Ionizing radiation (IR) is widely used as a main treatment for solid tumors, however, its potential influence and its role in the invasion and metastasis of cancer still remain unknown. In this study, we found that IR showed an inhibitory effect on the invasion of mutant p53 expressing cancer cells through targeting cyclin D1, which has been known as implicated in invasion and metastasis. Our data showed that gamma-irradiation (5 Gy) decreased trans-well migration of mutant p53 expressing cancer cells. It has been reported that following exposure to IR cyclin D1 is rapidly degraded via the ubiquitin pathway. We showed that IR-induced cyclin D1 degradation is restored after 24 hr in H1299 p53 negative cells. In contrast, cyclin D1 depletion was not recovered in H1299 mutant p53 cells, suggesting its inhibiting effect on cyclin D1 regulation. In addition, the levels of matrix metalloproteinase 9 were decreased in mutant p53 expressing cancer cells, indicating the reduction of cell migration and invasion. These data indicate that IR suppresses the restoration of cyclin D1 via the mutant p53, thus inhibiting the invasion of cancer cells expressing mutant p53. Citation Format: Shin-Hee Lee, Phillip Craigmile, Shiyong Wu. Ionizing radiation regulates mutant p53-mediated cancer cell invasiveness through targeting cyclin D1. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 507. doi:10.1158/1538-7445.AM2015-507