OS12.5 Small GTPase RHOE/RND3, a new critical regulator of NF-êB signaling in glioblastoma multiforme?

Background Abnormal activation of NF-κB signaling is a major mechanism of apoptosis resistance in glioblastoma multiforme (GBM). Therefore, better understanding of the regulation of NF-κB signaling has a significant impact for GBM therapy. Here, we uncovered a critical role of the small GTPase RND3 in regulating the p65 subunit of NF-κB and NF-κB signaling in GBM. MATERIALS AND METHODS Human GBM samples, GBM cells and a human orthotopic GBM-xenografted animal model were used. The mechanisms of RND3 in regulation of NF-κB signaling and GBM cell apoptosis were examined by luciferase assay, quantitative PCR, immunostaining, immunoblotting, immunofluorescence, co-immunoprecipitation, TUNEL staining, JC-1 analysis and flow cytometry. RESULTS Overexpression of RND3 led to reduced p65 activity in GBM cultured cells and a GBM animal model, indicating that the NF-κB pathway is negatively regulated by RND3 in GBM. Mechanistically, we found that RND3 bound p65 and promoted p65 ubiquitination, leading to decreased p65 protein levels. Furthermore, RND3 enhanced cleaved-caspase 3 levels and promoted apoptosis in GBM cells, and RND3 expression was positively correlated with cleaved-caspase 3 and IL-8 in human GBM samples. The effect of RND3 on promoting apoptosis disappeared when p65 ubiquitination was blocked by protease inhibitor carfilzomib or upon co-expression of ectopic p65. CONCLUSION RND3 binds p65 protein and promotes its ubiquitination, resulting in reduced p65 protein expression and inhibition of NF-κB signaling to induce GBM cell apoptosis.