RNF8 plays an important role in the radioresistance of human nasopharyngeal cancer cells in vitro

Abstract

Tumor residue or recurrence is common after radiation therapy for nasopharyngeal cancer (NPC) since the tumor cells can repair irradiation-induced DNA damage. The ubiquitination cascade mediates the assembly of repair and signaling proteins at sites of DNA double-strand breaks (DSBs). Ring finger protein 8 (RNF8) is an E3 ubiquitin ligase that triggers ubiquitination at the site of DSBs. The present study aimed to identify whether and how RNF8 small interfering RNA (siRNA) treatment enhances the radiosensitivity of irradiated human NPC cell lines. The CNE1, CNE2, and SUNE human NPC cell lines were stably transfected with a constructed RNF8-targeting siRNA expression vector. Western blotting was used to detect the effectiveness of RNF8 downregulation by RNF8 siRNA. The siRNA-transfected (RNF8-) and non-transfected (RNF8+) cells were irradiated at different doses by a linear accelerator. The growth inhibition ratio and apoptosis rate were detected by the methyl thiazolyl tetrazolium (MTT) assay and flow cytometry, respectively. The ataxia-telangiectasia mutated (ATM), DNA-PKcs, Chk1, Chk2, Nbs1 and Ku80 protein levels in each group were determined. The growth inhibition ratio and apoptotic percentage of RNF8- cells were higher than those of the RNF8+ cells in each of the three cell lines. Lower protein expression levels of Chk1, Chk2, ATM, and Nbs1 were observed in the irradiated RNF8- cells compared to the irradiated RNF8+ cells in each of the three cell lines (P<0.01). As a result, a conclusion could be drawn that RNF8 recruits and ubiquitinates many factors to repair DNA damage, including DSBs, thereby conferring radioresistance to NPC cells.

The Functions of DNA Damage Factor RNF8 in the Pathogenesis and Progression of Cancer

“…Furthermore, the expression of checkpoint proteins Chk1 and Chk2 and DNA damage proteins ATM and Nbs1 was reduced in RNF8 knockdown cells with irradiation treatment, which impeded DNA repair function. The repair capacity of irradiation-induced DNA damage is a common factor for NPC recurrence after radiation therapy [78]. These results suggest that RNF8 is required in NPC cells for resistance to radiation therapy.…”

“…In contrast, the DNA damage response function of RNF8 in certain cancers is involved in radiation therapy resistance [78,79]. When the telomere was already uncapped by deletion of TRF2, the E3 ligase activity of RNF8 in promoting H2A ubiquitination helped to induce C-NHEJ and further caused genomic instability [46].…”

Identification of the potential roles of ring finger protein 8 in TP53‑mutant breast cancer

“…However, a previous study has revealed that decreased RNF8 expression can significantly improve radiotherapy sensitivity in nasopharyngeal cancer, while inhibiting cell proliferation and increasing apoptosis (31). In breast cancer MCF-7 cells, overexpression of RNF8 can significantly increase epithelial-mesenchymal transition and it mainly promotes phosphorylation of GSK3β, further inhibiting its activity (10).…”

“…In addition, an increase in phosphorylation of β-catenin has been observed in RNF8-overexpressing cells (10). Furthermore, in the treatment of breast cancer using tamoxifen to block ERα, tamoxifen exerts anticancer effects mainly by blocking the ERα signaling pathway (31), but a previous study has revealed that RNF8 can activate the ERα signaling pathway and thus promote tumor cell proliferation (8). The aforementioned studies did not focus on p53 mutations.…”

Targeting RNF8 Effectively Reverse Cisplatin and Doxorubicin Resistance in Endometrial Cancer

“…Depletion of RNF8 retains Ku80 on DNA and impairs NHEJ e ciency [36]. Recent study found that RNF8 facilities doxorubicin resistance in cancer stem cells [37]and radiation resistance in nasopharyngeal cancer, bladder cancer [38,39]. These studies prompt us to investigate the role of RNF8 in NHEJ in EC.…”