Heat shock signalling and response in African trypanosomes

The core body temperature of mammals is tightly regulated, and although increased temperatures can be fatal, periods of fever can used as part of a strategy to prevent infections by killing temperature sensitive bacteria and viruses. The African trypanosomes are parasites that are transmitted by the bite of an infected tsetse fly in sub-Saharan Africa, and cause disease in farm animals and humans which results in periods of fever. The parasite is able to survive these during period of fever by making specific proteins that help it cope with the elevated temperature it experiences. The way in which the parasite is able to do this is not clear, but we do know that it is different to the way mammals respond to elevated temperatures.

This project will investigate the way in which the parasite is able to sense and respond to elevated temperatures using a combination of experimental techniques to study parasite cells grown in flasks. We will examine the types of proteins the parasites produces to allow it cope with elevated temperatures, and how this response is co-ordinated. Studying this response is important as it will help us to understand how the parasite adapts to periods of fever in their hosts, knowledge that will help in the fight against the diseases they cause in farm animals and humans. Improved fundamental understanding of these molecular mechanisms is also important for our understanding of metabolic diseases and cancers where dysregulation occurs.

The African trypanosomes Trypanosoma brucei and Trypanosoma congolense are vector borne parasites of domestic cattle and are a major cause of economic hardship in sub-Saharan Africa, with two sub-species of T. brucei also causing fatal infections in humans. Their ability to sense and respond to their host environment is critical for their survival and virulence, and is achieved despite a near complete lack of transcriptional control that results in a reliance on RNA binding proteins (RBPs).

Symptoms of human and animal African trypanosomiasis include periods of fever as high as 41 0C, eliciting a heat shock (HS) response in the parasites. Eukaryotic cells respond to HS by triggering a general arrest in protein translation and increasing HS protein (HSP) expression to aid protein folding and degradation. The eukaryotic HS response appears to be conserved in trypanosomes, but the mechanisms mediating the response are divergent.

In mammals HS translation arrest is triggered by the phosphorylation of eIF2alpha which blocks translation initiation, and up-regulation of HSP expression is regulated at the level of transcription. In T. brucei HS translational arrest is eIF2alpha-independent, and the zinc finger protein ZC3H11 binds to and stabilises HS responsive mRNAs to up-regulate HSPs expression. We have shown that in T. brucei HS alters the phosphorylation state of ZC3H11 and other RBPs that may play a role in translational arrest, P-body formation and upregulation of HSPs.

In this project we will used quantitative proteomics to measure the temporal changes in protein and phosphorylation state abundance that occur in T. brucei and T. congolense during HS and recovery. The functional role of phosphorylation sites on ZC3H11 and other candidate proteins will be determined, and the extent of conservation of HS sensing and response in T. congolense will be examined.