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Autophagy cargo receptors are secreted via extracellular vesicles and particles in response to endolysosomal inhibition or impaired autophagosome maturation

ABSTRACT: The endosome-lysosome (endolysosome) system plays central roles in both autophagic degradation and secretory pathways, including the exocytic release of extracellular vesicles and particles (EVPs). Although previous work has revealed important interconnections between autophagy and EVP-mediated secretion, our molecular understanding of these secretory events during endolysosome inhibition remains incomplete. Here, we delineate a secretory autophagy pathway upregulated in response to endolysosomal inhibition that mediates the EVP-associated extracellular release of autophagic cargo receptors, including p62/SQSTM1. This extracellular secretion is highly regulated and critically dependent on multiple ATGs required for the progressive steps of early autophagosome formation as well as Rab27a-dependent exocytosis. Furthermore, the disruption of autophagosome maturation, either due to genetic inhibition of the autophagosome-to-autolyosome fusion machinery or blockade via the SARS-CoV2 viral protein ORF3a, is sufficient to induce robust EVP-associated secretion of autophagy cargo receptors. Finally, we demonstrate that this ATG-dependent, EVP-mediated secretion pathway buffers against the intracellular accumulation of autophagy cargo receptors when classical autophagic degradation is impaired. Based on these results, we propose that secretory autophagy via EVPs functions as an alternate route to clear sequestered material and maintain proteostasis in response to endolysosomal dysfunction or impaired autophagosome maturation.

INSTRUMENT(S): Q Exactive Plus

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Hek-293t Cell, Cell Culture

SUBMITTER: Yu-Hsiu Lin

LAB HEAD: Andrew Leidal

PROVIDER: PXD031527 | Pride | 2022-03-03

REPOSITORIES: Pride

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Project description:Background & Aims: Other than hepatitis B or C virus infection, Hepatitis E virus (HEV) infection is generally asymptomatic or leads to acute and self-limiting hepatitis. However, the mechanism of host cell defense against HEV is unclear. Viruses are known to perturb host cellular metabolism to enable their replication and spread. AMP-activated protein kinase (AMPK) activation is crucial for the regulation of cell homeostasis. We thus investigated the role of AMPK in HEV infection. Methods: Huh7, THP1 and HepG2 cells inoculated with infectious HEV viral particle or Huh7 and organoids transfected with in vitro generated subgenomic or full-length GT3 (Kernow-C1 p6 strain) HEV RNA, namely, p6Luc or p6 were used to model HEV infection. Viral replication and genes expression were quantified. Activation of AMPK, innate immune response and autophagy process were assessed. Results: We found HEV infection can trigger AMPK activation by phosphorylation of AMPK at threonine 172 by transfecting HEV viral RNA into host cells or inoculating host cells with infectious HEV viral particle. The activation of AMPK is associated with HEV induced mitochondrial damage and ATP deficiency. Pharmacological activation of AMPK using 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) attenuated HEV replication, which was reversed by an AMPK inhibitor (compound C). Lentivirus-mediated knockdown of AMPK provided further evidence that AMPK has an antiviral effect on HEV replication. These results suggested that AMPK activation is a potent strategy of host cells for HEV clearance. Consistent with its antiviral effect, AMPK activation potentiated the expression of genes with antiviral properties (e.g., IFNs, ISG15, and IRF9) and inhibited inflammatory response (e.g., NF-KB NLRP3 and IL-1β). Meanwhile, HEV and activated AMPK also decreased autophagosome accumulation by decreasing induction of autophagy and autophagic degradation. Consistently, we found inhibition of AMPK efficiently augmented HEV induced autophagosome accumulation, evidenced by a marked increase in LC3II. Our previous study showed that rapamycin, an activator of autophagic induction by inhibiting mTOR, and Bafilomycin A1, an inhibitor of autophagic degradation, has a potent pro-HEV effect under AICAR treatment. Moreover, Wortmannin inhibiting autophagic induction recover AMPK inhibitor induced HEV replication. Together, these results suggested that HEV induced AMPK activation can serve to protect HEV infected cells from HEV infection by attenuating autophagosome and promoting innate immunity. Conclusions: Here we show that HEV infection can activate AMPK phosphorylation, which attenuates autophagosome accumulation and increases innate immune signaling. Thus, the AMPK activation in response to HEV infection is critical in host cells for rapid viral clearance by coordinating autophagic process and establishing persistent antiviral immunity.

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Autophagy cargo receptors are secreted via extracellular vesicles and particles in response to endolysosomal inhibition or impaired autophagosome maturation

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