Perforin-2 is a pore-forming effector of endocytic escape in cross-presenting dendritic cells

Abstract

During initiation of antiviral and antitumour T cell-mediated immune responses, dendritic cells (DCs) cross-present exogenous antigens on MHC class I. Cross-presentation relies on the unique leakiness of endocytic compartments in DCs, whereby internalised proteins escape into the cytosol for proteasome-mediated generation of MHC I-binding peptides. Given that type 1 conventional DCs excel at cross-presentation, we searched for cell-type specific effectors of endocytic escape. We devised an escape assay suitable for genetic screening and identified a pore-forming protein, perforin-2, as a dedicated effector exclusive to cross-presenting cells. Perforin-2 is recruited to antigen-containing compartments, where it undergoes maturation, releasing its pore-forming domain. Mpeg1-/- mice fail to efficiently prime CD8+ T cells to cell-associated antigens, revealing an important role of perforin-2 in cytosolic entry of antigens during cross-presentation.

The pore-forming apolipoprotein APOL7C drives phagosomal rupture and antigen cross-presentation by dendritic cells

“…First, while XP has been observed in a variety of APCs in vitro, only cDC1s appear to serve a non-redundant role in cross-priming to many types of viruses and tumours in vivo 1,9,10,[80][81][82][83] . Second, the XP of cell-associated antigens by cDC1s often involves the delivery of antigens to the cytosol 11,20,21,23,28,34,50,63 . In line with this, several groups have recently shown that, in cDC1s, endocytic organelles, including phagosomes, appear to be "damage prone" and to display signs of breached or ruptured membranes 11,23,27,28,65 .…”

“…MuTuDCs are frequently used to study XP, have a similar proteomic profile to primary cDC1s in vivo, and have shown evidence of phagosomal rupture 11,23,[28][29][30][31][32][33][34] . We first treated MuTuDCs with poly(I:C), which can trigger TLR3 that is particularly abundant on cDC1s and favours enhanced cross-priming 31,[35][36][37][38][39][40][41][42] .…”

“…For example, DNGR-1 has been found to signal via SYK and the NADPH oxidase for phagosomal rupture, which in turn releases phagocytosed proteins into the cytosol 11,22 . Also, a pore-forming protein present in the lumen of endocytic organelles in APCs called perforin-2 has been found to instigate the formation of non-selective pores in endocytic organelle membranes, which allows for the escape of endocytosed proteins to the cytosol 23 . These exciting new findings have led to entirely new questions.…”

The resolution of phagosomes

“…Accordingly, the transporters SLC15A3 and SLC15A4 mediate MDP efflux from phagolysosomes in macrophages and dendritic cells to promote NOD2 activation 63,65,179 (Figure 3). Additionally, the pore‐forming protein perforin 2 mediates export of ingested antigens in dendritic cells to promote cross‐presentation 194 . It is likely that other transporters and channels support innate immune signaling in phagocytes, but this requires further study.…”

“…Additionally, the pore-forming protein perforin 2 mediates export of ingested antigens in dendritic cells to promote cross-presentation. 194 It is likely that other transporters and channels support innate immune signaling in phagocytes, but this requires further study.…”