The GTPase-activating protein GRAF1 regulates the CLIC/GEEC endocytic pathway.
Clathrin-independent endocytosis is an umbrella term for a variety of endocytic pathways that internalize numerous cargoes independently of the canonical coat protein Clathrin [1, 2]. Electron-microscopy studies have defined the pleiomorphic CLathrin-Independent Carriers (CLICs) and GPI-Enriched Endocytic Compartments (GEECs) as related major players in such uptake [3, 4]. This CLIC/GEEC pathway relies upon cellular signaling and activation through small G proteins, but mechanistic insight into the biogenesis of its tubular and tubulovesicular carriers is lacking. Here we show that the Rho-GAP-domain-containing protein GRAF1 marks, and is indispensable for, a major Clathrin-independent endocytic pathway. This pathway is characterized by its ability to internalize bacterial exotoxins, GPI-linked proteins, and extracellular fluid. We show that GRAF1 localizes to PtdIns(4,5)P2-enriched, tubular, and punctate lipid structures via N-terminal BAR and PH domains. These membrane carriers are relatively devoid of caveolin1 and flotillin1 but are associated with activity of the small G protein Cdc42. This study provides the first specific noncargo marker for CLIC/GEEC endocytic membranes and demonstrates how GRAF1 can coordinate small G protein signaling and membrane remodeling to facilitate internalization of CLIC/GEEC pathway cargoes.
Lundmark
Richard
R
Medical Research Council, Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH, UK. richard.lundmark@medchem.umu.se
Doherty
Gary J
GJ
Howes
Mark T
MT
Cortese
Katia
K
Vallis
Yvonne
Y
Parton
Robert G
RG
McMahon
Harvey T
HT
D000818:Animals; D004705:Endocytosis / Q000235:genetics / Q000502:physiology*; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D050356:Lipid Metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D017434:Protein Structure, Tertiary; D051381:Rats; D015398:Signal Transduction
D020690:GTPase-Activating Proteins