Search

Ecotropic viral integration site-1 (EVI1) is one of the candidate oncogenes for human acute myeloid leukemia (AML) with chromosomal alterations at 3q26. High EVI1 expression (EVI1(high)) is a risk factor for AML with poor outcome. Using DNA microarray analysis, we previously identified that integrin α6 (ITGA6) was upregulated over 10-fold in EVI1(high) leukemia cells. In this study, we determined whether the increased expression of ITGA6 is associated with drug-resistance and increased cell adhesion, resulting in poor prognosis. To this end, we first confirmed the expression pattern of a series of integrin genes using semi-quantitative PCR and fluorescence-activated cell sorter (FACS) analysis and determined the cell adhesion ability in EVI1(high) leukemia cells. We found that the adhesion ability of EVI1(high) leukemia cells to laminin increased with the increased expression of ITGA6 and integrin β4 (ITGB4). The introduction of small-hairpin RNA against EVI1 (shEVI1) into EVI1(high) leukemia cells reduced the cell adhesion ability and downregulated the expression of ITGA6 and ITGB4. In addition, the overexpression of EVI1 in EVI1(low) leukemia cells enhanced their cell adhesion ability and increased the expression of ITGA6 and ITGB4. In a subsequent experiment, the introduction of shRNA against ITGA6 or ITGB4 into EVI1(high) AML cells downregulated their cell adhesion ability; however, the EVI1(high) AML cells transfected with shRNA against ITGA6 could not be maintained in culture. Moreover, treating EVI1(high) leukemia cells with neutralizing antibodies against ITGA6 or ITGB4 resulted in an enhanced responsiveness to anti-cancer drugs and a reduction of their cell adhesion ability. The expression of ITGA6 is significantly elevated in cells from relapsed and EVI1(high) AML cases; therefore, ITGA6 might represent an important therapeutic target for both refractory and EVI1(high) AML.

Ecotropic viral integration site-1 (EVI1) is an oncogenic transcription factor in human acute myeloid leukemia (AML) associated with poor prognosis. Because the drug-resistance of leukemia cells is partly dependent on cell quiescence in the bone marrow niche, EVI1 may be involved in cell cycle regulation in leukemia cells. As a candidate regulator of the cell cycle in leukemia cells with high EVI1 expression (EVI1(high)), we analyzed angiopoietin1 (Ang1), which is a down-regulated gene in EVI1-deficient mice and is involved in the quiescence of hematopoietic stem cells. The results of real-time PCR analyses showed that Ang1 is highly expressed in leukemia cell lines and primary AML cells with EVI1(high) expression. Introduction of shRNA against EVI1 into EVI1(high) leukemia cells down-regulated Ang1 expression. Moreover, knockdown of Ang1 in EVI1(high) leukemia cells promoted cell cycle progression and down-regulated the CDK inhibitor p18 (INK4c). Treatment with a decoy Tie2/Fc protein also down-regulated the expression of p18. These results suggest that Ang1/Tie2 signaling may suppress cell cycle progression via maintenance of G0/G1 phase through up-regulation of p18 expression. This mechanism may help to maintain EVI1(high) leukemia cells in the bone marrow niche and promote resistance to anti-cancer drugs., (Copyright © 2011. Published by Elsevier Inc.)