BCL2L1 and leukemia: Therefore, it was reasonable that the mechanism of inhibition of major WT1 isoform-mediated transcriptional activation of Bcl-xL and Bcl-2 by Ex4a(+)WT1 isoform might be competition with major WT1 isoform for interacting with the transcriptional co-activators other than WT1 itself, resulting in the abrogation of major WT1 isoform-mediated transcriptional activity in leukemia cells.