The role of the ubiquitin-like protein FAT10 in thymic selection

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The ubiquitin-like modifier FAT10 is covalently bound to hundreds of endogenous target proteins and serves as a signal for their degradation by the proteasome. While we have recently identified the E1 and E2 enzymes of FAT10 conjugation, the biological function of FAT10 has remained elusive. Recently we have found that FAT10 is most prominently expressed in mature dendritic cells and mouse thymic epithelial cells which both function as antigen presenting cells in negative selection of immature thymocytes. Here we investigate the hypothesis that FAT10 targets self proteins, expressed by mTECs in an Aire dependent manner, for presentation of MHC class I molecules for negative selection of self-reactive CD8+ T cells. We will investigate if MHC I surface expression and antigen presentation to T cell hybridomas differs between mTECs from wildtype and FAT10-/- mice. We will determine if the peripheral T cell repertoire and the TCR-Vβ usage differs between C57BL/6 wildtype and FAT10-/- mice. Overexpression of FAT10 in cell lines and elution of MHC I bound peptides will be used to assess if FAT10 expression changes the spectrum of MHC I ligands. FAT10 conjugates will be isolated from mouse mTEC cell lines and target proteins of FAT10 conjugation will be identified by mass spectrometry. Finally, by crossing several T cell receptor (TCR) transgenic mice with FAT10-/- mice, we will investigate if the negative selection of these TCRs is affected in the presence of the respective cognate antigen. We hope that our work will elucidate why FAT10 is so specifically expressed in mTECs and what biological function it serves in these cells.