Identification of PRMT1 as an AE9a-interacting protein. (A) AE9a-PRMT1 interaction is confirmed by both FLAG-IP and PRMT1-IP in 293T cells transiently expressing FLAG-tagged AE9a. Control lane (C) represents 293T cells transfected with empty vector. Endogenous PRMT1 associated with AE9a is enzymatically active as shown by in vitro methyltransferase assay on recombinant histone H4. (B) Interaction of endogenous AML1-ETO and PRMT1 in leukemic cells positive for t(8;21), Kasumi-1. Endogenous AML1-ETO is immunoprecipitated by PRMT1 Ab in Kasumi-1 cells. Reciprocal immunoprecipitation of AML1-ETO pulls down endogenous PRMT1 in Kasumi-1 cells. (C) Interaction of AE9a and Prmt1 in leukemic cells expressing HA-AE9a. Cell lysates from leukemic cells expressing HA-AE9a were subjected to HA-IP (human influenza hemagglutinin–immunoprecipitation) to pull down endogenous Prmt1.