| Research Abstract |
In this study, we investigated the signal-transduction mechanism brought by the mutant FLT3 kinase and screened the therapeutic agents which inhibit the proliferation or induce the differentiation in leukemia cells harboring FLT3 mutations, then obtained the following results.
1. We divided the intracellular region of the FLT3 into several segments and expressed each segment to Cos7 cells, then found the intramolecular association between the JM and TK regions.
2. Using the two-hybrid system, we found several molecules which specifically bind to the mutated or wild-type FLT3 JM region.
3. We analyzed the biological mechanism for inhibiting the G-CSF induced myeloid differentiation in mutant FLT3 expressing 32D cells by means of quantitating the expression level of myeloid differentiation associated genes. In mutant FLT3 expressing cells, the block of myeloid differentiation was shown to be resulted from the inhibition of MPO, C/EBP-α and CIEBP-ε genes.
4. We analyzed the expression level of the FLT3 transcript quantitatively in comparison with several gene alterations in 181 de novo AML cases. In AML cells, the mean expression level of the FLT3 transcript was 20,203 copies/μgRNA, while each level varied from 0 to 2,322,706 copies/μgRNA. A high expression level of FLT3 was related to FLT3/ITD (p=.0020), MLL-TD (p=.0121) and FLT3/D835Mt (p=.0463), but not to N-RAS or to p53 mutations. Overexpressed FLT3 revealed auto-phosphorylation, and had the same sensitivity to the FLT3 inhibitor as FLT3/ITD. Overexpression of FLT3 (over 200,000 copies/μgRNA) was an unfavorable prognostic factor for overall survival in 91 AML cases without FLT3/ITD. These results indicated that overexpression of FLT3 might distinguish a novel disease entity in AML without FLT3 mutations and serve as a therapeutic target for FLT3 inhibitors.
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