Dendritic cells (DC) are sentinels of the immune system. DC use a variety of surface receptors to survey their environment and induce anti-viral immunity. The C-type lectin-like receptor, Clec9A is specifically expressed on cDC1, which excel at cross-presentation of exogenous antigen on MHC I to induce antigen-specific CD8+ T cell responses. Clec9A recognises actin filaments exposed on the surface of dead/damaged cells and plays a vital role in the processing of dead cell-derived antigens, mediating their delivery to the cross-presentation pathway. Clec9A is therefore particularly important for inducing cytotoxic T cells that are able to directly kill virally-infected and cancer cells.
We have identified Clec9A-regulatory pathways that control Clec9A fate and function in DC. We demonstrated the E3 ubiquitin ligase RNF41 negatively regulates Clec9A levels and function through ubiquitination. Interestingly, RNF41 ubiquitinates the extracellular domain of Clec9A to regulate its fate and function, in contrast with classical ubiquitination-mediated regulation of cell surface receptor fate via ubiquitination of cytoplasmic receptor domains. Indeed, knockdown of RNF41 in cDC1 results in enhanced cross presentation of dead cell antigen. We have further identified novel Clec9A-interacting proteins, including the ER-associated Erlin1 and Erlin2 proteins, implicated in receptor ubiquitination and membrane translocation, that negatively regulate Clec9A fate and function. Our research is currently focussing on the role of Clec9A regulatory pathways in the control of Clec9A, damage recognition, receptor trafficking and antigen cross-presentation.
Our findings provide important insights into the mechanisms regulating damage recogntion and cross-presentation of antigen from virally infected cells, which is key to understanding viral immunity and has implications for development of immune modulation approaches via Clec9A.