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Epigenetic regulations play crucial roles in leukemogenesis and leukemia progression. SUV39H1 is the dominant H3K9 methyltransferase in the hematopoietic system, and its expression declines with aging. However, the role of SUV39H1 via its-mediated repressive modification H3K9me3 in leukemogenesis/leukemia progression remains to be explored. We found that SUV39H1 was down-regulated in a variety of leukemias, including MLL-r AML, as compared with normal individuals. Decreased levels of Suv39h1 expression and genomic H3K9me3 occupancy were observed in LSCs from MLL-r-induced AML mouse models in comparison with that of hematopoietic stem/progenitor cells. Suv39h1 overexpression increased leukemia latency and decreased the frequency of LSCs in MLL-r AML mouse models, while Suv39h1 knockdown accelerated disease progression with increased number of LSCs. Increased Suv39h1 expression led to the inactivation of Hoxb13 and Six1, as well as reversion of Hoxa9/Meis1 downstream target genes, which in turn decelerated leukemia progression. Interestingly, Hoxb13 expression is up-regulated in MLL-AF9-induced AML cells, while knockdown of Hoxb13 in MLL-AF9 leukemic cells significantly prolonged the survival of leukemic mice with reduced LSC frequencies. Our data revealed that SUV39H1 functions as a tumor suppressor in MLL-AF9-induced AML progression. These findings provide the direct link of SUV39H1 to AML development and progression.

Acute myeloid leukemia (AML) is a deadly cancer characterized by an expanded self-renewal capacity that is associated with the accumulation of immature myeloid cells. Emerging evidence shows that methyl-CpG-binding domain protein 2 (MBD2), a DNA methylation reader, often participates in the transcriptional silencing of hypermethylated genes in cancer cells. Nevertheless, the role of MBD2 in AML remains unclear. Herein, by using an MLL-AF9 murine model and a human AML cell line, we observed that loss of MBD2 could delay the initiation and progression of leukemia. MBD2 depletion significantly reduced the leukemia burden by decreasing the proportion of leukemic stem cells (LSCs) and inhibiting leukemia cell proliferation in serial transplantation experiments, thereby allowing leukemic blasts to transition to a more mature state reflecting normal myelopoiesis. Both gene expression analyses and bioinformatic studies revealed that MBD2 negatively modulated genes related to myeloid differentiation, and was necessary to sustain the MLL-AF9 oncogene-induced gene program. We further demonstrated that MBD2 could promote LSC cell cycle progression through epigenetic regulation of CDKN1C transcription probably by binding to its promoter region. Taken together, our data suggest that MBD2 promotes AML development and could be a therapeutic target for myeloid malignancies.

Little is known about the roles of Rictor/mTORC2 in the leukemogenesis of acute myeloid leukemia. Here, we demonstrated that Rictor is essential for the maintenance of mixed lineage leukemia (MLL)-driven leukemia by preventing leukemia stem cells (LSCs) from exhaustion. Rictor depletion led to a reactive activation of mTORC1 signaling by facilitating the assembly of mTORC1. Hyperactivated mTORC1 signaling in turn drove LSCs into cycling, compromised the quiescence of LSCs and eventually exhausted their capacity to generate leukemia. At the same time, loss of Rictor had led to a reactive activation of FoxO3a in leukemia cells, which acts as negative feedback to restrain greater over-reactivation of mTORC1 activity and paradoxically protects leukemia cells from exhaustion. Simultaneous depletion of Rictor and FoxO3a enabled rapid exhaustion of MLL LSCs and a quick eradication of MLL leukemia. As such, our present findings highlighted a pivotal regulatory axis of Rictor-FoxO3a in maintaining quiescence and the stemness of LSCs.

Leukemia often results in severe anemia, which may significantly contribute to patient mortality and morbidity. However, the mechanisms underlying defective erythropoiesis in leukemia have not been fully elucidated. In this study, we demonstrated that insufficient erythropoiesis in an immunocompetent acute myeloid leukemia (AML) murine model was due to reduced proliferation of megakaryocyte erythroid progenitors and increased apoptosis of erythroblasts. Colony-forming cell assays indicated that the leukemic bone marrow (BM) plasma inhibited erythroid colony formation, whereas they had no inhibitory effect on other types of colonies. Cytokine array analysis demonstrated that the chemokine CCL3 was elevated in the plasma of AML mice and patients. CCL3 inhibited erythroid differentiation of hematopoietic stem cells, common myeloid progenitors and especially megakaryocytic-erythroid progenitors. Administration of the CCR1 antagonist partially recovered the yield of erythroid colonies in the presence of CCL3 or leukemic BM plasma. Mechanistically, we observed an increase of p38 phosphorylation and subsequent downregulation of GATA1 after CCL3 treatment. Furthermore, knockdown of CCL3 attenuated leukemic progression and alleviated anemia. Therefore, our results demonstrate that elevated CCL3 in the leukemic environment suppresses erythropoiesis via CCR1-p38 activation, suggesting a novel mechanism for the erythroid defects observed in leukemia.

The catalytic activity of TET2 is essential for its myeloid malignancy-suppressive function in hematopoietic stem/progenitor cells

mTOR is a serine/threonine (Ser/Thr) protein kinase that responds to multiple signals, including growth factors, amino acids, energy status, stress, and oxygen, regulates cell survival, cell growth, the cell cycle, and cell metabolism, and maintains homeostasis [1]. Increased or decreased mTORC1 activity can alter HSC function and cause hematological disorders [2, 3]. Therefore, a comprehensive knowledge of mTOR is critical to understanding how HSCs function and maintain homeostasis in the hematopoietic system. In this review, we summarize recent advances in the understanding of the mTOR signaling pathway and its roles in hematopoiesis and leukemia. We also discuss pharmacological approaches to manipulate mTOR activity.

Human epithelial growth factor receptor 2 (HER2) is over-expressed in several malignancies and represents an important therapeutic target. Aptamers are oligonucleotides that may potentially serve as tumor-homing ligand with excellent affinity and specificity for targeted cancer therapy. However, aptamers need to have nuclease resistance in order to function in vivo. The aim of this study was to generate a novel HER2 thioaptamer with enhanced nuclease resistance.The HER2 thioaptamer is selected in an evolutionary process called systematic evolution of ligands by exponential enrichment.The thioaptamer could bind to the extracellular domain of HER2 with a K d of 172 nM and had minimal cross reactivity to trypsin or IgG. Moreover, the thioaptamer was found capable of binding with the HER2-positive breast cancer cells SK-BR-3 and MDA-MB-453, but not the HER2-negative cells MDA-MB-231. Notably, the thioaptamer HY6 largely maintained its structural integrity facing the nucleases in serum, while regular DNA aptamers were mostly digested. Additionally, the thioaptamer retained the capability of binding with the HER2-positive cells in the presence of serum, whereas non-thionated HER2 aptamer lost the binding function.The results indicated that the selected thioaptamer was more resistant to nuclease than regular DNA aptamers and might potentially function as a HER2-targeting ligand in complicated environment.

3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a pivotal regulator in the phosphoinositide 3-kinase (PI3K)-Akt signaling pathway that have been shown to play key roles in the functional development of B and T cells via activation of AGC protein kinases during hematopoiesis. However, the role of PDK1 in HSCs has not been fully defined. Here we specifically deleted the PDK1 gene in the hematopoietic system and found that PDK1-deficient HSCs exhibited impaired function and defective lineage commitment abilities. Lack of PDK1 caused HSCs to be less quiescent and to produce a higher number of phenotypic HSCs and fewer progenitors. PDK1-deficient HSCs were also unable to reconstitute the hematopoietic system. Notably, HSC function was more dependent on PDK1 than on mTORC2, which indicates that PDK1 plays a dominant role in the Akt-mediated regulation of HSC function. PDK1-deficient HSCs also exhibited reduced ROS levels, and treatment of PDK1-deficient HSCs with L-butathioninesulfoximine in vitro elevated the low ROS level and promoted colony formation. Therefore, PDK1 appears to contribute to HSC function partially via regulating ROS levels.

Acute leukemia characterized by chromosomal rearrangements requires additional molecular disruptions to develop into full-blown malignancy1,2, yet the cooperative mechanisms remain elusive. Using whole-genome sequencing of a pair of monozygotic twins discordant for MLL (also called KMT2A) gene-rearranged leukemia, we identified a transforming MLL-NRIP3 fusion gene3 and biallelic mutations in SETD2 (encoding a histone H3K36 methyltransferase)4. Moreover, loss-of-function point mutations in SETD2 were recurrent (6.2%) in 241 patients with acute leukemia and were associated with multiple major chromosomal aberrations. We observed a global loss of H3K36 trimethylation (H3K36me3) in leukemic blasts with mutations in SETD2. In the presence of a genetic lesion, downregulation of SETD2 contributed to both initiation and progression during leukemia development by promoting the self-renewal potential of leukemia stem cells. Therefore, our study provides compelling evidence for SETD2 as a new tumor suppressor. Disruption of the SETD2-H3K36me3 pathway is a distinct epigenetic mechanism for leukemia development.

The methyltransferase like 3 (METTL3)-containing methyltransferase complex catalyzes the N6-methyladenosine (m6A) formation, a novel epitranscriptomic marker; however, the nature of this complex remains largely unknown. Here we report two new components of the human m6A methyltransferase complex, Wilms' tumor 1-associating protein (WTAP) and methyltransferase like 14 (METTL14). WTAP interacts with METTL3 and METTL14, and is required for their localization into nuclear speckles enriched with pre-mRNA processing factors and for catalytic activity of the m6A methyltransferase in vivo. The majority of RNAs bound by WTAP and METTL3 in vivo represent mRNAs containing the consensus m6A motif. In the absence of WTAP, the RNA-binding capability of METTL3 is strongly reduced, suggesting that WTAP may function to regulate recruitment of the m6A methyltransferase complex to mRNA targets. Furthermore, transcriptomic analyses in combination with photoactivatable-ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) illustrate that WTAP and METTL3 regulate expression and alternative splicing of genes involved in transcription and RNA processing. Morpholino-mediated knockdown targeting WTAP and/or METTL3 in zebrafish embryos caused tissue differentiation defects and increased apoptosis. These findings provide strong evidence that WTAP may function as a regulatory subunit in the m6A methyltransferase complex and play a critical role in epitranscriptomic regulation of RNA metabolism.

CRISPR-Cas9 is a powerful genome editing technology, yet with off-target effects. Truncated sgRNAs (17nt) have been found to decrease off-target cleavage without affecting on-target disruption in 293T cells. However, the potency of 17nt sgRNAs relative to the full-length 20nt sgRNAs in stem cells, such as human mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs), has not been assessed. Using a GFP reporter system, we found that both 17nt and 20nt sgRNAs expressed by lentiviral vectors induce ~95% knockout (KO) in 293T cells, whereas the KO efficiencies are significantly lower in iPSCs (60–70%) and MSCs (65–75%). Furthermore, we observed a decrease of 10–20 percentage points in KO efficiency with 17nt sgRNAs compared to full-length sgRNAs in both iPSCs and MSCs. Off-target cleavage was observed in 17nt sgRNAs with 1-2nt but not 3-4nt mismatches; whereas 20nt sgRNAs with up to 5nt mismatches can still induce off-target mutations. Of interest, we occasionally observed off-target effects induced by the 17nt but not the 20nt sgRNAs. These results indicate the importance of balancing on-target gene cleavage potency with off-target effects: when efficacy is a major concern such as genome editing in stem cells, the use of 20nt sgRNAs is preferable.

Hypertrophic heart disease is a leading health problem in Western countries. Here we identified the small EF hand domain-containing protein Ca(2+) and integrin-binding protein-1 (CIB1) in a screen for previously unknown regulators of cardiomyocyte hypertrophy. Yeast two-hybrid screening for CIB1-interacting partners identified a related EF hand domain-containing protein, calcineurin B, the regulatory subunit of the prohypertrophic protein phosphatase calcineurin. CIB1 localizes primarily to the sarcolemma in mouse and human myocardium, where it anchors calcineurin to control its activation in coordination with the L-type Ca(2+) channel. CIB1 protein amounts and membrane association were enhanced in cardiac pathological hypertrophy, but not in physiological hypertrophy. Consistent with these observations, Cib1-deleted mice showed a marked reduction in myocardial hypertrophy, fibrosis, cardiac dysfunction and calcineurin-nuclear factor of activated T cells (NFAT) activity after pressure overload, whereas the degree of physiologic hypertrophy after swimming exercise was not altered. Transgenic mice with inducible and cardiac-specific overexpression of CIB1 showed enhanced cardiac hypertrophy in response to pressure overload or calcineurin signaling. Moreover, mice lacking Ppp3cb (encoding calcineurin A, beta isozyme) showed no enhancement in cardiac hypertrophy associated with CIB1 overexpression. Thus, CIB1 functions as a previously undescribed regulator of cardiac hypertrophy through its ability to regulate the association of calcineurin with the sarcolemma and its activation.

Among cyclin-dependent kinase inhibitors that control the G1 phase in cell cycle, only p18 and p27 can negatively regulate haematopoietic stem cell (HSC) self-renewal. In this manuscript, we demonstrate that p18 protein is a more potent inhibitor of HSC self-renewal than p27 in mouse models and its deficiency promoted HSC expansion in long-term culture. Single-cell analysis indicated that deleting p18 gene favoured self-renewing division of HSC in vitro. Based on the structure of p18 protein and in-silico screening, we further identified novel small-molecule inhibitors that can specifically block the activity of p18 protein. Our selected lead compounds were able to expand functional HSCs in a short-term culture. Thus, these putative small-molecule inhibitors for p18 protein are valuable for further dissecting the signalling pathways of stem cell self-renewal and may help develop more effective chemical agents for therapeutic expansion of HSC.

Background Leukemia is a systemic malignancy originated from hematopoietic cells. The extracellular environment has great impacts on the survival, proliferation and dissemination of leukemia cells. The spleen is an important organ for extramedullary hematopoiesis and a common infiltration site in lymphoid malignancies. Splenomegaly, frequently observed in T cell acute lymphoblastic leukemia (T-ALL), is associated with poor prognosis. However, how the spleen microenvironment distinctly affects T-ALL cells as opposed to bone marrow (BM) microenvironment has not been addressed. Methods A Notch1-induced mouse T-ALL model was applied in this study. Flow cytometry and two-photon fluorescence microscopy were used to analyze early distribution of T-ALL cells. MILLIPLEX® MAP Multiplex Immunoassay was performed to measure cytokine/chemokine levels in different microenvironments. Transwell and co-culture experiments were used to test the effects of splenic microenvironment in vitro. Splenectomy was performed to assess the organ specific impact on the survival of T-ALL-bearing mice. Results More leukemia cells were detected in the spleen than in the BM after injection of T-ALL cells by flow cytometry and two-photon fluorescence microscopy analysis. By screening a panel of cytokines/chemokines, a higher level of MIP-3β was found in the splenic microenvironment than BM microenvironment. In vitro transwell experiment further confirmed that MIP-3β recruits T-ALL cells which express a high level of MIP-3β receptor, CCR7. Furthermore, the splenic microenvironment stimulates T-ALL cells to express a higher level of MIP-3β, which further recruits T-ALL cells to the spleen. Co-culture experiment found that the splenic microenvironment more potently stimulated the proliferation and migration of T-ALL cells than BM. Moreover, the mice transplanted with T-ALL cells from the spleen had a shorter life span than those transplanted from BM, suggesting increased potency of the T-ALL cells induced by the splenic microenvironment. In addition, splenectomy prolonged the survival of leukemic mice. Conclusions Our study demonstrates an organ specific effect on leukemia development. Specifically, T-ALL cells can be potentiated by splenic microenvironment and thus spleen may serve as a target organ for the treatment of some types of leukemia. Electronic supplementary material The online version of this article (doi:10.1186/s13045-014-0071-7) contains supplementary material, which is available to authorized users.

Background Fanconi anemia (FA) is a rare inherited genetic syndrome with highly variable clinical manifestations. Fifteen genetic subtypes of FA have been identified. Traditional complementation tests for grouping studies have been used generally in FA patients and in stepwise methods to identify the FA type, which can result in incomplete genetic information from FA patients. Methods We diagnosed five pediatric patients with FA based on clinical manifestations, and we performed exome sequencing of peripheral blood specimens from these patients and their family members. The related sequencing data were then analyzed by bioinformatics, and the FANC gene mutations identified by exome sequencing were confirmed by PCR re-sequencing. Results Homozygous and compound heterozygous mutations of FANC genes were identified in all of the patients. The FA subtypes of the patients included FANCA, FANCM and FANCD2. Interestingly, four FA patients harbored multiple mutations in at least two FA genes, and some of these mutations have not been previously reported. These patients’ clinical manifestations were vastly different from each other, as were their treatment responses to androstanazol and prednisone. This finding suggests that heterozygous mutation(s) in FA genes could also have diverse biological and/or pathophysiological effects on FA patients or FA gene carriers. Interestingly, we were not able to identify de novo mutations in the genes implicated in DNA repair pathways when the sequencing data of patients were compared with those of their parents. Conclusions Our results indicate that Chinese FA patients and carriers might have higher and more complex mutation rates in FANC genes than have been conventionally recognized. Testing of the fifteen FANC genes in FA patients and their family members should be a regular clinical practice to determine the optimal care for the individual patient, to counsel the family and to obtain a better understanding of FA pathophysiology.

Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells using the reprogramming factors (Oct4, Sox2, Klf4 and c-Myc, also called OSKM).1 Cellular reprogramming and oncogenesis share many common features. The application of the iPS technology in cancers help us better understand the mechanism underlying the initiation and progression of cancer. Therefore, defining the reprogramming potential of cancer cells would provide unique opportunities to reveal epigenetic mechanisms and develop novel therapeutics for cancer. Because the reprogramming efficiency of cancer cells is paradoxically much lower than that of normal cells in general, only some handful types of cancer cells have been explored using the iPS technology.2 To date, in the hematopoietic system, Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines, human chronic myeloid leukemia cells, juvenile myelomonocytic leukemia cells and primary murine mixed lineage leukemia-AF9 acute myeloid leukemia cells have been successfully generated into iPS cells.3, 4, 5, 6 However, whether the primary malignant leukemic T cells can be reprogrammed into the iPS cells is still a mystery.