Taken together, these results suggested that 1) the activated state of ERM was key for P-gp-mediated function, particularly in enhancing lymphoblastic leukemia cell sensitivity to drug treatment, and 2) the association of P-gp with F-actin through the p-ERM proteins was crucial for the maintenance of P-gp polarization in MDR induced by CCR9/CCL25 signaling pathway. This evidence concerns the gene CCL25 and acute lymphoblastic leukemia.