Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 283, Issue 25, Pages 17341-17350Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M710360200
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- NIGMS NIH HHS [GM69961, R01 GM069961] Funding Source: Medline
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The hyaluronic acid receptor for endocytosis (HARE; also designated Stabilin-2) mediates systemic clearance of hyaluronan and chondroitin sulfates from the vascular and lymphatic circulations. The internalized glycosaminoglycans are degraded in lysosomes, thus completing their normal turnover process. Sinusoidal endothelial cells of human liver, lymph node, and spleen express two HARE isoforms of 315 and 190 kDa. Here we report that the 190- and 315-kDa HARE isoforms, expressed stably either in Flp-In 293 cell lines or as soluble ectodomains, specifically bind heparin (Hep). The K-d for Hep binding to purified 190- and 315-kDa HARE ectodomains was 17.2 +/- 4.9 and 23.4 +/- 5.3 nM, respectively. Cells expressing HARE readily and specifically internalized I-125-streptavidin-biotin-Hep complexes, which was inhibited > 70% by hyperosmolar conditions, confirming that uptake is mediated by the clathrin-coated pit pathway. Internalization of Hep occurred for many hours with an estimated HARE recycling time of similar to 12 min. Internalized fluorescent streptavidin-biotin-Hep was present in a typical endocytic vesicular pattern and was delivered to lysosomes. We conclude that HARE in the sinusoidal endothelial cells of lymph nodes and liver likely mediates the efficient systemic clearance of Hep and many different Hep-binding protein complexes from the lymphatic and vascular circulations.
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