Fas‐apoptotic inhibitory molecule 2 localizes to the lysosome and facilitates autophagosome‐lysosome fusion through the LC3 interaction region motif–dependent interaction with LC3

Abstract

Abbreviations: BafA1, bafilomycin A1; BI-1, bax inhibitor-1; CASP, caspase; ER, endoplasmic reticulum; FAIM2, Fas-apoptotic inhibitory molecule 2; GABARAP, GABA type A receptor-associated protein; IDPR, intrinsically disordered protein region; LIR, LC3-interacting region; MAP1LC3B, microtubuleassociated protein 1 light chain 3 beta; MTOR, mammalian target of rapamycin; shRNA, small hairpin RNA; STX17, syntaxin 17; TMBIM, transmembrane BAX inhibitor motif containing. AbstractFas-apoptotic inhibitory molecule 2 (FAIM2) is a member of the transmembrane BAX inhibitor motif-containing (TMBIM) family. TMBIM family is comprised of six anti-apoptotic proteins that suppress cell death by regulating endoplasmic reticulum Ca 2+ homeostasis. Recent studies have implicated two TMBIM proteins, GRINA and BAX Inhibitor-1, in mediating cytoprotection via autophagy. However, whether FAIM2 plays a role in autophagy has been unknown. Here we show that FAIM2 localizes to the lysosomes at basal state and facilitates autophagy through interaction with microtubule-associated protein 1 light chain 3 proteins in human neuroblastoma SH-SY5Y cells. FAIM2 overexpression increased autophagy flux, while autophagy flux was impaired in shRNA-mediated knockdown (shFAIM2) cells, and the impairment was more evident in the presence of rapamycin. In shFAIM2 cells, autophagosome maturation through fusion with lysosomes was impaired, leading to accumulation of autophagosomes. A functional LC3-interacting region motif within FAIM2 was essential for the interaction with LC3 and rescue of autophagy flux in shFAIM2 cells while LC3-binding property of FAIM2 was dispensable for the antiapoptotic function in response to Fas receptor-mediated apoptosis. Suppression of autophagosome maturation was also observed in a null mutant of Caenorhabditis elegans lacking xbx-6, the ortholog of FAIM2. Our study suggests that FAIM2 is a novel regulator of autophagy mediating autophagosome maturation through the interaction with LC3.

sc2MeNetDrug: A computational tool to uncover inter-cell signaling targets and identify relevant drugs based on single cell RNA-seq data

“…In the prediction of sc2MeNetDrug, we also identified several important genes related to autophagy ( Fig 4F ). Some have already been shown to be related to neuron degeneration and autophagy in AD like FAIM2 [ 27 ], BCL2 [ 28 ], and PRNP [ 29 ]. One hypothesis is that irregular autophagy stimulation results in increased amyloid-β production [ 30 ].…”

sc2MeNetDrug: A computational tool to uncover inter-cell signaling targets and identify relevant drugs based on single cell RNA-seq data

“…In the prediction of sc2MeNetDrug, we also identified several important genes related to autophagy ( Fig 4f ). Some have already been shown to be related to neuron degeneration and autophagy in AD like FAIM2 35 , BCL2 36 , and PRNP 37 . One hypothesis is that irregular autophagy stimulation results in increased amyloid-β production 38 .…”

Development of new tools to study lipidated mammalian ATG8

“…Our cellular assay showed that LIR(p62) or LIR(FAIM2) preferentially bind to the lipidated forms of LC3 subfamily proteins rather than GABARAP subfamily proteins on autophagic membranes, although they bind to all or none of the mATG8s in the non-lipidated form, respectively (Figures 1 and S1B-S1G). It has been consistently reported that p62 binds to both LC3B and GABARAP-L2 in the cytosol but only to LC3B in autophagic membranes, whereas FAIM2 only binds to lipidated LC3B (LC3B-II) via the LIR motif using co-IP experiments in cells 33,34 . Why then do some LIR motifs show different binding properties to mATG8 depending on its localization?…”