Ape1 guides DNA repair pathway choice that is associated with drug tolerance in glioblastoma

Thomas Ströbel,Serkan Tuna,Bruce Demple,Okay Saydam,Thomas Wurdinger,Adelheid Wöhrer,Sibylle Madlener,Klemens Vierlinger,Sarah Vose,Tonny Lagerweij,Brendan D Price,Nurten Saydam

doi:10.1038/s41598-017-10013-w

Abstract

Ape1 is the major apurinic/apyrimidinic (AP) endonuclease activity in mammalian cells, and a key factor in base-excision repair of DNA. High expression or aberrant subcellular distribution of Ape1 has been detected in many cancer types, correlated with drug response, tumor prognosis, or patient survival. Here we present evidence that Ape1 facilitates BRCA1-mediated homologous recombination repair (HR), while counteracting error-prone non-homologous end joining of DNA double-strand breaks. Furthermore, Ape1, coordinated with checkpoint kinase Chk2, regulates drug response of glioblastoma cells. Suppression of Ape1/Chk2 signaling in glioblastoma cells facilitates alternative means of damage site recruitment of HR proteins as part of a genomic defense system. Through targeting “HR-addicted” temozolomide-resistant glioblastoma cells via a chemical inhibitor of Rad51, we demonstrated that targeting HR is a promising strategy for glioblastoma therapy. Our study uncovers a critical role for Ape1 in DNA repair pathway choice, and provides a mechanistic understanding of DNA repair-supported chemoresistance in glioblastoma cells.

Highlights

Spontaneous hydrolytic decay of DNA or DNA glycosylase-mediated hydrolysis of N-glycosyl bonds generates apurinic/apyrimidinic (AP) sites at an estimated frequency of >10,000 per day in each human cell[1]
Methyl methane sulfonate (MMS), which generates methylated bases and AP sites in cellular DNA24 stimulated in vivo association of Ape[1] and Chk[2] in the cell, while temozolomide (TMZ), another DNA alkylating agent that is used in clinic for cancer chemotherapy, induced relatively weaker complex formation
We found that chromatin-bound form of Chk[2] protein was reduced in Ape1-siRNA treated cells (Fig. 1C,D; Fig. S2A–C), which was consistent with reduced levels of Chk[2] in total cell extracts of Ape1-depleted U2OS cells (Fig. S3A–C)

Summary

Introduction

Spontaneous hydrolytic decay of DNA or DNA glycosylase-mediated hydrolysis of N-glycosyl bonds generates apurinic/apyrimidinic (AP) sites at an estimated frequency of >10,000 per day in each human cell[1]. Ape[1] exhibits 3′-5′ exonuclease, 3′-phosphatase, and 3′-phosphodiesterase activities[8,9,10,11]. These additional activities of Ape[1] remove 3′-end blocking groups produced by radiation, ROS, or other DNA glycosylases[12]. A vital role for Ape[1] in mammalian cell viability has been shown[17,18,19,20,21], yet, the precise mechanism(s) in this requirement is not well understood. We discovered an additional, unpredicted role for Ape[1] in DNA repair pathway choice. Our study uncovers a unique Ape1-mediated genome maintenance mechanism, and highlights its importance in cancer chemoresistance

Methods

Results

Conclusion