Nonmyristoylated Abl proteins transform a factor-dependent hematopoietic cell line.

N-terminal myristoylation can promote the association of proteins with the plasma membrane, a property that is required for oncogenic variants of Src and Abl to transform fibroblastic cell types. The P210bcr/abl protein of chronic myelogenous leukemia cells is not myristoylated and does not stably transform NIH 3T3 fibroblasts; however, it will transform lymphoid and myeloid cell types in vitro and in vivo, suggesting that myristoylation is not required for Abl variants to transform hematopoietic cells. To test this hypothesis, we introduced point mutations that disrupt myristoylation into two activated Abl proteins, v-Abl and a deletion mutant of c-Abl (delta XB), and examined their ability to transform an interleukin-3-dependent lymphoblastoid cell line, Ba/F3. Neither of the nonmyristoylated Abl proteins transformed NIH 3T3 fibroblasts, but like P210bcr/abl, both were capable of transforming the Ba/F3 cells to factor independence and tumorigenicity. Nonmyristoylated Abl variants did not associate with the plasma membrane in the transformed Ba/F3 cells. These results demonstrate that Abl proteins can transform hematopoietic cells in the absence of membrane association and suggest that distinct functions of Abl are required for transformation of fibroblast and hematopoietic cell types.     

Alternative forms of the BCR-ABL oncogene have quantitatively different potencies for stimulation of immature lymphoid cells.

The Philadelphia chromosome (t9:22;q34:q11) is found in more than 90% of patients with chronic myelogenous leukemia, in 10 to 20% of patients with acute lymphocytic leukemia, and in 1 to 2% of patients with acute myelogenous leukemia. Alternative chimeric oncogenes are formed by splicing different sets of BCR gene exons on chromosome 22 across the translocation breakpoint to a common set of ABL oncogene sequences on chromosome 9. This results in an 8.7-kilobase mRNA that encodes the P210 BCR-ABL gene product commonly found in patients with chronic myelogenous leukemia or a 7.0-kilobase mRNA that produces the P185 BCR-ABL gene product found in most Philadelphia chromosome-positive patients with acute lymphocytic leukemia. To compare the efficiency of growth stimulation by these two proteins, we derived cDNA clones for each with identical 5' and 3' untranslated regions and expressed them from retrovirus vectors. Matched stocks were compared for potency to transform immature B-lymphoid lineage precursors. The growth-stimulating effects of P185 for this cell type were found to be significantly greater than those of P210. Structural changes in BCR may regulate the effectiveness of the ABL tyrosine kinase function, as monitored by lymphocyte growth response. Changes in mitogenic potency may help to explain the more acute leukemic presentation usually associated with expression of the P185 BCR-ABL oncogene.     

Induction of apoptosis in chronic myelogenous leukemia cells through nuclear entrapment of BCR-ABL tyrosine kinase

The chimeric BCR-ABL oncoprotein is the molecular hallmark of chronic myelogenous leukemia (CML). BCR-ABL contains nuclear import and export signals but it is localized only in the cytoplasm where it activates mitogenic and anti-apoptotic pathways. We have found that inhibition of the BCR-ABL tyrosine kinase, either by mutation or by the drug STI571, can stimulate its nuclear entry. By combining STI571 with leptomycin B (LMB) to block nuclear export, we trapped BCR-ABL in the nucleus and the nuclear BCR-ABL tyrosine kinase activates apoptosis. As a result, the combined treatment with STI571 and LMB causes the irreversible and complete killing of BCR-ABL transformed cells, whereas the effect of either drug alone is fully reversible. The combined treatment with STI571 and LMB also preferentially eliminates mouse bone marrow cells that express BCR-ABL. These results indicate that nuclear entrapment of BCR-ABL can be used as a therapeutic strategy to selectively kill chronic myelogenous leukemia cells.     

Selective transformation of primitive lymphoid cells by the BCR/ABL oncogene expressed in long-term lymphoid or myeloid cultures.

The BCR/ABL gene, formed by the Philadelphia chromosome translocation (Ph1) of human chronic myelogenous leukemia, encodes an altered ABL gene product, P210. P210 is strongly implicated in the malignant process of chronic myelogenous leukemia, but it precise role is unknown. Infection of long-term bone marrow cultures enriched for B-lymphoid cell types with a Moloney murine leukemia virus retroviral vector containing the BCR/ABL cDNA resulted in clonal outgrowths of immature B-lymphoid cells which expressed abundant P210 kinase activity. Surprisingly, infection of long-term myeloid lineage-enriched cultures also resulted in clonal outgrowths of immature B-lymphoid cells. The P210-expressing lymphoid cell lines resulting from either type of culture were resistant to the lethal effects of corticosteroids. These findings indicate that high levels of P210 expressed from a Moloney murine leukemia virus long terminal repeat preferentially stimulate the growth of immature B-lineage cells, and this effect is apparent even in myeloid lineage-enriched cultures, in which few if any lymphoid cells can be detected prior to infection.     

Distinct patterns of hematopoietic stem cell involvement in acute lymphoblastic leukemia

The cellular targets of primary mutations and malignant transformation remain elusive in most cancers. Here, we show that clinically and genetically different subtypes of acute lymphoblastic leukemia (ALL) originate and transform at distinct stages of hematopoietic development. Primary ETV6-RUNX1 (also known as TEL-AML1) fusions and subsequent leukemic transformations were targeted to committed B-cell progenitors. Major breakpoint BCR-ABL1 fusions (encoding P210 BCR-ABL1) originated in hematopoietic stem cells (HSCs), whereas minor BCR-ABL1 fusions (encoding P190 BCR-ABL1) had a B-cell progenitor origin, suggesting that P190 and P210 BCR-ABL1 ALLs represent largely distinct tumor biological and clinical entities. The transformed leukemia-initiating stem cells in both P190 and P210 BCR-ABL1 ALLs had, as in ETV6-RUNX1 ALLs, a committed B progenitor phenotype. In all patients, normal and leukemic repopulating stem cells could successfully be separated prospectively, and notably, the size of the normal HSC compartment in ETV6-RUNX1 and P190 BCR-ABL1 ALLs was found to be unaffected by the expansive leukemic stem cell population.     

Short interfering RNA (siRNA) targeting the Lyn kinase induces apoptosis in primary, and drug-resistant, BCR-ABL1(+) leukemia cells

We studied the effects of Lyn ablation on the survival of drug-resistant chronic myelogenous leukemia (CML) blast crisis cells using siRNA. Lyn siRNA reduced Lyn protein in both normal hematopoietic cells and BCR-ABL1-expressing (BCR-ABL1(+)) blasts by 80-95%. Within 48 h, siRNA-treated BCR-ABL1(+) blasts underwent apoptosis, whereas normal cells remained viable. This increased dependence on Lyn signaling for BCR-ABL1(+) blast survival provides the basis for rational treatment of drug-resistant CML blast crisis, particularly when lymphoid in nature.     

The Dbl homology domain of BCR is not a simple spacer in P210BCR-ABL of the Philadelphia chromosome

The Dbl homology (DH) domain of BCR in P210BCR-ABL (P210/WT) has been thought to have a negative effect on the activation of BCR-ABL because P185BCR-ABL, in which this region is physically deleted, has stronger biochemical and biological activities. To study the role of the DH domain of BCR in the background of P210/WT, the region was replaced with homologous sequences derived from Dbl (P210/Dbl) or CDC24 (P210/CDC24) or with irrelevant sequences from LacZ (P210/LacZ) or luciferase (P210/Luci). Surprisingly, the abilities to transform Rat1 cells or mouse bone marrow cells and induce growth factor independence in interleukin 3-dependent mouse Ba/F3 cells were retained only in P210/Dbl. However, even P210/Dbl could not achieve the wild type level of surviving potential against genotoxins in Rat1 cells and in Ba/F3 cells. Activation of Akt correlated with the biological changes in Rat1 cells but did not correlate with the biological changes in Ba/F3 cells. The DH domain was not tyrosine-phosphorylated in vitro, nor could we find any differences in peptide mapping between in vitro phosphorylated P210/WT and P210/Dbl. Although functions of the DH domain remain to be discovered, we propose that the DH domain makes positive contributions to P210BCR-ABL.     

Imatinib mesylate (STI-571) reduces Bcr-Abl-mediated vascular endothelial growth factor secretion in chronic myelogenous leukemia

A large and diverse spectrum of oncogenes has been implicated as a contributor to angiogenesis in solid tumors based, in part, on its ability to induce proangiogenic growth factors such as vascular endothelial growth factor (VEGF), and the fact that various anti-oncogenic signaling inhibitor drugs have been shown to reverse such proangiogenic effects both in vitro and in vivo. Because leukemias are now also considered to be angiogenesis-dependent malignancies, we asked whether a similar paradigm might exist for the BCR-ABL oncogene and the Bcr-Abl targeting drug, STI-571 (imatinib mesylate), in the context of chronic myelogenous leukemia (CML) cells. We found that levels of VEGF expression in BCR-ABL-positive K562 cells were reduced in vitro by treatment with STI-571 in a dose-dependent fashion. Transfection of BCR-ABL into murine myeloid 32D and human megakaryocyte MO7e hematopoietic cells resulted in enhanced VEGF expression, which could be further elevated by the exposure to cytokines such as interleukin 3 and granulocyte macrophage colony-stimulating factor. We also found that conditioned media taken from 32D-p210-transfected cells could stimulate human umbilical vein endothelial cells by increasing phosphorylation of VEGF-R2/KDR and the downstream serine/threonine kinase PKB/Akt, an important regulator of endothelial cell survival. Moreover, amplification of BCR-ABL in STI-571-resistant cells was associated with elevated VEGF expression levels which could be reversed by treatment with higher concentrations of STI-571. Taken together, our results implicate BCR-ABL as a possible regulator of CML angiogenesis and raise the possibility that STI-571 could mediate some of its anti-CML properties in vivo through an angiogenesis-dependent mechanism.     

CTP-BCR-ABL抗原肽负载树突状细胞体外致敏T淋巴细胞靶向杀伤CML细胞

BCR-ABL为慢性髓细胞白血病特异胞质抗原,为良好的免疫治疗靶标.该研究选择BCR-ABL融合位点的两段抗原肽SSKALQRPV(SS)、GFKQSSKAL(GF)为靶点,与胞质转导肽融合表达,负载小鼠骨髓源性树突状细胞.在胞质转导肽介导下,SS、GF短肽进入树突状细胞并定位于内质网,具备了被树突状细胞识别为内源性抗...     

Differences in oncogenic potency but not target cell specificity distinguish the two forms of the BCR/ABL oncogene.

Two forms of activated BCR/ABL proteins, P210 and P185, that differ in BCR-derived sequences, are associated with Philadelphia chromosome-positive leukemias. One of these diseases is chronic myelogenous leukemia, an indolent disease arising in hematopoietic stem cells that is almost always associated with the P210 form of BCR/ABL. Acute lymphocytic leukemia, a more aggressive malignancy, can be associated with both forms of BCR/ABL. While it is virtually certain that BCR/ABL plays a central role in both of these diseases, the features that determine the association of a particular form with a given disease have not been elucidated. We have used the bone marrow reconstitution leukemogenesis model to test the hypothesis that BCR sequences influence the ability of activated ABL to transform different types of hematopoietic cells. Our studies reveal that both P185 and P210 induce a similar spectrum of hematological diseases, including granulocytic, myelomonocytic, and lymphocytic leukemias. Despite the similarity of the disease patterns, animals given P185-infected marrow developed a more aggressive disease after a shorter latent period than those given P210-infected marrow. These data demonstrate that the structure of the BCR/ABL oncoprotein does not affect the type of disease induced by each form of the oncogene but does control the potency of the oncogenic signal.     

Signal transduction-based strategies for the treatment of chronic myelogenous leukemia

Recent studies of the BCR-ABL fusion protein, the product of the oncogene responsible for chronic myelogenous leukemia, have identified a number of signal transduction pathways that are activated by this tyrosine kinase. In some cases, these pathways are critical mediators of the growth stimulatory effects of the oncogene on hemopoietic cells. This knowledge has been translated into therapeutic strategies that directly target BCR-ABL or the signaling pathways that BCR-ABL activates. Promising results in animal models have led to the design of Phase 1 clinical trials, which are in progress or will be under way shortly. These studies are among the first to target a specific genetic abnormality in human cancer.     

The 5'' noncoding region of the human leukemia-associated oncogene BCR/ABL is a potent inhibitor of in vitro translation.

The mRNA encoding the chimeric BCR/ABL oncogene, which is transcribed from the Philadelphia chromosome in human chronic myelogenous leukemia, has a 5' noncoding sequence greater than 500 bases in length which is highly GC rich and contains a short open reading frame. This untranslated sequence has a dramatic inhibitory effect upon translational efficiency in vitro. However, when BCR/ABL message is expressed in certain cell types such as the NIH 3T3 cell line, the 5' noncoding region has little inhibitory effect on translational efficiency.