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Tyrosyl-DNA phosphodiesterase 1 (Tdp1) : a rhabdomyosarcoma therapy target and mitochondrial DNA repair enzyme Chowdhury, Md. Miraj Kobad


Tyrosyl-DNA phosphodiesterase 1 (TDP1) repairs blocked 3´ DNA termini to enable DNA repair. The H493R mutation in TDP1, which disrupts the active site of the enzyme and leads to formation of long-lived TDP1-DNA adducts, causes the progressive neurodegenerative disease spinocerebellar ataxia with axonal neuropathy 1 (SCAN1). Loss of function of TDP1 results in increased sensitivity towards several genotoxic agents including camptothecin analogues, bleomycin and ionizing radiation in vitro and in vivo. In this study, the rationale for using TDP1 as a therapeutic anticancer target and the role of functional loss of TDP1 in neurodegeneration were investigated. Using immunohistochemical staining, immunofluorescence microscopy, sub-cellular fractionation, immunoblotting, TUNEL assays, and PCR, TDP1 expression and the consequences of its loss were studied in different human tissues, tumor tissues, rhabdomyosarcoma cell lines and murine retina. Twenty-four out of twenty six different human tumors were TDP1 positive. Rhabdomyosarcoma cell lines expressing TDP1 in the mitochondria showed higher resistance to camptothecin compared to those not expressing TDP1 in the mitochondria. Loss of TDP1 reduced growth and increased camptothecin sensitivity in all rhabdomyosarcoma cell lines. To better understand the role of TDP1 in the mitochondria, I identified a tissue in mouse in which murine TDP1 is exclusively expressed in the mitochondria, photoreceptors, and found that Tdp1⁻/⁻ mice had degenerating rod and cone cells from postnatal day 11 associated with an increased level of oxidative mitochondrial DNA damage and apoptosis. These observations indicated that murine TDP1 plays an important role in mitochondria by repairing mitochondrial DNA and that murine TDP1 in mitochondria protects photoreceptors from degeneration. They also suggest that mitochondrial TDP1 renders cancer cells resistant to some chemotherapy and radiotherapy regimes, and that mitochondrial TDP1 is a potential anticancer target.

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