Characterization of a 60-kDa cell surface-associated transforming growth factor-beta binding protein that can interfere with transforming growth factor-beta receptor binding

We have characterized a 60-kDa transforming growth factor-P (TGF-p) binding protein that was originally identified on LNCaP adenocarcinoma prostate cells by affinity cross-linking of cell surface proteins by using l2Sl-TGF-p1. Binding of ,25i-TGF-p1 to the 60-kDa protein was competed by an excess of unlabeled TGFpl but not by TGF~p2, TGF~(33, activin, or osteogenic protein-1 (OP-1), also termed bone morphogenetic protein-7 (BMP-7). In addition/ no binding of 125lTGF-p2 and ;25l-TGF-p3 to the 60-kDa binding protein on LNCaP ceils could be demonstrated by using affinity labeling techniques. The 60-kDa TGF-p binding protein showed no immunoreactivity with antibodies against the known type I and type II receptors for members of the TGF-P superfamily. Treatment of LNCaP cells with 0.25 M NaCI, 1 iixg/ml heparin/ or 10 % glycerol caused a release of the 60-kDa protein from the cell surface. In addition/ we found that the previously described TGF-P type IV receptor on GH3 cells, which does not form a heteromeric complex with TGF-p receptors, could be released from the cell surface by these same treatments. This suggests that the 60-kDa protein and the similarly sized TGF-p type IV receptor are related proteins. The eluted 60-kDa LNCaP protein was shown to interfere with the binding of TGF-p to the TGF-p receptors, Thus, the cell surface-associated 60-kDa TGF-P binding protein may play a role in regulating TGF-p binding to TGF-P receptors. J. Cell. Physiol. 173:447-459, 1997. © 1997 Wiley-Liss, Inc,