title: Arf6-independent GPI-anchored protein-enriched early endosomal compartments fuse with sorting endosomes via a Rab5/phosphatidylinositol-3'-kinase-dependent machinery.
abstract: In the process of internalization of molecules from the extracellular milieu, a cell uses multiple endocytic pathways, consequently generating different endocytic vesicles. These primary endocytic vesicles are targeted to specific destinations inside the cell. Here, we show that GPI-anchored proteins are internalized by an Arf6-independent mechanism into GPI-anchored protein-enriched early endosomal compartments (GEECs). Internalized GPI-anchored proteins and the fluid phase are first visualized in GEECs that are acidic, primary endocytic structures, negative for early endosomal markers, Rab4, Rab5, and early endosome antigen (EEA)1. They subsequently acquire Rab5 and EEA1 before homotypic fusion with other GEECs, and heterotypic fusion with endosomes containing cargo from the clathrin-dependent endocytic pathway. Although, the formation of GEECs is unaffected by inhibition of Rab5 GTPase and phosphatidylinositol-3'-kinase (PI3K) activity, their fusion with sorting endosomes is dependent on both activities. Overexpression of Rab5 reverts PI3K inhibition of fusion, providing evidence that Rab5 effectors play important roles in heterotypic fusion between the dynamin-independent GEECs and clathrin- and dynamin-dependent sorting endosomes.
authors.affiliation: National Centre for Biological Sciences, UAS-GKVK Campus, Bangalore 560065, India.
authors.forename: Manjula
authors.initials: M
authors.lastname: Kalia
authors.forename: Sudha
authors.initials: S
authors.lastname: Kumari
authors.forename: Rahul
authors.initials: R
authors.lastname: Chadda
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Hill
authors.forename: Robert G
authors.initials: RG
authors.lastname: Parton
authors.forename: Satyajit
authors.initials: S
authors.lastname: Mayor
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D015415:Biomarkers; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology; D005459:Fluorides / Q000494:pharmacology; D015870:Gene Expression; D005799:Genes, Dominant; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000378:metabolism; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; D017607:Aluminum Compounds; D015415:Biomarkers; D005459:Fluorides; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D019869:Phosphatidylinositol 3-Kinases; D033921:Vesicular Transport Proteins; D020695:rab4 GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins; C093846:early endosome antigen 1; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse; C032311:aluminum fluoride