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RAD52 motif‐containing 1 (RDM1), a key regulator of DNA double‐strand break repair and recombination, has been reported to play an important role in the development of various human cancers, such as papillary thyroid carcinoma, neuroblastoma and lung cancer. However, the effect of RDM1 on osteosarcoma (OS) progression remains unclear. Here, this study mainly explored the connection between RDM1 and OS progression, as well as the underlying mechanism. It was found that RDM1 was highly expressed in OS cells compared with human osteoblast cells. Knockdown of RDM1 caused OS cell proliferation inhibition, cell apoptosis promotion and cell cycle arrest at G1 stage, whereas RDM1 overexpression resulted in the opposite phenotypes. Furthermore, RDM1 silencing leads to a significant decrease in tumour growth in xenograft mouse model. RDM1 also increased the protein levels of MEK 1/2 and ERK 1/2. All these findings suggest that RDM1 plays an oncogenic role in OS via stimulating cell cycle transition from G1 to S stage, and regulating MEK/ERK signalling pathway, providing a promising therapeutic factor for the treatment of OS. [ABSTRACT FROM AUTHOR]

Breast cancer is currently among the most common cancers in women, with almost 200,000 new cases diagnosed annually. Dysregulation of DNA repair pathways allows cells to accumulate damage and eventually mutations, with a subsequent reduction in DNA repair capacity in breast tissue, leading to tumorigenesis. One component of the DNA damage repair pathway is RAD52 motif‐containing 1 (RDM1), but the specific role of RDM1 in breast cancer and the underlying mechanism remain unclear. Here, we examined the role played by RDM1 in breast cancer cell culture using the HBL100 and MCF‐7 breast cancer cell lines. Disruption of RDM1 reduced in vitro cell proliferation and promoted apoptosis. Knockdown of RDM1 also induced up‐regulation of p53 levels, whereas RAD51 and RAD52, both involved in DNA repair, were down‐regulated. In addition, the in vivo growth of RDM1‐deficient cells was significantly repressed, suggesting that RDM1 is a novel oncogenic protein in human breast cancer cells. This study reveals a link between the DNA damage response pathway and oncogenic functionality in breast cancer. Accordingly, therapeutic targeting of RDM1 is a potential treatment strategy for breast cancer and overcoming drug resistance. [ABSTRACT FROM AUTHOR]