Elevated level of acetylation of APE1 in tumor cells modulates DNA damage repair.

Shiladitya Sengupta,Kishor K Bhakat,Heyu Song,Somsubhra Nath,Sutapa Ray,Shrabasti Roychoudhury,Anil K Mantha

doi:10.18632/oncotarget.12113

Abstract

Apurinic/apyrimidinic (AP) sites are frequently generated in the genome by spontaneous depurination/depyrimidination or after removal of oxidized/modified bases by DNA glycosylases during the base excision repair (BER) pathway. Unrepaired AP sites are mutagenic and block DNA replication and transcription. The primary enzyme to repair AP sites in mammalian cells is AP endonuclease (APE1), which plays a key role in this repair pathway. Although overexpression of APE1 in diverse cancer types and its association with chemotherapeutic resistance are well documented, alteration of posttranslational modification of APE1 and modulation of its functions during tumorigenesis are largely unknown. Here, we show that both classical histone deacetylase HDAC1 and NAD+-dependent deacetylase SIRT1 regulate acetylation level of APE1 and acetylation of APE1 enhances its AP-endonuclease activity both in vitro and in cells. Modulation of APE1 acetylation level in cells alters AP site repair capacity of the cell extracts in vitro. Primary tumor tissues of diverse cancer types have higher level of acetylated APE1 (AcAPE1) compared to adjacent non-tumor tissue and exhibit enhanced AP site repair capacity. Importantly, in the absence of APE1 acetylation, cells accumulate AP sites in the genome and show increased sensitivity to DNA damaging agents. Together, our study demonstrates that elevation of acetylation level of APE1 in tumor could be a novel mechanism by which cells handle the elevated levels of DNA damages in response to genotoxic stress and maintain sustained proliferation.

Highlights

Mammalian apurinic/apyrimidinic (AP) endo nuclease 1 (APE1) is a ubiquitous and multifunctional protein
We found that the fraction of APE1 present in acetylated form (AcAPE1/ total APE1) was significantly higher in tumor tissues as compared to adjacent non-tumor tissues (Figure 1D and Supplementary Figure S1A, S1B & S1C)
Because NAD+dependent non-classical histone deacetylase SIRT1 was shown to be involved in deacetylation of acetylated APE1 (AcAPE1) [39], we found that treatment with NAD+-dependent deacetylase inhibitor nicotinamide (NAM) increased the AcAPE1 level, while combined treatment of both NAM and classical deacetylase inhibitor trichostatin A (TSA) had an additive effect (Figure 2C; Supplementary Figure S2C)

Summary

Introduction

Mammalian apurinic/apyrimidinic (AP) endo nuclease 1 (APE1) is a ubiquitous and multifunctional protein. It plays a central role in the repair of AP sites generated either spontaneously or as an intermediate during the repair process of oxidative and drug-induced alkylation damage in the genome via the base excision repair (BER) pathway [1,2,3]. In addition to its DNA repair function, APE1 functions as a transcriptional coregulator of many genes involved in multiple cellular pathways [5,6,7,8,9,10,11]. APE1 was shown to activate DNA-binding of many stress-inducible transcription factors (including c-Jun, P53 and NF-kB) through its redox effector (Ref-1) function [11,12,13]. APE1 has a critical role in linking DNA repair to regulation of diverse signaling pathways

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