The linker of nucleoskeleton and cytoskeleton complex is required for X-ray-induced epithelial-mesenchymal transition

The linker of nucleoskeleton and cytoskeleton (LINC) complex has been implicated in various functions of the nuclear envelope, including nuclear migration, mechanotransduction and DNA repair. We previously revealed that the LINC complex component Sad1 and UNC84 domain containing 1 (SUN1) is required for sublethal-dose X-ray-enhanced cell migration and invasion. This study focused on epithelial-mesenchymal transition (EMT), which contributes to cell migration. Hence, the present study aimed to examine whether sublethal-dose X-irradiation induces EMT and whether LINC complex component SUN1 is involved in low-dose X-ray-induced EMT. This study showed that low-dose (0.5 Gy or 2 Gy) X-irradiation induced EMT in human breast cancer MDA-MB-231 cells. Additionally, X-irradiation increased the expression of SUN1. Therefore, SUN1 was depleted using siRNA. In SUN1-depleted cells, low-dose X-irradiation did not induce EMT. In addition, although the SUN1 splicing variant SUN1_916-depleted cells (containing 916 amino acids [AA] of SUN1) were induced EMT by low-dose X-irradiation like as non-transfected control cells, SUN1_888-depleted cells (which encodes 888 AA) were not induced EMT by low-dose X-irradiation. Moreover, since the Wnt/β-catenin signaling pathway regulates E-cadherin expression via the expression of the E-cadherin repressor Snail, the expression of β-catenin after X-irradiation was examined. After 24 hours of irradiation, β-catenin expression increased in non-transfected cells or SUN1_916-depleted cells, whereas β-catenin expression remained unchanged and did not increase in SUN1- or SUN1_888-depleted cells. Therefore, in this study, we found that low-dose X-irradiation induces EMT, and LINC complex component SUN1, especially SUN1_888, is required for X-ray-induced EMT via activation of the Wnt/β-catenin signaling pathway.