Cell death-associated sterile inflammation plays a critical role in a range of human diseases from cancer to autoimmunity. Damaged tissues are thought to elicit their inflammatory effects through the sudden release from cells of endogenous damage-associated molecular patterns (DAMPs) that serve to recruit and modulate the function of immune cells. What provided the impetuousness for this project was the discovery that purified extracellular actin elicited a JAK-STAT-dependent inflammatory response in the fruit fly (Drosophila melanogaster. The JAK-STAT pathway in fruit fly is activated by a broad range of cellular stresses including mechanical pressure, infection, and septic wounds. A unifying feature of all these forms of stress is cell death and it has been speculated that STAT activation might occur in response to the release of DAMPs during the disparate cellular insults, however, the nature and identity of these DAMPs remain obscure. The major objective of this project was to discover the actin sensor in Drosophila that senses actin to promotes a JAK-STAT response. Corrective action was taken during the early phases of this project to refocused on how a mammalian cytoskeletal sensor (DNGR-1, expressed on dendritic cells, signals to promote the presentation of exogenous antigens to cytotoxic T lymphocytes (CTLs), through a process called 'cross-presentation' (XP). Following cell death and plasma membrane rupture in mammals, Filamentous-actin (F-actin) is recognised as a DAMP by the C-type lectin receptor DNGR1, expressed on Type 1 conventional dendritic cells (cDC1), that signals to favour the cross-presentation of dead-cell-associated antigens to CTLs. The function of DNGR1 requires the presence of an immunoreceptor tyrosine-based activation motif (ITAM)-like domain in its intracellular tail that allows the recruitment and activation of the spleen tyrosine kinase (SYK). Mice that are deficient in DNGR-1 or SYK lack protective CTL responses to viral and tumor challenges. Therefore, an understanding of how cDC1, and DNGR-1 more specifically mediates XP is crucial to better understand immune control of cancer and viruses. Understanding how cDC1 promote presentation of exogenous antigens (e.g. from tumor cells) would constitute a big step forward in developing a new, and potentially more effective, category of immunotherapies.Therefore we sought to address what mechanism(s) does DNGR-1 utilize to mediate XP of dead-cell associated antigen? During this project, we demonstrated that DNGR-1 is a dedicated XP receptor that signals upon ligand engagement to promote phagosomal rupture. These rupturing events allow for the escape of phagosomal contents into the cytosol where they access the endogenous MHC class I antigen processing pathway. The activity of DNGR-1 maps to its signalling domain, which activates SYK and NADPH oxidase to cause phagosomal damage. These findings reveal the existence of innate immune receptors that couple ligand binding to endocytic vesicle damage to permit MHC class I antigen presentation of exogenous antigens and regulate adaptive immunity.
