scholarly journals Chromosome 21 Gain Is Dispensable for Transient Myeloproliferative Disorder (TMD) Development

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 2764-2764
Author(s):  
Julius Lukes ◽  
Eliska Potuckova ◽  
Julia Starkova ◽  
Jan Stary ◽  
Jan Zuna ◽  
...  
Keyword(s):  
Cell Line ◽  
Kinase Activity ◽  
Myeloproliferative Disorder ◽  
Chromosome 21 ◽  
Fusion Genes ◽  
Wild Type ◽  
Pathogenetic Role ◽  
Transient Myeloproliferative Disorder ◽  
The Impact

Abstract Transient myeloproliferative disorder (TMD) is a hematopoietic disease, characterized by a clonal proliferation of immature megakaryoblasts in the neonatal period occurring in approximately 10% of newborns with Down syndrome (DS). Rarely, TMD occurs in non-DS newborns but then it is associated with somatic trisomy 21 (tri21). Tri21 together with in-utero gained mutations in the GATA1 gene encoding a myeloid transcription factor are thus considered essential in TMD. Recently, we have identified a TMD with a typical manifestation and course in a newborn without DS/somatic tri21, which admits that tri21 is dispensable for TMD development. To elucidate the alternative TMD pathogenesis, we performed comprehensive genomic/transcriptomic profiling of this TMD case. We utilized high-density SNP array and whole exome and transcriptome sequencing (WES/RNAseq) to detect copy number changes, mutations and fusion genes. We did not find any aberrations on chromosome 21 and any fusion genes. Two focal intronic losses, likely representing benign germline variants, were found on chromosome X. In addition to 6 missense mutations affecting genes without established roles in hematopoietic disorders, we found in-frame deletions in the GATA1 and JAK1 genes. Both mutations are novel. The GATA1 D65_C228del mutation is predicted to result in an internally truncated protein - GATA1aber. Unlike GATA1s (resulting from GATA1 mutations in DS-TMD) which lacks the transactivation domain (TAD) but retains both Zinc fingers (ZF), GATA1aber lacks part of TAD and the N-terminal ZF. Nevertheless, we hypothesize that GATA1aber substitutes the pathogenetic role of GATA1s. The JAK1 gene encodes a non-receptor tyrosine-kinase engaged in the JAK/STAT signaling pathway. The identified mutation results in the loss of phenylalanine 636 (F636del), which is located in the pseudokinase domain and belongs to a conserved amino acid triad (F636-F575-V658) that is believed to mediate a structural switch controlling the JAK1 catalytic activity (Toms, Nat Struct Mol Biol, 2013). JAK1 mutations are implicated in various hematological malignancies including acute megakaryocytic leukemia, and we hypothesize that JAK1 F636del co-operates with GATA1aber on TMD pathogenesis via deregulation of cytokine/growth factor signaling. We cloned the coding sequences of GATA1aber and JAK1 F636del and transfected them into a model cell line in which we confirmed the expression of both in-silico predicted proteins. Their subcellular trafficking was analogous to that of their wild type counterparts; GATA1aber was found in the nucleus and JAK1 F636del in both the nucleus and cytoplasm. Next, we assessed the kinase activity of JAK1 F636del. To distinguish auto- from trans-phosphorylation, we utilized the JAK1 F636del construct harboring an inactivating mutation of an ATP-binding site (K908G). The JAK1 F636del (but not JAK1 F636del + K908G) was autophosphorylated on Y1034/Y1035 and induced STATs phosphorylation both under steady-state conditions and following non-specific stimulation with PMA. However, at all studied time points all phosphorylation levels were lower compared to wild-type JAK1. Moreover, unlike constitutively active JAK1 V658I, JAK1 F636del did not confer IL3-independent growth to the murine B-cell progenitor cell line BAF3. Interestingly, the transforming potential of double-mutated JAK1 (JAK1 V658I + F636del) was enforced compared to JAK1 V658I. These data show that F636del does not lead to constitutive activation, but in the same time it is not functionally neutral. As the impact of F636del on JAK1 function may vary depending on upstream signaling, we are currently assessing JAK1 F636 kinase activity/transforming potential in BAF3 cells stably expressing the IL6 receptor, which (unlike the IL3 receptor) directly activates JAK1 upon ligand binding. In the future, we plan to study the impact of JAK1 F636del on GATA1s induced deregulation of erythroid/megakaryocytic lineage development and to demonstrate "GATA1s-like" function of GATA1aber. To conclude, we identified two novel mutations affecting GATA1 and JAK1 as likely drivers in an alternative tri21-independent TMD pathogenesis. As the pathogenetic role of tri21 has been poorly understood so far, we believe that by clarifying an alternative mechanism of TMD development, we could improve our understanding of this intriguing disease in general. Support: GAUK 86218 Disclosures No relevant conflicts of interest to declare.

Increased Interferon-αa Signaling During Megakaryocyte Ontogeny: Implications for the Spontaneous Resolution of Down Syndrome Transient Myeloproliferative Disorder.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1272-1272 ◽  
Author(s):  
Karen Wieland ◽  
Andrew Woo ◽  
Thomas Akie ◽  
Alan B. Cantor
Keyword(s):  
Bone Marrow ◽  
Down Syndrome ◽  
Conflicts Of Interest ◽  
Fetal Liver ◽  
Myeloproliferative Disorder ◽  
Spontaneous Resolution ◽  
Chromosome 21 ◽  
Dependent Manner ◽  
Wild Type ◽  
Transient Myeloproliferative Disorder

Abstract Abstract 1272 Poster Board I-294 About ten percent of infants with Down syndrome (DS) are born with a transient myeloproliferative disorder (DS-TMD), which spontaneously resolves within the first few months of life. However, the basis for this resolution remains unknown. Acquired mutations leading to exclusive production of a short isoform of the transcription factor GATA-1 (GATA-1s) occur in all cases of DS-TMD, and knock-in mice that exclusively produce GATA-1s have hyperproliferation of megakaryocytes during early fetal liver hematopoiesis, but not during later developmental stages. In this study, we found striking upregulation of the interferon-αa (IFN-αa) receptor and multiple IFN-αa responsive genes, including Ifi203, Ifi205, Irf-1, Irf-8, and Ifitm6, in immunophenotypically isolated megakaryocyte progenitor cells (MkPs) from bone marrow versus embryonic day 13.5 (e13.5) fetal liver of wild type mice. These differences were confirmed at the protein level in megakaryocytes by in situ immunohistochemistry. Addition of IFN-αa to GATA-1s containing e13.5 fetal liver MkPs reduces their hyperproliferation in vitro in a dose-dependent manner. Conversely, injection of neutralizing IFN-αa/β antibodies, but not control IgG, into adult GATA-1s mice markedly increases the percentage of bone marrow CD41+ cells and morphologically recognizable megakaryocytes, in contrast to wild type mice. We propose that increases in IFN-αa signaling during megakaryocyte ontogeny may account for the developmental stage-specific effects of GATA-1s on megakaryocyte hyperproliferation, and possibly the spontaneous resolution of DS-TMD. Interestingly, the genes encoding the IFN-αa/β receptor are located on human chromosome 21 and are expressed at 1.6 times that in trisomy versus disomy 21 cells. We speculate that increased interferon alpha signaling during embryogenesis may be the basis for the strong selective pressure for GATA-1s producing mutations in trisomy 21 fetuses in the first place. Disclosures No relevant conflicts of interest to declare.

scholarly journals Similarities and differences between IL11 and IL11RA1 knockout mice for lung fibro-inflammation, fertility and craniosynostosis

2020 ◽  
Author(s):  
Benjamin Ng ◽  
Anissa A. Widjaja ◽  
Sivakumar Viswanathan ◽  
Jinrui Dong ◽  
Sonia P. Chothani ◽  
...  
Keyword(s):  
Knockout Mice ◽  
Lung Fibroblasts ◽  
Loss Of Function ◽  
Wild Type ◽  
Reduced Body ◽  
Body Weights ◽  
Show Evidence ◽  
Similarities And Differences ◽  
The Impact

AbstractGenetic loss of function (LOF) in IL11RA infers IL11 signaling as important for fertility, fibrosis, inflammation and craniosynostosis. The impact of genetic LOF in IL11 has not been characterized. We generated IL11-knockout (Il11-/-) mice, which are born in normal Mendelian ratios, have normal hematological profiles and are protected from bleomycin-induced lung fibro-inflammation. Noticeably, baseline IL6 levels in the lungs of Il11-/- mice are lower than those of wild-type mice and are not induced by bleomycin damage, placing IL11 upstream of IL6. Lung fibroblasts from Il11-/- mice are resistant to pro-fibrotic stimulation and show evidence of reduced autocrine IL11 activity. Il11-/- female mice are infertile. Unlike Il11ra1-/- mice, Il11-/- mice do not have a craniosynostosis-like phenotype and exhibit mildly reduced body weights. These data highlight similarities and differences between LOF in IL11 or IL11RA while establishing further the role of IL11 signaling in fibrosis and stromal inflammation.

scholarly journals Engineering of the Pyruvate Dehydrogenase Bypass inSaccharomyces cerevisiae: Role of the Cytosolic Mg2+ and Mitochondrial K+ Acetaldehyde Dehydrogenases Ald6p and Ald4p in Acetate Formation during Alcoholic Fermentation

2000 ◽  
Vol 66 (8) ◽  
pp. 3151-3159 ◽  
Author(s):  
Fabienne Remize ◽  
Emilie Andrieu ◽  
Sylvie Dequin
Keyword(s):  
Carbon Flux ◽  
Alcoholic Fermentation ◽  
Pyruvate Decarboxylase ◽  
Wine Yeast ◽  
Wild Type ◽  
Acetate Production ◽  
Wine Yeast Strain ◽  
Acetate Formation ◽  
The Impact

ABSTRACT Acetic acid plays a crucial role in the organoleptic balance of many fermented products. We have investigated the factors controlling the production of acetate by Saccharomyces cerevisiaeduring alcoholic fermentation by metabolic engineering of the enzymatic steps involved in its formation and its utilization. The impact of reduced pyruvate decarboxylase (PDC), limited acetaldehyde dehydrogenase (ACDH), or increased acetoacetyl coenzyme A synthetase (ACS) levels in a strain derived from a wine yeast strain was studied during alcoholic fermentation. In the strain with the PDC1gene deleted exhibiting 25% of the PDC activity of the wild type, no significant differences were observed in the acetate yield or in the amounts of secondary metabolites formed. A strain overexpressingACS2 and displaying a four- to sevenfold increase in ACS activity did not produce reduced acetate levels. In contrast, strains with one or two disrupted copies of ALD6, encoding the cytosolic Mg2+-activated NADP-dependent ACDH and exhibiting 60 and 30% of wild-type ACDH activity, showed a substantial decrease in acetate yield (the acetate production was 75 and 40% of wild-type production, respectively). This decrease was associated with a rerouting of carbon flux towards the formation of glycerol, succinate, and butanediol. The deletion of ALD4, encoding the mitochondrial K+-activated NAD(P)-linked ACDH, had no effect on the amount of acetate formed. In contrast, a strain lacking both Ald6p and Ald4p exhibited a long delay in growth and acetate production, suggesting that Ald4p can partially replace the Ald6p isoform. Moreover, the ald6 ald4 double mutant was still able to ferment large amounts of sugar and to produce acetate, suggesting the contribution of another member(s) of the ALDfamily.

scholarly journals CRISPR-Cas9 Mediated RNase L Knockout Regulates Cellular Function of PK-15 Cells and Increases PRV Replication

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Chao Sui ◽  
Dandan Jiang ◽  
Xiangju Wu ◽  
Xiaoyan Cong ◽  
Feng Li ◽  
...  
Keyword(s):  
Cell Line ◽  
Gene Editing ◽  
Rna Degradation ◽  
Type I ◽  
Rnase L ◽  
Agarose Gel Electrophoresis ◽  
Biological Functions ◽  
Wild Type ◽  
Induction Of Apoptosis

Ribonuclease L (RNase L) is an important antiviral endoribonuclease regulated by type I IFN. RNase L is activated by viral infection and dsRNA. Because the role of swine RNase L (sRNase L) is not fully understood, in this study, we generated a sRNase L knockout PK-15 (KO-PK) cell line through the CRISPR/Cas9 gene editing system to evaluate the function of sRNase L. After transfection with CRISPR-Cas9 followed by selection using puromycin, sRNase L knockout in PK-15 cells was further validated by agarose gel electrophoresis, DNA sequencing, and Western blotting. The sRNase L KO-PK cells failed to trigger RNA degradation and induced less apoptosis than the parental PK-15 cells after transfected with poly (I: C). Furthermore, the levels of ISGs mRNA in sRNase L KO-PK cells were higher than those in the parental PK-15 cells after treated with poly (I: C). Finally, both wild type and attenuated pseudorabies viruses (PRV) replicated more efficiently in sRNase L KO-PK cells than the parental PK-15 cells. Taken together, these findings suggest that sRNase L has multiple biological functions including cellular single-stranded RNA degradation, induction of apoptosis, downregulation of transcript levels of ISGs, and antiviral activity against PRV. The sRNase L KO-PK cell line will be a valuable tool for studying functions of sRNase L as well as for producing PRV attenuated vaccine.

Modulation of procaspase-7 self-activation by PEST amino acid residues of the N-terminal prodomain and intersubunit linker

2017 ◽  
Vol 95 (6) ◽  
pp. 634-643
Author(s):  
Juliano Alves ◽  
Miguel Garay-Malpartida ◽  
João M. Occhiucci ◽  
José E. Belizário
Keyword(s):  
Amino Acid ◽  
Large Subunit ◽  
Small Subunit ◽  
Cleavage Sites ◽  
Amino Acid Residues ◽  
Wild Type ◽  
Caspase 7 ◽  
Caspase Family ◽  
The Impact

Procaspase-7 zymogen polypeptide is composed of a short prodomain, a large subunit (p20), and a small subunit (p10) connected to an intersubunit linker. Caspase-7 is activated by an initiator caspase-8 and -9, or by autocatalysis after specific cleavage at IQAD198↓S located at the intersubunit linker. Previously, we identified that PEST regions made of amino acid residues Pro (P), Glu (E), Asp (D), Ser (S), Thr (T), Asn (N), and Gln (Q) are conserved flanking amino acid residues in the cleavage sites within a prodomain and intersubunit linker of all caspase family members. Here we tested the impact of alanine substitution of PEST amino acid residues on procaspase-7 proteolytic self-activation directly in Escherichia coli. The p20 and p10 subunit cleavage were significantly delayed in double caspase-7 mutants in the prodomain (N18A/P26A) and intersubunit linker (S199A/P201A), compared with the wild-type caspase-7. The S199A/P201A mutants effectively inhibited the p10 small subunit cleavage. However, the mutations did not change the kinetic parameters (kcat/KM) and optimal tetrapeptide specificity (DEVD) of the purified mutant enzymes. The results suggest a role of PEST-amino acid residues in the molecular mechanism for prodomain and intersubunit cleavage and caspase-7 self-activation.

Role of HFE in Hepatic Iron Overload: Novel Findings Demonstrate Direct Effects of Mutant C282Y on Hepcidin and Calreticulin mRNA Expression.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1549-1549
Author(s):  
Jorge P. Pinto ◽  
Pedro Ramos ◽  
Sergio de Almeida ◽  
Susana Oliveira ◽  
Laura Breda ◽  
...  
Keyword(s):  
Protective Effect ◽  
Cell Line ◽  
Mononuclear Cells ◽  
Hepatic Cell ◽  
Wild Type ◽  
Peripheral Blood Mononuclear ◽  
Mutant Proteins ◽  
Over Expression ◽  
Blood Mononuclear Cells

Abstract Studies done in non-hepatic cell lines, focusing on the interaction between HFE with TFR1 and β-2M proved insufficient to explain the discrepancies found in the clinical penetrance of hemochromatosis in subjects carrying the C282Y mutation. Our first goal was to investigate the role of HFE wild type (wt) and mutant proteins (C282Y and H63D) in a human hepatic cell line, focusing on the cellular localization and interaction of HFE with the expression of other iron related proteins. HFE mutant C282Y was found to be retained in the endoplasmic reticulum (ER). Thus, in addition, we investigated the effect of HFE wt and mutant proteins on Calreticulin, which is a chaperon protein that responds to ER stress and has a protective effect on oxidative damage in some cell lines. Here we report setting up a stable transfection of wt- and mutant-HFE in a hepatic cell line (HepG2) and examine the intracellular distribution of wt- and HFE mutants, their effect on iron intake independently of TFR1 and on the expression of other iron and ER stress response genes, namely Hepcidin and Calreticulin. In addition, we validated some of the novel effects of HFE on Calreticulin using peripheral blood mononuclear cells from HFE patients. The localization of the HFE variants was analyzed using KDEL and Golgin-97 as ER and the Golgi complex markers, respectively. HFE C282Y shows a high degree of overlap with the ER markers, confirming a retention of this variant in this organelle. Over-expression of the HFE wt impaired the intake of 55Fe relatively to transfected control cells (P<0.008) independently of TFR1, as demonstrated by RNAi silencing. Hamp RNA expression was decreased in cells over expressing C282Y in comparison to HFE wt cells (P<0.011). Finally over-expression of HFE wt decreases Calreticulin mRNA, whereas the C282Y had an opposite effect, compared to the control cell line. A similar result was observed in peripheral blood mononuclear cells (PMBC) of C282Y homozygous HFE patients, compared to wild type blood donors (P<0.006). Interestingly, this data suggest that synthesis of the HFE mutant C282Y triggers a protective effect on oxidative damage mediated by Calreticulin. In fact, HepG2 cells over-expressing C282Y showed lower levels of ROS than HFE wt (P<0.004). This observation might contribute to explain some of the discrepancies seen in the clinical penetrance of the disease in C282Y carrying subjects. The direct effect of the mutant HFE C282Y on mRNA expression of hepcidin also demonstrated here for the first time corroborates and provides a molecular basis for earlier reports of low hepcidin levels in HH patients and in Hfe-KO mice.

BCL2A1 Is A Survival and Immortalization Factor for Primitive Myeloid Hematopoietic Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3365-3365
Author(s):  
Jean-Yves Metais ◽  
Ashley E. Dunfee ◽  
Rodrigo T. Calado ◽  
Cynthia E. Dunbar
Keyword(s):  
Bone Marrow ◽  
Cell Line ◽  
Gene Product ◽  
Myeloid Leukemia ◽  
Hematopoietic Cells ◽  
Marker Genes ◽  
Empty Vector ◽  
Myeloid Progenitor ◽  
The Impact

Abstract We recently reported development of an acute myeloid leukemia in a rhesus macaque transplanted with autologous CD34+ cells transduced with a murine stem cell virus-derived replication defective retrovirus vector expressing only marker genes under control of the strong MCSV LTR. This animal had an unusual clonal reconstitution pattern the first year following transplant, with a single transduced myeloid progenitor cell clone accounting for up to 80% of then normal myelopoiesis (Kelly, 2005). The same vector-containing clone then transformed to AML five years following transplantation, and each tumor cell was shown to contain two vector insertions, one localized 20 kb upstream the CDw92 gene on chromosome 9, and the second localized in the first intron of BCL2A1 on chromosome 15 (Seggewiss, 2006), a gene in the anti-apoptotic BCL2 family not previously linked to myeloid leukemia. BCL2A1 was highly expressed in the tumor cells. This tumor was the first hematopoietic malignancy reported in a recipient of primitive cells transduced with a replication-incompetent vector containing only marker genes, and suggested that BCL2A1 could have potent effects on myeloid cell behavior. To investigate the impact of the BCL2A1 gene product on hematopoietic cells, we cloned the murine and human HA-tagged BCL2A1 cDNAs into lentivirus vectors and transduced the murine BaF3 hematopoietic cell line as a model to study the impact of expression of these proteins on hematopoiesis. We confirmed overexpression of the proteins in the producer cell line as well as in transduced cells by western blot using an anti-HA monoclonal antibody. BaF3 cell proliferation and survival are dependant on IL-3, and under IL-3 replete conditions overexpression of murine or human BCL2A1 did alter proliferation compared with untransduced cells or cells transduced with an empty vector. Removal of IL-3 from the cell culture media leads to rapid apoptosis of BaF3 cells, with cell cycle arrest in the G1 and an apoptotic subpopulation appearing within 24 hours of IL-3 removal. 45% untransduced or empty vector cells were apoptotic, and this fraction decreased to 30% and 15% respectively for BaF3 cells expressing murine or human BCL2A1. These results were confirmed by direct analysis of apoptosis. Only BaF3 cells over-expressing human BCL2A1 were still alive and arrested in G1 after 3 days of culture without IL-3. The murine BCL2A1 had similar but less striking effects. Gene expression analyses on the BaF3 cell populations are ongoing, to identify potential downstream targets of the BCL2A1 protein. The BCL2A1 and empty vectors were also utilized in murine bone marrow cell immortalization assay, previously utilized to identify genes impacting on the survival and expansion of primary myeloid progenitor cells (Du, 2005). In an initial set of experiments, clonal clonal expansion was obtained with marrow cells expressing murine (4 clones) and human (5 clones) BCL2A1 but not for empty vector or untransduced murine marrow. Mice have also been transplanted with primary bone marrow cells transduced with the BCL2A1 and control vectors, and are being followed for in vivo expansion of transduced clones and development of leukemia. In conclusion, we have confirmed the role of BCL2A1 as an anti-apoptotic protein, now in myeloid hematopoietic cells, and will continue to investigate the role of this gene product in hematopoiesis and leukemogenesis.

PAX5/TEL Exhibits a Dominant-Negative Role by Inhibiting the Expression of Genes Involved in BCR Signalling and Suppressing the Binding of Wild Type PAX5 to Its Direct Target Gene CD79A (mb-1) in a human Pre-B ALL Cell Line.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3455-3455
Author(s):  
Gabriela B. Iwanski ◽  
Nils Heinrich Thoennissen ◽  
PohYeen Lor ◽  
Norihiko Kawamata ◽  
Daniel Nowak ◽  
...  
Keyword(s):  
B Cell ◽  
Cell Line ◽  
Fusion Gene ◽  
Cell Receptor ◽  
Dominant Negative ◽  
Fusion Product ◽  
Wild Type ◽  
Rt Pcr ◽  
Downstream Target

Abstract Abstract 3455 Poster Board III-343 Acute lymphoblastic leukemia (ALL), one of the most common malignancies in childhood, is a heterogeneous disease with individual leukemia subtypes differing in their response to chemotherapy. Recent findings suggest that disruptions of B cell receptor (BCR) signalling pathways may be involved in the development of ALL. The transcription factor PAX5 is essential for the commitment of lymphoid progenitors to the B-lymphocytic lineage. In 30% of childhood B-ALL cases, PAX5 is a frequent target of aberrancies, showing monoallelic loss, point mutations, or chromosomal translocations, whereas the role of these aberrancies is still poorly understood. Using high resolution SNP-chip analysis, we have recently identified several candidate partner genes fused to PAX5 in pediatric ALL, ETV6 (TEL), FOXP1, AUTS2, C20orf112, which bind to PAX5 recognition sequences as strongly as wild-type PAX5 (wt PAX5) suppressing its transcriptional activity in a dominant-negative fashion. In order to study the role of PAX5/TEL in leukemic evolution of B-ALL, we transfected the leukemic BCP cell line Nalm 6, which endogenously expresses PAX5, with a retroviral vector encoding PAX5/TEL and confirmed its expression by Western blotting and RT-PCR. Previously, the fusion gene PAX5/TEL has been cloned into the retroviral vector pMSCV-IRES-GFP (MIGR) from a patient diagnosed with B-cell precursor ALL (BCP) with t(9;12)(q11;p13). This fusion product consists of the 5′-end NH2 terminal region of the PAX5 gene and the almost whole sequence of the TEL gene. PAX5/TEL-MIGR expressing cells were sorted for GFP and analyzed by gene expression profiling on Affymetrix HG-U133 plus 2.0 Array in comparison to cells transfected with vector control (MIGR) and a MIGR vector encoding wt PAX5 (wtPAX5/MIGR). The probes were normalized with the Affymetrix MAS5.0 software. Probes were considered to be differentially expressed with a fold change ≤ 2 or ≥ 2, respectively. We identified a set of about 200 genes that were differentially expressed in the PAX5/TEL expressing cells, most of which were downregulated, compared to the controls. A subset of these genes encodes proteins important for BCR signalling: RAG1, one of two key mediators in the process of V(D)J recombination, VPREB3, which is involved in the early phase of pre-BCR assembly, the Runt domain transcription factor Runx1 (AML1) and FOXP1. The latter two genes are fusion partners of PAX5 in pediatric B-ALL and loss of FOXP1 leads to impaired DH–JH and VH–DJH rearrangement. Additionally, we found BACH2, which plays an important role during B-cell development, as well as protein kinase C-epsilon (PKCe) to be downregulated. PKCe is highly expressed in B cells linking the BCR to the activation of mitogen-activated protein kinases (MAPK). We confirmed the downregulation of the affected genes by RT-PCR. Strikingly, VPREB3 expression showed a significant downregulation of up to 170-fold, and RAG1 up to 90-fold. Loss of the RAG1/2 locus has been found in four precursor B-cell ALL cases, which indicates that defects in this process might contribute to leukemogenesis. We also detected a significant decrease in the expression of wt PAX5 as well as its direct downstream target CD79A (mb-1). CD79A (mb-1) encodes the B cell receptor component Ig-a and its early B cell-specific mb-1 promoter is a target for regulation by early B cell-specific transcription factors like E2A, early B cell factor (EBF), and PAX5. The latter is important for the activation of the mb-1 promoter by recruiting Ets proteins through protein-protein interactions. We investigated the binding efficiency of wt PAX5 to the promoter region of CD79A by chromatin-immunoprecipitation (ChIP). For the ChIP assay, we used a PAX5 antibody detecting the C-terminal region of PAX5 so that the antibody can bind the wt PAX5 but not the fusion product PAX5/TEL of which the C-terminal side is fused to TEL. Binding of wt PAX5 to the promoter region of CD79A was diminished by expression of the PAX5/TEL-fusion protein compared to the controls, leading to repression of CD79A, which we also confirmed by RT-PCR. In conclusion, we show that the expression of PAX5/TEL in a leukemic cell line has a repressor function on the expression of wt PAX5 as well as other genes important in BCR signalling. Also, we demonstrated that PAX5/TEL has a negative impact on the binding affinity of one of the direct downstream target genes of wt PAX5. Our results indicate a repressor role of the fusion gene PAX5/TEL including BCR signalling and point towards its contribution to leukemic transformation. 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.

p27 Is Mislocalized to the Cytoplasm by BCR-ABL In a Kinase-Independent Manner and Contributes to Leukemogenesis

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 512-512
Author(s):  
Anupriya Agarwal ◽  
Ryan J Meckenzie ◽  
Thomas O'Hare ◽  
Kavin B Vasudevan ◽  
Dorian H LaTocha ◽  
...  
Keyword(s):  
Tumor Suppressor ◽  
Kinase Activity ◽  
Immunofluorescence Microscopy ◽  
Independent Effect ◽  
Histopathological Analysis ◽  
Imatinib Treatment ◽  
Wild Type ◽  
Abl Kinase

Abstract Abstract 512 Background: BCR-ABL promotes cell cycle progression by interfering with the regulatory functions of p27, a cyclin dependent kinase (Cdk) inhibitor and tumor suppressor. We have previously shown that BCR-ABL kinase activity promotes degradation of nuclear p27 (Agarwal, A. et al. Blood 2008). Additionally, in primary CML cells, p27 is mislocalized to the cytoplasm, thereby relieving Cdks from p27 inhibition. Results from studies of solid tumors show that cytoplasmic p27 can actively contribute to oncogenesis, raising the question of whether cytoplasmic p27 in CML cells may actively promote leukemogenesis rather than merely compromise Cdk inhibition. We hypothesize that BCR-ABL disrupts p27 function in a dual manner by reducing nuclear p27, where p27 normally serves as a tumor suppressor, and by increasing cytoplasmic p27, where it might have oncogenic activity. Experimental Approach and Results: Immunoblotting of nuclear and cytoplasmic lysates of CD34+ cells from 11 CML patients revealed that p27 localization is predominantly cytoplasmic in the majority of patients (10/11; 91%) irrespective of disease phase, while p27 was mostly nuclear in normal controls. Similar results were obtained by immunofluorescence microscopy. Imatinib treatment increased nuclear p27 suggesting that nuclear p27 levels are regulated by BCR-ABL kinase activity. However, imatinib does not alter cytoplasmic p27 levels, suggesting that cytoplasmic mislocalization of p27 is a kinase-independent effect of BCR-ABL. Kinase-independent regulation of cytoplasmic p27 localization was also tested by immunofluorescence microscopy of p27−/− MEFs engineered to express active or kinase-dead BCR-ABL in combination with wild-type p27. In these cells cytoplasmic p27 abundance was increased both by kinase-active or kinase-dead BCR-ABL as compared to the vector control. To interrogate the role of p27 in vivo we retrovirally transduced p27+/+ or p27−/− bone marrow with BCR-ABL-GFP retrovirus and sorted Lin-/c-Kit+/Sca-I+ cells by FACS, allowing for injection of exactly matched numbers of BCR-ABL-expressing GFP+ cells (5000/animal). Median survival was significantly reduced for recipients of p27−/− marrow as compared to p27+/+ controls (34 days vs. 93 days p<0.0001). Recipients of p27−/− marrow also exhibited significantly increased white blood cell (4.5-fold) and platelet counts (3.9-fold) as well as spleen size (6-fold) and liver size (1.6-fold). Accordingly, there was more pronounced leukemic infiltration of myeloid precursors on histopathology as compared to controls. An in vivo competition experiment performed by injecting equal numbers of BCR-ABL-transduced p27−/− and p27+/+ marrow cells in congenic recipients resulted in leukemias in recipient mice (N=8) that were derived exclusively from p27−/− cells. In total, these results suggest that the net function of p27 in CML is tumor suppressive. To functionally dissect the role of nuclear and cytoplasmic p27, we used p27T187A transgenic mice (in which nuclear p27 degradation is reduced) and p27S10A mice (in which p27 export to the cytoplasm is reduced resulting in predominantly nuclear p27). Mice of matched genetic background were used as p27WT controls in CML retroviral transduction/transplantation experiments. In both cases, survival was prolonged compared to controls: 25 vs. 21 days for p27T187A (p=0.05) and 32 vs. 23 days for p27S10A (p=0.01). This suggests that stabilization of nuclear p27 (p27T187A) and more significantly lack of cytoplasmic p27 (p27S10A) attenuate BCR-ABL-mediated leukemogenesis. Consistent with this, autopsy and histopathological analysis revealed reduced hepatosplenomegaly (p27T187A mice) and improved cell differentiation with a relative increase of mature neutophils (p27S10A mice) as compared to wild-type controls. Conclusions: These results provide in vivo evidence that p27 has genetically separable dual roles in CML as both a nuclear tumor suppressor and cytoplasmic oncogene. A kinase-independent activity of BCR-ABL contributes to leukemogenesis through aberrant p27 localization to the cytoplasm. This oncogene activity is independent from the kinase-dependent degradation of nuclear p27. We speculate that the inability of tyrosine kinase inhibitors to reverse cytoplasmic p27 mislocalization may contribute to disease persistence despite effective inhibition of BCR-ABL kinase activity. Disclosures: Deininger: Novartis: Consultancy; BMS: Consultancy; Ariad: Consultancy; genzyme: Research Funding.

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