miR-214-mediated downregulation of RNF8 induces chromosomal instability in ovarian cancer cells

Defective DNA damage response (DDR) is frequently associated with carcinogenesis. Abrogation of DDR leads to chromosomal instability, a most common characteristic of tumors. However, the molecular mechanisms underlying regulation of DDR are still elusive. The ubiquitin ligase RNF8 mediates the ubiquitination of γH2AX and recruits 53BP1 and BRCA1 to DNA damage sites which promotes DDR and inhibits chromosomal instability. Though RNF8 is a key player involved in DDR, regulation of its expression is still poorly understood. Here, we show that miR-214 could abrogate DDR by repressing RNF8 expression through direct binding to 3′-untranslated region (3′ UTR) of RNF8 mRNA in human ovarian cancer cells. Antagonizing miR-214 by expressing its inhibitors in A2780 cells significantly increased RNF8 expression and thus promoted DNA damage repair. Consistent with the role of miR-214 in regulating RNF8 expression, the impaired DNA repair induced by miR-214 overexpression can be rescued by overexpressing RNF8 mRNA lacking the 3′ UTR. Together, our results indicate that down-regulation of RNF8 mediated by miR-214 impedes DNA damage response to induce chromosomal instability in ovarian cancers, which may facilitate the understanding of mechanisms underlying chromosomal instability.

缺陷型DNA损伤应答（DNA damage response, DDR）常与癌变相关。DDR的缺失会引发染色体不稳定性——这是肿瘤最为常见的特征之一。然而，调控DDR的分子机制仍不甚明晰。泛素连接酶RNF8可介导γH2AX的泛素化，并将53BP1与BRCA1招募至DNA损伤位点，从而促进DDR并抑制染色体不稳定性。尽管RNF8是参与DDR的关键因子，但其表达的调控机制仍鲜为人知。
本研究证实，在人卵巢癌细胞中，miR-214可通过直接结合RNF8信使RNA（mRNA）的3'非翻译区（3' UTR）抑制RNF8的表达，从而阻断DDR。在A2780细胞中过表达miR-214抑制剂以拮抗miR-214，可显著上调RNF8的表达，进而促进DNA损伤修复。与miR-214调控RNF8表达的作用一致，过表达缺失3' UTR的RNF8 mRNA，可挽救miR-214过表达所导致的DNA修复缺陷。
综上，本研究结果表明，miR-214介导的RNF8表达下调会阻碍DNA损伤应答，进而诱导卵巢癌细胞发生染色体不稳定性；该发现或有助于阐明染色体不稳定性的潜在发生机制。