Role of the Multifunctional DNA Repair and Redox Signaling Protein Ape1/Ref-1 in Cancer and Endothelial Cells: Small-Molecule Inhibition of the Redox Function of Ape1

Abstract

The DNA base excision repair pathway is responsible for the repair of DNA damage caused by oxidation/alkylation and protects cells against the effects of endogenous and exogenous agents. Removal of the damaged base by creates a baseless (AP) site. AP endonuclease1 (Ape1) acts upon this site to continue the BER pathway repair. Failure to repair baseless sites leads to DNA strand breaks and cytotoxicity. In addition to Ape1's repair role, it also functions as a major redox signaling factor to reduce and activate transcription factors such as AP1, p53, HIF-1α and others which control the expression of genes important for cell survival and cancer promotion and progression. Thus the Ape1 protein interacts with proteins involved in DNA repair, growth signaling pathways and pathways involved in tumor promotion and progression. While knockdown studies using siRNA have been informative in studying the role of Ape1 in both normal and cancer cells, knocking down Ape1 does not reveal the individual role of Ape1's redox or repair functions. The identification of small molecule inhibitors of specific Ape1 functions is critical for mechanistic studies and translational applications. Here we discuss small molecule inhibition of Ape1 redox and its effect on both cancer and endothelial cells.

APE1/Ref‐1 knockdown in pancreatic ductal adenocarcinoma – characterizing gene expression changes and identifying novel pathways using single‐cellRNAsequencing

“…This small‐molecule inhibitor does not affect APE1's DNA repair function (Luo et al ., 2008), thereby allowing us to determine the result of blockade of the redox activity of APE1 while not affecting DNA repair, unlike the siRNA studies. Using APE1 redox‐specific inhibitor APX3330, we tested four genes that showed reduced expression in siAPE1 cells to examine whether this downregulation was due to impaired APE1 redox activity.…”

“…While this study identifies four genes as being regulated by APE1 redox activity, this will be further addressed in future studies using the specific APE1 redox signaling inhibitor, APX3330, as well as second‐generation analogs. APX3330 is a novel, oral anticancer agent that specifically and selectively inhibits APE1 redox activity without affecting APE1 endonuclease DNA repair activity (Fishel et al ., 2010; Luo et al ., 2008; Su et al ., 2011). It is the first drug to target APE1 in cancer and enters clinical trials in 2017.…”

Identification and Characterization of Mitochondrial Targeting Sequence of Human Apurinic/Apyrimidinic Endonuclease 1

“…Ten million HeLa cells were collected and resuspended in 500 l of hypotonic lysis buffer. After incubation for 10 min, the nuclei were collected by centrifugation at 500 ϫ g, and the nuclear pellet was resuspended and incubated with 100 3 The abbreviations used are: MTS, mitochondrial targeting sequence; GFP, green fluorescent protein; NLS, nuclear localization signal; PBS, phosphate-buffered saline; EGFP, enhanced GFP.…”

“…On the other hand, APE1 also exerts unique redox activity to regulate the DNA binding affinity of certain transcriptional factors by controlling the redox status of their DNA-binding domain (2). Inhibition of the redox function of APE1 blocks murine endothelial cell growth and angiogenesis and also blocks the growth of human tumor cell lines (3). The biological importance of APE1 is highlighted by the finding that APE1 knockout mice exhibit an embryonic lethal phenotype (4).…”

“…Protein import studies with isolated mitochondria indicate that Tom20 and Tom22 function as a heterodimer receptors for the typical mitochondrial preproteins that carry the cleavable N-terminal mitochondrial targeting sequence (MTS). 3 This signal is classically characterized as an N-terminal motif predicted to form an amphipathic helix that is ϳ15-70 residues in length and enriched in positively charged basic residues (17). Tom70 is reported to be required for the import of noncleavable preproteins that have been shown to have specificity for carrier proteins destined for the inner mitochondrial membrane (18).…”