Characterization of a 150 kDa accessory receptor for TGF-β1 on keratinocytes: Direct evidence for a GPI anchor and ligand binding of the released form

✍ Scribed by B.Y.Y. Tam; D. Larouche; L. Germain; N.M. Hooper; A. Philip

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 312 KB
• Volume: 83
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.1074

✦ Synopsis

Abstract

Transforming growth factor‐β (TGF‐β) is a key modulator of epidermal development and homeostasis, and has been shown to potently regulate keratinocyte migration and function during wound repair. There are three cloned TGF‐β receptors termed type I, type II, and type III that are found on most cell types. The types I and II are the signaling receptors, while the type III is believed to facilitate TGF‐β binding to the types I and II receptors. Recently, we reported that in addition to these receptors, human keratinocytes express a 150 kDa TGF‐β1 binding protein (r150) which forms a heteromeric complex with the TGF‐β signaling receptors. This accessory receptor was described as glycosyl phosphatidylinositol‐specific anchored based on its sensitivity to phosphatidylinositol phospholipase C (PIPLC). In the present study, we demonstrate that the GPI‐anchor is contained in r150 itself and not on a tightly associated protein and that it binds TGF‐β1 with an affinity similar to those of the types I and II TGF‐β signaling receptors. Furthermore, the PIPLC released (soluble) form of this protein is capable of binding TGF‐β1 independently from the signaling receptors. In addition, we provide evidence that r150 is released from the cell surface by an endogenous phospholipase C. Our observation that r150 interacts with the TGF‐β signaling receptors, together with the finding that the soluble r150 binds TGF‐β1 suggest that r150 in either its membrane anchored or soluble form may potentiate or antagonize TGF‐β signaling. Elucidating the mechanism by which r150 functions as an accessory molecule in TGF‐β signaling may be critical to understanding the molecular mechanisms underlying the regulation of TGF‐β action in keratinocytes. J. Cell. Biochem. 83: 494–507, 2001. © 2001 Wiley‐Liss, Inc.