DNA Damage Response:Chromosome Instability In Hybrid Cells And Regulation Of RNF8by MiR-214

In many interspecific hybrid cells, the chromosomes from one parental set preferentially lose, while those from the other parent are retained. In human-mouse hybrid cells, the extensive chromosomal elimination of human genome often occurs. Several hypotheses were proposed to explain the mechanisms underlying the elimination of uniparental chromosomes in the interspecific hybrid cells formed by sexual hybridization or artificial cell fusion, such as asynchronous chromosome segregation, asynchronous nucleoprotein synthesis or spatial separation of parental genomes, etc. However, these hypotheses were derived from the observations on small numbers of fixed cells, and the underlying mechanisms are still elusive. Live cell imaging can be used to observe the dynamics of chromosomes during progression of cell cycle, to determine the way of chromosome loss. Here, we for the first time found that the elimination of human chromosomes is progressive through the loss of fragmented chromosomes. The results showed that the elimination of human chromosomes in human-mouse hybrid cells is accompanied by continued cell division at the presence of DNA damage on human chromosomes. Deficiency in DNA damage repair on human chromosomes occurs after cell fusion. Furthermore, increasing the level of DNA damage on human chromosomes by irradiation accelerates human chromosome loss in hybrid cells. Our results indicate that the elimination of human chromosomes in human-mouse hybrid cells results from unrepaired DNA damage on human chromosomes. Altogether, we study CIN in human-mouse hybrid cells formed by cell fusion and provide direct evidence for a novel mechanism underlying CIN, which may facilitate the understanding of carcinogenesis. Furthermore, our results show that human-mouse hybrid cells may be as a good model to facilitate the research on the mechanisms of DNA damage response. A defective DNA damage response in tumours is frequently associated with carcinogenesis. The DNA damage response includes sensing DNA lesions, signal transduction and promoting damage repair. Abrogation of this response can cause chromosome instability, which is a common characteristic of most tumours. However, the underlying molecular mechanisms on the regulation of this network are still elusive. The ubiquitin ligase RNF8mediates the ubiquitination of H2AX to recruit53BP1and BRCAl at DNA damage sites, further promoting DNA damage response and inhibiting chromosomal instability. Though RNF8is a key protein involved in the DNA damage response, regulation of its expression is poorly understood. Here, we show that miR-214represses RNF8expression in ovarian cancer cell lines, by binding to its3’-untranslated region and so impairs the DNA damage response, while antagonizing miR-214increases RNF8expression and thus improves the level of DNA damage repair. Consistent with the role of miR-214in regulating RNF8level, the impaired DNA repair induced by miR-214over-expression can be rescued by over-expressing RNF8without3’-untranslated region. Together, these results suggest that miR-214-mediated down-regulation of RNF8impedes DNA damage response to induce chromosome instability in ovarian cancers, which may facilitates the understanding of mechanisms of chromosome instability.