| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2004: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2003: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Leukemogenesis was investigated with molecular biological methods using bcr/abl cDNA micro-injection into eggs. Micro type bcr-abl (p230 bcr/abl) transcript was revealed to make CML patients atypical clinical courses other than typical CML. A novel transgenic mouse expressing p230 bcr/abl cDNA was succeeded to make. The transgenic mouse has a disease phenotype of CML with thrombocytosis. Transgenic mice expressing abnormal p51/p63 or the novel gene are now under making. Biological function of abnormalities of these p51/p63 and the novel gene are investigating with mutagenesis method. The reported transgenic mice expressed the p230 BCR/ABL gene under control of the promoter of the long terminal repeat, PCMV, of the murine stem cell virus of the MSCV vector. Two founder mice exhibited myeloproliferative disease(MPD) mimicking CML. The disease phenotype of the MPD caused by P230BCR/ABL was characterized by mild granulocytosis, a high platelet count, infiltration of megakaryocytes in some
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organs, and a longer disease latency compared with the MPD caused by P210 BCR/ABL. The leukemic cells expanded extramedullarily in the liver. Many immature and mature granulocytes and many megakaryocytes had infiltrated various tissues, i.e., the lung, spleen, bone marrow and kidney. The phenotype of the blasts analysed by immunohistochemistry and flow cytometry revealed the characteristics of the myeloblasts. The leukocyte counts for the transgenic progeny gradually increased after 11 months. The mean platelet counts gradually increased after 9 months of age. MPD becomes overt 13-15 months after birth.
The reason for making this MPD model mice may be its use of the p230 BCR/ABL gene, which is less cytotoxic than p210 BCR/ABL. The level of bcr/abl expression is low in all tissues except the hematopoietic cells[29]. This limited expression pattern may permit successful creation of MPD model mice.
There is a hypothesis that in humans the relative level of BCR/ABL expression may be a determinant in the severity of the phenotype of BCR/ABL-positive leukemia. Patients having P230 BCR/ABL had the two disease phenotype of Ph-positive ET or chronic neutrophilic leukemia(CNL) [36,39,40]. The disease phenotypes of ET and CNL are possibly a result of the expression level of the P230 BCR/ABL protein. The difference in the expression level may influence the disease phenotype in the transgenic mice. To clarify this, additional molecular studies will be needed. The transgenic mouse system using PCMV expresses P230 BCR/ABL transcripts at a high level [29]. This evidence of an overt disease phenotype in P230 BCR/ABL expression model mouse supports the hypothesis.
A second hypothesis is the existernce of molecular differences in bcr/abl molecules [41-43]. Molecular differences between p210 BCR/ABL cDNA and p230 BCR/ABL cDNA may be an important disease determinant in both humans and transgenic mice. P210 and P230 BCR/ABL contain some potential functional motifs encoded by the BCR portion of the fusion gene. The Dbl-like and pleckstrin homology domains exist in the bcr sequence of both P210 and P230 Bcr/Abl [43]. The CalB and GAP^<rac> domains [44,45] in P230 Bcr/Abl may directly influence the ability of this protein to transform various hematopoietic precursors by inhibition of lymphoid development and/or by promotion of myeloid and megakaryocyte development. It is possible that the additional her sequences included within P230 BCR/ABL, specifically the GAP^<rac> domain, may function to partially abrogate the properties of activated p21 Rac in P230 Bcr/Abl-expressing hematopoietic cells. These potential motifs might be involved in the differences in the disease phenotype between P210 BCR/ABL and P230 BCR/ABL transgenic mice. Less
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