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PubMed1998

Protein tyrosine phosphatase 1B antagonizes signalling by oncoprotein tyrosine kinase p210 bcr-abl in vivo.

The p210 bcr-abl protein tyrosine kinase (PTK) appears to be directly responsible for the initial manifestations of chronic myelogenous leukemia (CML). In contrast to the extensive characterization of the PTK and its effects on cell function, relatively little is known about the nature of the protein tyrosine phosphatases (PTPs) that may modulate p210 bcr-abl-induced signalling. In this study, we have demonstrated that expression of PTP1B is enhanced specifically in various cells expressing p210 bcr-abl, including a cell line derived from a patient with CML. This effect on expression of PTP1B required the kinase activity of p210 bcr-abl and occurred rapidly, concomitant with maximal activation of a temperature-sensitive mutant of the PTK. The effect is apparently specific for PTP1B since, among several PTPs tested, we detected no change in the levels of TCPTP, the closest relative of PTP1B. We have developed a strategy for identification of physiological substrates of individual PTPs which utilizes substrate-trapping mutant forms of the enzymes that retain the ability to bind to substrate but fail to catalyze efficient dephosphorylation. We have observed association between a substrate-trapping mutant of PTP1B (PTP1B-D181A) and p210 bcr-abl, but not v-Abl, in a cellular context. Consistent with the trapping data, we observed dephosphorylation of p210 bcr-abl, but not v-Abl, by PTP1B in vivo. We have demonstrated that PTP1B inhibited binding of the adapter protein Grb2 to p210 bcr-abl and suppressed p210 bcr-abl-induced transcriptional activation that is dependent on Ras. These results illustrate selectivity in the effects of PTPs in a cellular context and suggest that PTP1B may function as a specific, negative regulator of p210 bcr-abl signalling in vivo.

Adaptor Proteins, Signal Transducing↗

PubMed2005

BCR-ABL induces the expression of Skp2 through the PI3K pathway to promote p27Kip1 degradation and proliferation of chronic myelogenous leukemia cells.

Chronic myelogenous leukemia (CML) is characterized by the expression of the BCR-ABL tyrosine kinase, which results in increased cell proliferation and inhibition of apoptosis. In this study, we show in both BCR-ABL cells (Mo7e-p210 and BaF/3-p210) and primary CML CD34+ cells that STI571 inhibition of BCR-ABL tyrosine kinase activity results in a G(1) cell cycle arrest mediated by the PI3K pathway. This arrest is associated with a nuclear accumulation of p27(Kip1) and down-regulation of cyclins D and E. As a result, there is a reduction of the cyclin E/Cdk2 kinase activity and of the retinoblastoma protein phosphorylation. By quantitative reverse transcription-PCR we show that BCR-ABL/PI3K regulates the expression of p27(Kip1) at the level of transcription. We further show that BCR-ABL also regulates p27(Kip1) protein levels by increasing its degradation by the proteasome. This degradation depends on the ubiquitinylation of p27(Kip1) by Skp2-containing SFC complexes: silencing the expression of Skp2 with a small interfering RNA results in the accumulation of p27(Kip1). We also demonstrate that BCR-ABL cells show transcriptional up-regulation of Skp2. Finally, expression of a p27(Kip1) mutant unable of being recognized by Skp2 results in inhibition of proliferation of BCR-ABL cells, indicating that the degradation of p27(Kip1) contributes to the pathogenesis of CML. In conclusion, these results suggest that BCR-ABL regulates cell cycle in CML cells at least in part by inducing proteasome-mediated degradation of the cell cycle inhibitor p27(Kip1) and provide a rationale for the use of inhibitors of the proteasome in patients with BCR-ABL leukemias.

Benzamides↗

PubMed2003

Inhibition of bcr-abl gene expression by small interfering RNA sensitizes for imatinib mesylate (STI571).

Bcr-Abl proteins are effective inducers of the leukemic phenotype in chronic myeloid leukemia (CML) and distinct variants of acute lymphoblastic leukemia (ALL). Targeting bcr-abl by treatment with the selective tyrosine kinase inhibitor imatinib has proved to be highly efficient for controlling leukemic growth. However, it is unclear whether imatinib is sufficient to eradicate the disease because of primary or secondary resistance of leukemic cells. Therefore, targeting Bcr-Abl with an alternative approach is of great interest. We demonstrate that RNA interference (RNAi) with a breakpoint-specific short-interfering RNA (siRNA) is capable of decreasing Bcr-Abl protein expression and of antagonizing Bcr-Abl-induced biochemical activities. RNAi selectively inhibited Bcr-Abl-dependent cell growth. Furthermore, bcr-abl-homologous siRNA increased sensitivity to imatinib in Bcr-Abl-overexpressing cells and in a cell line expressing the imatinib-resistant Bcr-Abl kinase domain mutation His396Pro, thereby antagonizing 2 of the major mechanisms of resistance to imatinib.

Antineoplastic Agents↗

PubMed2004

Chlorogenic acid inhibits Bcr-Abl tyrosine kinase and triggers p38 mitogen-activated protein kinase-dependent apoptosis in chronic myelogenous leukemic cells.

We report that chlorogenic acid (Chl) induces apoptosis of several Bcr-Abl-positive chronic myelogenous leukemia (CML) cell lines and primary cells from CML patients in vitro and destroys Bcr-Abl-positive K562 cells in vivo. In contrast, this compound has no effect on the growth and viability of Bcr-Abl-negative lymphocytic and myeloid cell lines and primary CML cells. Sodium chlorogenate (NaChl) exhibits 2-fold higher efficiency in killing K562 cells compared with Chl. NaChl also induces growth inhibition of squamous cell carcinoma (HSC-2) and salivary gland tumor cells (HSG), although at 50-fold higher concentration. NaChl inhibits autophosphorylation of p210(Bcr-Abl) fusion protein rapidly. We demonstrate that p38 phosphorylation is increased in Bcr-Abl-positive cells after treatment with NaChl and closely paralleled the inhibition of Bcr-Abl phosphorylation. NaChl did not increase phosphorylation of p38 in Bcr-Abl-negative cells including HSC-2 and HSG that are responsive to this compound, indicating that p38 activation by NaChl is dependent on Bcr-Abl kinase inhibition. Inhibition of p38 activity by SB203580 significantly reduced NaChl-induced apoptosis of K562 cells, whereas activation of p38 by anisomycin augmented the apoptosis. These findings indicate that inhibition of Bcr-Abl kinase leading to activation of p38 mitogen-activated protein (MAP) kinase may play an important role in the anti-CML activity of Chl.

Apoptosis↗

PubMed1999

p190 bcr-abl rearrangement: a secondary cytogenetic event in some chronic myeloid disorders?

BACKGROUND AND OBJECTIVE: A small number of chronic myeloproliferative disorders with hematologic features of chronic myelomonocytic leukemia (CMML) or atypical chronic myeloid leukemia and Ph1 chromosome with m-BCR rearrangement have been reported (p190 CMPD). We report here 3 new cases of p190 CMPD that had unusual features. In 2 of the cases the m-BCR rearrangement appeared to be a secondary event. DESIGN AND METHODS: Patients were studied by cytogenetic, FISH, and molecular biology analyses and followed-up clinically. RESULTS: The first patient initially had typical 5q- syndrome, without m-BCR rearrangement. Five years later, she developed hematologic features of CMML, with t(9;22) translocation, m-BCR rearrangement and high levels of p190 BCR-ABL transcript. The second patient initially had hematologic characteristics of chronic myeloid leukemia (CML) with t(9;22) translocation and m-BCR rearrangement but also other complex cytogenetic findings including 17p rearrangement. Monocytosis developed during the course of the disease. The third patient initially had agnogenic myeloid metaplasia (AMM). Five years later, while the hematologic characteristics were still those of AMM, a first karyotype showed a t(9;22) translocation and molecular analysis showed a very low level of p190 BCR-ABL transcript. Four years later, the patient developed hematologic features of atypical CML with blood monocytosis, t(9;22) and much greater (100 fold) p190 BCR-ABL transcript levels. INTERPRETATION AND CONCLUSIONS: Our 3 cases and review of the previously published cases show the variability of clinical features of p190 positive CMPD. Our results also suggest that, at least in some cases, p190 BCR-ABL rearrangement could be a secondary event in the course of a myeloid disorder.

Chromosomes, Human, Pair 22↗

PubMed2002

[Bcr-Abl inhibition as molecular therapy approach in chronic myeloid leukemia].

BACKGROUND: Bcr-Abl, a constitutively activated tyrosine kinase, is a product of the Philadelphia chromosome (Ph) translocation t(9;22), present in nearly all cases of chronic myeloid leukemia (CML) and in about 20% of cases with acute lymphoblastic leukemia. CML, a myeloproliferative disorder, progresses through three phases--chronic phase, accelerated phase and blast crisis. Current therapies include drug regimens such as interferon alpha, hydroxyurea, busulfan or allogeneic bone marrow transplantation, the only curative treatment for CML, which is, however, limited to younger patients with a suitable donor. INHIBITION OF BCR-ABL AS EFFECTIVE AND SELECTIVE TREATMENT IN CML: In vitro studies and studies in animal models have shown, that Bcr-Abl is the molecular cause CML. Therefore inhibition of the Bcr-Abl tyrosine kinase is expected to be an effective and selective treatment modality for CML. STI571 was shown to be a competitive inhibitor at the ATP-binding site of the Bcr-Abl tyrosine kinase, the platelet-derived growth factor receptor and c-kit tyrosine kinases. It shows effects on proliferation and survival of Bcr-Abl-expressing cells without affecting normal cells or Ph-negative leukemic cells. DRUG RESISTANCE TO STI571: Several mechanisms of resistance have been identified from in vitro studies with Bcr-Abl-positive cell lines. Mechanisms include amplification or overexpression of Bcr-Abl or an increased expression of P-gly-coprotein. In a mouse model the binding of STI571 to acidic alpha 1 glycoprotein (AAG) has been proposed to be involved in the development of STI571 resistance. Recent studies with clinical samples from resistant patients have shown that point mutations in the kinase domain of Bcr-Abl play a role in the development of resistance to STI571. CONCLUSIONS: STI571 is a promising example of a moleculary targeted therapy directed towards the molecular cause of CML. To maximize the therapeutic value and to avoid the induction of resistance, a combination of the drug with other chemotherapies should be considered. According to its pharmacological profile, STI571 could also be useful in the treatment of tumors with deregulated PDGF receptor or c-kit signaling, e.g., in chronic myelomonocytic leukemia with a t(5;12) chromosomal translocation or in cases with gastrointestinal stromal tumors (GIST). STI571 shows a new paradigm in the development of new targeted therapies for the treatment of malignant diseases.

Animals↗

PubMed2002

Characterization of potent inhibitors of the Bcr-Abl and the c-kit receptor tyrosine kinases.

The early stage of chronic myelogenous leukemia (CML) is caused by the tyrosine kinase Bcr-Abl. Imatinib mesylate (also known as STI-571 and Gleevec), a tyrosine kinase inhibitor, has shown encouraging results in CML clinical trials and has become a paradigm for targeted cancer therapeutics. Recent reports of resistance to imatinib argue for further development of therapies for CML. During studies of signal transduction, we observed that the pyrido[2,3-d]pyrimidine src tyrosine kinase inhibitor PD173955 inhibited Bcr-Abl-dependent cell growth. Subsequently, a related compound, PD180970, was reported as a potent inhibitor of Bcr-Abl. We have compared the potency of these two compounds and four other analogues with imatinib on Bcr-Abl-dependent cell growth, cytokine-dependent cell growth, and tyrosine kinase inhibition. PD173955 inhibited Bcr-Abl-dependent cell growth with an IC(50) of 2-35 nM in different cell lines. Fluorescence-activated cell-sorting analyses of cells treated with PD173955 showed cell cycle arrest in G(1). PD173955 has an IC(50) of 1-2 nM in kinase inhibition assays of Bcr-Abl, and in cellular growth assays it inhibits Bcr-Abl-dependent substrate tyrosine phosphorylation. Of the six pyrido[2,3-d]pyrimidine analogues studied, PD166326 was the most potent inhibitor of Bcr-Abl-dependent cell growth. PD173955 inhibited kit ligand-dependent c-kit autophosphorylation (IC(50) = approximately 25 nM) and kit ligand-dependent proliferation of M07e cells (IC(50) = 40 nM) but had a lesser effect on interleukin 3-dependent (IC(50) = 250 nM) or granulocyte macrophage colony-stimulating factor (IC(50) = 1 microM)-dependent cell growth. These compounds are potent inhibitors of both the Bcr-Abl and c-kit receptor tyrosine kinases and deserve further study as potential treatments for both CML and for diseases in which c-kit has a role.

Cell Division↗

PubMed1992

[Analysis of breakpoints on BCR gene in acute leukemia patients with Ph1 chromosome].

Eight cases with Ph1 positive acute leukemia (7 of acute lymphocytic leukemia: ALL, and one of acute myelocytic leukemia: AML) were studied molecular biologically to identify location of breakpoints on BCR gene in each patient. Six of the 8 patients (5 of ALL and 1 of AML) had rearrangements at bcr (M-BCR) region. Their locations of the breakpoint in M-BCR were similar to those of 59 chronic myelocytic leukemia patients. One of the remaining two patients had gene rearrangements at m-BCR-1 region in BCR intron 1, and the last patient did not have gene rearrangements at any site of m-BCR-1 and IgL C lambda region. Two cases had gene deletion at either 3' or 5' side of the bcr. A patient with bcr rearrangement was also analyzed by PCR method with reverse transcriptase (RT-PCR) and had simultaneous expressions of bcr3-abl and bcr2-abl chimeric mRNAs. These results indicate that Ph1 positive acute leukemia have heterogeneous characteristics in terms of the molecular biology. The molecular analysis will help for classifying the leukemic types and for elucidating the pathogenesis in Ph1 positive acute leukemia.

Acute Disease↗

PubMed2005

Circulating bcr-abl-specific CD8+ T cells in chronic myeloid leukemia patients and healthy subjects.

BACKGROUND AND OBJECTIVES: The fusion oncoprotein bcr-abl that characterizes chronic myeloid leukemia (CML) is a leukemia-specific antigen, which may be immunogenic in vivo. KQSSKALQR and GFKQSSKAL, peptide sequences spanning the b3a2 bcr-abl junction, have affinity for HLA-A3 and HLA-B8, respectively, and we have shown the presence of KQSSKALQR on the surface of CML cells. We analyzed the existence of bcr-abl-specific T cells in vivo and correlated their presence to contemporary disease burden. DESIGN AND METHODS: We investigated circulating CD8+ T lymphocytes directed against the bcr-abl junction, using fluorochrome-labeled tetramers of HLA-A3 with KQSSKALQR and of HLA-B8 with GFKQSSKAL, and flow cytometry analysis. Using chromium-release assays and interferon-g ELISPOT assays, we also studied the functionality of these expanded T cells. RESULTS: Eight of 12 b3a2+ HLA-A3+ and/or HLA-B8+ CML patients studied serially on at least three occasions had bcr-abl junction-specific CD8+ T cells. Specific T cells were more likely to be found in patients with a low leukemic burden (p=0.03). Three of 18 HLA-A3+ and/or HLA-B8+ healthy donors had bcr-abl junction-specific T cells, though these were not detected in any of 13 subjects who were HLA-A3- and HLA-B8-. Bcr-abl-specific T cells were expandable in vitro in three of seven healthy donors and five of seven CML patients. INTERPRETATION AND CONCLUSIONS: Bcr-abl-specific T cells are detectable in CML patients, and might contribute to leukemic control. The occurrence of specific CD8+ T cells in some healthy donors might represent an immune response to occult BCR-ABL rearrangements.

Adult↗

PubMed2006

[Importance of quantitative evaluation of BCR-ABL transcripts using real-time PCR for effective treatment of chronic myeloid leukemia].

BACKGROUND: Molecular biology methods based on reverse transcription and polymerase chain reaction (RT-PCR) are able to detect the presence of BCR-ABL transcripts in chronic myeloid leukemia (CML). In this study we present our experience with monitoring of residual disease using real-time PCR with hybridization probes detection in patients treated with imatinib mesylate and in collected peripheral blood progenitor cells (PBPC). METHODS AND RESULTS: We measured the level of BCR-ABL transcripts in peripheral blood cells of 27 subjects before and in the course of the imatinib treatment. The median of relative quantity of BCR-ABL in the blood before imatinib therapy was 2.55%. The number of the transcripts in 23 imatinib-sensitive subjects decreased to 0.02% in 6 months. After 12 months of the treatment the BCR-ABL median was 0.005%. Subsequent levels fluctuated between values below the detection limit (DL, 0.001%) and 0.005%. Three patients were primarily resistant to imatinib with the BCR-ABL range of 0.13%-11.7% during the treatment. One subject showed marks of molecular relapse after 18 months of the treatment. Only two of 16 filgrastim-stimulated patients had BCR-ABL levels in the blood and in collected PBPC below DL. In other subjects BCR-ABL transcripts were determined within the measurable range of RT-PCR. CONCLUSIONS: Taking into account prognostic importance, the measurement of BCR-ABL transcripts is an effective approach to monitoring of residual CML kinetics. Evaluation of BCR-ABL levels in collected PBPC can complete information on quality of the cells in potential autotransplants, and choose subsequent therapeutic protocols and patient prognosis.

Adult↗

PubMed1993

Long persistent bcr-abl positive transcript detected by polymerase chain reaction after marrow transplant for chronic myelogenous leukemia without clinical relapse: a study of 64 patients.

We report here the results of polymerase chain reaction (PCR) for bcr-abl transcript and clinical details derived from 64 chronic myelogenous leukemia (CML) patients after allogeneic bone marrow transplantation (BMT). A total of 139 samples (2 to 220 weeks after BMT) were analyzed and bcr-abl transcript was detected in 99 samples from 52 patients. Patients were defined as bcr-abl early negative (EN) if they had > or = 1 negative PCR result < or = 1 year post-BMT (n = 13), and bcr-abl late positive (LP) if they had > or = 1 positive PCR result > or = 1 year post-BMT (n = 21). Among LP patients, only two patients had hematologic/cytogenetic (clinical) relapse. Another 19 LP patients remained in clinical remission 7 to 130 weeks after positive analysis for bcr-abl transcript, including 5 patients who had persistent bcr-abl transcript detectable even 2 years after BMT. To estimate the relationship between clinical data and residual bcr-abl transcript, EN patients are compared with LP patients. However, no clinical data studied were significantly associated with the persistent PCR positivity. If only patients in chronic phase are compared, the t-test showed significant correlation between leukocyte count just before BMT and sustained bcr-abl transcript (P < .05). These results suggest that PCR positivity is frequently observed in CML patients who sustain clinical remission after BMT, without being predictive of imminent clinical relapse. Tumor burden at the time of BMT may play an important role in the latency of bcr-abl positivity after BMT.

Adolescent↗

PubMed1998

A two-color BCR-ABL probe that greatly reduces the false positive and false negative rates for fluorescence in situ hybridization in chronic myeloid leukemia.

The t(9;22) translocation resulting in the fusion of BCR and ABL genes is pathognomonic in chronic myeloid leukemia (CML) and may be investigated at the molecular level using fluorescence in situ hybridization (FISH). Two-color BCR-ABL probes visualizing one fusion signal (1F FISH) have high false positive rates (FPR) and false negative rates (FNR). The FPR is a result of the random spatial association of probe signals within normal interphase cells so that some cells appear to contain the BCR-ABL fusion gene. The FNR of 1F FISH probes depends on the distance between the BCR and ABL probes hybridized to the BCR-ABL fusion gene (< or =368 kb); the "gap" between the signals causing the cell to be interpreted as normal. To overcome these difficulties, a two-color probe was used, employing four yeast artificial chromosome (YAC) sequences that span the breakpoint regions of the BCR and ABL genes and that visualize the two fusion signals BCR-ABL and ABL-BCR in CML cells (2F FISH). The FNR for the 2F FISH probes was assessed on clonal Ph+ granulocyte-macrophage-colony-forming cell (CFU-GM) derived colonies and was reduced to 0.4% (2/450), compared with an FNR of 13.5% (111/823) with 1F FISH. The FPR in normal mononuclear cells for the 2F FISH was 0. 19 +/- 0.12% (3/1,700), whereas the FPR using 1F FISH was 4.5 +/- 2.3% (63/1,294). The 2F FISH can thus be used to evaluate very small frequencies of BCR-ABL-positive and -negative interphase cells and may be of use in the clinical monitoring of CML.

Adult↗

PubMed1998

Regulation of the c-jun gene in p210 BCR-ABL transformed cells corresponds with activity of JNK, the c-jun N-terminal kinase.

Activity of the c-jun N-terminal kinase (JNK) has been shown in hematopoietic cells transformed by p210 BCR-ABL. However, analysis has not been reported for hematopoietic cells on the consequences of this activity for c-jun promoter regulation within its distinctive proximal 8-base consensus CRE-like element, an element linked to JNK-mediated increase in c-jun transcription. In the present study, regulation of the proximal c-jun promoter was studied in murine myeloid cells transformed by p210 BCR-ABL. Promoter regulation in p210 BCR-ABL transformed cells was compared with regulation of the promoter in nontransformed interleukin-3 (IL-3)-dependent parental cells. The composition of nuclear AP-1 proteins contained within cells with p210 BCR-ABL, and their binding to the c-jun promoter proximal CRE-like element, was compared with the composition and binding of AP-1 proteins in IL-3-treated parental cells without p210 BCR-ABL. The present analysis found fivefold increased c-jun transcription occurring in p210 BCR-ABL transformed murine myeloid cells possessing a corresponding magnitude of increased kinase activity of JNK, compared with IL-3-stimulated parental cells. Augmented JNK activity was accompanied by increased nuclear abundance of c-jun and c-fos proteins that bound specifically to the proximal c-jun promoter CRE element. Also, representative human leukemic cell lines expressing p210 BCR-ABL and possessing abundant kinase activity of JNK, when compared with parental cells that were deficient in JNK activity, had increased c-jun and c-fos proteins. Finally, to show the relevance of these observations in model systems, we studied blast cells from patients with Philadelphia chromosome-positive acute leukemic transformation, and observed comparable activities of JNK catalysis and c-jun/AP-1 protein relative to the cell lines that possessed p210 BCR-ABL and JNK activity. These studies provide a basis for investigating the set of downstream genes which augmented c-jun/AP-1 activity enlists in the process of transformation by p210 BCR-ABL.

Animals↗

PubMed1999

GCKR links the Bcr-Abl oncogene and Ras to the stress-activated protein kinase pathway.

The Bcr-Abl oncogene, found in Philadelphia chromosome-positive myelogenous leukemia (CML), activates Ras and triggers the stress-activated protein kinase (SAPK or Jun NH2-terminal kinase [JNK]) pathway. Interruption of Ras or SAPK activation dramatically reduces Bcr-Abl-mediated transformation. Here, we report that Bcr-Abl through a Ras-dependent pathway signals the serine/threonine protein kinase GCKR (Germinal Center Kinase Related) leading to SAPK activation. Either an oncogenic form of Ras or Bcr-Abl enhances GCKR catalytic activity and its activation of SAPK, whereas inhibition of GCKR impairs Bcr-Abl-induced SAPK activation. Bcr-Abl mutants that are impaired for GCKR activation are also unable to activate SAPK. Consistent with GCKR being a functional target in CML, GCKR is constitutively active in CML cell lines and found in association with Bcr-Abl. Our results indicate that GCKR is a downstream target of Bcr-Abl and strongly implicate GCKR as a mediator of Bcr-Abl in its transformation of cells.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed1999

BCR binds to the xeroderma pigmentosum group B protein.

The BCR gene is involved in the formation of the BCR-ABL oncogene responsible for the pathogenesis of Philadelphia chromosome-positive human leukemias. We have previously shown that P210 BCR-ABL binds to the xeroderma pigmentosum group B protein (XPB) through the portion of BCR that is homologous to the catalytic domain of GDP-GTP exchangers such as yeast CDC24 and Dbl. In the baculovirus overexpression system which facilitates binding of coexpressed proteins, we now show that XPB binds to the intact BCR protein efficiently but not to CDC24 or Dbl, suggesting specificity of this interaction. The binding of endogenous BCR and XPB proteins was also detected in Hela cells, and this was inhibited by a blocking peptide. Full-length (1-782) XPB and its truncated form (203-782), which does not contain the nuclear localization signal, were tagged with glutathione S-transferase (GST) and were expressed in Rat1 fibroblasts. GST-XPB(203-782) was localized predominantly in the cytoplasm and bound to BCR but not to p62, one of the other components in TFIIH. GST-XPB(1-782) was largely in the nucleus and bound to p62 and BCR. Although the biological significance of the binding remains to be uncovered, BCR binds to the XPB/p62 complex.

Animals↗

PubMed2004

Prostate apoptosis response gene-4 (par-4) abrogates the survival function of p185(BCR-ABL) in hematopoietic cells.

OBJECTIVE: Prostate apoptosis response gene-4 (par-4) is deregulated in acute and chronic lymphatic leukemia. Given its pro-apoptotic role in neoplastic lymphocytes and evidence that par-4 antagonizes oncogenic Ras in solid tumors, we hypothesized that par-4 may act as a tumor suppressor impairing transformation induced by p185(BCR-ABL). MATERIALS AND METHODS: The capacity of par-4 to interfere with factor independence induced by p185(BCR-ABL) and V12ras was evaluated by analysis of factor-independent growth of p185(BCR-ABL)/ par-4 and V12ras/par-4 transduced cells. The expression of par-4 and p185(BCR-ABL) by the respective constructs was controlled by Western blot analysis. Activated Ras was detected by pull-down assay in the cell clones expressing p185(BCR-ABL) in the absence and presence of par-4. RESULTS: Expression of p185(BCR-ABL) causes factor independence, signifying a conversion toward a transformed phenotype in hematopoietic precursors. We demonstrate that par-4 completely abolishes factor independence induced by p185(BCR-ABL) and partially abrogates factor independence caused by activated V12ras. Evaluating the underlying molecular mechanisms, we show that par-4 hinders activation of oncogenic Ras and causes concomitant disruptions of p185(BCR-ABL)-mediated signaling. CONCLUSION: We provide the first evidence that par-4 exhibits an antitransforming capacity by antagonizing p185(BCR-ABL)-induced factor-independent proliferation in hematopoietic cells.

Animals↗

PubMed2004

Antisense inhibition of Bcr-Abl/c-Abl synthesis promotes telomerase activity and upregulates tankyrase in human leukemia cells.

Clinical studies in chronic myelogenous leukemia demonstrate that the overexpression of Bcr-Abl tyrosine kinase is usually accompanied by relatively low telomerase activity in the chronic phase, which reverts to a high activity in blast crisis. The present study was designed to investigate the cross-talk between both enzymes, using Bcr-Abl-positive K-562 and Bcr-Abl-negative Jurkat cell lines, treated with antisense oligodeoxyribonucleotides (ODNs) against Bcr-Abl/c-Abl mRNA. The decreased amount and enzyme activity of Bcr-Abl/c-Abl provoked telomerase activation in both cell lines. After short-term treatment with anti-Bcr-Abl/c-Abl ODNs (6 days), no variations in hTERT and phospho-hTERT were detected. The decreased amount of Bcr-Abl/c-Abl was accompanied by: alterations in telomeric associated proteins-overexpression of tankyrase and decreased amount of TRF1/Tin2, cell growth arrest of K-562 cells, reaching a plateau after 6 days treatment, and increased proliferating activity of Jurkat cells. No changes in telomere length were detected after short-term treatment. In contrast, after long-term treatment with anti-Bcr-Abl/c-Abl ODNs (36 days), a significant elongation of telomeres and enhancement of hTERT were established, accompanied by an increased proliferating activity of both cell lines. These data provide evidence that the inhibition of Bcr-Abl or c-Abl synthesis keeps a potential to restore or induce cell proliferation through telomere lengthening control and telomerase activation.

Base Sequence↗

PubMed2000

Abl kinase but not PI3-kinase links to the cytoskeletal defects in Bcr-Abl transformed cells.

OBJECTIVE: The purpose of this study was to investigate the contribution of Abl kinase and phosphatidylinositol 3-kinase (PI3-kinase) to the altered adhesive properties and cytoskeletal defects in a Bcr-Abl transformed fibroblast cell model. MATERIALS ANID METHODS: Two fibroblast cell lines stably transfected with Bcr-Abl were compared to their parental counterparts for alterations in their adhesive properties in an attachment assay and for abnormalities in their cytoskeletal architecture by immunofluorescence microscopy. Cells then were treated with specific inhibitors of either the Abl kinase CGP57148 or the PI3-kinase LY294002 to determine whether these treatments would restore normal cytoarchitecture and adhesion. RESULTS: [corrected] Significant defects in cytoskeletal architecture were observed using this fibroblast model of Bcr-Abl expression. Specific changes include loss of stress fibers and focal adhesions, which correlated with an adhesive defect. [corrected] Treatment of Bcr-Abl expressing cells with CGP57148, but not LY294002, resulted in reversion of cells to a near-normal phenotype, as assessed by immunofluorescence and attachment of Bcr-Abl transformed fibroblasts. CONCLUSIONS: Our studies demonstrate that Bcr-Abl tyrosine kinase but not PI3- kinase activity is required for maintenance of cytoskeletal rearrangements resulting from Bcr-AbI expression. Further, inhibition of Abl kinase restored normal adhesive properties to the Bcr-Abl-expressing cells, demonstrating the contribution of Bcr-Abl kinase activity to abnormal cytoskeletal function.

3T3 Cells↗