Enforced E47 Expression Has Differential Effects on Lmo2-Induced T-Cell Leukemia

Abstract 4637

Lmo2 is one of the most commonly deregulated oncogenes in human T-cell acute lymphoblastic leukemia (T-ALL). In mouse models, Lmo2 overexpression causes a differentiation block before the onset of T-ALL at a developmental stage that is similar to the block seen in E47 knockout mice. Furthermore, Lmo2 and E47 are part of an oligomeric protein complex in hematopoietic stem and progenitor cells. Since E47 knockout mice also develop T-ALL, it has been hypothesized that Lmo2 may induce T-ALL by redirecting E47 activity away from its normal target genes. We noted downregulation of many E2A targets in Lmo2-induced T-ALL. To directly test whether E47 is required in Lmo2-induced T-ALLs, we transduced four stable T-ALL lines established from Lmo2 transgenic mice with retrovirus expressing E47 fused with estrogen receptor. All 4 lines tolerated stable high- level protein expression of E47-ER with no change in from their baseline growth rates. The E47-ER fusion protein allowed forced dimerization upon treatment with 4-hydroxytamoxifen. Tamoxifen treatment increased expression CD4 and other described E2A targets in all 4 T-ALL lines; but two lines underwent G0/G1 cell cycle arrest. Our data suggest that E47 deficiency is not a universal feature of Lmo2- induced T-ALL and E47 forced expression has differential effects on T-ALL.