FLT3, CD32, PU.1, ERG, uPAR, and TAP2 Are Strongly Associated with the Progression of Chronic Myeloid Leukemia and Combination of Small Interference RNA of FLT3 and STI571 Synergistically Induced Apoptosis of K562 Cells

To characterize molecular mechanisms by which transition from chronic phase to blast crisis in chronic myeloid leukemia (CML) for developing novel therapeutic targets, we analyzed gene-expression profiles of leukemic cells from 12 patients in chronic phase and 9 patients in blast crisis using a 8.7K cDNA chip. We identified 89 genes that were up-regulated as well as 54 genes that were down-regulated in blast crisis of CML. The expression profile included oncogenes, tumor suppression genes, and human genes encoding proteins involved in transcription, signal transduction, metabolism, cell growth, differentiation, apoptosis and immune functions. 18 genes were selected among the up-regulated group for analysis using real-time PCR. Real-time PCR data indicated that the expression of FLT3 (p < 0.001), CD32 (p < 0.001), ERG (p < 0.001), uPAR (p < 0.001), MAD (p < 0.001) and TAP2 (p < 0.001) showed statistically significant difference between chronic phase and blast crisis. For further analysis, we utilized small hairpin RNAs (shRNAs), also referred to as small interfering RNAs, to target human FLT3. These small interfering RNA constructs significantly inhibited FLT3 expression at mRNA and protein levels in K562 cells. After treating both the FLT3 knockdown cells and control cells (FLT3 wild type) with STI571, MTT assay and the expression patterns of apoptosis related genes (PARP, caspase-3, Bax) were examined. MTT assay and caspase-3 activity assay showed that silencing of the gene for FLT3 significantly reduced cell viability and ultimately facilitated the induction of apoptotic cell death by STI571. These findings uncovered evidence of a complex signaling network operating down-stream of FLT3 that actively contributes to tumor progression. Thus, RNA interference-directed targeting of FLT3 can be a potential candidate anticancer agent in association with STI571 against chronic myeloid leukemia.