Functional analysis of the DNA repair enzyme Tyrosyl-DNA phosphodiesterase 1 (TDP1) in Trypanosoma brucei brucei
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In order to evaluate the suitability of the DNA repair enzyme tyrosyl-DNA phosphodiesterase 1 (TDP1) as a potential drug target for an anti-parasite therapy, we are studying its role in the bloodstream form of Trypanosoma brucei brucei, the eukaryotic parasite that causes African Sleeping Sickness. Eukaryotic TDP1 removes covalently trapped topoisomerase IB and other adducts from the 3’ end of the DNA at DNA strand breaks. Covalent topoisomerase IB stalling is caused by endogenous DNA damage and by anti-cancer drugs such as camptothecin (CPT). A potential approach could be to use TDP1 inhibitors synergistically with CPT in a combined anti-parasite therapy. T. brucei TDP1 knock out cells are hypersensitive to CPT and accumulate in the late S phase of the cell cycle upon treatment with the drug. The CPT hypersensitivity of the TDP1-/- cells can be fully rescued through ectopic expression of wild type TDP1. The catalytic activity of TDP1 is required for complementation of the CPT sensitivity since overexpression of a catalytically inactive mutant form of TDP1 further sensitises TDP1-/- cells to CPT. In this context, expression of the mutant H358N, which shows reduced activity, also increases sensitivity of TDP1-/- cells to the drug. Surprisingly, expressing TDP1 carrying an analogous mutation to the one that causes SCAN1, a human neurodegenerative disease, does not sensitise TDP1-/- cells further. With this unique set of mutant TDP1 proteins in a TDP1-/- background we hope to answer questions concerning TDP1 function that have so far been elusive.