Post-translational modifications of Runx1 regulate its activity in the cell

RUNX1 methylation as a cancer biomarker in differentiating papillary thyroid cancer from benign thyroid nodules

Aim: It remains a challenge to accurately identify malignancy of thyroid nodules when biopsy is indeterminate. The authors aimed to investigate the abnormal DNA methylation signatures in papillary thyroid cancer (PTC) compared with benign thyroid nodules (BTNs). Methods: The authors performed genome profiling by 850K array and RNA sequencing in early-stage PTC and BTN tissue samples. The identified gene was validated in two independent case-control studies using mass spectrometry. Results: Hypomethylation of RUNX1 in PTC was identified and verified (all odds ratios: ≥1.50). RUNX1 methylation achieved good accuracy in differentiating early-stage PTC from BTNs, especially for younger women. Conclusion: The authors disclosed a significant association between RUNX1 hypomethylation and PTC, suggesting RUNX1 methylation as a potential biomarker for companion diagnosis of malignant thyroid nodules.

RUNX1 gene expression in Egyptian acute myeloid leukemia patients: may it have therapeutic implications?

Background

Acute myeloid leukemia represents the highest percentage of all adult acute leukemia variants. Runt-related transcription factor1 (RUNX1), a transcription factor with a known tumor suppressor function, was recently reported as a tumor promoter in acute myeloid leukemia (AML). We investigated the role of RUNX1 gene expression level in Egyptian AML patients and delineated its clinical significance.

Results

We measured RUNX1 gene expression level using reverse transcription-quantitative polymerase chain reaction and found that the RUNX1 gene expression level was significantly higher than the control group (p < 0.001). Patients with FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations had a higher expression level of RUNX1 (p = 0.023). The male patients expressed a significantly higher level of RUNX1 (p = 0.046).

Conclusions

The RUNX1 gene is highly expressed in Egyptian AML patients. It has a relation to FLT3-ITD, which may give a clue that patients carrying this mutation may benefit from new treatments that target RUNX1 in the future. Further studies on a larger number of patients with different ethnic groups may give a clearer vision of the therapeutic implications of a new molecular target.

Two faces of RUNX3 in myeloid transformation

RUNX3, a transcription factor, has been implicated as a tumor suppressor in various cancers, including hematological malignancies; however, recent studies revealed an oncogenic function of RUNX3 in the pathogenesis of myeloid malignancies, such as myelodysplastic syndrome and acute myeloid leukemia. In contrast to the high frequency of mutations in the RUNX1 gene, deletion of and loss-of-function mutations in RUNX3 are rarely detected in patients with hematopoietic malignancies. Although RUNX3 is expressed in normal hematopoietic stem and progenitor cells, its expression decreases with aging in humans. The loss of Runx3 did not result in the development of lethal hematological diseases in mice despite the expansion of myeloid cells. Therefore, RUNX3 does not appear to initiate the transformation of normal hematopoietic stem cells. However, the overexpression of RUNX3 inhibits the expression and transcriptional function of the RUNX1 gene, but activates the expression of key oncogenic pathways, such as MYC, resulting in the transformation of premalignant stem cells harboring a driver genetic mutation. We herein discuss the mechanisms by which RUNX3 is activated and how RUNX3 exerts oncogenic effects on the cellular function of and transcriptional program in premalignant stem cells to drive myeloid transformation.

RUNX1: an emerging therapeutic target for cardiovascular disease

Runt-related transcription factor-1 (RUNX1), also known as acute myeloid leukaemia 1 protein (AML1), is a member of the core-binding factor family of transcription factors which modulate cell proliferation, differentiation, and survival in multiple systems. It is a master-regulator transcription factor, which has been implicated in diverse signalling pathways and cellular mechanisms during normal development and disease. RUNX1 is best characterized for its indispensable role for definitive haematopoiesis and its involvement in haematological malignancies. However, more recently RUNX1 has been identified as a key regulator of adverse cardiac remodelling following myocardial infarction. This review discusses the role RUNX1 plays in the heart and highlights its therapeutic potential as a target to limit the progression of adverse cardiac remodelling and heart failure.

Overexpression of RUNX3 Represses RUNX1 to Drive Transformation of Myelodysplastic Syndrome

RUNX3, a RUNX family transcription factor, regulates normal hematopoiesis and functions as a tumor suppressor in various tumors in humans and mice. However, emerging studies have documented increased expression of RUNX3 in hematopoietic stem/progenitor cells (HSPC) of a subset of patients with myelodysplastic syndrome (MDS) showing a worse outcome, suggesting an oncogenic function for RUNX3 in the pathogenesis of hematologic malignancies. To elucidate the oncogenic function of RUNX3 in the pathogenesis of MDS in vivo, we generated a RUNX3-expressing, Tet2-deficient mouse model with the pancytopenia and dysplastic blood cells characteristic of MDS in patients. RUNX3-expressing cells markedly suppressed the expression levels of Runx1, a critical regulator of hemaotpoiesis in normal and malignant cells, as well as its target genes, which included crucial tumor suppressors such as Cebpa and Csf1r. RUNX3 bound these genes and remodeled their Runx1-binding regions in Tet2-deficient cells. Overexpression of RUNX3 inhibited the transcriptional function of Runx1 and compromised hematopoiesis to facilitate the development of MDS in the absence of Tet2, indicating that RUNX3 is an oncogene. Furthermore, overexpression of RUNX3 activated the transcription of Myc target genes and rendered cells sensitive to inhibition of Myc-Max heterodimerization. Collectively, these results reveal the mechanism by which RUNX3 overexpression exerts oncogenic effects on the cellular function of and transcriptional program in Tet2-deficient stem cells to drive the transformation of MDS. SIGNIFICANCE: This study defines the oncogenic effects of transcription factor RUNX3 in driving the transformation of myelodysplastic syndrome, highlighting RUNX3 as a potential target for therapeutic intervention.

Benzodiazepines Drive Alteration of Chromatin at the Integrated HIV-1 LTR

Antiretroviral therapy (ART) lowers human immunodeficiency virus type 1 (HIV-1) viral load to undetectable levels, but does not eliminate the latent reservoir. One of the factors controlling the latent reservoir is transcriptional silencing of the integrated HIV-1 long terminal repeat (LTR). The molecular mechanisms that control HIV-1 transcription are not completely understood. We have previously shown that RUNX1, a host transcription factor, may play a role in the establishment and maintenance of HIV-1 latency. Prior work has demonstrated that inhibition of RUNX1 by the benzodiazepine (BDZ) Ro5-3335 synergizes with suberanilohydroxamic acid (SAHA) to activate HIV-1 transcription. In this current work, we examine the effect of RUNX1 inhibition on the chromatin state of the integrated HIV-1 LTR. Using chromatin immunoprecipitation (ChIP), we found that Ro5-3335 significantly increased the occupancy of STAT5 at the HIV-1 LTR. We also screened other BDZs for their ability to regulate HIV-1 transcription and demonstrate their ability to increase transcription and alter chromatin at the LTR without negatively affecting Tat activity. These findings shed further light on the mechanism by which RUNX proteins control HIV-1 transcription and suggest that BDZ compounds might be useful in activating HIV-1 transcription through STAT5 recruitment to the HIV-1 LTR.

Rasip1 is a RUNX1 target gene and promotes migration of NSCLC cells

Background

Runt-related transcription factor 1 (RUNX1), an essential regulator of hematopoiesis, is overexpressed in patients with nonsmall-cell lung cancer (NSCLC) and is correlated with enhanced metastatic ability. Ras-interacting protein 1 (Rasip1), a potential oncogene, is required for blood vessel formation, and recently, it has been shown that Rasip1 is widely expressed in NSCLC patients. We noticed that Rasip1 promoter contains several potential RUNX1-binding sequences. However, the relationship between Rasip1 and RUNX1 in NSCLC is still unknown. In this study, the potential function of RUNX1 involving in Rasip1 expression and the potential role of Rasip1 in lung cancer cells were investigated.

Materials and methods

Rasip1 and RUNX1 expressions were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blotting in NSCLC cells lines. A549 and H1299 cells were transfected with plasmids or interfering RNA (siRNA) to upregulate or downregulate the expression of Rasip1 and RUNX1. Cell motility was assessed by transwell and wound-healing assay. Location of Rasip1 and RUNX1 was detected via immunofluorescence. Meanwhile, chromatin immunoprecipitation was done using an anti-RUNX1 antibody. Rasip1 promoter was constructed, and cells were lysed for the analysis of luciferase activity.

Results

In this study, we showed that ectopic expression or knockdown of RUNX1 resulted in a significant increase or reduction in Rasip1 expression, respectively. RUNX1 bound directly to a specific DNA sequence within Rasip1 promoter and modulated its transcription. Furthermore, silencing of Rasip1 inhibited the migration of RUNX1-overexpressing NSCLC cells through inactivation of Rac1 pathway. Moreover, we found that Rasip1 was expressed ubiquitously in NSCLC cells lines and enhanced cell migration. In addition, EGFR signaling was involved both in the expression and the subcellular localization of Rasip1.

Conclusion

Our data indicated that Rasip1 is regulated in part by the transcription factor RUNX1 and might be developed as a therapeutic target for NSCLC.

Protein arginine methyltransferase 6 controls erythroid gene expression and differentiation of human CD34+ progenitor cells

Hematopoietic differentiation is driven by transcription factors, which orchestrate a finely tuned transcriptional network. At bipotential branching points lineage decisions are made, where key transcription factors initiate cell type-specific gene expression programs. These programs are stabilized by the epigenetic activity of recruited chromatin-modifying cofactors. An example is the association of the transcription factor RUNX1 with protein arginine methyltransferase 6 (PRMT6) at the megakaryocytic/erythroid bifurcation. However, little is known about the specific influence of PRMT6 on this important branching point. Here, we show that PRMT6 inhibits erythroid gene expression during megakaryopoiesis of primary human CD34⁺ progenitor cells. PRMT6 is recruited to erythroid genes, such as glycophorin A. Consequently, a repressive histone modification pattern with high H3R2me2a and low H3K4me3 is established. Importantly, inhibition of PRMT6 by shRNA or small molecule inhibitors leads to upregulation of erythroid genes and promotes erythropoiesis. Our data reveal that PRMT6 plays a role in the control of erythroid/megakaryocytic differentiation and open up the possibility that manipulation of PRMT6 activity could facilitate enhanced erythropoiesis for therapeutic use.

Loss of RUNX1/AML1 arginine-methylation impairs peripheral T cell homeostasis

RUNX1 (previously termed AML1) is a frequent target of human leukaemia-associated gene aberrations, and it encodes the DNA-binding subunit of the Core-Binding Factor transcription factor complex. RUNX1 expression is essential for the initiation of definitive haematopoiesis, for steady-state thrombopoiesis, and for normal lymphocytes development. Recent studies revealed that protein arginine methyltransferase 1 (PRMT1), which accounts for the majority of the type I PRMT activity in cells, methylates two arginine residues in RUNX1 (R206 and R210), and these modifications inhibit corepressor-binding to RUNX1 thereby enhancing its transcriptional activity. In order to elucidate the biological significance of these methylations, we established novel knock-in mouse lines with non-methylable, double arginine-to-lysine (RTAMR-to-KTAMK) mutations in RUNX1. Homozygous Runx1(KTAMK) (/) (KTAMK) mice are born alive and appear normal during adulthood. However, Runx1(KTAMK) (/) (KTAMK) mice showed a reduction in CD3(+) T lymphoid cells and a decrease in CD4(+) T cells in peripheral lymphoid organs, in comparison to their wild-type littermates, leading to a reduction in the CD4(+) to CD8(+) T-cell ratio. These findings suggest that arginine-methylation of RUNX1 in the RTAMR-motif is dispensable for the development of definitive haematopoiesis and for steady-state platelet production, however this modification affects the role of RUNX1 in the maintenance of the peripheral CD4(+) T-cell population.

RUNX1 represses the erythroid gene expression program during megakaryocytic differentiation

The activity of antagonizing transcription factors represents a mechanistic paradigm of bidirectional lineage-fate control during hematopoiesis. At the megakaryocytic/erythroid bifurcation, the cross-antagonism of krueppel-like factor 1 (KLF1) and friend leukemia integration 1 (FLI1) has such a decisive role. However, how this antagonism is resolved during lineage specification is poorly understood. We found that runt-related transcription factor 1 (RUNX1) inhibits erythroid differentiation of murine megakaryocytic/erythroid progenitors and primary human CD34(+) progenitor cells. We show that RUNX1 represses the erythroid gene expression program during megakaryocytic differentiation by epigenetic repression of the erythroid master regulator KLF1. RUNX1 binding to the KLF1 locus is increased during megakaryocytic differentiation and counterbalances the activating role of T-cell acute lymphocytic leukemia 1 (TAL1). We found that corepressor recruitment by RUNX1 contributes to a block of the KLF1-dependent erythroid gene expression program. Our data indicate that the repressive function of RUNX1 influences the balance between erythroid and megakaryocytic differentiation by shifting the balance between KLF1 and FLI1 in the direction of FLI1. Taken together, we show that RUNX1 is a key player within a network of transcription factors that represses the erythroid gene expression program.

Posttranslational modifications of RUNX1 as potential anticancer targets

The transcription factor RUNX1 is a master regulator of hematopoiesis. Disruption of RUNX1 activity has been implicated in the development of hematopoietic neoplasms. Recent studies also highlight the importance of RUNX1 in solid tumors both as a tumor promoter and a suppressor. Given its central role in cancer development, RUNX1 is an excellent candidate for targeted therapy. A potential strategy to target RUNX1 is through modulation of its posttranslational modifications (PTMs). Numerous studies have shown that RUNX1 activity is regulated by PTMs, including phosphorylation, acetylation, methylation and ubiquitination. These PTMs regulate RUNX1 activity either positively or negatively by altering RUNX1-mediated transcription, promoting protein degradation and affecting protein interactions. In this review, we first summarize the available data on the context- and dosage-dependent roles of RUNX1 in various types of neoplasms. We then provide a comprehensive overview of RUNX1 PTMs from biochemical and biologic perspectives. Finally, we discuss how aberrant PTMs of RUNX1 might contribute to tumorigenesis and also strategies to develop anticancer therapies targeting RUNX1 PTMs.

PRMT4 blocks myeloid differentiation by assembling a methyl-RUNX1-dependent repressor complex

Defining the role of epigenetic regulators in hematopoiesis has become critically important, because recurrent mutations or aberrant expression of these genes has been identified in both myeloid and lymphoid hematological malignancies. We found that PRMT4, a type I arginine methyltransferase whose function in normal and malignant hematopoiesis is unknown, is overexpressed in acute myelogenous leukemia patient samples. Overexpression of PRMT4 blocks the myeloid differentiation of human stem/progenitor cells (HSPCs), whereas its knockdown is sufficient to induce myeloid differentiation of HSPCs. We demonstrated that PRMT4 represses the expression of miR-223 in HSPCs via the methylation of RUNX1, which triggers the assembly of a multiprotein repressor complex that includes DPF2. As part of the feedback loop, PRMT4 expression is repressed posttranscriptionally by miR-223. Depletion of PRMT4 results in differentiation of myeloid leukemia cells in vitro and their decreased proliferation in vivo. Thus, targeting PRMT4 holds potential as a novel therapy for acute myelogenous leukemia.

RUNX1: A microRNA hub in normal and malignant hematopoiesis

Hematopoietic development is orchestrated by gene regulatory networks that progressively induce lineage-specific transcriptional programs. To guarantee the appropriate level of complexity, flexibility, and robustness, these networks rely on transcriptional and post-transcriptional circuits involving both transcription factors (TFs) and microRNAs (miRNAs). The focus of this review is on RUNX1 (AML1), a master hematopoietic transcription factor which is at the center of miRNA circuits necessary for both embryonic and post-natal hematopoiesis. Interference with components of these circuits can perturb RUNX1-controlled coding and non-coding transcriptional programs in leukemia.

RUNX family: Regulation and diversification of roles through interacting proteins

The Runt-related transcription factors (RUNX) belong to an ancient family of metazoan genes involved in developmental processes. Through multiple protein-interacting partners, RUNX proteins have been implicated in diverse signaling pathways and cellular processes. The frequent inactivation of RUNX genes in cancer indicates crucial roles for RUNX in tumor suppression. This review discusses the abilities of RUNX proteins, in particular RUNX3, to integrate oncogenic signals or environmental cues and to initiate appropriate tumor suppressive responses.

Tyrosyl phosphorylation toggles a Runx1 switch

The Runx1 transcription factor is post-translationally modified by seryl/threonyl phosphorylation, acetylation, and methylation that control its interactions with transcription factor partners and epigenetic coregulators. In this issue of Genes & Development, Huang and colleagues (pp. 1587-1601) describe how the regulation of Runx1 tyrosyl phosphorylation by Src family kinases and the Shp2 phosphatase toggle Runx1's interactions between different coregulatory molecules.

AML1-ETO driven acute leukemia: insights into pathogenesis and potential therapeutic approaches

The AML1-ETO fusion transcription factor is generated by the t(8;21) translocation, which is present in approximately 4%-12% of adult and 12%-30% of pediatric acute myeloid leukemia (AML) patients. Both human and mouse models of AML have demonstrated that AML1-ETO is insufficient for leukemogenesis in the absence of secondary events. In this review, we discuss the pathogenetic insights that have been gained from identifying the various events that can cooperate with AML1-ETO to induce AML in vivo. We also discuss potential therapeutic strategies for t(8;21) positive AML that involve targeting the fusion protein itself, the proteins that bind to it, or the genes that it regulates. Recently published studies suggest that a targeted therapy for t(8;21) positive AML is feasible and may be coming sometime soon.

Correlation of SRSF1 and PRMT1 expression with clinical status of pediatric acute lymphoblastic leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most frequently-occurring malignant neoplasm in children, but the pathogenesis of the disease remains unclear. In a microarray assay using samples from 100 children with ALL, SFRS1 was found to be up-regulated. Serine/arginine-rich splicing factor 1 (SRSF1, also termed SF2/ASF), encoded by the SFRS1 gene, had been shown to be a pro-oncoprotein. Our previous study indicated that SRSF1 can be methylated by protein arginine methyltransferase 1 (PRMT1) in vitro; however, the biological function of SRSF1 and PRMT1 in pediatric ALL are presently unknown.

METHODS

Matched, newly diagnosed (ND), complete remission (CR) and relapse (RE) bone marrow samples from 57 patients were collected in order to evaluate the expression patterns of SRSF1 and PRMT1. The potential oncogenic mechanism of SRSF1 and PRMT1 in leukemogenesis was also investigated.

RESULTS

We identified significant up-regulation of SRSF1 and PRMT1 in the ND samples. Importantly, the expression of SRSF1 and PRMT1 returned to normal levels after CR, but rebounded in the RE samples. Our observation that SRSF1 could predict disease relapse was of particular interest, although the expression patterns of SRSF1 and PRMT1 were independent of the cytogenetic subtypes. In pre-B-cell lines, both SRSF1 and PRMT1 expression could be efficiently attenuated by the clinical chemotherapy agents arabinoside cytosine (Ara-c) or vincristine (VCR). Moreover, SRSF1 and PRMT1 were associated with each other in leukemia cells in vivo. Knock-down of SRSF1 resulted in an increase in early apoptosis, which could be further induced by chemotherapeutics.

CONCLUSIONS

Our results indicate that SRSF1 serves as an anti-apoptotic factor and potentially contributes to leukemogenesis in pediatric ALL patients by cooperating with PRMT1.

Histone arginine methylation keeps RUNX1 target genes in an intermediate state

The coordinated recruitment of epigenetic regulators of gene expression by transcription factors such as RUNX1 (AML1, acute myeloid leukemia 1) is crucial for hematopoietic differentiation. Here, we identify protein arginine methyltransferase 6 (PRMT6) as a central functional component of a RUNX1 corepressor complex containing Sin3a and HDAC1 in human hematopoietic progenitor cells. PRMT6 is recruited by RUNX1 and mediates asymmetric histone H3 arginine-2 dimethylation (H3R2me2a) at megakaryocytic genes in progenitor cells. H3R2me2a keeps RUNX1 target genes in an intermediate state with concomitant H3K27me3 and H3K4me2 but not H3K4me3. Upon megakaryocytic differentiation PRMT6 binding is lost, the H3R2me2a mark decreases and a coactivator complex containing WDR5/MLL and p300/pCAF is recruited. This leads to an increase of H3K4me3 and H3K9ac, which result in augmented gene expression. Our results provide novel mechanistic insight into how RUNX1 activity in hematopoietic progenitor cells maintains differentiation genes in a suppressed state but poised for rapid transcriptional activation.

Expression of RUNX1 isoforms and its target gene BLK in childhood acute lymphoblastic leukemia

Bone marrow samples from children with acute lymphoblastic leukemia were analyzed for the expression of RUNX1a/b/c isoforms. Obtained patterns were associated with genetic abnormalities and the expression of the RUNX1 regulated gene BLK. RUNX1c was present in all patients, but the expected over-expression of RUNX1a was not observed. Over-expression of total RUNT domain isoforms was detected in patients with extra RUNX1 copies, and unexpectedly, in those with t(4;11). Only expression of the total RUNT domain-containing isoforms and BLK presented positive correlation. Results suggest a more complex role of RUNX1 in leukemogenesis than the proposed antagonism between the isoforms.

SARS coronavirus 3b accessory protein modulates transcriptional activity of RUNX1b

Background

The causative agent of severe acute respiratory syndrome, SARS coronavirus (SARS-CoV) genome encodes several unique group specific accessory proteins with unknown functions. Among them, accessory protein 3b (also known as ORF4) was lately identified as one of the viral interferon antagonist. Recently our lab uncovered a new role for 3b in upregulation of AP-1 transcriptional activity and its downstream genes. Thus, we believe that 3b might play an important role in SARS-CoV pathogenesis and therefore is of considerable interest. The current study aims at identifying novel host cellular interactors of the 3b protein.

Methodology/Principal Findings

In this study, using yeast two-hybrid and co-immunoprecipitation techniques, we have identified a host transcription factor RUNX1b (Runt related transcription factor, isoform b) as a novel interacting partner for SARS-CoV 3b protein. Chromatin immunoprecipitaion (ChIP) and reporter gene assays in 3b expressing jurkat cells showed recruitment of 3b on the RUNX1 binding element that led to an increase in RUNX1b transactivation potential on the IL2 promoter. Kinase assay and pharmacological inhibitor treatment implied that 3b also affect RUNX1b transcriptional activity by regulating its ERK dependent phosphorylation levels. Additionally, mRNA levels of MIP-1α, a RUNX1b target gene upregulated in SARS-CoV infected monocyte-derived dendritic cells, were found to be elevated in 3b expressing U937 monocyte cells.

Conclusions/Significance

These results unveil a novel interaction of SARS-CoV 3b with the host factor, RUNX1b, and speculate its physiological relevance in upregulating cytokines and chemokine levels in state of SARS virus infection.

The ability of MLL to bind RUNX1 and methylate H3K4 at PU.1 regulatory regions is impaired by MDS/AML-associated RUNX1/AML1 mutations

The mixed-lineage leukemia (MLL) H3K4 methyltransferase protein, and the heterodimeric RUNX1/CBFβ transcription factor complex, are critical for definitive and adult hematopoiesis, and both are frequently targeted in human acute leukemia. We identified a physical and functional interaction between RUNX1 (AML1) and MLL and show that both are required to maintain the histone lysine 4 trimethyl mark (H3K4me3) at 2 critical regulatory regions of the AML1 target gene PU.1. Similar to CBFβ, we show that MLL binds to AML1 abrogating its proteasome-dependent degradation. Furthermore, a subset of previously uncharacterized frame-shift and missense mutations at the N terminus of AML1, found in MDS and AML patients, impairs its interaction with MLL, resulting in loss of the H3K4me3 mark within PU.1 regulatory regions, and decreased PU.1 expression. The interaction between MLL and AML1 provides a mechanism for the sequence-specific binding of MLL to DNA, and identifies RUNX1 target genes as potential effectors of MLL function.

A-to-I RNA editing: the "ADAR" side of human cancer

Carcinogenesis is a complex, multi-stage process depending on both endogenous and exogenous factors. In the past years, DNA mutations provided important clues to the comprehension of the molecular pathways involved in numerous cancers. Recently, post-transcriptional modification events, such as RNA editing, are emerging as new players in several human diseases, including tumours. A-to-I RNA editing changes the nucleotide sequence of target RNAs, introducing A-to-I/G "mutations". Since ADAR enzymes catalyse this nucleotide conversion, their expression/activity is essential and finely regulated in normal cells. This review summarizes the available knowledge on A-to-I RNA editing in the cancer field, giving a new view on how ADARs may play a role in carcinogenesis.

The leukemogenicity of AML1-ETO is dependent on site-specific lysine acetylation

The chromosomal translocations found in acute myelogenous leukemia (AML) generate oncogenic fusion transcription factors with aberrant transcriptional regulatory properties. Although therapeutic targeting of most leukemia fusion proteins remains elusive, the posttranslational modifications that control their function could be targetable. We found that AML1-ETO, the fusion protein generated by the t(8;21) translocation, is acetylated by the transcriptional coactivator p300 in leukemia cells isolated from t(8;21) AML patients, and that this acetylation is essential for its self-renewal-promoting effects in human cord blood CD34(+) cells and its leukemogenicity in mouse models. Inhibition of p300 abrogates the acetylation of AML1-ETO and impairs its ability to promote leukemic transformation. Thus, lysine acetyltransferases represent a potential therapeutic target in AML.

Chromatin regulation by RUNX1

The transcription factor RUNX1 is essential for definitive hematopoiesis and is required for the expression of a number of important hematopoietic regulator genes. It was recently shown that RUNX1 acts within a narrow developmental window during which it cannot be replaced by other members of the RUNX transcription factor family. Studies of the molecular basis of this phenomenon revealed that RUNX1 is required for the opening of chromatin of important hematopoietic regulator genes and for the formation, but not the maintenance of stable transcription factor complexes on these genes. However, the chromatin opening activity of RUNX1 is context dependent, indicating that it cooperates with alternate transcription factors at different stages of hematopoietic development. This review summarizes recent results on the regulation of chromatin structure by RUNX1 in developing hematopoietic cells.