INTRACELLULAR-LOCALIZATION OF 8-OXO-DGTPASE IN HUMAN-CELLS, WITH SPECIAL REFERENCE TO THE ROLE OF THE ENZYME IN MITOCHONDRIA

We examined the intracellular distribution of 8-oxo-dGTPase (8-oxo-7,8 -dihydrodeoxyguanosine triphosphatase) encoded by the MTH1 gene, a hum an mutator homologue. The activity of 8-oxo-dGTPase mainly located in cytosolic and mitochondrial soluble fractions of Jurkat cells, a human T-cell leukemia line. Electron microscopic immunocytochemistry, using a specific antibody against MTH1 protein, showed localization of MTH1 protein in the mitochondrial matrix. Activity in the mitochondria acc ounted for about 4% of the total activity. The specific activity in th e mitochondrial soluble fraction (8093 units/mg protein) was as high a s that in the cytosolic fraction (8111 unit/mg protein). The 8-oxo-dGT Pase activities in cytosolic and mitochondrial soluble fractions co-el uted with MTH1 protein by anion-exchange chromatography, and the molec ular mass of the mitochondrial MTH1 protein was much the same as that of the cytosolic MTH1 protein (about 18 kDa). HeLa cells expressing MT H1 cDNA showed an increased cytoplasmic signal together with a weak si gnal in the nucleus in in situ immunostaining of MTH1 protein, and the overexpressed MTH1 protein was recovered from both cytosolic and mito chondrial fractions. Thus, the 8-oxo-dGTPase encoded by MTH1 gene is l ocalized. in mitochondria and cytosol.