Reciprocal t(9;22) ABL/BCR fusion proteins: leukemogenic potential and effects on B cell commitment

Background: t(9;22) is a balanced translocation, and the chromosome 22 breakpoints (Philadelphia chromosome – Ph+) determine formation of different fusion genes that are associated with either Ph+ acute lymphatic leukemia (Ph+ ALL) or chronic myeloid leukemia (CML). The "minor" breakpoint in Ph+ ALL encodes p185BCR/ABL from der22 and p96ABL/BCR from der9. The "major" breakpoint in CML encodes p210BCR/ABL and p40ABL/BCR. Herein, we investigated the leukemogenic potential of the der9-associated p96ABL/BCR and p40ABL/BCR fusion proteins and their roles in the lineage commitment of hematopoietic stem cells in comparison to BCR/ABL. Methodology: All t(9;22) derived proteins were retrovirally expressed in murine hematopoietic stem cells (SL cells) and human umbilical cord blood cells (UCBC). Stem cell potential was determined by replating efficiency, colony forming - spleen and competitive repopulating assays. The leukemic potential of the ABL/BCR fusion proteins was assessed by in a transduction/transplantation model. Effects on the lineage commitment and differentiation were investigated by culturing the cells under conditions driving either myeloid or lymphoid commitment. Expression of key factors of the B-cell differentiation and components of the preB-cell receptor were determined by qRT-PCR. Principal Findings: Both p96ABL/BCR and p40ABL/BCR increased proliferation of early progenitors and the short term stem cell capacity of SL-cells and exhibited own leukemogenic potential. Interestingly, BCR/ABL gave origin exclusively to a myeloid phenotype independently from the culture conditions whereas p96ABL/BCR and to a minor extent p40ABL/BCR forced the B-cell commitment of SL-cells and UCBC. Conclusions/Significance: Our here presented data establish the reciprocal ABL/BCR fusion proteins as second oncogenes encoded by the t(9;22) in addition to BCR/ABL and suggest that ABL/BCR contribute to the determination of the leukemic phenotype through their influence on the lineage commitment

p185(BCR/ABL) has a lower sensitivity than p210(BCR/ABL) to the allosteric inhibitor GNF-2 in Philadelphia chromosome-positive acute lymphatic leukemia

Background: The t(9;22) translocation leads to the formation of the chimeric breakpoint cluster region/c-abl oncogene 1 (BCR/ABL) fusion gene on der22, the Philadelphia chromosome. The p185(BCR/ABL) or the p210(BCR/ABL) fusion proteins are encoded as a result of the translocation, depending on whether a "minor" or "major" breakpoint occurs, respectively. Both p185(BCR/ABL) and p210(BCR/ABL) exhibit constitutively activated ABL kinase activity. Through fusion to BCR the ABL kinase in p185(BCR/ABL) and p210(BCR/ABL) "escapes" the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. A novel class of compounds including GNF-2 restores allosteric inhibition of the kinase activity and the transformation potential of BCR/ABL. Here we investigated whether there are differences between p185(BCR/ABL) and p210(BCR/ABL) regarding their sensitivity towards allosteric inhibition by GNF-2 in models of Philadelphia chromosome-positive acute lymphatic leukemia. Design and methods: We investigated the anti-proliferative activity of GNF-2 in different Philadelphia chromosome-positive acute lymphatic leukemia models, such as cell lines, patient-derived long-term cultures and factor-dependent lymphatic Ba/F3 cells expressing either p185(BCR/ABL) or p210(BCR/ABL) and their resistance mutants. Results: The inhibitory effects of GNF-2 differed constantly between p185(BCR/ABL) and p210(BCR/ABL) expressing cells. In all three Philadelphia chromosome-positive acute lymphatic leukemia models, p210(BCR/ABL)-transformed cells were more sensitive to GNF-2 than were p185BCR/ABL-positive cells. Similar results were obtained for p185(BCR/ABL) and the p210(BCR/ABL) harboring resistance mutations. Conclusions: Our data provide the first evidence of a differential response of p185(BCR/ABL)- and p210(BCR/ABL)- transformed cells to allosteric inhibition by GNF-2, which is of importance for the treatment of patients with Philadelphia chromosome-positive acute lymphatic leukemia

Immunocytochemical study of BCR and bcr-abl localization in K562 cells

Aim: To obtain polyclonal antibodies against recombinant proteins recognizing Bcr domain and fusion region of Bcr-Abl and analyze the patterns of intracellular distribution of Bcr and Bcr-Abl proteins in K562 cells of chronic myelogenous leukemia. Methods: The coding sequences of DН and РН domains of Bcr-Abl were cloned, and the recombinant proteins were expressed in E. coli. The rabbit polyclonal antibodies were produced and used for immunocytochemical study of Bcr and Bcr-Abl localization in K562 cells. Results: The gene constructs containing sequences coding for DН and РН domains of Bcr-Abl have been obtained. The antibodies with relative specificity to corresponding recombinant proteins differ by the patterns of their intracellular reactivity with Bcr- and Bcr-Abl related structures. While Bcr protein is located predominantly perinuclearly, antibody against hybrid Bcr-Abl protein is reacted with the structures in cell periphery, namely on cell membranes. Conclusion: Antibodies against DН and РН domains of Bcr-Abl react with proteins located differently in chronic myelogenous leukemia cells. The difference in intracellular localization of Bcr and Bcr-Abl may be attributable to the different domains interacting with different multiprotein complexes

Combination of \u3cem\u3eBcr-Abl\u3c/em\u3e-specific RNA Interference with lmatinib Treatment in the K-562 Cell Line

RNA interference (RNAi) involves the specific repression of the translation of a gene through mRNA degradation. Its application has been extended to a variety of studies both in vitro and in vivo. The Bcr-Abl translocation is the cytogenetic marker for chronic myelogenous leukemia (CML) and has been studied extensively. The K-562 cell line possesses the Bcr-Abl fusion gene and has been established as a model for RNAi. Imatinib mesylate (Gleeved) is a proven specific inhibitor of the Bcr-Abl tyrosine kinase. The aim of this study was to combine K-562 cells primes with short interfering RNA (siRNA) targeting the Bcr-Abl fusion site with treatment with Gleevec. Two different preperations of siRNA: homogenous-synthetic Bcr-Abl and heterogeneous-transcribed-digested Bcr-Abl were used to silence the Bcr-Abl fusion gene. The synthetic siRNA consisted of a homogenous mixture of 21nt long double stranded RNA duplexes specific for the Bcr-Abl fusion site. The transcribed-digested Bcr-Abl siRNA were generated using an in vitro transcription method producing a 450 bp cloned fragment with the Bcr-Abl fusion site in the center of the cloned region. This cloned fragment was further digested with RNAse III to produce a heterogeneous mizture of Bcr-Abl 19-21nt siRNA duplexes. We demonstrated a 70% down-regulation of the Bcr-Abl mRNA through real time PCR and RT-PCR as well as a 75% down-regulation of the Bcl-Abl and Bcl-XL proteins in K-562 cells transfected with synthetic Bcr-Abl siRNA. The IC50 of Gleevec alone in the K-562 subline F1 was lowered from 0.2μM to 0.06μM in cells transfected with both preparations of Bcr-Abl siRNA, while no effect was observed in an irrelevant siRNA control. This suggests an additive relationship between Gleevec and Bcr-Abl-specific-siRNA treated cells. An increase in apoptosis was also seen in K-562 cells primes with Bcr-Abl siRNA and treated with Gleevec indicating the additive relationship between Gleevec and Bcr-Abl siRNA. These results indicate that priming K-562 cells with Bcr-Abl siRNA correlate with a decrease in the effective dose of Gleevec required to inhibit the Bcr-Abl protein

BCR and its mutants, the reciprocal t(9;22)-associated ABL/BCR fusion proteins, differentially regulate the cytoskeleton and cell motility

BACKGROUND: The reciprocal (9;22) translocation fuses the bcr (breakpoint cluster region) gene on chromosome 22 to the abl (Abelson-leukemia-virus) gene on chromosome 9. Depending on the breakpoint on chromosome 22 (the Philadelphia chromosome – Ph+) the derivative 9+ encodes either the p40((ABL/BCR) )fusion transcript, detectable in about 65% patients suffering from chronic myeloid leukemia, or the p96((ABL/BCR) )fusion transcript, detectable in 100% of Ph+ acute lymphatic leukemia patients. The ABL/BCRs are N-terminally truncated BCR mutants. The fact that BCR contains Rho-GEF and Rac-GAP functions strongly suggest an important role in cytoskeleton modeling by regulating the activity of Rho-like GTPases, such as Rho, Rac and cdc42. We, therefore, compared the function of the ABL/BCR proteins with that of wild-type BCR. METHODS: We investigated the effects of BCR and ABL/BCRs i.) on the activation status of Rho, Rac and cdc42 in GTPase-activation assays; ii.) on the actin cytoskeleton by direct immunofluorescence; and iii) on cell motility by studying migration into a three-dimensional stroma spheroid model, adhesion on an endothelial cell layer under shear stress in a flow chamber model, and chemotaxis and endothelial transmigration in a transwell model with an SDF-1α gradient. RESULTS: Here we show that both ABL/BCRs lost fundamental functional features of BCR regarding the regulation of small Rho-like GTPases with negative consequences on cell motility, in particular on the capacity to adhere to endothelial cells. CONCLUSION: Our data presented here describe for the first time an analysis of the biological function of the reciprocal t(9;22) ABL/BCR fusion proteins in comparison to their physiological counterpart BCR

Association of HLA Class I and Class II genes with bcr-abl transcripts in leukemia patients with t(9;22) (q34;q11)

BACKGROUND: Based on the site of breakpoint in t(9;22) (q34;q11), bcr-abl fusion in leukemia patients is associated with different types of transcript proteins. In this study we have seen the association of HLA genes with different types of bcr-abl transcripts. The association could predict the bcr-abl peptide presentation by particular HLA molecules. METHODS: The study included a total of 189 patients of mixed ethnicity with chronic myelogenous leukemia and acute lymphocytic leukemia who were being considered for bone marrow transplantation. Typing of bcr-abl transcripts was done by reverse transcriptase PCR method. HLA typing was performed by molecular methods. The bcr-abl and HLA association was studied by calculating the relative risks and chi-square test. RESULTS: Significant negative associations (p < 0.05) were observed with HLA-A*02 (b2a2, e1a2), -A*68 (b2a2, b3a2, e1a2), -B*14 (b2a2, b3a2, e1a2), -B*15 (b2a2, b3a2), -B*40 (b2a2), -DQB1*0303 (b2a2, b3a2), -DQB1*0603 (b2a2), -DRB1*0401 (e1a2), -DRB1*0701 (b3a2), and -DRB1*1101 (b2a2). CONCLUSIONS: The negative associations of a particular bcr-abl transcript with specific HLA alleles suggests that these alleles play a critical role in presenting peptides derived from the chimeric proteins and eliciting a successful T-cell cytotoxic response. Knowledge of differential associations between HLA phenotypes and bcr-abl fusion transcript types would help in developing better strategies for immunization with the bcr-abl peptides against t(9;22) (q34;q11)-positive leukemia

Fusion Gene Bcr-abl : From Etiopathogenesis to the Management of Chronic Myeloid Leukemia

Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm. CML is relative frequent disorder. Most of CML patients have Philadelphia chromosome (Ph),which is derived from a reciprocal translocation between chromosome 9 and 22, t(9;22)(q34;ql1), generating the BCRABLfusion gene. In general, there are 3 breakpoint cluster regions in BCR gene : mayor(M-bcr), minor (m-bcr) and micro (μ-bcr). The BCR-ABL gene encodes proteins that vary in size depending on the breakpoint in the BCR gene. However, these proteins share a high tyrosine kinase activity. In the absence of activating stimuli, BCR-ABL tyrosine kinase able to transferphosphate from ATP (autophosphorilation) to tyrosine residues on various substrates in the cell. It actives intracelluler signaling pathways. These pathways cause increase proliferation or decrease apoptosis and differentiation of a hematopoietic stem cell; and defect in adherence of myeloid progenitors to marrow stroma resulting in CML. These discoveries determined that BCR-ABL fusion gene is critical event in etiopathogenesis of CML and a ideal target for therapy. Therapy of CML patients with BCRABL fusion gene-positif is by block autophosphorilation mechanism by Tyrosine Kinase Inhibitor (TKI), example imatinib. Molecular method to detect BCR-ABL transcript is necessary for monitoring response to TKI in CML pateints

Dissecting BCR-ABL Variant Signaling Pathways Using Novel Interactome Identification Strategies

Cell signaling is an essential function of cells and tissues. Understanding cell signaling necessitates technologies that can identify protein-protein interactions as well as post translational modifications to proteins within protein complexes. The goals of this study are (1) to understand how BCR-ABL variants differentially signal to produce different clinical/experimental phenotypes and (2) to develop novel interactome detection strategies to understand signaling. This dissertation describes an integrated approach of the use of proximity dependent labeling protein-protein interaction analysis assays coupled with global phosphorylation analysis to investigate the differences in signaling between two variants the oncogenic fusion protein, BCR-ABL. Two major types of leukemogenic BCR-ABL fusion proteins are p190BCR-ABL and p210BCR-ABL. Although the two fusion proteins are closely related, they can lead to different clinical outcomes. A thorough understanding of the signaling programs employed by these two fusion proteins is necessary to explain these clinical differences. Our findings suggest that p190BCR-ABL and p210BCR-ABL differentially activate important signaling pathways, such as JAK-STAT, and engage with molecules that indicate interaction with different subcellular compartments. In the case of p210BCR-ABL, we observed an increased engagement of molecules active proximal to the membrane and in the case of p190BCR-ABL, an engagement of molecules of the cytoskeleton. These differences in signaling could underlie the distinct leukemogenic process induced by these two protein variants. Additionally, this dissertation also describes the development of a novel interactome detection strategy, called Biotinylation Site Identification Technology (BioSITe), which increases the sensitivity and specificity of proximity dependent biotin labeling technologies. When applied to BCR-ABL variants, BioSITe provides structural information about BCR-ABL interacting proteins and the degree of proximity these proteins are to BCR-ABL. Finally, this thesis demonstrates the use of isotopically labeled biotin for quantitative BioSITe experiments, applied to BCR-ABL variants, simplifies differential interactome analysis

Targeting the oligomerization of BCR/ABL by membrane permeable competitive peptides inhibits the proliferation of Philadelphia Chromosome positive leukemic cells

The BCR/ABL fusion protein is the hallmark of Philadelphia Chromosome positive (Ph+) leukemia. The constitutive activation of the ABL-kinase in BCR/ABL cells induces the leukemic phenotype. Targeted inhibition of BCR/ABL by small molecule inhibitors reverses the transformation potential of BCR/ABL. Recently, we definitively proved that targeting the tetramerization of BCR/ABL mediated by the N-terminal coiled-coil domain (CC) using competitive peptides, representing the helix-2 of the CC, represents a valid therapeutic approach for treating Ph+ leukemia. To further develop competitive peptides for targeting BCR/ABL, we created a membrane permeable helix-2 peptide (MPH-2) by fusing the helix-2 peptide with a peptide transduction tag. In this study, we report that the MPH-2: (i) interacted with BCR/ABL in vivo; (ii) efficiently inhibited the autophosphorylation of BCR/ABL; (iii) suppressed the growth and viability of Ph+ leukemic cells; and (iv) was efficiently transduced into mononuclear cells (MNC) in an in vivo mouse model. This study provides the first evidence that an efficient peptide transduction system facilitates the employment of competitive peptides to target the oligomerization interface of BCR/ABL in vivo

The COOH terminus of the c-Abl tyrosine kinase contains distinct F- and G-actin binding domains with bundling activity

The myristoylated form of c-Abl protein, as well as the P210bcr/abl protein, have been shown by indirect immunofluorescence to associate with F-actin stress fibers in fibroblasts. Analysis of deletion mutants of c-Abl stably expressed in fibroblasts maps the domain responsible for this interaction to the extreme COOH-terminus of Abl. This domain mediates the association of a heterologous protein with F-actin filaments after microinjection into NIH 3T3 cells, and directly binds to F-actin in a cosedimentation assay. Microinjection and cosedimentation assays localize the actin-binding domain to a 58 amino acid region, including a charged motif at the extreme COOH-terminus that is important for efficient binding. F-actin binding by Abl is calcium independent, and Abl competes with gelsolin for binding to F- actin. In addition to the F-actin binding domain, the COOH-terminus of Abl contains a proline-rich region that mediates binding and sequestration of G-actin, and the Abl F- and G-actin binding domains cooperate to bundle F-actin filaments in vitro. The COOH terminus of Abl thus confers several novel localizing functions upon the protein, including actin binding, nuclear localization, and DNA binding. Abl may modify and receive signals from the F-actin cytoskeleton in vivo, and is an ideal candidate to mediate signal transduction from the cell surface and cytoskeleton to the nucleus