Internalization but not binding of thrombospondin-1 to low density lipoprotein receptor-related protein-1 requires heparan sulfate proteoglycans

✍ Scribed by Shuxia Wang; Mary E. Herndon; Sripriya Ranganathan; Svetlana Godyna; Jack Lawler; W. Scott Argraves; Gene Liau

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 197 KB
• Volume: 91
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.10781

✦ Synopsis

Abstract

The amino‐terminal domain of the extracellular matrix (ECM) protein thrombospondin‐1 (TSP‐1) mediates binding to cell surface heparan sulfate proteoglycans (HSPG) as well as binding to the endocytic receptor, low density lipoprotein‐related protein (LRP‐1). We previously found that recombinant TSP‐1 containing the amino‐terminal residues 1–214, retained both of these interactions (Mikhailenko et al. [1997]: J Biol Chem 272:6784–6791). Here, we examined the activity of a recombinant protein containing amino‐terminal residues 1–90 of TSP‐1 and found that this domain did not retain high‐affinity heparin‐binding. The loss of heparin‐binding correlated with decreased binding to the fibroblast cell surface. However, both ligand blotting and solid phase binding studies indicate that this truncated fragment of TSP‐1 retained high‐affinity binding to LRP‐1. Consistent with this, it also retained the ability to block the uptake and degradation of ^125^I‐TSP‐1. However, TSP‐1~1–90~ itself was poorly endocytosed and this truncated amino‐terminal domain was considerably more effective than the full‐length heparin‐binding domain (HBD) of TSP‐1 in blocking the catabolism of endogenously expressed TSP‐1. These results indicate that TSP‐1 binding to LRP‐1 does not require prior or concomitant interaction with cell surface HSPG but suggest subsequent endocytosis requires high‐affinity heparin‐binding. © 2004 Wiley‐Liss, Inc.