The Study Of Mutation Of Tyrosine Kinase In Molecular Pathogenesis Of Acute Myeloid Leukemia

There are two categories of mutations or gene rearrangements which play important role in molecular mechanisms of leukemogenesis. One class of mutations or gene rearrangements involving mostly tyrosine kinase gene such as BCR/ABL of chronic myelogenous leukemia (CML) confer a proliferative and/or survival advantage to hematopoietic progenitors, and second class of mutations involving mostly transcription factor associated with hematopoietic cell differentiation such as PML/RARαor C/EBPαmutation serve primarily to impair hematopoietic differentiation and subsequent apoptosis of cells. In mice model study it has been shown that the cooperation of two categories of mutations or gene rearrangements results in phenotype of acute myeloid leukemia (AML) including blast crisis of CML. In clinical setting, though FLT3-ITD mutation and PML/RARαin acute promyelocytic leukemia (APL) patients as well as c-KIT mutation and AML1/ETO in AML-M2b patients have been reported, the molecular defect involving two categories of mutation are largely unidentified. Although disruption-of-function mutation in transcription factors required for normal hematopoietic development can block differentiation of hematopoietic stem cell, it is not sufficient to induce AML phenotype in mice model study. The available evidence indicates that activating mutations in the hematopoietic tyrosine kinases FLT3 and c-KIT, and in N-RAS and K-RAS, confer proliferative advantage to hematopoietic progenitors and cooperate with disruption-of-function mutations in hematopoietic transcription factors to cause an full-blown phenotype of AML. We focused on the mutation of hematopoietic tyrosine kinases such as FLT3, PDGFRβ, KDR, CSF2Rβas well as downstream negative regulation molecular such as SOCS1, PIAS3 and SHIP in AML.The FLT3 (FMS-like tyrosine kinase 3) gene encodes a membrane-bound receptor tyrosine kinase (RTK) that has a crucial role in normal haematopoiesis. Recently, FLT3 mutations have been found in patients with ALL, MDS and AML (15～35%), making FLT3 one of the most frequently mutated genes in haematological malignancies. The most common form of FLT3 mutation are internal tandem duplications (ITD) and Asp835 point mutation. We screened the mutation of FLT3-ITD in the juxtamembrane region of FLT3 gene in Chinese patients with hematological malignancies by PCR and cloning sequencing to investigate the significance in leukemogenesis and prognosis. A total of 484 patients with hematological malignancies were enrolled in the study, and 27 patients (5.6%) were found to have ITD mutation in exons 14 and 15 of FLT3 gene. The results of cloning sequencing indicated that the length of duplicated fragment varies from 54 to 215 base pairs, and the reading frame of the transcript is always preserved. Among these 27 FLT3-ITD patients 26 are AML patients and another one is ALL patient, which respectively accounts for 9.5% of 273 AML patients and 1.6% of 61 ALL patients. FLT3-ITD was associated with leukocytosis and a high percentage of bone marrow blast cells (P<.001 for both) and with poor prognosis of AML patients. FLT3 aberrations(including FLT3-ITD and Asp835 point mutation) were also remarkably associated with AML patients following MDS or MDS/MPD(P<.05).We also identified a new mutation(A>T,Q1153L) of SH2-containing inositol phosphatase(SHIP) in a AML patients following MDS, which serves as downstream scaffold molecular of RTK signal pathway and negatively regulates hematopoietic cell proliferation. It reminds us that mutation of SHIP or RTK such as FLT3 may also play a important role in MDS progression to AML emerged as a second hit.