Abstract 1991: PDCD4 de-repression of Bcl-xl IRES-mediated translation leads to enhanced chemo-resistance of glioblastoma multiforme tumors.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Glioblastoma multiforme (GBM) is the most prevalent form of tumor of the central nervous system with an average survival time of less than one year. Given the location and characteristics of GBM only limited treatment options are available, thus understanding the mechanisms of GBM formation or progression may lead to the development of novel treatment options. Strikingly, a common feature of GBM is the loss of expression of the tumor suppressor programmed cell death 4 (PDCD4) which correlates with adverse outcomes for patients in response to chemo- or radiation therapy. Through both transcriptional and translational regulation, PDCD4 has been shown to regulate many proteins within the cell, although the precise mechanism of target selection is not known. We have hypothesised that silencing of PDCD4 in glioblastomas leads to an altered expression of apoptosis-regulating proteins resulting in the suppression of apoptotic signals and enhanced chemo-resistance. Indeed, we show that low levels of PDCD4 correlate with an increase in the anti-apoptotic Bcl-xL protein. Importantly, Bcl-xL is regulated at the level of protein synthesis through the internal ribosome entry site (IRES) in its 5’ untranslated region (UTR). We further show that PDCD4 regulates the activity of the Bcl-xL IRES, and is therefore an IRES specific translational regulator. Importantly, reintroduction of PDCD4 into glioblastoma cells or directly inhibiting Bcl-xL with the chemical inhibitor ABT-737 sensitizes these cells to doxorubicin, thus enhancing cell death. In summary, our work provides a novel role for PDCD4 as a translational regulator of Bcl-xL as well as a potential therapeutic option for the treatment of GBM. Citation Format: Urszula Liwak, Lindsay E. Jordan, Federico Roncaroli, Martin Holcik. PDCD4 de-repression of Bcl-xl IRES-mediated translation leads to enhanced chemo-resistance of glioblastoma multiforme tumors. [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 1991. doi:10.1158/1538-7445.AM2013-1991