[Abstract unavailable

The p62/SQSTM1 (sequestosome 1) protein, which acts as a cargo receptor for autophagic degradation of ubiquitinated targets, is up-regulated by various stressors. Induction of the p62 gene by oxidative stress is mediated by NF-E2-related factor 2 (NRF2) and, at the same time, p62 protein contributes to the activation of NRF2, but hitherto the mechanisms involved were not known. Herein, we have mapped an antioxidant response element (ARE) in the p62 promoter that is responsible for its induction by oxidative stress via NRF2. Chromatin immunoprecipitation and gel mobility-shift assays verified that NRF2 binds to this cis-element in vivo and in vitro. Also, p62 docks directly onto the Kelch-repeat domain of Kelch-like ECH-associated protein 1 (KEAP1), via a motif designated the KEAP1 interacting region (KIR), thereby blocking binding between KEAP1 and NRF2 that leads to ubiquitylation and degradation of the transcription factor. The KIR motif in p62 is located immediately C-terminal to the LC3-interacting region (LIR) and resembles the ETGE motif utilized by NRF2 for its interaction with KEAP1. KIR is required for p62 to stabilize NRF2, and inhibition of KEAP1 by p62 occurs from a cytoplasmic location within the cell. The LIR and KIR motifs cannot be engaged simultaneously by LC3 and KEAP1, but because p62 is polymeric the interaction between KEAP1 and p62 leads to accumulation of KEAP1 in p62 bodies, which is followed by autophagic degradation of KEAP1. Our data explain how p62 contributes to activation of NRF2 target genes in response to oxidative stress through creating a positive feedback loop.

SUMMARY Selective autophagy performs an array of tasks to maintain intracellular homeostasis, sterility, and organellar and cellular functionality. The fidelity of these processes depends on precise target recognition and limited activation of the autophagy apparatus in a localized fashion. Here we describe cooperation in such processes between the TRIM family and Galectin family of proteins. TRIMs, which are E3 ubiquitin ligases, displayed propensity to associate with Galectins. One specific TRIM, TRIM16, interacted with Galectin-3 in an ULK1-dependent manner. TRIM16, through integration of Galectin- and ubiquitin-based processes, coordinated recognition of membrane damage with mobilization of the core autophagy regulators ATG16L1, ULK1, and Beclin 1 in response to damaged endomembranes. TRIM16 affected mTOR, interacted with TFEB and influenced TFEB’s nuclear translocation. The cooperation between TRIM16 and Galectin-3 in targeting and activation of selective autophagy protects cells from lysosomal damage and Mycobacterium tuberculosis invasion.

SUMMARY Autophagy, a homeostatic process whereby eukaryotic cells target cytoplasmic cargo for degradation, plays a broad role in health and disease states. Here we screened the TRIM family for roles in autophagy and found that half of TRIMs modulated autophagy. In mechanistic studies we show that TRIMs associate with autophagy factors and act as platforms assembling ULK1 and Beclin 1 in their activated states. Furthermore, TRIM5α acts as a selective autophagy receptor. Based on direct sequence-specific recognition, TRIM5α delivered its cognate cytosolic target, a viral capsid protein, for autophagic degradation. Thus, our study establishes that TRIMs can function both as regulators of autophagy and as autophagic cargo receptors, and reveals a new basis for selective autophagy in mammalian cells.

As malignant tumours develop, they interact intimately with their microenvironment and can activate autophagy1, a catabolic process which provides nutrients during starvation. How tumours regulate autophagy in vivo and whether autophagy affects tumour growth is controversial2. Here we demonstrate, using a well characterized Drosophila melanogaster malignant tumour model3,4, that non-cell-autonomous autophagy is induced both in the tumour microenvironment and systemically in distant tissues. Tumour growth can be pharmacologically restrained using autophagy inhibitors, and early-stage tumour growth and invasion are genetically dependent on autophagy within the local tumour microenvironment. Induction of autophagy is mediated by Drosophila tumour necrosis factor and interleukin-6-like signalling from metabolically stressed tumour cells, whereas tumour growth depends on active amino acid transport. We show that dormant growth-impaired tumours from autophagy-deficient animals reactivate tumorous growth when transplanted into autophagy-proficient hosts. We conclude that transformed cells engage surrounding normal cells as active and essential microenvironmental contributors to early tumour growth through nutrient-generating autophagy.

Autophagy is a process delivering cytoplasmic components to lysosomes for degradation. Autophagy may, however, play a role in unconventional secretion of leaderless cytosolic proteins. How secretory autophagy diverges from degradative autophagy remains unclear. Here we show that in response to lysosomal damage, the prototypical cytosolic secretory autophagy cargo IL-1b is recognized by specialized secretory autophagy cargo receptor TRIM16 and that this receptor interacts with the R-SNARE Sec22b to recruit cargo to the LC3-II + sequestration membranes. Cargo secretion is unaffected by downregulation of syntaxin 17, a SNARE promoting autophagosome-lysosome fusion and cargo degradation. Instead, Sec22b in combination with plasma membrane syntaxin 3 and syntaxin 4 as well as SNAP-23 and SNAP-29 completes cargo secretion. Thus, secretory autophagy utilizes a specialized cytosolic cargo receptor and a dedicated SNARE system. Other unconventionally secreted cargo, such as ferritin, is secreted via the same pathway.

TRIM20 and TRIM21 are mediators of IFN-γ–induced autophagy, which act as autophagic receptor regulators that target specific inflammasome components and type I interferon response regulators for degradation by precision autophagy.

Background:The ULK complex regulates autophagy, but how it interacts with the basal autophagy apparatus is unknown. Results: ULK1, -2, ATG13, and FIP200 bind to ATG8 family proteins via LIR (LC3 interacting region) motifs. Conclusion: ATG8 family proteins act as scaffolds anchoring the ULK complex on autophagosomes. Significance: We define sequence requirements for the LIR motifs and suggest how the ULK complex interacts with autophagosomes.