AUF1 Recognizes 8-Oxo-Guanosine Embedded in DNA and Stimulates APE1 Endoribonuclease Activity.

Aims: The existence of modified ribonucleotide monophosphates embedded in genomic DNA, as a consequence of oxidative stress conditions, including 8-oxo-guanosine and ribose monophosphate abasic site (rAP), has been recently highlighted by several works and associated with oxidative stress conditions. Although human apurinic-apyrimidinic endodeoxyribonuclease 1 (APE1), a key enzyme of the base-excision repair pathway, repairs rAP sites and canonical deoxyribose monophosphate abasic sites with similar efficiency, its incision-repairing activity on 8-oxo-guanosine is very weak. The aims of this work were to: (i) identify proteins able to specifically bind 8-oxo-guanosine embedded in DNA and promote APE1 endoribonuclease activity on this lesion, and (ii) characterize the molecular and biological relevance of this interaction using human cancer cell lines. Results: By using an unbiased proteomic approach, we discovered that the AU-rich element RNA-binding protein 1 (AUF1) actively recognizes 8-oxo-guanosine and stimulates the APE1 enzymatic activity on this DNA lesion. By using orthogonal approaches, we found that: (i) the interaction between AUF1 and APE1 is modulated by H2O2-treatment; (ii) depletion of APE1 and AUF1 causes the accumulation of single- and double- strand breaks; and (iii) both proteins are involved in modulating the formation of DNA:RNA hybrids. Innovation: These results establish unexpected functions of AUF1 in modulating genome stability and improve our knowledge of APE1 biology with respect to 8-oxo-guanosine embedded in DNA. Conclusion: By showing a novel function of AUF1, our findings shed new light on the process of genome stability in mammalian cells toward oxidative stress-related damages. Antioxid. Redox Signal. 39, 411-431.

Dual Role of Nitric Oxide in Regulating the Response of ß Cells to DNA Damage.

SIGNIFICANCE: Cytokines released in and around pancreatic islets during islet inflammation are believed to contribute to impaired ß cell function and ß cell death during the development of diabetes. Nitric oxide, produced by ß cells in response to cytokine exposure, controls many of the responses of ß cells during islet inflammation. Recent Advances: Although nitric oxide has been shown to inhibit insulin secretion and oxidative metabolism and induce DNA damage in ß cells, it also activates protective pathways that promote recovery of insulin secretion and oxidative metabolism and repair of damaged DNA. Recent studies have identified a novel role for nitric oxide in selectively regulating the DNA damage response in ß cells. CRITICAL ISSUES: Does nitric oxide mediate cytokine-induced ß cell damage, or is nitric oxide produced by ß cells in response to cytokines to protect ß cells from damage? FUTURE DIRECTIONS: ß cells appear to be the only islet endocrine cell type capable of responding to proinflammatory cytokines with the production of nitric oxide, and these terminally differentiated cells have a limited capacity to regenerate. It is likely that there is a physiological purpose for this response, and understanding this could open new areas of study regarding the loss of functional ß cell mass during diabetes development.