Mitochondrial tyrosyl-DNA phosphodiesterase 2 and its TDP2 short isoform

Tyrosyl-DNA phosphodiesterase 2 (TDP2) repairs abortive topoisomerase II cleavage complexes. Here, we identify a novel short isoform of TDP2 (TDP2) expressed from an alternative transcription start site. TDP2 contains a mitochondrial targeting sequence, contributing to its enrichment in the mitochondria and cytosol, while full-length TDP2 contains a nuclear localization signal and the ubiquitin-associated domain in the N-terminus. Our study reveals that both TDP2 isoforms are present and active in the mitochondria. Comparison of isogenic wild-type () and knockout () DT40 cells shows that cells are hypersensitive to mitochondrial-targeted doxorubicin (mtDox), and that complementing cells with human restores resistance to mtDox. Furthermore, mtDox selectively depletes mitochondrial DNA in cells. Using CRISPR-engineered human cells expressing only the TDP2 isoform, we show that TDP2 also protects human cells against mtDox. Finally, lack of TDP2 in the mitochondria reduces the mitochondria transcription levels in two different human cell lines. In addition to identifying a novel TDP2 isoform, our report demonstrates the presence and importance of both TDP2 isoforms in the mitochondria.