TLR and NLRP3 inflammasome-dependent innate immune responses to tumor-derived autophagosomes (DRibbles).

Y Xing,R Cao,H-M Hu

doi:10.1038/cddis.2016.206

Abstract

Autophagosomes derived from tumor cells, also referred to as defective ribosomal products in blebs (DRibbles), have been previously shown to stimulate potent T-cell responses and mediate tumor regression when used as therapeutic cancer vaccines in multiple preclinical cancer models. In this report, we investigated the underlining mechanisms by which DRibbles induced T-cell activation, particularly how DRibbles activated antigen-presenting cells (APCs). We found that DRibbles could induce a rapid differentiation of monocytes and DC precursor (pre-DC) cells into functional APCs. DRibbles triggered innate receptor signaling via Toll-like Receptors (TLR)-2, TLR4, TLR7, TLR8, and nucleotide-binding oligomerization domain-containing protein 2 (NOD2), but not TLR3, TLR5, or TLR9. DRibbles induced PBMCs to produce pro-inflammatory cytokines, such as IL-6, IL-10, TNF-α, and IL-1β. DRibbles induced IL-1β release from PBMC or THP-1 cells without LPS priming, but required the core machinery of NLRP3 inflammasomes. Active endocytosis was required for inflammasome activation and cross presentation, and blocking endosome acidification or the ER-associated degradation (ERAD) pathway resulted in opposite effects on these two processes. Our data show that DRibbles could induce strong innate immune responses via multiple pattern recognition receptors, and explain why DRibbles could function as excellent antigen carriers to induce adaptive immune responses to both tumor cells and viruses. In contrast to the well-established inhibitory effect of autophagy on the inflammasome activation of APCs, our study demonstrates that isolated autophagosomes (DRibbles) from antigen donor cells activate inflammasomes by providing first and second signals required for IL-1β production by PMBC.

Highlights

Autophagy is a well-conserved cellular stress response pathway that enables organisms either as a unicellular eukaryote or complex metazoan to survive extreme conditions.[1]
The danger factor binding to pattern recognition receptors (PRRs) activates the transcription factor nuclear factor-κB (NF-κB), which induces the generation of a subunit of inflammasomes, such as NLRP3, and IL-1β precursor
A similar pattern was observed when DRibbles from different cell lines were used. These results show that DRibbles are capable of acting through multiple Toll-like receptor (TLR), as well as the PRR NOD2, which likely contributes to release of inflammatory cytokines

Summary

Introduction

Autophagy is a well-conserved cellular stress response pathway that enables organisms either as a unicellular eukaryote or complex metazoan to survive extreme conditions.[1] For unicellular organisms, the survival is largely dependent on the autophagy pathway as a cell-intrinsic defense mechanism to acquire nutrients by recycling damaged proteins and other biomolecules. Autophagy serves an important role as a cell-intrinsic defense mechanism and a key regulator of inflammatory responses. Danger signals generated by cellular damage are recognized by host innate immune cells via innate immune signaling receptors, called pattern recognition receptors (PRRs). Tumor-derived autophagosomes (DRibbles) contain abundant materials like DNA, RNA, proteins, which could function as potent danger signals.[8] In this study, we investigated whether DRibbles could deliver both signal 1 and 2 for NLRP3-dependent inflammasome activation. The role of endocytosis, protein retro-translocation and ERAD pathway in inflammasome activation was examined

Methods

Results

Conclusion