A novel requirement for C. elegans Alix/ALX-1 in RME-1-mediated membrane transport.
BACKGROUND
Alix/Bro1p family proteins have recently been identified as important components of multivesicular endosomes (MVEs) and are involved in the sorting of endocytosed integral membrane proteins, interacting with components of the ESCRT complex, the unconventional phospholipid LBPA, and other known endocytosis regulators. During infection, Alix can be co-opted by enveloped retroviruses, including HIV, providing an important function during virus budding from the plasma membrane. In addition, Alix is associated with the actin cytoskeleton and might regulate cytoskeletal dynamics.


RESULTS
Here we demonstrate a novel physical interaction between the only apparent Alix/Bro1p family protein in C. elegans, ALX-1, and a key regulator of receptor recycling from endosomes to the plasma membrane, called RME-1. The analysis of alx-1 mutants indicates that ALX-1 is required for the endocytic recycling of specific basolateral cargo in the C. elegans intestine, a pathway previously defined by the analysis of rme-1 mutants. The expression of truncated human Alix in HeLa cells disrupts the recycling of major histocompatibility complex class I, a known Ehd1/RME-1-dependent transport step, suggesting the phylogenetic conservation of this function. We show that the interaction of ALX-1 with RME-1 in C. elegans, mediated by RME-1/YPSL and ALX-1/NPF motifs, is required for this recycling process. In the C. elegans intestine, ALX-1 localizes to both recycling endosomes and MVEs, but the ALX-1/RME-1 interaction appears to be dispensable for ALX-1 function in MVEs and/or late endosomes.


CONCLUSIONS
This work provides the first demonstration of a requirement for an Alix/Bro1p family member in the endocytic recycling pathway in association with the recycling regulator RME-1.
Shi
Anbing
A
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854, USA.
Pant
Saumya
S
Balklava
Zita
Z
Chen
Carlos Chih-Hsiung
CC
Figueroa
Vanesa
V
Grant
Barth D
BD
D000818:Animals; D030801:Animals, Genetically Modified; D001693:Biological Transport, Active / Q000235:genetics; D017173:Caenorhabditis elegans / Q000235:genetics / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004705:Endocytosis / Q000235:genetics; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D018398:Homeodomain Proteins; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000737:chemistry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
C109773:ALX-1 protein, C elegans; C525389:BRO-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D018398:Homeodomain Proteins; D008565:Membrane Proteins; C486205:RME-1 protein, C elegans; D012097:Repressor Proteins; D033921:Vesicular Transport Proteins