Analysis of the biologic properties of p230 Bcr-Abl reveals unique and overlapping properties with the oncogenic p185 and p210 Bcr-Abl tyrosine kinases

The reciprocal translocation between chromosomes 9 and 22 that fuses coding sequences of the Bcr and Abl genes is responsible for a remarkably diverse group of hematologic malignancies. A newly described 230-kd form of Bcr-Abl has been associated with an indolent myeloproliferative syndrome referred to as chronic neutrophilic leukemia. We have cloned the corresponding gene and examined the biologic and biochemical properties of p230 Bcr-Abl after retroviral-mediated gene transfer into hematopoietic cell lines and primary bone marrow cells. p230 Bcr-Abl-expressing 32D myeloid cells were fully growth factor-independent and activated similar signal transduction pathways as the well-characterized p210 and p185 forms of Bcr-Abl. In contrast, primary mouse bone marrow cells expressing p230 required exogenous hematopoietic growth factors for optimal growth, whereas p185- and p210-expressing cells were independent of growth factors. The 3 Bcr-Abl proteins exerted different effects on differentiation of bone marrow cells. p185 induced outgrowth of lymphoid precursors capable of tumor formation in immunodeficient mice. In contrast, p210- and p230-expressing bone marrow cells caused limited outgrowth of lymphoid precursors that failed to form tumors in immunodeficient mice. Removal of cytokines and autologous stroma from Bcr-Abl-expressing bone marrow cultures produced the expansion of distinct lineages by the various Bcr-Abl proteins. p185 drove expansion of cytokine-independent lymphoid progenitors, while p210 and p230 generated cytokine-independent monocyte/myeloid cells. These findings suggest that the different Bcr-Abl fusion proteins drive the expansion of different hematopoietic populations, which may explain the association of the various Bcr-Abl oncoproteins with different spectra of human leukemias. (Blood. 2000;95:2913-2921)

Efficient and rapid induction of a chronic myelogenous leukemia-like myeloproliferative disease in mice receiving P210 bcr/abl-transduced bone marrow

Expression of the 210-kD bcr/abl fusion oncoprotein can cause a chronic myelogenous leukemia (CML)-like disease in mice receiving bone marrow cells transduced by bcr/abl-encoding retroviruses. However, previous methods failed to yield this disease at a frequency sufficient enough to allow for its use in the study of CML pathogenesis. To overcome this limitation, we have developed an efficient and reproducible method for inducing a CML-like disease in mice receiving P210 bcr/abl-transduced bone marrow cells. All mice receiving P210 bcr/abl-transduced bone marrow cells succumb to a myeloproliferative disease between 3 and 5 weeks after bone marrow transplantation. The myeloproliferative disease recapitulates many of the hallmarks of human CML and is characterized by high white blood cell counts and extensive extramedullary hematopoiesis in the spleen, liver, bone marrow, and lungs. Use of a retroviral vector coexpressing P210 bcr/abl and green fluorescent protein shows that the vast majority of bcr/abl-expressing cells are myeloid. Analysis of the proviral integration pattern shows that, in some mice, the myeloproliferative disease is clonal. In multiple mice, the CML-like disease has been transplantable, inducing a similar myeloproliferative syndrome within 1 month of transfer to sublethally irradiated syngeneic recipients. The disease in many of these mice has progressed to the development of acute lymphoma/leukemia resembling blast crisis. These results demonstrate that murine CML recapitulates important features of human CML. As such, it should be an excellent model for addressing specific issues relating to the pathogenesis and treatment of this disease.

Oncogenic Abl and Src tyrosine kinases elicit the ubiquitin-dependent degradation of target proteins through a Ras-independent pathway

Oncogenic forms of the Abl and Src tyrosine kinases trigger the destruction of the Abi proteins, a family of Abl-interacting proteins that antagonize the oncogenic potential of Abl after overexpression in fibroblasts. The destruction of the Abi proteins requires tyrosine kinase activity and is dependent on the ubiquitin-proteasome pathway. We show that degradation of the Abi proteins occurs through a Ras-independent pathway. Significantly, expression of the Abi proteins is lost in cell lines and bone marrow cells isolated from patients with aggressive Bcr-Abl-positive leukemias. These findings suggest that loss of Abi proteins may be a component in the progression of Bcr-Abl-positive leukemias and identify a novel pathway linking activated nonreceptor protein tyrosine kinases to the destruction of specific target proteins through the ubiquitin-proteasome pathway.

Local re-utilization of thymidine in normal mouse tissues as measured with iododeoxyuridine

Thymidine (TdR) and its analogue, iododeoxyuridine (IdUdr), were used to quantitate nucleoside re-utilisation in vivo. Significantly different results obtained, however, depending upon what form of isotopically labelled iododeoxyuridine is used. No measurable local thymidine re-utilization was found in mouse thymus, spleen or bone marrow when the retention of [3H]IdUdR was compared with [14C]TdR. On the other hand, significant differences were found between the retention of [125I]IdUdR and [3H]IdUdR, which is attributed to de-iodination of iododeoxyuridine. Some thymidine re-utilization was found in duodenum using both [3H]IdUdR and [125I]IdUdR. Information on the in vivo distribution of TdR and the contention that a large degree of TdR re-utilization in the thymus is evidence of extensive cell death must be re-interpreted in the light of these results. In addition, evidence for little or no local re-utilization in some tissues will greatly simplify the use of [11C]TdR as an imaging agent for measuring tissue proliferation in vivo with positron emission tomography (PET).

Cellular sources of thymidine nucleotides: studies for PET

The relative utilization of endogenously synthesized thymidine nucleotides and exogenously supplied thymidine analog was compared in a number of mammalian cell lines, tissues, and tumors. To measure the relative utilization, cells were incubated in tissue culture media containing the thymidine analog [3H]-5-bromo-2'-deoxyuridine (BUDR). After extraction of the DNA, the degree of substitution of the thymidine by BUDR was determined by density gradient centrifugation. All the cell lines and tissues tested utilized both exogenous BUDR and endogenous thymidine sources to a similar extent. The relative utilization of the exogenous pathway could be manipulated by varying the exogenous concentration of BUDR. Our results demonstrate that one can predict the relative utilization of these two pathways and can calculate the effective specific activity of the intracellular thymidine nucleotide pool. Such information is needed in interpreting 11C-labeled thymidine uptake as measured by positron emission tomography.