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Double-strand breaks (DSBs) are repaired through two major pathways, homology-directed recombination (HDR) and non-homologous end joining (NHEJ). The choice between these two pathways is largely influenced by cell cycle phases. HDR can occur only in S/G2 when sister chromatid can provide homologous templates, whereas NHEJ can take place in all phases of the cell cycle except mitosis. Central to NHEJ repair is the Ku70/80 heterodimer which forms a ring structure that binds DSB ends and serves as a platform to recruit factors involved in NHEJ. Upon completion of NHEJ repair, DNA double strand-encircling Ku dimers have to be removed. The removal depends on ubiquitylation and proteasomal degradation of Ku80 by the ubiquitin E3 ligases RNF8. Here we report that RNF8 is a substrate of APCCdh1 and the latter keeps RNF8 level in check at DSBs to prevent premature turnover of Ku80. [ABSTRACT FROM AUTHOR]

Histone ubiquitination regulates sperm formation and is important for nucleosome removal during spermatogenesis. RNF8 is an E3 ubiquitin ligase, and RAD6B is an E2 ubiquitin-conjugating enzyme. Both proteins participate in DNA damage repair processes via histone ubiquitination. Loss of RNF8 or RAD6B can lead to sterility in male mice. However, the specific mechanisms regulating these ubiquitin-mediated processes are unclear. In this study, we found that RNF8 knockout mice were either subfertile or sterile based on the numbers of offspring they produced. We explored the mechanism by which RAD6B and RNF8 knockouts cause infertility in male mice and compared the effects of their loss on spermatogenesis. Our results demonstrate that RAD6B can polyubiquitinate histones H2 A and H2B. In addition, RNF8 was shown to monoubiquitinate histones H2 A and H2B. Furthermore, we observed that absence of histone ubiquitination was not the only reason for infertility. Senescence played a role in intensifying male sterility by affecting the number of germ cells during spermatogenesis. In summary, both histone ubiquitination and senescence play important roles in spermatogenesis. [ABSTRACT FROM AUTHOR]

The cellular response to DNA double-strand breaks is orchestrated by the protein kinase ATM, which phosphorylates key actors in the DNA repair network. WRAP53β is a multifunctional protein that controls trafficking of factors to Cajal bodies, telomeres and DNA double-strand breaks but what regulates the involvement of WRAP53β in these separate processes remains unclear. Here, we show that in response to various types of DNA damage, including IR and UV, WRAP53β is phosphorylated on serine residue 64 by ATM with a time-course that parallels its accumulation at DNA lesions. Interestingly, recruitment of phosphorylated WRAP53β (pWRAP53βS64) to sites of such DNA damage promotes its interaction with γH2AX at these locations. Moreover, pWRAP53βS64stimulates the accumulation of the repair factor 53BP1 at DNA double-strand breaks and enhances repair of this type of damage via homologous recombination and non-homologous end joining. At the same time, phosphorylation of WRAP53β is dispensable for its localization to Cajal bodies, where it accumulates even in unstressed cells. These findings not only reveal ATM to be an upstream regulator of WRAP53β, but also indicates that phosphorylation of WRAP53β at serine 64 controls its involvement in the DNA damage response and may also restrict its other functions. [ABSTRACT FROM PUBLISHER]

We recently demonstrated that WRAP53β acts as a key regulator of ubiquitin-dependent repair of DNA double-strand breaks. Here, we applied the proximity ligation assay (PLA) to show that at such breaks WRAP53β accumulates in close proximity to γH2AX and, furthermore as demonstrated by their co-immunoprecipitation (IP) binds to γH2AX, in a manner dependent on the ATM and ATR kinases. Moreover, formation of complexes between MDC1 and both its partners RNF8 and phosphorylated ATM was visualized. The interaction of MDC1 with RNF8, but not with ATM requires WRAP53β, suggesting that WRAP53β facilitates the former interaction without altering phosphorylation of MDC1 by ATM. Furthermore, our findings highlight PLA as a more sensitive method for the analysis of recruitment of repair factors and complex formation at DNA breaks that are difficult to detect using conventional immunofluorescence. [ABSTRACT FROM PUBLISHER]

Increasing evidence indicates that polymorphisms in genes relevant to spermatogenesis might modulate the efficiency of reproduction in men. Ring finger protein 8 ( RNF8) and bromodomain testis-specific ( BRDT) are two candidate genes associated with spermatogenesis. Here, we considered potential associations of 14 single nucleotide polymorphisms (SNPs) in RNF8 and BRDT genes in Chinese patients with non-obstructive azoospermia (NOA). We analyzed 361 men with NOA and 368 fertile controls by using Sequenom iplex technology. Our data did not reveal any variants associated with NOA susceptibility. However, we observed that rs104669 and rs195432 of RNF8 were in strong linkage disequilibrium. Haplotype analysis of the two SNPs indicated that the haplotype AC reduced the risk of NOA and the haplotype TC significantly evaluated the risk of NOA. Moreover, the RNF8 variants rs195432 (C/A p = 0.030), rs195434 (T/C p = 0.025), and rs2284922 (T/C p = 0.034) were correlated with the smaller testis volume. [ABSTRACT FROM AUTHOR]

Purpose: The E3 ubiquitin ligase RNF8 regulates the accumulation or removal of a number of proteins at DNA lesions, thereby playing a critically important role in DNA damage response. The present study investigated the possibility of using RNF8 as a new target in the radiation treatment of human non-small cell lung cancer. Methods and materials: We used RNA interference technology to silence the expression of RNF8 in A549 cells, and then detected the radiation response by colony forming assays. DNA repair was monitored by γ-H2AX foci formation after RNF8 depletion. Expression of Ku70 and Rad51 were assessed by immunofluorescent staining and Western blotting. Cell cycle and apoptosis were measured by flow cytometry assays. Results: After lentivirus-mediated siRNA transfection, expression of RNF8 in A549 cells downregulated which led to an increased radiosensitivity and impaired DNA repair. RNF8 knockdown did not affect Ku70 expression, however, Rad51, a key player in homologous recombination (HR) repair, was abrogated at sites of DNA damage. Furthermore, we observed an extended G2/M arrest and an increased induction of apoptosis after ionizing radiation in the absence of RNF8. Conclusions: RNF8 silencing effectively downregulates Rad51 therefore maybe impairing HR repair, and prolongs the G2/M accumulation as well as cell apoptosis upon radiation, which all suggest an enhanced radiosensitivity on A549 cells. [ABSTRACT FROM AUTHOR]

DNA repair activities at DNA double-strand breaks (DSBs) are under control of regulatory ubiquitylation events governed by the RNF8 and RNF168 ubiquitin-ligases. Defects in this regulatory mechanism, as with mutation of other key DNA damage-response factors, lead to genomic instability and cancer, presumably due to impaired repair of DNA lesions. Recent work revealed that RNF8 and RNF168 also play critical roles at natural chromosome ends, when no longer adequately shielded by telomeres. In contrast to repair of DSBs being needed to maintain genome integrity, repair activities at telomeres create chromosome end-to-end fusions that threaten genome integrity. Upon cell division these telomere fusions give rise to genomic alterations and instability via chromosomal missegregration and initiation of breakage-fusion-bridge cycles. Here, I discuss the role of RNF8 at natural chromosome ends and its (potential) consequences. [ABSTRACT FROM AUTHOR]