Abstract 2155: Inhibition of the ERK1/2 pathway by RanBPM

Abstract Ran binding protein-M (RanBPM, also called RanBP9) is a nucleo-cytoplasmic protein that has been implicated in a multitude of cellular roles, including the regulation of transcription, protein modifications and stability, and extracellular receptor signaling pathways. However its function within the cell remains largely unknown. Previous studies in our lab have identified RanBPM as a pro-apoptotic protein that mediates its effects through modulation of Bcl-2 and Bcl-XL levels. Here we present evidence that RanBPM functions to regulate apoptotic activation through regulation of the ERK1/2 signaling pathway. First, we determined that siRNA-mediated knockdown of RanBPM expression led to elevated Bcl-2 and Bcl-XL mRNA expression, suggesting regulation by RanBPM at the transcriptional level. Additionally, expression of RanBPM affected ectopically expressed Bcl-2 protein levels. Together, these findings suggested that RanBPM regulated the expression of Bcl-2 and Bcl-XL at both the transcriptional and post-translational levels. The ERK1/2 signaling cascade has previously been shown to regulate the expression of Bcl-2 and Bcl-XL at both the transcriptional and post-translational levels. We found that that RanBPM-deficient cells exhibited enhanced ERK1/2 phosphorylation and activation, while re-expression of RanBPM led to a marked decrease in the levels of phosphorylated ERK1/2. Furthermore, enhanced ERK1/2 activation in RanBPM-deficient cells contributed to the elevated levels of Bcl-2 expression observed in these cells, as inhibition of ERK1/2 activation correlated with decreased Bcl-2 protein expression. We characterized regulation of ERK1/2 signaling by RanBPM, and identified that RanBPM targets this pathway downstream of Ras, through modulation of c-Raf stability. Our studies revealed that downregulation of RanBPM expression promotes phosphorylation and stabilization of c-Raf, leading to elevated c-Raf protein expression. Finally we observed that downregulation of RanBPM expression promotes cellular transformation, as RanBPM-deficient cells exhibit increased cell growth rates and enhanced cell migration. Together, these findings suggested that RanBPM acts as a novel inhibitor of ERK1/2 signaling, and that downregulation of RanBPM expression leads to oncogenic transformation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2155. doi:1538-7445.AM2012-2155