NDRG2 Sensitizes Myeloid Leukemia to Arsenic Trioxide via GSK3-NDRG2-PP2A Complex Formation

Abstract

N-Myc downstream-regulated gene 2 (NDRG2) was characterized as a tumor suppressor, inducing anti-metastatic and anti-proliferative effects in several tumor cells. However, NDRG2 functions on anticancer drug sensitivity, and its molecular mechanisms are yet to be fully investigated. In this study, we investigated the mechanism of NDRG2-induced sensitization to As2O3 in the U937 cell line, which is one of the most frequently used cells in the field of resistance to As2O3. NDRG2-overexpressing U937 cells (U937-NDRG2) showed a higher sensitivity to As2O3 than mock control U937 cell (U937-Mock). The higher sensitivity to As2O3 in U937-NDRG2 was associated with Mcl-1 degradation through glycogen synthase kinase 3 (GSK3) activation. Inhibitory phosphorylation of GSK3 was significantly reduced in U937-NDRG2, and the reduction was diminished by okadaic acid, a protein phosphatase inhibitor. NDRG2 mediated the interaction between GSK3 and protein phosphatase 2A (PP2A), inducing dephosphorylation of GSK3 at S9 by PP2A. Although the C-terminal deletion mutant of NDRG2 (C NDRG2), which could not interact with PP2A, interacted with GSK3, the mutant failed to dephosphorylate GSK3 at S9 and increased sensitivity to As2O3. Our findings suggest that NDRG2 is a kind of adaptor protein mediating the interaction between GSK3 and PP2A, inducing GSK3 activation through dephosphorylation at S9 by PP2A, which increases sensitivity to As2O3 in U937 cells.