A WD-domain protein that is associated with and phosphorylated by the type II TGF-β receptor

Abstract

TRANSFORMING growth factor-β (TGF-β) is the prototype for a family of extracellular polypeptides that affect cell proliferation and differentiation, and tissue morphogenesis1. TGF-β signalling is mediated by two types of serine/threonine kinase receptors, the type I and II receptors, which are able to form a heteromeric complex2. No cytoplasmic proteins that associate with these receptors in vivo, or are their kinase targets, have yet been described. We have now identified a WD-domain-containing protein, TRIP-1, which specifically associates with the type II TGF-β receptor in a kinase-dependent way. TRIP-1 does not interact with the type II activin or type I receptors, but associates with the heteromeric TGF-β receptor complex. TRIP-1 is phosphorylated on serine and threonine by the receptor kinase, strongly suggesting that it has a role in TGF-β signalling. This is supported by coexpression of TRIP-1 and type II receptor during development. The existence of TRIP-1 homologues in plant and yeast suggests a conserved function in all eukaryotes. © 1995, Nature Publishing Group. All Rights Reserved.