Human Ape2 protein has a 3′–5′ exonuclease activity that acts preferentially on mismatched base pairs

DNA damage, such as abasic sites and DNA strand breaks with 3′-phosphate and 3′-phosphoglycolate termini present cytotoxic and mutagenic threats to the cell. Class II AP endonucleases play a major role in the repair of abasic sites as well as of 3′-modified termini. Human cells contain two class II AP endonucleases, the Ape1 and Ape2 proteins. Ape1 possesses a strong AP-endonuclease activity and weak 3′-phosphodiesterase and 3′–5′ exonuclease activities, and it is considered to be the major AP endonuclease in human cells. Much less is known about Ape2, but its importance is emphasized by the growth retardation and dyshematopoiesis accompanied by G2/M arrest phenotype of the APE2-null mice. Here, we describe the biochemical characteristics of human Ape2. We find that Ape2 exhibits strong 3′–5′ exonuclease and 3′-phosphodiesterase activities and has only a very weak AP-endonuclease activity. Mutation of the active-site residue Asp 277 to Ala in Ape2 inactivates all these activities. We also demonstrate that Ape2 preferentially acts at mismatched deoxyribonucleotides at the recessed 3′-termini of a partial DNA duplex. Based on these results we suggest a novel role for human Ape2 as a 3′–5′ exonuclease

Role of PCNA-dependent stimulation of 3′-phosphodiesterase and 3′–5′ exonuclease activities of human Ape2 in repair of oxidative DNA damage

Human Ape2 protein has 3′ phosphodiesterase activity for processing 3′-damaged DNA termini, 3′–5′ exonuclease activity that supports removal of mismatched nucleotides from the 3′-end of DNA, and a somewhat weak AP-endonuclease activity. However, very little is known about the role of Ape2 in DNA repair processes. Here, we examine the effect of interaction of Ape2 with proliferating cell nuclear antigen (PCNA) on its enzymatic activities and on targeting Ape2 to oxidative DNA lesions. We show that PCNA strongly stimulates the 3′–5′ exonuclease and 3′ phosphodiesterase activities of Ape2, but has no effect on its AP-endonuclease activity. Moreover, we find that upon hydrogen-peroxide treatment Ape2 redistributes to nuclear foci where it colocalizes with PCNA. In concert with these results, we provide biochemical evidence that Ape2 can reduce the mutagenic consequences of attack by reactive oxygen species not only by repairing 3′-damaged termini but also by removing 3′-end adenine opposite from 8-oxoG. Based on these findings we suggest the involvement of Ape2 in repair of oxidative DNA damage and PCNA-dependent repair synthesis

Mutations at the Subunit Interface of Yeast Proliferating Cell Nuclear Antigen Reveal a Versatile Regulatory Domain

Acknowledgments We thank Szilvia Minorits for technical assistance. I.U. conceived and designed the project and wrote the manuscript. All authors participated in designing and performing the experiments, and analyzing the results. The authors declare no competing financial interests. This work was also supported by a grant from the National Research, Development and Innovation Office GINOP-2.3.2-15-2016-00001. Funding: This work was supported by Hungarian Science Foundation Grant OTKA 109521 and National Research Development and Innovation Office GINOP-2.3.2-15-2016-00001. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Gastrointestinal stromal tumours: ESMO-EURACAN-GENTURIS Clinical Practice Guidelines for diagnosis, treatment and follow-up

Gastrointestinal stromal tumours (GISTs) are malignant mesenchymal tumours with a variable clinical behaviour, marked by differentiation towards the interstitial cells of Cajal. GISTs belong to the family of soft tissue sarcomas (STSs) but are treated separately due to their peculiar histogenesis, clinical behaviour and specific therapy. This European Society for Medical Oncology (ESMO)–European Reference Network for Rare Adult Solid Cancers (EURACAN)–European Reference Network for Genetic Tumour Risk Syndromes (GENTURIS) Clinical Practice Guideline (CPG) will cover GISTs while other STSs are covered in the ESMO–EURACAN–European Reference Network for Paediatric Oncology (ERN PaedCan)–GENTURIS STS CPG

Soft tissue and visceral sarcomas: ESMO-EURACAN-GENTURIS Clinical Practice Guidelines for diagnosis, treatment and follow-up

Soft tissue sarcomas (STSs) comprise ∼80 entities defined by the World Health Organization (WHO) classification based on a combination of distinctive morphological, immunohistochemical and molecular features.1 These ESMO–EURACAN–GENTURIS (European Society for Medical Oncology; European Reference Network for Rare Adult Solid Cancers; European Reference Network for Genetic Tumour Risk Syndromes) Clinical Practice Guidelines (CPGs) will cover STSs, with the exception of gastrointestinal stromal tumours (GISTs) that are covered in the ESMO–EURACAN–GENTURIS GIST CPGs.2 EURACAN and GENTURIS are the European Reference Networks connecting European institutions, appointed by their governments, to cover rare adult solid cancers and genetic cancer risk syndromes, respectively. Extraskeletal Ewing sarcoma, round cell sarcoma with EWSR1-non-ETS fusion and sarcomas with CIC rearrangements and BCOR genetic alterations are covered by the ESMO–EURACAN–GENTURIS–ERN PaedCan (European Reference Network for Paediatric Oncology) bone sarcomas CPG.3 Kaposi's sarcoma, embryonal and alveolar rhabdomyosarcoma are not discussed in this manuscript, while pleomorphic rhabdomyosarcoma is viewed as a high-grade, adult-type STS. Finally, extraskeletal osteosarcoma is also a considered a high-grade STS, whose clinical resemblance with osteosarcoma of bone is doubtful. The methodology followed during the consensus meeting is specified at the end of the manuscript in a dedicated paragraph

Bone sarcomas: ESMO-EURACAN-GENTURIS-ERN PaedCan Clinical Practice Guideline for diagnosis, treatment and follow-up

This Clinical Practice Guideline provides key recommendations on the management of bone sarcomas. // Recommendations have been agreed following a consensus meeting of representatives from ESMO, EURACAN, GENTURIS and ERNPaedCan. // Authorship includes a multidisciplinary group of experts from different institutions and countries worldwide

Bone sarcomas: ESMO–EURACAN–GENTURIS–ERN PaedCan Clinical Practice Guideline for diagnosis, treatment and follow-up

Production costs have been covered by ESMO from central funds

Mutator Suppression and Escape from Replication Error–Induced Extinction in Yeast

Cells rely on a network of conserved pathways to govern DNA replication fidelity. Loss of polymerase proofreading or mismatch repair elevates spontaneous mutation and facilitates cellular adaptation. However, double mutants are inviable, suggesting that extreme mutation rates exceed an error threshold. Here we combine alleles that affect DNA polymerase δ (Pol δ) proofreading and mismatch repair to define the maximal error rate in haploid yeast and to characterize genetic suppressors of mutator phenotypes. We show that populations tolerate mutation rates 1,000-fold above wild-type levels but collapse when the rate exceeds 10−3 inactivating mutations per gene per cell division. Variants that escape this error-induced extinction (eex) rapidly emerge from mutator clones. One-third of the escape mutants result from second-site changes in Pol δ that suppress the proofreading-deficient phenotype, while two-thirds are extragenic. The structural locations of the Pol δ changes suggest multiple antimutator mechanisms. Our studies reveal the transient nature of eukaryotic mutators and show that mutator phenotypes are readily suppressed by genetic adaptation. This has implications for the role of mutator phenotypes in cancer