112 - Tyrosine Nitration is Necessary for the Survival of Schwannoma Cells

Abstract

Production of peroxynitrite and formation of nitrotyrosine, implicated in cell death in neurodegeneration and inflammatory conditions, is also found in multiple tumors. Paradoxically, whether tyrosine nitration plays a role in tumor cell survival is unknown. Neurofibromatosis Type 2 (NF2) is caused by mutations in the merlin tumor suppressor gene, leading to merlin loss-of-function and schwannoma formation. Here we report that tyrosine nitration regulates energy metabolism and supports NF2-associated schwannoma cell survival. Schwannomas from NF2 patients and human and mouse merlin-deficient Schwann cells (MD-SC) showed increased levels of nitrotyrosine compared with wild type (WT)-SC, together with decreased expression of manganese superoxide dismutase and increased expression of neuronal nitric oxide synthase. There was a significant decrease in survival of MD-SC but not WT-SC upon: 1) inhibition of nitric oxide production, 2) superoxide and peroxynitrite scavenging, and 3) prevention of tyrosine nitration by urate, suggesting that one or more nitrated proteins are necessary for MD-SC survival. In addition, the levels and activity of mitochondrial complex I to IV were decreased in MD-SC compared with WT-SC, associated with decreased mitochondrial oxygen consumption and membrane potential, without changes in mitochondrial content. Tyrosine nitration prevention in MD-SC increased the levels and activity of the mitochondrial electron transport chain complexes, as well as the mitochondrial function to WT-SC levels. Moreover, nitrated Hsp90, an oxidized protein we showed down-regulates mitochondrial activity, was associated with mitochondria in MD-SC and schwannomas from NF2 patients. This is one of many nitrated proteins present in these cells. The identification of additional nitrated proteins supporting schwannoma cell survival could provide novel targets for the treatment of solid tumors where these nitrated proteins are present.