RNF2, also known as Ring1B/Ring2, is a component of the polycomb repression complex 1. RNF2 is highly expressed in many tumors, suggesting that it might have an oncogenic function, but the mechanism is unknown. Here, we show that knockdown of RNF2 significantly inhibits both cell proliferation and colony formation in soft agar, and induces apoptosis in cancer cells. Knockdown of RNF2 in HCT116 p53+/+ cells resulted in significantly more apoptosis than was observed in RNF2 knockdown HCT116 p53-/- cells, indicating that RNF2 knockdown-induced apoptosis is partially dependent on p53. Various p53-targeted genes were increased in RNF2 knockdown cells. Further studies revealed that in RNF2 knockdown cells, the p53 protein level was increased, the half-life of p53 was prolonged and p53 ubiquitination was decreased. In contrast, cells overexpressing RNF2 showed a decreased p53 protein level, a shorter p53 half-life and increased p53 ubiquitination. Importantly, we found that RNF2 directly binds with both p53 and MDM2 and promotes MDM2-mediated p53 ubiquitination. RNF2 overexpression could also increase the half-life of MDM2 and inhibit its ubiquitination. The regulation on p53 and MDM2 stability by RNF2 was also observed during the etoposide-induced DNA damage response. These results provide a possible mechanism explaining the oncogenic function of RNF2, and because RNF2 is important for cancer cell survival and proliferation, it might be an ideal target for cancer therapy or prevention.
Bibliographical noteFunding Information:
We thank Dr Bert Vogelstein (Johns Hopkins Oncology Center) for the HCT116 p53+/+, HCT116 p53−/− cells, Dr Seongman Kang (Korea University, South Korea) for the pCDNA3-Xpress-RNF2 plasmid. We also thank Dr Yibin Deng at The Hormel Institute for very helpful discussion and advice. We thank Tonya M Poorman for help submitting our manuscript.This work was supported by The Hormel Foundation and National Institutes of Health Grants CA077646, CA027502, CA111536, CA120388, R37CA081064, ES017548 and the National Natural Sciences Foundation of China (No. 81171924).