Plasma membrane contributes to the formation of pre-autophagosomal structures

Abstract

Autophagy is a catabolic process where lysosomes degrade intracytoplasmic contents transported in double-membraned autophagosomes. Autophagosomes are formed by elongation and fusion of phagophores, which derive from pre-autophagosomal structures. The membrane origins of autophagosomes are unclear and may involve multiple sources, including the endoplasmic reticulum and mitochondria. Here we show in mammalian cells that clathrin heavy-chain interacts with Atg16L1, and is involved in the formation of Atg16L1-positive early autophagosome precursors. Inhibition of clathrin-mediated internalisation reduced the formation of both Atg16L1-positive precursors and mature autophagosomes, while Atg16L1 associated with clathrin-coated structures. We tested and demonstrated that the plasma membrane (PM) directly contributes to the formation of early Atg16L1-positive autophagosome precursors. This may be particularly important during periods of increased autophagosome formation, as the plasma membrane may serve as a large membrane reservoir that allows cells periods of autophagosome synthesis at levels many-fold higher than under basal conditions, without compromising other processes.

Interaction between autophagic vesicles and the Coxiella-containing vacuole requires CLTC (clathrin heavy chain)

“…CLTC is also present on mature autophagosomes, colocalizing with LC3B during initiation of autophagy [22]. Additionally, given that CLTC has been shown to interact with ATG16L1, which mediates earlier stages of autophagosome development, it is possible that CLTC may also contribute to other stages of autophagy [20]. In this study, Coxiella is used as a tool to demonstrate that fusion of autophagosomes with lysosomes involves CLTC.…”

“…A link between CLTC and autophagy has recently been discovered with the observation that CLTC is required both for autophagosome formation and in the later stages for regulation of autophagic lysosomal reformation [20,21]. In addition, it has been reported that CLTC colocalizes with LC3B upon induction of autophagy [22].…”

“…In addition, it has been reported that CLTC colocalizes with LC3B upon induction of autophagy [22]. CLTC has also been shown to bind ATG16L1 (autophagy related 16 like 1), an essential protein in the autophagy process, and OCRL (inositol polyphosphate-5-phosphatase), a protein that colocalizes with lysosomes upon induction of autophagy [20,23]. Hence, there is a growing body of research that indicates a role for CLTC in autophagy, although the functional role of CLTC at autophagosomes remains unknown.…”

Phospholipase D1 regulates autophagic flux and clearance of α-synuclein aggregates

“…Membranes derived from the Golgi, endoplasmic reticulum, mitochondria, and plasma membrane have been implicated as the source membranes. [20][21][22][23][24][25] It is possible that vesicles from multiple membrane sources may fuse heterotypically to generate APs. This early fusion steps may involve lipidhydrolyzing enzymes, possibly PLD.…”

Autophagy at the crossroads of catabolism and anabolism

“…Although evidence supports the idea that nucleation of the isolation membrane occurs at a distinct site emanating from the endoplasmic reticulum (ER), termed the omegasome 17 , other sources of membrane contribute to autophagosome formation, including ER-Golgi intermediate compartments, ERmitochondri a junctions, mitochondria, endosomes and the plasma membrane [17][18][19][20][21][22] . Taken together, these studies highlight the complexities of autophagy initiation in mammals.…”