IFN-γ-induced autophagy is regulated by S100A10 and required for exophagy of annexin A2

Abstract

During the process of autophagy the autophagy-related (ATG) proteins are translocated to autophagosome formation sites In this study we demonstrate that S100A10 is required for ULK1 localization to autophagosome formation sites Silencing of S100A10 reduces IFN-γ-induced autophagosome formation We also determined the role of annexin A2 (ANXA2) a binding protein of S100A10 which has been reported to promote phagophore assembly Silencing of ANXA2 reduced S100A10 expression However overexpression of S100A10 in ANXA2-silenced cells was still able to enhance autophagosome formation suggesting that ANXA2 regulates IFN-γ-induced autophagy through S100A10 We also observed that S100A10 interacted with ULK1 after IFN-γ stimulation and S100A10 knockdown prevented ULK1 localization to autophagosome formation sites The release of HMGB1 was inhibited in S100A10 knockdown cells These results elucidate the importance of S100A10 in autophagosome formation and reveal the relationship between S100A10 and ULK1 in IFN-γ-induced autophagy We previously demonstrated that IFN-γ-triggered ANXA2 secretion is associated with exosomal release Furthermore S100A10 is required for IFN-γ-induced unconventional exosome secretion of ANXA2 Therefore we investigated the potential roles of IFN-γ-induced autophagic pathway in exosomal secretion of ANXA2 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 the regulation of S100A10 in IFN-γ-induced autophagy and a novel route of IFN-γ-induced exophagy of ANXA2 Connecting the two findings IFN-γ-induced S100A10 interacts with ULK1 to trigger autophagosome formation and then ANXA2 is engulfed by autophagosome ANXA2-containing autophagosome fuses with MVB and further fuses with the plasma membrane to release ANXA2-containing exosomes Therefore ANXA2 translocates to cell surface to enhance efferocytosis Efferocytosis is important in prevention of autoimmune and inflammatory disorders Furthermore HMGB1 is associated with the regulation of chronic in?ammation Therefore our results indicate that S100A10-mediated autophagy as well as exophagy of ANXA2 may contribute to immune system balance

Date of Award	2016 Dec 13
Original language	English
Supervisor	Yee-Shin Lin (Supervisor)