CHOP (C/EBP homologous protein) and ASNS (asparagine synthetase) induction in cybrid cells harboring MELAS and NARP mitochondrial DNA mutations

Mitochondrial dysfunction caused by mutations in mitochondrial DNA (mtDNA) is related to a variety of diseases including MELAS and NARP syndromes. However, little is known about the intracellular responses induced by mtDNA mutations. In order to identify genes whose expression is altered as a result of the presence of mtDNA mutations, DNA microarray analysis was performed using human 143B osteosarcoma cells harboring 3243A > G [tRNA-Leu (UUR)] and 8993T > G [ATPase6 Leu156Arg] mtDNA mutations associated with MELAS and NARP syndromes (2SD and NARP3-1 cybrid cells), respectively. We found that mRNA and protein levels of ATF4, CHOP and ASNS were upregulated in 2SD and NARP3-1 cells as compared with parental cells. Reporter assays demonstrated that transcription of CHOP and ASNS genes was upregulated through the AARE (amino acid regulatory element) and NSRE-1 (nutrient-sensing response element-1) enhancer elements to which ATF4 binds, respectively. Furthermore, knockdown of ATF4 by RNA interference reduced CHOP and ASNS transcription in 2SD and NARP3-1 cells. These results suggest that the presence of mtDNA mutations elicits upregulation of CHOP and ASNS genes through the elevation of ATF4 expression and its binding to the AARE and NSRE-1, respectively.