Mitochondrial DNA Integrity Is Maintained by APE1 in Carcinogen-Induced Colorectal Cancer

Abstract

Changes in mitochondrial DNA (mtDNA) integrity have been reported in many cancers, however, the contribution of mtDNA integrity to tumorigenesis is not well understood. We used a transgenic mouse model that is haploinsufficient for the apurinic/apyrimidinic endonuclease 1 (Apex1+/-) gene, which encodes the base excision repair (BER) enzyme APE1, to determine its role in protecting mtDNA from the effects of azoxymethane (AOM), a carcinogen used to induce colorectal cancer (CRC). Repair kinetics of AOM-induced mtDNA damage was evaluated using quantitative PCR after a single AOM dose and a significant induction in mtDNA lesions in colonic crypts from both wild type (WT) and Apex1+/-animals were observed. However, Apex1+/- mice had slower repair kinetics in addition to decreased mtDNA abundance. Tumors were also induced using multiple AOM doses and both WT and Apex1+/-animals exhibited significant loss in mtDNA abundance. Surprisingly, no major differences in mtDNA lesions were observed in tumors from WT and Apex1+/-animals, whereas a significant increase in nuclear DNA lesions was detected in tumors from Apex1+/- mice. Finally, tumors from Apex1+/-mice displayed an increased proliferative index and histological abnormalities. Taken together, these results demonstrate that APE1 is important for preventing changes in mtDNA integrity during AOM-induced CRC. Implications: Azoxymethane, a colorectal cancer carcinogen, generates damage to the mitochondrial genome and the BER enzyme APE1 is required to maintain its integrity.

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

“…Mitochondrial dysfunction is believed to play a role in Huntington's disease pathology, and prior studies have demonstrated that APE1 is important for the maintenance of mitochondrial function (Li et al ., 2012; Siddiqui et al ., 2012). APE1 is also known to participate in mitochondrial DNA repair functions (Ballista‐Hernandez et al ., 2017; Stuart et al ., 2004; Vascotto et al ., 2009). While APE1 is known to influence these pathways, this study expands our understanding of APE1 within the cell by implicating the genes in the pathways that are affected by APE1 knockdown.…”

“…One previously linked pathway of particular interest is the mitochondrial dysfunction pathway. APE1 redox and repair activity has previously been shown to be responsible for maintaining and repairing mitochondrial DNA (Ballista‐Hernandez et al ., 2017; Li et al ., 2012; Siddiqui et al ., 2012; Stuart et al ., 2004; Vascotto et al ., 2009). The results of our studies presented here identify, for the first time, the genes responsible for these functions.…”

Activation of cyclin D1 affects mitochondrial mass following traumatic brain injury

“…The primer sequences were as follows: Cox2, 5’-GCCGACTAAATCAAGCAACA-3’ (forward) and 5’-CAATGGGCATAAAGCTATGG-3’ (reverse); and β-globin, 5 ‘-GAAGCGATTCTAGGGAGCAG-3’ (forward) and 5’-GGAGCAGC GATTCTGAGTAGA-3’ (reverse). The relative mtDNA to nuclear DNA copy number ratio was determined using the comparative DDCT method (Ballista-Hemandez et al, 2017; Gonzalez-Hunt et al, 2016; Lien et al, 2017), in which NDl/β-globin and Cox2/β-globin ratios were calculated.…”

The Biological Role of Apurinic/Apyrimidinic Endonuclease1/Redox Factor-1 as a Therapeutic Target for Vascular Inflammation and as a Serologic Biomarker

“…APE1/Ref-1 interacts with the mitochondrial import and assembly protein Mia40, which is responsible for APE1/Ref-1 trafficking into the mitochondria [42]. A recent study using haploinsufficient APE1/Ref-1 mice revealed slower repair kinetics of azoxymethane-induced mitochondrial DNA damage, suggesting that APE1/Ref-1 is important for preventing changes in mitochondrial DNA integrity during azoxymethane-induced colorectal cancer [43].…”