Apoptosis is a major pathway of cell death that is induced by most of the state of the art chemotherapeutics or by radiotherapy. Understanding the mechanisms of apoptosis is therefore essential to predict cancer cell response to current treatment and to develop new adjuvant drugs for better treatment regimes. As example, the DNA damaging agents oxaliplatin and the topoisomerase I inhibitor iriotecan activate the tumour suppressor gene p53 while receptor kinase inhibitors deactivate the pro survival protein kinase B (PKB/AKT). P53 activation and PKB/AKT deactivation lead to up-regulation of pro-apoptotic members of the BCL2-protein family. The interaction between pro-survival and pro-apoptotic BCL2 family members is the first important control step during apoptosis execution.
Several pro-survival and pro-apoptotic BCL2 proteins are currently know. Genotoxic or serum deprivation stress both transcriptionally induce a different set of pro-apoptotic BCL2 proteins, and each pro-apoptotic BCL2 protein interacts with a set of pro-survival BCL2 proteins in a specific way. Eventually, the relative abundance and the kinetic of the interaction of pro-survival and pro-apoptotic BCL2 proteins decides whether apoptosis proceeds or is abandoned. In particular, I will investigate how different existing therapeutics such as oxaliplatin, irinotecan, or cetuximab induces a specific set of pro-apoptotic BCL2 members and how different expressions of pro-survival and pro-apoptotic BCL2 members and different expressions in human carcinoma cell lines translate into a decision on apoptosis and survival. Moreover, I will investigate the potential of novel pharmacophores such as Navitoclax (Abbot) or gossypol that mimetic pro-apototic BCL2 proteins and investigate how they might overcome apoptosis impairment in cell lines that do not respond to conventional treatment.
My research aims to provide computational models to analyse the interaction of pro-apototic and pro-survival BCL2 proteins of apoptosis and validate their predictions in biochemistry and single cell experiments (Aim 3.1).
If apoptosis proceeds beyond this control step, two apoptotic proteins, cyt-c and Smac are released from the mitochondrial outer membrane. Cyt-c induces a conformation change of the cytosolic protein APAF-1, which oligomerises, and activates caspase-9 and caspase-3. One activated, caspase-3 cleaves DNA and cytoskeleton. However, as a second control step to prevent subliminal apoptosis, the pro-survival protein XIAP can bind to and deactivate caspase-3 and caspase-9. In turn, XIAP’s pro-survival function is attenuated by pro-apoptotic protein Smac. Also in this final step of apoptosis, even small de-regulations in levels of these proteins can severely impair apoptosis (Hector et al., 2011). However, this interaction step is particularly complex with several positive and negative feedback loops. Combination of methods from control theory such as bistability and robustness analysis with biochemistry and single cell imaging has been proven fruitful for the field (Eissing et al., 2004; Tuffy et al., 2010).
We therefore provide computational models of protein-protein interaction downstream of mitochondrial release.