Autophagy restricts mitochondrial DNA damage-induced release of ENDOG (endonuclease G) to regulate genome stability.

ABSTRACT

Genotoxic insult causes nuclear and mitochondrial DNA damages with macroautophagy/autophagy induction. The role of mitochondrial DNA (mtDNA) damage in the requirement of autophagy for nuclear DNA (nDNA) stability is unclear. Using site-specific DNA damage approaches, we show that specific nDNA damage alone does not require autophagy for repair unless in the presence of mtDNA damage. We provide evidence that after IR exposure-induced mtDNA and nDNA damages, autophagy suppression causes non-apoptotic mitochondrial permeability, by which mitochondrial ENDOG (endonuclease G) is released and translocated to nuclei to sustain nDNA damage in a TET (tet methylcytosine dioxygenase)-dependent manner. Furthermore, blocking lysosome function is sufficient to increase the amount of mtDNA leakage to the cytosol, accompanied by ENDOG-free mitochondrial puncta formation with concurrent ENDOG nuclear accumulation. We proposed that autophagy eliminates the mitochondria specified by mtDNA damage-driven mitochondrial permeability to prevent ENDOG-mediated genome instability. Finally, we showed that HBx, a hepatitis B viral protein capable of suppressing autophagy, also causes mitochondrial permeability-dependent ENDOG mis-localization in nuclei and is linked to hepatitis B virus (HBV)-mediated hepatocellular carcinoma development.Abbreviations 3-MA 3-methyladenine; 5-hmC 5-hydroxymethylcytosine; ACTB actin beta; ATG5 autophagy related 5; ATM ATM serine/threonine kinase; DFFB/CAD DNA fragmentation factor subunit beta; cmtDNA cytosolic mitochondrial DNA; ConA concanamycin A; CQ chloroquine; CsA cyclosporin A; Dox doxycycline; DSB double-strand break; ENDOG endonuclease G; GFP green fluorescent protein; Gy gray; H2AX H2A.X variant histone; HBV hepatitis B virus; HBx hepatitis B virus X protein; HCC hepatocellular carcinoma; I-PpoI intron-encoded endonuclease; IR ionizing radiation; MAP1LC3/LC3 microtubule associated protein 1 light chain 3; MOMP mitochondrial outer membrane permeability; mPTP mitochondrial permeability transition pore; mtDNA mitochondrial DNA; nDNA nuclear DNA; 4-OHT 4-hydroxytamoxifen; rDNA ribosomal DNA; ROS reactive oxygen species; SQSTM1/p62 sequestosome 1; TET tet methylcytosine dioxygenase; TFAM transcription factor A, mitochondrial; TOMM20 translocase of outer mitochondrial membrane 20; VDAC voltage dependent anion channel.