The BAX-binding protein MOAP1 associates with LC3 and promotes closure of the phagophore

Abstract

MOAP1 (modulator of apoptosis 1) is a BAX-binding protein tightly regulated by the ubiquitinproteasome system. Apoptotic stimuli stabilize MOAP1 protein and facilitate its interaction with BAX to promote apoptosis. Here we show that in contrast to being resistant to apoptotic stimuli, MOAP1deficient cells are hypersensitive to cell death mediated by starvation rendered by EBSS treatment. MOAP1-deficient cells exhibited impairment in macroautophagy/autophagy signaling induced by EBSS. Mechanistic analysis revealed that MOAP1-deficient cells had no notable defect in the recruitment of the pre-autophagosomal phosphatidylinositol-3-phosphate (PtdIns3P)-binding proteins, ZFYVE1/DFCP1 and WIPI2, nor in the LC3 lipidation mechanism regulated by the ATG12-ATG5-ATG16L1 complex upon EBSS treatment. Interestingly, MOAP1 is required for facilitating efficient closure of phagophore in the EBSStreated cells. Analysis of LC3-positive membrane structures using Halo-tagged LC3 autophagosome completion assay showed that predominantly unclosed phagophore rather than closed autophagosome was present in the EBSS-treated MOAP1-deficient cells. The autophagy substrate SQSTM1/p62, which is normally contained within the enclosed autophagosome under EBSS condition, was also highly sensitive to degradation by proteinase K in the absence of MOAP1. MOAP1 binds LC3 and the binding is critically dependent on a LC3-interacting region (LIR) motif detected at its N-terminal region. Re-expression of MOAP1, but not its LC3-binding defective mutant, MOAP1-LIR, in the MOAP1-deficient cells, restored EBSS-induced autophagy. Together, these observations suggest that MOAP1 serves a distinct role in facilitating autophagy through interacting with LC3 to promote efficient phagophore closure during starvation.

Autophagosome Biogenesis

“…Although ESCRTs mediate the final closure of phagophores, several other proteins contribute to closure because they are involved in phagophore growth and shaping, which are essential prerequisites for eventual closure. For instance, members of the Atg8 family of ubiquitin-like proteins, which mediate phagophore expansion, are required for phagophore closure [82], and so are some of their regulators [83][84][85].…”

Revealing the Roles of MOAP1 in Diseases: A Review

“…Liu et al observed abnormal expression of BCL2 protein in NSCLC and showed that BCL2 and MCL1 amplification is related to drug resistance [ 32 ]. Chan et al found that MOAP1 can directly or indirectly interact with BCL2 family proteins, which promotes its role in lung cancer [ 15 ] ( Figure 2 ).…”

“…MOAP1 is recruited to p62 corpuscles by the induction of formation stimulated by cellular stress and reducing their levels independently of the autophagy pathway [ 14 ]. Interestingly, MOAP1 was found to be an LC3-binding protein, which plays a unique role in promoting autophagy by interacting with LC3 to promote efficient shutdown of autophagy during starvation [ 15 ].…”

p62/SQSTM1 in liver diseases: the usual suspect with multifarious identities

“…Point mutants of MOAP‐1 with exquisite function in regulating apoptosis or p62 bodies were identified, suggesting that functions of MOAP‐1 in regulating apoptosis and p62 bodies might be separable [73]. Moreover, MOAP‐1 was recently found to associate with LC3 and promote closure of the phagophore, thereby facilitating autophagy in the context of starvation mediated by nutrient withdrawal under EBSS condition [84]. Although disassembly of p62 bodies by MOAP‐1 does not appear to depend on autophagy [73], it remains possible that association of MOAP‐1 with LC3 may subsequently aid clearance of the remnants from the disassembled p62 bodies.…”