Circ_002363 is regulated by the RNA binding protein BCAS2 and inhibits neodymium oxide nanoparticle-induced DNA damage by non-homologous end-joining repair

Neodymium oxide nanoparticles (NPs-Nd₂O₃) are increasingly being used in industry and biomedicine, causing adverse health effects such as lung disease. However, the underlying molecular mechanisms controlling these adverse consequences are unknown at present. In this study, a human bronchial epithelial cell line (16HBE) was exposed to increasing concentrations of NPs-Nd₂O₃, and Sprague-Dawley rats were treated with NPs-Nd₂O₃ by intratracheal instillation. We found that NPs-Nd₂O₃ exposure induced DNA damage and down-regulated levels of circular RNA (circRNA) circ_002363 in 16HBE cells as well as in rat lung tissue. We also observed that circ_002363 levels in the serum of workers employed in the production of NPs-Nd₂O₃ diminished as the work time progressed, suggesting that circ_002363 may be a potential biomarker of lung injury. Functional experiments showed that circ_002363 significantly inhibited DNA damage induced by NPs-Nd₂O_3. RNA pull-down and western blot assays found that circ_002363 interacted with proteins PARP1/Ku70/Ku80/Rad50, which are critical participants in non-homologous end-joining (NHEJ) DNA repair. Moreover, we found that formation of circ_002363 was regulated by the RNA binding protein Breast Carcinoma Amplified Sequence 2 (BCAS2). The BCAS2 protein affected circ_002363 expression through interaction with Pre-DNA2, the host gene of circ_002363, in NPs-Nd₂O_3-exposed 16HBE cells. In conclusion, our findings show first that circ_002363, which is regulated by BCAS2, acts as regulator of DNA damage via the NHEJ pathway. These results enhance our understanding of the regulatory mechanisms controlling the actions of circular RNAs and highlight the relationship between genetics and epigenetics in the development of diseases following exposure to environmental chemicals.