Abstract 1025: Rac1 is a novel binding partner of the anti-apoptotic protein Bcl-2

We have previously reported that Bcl-2 expression resulted in an increase in intracellular superoxide anion and that a dominant negative mutant of the small GTPase Rac1 sensitized Bcl-2 expressing cells to apoptosis. Here we report that silencing and functional inhibition of Rac1 blocks Bcl-2 mediated increases in intracellular and mitochondrial superoxide levels in tumor cells. We provide evidence that this effect is mediated via specific interaction between the two proteins using co-immunoprecipitation, confocal and electron microscopy, as well as GST-fusion proteins. Analysis of the sub-cellular localization of these proteins revealed increased association of Bcl-2 and mitochondrial Rac1 in Bcl-2 overexpressing cells. This interaction can be blocked in vitro and in vivo by BH3 mimetics such as HA14-I, BH3-I as well as synthetic Bcl-2 BH3 domain peptides. That this interaction is functionally relevant is supported by the ability of the Bcl-2 BH3 peptide to inhibit intracellular superoxide production as well as overcome drug resistance in Bcl-2 overexpressing cells. Lastly, using patient-derived primary tissues, we observed the interaction only in cancerous tissues with marked overexpression of Bcl-2 and not in peripheral blood leukocytes or samples from non-cancerous tissue. These data provide a novel facet in the biology of Bcl-2 with potential implications for targeted anti-cancer drug design. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1025.