The conserved cysteine protease, caspase-2 is a tumour suppressor with known functions in apoptosis, DNA damage and oxidative stress responses and in ageing. Our recent findings have now demonstrated an important role for caspase-2 in preventing the survival of aberrant mitotic cells including cells with abnormal chromosome content (aneuploid cells). We are now interested in determining whether this is the mechanism by which caspase-2 mediates its tumour suppressor function.

Our published data have shown that caspase-2-deficient primary cells, tumours and BM from aged mice have high levels of aneuploidy. In addition, our recent live-cell imaging data of primary splenocytes show that caspase-2 deficiency promotes survival of aberrant cells following mitotic failure, including abnormally giant, multi-nucleated and aneuploid cells. Interestingly, these features are seen in primary cells following pro-longed mitotic arrest, in mouse models of oxidative stress and are associated with accelerated hepatocellular carcinoma in mice following treatment with the liver carcinogen diethylnitrosamine.

Our findings demonstrate that the observed increase in aneuploidy is in part caused by reduced cleavage of Bid and reduced activation of the canonical apoptosis pathway. Furthermore, we have generated a caspase-2 catalytic mouse mutant (C320S) and demonstrated that caspase-2 protease activity is required to limit aneuploidy following pro-longed mitotic arrest. Therefore, caspase-2-mediated apoptosis of aneuploid cells is one mechanism that can restrain aneuploidy tolerance that may underlie the tumour suppressor function of caspase-2. Recent findings now demonstrate that caspase-2 can prevent aneuploidy by inducing Mdm2 cleavage and p53-mediated cell cycle arrest following cytokinesis failure caused by supernumerary centrosomes. This suggests that caspase-2 can mediate two distinct pathways to prevent aneuploidy. We are currently investigating the mechanisms linking mitotic aberrations to caspase-2 activation that can decide the fate of caspase-2 signalling. As part of this we have used proteomics approaches to investigate the post-translational mechanisms (PTMs) that regulate caspase-2. We have identified several novel phosphorylation sites in caspase-2 that appear to be differentially regulated during mitotic arrest. In addition, we have identified several ubiquitination sites in caspase-2 and are currently validating and characterizing the role of these PTMs in caspase-2 activation and function in restraining aneuploidy. Our studies are also using established mouse aneuploidy and tumour models to decipher the importance of caspase-2 function in limiting aneuploidy and the role of this in tumour suppression.