Effect of the dominant-negative ikaros isoform 6 (Ik6) on cell function and drug sensitivity in acute lymphoblastic leukemia cell lines

Abstract Objective IKZF1 deletions occur commonly in patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) and predict a poor outcome. IK6 is a functional deficiency subtype of IKZF1, with the deletion of the N-terminal zinc finger structures (DNA binding regions). We aimed to explore the effect of IK6 on the biological function of ALL cells, the sensitivity of commonly used chemotherapeutic drugs in vitro, and its mechanism. Methods We constructed SUP-B15 cells with IK6 knocked down and NALM-6 cells overexpressed IK6. Western blot analysis was used to detect the effect of knockdown and overexpression. CCK-8 was used to detect cell proliferation and drug sensitivity. PI method was used to detect cell cycle. Annexin V-PI method was used to detect cell apoptosis. The target cells were co-cultured with human stromal cells, and after co-culture, the cell migration ability was detected by Transwell method. Finally, the RNA sequencing results of SUP-B15 cells interfering with IK6 were analyzed by GSEA software. Results We analyzed the effect of IK6 on functions of Ph-positive and Ph-negative ALL cells. SUP-B15 cells with Ik6-knockdown lost proliferation advantage and exhibited decreased proportion in static phase (G0/G1), increased proportion in synthetic phase (S), with down-regulation of CDK4, P27 and BCL-2. The sensitivity to dexamethasone increased, but no significant change in the susceptibility to imatinib and dasatinib. Migration ability of SUP-B15 cells with Ik6-knockdown significantly decreased when co-cultured with human stromal cells. NALM-6 cells overexpressed IK6 showed increased ratio of G0/G1 phase cells and the proportion of apoptotic cells was significantly increased. CDK4 and E2F1 were down-regulated in NALM-6 cells overexpressed IK6, meanwhile Cyclin E and P27 were up-regulated. GSEA analysis in Ik6-knockdown SUP-B15 cells showed several signaling pathways altered, which involved in cell adhesion and migration related Leukocyte Transendothelial Migration Signaling Pathway, VEGF Signaling Pathway, AXON Guidance Signaling Pathway, Tight Junction Pathway and the cell function related MAPK Signaling Pathway. Conclusions IK6 expression affects the biological characteristics of ALL cells, and may change the sensitivity of cells to dexamethasone. These alterations may relate with some signal pathways (such as MAPK). Whether the effect of IK6 on cell adhesion and migration ability is related to BCR-ABL fusion gene remains to be further explored. Keywords ALL, IKZF1, IK6, drug sensitivity, signaling pathway