13 A MITOCHONDRIA-TARGETED DNA REPAIR ENZYME, HOGG-1, PREVENTS OXIDANT-INDUCED A549 CELL APOPTOSIS BY PRESERVING MITOCHONDRIAL ACONITASE. (1st March 2007) - Panduri, V.
Abstract : Oxidant-induced alveolar epithelial cell (AEC) apoptosis is implicated in mediating lung injury, fibrosis, and malignant transformation by mechanisms that are not fully established. We previously reported that oxidative stress (eg, amosite asbestos or H2 O2 ) induces mitochondria-regulated AEC apoptosis and that overexpression of a mitochondria-targeted DNA repair enzyme, human 8-oxoguanine-DNA glycosylase 1 (mt-hOgg-1), is protective. In this study, we explore the mechanism underlying the protective effects of mt-hOgg-1 (kind gift of Dr. M. Gillespie). We find that the protective effects are not due to redox activity of mt-hOgg-1 since, compared with empty vector controls, mt-hOgg-1 overexpressing A549 cells did not alter asbestos-induced ROS production as assessed by either DCF fluorescence or an adenovirally expressed redox sensor (ro-GFP) targeted to the mitochondria. As expected, mt-hOgg-1 enhanced DNA repair assessed by an 8-oxoG incision assay (1.7 ± 0.2-fold vs control; p < .05). Both asbestos and H2 O2 reduced mitochondria (mt)-aconitase activity and protein expression, but, notably, these effects were completely blocked in mt-hOgg-1 over-expressing A549 cells. Immunoprecipitation studies show that hOgg-1, similar to frataxin, coprecipitates with mt-aconitase. We also found that hOgg-1 mutants that completely lack 8-oxoguanine DNA repair activity (V317, Long AB; kind gift of Dr. V. Bohr) blocked oxidant-induced caspase 9 activation and DNA fragmentation comparable to wild-type hOgg-1. We conclude that mt-hOgg-1 has a dual function as a DNA repair protein as well as a mt-aconitase chaperone. These data suggest a novel role of Mt-hOgg-1 preservation of AEC mitochondria aconitase in the pathogenesis of oxidant-induced lung toxicity. Funding: VA Merit Award (DK), NIH-HL67835-01 (GRSB).