ALBERT

Description: TWIST is a basic helix-loop-helix transcription factor that specifies Drosophila mesoderm development. In mammals there are 2 members, TWIST1 and TWIST2. TWIST2 is a regulator of osteoblasts and muscle development and plays a critical role in the epithelial-mesenchymal transition process, as well as in cancer initiation and metastasis. Twist2-deficient mice develop a myeloproliferative disease. These findings led us to query a potential role of TWIST2 in normal and leukemic (CML) human hematopoietic cells. RT-PCR and immuno-fluorescence analysis of CD34+ bone marrow (BM) cells obtained from healthy donors demonstrated their expression of TWIST2 transcripts and protein. Lentiviral vector-mediated knockdown of TWIST2 with 2 independent shRNA sequences enhanced the erythroid and granulopoietic colony-forming activity of transduced normal BM cells ∼2-fold compared with control transduced cells (n=3, p

Description: Recent improvements in the development of methods for isolating functionally validated populations of nearly pure (〉20%) murine hematopoietic stem cells (HSCs) have made it possible to analyze the molecular basis of the properties of these cells with increased precision. One intriguing feature of HSCs is the change they undergo in many of their key properties during development - a change that affects the control of their self-renewal, cycling status, differentiated progeny output and steel factor sensitivity. To investigate how these differences are mediated, we undertook a genome-wide analysis of the transcripts present in highly purified fetal and adult HSCs using an adaptation of the LongSAGE methodology that allows its application to small numbers of cells (10 ng of RNA) by inclusion of an initial PCR amplification step that preserves the transcript repertoire while excluding less than 0.25% of the transcripts. The LongSAGE methodology was adopted because it is sequence-based and thus quantitative and independent of prior knowledge of expressed genes or variations in their hybridization to matching or related cDNAs, ESTs or derived oligos. A suspension of 10,000 lin-Sca-1+CD43+Mac1+ fetal liver (FL) cells (∼20% pure HSCs as determined by 16-week limiting dilution and single cell transplantation experiments) was obtained from embryonic day 14.5 fetuses. From these cells, we generated a 160,000-tag LongSAGE library containing 7865 tags that map uniquely to the mouse genome (using the RefSeq database through DiscoverySpace; www.bcgsc.ca/DiscoverySpace). A suspension of 3700 CD45midlin-Rho-SP cells (∼30% pure HSCs) was isolated from adult mouse bone marrow (BM) and then used to generate a 37,000-tag LongSAGE library (956 uniquely mapped tags). Both of these libraries contained tags identifying transcripts that have been previously reported to be associated with HSCs from FL and/or adult BM, including c-kit, pbx-1, tgf-β, cul-4a, PrP, c-myc, robo1, sox17, as well as a number of Smarc transcripts, ubiquitin ligase transcripts and TNF-related transcripts. As a first test of the utility of the libraries, we looked for differences in the expression of genes that have been broadly associated with differences in cellular proliferative activity. This comparison identified many such tags in the FL HSC library that were absent from the adult BM HSC library, including multiple cyclins (A2, B2, C, D1, D2, D3, E1, F, H, I, J L1, L2), cdc20, cdc5b, and plk, as well as 34 of the top 50 “proliferation” genes identified by Venezia et al (PLoS Biology, 2004) to be selectively expressed in adult BM HSCs that had been stimulated to proliferate. Other transcripts that were present at significantly higher levels in the FL HSC library (95% C.I. using Audic Claverie statistics) included msl2, rbx1, lmo2, pfn1, and 16 members of the tripartite motif protein (trim) family. Conversely, many transcripts for components of the proteosome, involved in nucleic acid binding, and transcripts coding for proteins with receptor activity were present at higher levels (or uniquely) in the adult BM HSC library. Taken together, these findings establish the validity and potential of these permanent HSC transcriptome resources for further investigation of mechanisms that determine the different biology of fetal and adult HSCs.

Description: Ahi-1/AHI-1 (Abelson helper integration site-1) encodes a family of protein isoforms containing one Src homology 3 (SH3) domain and multiple tryptophan-aspartic acid 40 (WD40)–repeat domains. The function of these proteins is unknown, but involvement in leukemogenesis has been suggested by the high frequency of Ahi-1 mutations seen in certain virus-induced murine leukemias. Here we show that in both mice and humans, Ahi-1/AHI-1 expression is highest in the most primitive hematopoietic cells with specific patterns of down-regulation in different lineages. Cells from patients with chronic myeloid leukemia (CML; n = 28) show elevated AHI-1 transcripts in all disease phases and, in chronic phase, in the leukemic cells at all stages of differentiation, including quiescent (G0) CD34+ cells as well as terminally differentiating cells. In the most primitive lin–CD34+CD38– CML cells, transcripts for the 2 shorter isoforms of AHI-1 are also increased. Although 15 of 16 human lymphoid and myeloid leukemic cell lines showed aberrant control of AHI-1 expression, this was not seen in blasts obtained directly from patients with acute Philadelphia chromosome–negative (Ph–) leukemia (n = 15). Taken together, our results suggest that down-regulation of AHI-1 expression is an important conserved step in primitive normal hematopoietic cell differentiation and that perturbations in AHI-1 expression may contribute to the development of specific types of human leukemia.

Description: The chronic phase of CML is sustained by rare BCR-ABL+ stem cells. These cells share many properties with normal pluripotent hematopoietic stem cells, but also differ in critical ways that alter their growth, drug responsiveness and genome stability. Understanding the molecular mechanisms underlying the biological differences between normal and CML stem cells is key to the development of more effective CML therapies. To obtain new insights into these mechanisms, we generated Long Serial Analysis of Gene Expression (SAGE) libraries from paired isolates of highly purified lin-CD34+CD45RA-CD36- CD71-CD7-CD38+ and lin-CD34+CD45RA-CD36-CD71-CD7-CD38- cells from 3 chronic phase CML patients (all with predominantly Ph+/BCR-ABL+ cells in both subsets) and from 3 control samples: a pool of 10 normal bone marrows (BMs), a single normal BM and a pool of G-CSF-mobilized blood cells from 9 donors. In vitro bioassays showed the CD34+CD38+ cells were enriched in CFCs (CML: 3–20% pure; normal: 4–19% pure) and the CD34+CD38- cells were enriched in LTC-ICs (CML: 0.2–26% pure; normal: 12–52% pure). Each of the 12 libraries was then sequenced to a depth of ~200,000 tags and tags from libraries prepared from like phenotypes were compared between genotypes using DiscoverySpace software and hierarchical clustering. 1687 (355 with clustering) and 1258 (316 with clustering) transcripts were thus identified as differentially expressed in the CML vs control CD34+CD38− and CD34+CD38+ subsets, respectively. 266 of these transcripts (11 with clustering) were differentially expressed in both subsets. The differential expression of 5 genes (GAS2, IGF2BP2, IL1R1, DUSP1 & SELL) was confirmed by real-time PCR analysis of lin-CD34+ cells isolated from an additional 5 normal BMs and 11 CMLs, and lin-CD34+CD38− cells from an additional 2 normal BMs and 2 CMLs (with dominant Ph+ cells). GAS2 and IL1R1 transcript levels were correlated with BCR-ABL transcript levels in both primitive subsets, and predicted differences in expression of IL1R1 and SELL were apparent within 3 days in CD34+ cord blood cells transduced with a lenti-BCR-ABL-IRES-GFP vs a control lenti-GFP vector (n=3). These findings support a direct role of BCR-ABL in perturbing the expression of these 3 genes. Further comparison of the meta CD34+CD38− and CD34+CD38+ CML cell libraries with most publicly accessible SAGE data revealed 69 novel tags in the CD34+ CML cells that correspond to unique but conserved genomic sequences. Nine of these were recovered by 5′- and 3′- RACE applied to cDNAs pooled from several human leukemic cell lines. These results illustrate the power of SAGE to reveal key components of the transcriptomes of rare human CML stem cell populations including transcripts of genes not previously known to exist. Continuing investigation of their biological roles in primary CML cells and primitive BCR-ABL-transduced human cells offer important strategies for delineating their potential as therapeutic targets.

Description: Chronic myeloid leukemia (CML) arises from a hematopoietic stem cell that acquires a BCR-ABL fusion gene. During the chronic phase of the disease, this cell produces an expanding multi-lineage clone that usually comes to dominate all terminal stages of myelopoiesis. However, eventually, further mutations are acquired which cause progression to a rapidly fatal acute leukemia. To obtain new insights into the molecular perturbations that cause CML stem cells to initiate chronic phase disease, we generated Long Serial Analysis of Gene Expression (LongSAGE) libraries (∼200,000 tags/library) from extracts of highly purified lin−CD34+CD45RA−CD36−CD71−CD7−CD38+ and lin−CD34+CD45RA−CD36−CD71−CD7−CD38− normal bone marrow (BM) and G-CSF-mobilized peripheral blood (G-mPB) cells as well as cells from 3 chronic phase CML patients with predominantly Ph+/BCR-ABL+ cells in both of these very primitive cell subsets. Long term culture-initiating cell (LTC-IC) and direct colony-forming cell (CFC) assays performed on an aliquot of each of these cell populations showed the frequency of LTC-IC were 4 to 130-fold higher in the 34+38− cells than in the matching 34+38+ cells with the opposite trend for the CFCs. Comparison of the tags present in the pooled CML and pooled normal BM and G-mPB libraries revealed many differentially expressed genes. Real-time RT-PCR analysis of lin−CD34+ cells from 14 chronic phase CML patients and 3 normal BMs confirmed the differential expression of 14 candidate transcripts identified by SAGE (changes ranging from 3-fold lower to 80-fold higher in the CML cells, p2 kb away from known transcripts, and of these 32, 3 were confirmed to represent novel transcripts using a PCR approach. These results illustrate the potential of SAGE to reveal novel as well as known components in the transcriptomes of rare normal and cancer stem cell populations. Investigation of their roles in primitive human cells transduced with BCR-ABL and BCR-ABL+ cell lines indicates the utility of these models for further delineation of the complex effects of BCR-ABL expression in chronic phase CML stem cells.

Description: Abstract 3141 TWIST encodes a typical basic helix-loop-helix transcription factor. Twist-2, as a member of this family was recently identified as a negative regulator of normal murine myelopoiesis (Sharabi AB. et al. PLoS Biol. 2008, 6:2786-2800), however the expression and functional role of TWIST2 in normal and leukemic human myeloid cells is poorly understood. To address this, we detected the transcript expression of TWIST2 from CD34+ cells of 19 AML patients compared with those of their normal counterparts from 6 healthy donors, and found that the expression of this transcript was 5-fold decreased in the patients. A lentiviral vector, which could only express YFP was used as control; and then the other lentiviral vector to express TWIST2 plus YFP was constructed and validated to efficiently infect various human AML cell lines including THP-1, Dami, HEL, HL60, NB4 and SHI-1. Using all these cell lines, we found that averagely the control cells could expand in the liquid culture 46-fold within 6 days, however the TWIST2 overexpressed cells could only increase 7-fold; moreover in the colony-forming cell (CFC) assays with both Dami and THP-1 cells, the TWIST2 overexpressed cells lost nearly 80% CFC capacities compared with those of control cells (n=3, P

Description: Zinc Finger protein, X-linked (ZFX) is a transcriptional regulator, which controls the self-renewal of both embryonic and hematopoietic stem cells and participates in pathogenesis of various cancers. Zfx deficiency impairs Notch intracellular domain (NotchIC) induced acute T-cell leukemia (T-ALL) or MLL-AF9 induced acute myeloid leukemia (AML) in mice models. However, the function of ZFX in chronic myeloid leukemia (CML) stem/progenitor cells has not been elucidated yet. In the present study, qRT-PCR analysis showed that ZFX expression was significantly higher in CD34+ cells from CML patients in chronic phase (CP) (n=8, 3.1-fold, P=0.0052) and patients in blast crisis (BC) (n=8, 18.6-fold, P=0.0050) compared with that in healthy donors (n=4). Two independent shRNA sequences against ZFX were delivered in CD34+ cells with lentiviral vector. The silence of ZFX had a stronger inhibitory effect on colony-forming cell (CFC) ability of CML CD34+ cells (75±5%) than that of healthy donor CD34+ cells (44±5%). Furthermore, ZFX silencing augmented Imatinib Mesylate (IM) sensitivity of CML CD34+ cells, especially in IM-resistant samples; due to the fact that ZFX silencing increased apoptosis induced by IM. To obtain the molecular insights of how ZFX acts, we generated transcriptome data comparing ZFX silenced CML CD34+ cells with control cells. qRT-PCR data validated that ZFX silencing caused a significantly declined expression of WNT3 in K562, MEG-01 and CML CD34+ cells (n=5). In addition, ZFX silencing decreased WNT3 protein expression as well. Interestingly, WNT3 had significantly higher expression in CD34+ cells from patients in CP (n=10, 5-fold, P=0.0006) compared with that in healthy donors (n=8). Silence of WNT3 inhibited the growth of K562 cells and enhanced IM sensitivity of these cells as well. Overexpression of WNT3 restored the growth inhibition and IM hypersensitivity upon ZFX silencing. Chromatin immunoprecipitation (ChIP) analysis revealed that ZFX was able to bind with WNT3 promoter, and luciferase assay showed that ZFX silencing significantly decreased the activity of WNT3 promoter. Finally, we also found that the expressions of c-Myc and cyclin D1 were reduced by ZFX silencing or WNT3 silencing, suggesting decreased WNT/Catenin signaling. Taken together, we have demonstrated that ZFX is aberrantly expressed in CML stem/progenitor cells, and it modulates the growth and IM response of CML stem/progenitor cells via wnt/Catenin pathway indicating ZFX is a new regulator of CML stem/progenitor cells, which deepens the understanding of CML pathology and potentially provides clues for novel therapies against this disease. Disclosures No relevant conflicts of interest to declare.

Description: Growth arrest-specific 2 (GAS2) has multiple functions including the regulation of cell morphology, cell cycle, apoptosis and calpain activity.GAS2 has a dual function in cancer cells, however its expression and underlying mechanism in human T-cell acute lymphoblastic leukemia (T-ALL) remain unclear. In the present study, qRT-PCR analysis showed that GAS2 has significantly higher expression (155.5-fold, P=0.0048) in CD3+ cells from T-ALL patients (n=25) than healthy donors (n=13). GAS2 was present in Jurkat cells, while absent in MOLT-4 or HPB-ALL cells. A tiny CpG island of GAS2 was almost fully methylated in both MOLT-4 (100%) and HPB-ALL cells (80%), while 40% methylation in Jurkat cells; suggesting that DNA methylation played a subtle role in regulating GAS2 expression. Two independent shRNA sequences were delivered into Jurkat cells with lentiviral vector. GAS2 silencing inhibited the growth and colony-forming cell (CFC) production significantly. Conversely, GAS2 overexpression enhanced the growth and CFC production of both MOLT-4 and HPB-ALL cells. In addition, GAS2 overexpression promoted HPB-ALL cell induced leukemia in a xenoengraftment model (5 mice in each control group). In GAS2 expressed group, the disease latency was shortened, the splenomegaly was more severe than control group (0.35±0.04g vs. 0.27±0.05g), and more leukemic cells were present in bone marrow (85±3% vs. 45±7%). To obtain the molecular insights of how GAS2 acts, RNA-seq data comparing GAS2 silenced Jurkat cells with control cells were generated. Several Notch signaling molecules were inhibited, including NOTCH1, HES1 and HES4. Despite the differential expression of these transcripts was validated in Jurkat cells, GAS2 overexpression did not elevated the expression of these transcripts in MOLT-4 or HPB-ALL cells, suggesting GAS2 did not have a consistent impact on Notch signaling. However, we found that GAS2 silencing reduced CXCR4 protein expression in Jurkat cells and GAS2 overexpression enhanced CXCR4 protein expression in MOLT-4 cells, while CXCR4 transcript was not altered upon GAS2 manipulation. Consequently, GAS2 silencing significantly reduced migration ability of Jurkat cells and GAS2 overexpression enhanced migration ability of MOLT-4 cells. Overexpression of CXCR4 "rescued" the inhibited CFC production and migration upon GAS2 silencing. A truncated GAS2 (Δ171-313) coined as GAS2DN (dominant negative form of GAS2) has been known to inhibit normal function of GAS2. Herein, we showed that GAS2DN inhibited the growth of Jurkat cells and the expression of CXCR4. To delineate the role of calpain1 and calpain2 in GAS2 function, shRNA sequences against calpain1 and calpain2 was delivered into GAS2DN expressed Jurkat cells respectively, the results showed that calpain2 but not calpain1 silencing was able to enhance the cell growth and CXCR4 expression. Taken together, the present study has demonstrated that GAS2 is aberrantly expressed in human T-ALL cells, which promotes the growth of T-ALL cells partially via its post-transcriptional regulation of CXCR4 depending on calpain2 activity. These data provide new insights of the pathogenesis of T-ALL and possibly new clues to improve the management of the disease. Disclosures No relevant conflicts of interest to declare.

Description: Key Points SATB1 is specifically overexpressed in the CD30+ lymphoma cells in cutaneous CD30+ lymphoproliferative disease. SATB1 promotes proliferation of CD30+ lymphoma cells by direct transcriptional repression of cell cycle inhibitor p21.

Description: Hematopoietic stem cells (HSCs) are generally defined by their dual properties of pluripotency and extensive self-renewal capacity. However, a lack of experimental clarity as to what constitutes extensive self-renewal capacity coupled with an absence of methods to prospectively isolate long-term repopulating cells with defined self-renewal activities has made it difficult to identify the essential components of the self-renewal machinery and investigate their regulation. We now show that cells capable of repopulating irradiated congenic hosts for 4 months and producing clones of cells that can be serially transplanted are selectively and highly enriched in the CD150+ subset of the EPCR+CD48−CD45+ fraction of mouse fetal liver and adult bone marrow cells. In contrast, cells that repopulate primary hosts for the same period but show more limited self-renewal activity are enriched in the CD150− subset. Comparative transcriptome analyses of these 2 subsets with each other and with HSCs whose self-renewal activity has been rapidly extinguished in vitro revealed 3 new genes (VWF, Rhob, Pld3) whose elevated expression is a consistent and selective feature of the long-term repopulating cells with durable self-renewal capacity. These findings establish the identity of a phenotypically and molecularly distinct class of pluripotent hematopoietic cells with lifelong self-renewal capacity.