Signalling intracellular infection: a potential major role for proteasome-catalyzed peptide-splicing.

Proteasomes play a dominant role in intracellular protein degradation and thereby regulate many cellular processes. The peptide products, produced as a consequence of proteolysis, may enter the MHC class I antigen processing pathway for display on the cell surface. This allows CD8+ T cells to detect and react to intracellular aberrancies, such as infections. Recently, it was discovered that an unexpected large fraction of peptides, presented by cell surface MHC class I molecules on human cells, are spliced (hybrid) peptides generated by Proteasome-Catalyzed ligation of peptides / ‘Peptide Splicing’ (PCPS). To examine whether spliced peptides are a target of CD8+ T cells responding to infection, we joined forces with the scientists that performed the named study, to develop a reverse immunology-based approach to identify proteasome-generated spliced epitopes. Applying this strategy, we were first to demonstrate that mouse CD8+ T cells elicited by infection with an intracellular bacterium, recognize linear, as well as spliced bacterium-derived epitopes. In this proposal, we aim to apply the unique expertise available in my lab and that of our collaborators to determine to which extent PCPS plays a role in shaping the antigenic landscape on cells infected with intracellular pathogens. We will explore the mechanistic aspects of spliced epitope generation, focusing on the role of a proteasome regulator (PA28) that is upregulated by infection. We will further determine whether the presented spliced, pathogen-derived peptides are a major target of CD8+ T cells, responding to infection. Thereby, we will establish the immunological relevance of PCPS.