Biological effects of high-LET (linear energy transfer) radiation have received increasing attention, particularly in the context of more efficient radiotherapy and space exploration. Efficient cell killing by high-LET radiation depends on the physical ability of accelerated particles to generate complex DNA damage, which is largely mediated by LET. However, the characteristics of DNA damage and repair upon exposure to different particles with similar LET parameters remain unexplored. We employed high-resolution confocal microscopy to examine phosphorylated histone H2AX (γH2AX)/p53-binding protein 1 (53BP1) focus streaks at the microscale level, focusing on the complexity, spatiotemporal behaviour and repair of DNA double-strand breaks generated by boron and neon ions accelerated at similar LET values (∼135 keV μm⁻¹) and low energies (8 and 47 MeV per n, respectively). Cells were irradiated using sharp-angle geometry and were spatially (3D) fixed to maximize the resolution of these analyses. Both high-LET radiation types generated highly complex γH2AX/53BP1 focus clusters with a larger size, increased irregularity and slower elimination than low-LET γ-rays. Surprisingly, neon ions produced even more complex γH2AX/53BP1 focus clusters than boron ions, consistent with DSB repair kinetics. Although the exposure of cells to γ-rays and boron ions eliminated a vast majority of foci (94% and 74%, respectively) within 24 h, 45% of the foci persisted in cells irradiated with neon. Our calculations suggest that the complexity of DSB damage critically depends on (increases with) the particle track core diameter. Thus, different particles with similar LET and energy may generate different types of DNA damage, which should be considered in future research.

The cellular transition to senescence is associated with extensive chromatin reorganization and gene expression changes. Recent studies appeared implying an association of lamin B1 (LB1) reduction with chromatin rearrangement in human fibroblasts promoted to senescence, while the mechanisms and structural features of these relations were not yet clarified. In this work we examined the functions of LB1 and lamin B receptor (LBR) in human cancer cells. We found that both LB1 and LBR tend to deplete during cancer cells transfer to senescence by γ-irradiation. A functional study employing silencing of LBR by shRNA constructs revealed reduced LB1 levels suggesting that regulation of both proteins is interrelated. Reduced expression of LBR resulted in the relocation of centromeric heterochromatin (CSH) from the inner nuclear membrane (INM) to nucleoplasm associated with its unfolding. It indicates that LBR tethers heterochromatin to INM in cycling cancer cells and that LB1 is an integral part to this tethering. Down-regulations of LBR and LB1 at the onset of senescence are thus necessary for the release of heterochromatin from binding to the lamina, resulting in changes in chromatin architecture and gene expression. However, senescence phenotype was not manifested in lines with reduced LBR and LB1 expression suggesting that other factors such as the DNA damage are needed for senesce trigger. We conclude that the primary response of cells to various stresses leading to senescence consists in down-regulation of LBR and LB1 to attain reversal of chromatin architecture.