Clathrin-independent carriers form a high capacity endocytic sorting system at the leading edge of migrating cells.
Although the importance of clathrin- and caveolin-independent endocytic pathways has recently emerged, key aspects of these routes remain unknown. Using quantitative ultrastructural approaches, we show that clathrin-independent carriers (CLICs) account for approximately three times the volume internalized by the clathrin-mediated endocytic pathway, forming the major pathway involved in uptake of fluid and bulk membrane in fibroblasts. Electron tomographic analysis of the 3D morphology of the earliest carriers shows that they are multidomain organelles that form a complex sorting station as they mature. Proteomic analysis provides direct links between CLICs, cellular adhesion turnover, and migration. Consistent with this, CLIC-mediated endocytosis of key cargo proteins, CD44 and Thy-1, is polarized at the leading edge of migrating fibroblasts, while transient ablation of CLICs impairs their ability to migrate. These studies provide the first quantitative ultrastructural analysis and molecular characterization of the major endocytic pathway in fibroblasts, a pathway that provides rapid membrane turnover at the leading edge of migrating cells.
Howes
Mark T
MT
The Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia.
Kirkham
Matthew
M
Riches
James
J
Cortese
Katia
K
Walser
Piers J
PJ
Simpson
Fiona
F
Hill
Michelle M
MM
Jones
Alun
A
Lundmark
Richard
R
Lindsay
Margaret R
MR
Hernandez-Deviez
Delia J
DJ
Hadzic
Gordana
G
McCluskey
Adam
A
Bashir
Rumasia
R
Liu
Libin
L
Pilch
Paul
P
McMahon
Harvey
H
Robinson
Phillip J
PJ
Hancock
John F
JF
Mayor
Satyajit
S
Parton
Robert G
RG
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D015415:Biomarkers / Q000378:metabolism; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002465:Cell Movement / Q000502:physiology*; D016764:Cell Polarity; D002966:Clathrin / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism
D015415:Biomarkers; D051242:Caveolin 1; D002966:Clathrin