Abstract 4048: Aggresome formation is regulated by RanBPM through an interaction with HDAC6.

Abstract

Abstract RanBPM (Ran-binding protein M, also called RanBP9) is a nucleocytoplamsic protein that has been implicated in a number of cellular processes including cell adhesion, migration and gene transcription. It has been hypothesized to be a scaffolding protein, but its function remains poorly understood. In previous studies we documented the relocalization of RanBPM from the nucleus to the cytoplasm in response to ionizing radiation (IR) treatment. Subsequent analysis showed that IR triggered cytoplasmic RanBPM relocalization in perinuclear dots or foci often located close to an invagination of the nucleus. Upon further investigation, the RanBPM aggregates were identified as aggresomes, which have not been previously documented to occur in response to IR. Aggresomes are aggregates of misfolded/ubiquitinated proteins resulting from improper protein assembly, aberrant modifications and/or environmental stress. These misfolded/ubiquitinated proteins are normally cleared by chaperone-mediated refolding or by proteasomal degradation through the ubiquitin-proteasome system. In conditions where these systems are impaired or overwhelmed, misfolded proteins accumulate in specific perinuclear structures called aggresome. Further analysis confirmed that the RanBPM foci were indeed aggresomes by assessing co-localization of RanBPM with HDAC6, which is required for aggresome formation. Further, we showed RanBPM also formed aggresome in response to treatment with the proteasome inhibitor MG132. To determine the effect of RanBPM downregulation on aggresome formation, we assessed aggresome formation by HDAC6 in RanBPM shRNA and control shRNA Hela and HEK cells. RanBPM downregulation resulted in significantly lower number of aggresomes both after MG132 and IR treatment, suggesting that RanBPM is essential in aggresome formation. Confocal microscopy analysis showed that RanBPM and HDAC6 co-localize within the aggresome and co-immunoprecipitation studies detected an interaction between the two proteins. Downregulation of RanBPM also resulted in decreased acetylated α-tubulin, suggesting that RanBPM regulates HDAC6 activity. Altogether these results suggest that RanBPM may regulate aggresome formation through an interaction with HDAC6. The molecular details of this regulation are currently under investigation. Citation Format: Louisa Salemi, Ahmad Almawi, Karen Lefebvre, Caroline Schild Poulter. Aggresome formation is regulated by RanBPM through an interaction with HDAC6. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4048. doi:10.1158/1538-7445.AM2013-4048