Exophagy of annexin A2 via RAB11, RAB8A and RAB27A in IFN-γ-stimulated lung epithelial cells

Abstract

Annexin A2 (ANXA2), a phospholipid-binding protein, has multiple biological functions depending on its cellular localization. We previously demonstrated that IFN-γ-triggered ANXA2 secretion is associated with exosomal release. Here, we show that IFN-γ-induced autophagy is essential for the extracellular secretion of ANXA2 in lung epithelial cells. We observed colocalization of ANXA2-containing autophagosomes with multivesicular bodies (MVBs) after IFN-γ stimulation, followed by exosomal release. IFN-γ-induced exophagic release of ANXA2 could not be observed in ATG5-silenced or mutant RAB11-expressing cells. Furthermore, knockdown of RAB8A and RAB27A, but not RAB27B, reduced IFN-γ-triggered ANXA2 secretion. Surface translocation of ANXA2 enhanced efferocytosis by epithelial cells, and inhibition of different exophagic steps, including autophagosome formation, fusion of autophagosomes with MVBs, and fusion of amphisomes with plasma membrane, reduced ANXA2-mediated efferocytosis. Our data reveal a novel route of IFN-γ-induced exophagy of ANXA2.

Lysosomal Exocytosis, Exosome Release and Secretory Autophagy: The Autophagic- and Endo-Lysosomal Systems Go Extracellular

“…These findings indicate that the formation of autophagosomes, MVBs and their fusion with plasma membrane are all relevant processes for annexin 2 release and suggest the secretion of amphisomes carrying both exosome and autophagy markers. As in the case of IL1β secretion, this process requires Rab8A [143]. In 2012, a study by Griffiths et al [144] provided evidence that mature reticulocytes internalize plasma membrane in glycophorin A containing vesicles.…”

The interplay between exosomes and autophagy – partners in crime

“…Another report further demonstrated the possibility of amphisomes serving secretory functions in lung epithelial cells. Here, interferon-γ (IFN-γ)-induced autophagydependent exosome secretion of annexin A2 (ANXA2), which likely took place through amphisomes (Chen et al, 2017). IFN-γ treatment caused the colocalization of LC3B, CD63 and ANXA2 on amphisomes.…”

The Virtuous Cycle of Axon Growth: Axonal Transport of Growth‐Promoting Machinery as an Intrinsic Determinant of Axon Regeneration

“…Perhaps recycling autophagy (as opposed to degradative) is more suited to axon regeneration? There is strong evidence for the involvement of Rab11 in both the generation of the autophagosome (as mentioned above) and also in mediating traffic away from autophagosomes toward multivesicular bodies and exocytosis (Fader et al, ; Chen et al, ). Given the difference in Rab11 transport between non‐regenerative and regenerative axons, it may be that there are differences in the way autophagy functions in the axons of various neuronal types, that might contribute to their differential regenerative ability.…”