Apurinic/apyrimidinic endonuclease 1 performs multiple roles in controlling the outcome of cancer cells toward radiation and chemotherapeutic agents

Many endogenous and exogenous sources produce reactive oxygen species such as superoxide radical anions and hydrogen peroxide that are converted to the highly reactive form, hydroxyl radical. It is this latter species that can damage several macromolecules in the cells, in particular, the DNA to produce a variety of DNA lesions. These DNA lesions include oxidatively damaged purine and pyrimidine bases, as well as single-strand and double-strand breaks. These unrepaired DNA lesions lead to base substitutions, deletions, insertions, and rearrangements of the chromosome, ultimately altering the stability of the genome. Maintaining the integrity of the genome is essential to prevent various diseases such as several types of cancers. There are several DNA repair pathways including base-excision repair (BER), nucleotide-excision repair, mismatch repair, homologous recombination, and nonhomologous end joining that operate in the human cells to prevent genomic instability. Each of these DNA repair pathways consists of multiple enzymes that execute specific function (s). This review focuses on a key enzyme apurinic/apyrimidinic endonuclease 1 (APE1) that belongs to the BER pathway that plays a pivotal role in the removal of modified DNA bases. We provide an overview of the multifaceted roles performed by APE1, which also serves as a redox factor and referred to as redox effector factor 1 (Ref-1) or APE1/Ref-1. In addition, we discuss more recent findings whereby (i) peroxiredoxin 1 controls the redox activity of APE1 and (ii) CUT-like homeobox 1 protein, a transcription factor that binds to DNA and stimulates the DNA repair activities of APE1 to confer resistance to radio- and chemotherapy.