YAF2-Mediated YY1-Sirtuin6 Interactions Responsible for Mitochondrial Downregulation in Aging Tunicates.

In budding tunicates, aging accompanies a decrease in the gene expression of mitochondrial transcription factor A (), and the transfection of mRNA stimulates the mitochondrial respiratory activity of aged animals. The gene expression of both the transcriptional repressor Yin-Yang-1 () and corepressor Sirtuin6 () increased during aging, and the cotransfection of synthetic mRNA of and synergistically downregulated gene expression. Pulldown assays of proteins indicated that YY1-associated factor 2 (YAF2) was associated with both YY1 and SIRT6. Protein cross-linking confirmed that YAF2 bound YY1 and SIRT6 with a molar ratio of 1:1. YY1 was bound to CCAT- or ACAT-containing oligonucleotides in the 5' flanking region of the gene. Chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) showed that SIRT6 specifically induced the histone H3 lysine 9 (H3K9) deacetylation of the upstream region. YY1 and YAF2 accelerated SIRT6-induced H3K9 deacetylation. and mRNA transfection attenuated mitochondrial respiratory gene expression and blocked MitoTracker fluorescence. In contrast, the SIRT6 inhibitor and mRNA antagonized the inhibitory effects of and , indicating that acts on mitochondria downstream of and . We concluded that in the budding tunicate Polyandrocarpa misakiensis, YY1 recruits SIRT6 via YAF2 to the gene, resulting in aging-related mitochondrial downregulation.