Because of the complexity of DNA
Because of the complexity of DNA damage and its repair, several pathways are candidates in HN2-induced DPC repair. Considering the 23kDa molecular weight of MGMT, NER may be ineffective for MGMT-adduct removal. This presumption is supported by that the mRNA level of ERCC1, a core gene in NER pathway, did not change (data not shown), while FANCD2 and BRCA2 were upregulated, suggesting the activation of HR pathway. Stingele established a systemic model of DPC repair, which described two solutions for coping with DPC (Stingele et al., 2015, Stingele and Jentsch, 2015). Bulky protein component is broken-down by proteolysis via DPC protease, which allows replication progress. It has be proven that the proteolysis is nonspecific in yeast, because Wss1 targets any protein substrate that is conjugated on the DNA strand but does not discriminate the exact type of the substrate (Stingele and Jentsch, 2015). However, remaining peptide may lead to translesion synthesis (TLS) and then cause mutagenesis. In addition, when Dynasore are deficient in DPC repair, replication stress may cause DSB. Under these conditions, HR is needed for DPC tolerance, although unrepaired DPC may induce genome rearrangements and instability (Stingele et al., 2015, Stingele and Jentsch, 2015). Usually, the cross–linking-disabled MGMT is degraded by ubiquitination (Pegg, 2011). Coincidently, mammalian DVC1, the ortholog of yeast Wss1, possesses an interaction domain for either ubiquitin or small ubiquitin-like modifier (SUMO) near the C-terminal (Stingele et al., 2015). However, the exact function of DVC1 in DPC repair has not been confirmed experimentally. In the present study, we tried to elucidate the role of DVC1 in HN2-induced DPC repair. Fortunately, it was proven that DVC1 indeed plays a key role in the repair of both tDPC and mDPC in a p97-dependent manner. HN2 exposure induced DVC1 upregulation of transcription starting from 1h and of translation from 6h. Inhibition of proteasome promoted moderate tDPC formation and robust mDPC formation after HN2 injury. DVC1 knockdown induced a higher mDPC level in normal culture and even more mDPC formation when inflicted with HN2. All these data suggested the upregulation of DVC1 is preferentially important for the cleavage of mDPC. The localization of DVC1 to sites of DNA damage requires the ability of the DVC1 UBZ domain to bind to ubiquitin polymers and a conserved PCNA-interacting motif (Davis et al., 2012). It is newly identified that p97 facilitates the extraction of TLS polymerase (Pol) η, and a highly speculative possibility is that DVC1 degrades proteins after release from sites of DNA damage by p97 (Davis et al., 2012). At the present stage, we confirmed the necessity of p97 in processing mDPC, but it is still not known if ubiquitylation and subsequent segregation of mDPC are necessary before proteolysis by DVC1 and degradation by proteasome, which is worthy of further investigation.
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Conflicts of interest
Grant support Natural Science Foundation of China (81302862).
Introduction Over 50 years ago the great biochemist Otto Warburg proposed that oxygen metabolism was a key factor in cancer induction. Indeed, experimental evidence that mutagenic and toxic DNA lesions are generated by reactive oxygen species was subsequently reported. However, in widely quoted studies from the last decade, the level of endogenous oxidative damage had been overestimated as it included oxidised bases formed during the isolation of DNA. These reports so influenced the field that many accounts of endogenous DNA damage have failed to consider other causes , . Current estimates suggest that oxidative DNA damage due to reactive oxygen species and lipid peroxidation products occurs at levels similar to other deleterious events, such as hydrolytic depurination and deamination; incorporation of damaged deoxynucleoside triphosphates into DNA; and reaction with endogenous alkylating agents , , .