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. Repair kinetics of AOM-induced mtDNA damage was evaluated using qPCR 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 histologic abnormalities. Taken together, these results demonstrate that APE1 is important for preventing changes in mtDNA integrity during AOM-induced colorectal cancer.Implications: AOM, a colorectal cancer carcinogen, generates damage to the mitochondrial genome, and the BER enzyme APE1 is required to maintain its integrity. Mol Cancer Res; 15(7); 831-41. ©2017 AACR.
Subject(s)
Colorectal Neoplasms/genetics , DNA Damage/drug effects , DNA, Mitochondrial/drug effects , DNA-(Apurinic or Apyrimidinic Site) Lyase/genetics , Animals , Azoxymethane/toxicity , Carcinogens/toxicity , Colorectal Neoplasms/chemically induced , Colorectal Neoplasms/pathology , DNA Repair/drug effects , Disease Models, Animal , Genome, Mitochondrial , Humans , Mice , Mice, TransgenicABSTRACT
AMP kinase (AMPK) plays an important role in the regulation of energy metabolism in cardiac cells. Furthermore, activation of AMPK protects the heart from myocardial infarction and heart failure. The present study examines whether or not AMPK affects the peroxisome proliferator-activated receptor-α (PPARα)/mitochondria pathway in response to acute oxidative stress in cultured cardiomyocytes. Cultured H9c2 rat embryonic cardioblasts were exposed to H2O2-induced acute oxidative stress in the presence or absence of metformin, compound C (AMPK inhibitor), GW6471 (PPARα inhibitor), or A-769662 (AMPK activator). Results showed that AMPK activation by metformin reverted oxidative stress-induced inactivation of AMPK and prevented oxidative stress-induced cell death. In addition, metformin attenuated reactive oxygen species generation and depolarization of the inner mitochondrial membrane. The antioxidative effects of metformin were associated with the prevention of mitochondrial DNA damage in cardiomyocytes. Coimmunoprecipitation studies revealed that metformin abolished oxidative stress-induced physical interactions between PPARα and cyclophilin D (CypD), and the abolishment of these interactions was associated with inhibition of permeability transition pore formation. The beneficial effects of metformin were not due to acetylation or phosphorylation of PPARα in response to oxidative stress. In conclusion, this study demonstrates that the protective effects of metformin-induced AMPK activation against oxidative stress converge on mitochondria and are mediated, at least in part, through the dissociation of PPARα-CypD interactions, independent of phosphorylation and acetylation of PPARα and CypD.
