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Blood, 15 June 2007, Vol. 109, No. 12, pp. 5411-5421. Prepublished online as a Blood First Edition Paper on March 8, 2007; DOI 10.1182/blood-2006-06-032490.
NEOPLASIA Role of BCR/ABL gene-expression levels in determining the phenotype and imatinib sensitivity of transformed human hematopoietic cells1 Department of Hematopoietic Stem Cell and Leukemia Research, Division of Hematology and Hematopoietic Cell Transplantation (HCT), and 2 Division of Virology, City of Hope National Medical Center, Duarte, CA Increased levels of Bcr-Abl expression in chronic myelogenous leukemia (CML) cells are associated with disease progression and imatinib (IM) resistance. However, it is not clear if these associations are a direct result of elevated Bcr-Abl expression. We used a human transduction model of CML to directly investigate the role of varying Bcr-Abl expression levels in determining the phenotype and IM sensitivity of hematopoietic cells. CD34+ cells were transduced with vectors coexpressing Bcr-Abl and GFP, and cells expressing low and high levels of GFP and Bcr-Abl (BAlo and BAhi) were selected. BAhi cells demonstrated enhanced activation of downstream proliferative and antiapoptotic signaling and enhanced proliferation and survival compared to BAlo cells. Freshly isolated BAhi CD34+ cells and cell lines demonstrated increased IM-mediated growth inhibition likely reflecting Bcr-Abl dependence for growth and survival. CD34+ cells expressing BCR/ABL kinase-mutant genes demonstrated resistance to IM-mediated inhibition of proliferation and viability, which was not enhanced by increased expression of BCR/ABL kinase-mutant genes. We conclude that Bcr-Abl overexpression results in increased proliferation and antiapoptotic signaling in CD34+ cells, but may not play a direct role in IM resistance in progenitor cells expressing either wild-type or mutant BCR/ABL genes.
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