Molecular mechanisms in ageing and cancer : Redox signalling & proteome-wide protein turnover

Cells are exposed to reactive oxygen species (ROS) that derive both from internal and external sources. The formation of cellular ROS is linked to ageing and age-related diseases like cancer. Because of conflicting data, the link between ROS and ageing or cancer is not exactly clear. ROS are in some ageing studies found to decrease lifespan and in other studies found to act as a pro-survival factor. These conflicting data demonstrates that more research is needed to unravel the signalling and damaging effects of ROS. Knowledge of the different effects that ROS can have in time, in space and on individual proteins within cells can subsequently be used to predict whether ROS is beneficial or harmful in a certain situation. To increase this knowledge this thesis describes amongst others the effects that ROS can have on individual proteins that are known to be involved in ageing and age-related diseases as cancer (e.g. FOXO/DAF-16 and p16) via cysteine-dependent redox signalling. In this thesis we studied the functional effects of redox regulation of DAF-16 in C. elegans. Redox signalling towards FOXO4 (human homolog of DAF-16) was already known to induce its nuclear transport via a cysteine-dependent binding to the nuclear importer transportin-1. We show here that the delayed nuclear translocation of DAF-16 upon transportin-1 knockdown is accompanied by a paradoxical increase in DAF-16-dependent thermotolerance and longevity. Furthermore we could show here that cysteine- and possibly redox-dependent signalling towards FOXO/DAF-16 plays a role in developmental rate and thermotolerance in the model organism C. elegans. In addition we studied the redox control of the human tumour suppressor and cell cycle regulator p16. We show that the dynamics of a p16 imposed cell cycle arrest are altered under oxidizing conditions in a cysteine-dependent manner. Our data suggests that these changed dynamics and the related decrease in inhibitory capacity of p16 could be caused by a combination of a conformational change and the effect of a redox- and cysteine-dependent binding partner. Another theme of this thesis is protein homeostasis. The loss of protein homeostasis is a hallmark of ageing and age-related diseases. Protein synthesis or degradation, two components of protein homeostasis are often altered in models of ageing but the exact relation between protein turnover and ageing is, just as the effect of ROS on ageing, unclear. To increase the knowledge of the relationship between protein turnover and ageing we studied proteome-wide protein turnover in several C. elegans models of longevity and age-related diseases (Parkinson’s). To study proteome-wide protein turnover, a quantitative mass-spectrometry based method was set up that enabled the estimation of the half-life of individual proteins. With this method we found large changes in average protein half-lifes when comparing different C. elegans models of longevity and age-related disease (Parkinson’s). We found that protein turnover, at least in the developing animal does not necessarily correlate with eventual lifespan or healthspan. Furthermore, the total shift of protein turnover, and biological component analysis suggest that protein turnover is probably regulated at organismal level