Cytoplasm damage induced defensive cellular response in microbeam targeted mammalian cells

Primary target of radiation is the cellular DNA, but consequence of cytoplasmic damage is yet to be understood. To distinguish the cellular responses triggered from DNA damage and cytoplasmic damage, microbeam would be most effective technology. Microbeam which is a highly advanced technology that enables studies to target cells efficiently with several micrometer sized beam and desired amount of radiation. SPICE-QST microbeam provides 3.4 MeV protons beam of a size of below 2-μm in diameter size, which can be targeted to cytoplasm and/ or nucleus of the mammalian cells. We performed a cytoplasm targeted irradiation (Cyto-IR) of the WI-38 cells to investigate the cytoplasmic damage response. We focused on the activation of nuclear factor (erythroid-derived 2)-like 2 (NRF2) and its antioxidative signaling pathway. As a result, Cyto- IR induced mitochondria fragmentation, which accelerated the mitochondrial superoxide (MitoSOX) production. MitoSOX triggered the NRF2 nucleus translocation and upregulated the expression of its target genes, such as heme oxygenase 1. In addition, we found that cytoplasmic irradiation induced upregulation of ERK 1/2 and resulted radiation-adaptive response to later X-ray exposure. NRF2 antioxidative response is suggested to play a key role against DNA damage under cytoplasmic irradiation. Cytoplasmic damage triggered signaling pathway would be important in understanding the mechanism of defensive role of mammalian cells against radiation. (author)