Stabilin-1 and stabilin-2 are both directed into the early endocytic pathway in hepatic sinusoidal endothelium via interactions with clathrin/AP-2, independent of ligand binding.
Liver sinusoidal endothelial cells (LSECs) mediate clearance of hyaluronan (HA) and scavenger receptor ligands, for example, advanced glycation end product (AGE)-modified proteins and oxidized lipids from the circulation. We recently cloned stabilin-1 and -2, two members of a novel family of transmembrane proteins expressed in LSECs. By using primary LSECs and HEK293 cells separately expressing either stabilin, we have investigated their roles in the early events of endocytosis with respect to localization, ligand-binding properties, and associations with clathrin and adaptor protein (AP)-2. Both stabilins were present at the cell surface, although surface levels of stabilin-1 were limited. In addition, stabilins were present in early endosomal antigen (EEA)-1+ organelles colocalizing with endocytosed AGE-modified bovine serum albumin (BSA). Treating cells with monensin further pronounced this distribution. Recombinant stabilin-2, but not recombinant stabilin-1, bound HA and the scavenger receptor ligands AGE-modified BSA, formaldehyde-treated BSA, and collagen N-terminal propeptides. In LSECs, both stabilins were associated with clathrin and AP-2, but not with each other. These interactions did not change upon addition of exogenous HA, suggesting that stabilins are constitutively internalized. In conclusion, hepatic stabilins are both present in the early endocytic pathway, associating with clathrin/AP-2, but whereas stabilin-2 has a clear scavenging profile, stabilin-1 does not recognize these ligands.
Hansen
Berit
B
Department of Dermatology, University Medical Centre Mannheim, Ruprecht-Karls University Heidelberg, Mannheim, Germany.
Longati
Paola
P
Elvevold
Kjetil
K
Nedredal
Geir-Ivar
GI
Schledzewski
Kai
K
Olsen
Randi
R
Falkowski
Martin
M
Kzhyshkowska
Julia
J
Carlsson
Fredrik
F
Johansson
Staffan
S
Smedsrød
Bård
B
Goerdt
Sergij
S
Johansson
Sophie
S
McCourt
Peter
P
D000595:Amino Acid Sequence; D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D042783:Endothelial Cells / Q000378:metabolism*; D006820:Hyaluronic Acid / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D008985:Monensin / Q000633:toxicity; D051381:Rats; D016201:Receptors, Lymphocyte Homing; D013552:Swine; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism
D015816:Cell Adhesion Molecules, Neuronal; D002966:Clathrin; D004268:DNA-Binding Proteins; D016201:Receptors, Lymphocyte Homing; C449926:STAB1 protein, human; C449927:STAB2 protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D006820:Hyaluronic Acid; D008985:Monensin