Cancer is caused by the uncontrolled proliferation of aberrant cells that harbour multiple oncogenic mutations in signaling pathways implicated in growth and cell death. Most of today’s anticancer therapies lead to destruction of tumour cells by apoptosis. However, mutations leading to the development of cancer not only promote tumour progression, but often allow cells to avoid apoptotic death and thus result in resistance to treatment. Fortunately, many pathways lead to apoptosis and alternative cell death programmes do exist. Advances in the knowledge about how apoptosis and alternative cell death are activated are important and could pave the way for the development of alternative therapies. Using lymphoid cell lines, in particular Jurkat T cells, we have studied cell death pathways induced by an antiviral response or a prolonged endoplasmic reticulum (ER) stress. First, we have studied the involvement of RIP1 and the activation of dsRNA-activated protein kinase (PKR) in external dsRNA-induced apoptotic and necrotic cell death in Jurkat T cell lymphoma. Our findings suggest that RIP1 is implicated in apoptosis and necrosis induced by dsRNA and a caspase-dependent mode of activation of PKR in apoptosis. PKR is cleaved in two fragments, PKR-ND containing the N-terminal domain of PKR and PKR-KD containing the kinase domain. The PKR-KD fragment interacts with and activates intact PKR. PKR-ND facilitates the interaction of PKR-KD with full-length PKR and thus the activation of the kinase and amplifies the translation inhibitory signal. Secondly, we explored the pathways leading to caspase activation and the involvement of Bcl2 pro-apoptotic members and RIP1 in cell death induced by ER stress in Jurkat T cells. Our results show that caspases-3, -8 and -9 are implicated in apoptosis induced by brefeldin-A (BFA). Using caspase-8 and FADD deficient Jurkat T cells, we demonstrate that these proteins are redundant for BFA induced apoptosis. In Bcl2 overexpressing Jurkat cells exposed to BFA, survival was tremendously improved, although a fraction of the cells died by necrosis. Interestingly, caspase-8 deficient cells were more resistant to thapsigargin and Bcl2 overexpression had no effect on the cytotoxicity of this inhibitor, suggesting that BFA and thapsigargin induce distinct cell death signaling pathways. Comparing Bcl2-like proteins expression in BFA induced apoptotic with necrotic cells; we demonstrate significant 9 differences suggesting that different Bcl2 like proteins may play a role in distinct ER stress induced cell death pathways. To conclude these results bring new data about apoptotic and necrotic pathways induced by an antiviral response and ER stress in lymphoid cell lines. Alternative cell death pathways induced by dsRNA or ER stress could be interesting pathways in developing new cancer therapies.
|Date of Award||20 Aug 2010|
|Supervisor||Martine Raes (Supervisor), Thierry Arnould (Jury), Alex SAELENS (Jury), Isabelle Hamer (President), Guy BERCHEM (Jury) & Michael KALAI (Co-Supervisor)|