Induction of paraptotic cell death in breast cancer cells by an iron chelator involved activation of UPR/MAPK pathway and inactivation of PI3K/AKT/mTOR.

Abstract

Breast cancer is the most frequently diagnosed cancer in the world, but its treatment effect is limited, so new treatment strategies are needed. An iron chelator, 2,2'-di-pyridineketone hydrazone dithiocarbamate butyric acid ester (DpdtbA), exerts significant growth inhibition in breast cancer cell lines. Our data showed that DpdtbA treatment significantly promoted extensive cytoplasmic vacuolization derived from the endoplasmic reticulum, mitochondrial swelling, and Alix downregulation in MDA-MB-231 and SK-BR-3 cell lines. Furthermore, cytoplasmic vacuolation could be abolished by cycloheximide (CHX) and antioxidant N-acetylcysteine (NAC), indicating that vacuole formation required new protein synthesis and was ROS-dependent. These results support that DpdtbA is able to induce paraptosis, a programmed cell death pattern. The enhanced cytoplasmic Ca2+after DpdtbA treatment or deceased Ca2+ upon co-treatment with the Ca2+ chelator (BAPTA-AM) prompted that ROS production may partially correlate with the Ca2+-mediated decrease in mitochondrial membrane potential. In addition, DpdtbA triggered ER stress and accumulation of unfolded proteins, leading to the activation of p-PERK/p-EIF2α and p-IRE1/ATF4/chop pathway, inactivation of ATF6 (activating transcription factor 6) that may contribute to the anti-proliferative effect. Furthermore, our data showed that DpdtbA treatment not only led to excessive activation of MAPKs (mitogen activated protein kinases) signaling, but also resulted in inactivation of the PI3K/AKT/mTOR pathway, both of which were involved in the regulation of paraptosis. The results demonstrated that paraptotic cell death induced by an iron chelator in breast cancer cells was partially involved in Ca2+-mediated ROS production, UPR(unfolded protein response)/MAPKs activation, and PI3K/AKT/mTOR inactivation.