Endocytic Sorting and Recycling Require Membrane Phosphatidylserine Asymmetry Maintained by TAT-1/CHAT-1

Abstract

Endocytic sorting is achieved through the formation of morphologically and functionally distinct sub-domains within early endosomes. Cargoes destined for recycling are sorted to and transported through newly-formed tubular membranes, but the processes that regulate membrane tubulation are poorly understood. Here, we identified a novel Caenorhabditis elegans Cdc50 family protein, CHAT-1, which acts as the chaperone of the TAT-1 P4-ATPase to regulate membrane phosphatidylserine (PS) asymmetry and endocytic transport. In chat-1 and tat-1 mutants, the endocytic sorting process is disrupted, leading to defects in both cargo recycling and degradation. TAT-1 and CHAT-1 colocalize to the tubular domain of the early endosome, the tubular endocytic recycling compartment (ERC), and the recycling endosome where PS is enriched on the cytosolic surface. Loss of tat-1 and chat-1 function disrupts membrane PS asymmetry and abrogates the tubular membrane structure. Our data suggest that CHAT-1 and TAT-1 maintain membrane phosphatidylserine asymmetry, thus promoting membrane tubulation and regulating endocytic sorting and recycling.

Lipid flippase modulates olfactory receptor expression and odorant sensitivity in Drosophila

“…In yeast, the major phenotype associated with loss of P4-ATPase function is abnormal transport vesicle budding from the transgolgi network (19,33,34). Similar defects in cargo sorting have been observed in Caenorhabditis elegans Tat-1 mutants (35), and other C. elegans P4-ATPase mutants are defective for phagocytosis of dead cells and regulation of ectosome production (35)(36)(37)(38). Proper lipid localization may be required for vesicle docking or receptor recycling leading to reduced receptor levels in the cilia.…”

The Intestinal Copper Exporter CUA-1 Is Required for Systemic Copper Homeostasis in Caenorhabditis elegans

“…P vha-6 ::CUA-1.1::GFP localized to basolateral membranes and to intracellular compartments, reminiscent of basolateral sorting and recycling endosomes in the C. elegans intestine (Fig. 4A) (29). Importantly, the embryonic lethal phenotype of cua-1 (ok904) mutant can be rescued by intestine-specific expression of CUA-1.1::GFP (Fig.…”

SEC-10 and RAB-10 coordinate basolateral recycling of clathrin-independent cargo through endosomal tubules in Caenorhabditis elegans

“…3B). To confirm the endosomal identity of this tubular network, the mCherry-TRAM transgene, which labels the endosomal reticulum (ER) (35,36), was introduced into hTAC-GFP transgenic worms (Fig. S4).…”

“…To verify the generality of our finding, we further examined two other endogenous CIE cargo proteins: GLUT1 and DAF-4 (dauer formation-defective-4), the C. elegans homolog of type II BMP (bone morphogenetic protein) receptor. Both proteins are CIE cargoes that are transported via the Arf6-associated itinerary (2,35,41). As shown in Fig.…”