Phosphatidylinositol 4-kinase II β downregulation induces ER stress mediated ROS generation and increases radio-sensitivity in MCF-7

Abstract

AbstractType II phosphatidylinositol 4-kinase has historically been associated with vesicular trafficking and growth factor receptor signaling. Recently, it was shown to influence apoptosis, cell adhesion, motility, and inflammatory reactions. Previous study from our group showed that down regulation of PtdIns 4-kinase II β inhibits NF-κB translocation to the nucleus and induce apoptosis in cancer cell lines. Since, NF-κB regulates redox homeostasis and stress signaling, the role of PtdIns 4-kinase II β in regulating these signaling cascades was investigated using human breast cancer cell line (MCF-7 cells). Knockdown of PtdIns 4-kinase II β inhibited NF-κB nuclear translocation and down regulated Bcl-2 and AKT-3 mRNA levels. Silencing of PtdIns 4-kinase II β increased ROS levels with a concomitant decrease in GSH: GSSG ratio, increased DNA damage and induced apoptosis. Inhibition of NADPH oxidase (NOX) activity restored redox homeostasis. Since NOX gets activated during ER stress and the resultant increase in ROS can induce apoptosis, we studied the role of PtdIns 4-kinase II β shRNA in ER stress and observed an increase in ER stress markers, pERK, IRE-1α, BiP and PDI and up regulation of GADD153. At cellular level, these cells showed ER deformity. ROS scavengers and ER chemical chaperone could rescue MCF-7 cells from PtdIns 4-kinase II β shRNA induced apoptosis. These results indicate involvement of PtdIns4-kinase II β in regulation of ER function. Interestingly, irradiation of MCF-7 cells increased PtdIns 4-kinase II β mRNA levels and knock-down of PtdIns 4-kinase II β increased radio-sensitivity of the cells indicating potential role of PtdIns 4-kinase II β in cancer radio-resistance.