Flt3/ITD Blocks Myeloid Differentiation Of Hematopoietic Cells By Up-Regulating Runx1

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3808-3808
Author(s):  
Tomohiro Hirade ◽  
Mariko Abe ◽  
Chie Onishi ◽  
Seiji Yamaguchi ◽  
Seiji Fukuda
Keyword(s):  
Conflicts Of Interest ◽  
Hematopoietic Cells ◽  
Cell Number ◽  
Dominant Negative ◽  
Leukemia Cells ◽  
Myeloid Differentiation ◽  
Differentiation And Proliferation ◽  
Runx1 Expression ◽  
Novel Therapeutic

Abstract Internal-Tandem-Duplication mutations in the FLT3 (FLT3/ITD) gene are detected in 30% of patients with acute myeloid leukemia (AML) and are associated with extremely poor prognoses. The lack of significant efficacy of FLT3/ITD inhibitors underscores the need to identify FLT3/ITD-specific signaling pathways that are distinct from those that occur in normal hematopoietic cells to develop novel therapeutic approaches. FLT3/ITD is classified as a “class I mutation” that drives the proliferation of leukemia cells. In addition to mutation of FLT3/ITD, a “class II mutation” that blocks differentiation of the pre-leukemic clone is generally required for the development of AML. For instance, dominant negative mutations of RUNX1 are occasionally found in patients with AML. These mutations of RUNX1 cause AML by blocking the differentiation of leukemia cells in combination with the mutation of FLT3/ITD. RUNX1 is a core-binding transcription factor and plays an important role in hematopoietic homeostasis, particularly differentiation and proliferation. Loss of RUNX1 blocks hematopoietic differentiation and is associated with the emergence of a primitive hematopoietic compartment, suggesting that RUNX1 generally induces differentiation of hematopoietic cells. However, the functional role of RUNX1 as a down-stream effector of FLT3/ITD has not been characterized. Herein, we investigated the role of Runx1 in aberrant proliferation and differentiation of hematopoietic cells induced by Flt3 /ITD. A comparison of RUNX1 expression levels in AML patients for whom information has been deposited in the public gene expression profile database (GSE1159) revealed that RUNX1 mRNA expression was significantly higher in FLT3/ITD+AML cells (N=78) than in FLT3/ITD-AML cells (N=190, P<0.05). The mRNA microarray analysis consistently demonstrated that Runx1 is up-regulated by Flt3/ITD in Ba/F3 cells. Up-regulation of Runx1 by Flt3/ITD was validated in Ba/F3 cells and 32D cells by quantitative RT-PCR. Incubation of control 32D cells with 20 ng/ml of G-CSF increased the number of Gr-1+/Mac-1+cells, whereas the induction of myeloid differentiation by G-CSF was abrogated by the overexpression of Flt3/ITD in 32D cells. By contrast, transduction of shRNA specific for Runx1 into Flt3/ITD+32D cells inhibited the expression of Runx1 mRNA by 60 % but increased the number and the proportion of Gr-1+/Mac-1+cells ; these effects were enhanced by incubation with G-CSF. These data indicate that Runx1 mediates the block of differentiation toward the myeloid lineage that is induced by Flt3/ITD. Moreover, the number of colony-forming units (CFU) over-expressing Flt3/ITD cultured in the absence of growth factors was reduced by Runx1-shRNA without affecting the total cell number in the suspension culture, as compared to Flt3/ITD+32D cells transduced with control-shRNA. This implies that antagonizing Runx1 facilitates the production of terminally differentiated cells that have lost colony-forming ability, thereby reducing the CFU number without altering the total number of cells. Finally, Runx1-shRNA inhibited the formation of secondary CFU colonies derived from the primary Flt3-ITD-over-expressing CFU colonies. Our results suggest that Flt3/ITD blocks myeloid differentiation of Flt3/ITD+cells by up-regulating Runx1 expression. The blocking of differentiation mediated by Runx1 in Flt3/ITD+cells is in contrast to the cell differentiation-inducing role of Runx1 in normal hematopoiesis, suggesting that the function of Runx1 in Flt3/ITD+cells may be distinct from that in normal cells. The reduction of secondary CFU colonies by Runx1-shRNA suggests that Runx1 may mediate self-renewal of Flt3/ITD+hematopoietic progenitor cells. These findings suggest that antagonizing RUNX1 may represent a novel therapeutic strategy to induce terminal differentiation of FLT3/ITD+AML cells in AML patients, in addition to inhibiting their aberrant proliferation. Disclosures: No relevant conflicts of interest to declare.

Re-Expression of the AML1/ETO Target Gene LAT2/NTAL/LAB Results In Direct Interference with Myeloid Differentiation In AML1/ETO-Positive Cells

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2474-2474
Author(s):  
Jesus Duque-Afonso ◽  
Aitomi Essig ◽  
Leticia M Solari ◽  
Tobias Berg ◽  
Heike L. Pahl ◽  
...  
Keyword(s):  
Western Blot ◽  
Cell Lines ◽  
Functional Role ◽  
Target Gene ◽  
Conflicts Of Interest ◽  
Myeloid Cell ◽  
Leukemia Cells ◽  
Myeloid Differentiation ◽  
Granulocytic Differentiation

Abstract Abstract 2474 Background: The leukemia-specific oncofusion protein AML1/ETO regulates different target genes, including the LAT2 gene (encoding the adaptor molecule LAT2/NTAL/LAB), which is epigenetically repressed by AML1/ETO as we have previously described. LAT2 is phosphorylated by c-kit and has a role in mast cell and B cell activation. To address the functional role of LAT2 during myeloid differentiation, expression studies were performed in myeloid cell lines, and LAT2 was overexpressed by retroviral gene transfer in AML1/ETO-positive Kasumi-1 cells and AML1/ETO-negative U-937 cells. Methods: To induce monocytic and granulocytic differentiation, the myeloid cell lines U-937, HL-60 and NB4 were treated with PMA and ATRA, respectively, and LAT2 expression measured by both Northern and Western blot. LAT2 was overexpressed in Kasumi-1 and U-937 cells by use of the retroviral vector pMYSiG-IRES-GFP. Virus was produced in 293T cells and titrated in TE671 cells. Following transduction, GFP-positive cells were sorted by fluorescence-activated cell sorting (FACS). Transduced cells were treated with PMA (2 and 10 nM for 24 and 48 hours) and ATRA (0.1 μM and 0.5 μM for 48 and 96 hours), respectively. Results: The AML1/ETO-negative myeloid cell lines HL-60, NB4 and U-937 readily expressed LAT2, which was further upregulated by PMA, and transiently downregulated with ATRA. In the AML1/ETO-positive Kasumi-1 and SKNO-1 cells, LAT2 expression was absent. To address the functional role of this repression, forced expression of LAT2 was achieved in Kasumi-1 and U-937 cells and resulted in effective processing of LAT2 protein (confirmed by Western blot), and a decrease in the expression of the differentiation markers CD11b and CD11c (FACS analysis) in Kasumi-1 but not U-937, with only minor effects of LAT2 overexpression upon apoptosis and cell growth arrest. Notably, during both PMA- and ATRA-induced differentiation, a striking maturation block occurred in Kasumi-1 (measured by CD11b/CD11c expression, observed at different doses and time points of these treatments), while differentiation of U-937 cells was unimpaired by overexpression of LAT2. Conclusions: In AML1/ETO-negative leukemia cells, LAT2 expression is differentially regulated during monocytic and granulocytic differentiation. In AML1/ETO-positive leukemia cells, in which LAT2 is repressed, LAT2 re-expression imposes a striking maturation block. Graded expression of this novel AML1/ETO target gene may therefore play an important role in maintaining the phenotypic characteristics of this leukemia subtype. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Sumoylation of Pyruvate Kinase M2 Inhibits Myeloid Differentiation in Hematopoietic Cells

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 3919-3919
Author(s):  
Li Xia ◽  
Xin-Ran Wang ◽  
Ran Wei ◽  
Jin-Song Yan ◽  
Guo-Qiang Chen ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Pyruvate Kinase ◽  
Nuclear Localization ◽  
Conflicts Of Interest ◽  
Critical Role ◽  
Hematopoietic Cells ◽  
Leukemic Cells ◽  
Myeloid Differentiation ◽  
Significant Shift

Abstract The pyruvate kinase (PK) is a rate-limiting glycolytic enzyme catalyzing the dephosphorylation of phosphoenolpyruvate to pyruvate. M2 form of PK (PKM2) is expressed during embryogenesis and is the predominant form in tumors of different types. In contrast to the essential role of PKM2 in solid tumors, much less is known about the effects of PKM2 in hematopoietic cells and the development of leukemia. Here we found that PKM2 is modified by small ubiquitin-like modifier 1(SUMO1), which can be reduced by a SUMO1-specific protease SENP1 in hematopoietic cells. SUMOylation induced nuclear localization and conformation change from tetramer to dimer of PKM2. Importantly, SUMOylation of PKM2 is prevalent in a variety of leukemic cell lines as well as primary samples from patients with hematologic malignancies. In consistency, predominant nuclear localization and dimeric forms of PKM2 in leukemic cells were observed. Using in vitro SUMOylation reaction-coupled liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS), we identified K270 lysine residue of PKM2 as the SUMOylation target. Replacement of endogenous PKM2 with mutant PKM2K270 showed a significant shift of PKM2 from tetramer to dimer. To investigate the potential leukemogenic effect of PKM2 SUMOylation, murine hematopoietic progenitor 32D clone 3 (32Dcl3) transfectants expressing wild type(WT) or mutant PKM2K270 were generated and G-CSF-induced differentiation was evaluated by morphology appearance and expression of myeloid associated surface markers CD11b and Gr-1. The results showed that expression of WT PKM2 but not mutant PKM2K270 significantly blocked myeloid differentiation. Further investigations revealed that SUMO1 modification of PKM2 at K270 is essential in mediating the interaction between PKM2 and Runt-related transcription factor 1(RUNX1), a master transcriptional factor implicated in the differentiation of hematopoietic cells. This interaction led to a downregulation of RUNX1 during G-CSF-induced myeloid differentiation of 32D cells, which could be abrogated by expression of mutant PKM2K270. Collectively, these data indicated that SUMOylated PKM2 blocks myeloid differentiation through suppressing RUNX1. These findings reveal a novel nonmetabolic function of PKM2 in modulating myeloid differentiation and highlight the critical role of SUMOylation in leukemogenesis. Disclosures No relevant conflicts of interest to declare.

scholarly journals Zebra "Fishing" the Role of Granulin in Hematopoiesis

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 1194-1194
Author(s):  
Raquel Espin Palazon ◽  
Xiaoyi Cheng ◽  
Clyde A Campbell ◽  
Liangdao Li ◽  
Bettina Schmid ◽  
...  
Keyword(s):  
Animal Model ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Hematopoietic Cells ◽  
Cell Types ◽  
Myeloid Differentiation ◽  
Hematopoietic System ◽  
High Conservation

Granulin (GRN) is a multifunctional protein with anti-inflammatory properties and involved in neurological diseases and tumorigenesis. It contains several cysteine-rich motifs that are unique to this protein, which are conserved from sponges to humans indicating their ancient evolutionary origin. Despite being highly expressed by certain hematopoietic cell lineages, the role that GRN plays in hematopoiesis has reminded elusive. The multifunctional nature of this protein, together with its wide expression in all mammalian cell types has challenged the characterization of its functional role in hematopoiesis due to its effects on other tissues. Therefore, we took advantage of the whole genomic duplication of the zebrafish (Danio rerio) and the high conservation of the cysteine-rich motifs among the zebrafish and human granulins to address this knowledge gap and explore their role in hematopoiesis in vivo. The whole genome duplication that separated teleost fish from mammals resulted in two copies of the granulin gene in the zebrafish (Granulin a and Granulin b, Grna and Grnb respectively). This has allowed us an unprecedented view into the function of this protein in hematopoiesis. We show that like mammals, grnb transcripts are found in all cell types, including hematopoietic cells. In contrast, grna is restricted to hematopoietic cells, including myeloid populations. The distinct cell expression of grna and grnb suggests that, in the zebrafish, grna evolved to specifically function in hematopoiesis, while grnb may have taken on the rest of the biological roles assigned to the mammalian granulin. The zebrafish is an animal model with unique advantages for in vivo studies. Its external development allows us to circumvent the challenges of in utero experimentation required using mammals, permitting the use of non-invasive imaging techniques to study developmental hematopoiesis. In addition, more than 70% of genes identified in the zebrafish are conserved in humans. These, together with its high conservation with the human hematopoietic system has led to a greater understanding and prevention of human hematologic diseases by using this elegant animal model. These unique advantages of the zebrafish, in addition to its genetic amenability allowed us to generate Grna and Grnb single mutants and identify their impact in the hematopoietic system in vivo. While the absence of Grnb did not affect the development of the hematopoietic system, lack of Grna led to decreased differentiation of myeloid precursors into neutrophils and macrophages. Therefore, Grna knockout allowed us to disrupt the hematopoietic function of granulin while keeping unaltered its function in the brain and other non-hematopoietic tissues. Although viable, adult Grna mutants developed kidney marrow (the fish analogous to the mammalian bone marrow) failure, with increased progenitors and decreased mature myeloid cells. Mechanistically, we found that pu.1, the main transcription factor that leads to myeloid differentiation, directly bound grna enhancers, upregulating its expression. We have demonstrated that Grna enhanced myeloid gene expression, and decreased gata1 expression thereby facilitating myeloid differentiation and inhibiting the erythroid genetic program. Finally, we show that these findings in the zebrafish are also conserved in humans. Altogether, we have identified the hematopoietic role of granulin without disturbing its biological functions in other tissues. We have unveiled a powerful and novel master regulator for myeloid differentiation that could potentially be utilized for the treatment of hematological disorders such as neutropenia and leukemia. Disclosures No relevant conflicts of interest to declare.

Kinase Activity of RTKs Is Dispensable for Factor Independent Growth and Transformation of a Myeloid Cell Line 32D in the Presence of Cbl Mutants.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3970-3970
Author(s):  
◽  
Srinivasa Rao Bandi ◽  
Marion Rensinghoff ◽  
Rebekka Grundler ◽  
Lara Tickenbrock ◽  
...  
Keyword(s):  
Cell Line ◽  
Tyrosine Kinases ◽  
Kinase Activity ◽  
Kinase Inhibitors ◽  
Conflicts Of Interest ◽  
Myeloid Cell ◽  
Dominant Negative ◽  
Class Iii ◽  
Primary Resistance

Abstract Abstract 3970 Poster Board III-906 Purpose The Cbl proto-oncogene products have emerged as important components of the signal transduction cascades downstream of both non-receptor and receptor tyrosine kinases (RTKs). By regulation of receptor trafficking and degradation, they have been shown to tightly regulate the intensity and amplitude of RTK activation. c-Kit belongs to the family of the class-III RTKs and plays an important role in the pathogenesis of acute myeloid leukemia (AML). So far, very little is known about the role of c-Cbl mutants in the role of c-Kit signaling. Results We analyzed the interaction of c-Cbl with c-Kit and the functional relevance of this interaction in the IL-3-dependent murine myeloid progenitor cell line 32Dcl3. We recently identified the first c-Cbl mutation in human disease in an AML patient, named Cbl-R420Q. Co-expression of two different dominant negative mutants of c-Cbl (Cbl-R420Q or Cbl-70Z) with Kit induced cytokine-independent proliferation, survival and clonogenic growth. Importantly, transformation was observed also with kinase-dead forms of Kit and Flt3 in the presence of Cbl-70Z, but not in the absence of Kit or Flt3, suggesting a mechanism dependent on RTKs, but independent of their kinase activity. Instead, transformation appeared to depend on Src family kinases (SFKs), as c-Cbl co-immunoprecipitated with SFKs and SFK inhibition abolished transformation. Conclusion Our results indicate that c-Cbl has an important role in c-Kit signal mitigation. They demonstrate that disturbed mechanisms of c-Kit internalization have important implications for its transforming potential, possibly in the development of AML. Furthermore, these findings may explain primary resistance to tyrosine kinase inhibitors targeted at RTKs. Disclosures: No relevant conflicts of interest to declare.

Deacetylase Inhibitor Cocktails Provide Striking Synergistic Interactions in Human Leukemia Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 4404-4404
Author(s):  
Michele Cea ◽  
Antonia Cagnetta ◽  
Floriana Fruscione ◽  
Santina Bruzzone ◽  
Gabriele Zoppoli ◽  
...  
Keyword(s):  
Hydroxamic Acid ◽  
Mononuclear Cells ◽  
Conflicts Of Interest ◽  
Hdac Inhibitors ◽  
Leukemia Cell ◽  
Lymphocytic Leukemia ◽  
Dominant Negative ◽  
Myelogenous Leukemia ◽  
Leukemia Cells ◽  
Human Leukemia

Abstract Abstract 4404 Cancer cells almost invariably exhibit aberrant histone deacetylase (HDAC) activity leading to changes in chromatine structure, altered gene expression, poor differentiation, impaired apoptosis and increased proliferation. Accordingly, virtually all the HDAC inhibitors currently available show some degree of antitumor activity in preclinical cancer models and several of these compounds are currently under investigation or already approved for the treatment of human malignancies. Such is the case of the hydroxamic acid derivative suberoylanilide hydroxamic acid (Vorinostat, Zolinza), approved for the treatment of cutaneous T cell lymphomas. Sirtuins are a large family of deacetylases characterized by a unique, NAD+-dependent enzymatic mechanism. In addition to their established role in metabolism and longevity, recent evidence points to an emerging role for sirtuins in carcinogenesis. In the attempt to identify drug combinations that would increase the activity of traditional HDAC inhibitors we have explored the combination of valproic acid (VA) and butyrate (BU) with the sirtuin inhibitors cambinol and sirtinol in primary B-cell chronic lymphocytic leukemia (B-CLL) cells (n=35), acute myelogenous leukemia (AML) cells (n=10) and leukemia cell lines. Cell viability was assessed by propidium iodide staining and flow cytometry. Combination indices were determined using the median-effect method. In leukemia cells, exposure to sirtuin inhibitors synergistically increased VA and BU mediated cytotoxicity. Conversely, these drugs were poorly active and failed to show any cooperation in healthy cells, including peripheral blood mononuclear cells and fibroblasts, suggesting a cancer-specific mode of action. Similar results were obtained by combining VA or BU with the Nampt inhibitor APO866, which reduces intracellular NAD+ levels and thereby prevents sirtuin activity. Remarkably, SIRT1 and SIRT6 inhibition per se did not seem to account for cell demise upon HDAC inhibition since expression of a dominant negative SIRT1 isoform or RNA interference-mediated SIRT6 silencing failed to increase VA and BU activity. Our data indicate a specific requirement by leukemia cells for sustained sirtuin activity when classical HDACs are inhibited. This feature is suitable to be therapeutically exploited by combining sirtuin inhibitors or APO866 with classical HDAC inhibitors especially for the treatment of hematological malignancies. Disclosures: No relevant conflicts of interest to declare.

Negative Effects of GM-CSF Signaling In t(8;21)-Induced Leukemia

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3163-3163
Author(s):  
Shinobu Matsuura ◽  
Ming Yan ◽  
Eun-Young Ahn ◽  
Miao-Chia Lo ◽  
David Dangoor ◽  
...  
Keyword(s):  
Myeloid Leukemia ◽  
Sex Chromosome ◽  
De Novo ◽  
Conflicts Of Interest ◽  
Hematopoietic Cells ◽  
Receptor Activation ◽  
Pseudoautosomal Region ◽  
Wild Type ◽  
Gm Csf

Abstract Abstract 3163 The t(8;21)(q22;q22) translocation is one of the most common chromosomal translocations in de novo acute myeloid leukemia (AML). The 8;21 translocation is often associated with additional cytogenetic abnormalities. The loss of the sex chromosome (LOS) is by far the most frequent abnormality found in association with the t(8;21) leukemia, accounting for 32–59% of patients, in contrast to other types of AML in which the LOS occurs in less than 5% of patients. To evaluate the role of sex chromosome deletion in t(8;21)-related leukemogenesis, hematopoietic cells from a mouse line with only one sex chromosome were used in retrovirus-mediated t(8;21) (AML1-ETO) expression and transplantation assays. The absence of leukemia in those animals suggested that a gene present in the pseudoautosomal region of sex chromosomes in humans but not in mice may be the target gene in LOS. The granulocyte-macrophage colony-stimulating factor receptor α (GM-CSFRα) gene is one such gene and is also known to be involved in myeloid cell survival, proliferation and differentiation. The GM-CSFRα gene is specifically down-regulated in AML patients with t(8;21), but not in other common translocations (Valk PJM et al, NEJM, 2004). The GM-CSFR complex is composed of α and βc subunits that assemble into a complex for receptor activation and signaling. To investigate the role of GM-CSFR signaling in t(8;21)-mediated leukemogenesis, GM-CSFR common β subunit knockout (GM-CSFRβc-/-) mice were used in our studies as a model for deficient GM-CSFR signaling. Transduction of AML1-ETO in hematopoietic cells from GM-CSFRβc-/- resulted in myeloid leukemia of a median survival time of 225 days, high percentage of blasts in peripheral blood and bone marrow, anemia, thrombocytopenia, hepatomegaly and splenomegaly. Comparison of wild-type and GM-CSFRβc-/- cells in the same transplantation resulted in development of AML1-ETO-induced leukemia at higher penetrance in GM-CSFRβc-/- cells (28.5% vs 100%). Moreover, the latency of leukemia was shorter in GM-CSFRβc-/- cells than in wild-type cells after transduction of AML1-ETO9a. Analysis of the hematopoietic compartment of healthy GM-CSFRβc-/- mice detected no significant abnormalities in the immature hematopoietic compartment (LSK, CMP, GMP, MEP), suggesting that AML1-ETO expression is required for leukemia to occur. In vitro, expression of AML1-ETO alone is sufficient for the immortalization of normal hematopoietic cells, as demonstrated by serial replating capacity of cells in methylcellulose colony assay. Addition of mGM-CSF to the basic cytokine cocktail (mIL-3, hIL-6, mSCF, hEPO) did not significantly affect number, type, size, and cell composition of colony cells. In contrast, the addition of mGM-CSF eliminated the replating capacity of AML1-ETO expressing cells, although they survived longer than control vector-infected cells. The results suggest that activation of GM-CSF signaling can specifically abrogate the self-renewal ability of potential leukemic stem cells in the early immortalization phase. These results support a possible tumor suppressor role of GM-CSF in leukemogeneis by AML1-ETO and may provide clues to understand how AML1-ETO corrupts normal GM-CSF signals to its own advantage for leukemogenic transformation. Disclosures: No relevant conflicts of interest to declare.

The Role of c-Abl in Jak2 Activation in IL-3-Dependent Cells

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1672-1672
Author(s):  
Wenjing Tao ◽  
Xiaohong Leng ◽  
Ralph B. Arlinghaus
Keyword(s):  
Cell Survival ◽  
Kinase Activity ◽  
Conflicts Of Interest ◽  
Hematopoietic Cells ◽  
Chromosomal Translocation ◽  
Kinase Domain ◽  
Bimolecular Fluorescence Complementation ◽  
Abl Kinase ◽  
A Minor

Abstract Abstract 1672 The reciprocal chromosomal translocation of Abl and Bcr locus [t(9: 22)] is present in 95% of chronic myeloid leukemia (CML) patients. The resulting Bcr-Abl oncoprotein contains a persistently activated tyrosine kinase activity that activates Jak2/Stat5 signaling pathways. Little is known about the molecular mechanism of Jak2 activation in Bcr-Abl positive CML cells, except that the IL-3 receptor is required (Tao et al., Oncogene 2008). We found that the Jak2 activity (measured by pY1007/1008) in 32D mouse hematopoietic cells steadily diminished immediately upon IL-3 withdrawal. However, expression of kinase-inactive form of Bcr-Abl (p210K1172R) in 32D cells maintained Jak2 activity for up to 8 hrs after IL-3 withdrawal. Our previous studies have shown that the C-terminal region (CT-4) of c-Abl binds to Jak2 as does the kinase domain of c-Abl (Xie et al. Oncogene, 2001). We found that Jak2 activation depends on its binding to the CT-4 region of c-Abl using Bimolecular fluorescence complementation assays. In order to examine the role of c-Abl in Jak2 activation, we expressed c-Abl in both 32D cells (32D-Abl) and 32D cells expressing p210K1172R (32D-p210K1172R+Abl). We found that unlike 32D-Abl cells which remained cytokine-dependent, a minor population (∼7%) of 32D- p210K1172R+Abl cells gained growth independency of IL-3. Compared to 32D-Abl cells in which the level of Jak2 activity was barely detected by pY1007/1008 antibody, 32D-p210K1172R+Abl cells showed a dramatic elevation of Jak2 activation, indicating that c-Abl alone is unable to induce Jak2 activation in hematopoietic cells. Phosphorylation on p210Y177 in 32D-p210K1172R+Abl cells was also strongly increased, indicative of activated Jak2 activity (Samanta et al., Leukemia 2011). We found that 32D-p210K1172R+Abl cells were sensitive to Imatinib Mesylate (IM), as 80% of 32D-p210K1172R+Abl cells were apoptotic after treatment with 5μM IM for 24hrs, indicating that the cell survival depends on the activated c-Abl kinase. The apoptosis induced by IM in 32D-p210K1172R+Abl cells could be effectively rescued by addition of IL-3, indicating the importance of Jak2 activation through IL-3 pathway in maintaining cell survival. The above results suggest that a higher level of c-Abl enables cells expressing a Bcr-Abl kinase defective protein to acquire cytokine-independent growth. The elevation of Jak2 activity in 32D-p210K1172R+ABL cells correlated with the increased c-Abl kinase activity. We propose that the c-Abl kinase plays two crucial roles in these Bcr-Abl kinase mutant cells: 1) making cells cytokine-independent for growth, and 2) promoting persistent Jak2 activation. These results lead us to propose that the Abl kinase domain within Bcr-Abl promotes Jak2 activation by binding to the Jak2 kinase. As our recent findings indicate that Jak2 is a dominant player in CML (Samanta et al., Leukemia 2011) and particularly in later stages of Bcr-Abl positive CML, we propose that the inhibition of both Jak2 and Bcr-Abl kinase activities will result in a near complete elimination of leukemia cells including CD34+CML progenitor cells. Disclosures: No relevant conflicts of interest to declare.

A Critical Role of Mir-9 in Myelopoesis and EVI1-Induced Leukemogenesis.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2332-2332
Author(s):  
Vitalyi Senyuk ◽  
Yunyuan Zhang ◽  
Yang Liu ◽  
Ming Ming ◽  
Jianjun Chen ◽  
...  
Keyword(s):  
Cell Transformation ◽  
Conflicts Of Interest ◽  
Critical Role ◽  
Ectopic Expression ◽  
Myeloid Differentiation ◽  
Dna Hypermethylation ◽  
Hematopoietic Stem

Abstract Abstract 2332 MicroRNA-9 (miR-9) is required for normal neurogenesis and organ development. The expression of miR-9 is altered in several types of solid tumors suggesting that it may have a function in cell transformation. However the role of this miR in normal hematopoiesis and leukemogenesis is unknown. Here we show that miR-9 is expressed at low levels in hematopoietic stem/progenitor cells (HSCs/HPCs), and that it is upregulated during hematopoietic differentiation. Ectopic expression of miR-9 strongly accelerates terminal myelopoiesis, while promoting apoptosis in vitro and in vivo. In addition, the inhibition of miR-9 in HPC with a miRNA sponge blocks myelopoiesis. EVI1, required for normal embryogenesis, and is considered an oncogene because inappropriate upregulation induces malignant transformation in solid and hematopoietic cancers. In vitro, EVI1 severely affects myeloid differentiation. Here we show that EVI1 binds to the promoter of miR-9–3 leading to DNA hypermethylation of the promoter as well as repression of miR-9. We also show that ectopic miR-9 reverses the myeloid differentiation block that is induced by EVI1. Our findings suggest that inappropriately expressed EVI1 delays or blocks myeloid differentiation, at least in part by DNA hypermethylation and downregulation of miR-9. It was previously reported that FoxOs genes inhibit myeloid differentiation and prevent differentiation of leukemia initiating cells. Here we identify FoxO3 and FoxO1 as new direct targets of miR-9 in hematopoietic cells, and we find that upregulation of FoxO3 in miR-9-positive cells reduces the acceleration of myelopoiesis. These results reveal a novel role of miR-9 in myelopoiesis and in the pathogenesis of EVI1-induced myeloid neoplasms. They also provide new insights on the potential chromatin-modifying role of oncogenes in epigenetic changes in cancer cells. Disclosures: No relevant conflicts of interest to declare.

Unraveling a Novel Mechanism of Stat5 Regulation by FAK and Rac1 in Flt3ITD Induced Leukemogenesis

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 858-858
Author(s):  
Anindya Chatterjee ◽  
Joydeep Ghosh ◽  
Baskar Ramdas ◽  
Sasidhar Vemula ◽  
Holly Martin ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Essential Role ◽  
Nuclear Translocation ◽  
Conflicts Of Interest ◽  
Myeloproliferative Neoplasms ◽  
Dominant Negative ◽  
Post Transplantation ◽  
Pharmacological Inhibition ◽  
F 14

Abstract Abstract 858 Multiple genetic checks and balances regulate the complex process of hematopoiesis. Despite these measures, mutations in crucial regulatory genes are still known to occur, which in some cases results in abnormal hematopoiesis, including leukemogenesis and/or myeloproliferative neoplasms (MPN). An example of a mutated gene that contributes to leukemogenesis is the FMS- like tyrosine kinase 3 (Flt3) that encodes a receptor tyrosine kinase, which plays an essential role in normal hematopoiesis. Interestingly, Flt3 is one of the most frequently mutated genes (∼30%) in acute myeloid leukemia (AML). Although various pathways downstream of Flt3 activation that lead to leukemic transformation have been extensively studied, effective treatment options for Flt3ITD mediated leukemogenesis is still warranted. In this study we used genetic, pharmacological and biochemical approaches to identify a novel role of Focal adhesion kinase (FAK) in Flt3ITD induced leukemogenesis. We observed hyperactivation of FAK in Flt3ITD expressing human and mouse cell. Treatment with FAK specific small molecule inhibitors F-14 and Y-11, inhibited proliferation and induced cell death of Flt3ITD expressing cells. Similarly, treatment of primary AML patient samples (n=9) expressing Flt3ITD mutations with F-14 inhibited their proliferation. Consistently expression of a dominant negative domain of FAK (FRNK) inhibited hyperproliferation and induced death of Flt3ITD bearing cells. Further, low-density bone marrow (LDBM) cells derived from FAK−/− mice transduced with Flt3ITD showed significantly reduced growth compared to wild-type (WT) LDBM cells transduced with Flt3ITD. We also observed hyperactivation of Rac1 in Flt3ITD expressing cells downstream of FAK, which was downregulated upon treatment with FAK inhibitor F-14 and Y11. Moreover, expression of dominant negative Rac1N17, or treatment with Rac1 inhibitor NSC23766 inhibited hyperproliferation of ITD bearing cells. We next wanted to ascertain the underlying mechanism of FAK mediated activation of Rac1 in Flt3ITD expressing cells. Toward this end, we found RacGEF Tiam1 to be hyperactive in Flt3ITD expressing cells, which was downregulated upon pharmacological inhibition of FAK. A Tiam1-Rac1 complex was also co-immunoprecipitated from Flt3ITD bearing cells, and this association was perturbed upon pharmacological inhibition of FAK. While, Stat5 a key molecule in Flt3ITD mediated leukemic progression, is activated and recruited to the nucleus to express Stat5 responsive genes; however the mechanism of Stat5 translocation to the nucleus is unknown. We observed a novel mechanism involving FAK and Rac1GTPase, in regulating the nuclear translocation of active Stat5. Pharmacological inhibition of FAK and Rac1 resulted in reduced Rac1 and STAT5 translocation into the nucleus, indicating a role of FAK-Rac-STAT5 signaling in Flt3ITD induced leukemogenesis. More importantly, expression of Flt3ITD in Rac1−/− or FAK−/− LDBM cells, showed inhibition of Stat5 activation and its failure to translocate into the nucleus when compared to Flt3ITD expression in WT-LDBM cells. We also observed association between active Rac1 and active Stat5 in the nucleus and in whole cell lysates of Flt3ITD bearing cells, and also in human AML patient samples (n=3), which was attenuated upon pharmacological inhibition of FAK. To determine the effect of FAK inhibition in vivo on Flt3ITD induced MPN, syngeneic transplantation was performed, and mice were treated with vehicle or with FAK inhibitor F-14. While vehicle treated mice developed MPN within 30 days, mice treated with F-14 showed significant overall survival (*p<0.02) and over 50% F-14 treated mice survived till 60 days post transplantation. Inhibition of kinases, and other signaling molecules, that are deregulated in cancer is an exciting new therapeutic strategy. This study indicate an essential role of FAK and Rac1 molecules in Flt3ITD mediated proliferation, survival and leukemogenesis, and demonstrates a novel mechanistic role of FAK/Rac1 in translocating active Stat5 into the nucleus and regulates transformation. To our knowledge, this is also the first time a role of RacGEF Tiam1 is observed in Flt3ITD induced leukemogenesis. Overall, this study demonstrates inhibition of FAK and Rac1 as potentially novel targets, and provides an alternative approach in treating humans suffering from Flt3-ITD induced AML. Disclosures: No relevant conflicts of interest to declare.

Gtpase Immunity-Associated Protein Family Member 4 Contributes to the Enhanced Expansion of HSPCs in RUNX1 Deficient Mice

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4344-4344
Author(s):  
Amanda Scholl ◽  
Kentson Lam ◽  
Alex Muselman ◽  
Tingdong Tang ◽  
Shinobu Matsuura ◽  
...  
Keyword(s):  
Family Member ◽  
Conflicts Of Interest ◽  
Protein Family ◽  
Dominant Negative ◽  
Negative Regulator ◽  
Wild Type ◽  
Double Knockout ◽  
Hematopoietic Stem ◽  
Myeloid Progenitor

Abstract RUNX1 is the transcription factor described as the master regulator of hematopoiesis. Due to its central role during blood development, numerous RUNX1 mutations have been reported in hematologic abnormalities. Mice null for Runx1 die during embryogenesis, lacking definitive HSCs. Conditional Runx1Δ/Δ mice are viable, but exhibit a variety of blood abnormalities. The most salient defect in these Runx1Δ/Δ mice is expansion of the hematopoietic stem and progenitor cell (HSPC) population, measured as an increase in number of lineage negative, Sca1 positive, cKit positive (LSK) cells. A shortened form of RUNX1 (RUNX1SF) lacking the C-terminal and part of the N-terminal domain (41-214) acts as a dominant negative regulator of RUNX1 and hence also models RUNX1 loss-of-function. A differential gene expression analysis of HSPCs derived from Runx1Δ/Δ compared to wild type mice uncovered GTPase immunity-associated protein family member 4 (GIMAP4) as one of the genes most highly upregulated. Previous studies have focused almost exclusively on the role of GIMAP4 as a pro-apoptotic protein during T-cell development. This study illuminates a novel non-apoptotic role of GIMAP4 in a formerly unstudied HSPC context. Runx1Δ/Δ mice were crossed with Gimap4-/- mice to generate a double knockout (dKO) mouse line. These dKO mice exhibited attenuated HSPC proliferation in comparison to Runx1Δ/Δ mice, suggesting that GIMAP4 functions in this HSPC expansion phenotype. BMT experiments using lethally irradiated C57 mice and RUNX1SF transduced wild type versus Gimap4-/-bone marrow confirmed this result. GIMAP4 also worked independently and coordinately with RUNX1 to influence individual progenitor populations. Common lymphoid progenitors (CLP) were affected only by GIMAP4. Gimap4-/- mice exhibited an expansion of the CLP population, consistent with its pro-apoptotic role in lymphoid populations. Conversely, both RUNX1 and GIMAP4 coordinately exerted an effect on myeloid progenitor populations. Runx1Δ/Δ mice harbored expanded granulocyte-macrophage progenitor (GMP) and common myeloid progenitor (CMP) populations. This expansion was not observed when GIMAP4 was also ablated. This suggests a pro-proliferative role of GIMAP4 specifically in myeloid populations. These opposing roles of GIMAP4 in lymphoid versus myeloid cells suggest a more contextual, cell-specific role of this GTPase protein. Ultimately, this study provides insight into how RUNX1 and GIMAP4 may coordinate to maintain HSPC homeostasis. Disclosures No relevant conflicts of interest to declare.

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