Cell biology: Receptors for selective recycling.

Abstract

Two studies show that the engulfment of certain intracellular membranous structures by vesicles called autophagosomes regulates the structures' degradation in a selective, receptor-protein-mediated manner. See Letters p.354 & p.359 The endoplasmic reticulum (ER) is a complex network of membranes involved in protein and lipid synthesis, ion homeostasis, protein quality control and organelle communication. It is also a source of membrane-bounded vesicles called autophagosomes, the vehicles for the self-digesting cellular process of autophagy. Two papers published online this week [in this issue of Nature] show how the ER itself is targeted for degradation by autophagy — a process that could ensure constant ER turnover in response to cellular requirements. Ivan Dikic and coworkers find the protein FAM134B is an ER-resident receptor that facilitates 'ER-phagy'. Downregulation of this protein — mutations of which can cause sensory neuropathy in humans — resulted in expanded ER structures and degeneration of mouse sensory neurons. Hitoshi Nakatogawa and colleagues show that the same phenomenon is conserved in yeast, where Atg40 is enriched in the cortical and cytoplasmic ER, loading these ER subdomains into autophagosomes. A further ER-phagy receptor, Atg39, localizes to the perinuclear ER (or the nuclear envelope) and induces autophagic sequestration of a part of the nucleus, thus ensuring cell survival under nitrogen-deprived conditions.