RAB20 and precursor B-cell acute lymphoblastic leukemia: Since the treatment of B-ALL cells with a specific PP1 inhibitor, tautomycin, strongly affects Ikaros binding to the RAB20 promoter and repression of RAB20 transcription, we tested whether the interaction between Ikaros and PP1 affects the ability of Ikaros to repress RAB20. The wild-type Ikaros or the Ikaros mutant that contains alanine point mutations at amino acids 465 and 467 that disrupt Ikaros–PP1 interactions (IKZF1-465-7A) was transfected into 293T cells, and the effect of the Ikaros–PP1 interaction on Ikaros’ function in regulating RAB20 expression was analyzed.