The Clinical Significance And Mechanism Of FLT3 Gene Overexpression In Acute Myeloid Leukemia With T(8;21)

Objective:Acute myeloid leukemia is a highly heterogeneous aggressive blood disease caused by the differentiation and maturation disorders、 apoptosis decline and malignant clonal proliferation of myeloid cells. The most common chromosomal translocation of AML is t(8;21)(q22;q22), generating the AML1/ETO fusion gene. AML cannot be developed by the only expression of AML1/ETO fusion protein. The occurrence of other genetic abnormalities is necessary too. This study was aimed to investigate the expression levels of FLT3 gene in acute myeloid leukemia with maturation (AML-M2) patients carrying AML1/ETO fusion gene, and analyze its relation with clinical and laboratorial features and prognosis.Methods:RQ-PCR methods were used to detect the expression levels of FLT3 in 21 AML-M2 patients with AML1/ETO of PLA Hospital from 2008 to 2012.The correlation of the expression levels of FLT3 with clinical features,other laboratorial examinations and disease prognosis were analyzed.Then,we use PCR、RQ-PCR、 Western Blot、CCK-8 and Flow cytometry to observe the different expression of FLT3 and STAT5 bewteen AML1/ETO positive and negative cell lines.Results:Gene expression levels of FLT3 (FLT3 gene/ reference gene) in patients at initial diagnosis were 1.65%～261.5%. The expression levels of FLT3 over 35% was defined as HIGH GROUP (12),while the expression levels below 35% was defined as LOW GROUP (9). The proportion of patients with extramedullary infiltration in HIGH GROUP was higher than it in LOW GROUP (25% VS 0%,p=0.2286).The proportion of patients at initial diagnosis with white blood cell＞10 × 109/L in HIGH GROUP was higher than that in LOW GROUP (66.67% VS 22.22%). The differences in relapse rate (72.72% vs 22.22%,p=0.0805)and the mortality rate (50% vs 11.11%,p=0.0614) between the two group were not significant,but there was a clear trend that the LOW GROUP has a higher CR rate and a lower relapse rate and mortality rate.The expression of STAT5a/ STAT5b/p- STAT5b protein in AML1/ETO positive cell lines was absolutely higher than AML1/ETO negative cell lines.Exposed to FLT3 and STAT5 inhibitors, AML1/ETO positive cell lines have higher apoptosis rate and lower cell proliferation rate.It implies that the collaboration of FLT3 and AML1/ETO may effect the STAT5 pathway.Conclusion:The expression of FLT3 in t(8;21) AML is different. FLT3 gene high expression levels in AML-M2 patients with AML1/ETO have a higher rate of relapse and hence poor prognosis. The collaboration of FLT3 and AML1/ETO may effect the STAT5 pathway. It is important to detect FLT3 expression levels in routine clinical practice for patient’s risk stratification, prognostic evaluation and effective treatment selection.