Abstract 925: Rit GTPase Protects Cells from Oxidative Damage
Signaling cascades that contribute to the regulation of cellular survival influence many cardiovascular diseases. Elucidating the mechanisms of these cascades is thus important for understanding basic biology and for therapeutic intervention. We have identified an evolution-arily conserved group of Ras-related GTPases, including two mammalian genes (Rit and Rin) and a single Drosophila ortholog (Ric), that we hypothesize plays a critical role in trophic factor-mediated anti-apoptotic signaling. Expression of activated Rit in PC6 cells induces potent activation of the MAP kinases ERK1/2 and p38, and promotes neurite outgrowth and cell survival. Furthermore, RNAi-mediated Rit silencing sensitized PC6 cells to a wide variety of stresses, in part by inhibiting NGF-mediated activation of ERK and p38 MAP kinases and CREB. Here we present studies from two genetic models designed to further assess our hypothesis. First, we generated a transgenic mouse over-expressing constitutively activated Rit (RitL79). To begin to assess the contribution of Rit signaling to cellular survival, we examined the ability of cortical neuronal cultures isolated from Rit-TG versus wild-type littermates to survive reactive-oxygen-species (ROS)-mediated cell death. Cell viability for wild-type cortical neurons following a 4 h exposure to H2O2 (60 μM) was reduced approximately 90%, while cortical neurons isolated from Rit-TG mice were largely unaffected by this treatment. Thus, RitL79-mediated signaling protects cortical neurons against ROS-mediated apoptosis. As further confirmation of the important role this protein family plays in survival from stress, we generated a Drosophila strain null for D-Ric. Mutants are homozygous viable and show no obvious developmental abnormalities. However, D-Ric mutants are susceptible to environmental stresses, including heat stress and dry starvation. Taken together, these studies suggest a conserved role for Rit/Ric in promoting cellular survival and suggest that Rit signaling is a potential target for pharmaceutical intervention. We look forward to assessing Rit’s role in other systems including cardiac and vascular cell types.
This work was supported by a Predoctoral Fellowship from the AHA.