Picosecond pulsed electric fields induce apoptosis in HeLa cells via the endoplasmic reticulum stress and caspase-dependent signaling pathways

The non-invasive treatment of tumors with preserved fertility holds great promise. The application of pulsed electric field (PEP) is a new biomedical engineering technique for tumor therapy. Picosecond pulsed electric fields (psPEF) can be transferred to target deep tissue non-invasively and precisely; however, research of the biological effects of psPEF on cells is limited. Electric theory predicts that when the pulse duration decreases to nanoseconds and picoseconds, it will mainly affect organelles and lead to intracellular electromanipulations. Previous studies have shown that psPEF targets the mitochondria and induces apoptosis through a mitochondrial-mediated pathway in He La cells. The endoplasmic reticulum is also involved in the intrinsic pathways of apoptosis. In the present study, He La cells were exposed to psPEF to investigate the underlying mechanisms of apoptosis. MTT assay demonstrated that psPEF displayed strong growth inhibitory effects on He La cells. Treatment with psPEF led to marked cell apoptosis and cell cycle arrest at the G(2)/M phase. In addition, psPEF affected the phosphorylation levels of endoplasmic reticulum sensors and upregulated the expression of glucose-regulated protein 78 (GRP78), glucose-regulated protein 94 (GRP94) and CCAAT enhancer-binding protein (C/EBP) homologous protein (CHOP). These changes were accompanied by the elevation of intracellular Ca2+ concentrations. Furthermore, the activation of caspase-12, -9 and -3, led to the release of cytochrome c, as well as the upregulation of Bax and the downregulation of Bcl-2, as observed in the He La cells. Taken together, these data suggest that psPEF is an efficient apoptosis-inducing agent for He La cells, which exerts its effects, at least partially, via the endoplasmic reticulum stress and caspase-dependent signaling pathways.