Title: How does specificity within the ubiquitin system regulate the activation and resolution of T cell responses?
Funder: The Academy of Medical Sciences

Abstract: T cell activation must be tightly controlled to ensure robust clearance of invading pathogens whilst minimising collateral damage to host tissues and inappropriate responses to self-antigens. The signalling pathways downstream of T cell receptor engagement are therefore subject to multiple layers of regulation, and failures in these systems can result in autoimmune disease. One key regulatory mechanism is the ubiquitin-proteasome system (UPS), the primary route through which the cell achieves selective protein degradation. Knockout of multiple E3 ubiquitin ligases results in autoimmune phenotypes by lowering the threshold for T cell activation, but our understanding of these pathways is critically limited by an inability to identify the relevant substrates. Thus, my goal is to identify and characterise the substrates of E3 ubiquitin ligases that regulate the activation of human CD4+ T cells. The genetic screening techniques that I have developed are ideally suited to address this important question. The key enabling technology is Global Protein Stability (GPS), an expression screening approach, which, when combined with a human ‘ORFeome’ library (comprising ~14,000 open reading frames), is capable of proteome-wide stability profiling. By adapting the GPS platform to enable stability profiling in primary human CD4+ T cells, I will (1) define proteins that exhibit differential stability in resting and activated T cells, and (2) delineate the substrates of E3 ubiquitin ligases known to restrain T cell activation. This work will establish how specificity within the ubiquitin system regulates immune cell function, and identify optimal targets for potential therapeutic intervention in autoimmune diseases.

Lay abstract: Proteins are the key action molecules in the cell, and our cells constantly monitor their internal environment to ensure that they have the optimal set of proteins. Protein balance is achieved by (1) strictly controlling the manufacture of new proteins, but also by (2) efficiently destroying existing proteins that are damaged or no longer required. I want to understand how cells decide when to degrade particular proteins, and how they selectively target such proteins for disposal. This work is important because failures in protein degradation underlie a wide variety of diseases, but our ability to design new drug therapies to treat these diseases is hampered by a lack of fundamental understanding of how protein degradation is achieved in healthy cells. This project will study how protein degradation controls the behaviour of a specific group of immune cells called T cells. T cells must organise a robust immune response when they encounter invading pathogens, but uncontrolled T cell activation can result in attack against the body’s own cells, leading to autoimmune diseases such as inflammatory bowel disease and rheumatoid arthritis. Using a technique which allows the abundance of ~14,000 proteins tagged with a fluorescent marker to be measured in a single experiment, I will determine the overall protein composition of T cells before and after activation. Comparing these two datasets will allow me to uncover key regulators of T cell activation, which may be attractive targets for future therapies to treat autoimmune disorders.

Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: INFLAMMATORY AND IMMUNE SYSTEM