| Autophagy,an evolutionally conserved and lysosome-mediated degradation pathway in eukaryotic cells,is the major quality control machinery to maintaining homeostasis through clearing the misfolded protein aggregates and the dysfunctional organelles.In this process,isolation membranes derived from the endoplasmic reticulum membranes in cells,expanse and elongate to form the double-membrane autophagosomes which sequestrate the intracellular materials,and then fuse with lysosome for digestion.There is emerging evidence has revealed that the microtubule-associated protein 1 light chain 3(MAP1LC3/LC3)which is the mammalian homolog of yeast Atg8,playing a pivotal role in autophagosomes biogenesis.Recent study has found that the nuclear pool and the nucleus-to-cytoplasm translocation of LC3 are required for the autophagosome biogenesis in mammalian cells.In starved cells,nuclear deacetylated-LC3 interacts with TP53INP2,which redistributes LC3 into cytoplasm for lipidation.Intriguingly,after shifting to the cytoplasm,TP53INP2 can associate with autophagosome,suggesting that TP5 3INP2 has a role in autophagy regulation beside carrying deacetylated-LC3 out of the nucleus.In this study,we find that in the cytoplasm,TP5 3INP2 further contributes to autophagosome formation by promoting LC3-ATG7 binding.Expression of cytoplasm-located N-terminal region of TP53IINP2,which contains the LC3-interacting region,significantly induced LC3-PE generation and autophagosome formation.In the cytoplasm,TP53INP2 colocalized to preautophagosomal membrane structures including ULK1,BECN1 or DFCP1.However,deletion of TP53INP2 did not affect the formation of these structures,knockout of BECNI or Atg5,or mutations disrupting TP53INP2 from LC3 interaction,inhibited the membrane binding of TP53INP2.In the cytoplasm,TP53INP2 direct interacts with ATG7 to form an LC3-TP53INP2-ATG7 heterocomplex.Impairment of TP53INP2-LC3 or TP53INP2-ATG7 binding effectively reduced LC3-ATG7 interaction.Taking together,our results have identified that by shifting from the nucleus to the cytoplasm,TP53INP2 is targeted to preautophagosomal membranes accompanied by LC3,where it facilitates autophagosome formation by enhancing LC3-ATG7 interaction. |
