Christopher Y; Vijay, Priyanka; Chung, Stephen S; Stern, Diana; Klimek, Virginia; Mason, Christopher E

ISSN: 1873-2399 

Blood. 2015:126(23).DOI: 

Analysis of Myelodysplastic Syndrome Stem Cells at Single Cell Resolution during DNA Methyltransferase Inhibitor Therapy [Meeting Abstract]

Chung, Stephen S; Vijay, Priyanka; Stern, Diana L; O'Sullivan, Deirdre; Klimek, Virginia M; Mason, Christopher; Park, Christopher Y

ISSN: 1528-0020 

Cancer research. 2015:75.DOI: 10.1158/1538-7445.AM2015-3566

Targeting CD99 in T-cell neoplasms [Meeting Abstract]

Tavakkoli, Montreh; Lee, Dong H; Chung, Stephen S; Park, Christopher Y

ISSN: 1538-7445