R. Butzow et al., A 60-KD PROTEIN MEDIATES THE BINDING OF TRANSFORMING GROWTH-FACTOR-BETA TO CELL-SURFACE AND EXTRACELLULAR-MATRIX PROTEOGLYCANS, The Journal of cell biology, 122(3), 1993, pp. 721-727
The biological activity of many cytokines is regulated by binding prot
eins present at the cell surface, in extracellular matrices or in solu
ble phase. We describe here a TGF-beta binding protein that is both an
extracellular matrix and a cell surface protein. When intact extracel
lular matrices of HEP-G2 cells were affinity cross-linked with I-125-T
GF-beta1, two major binding components were seen: a 250-kD, proteoglyc
an-like molecule, presumed to be betaglycan, and a 60-kD protein. The
60-kD TGF-beta-binding protein was also present at the cell surface. I
t could be released from the cell surface by treating cells with high
salt, heparin, chondroitin sulfate, heparitinase, or chondroitinase, i
ndicating that it is bound to heparan sulfate and chondroitin sulfate
proteoglycans. The 60-kD protein bound TGF-beta1 with an apparent diss
ociation constant of 1.6 nM, and there were 30,000 binding sites per c
ell at the cell surface. In addition to the HEP-G2 cells and another h
epatoma cell line, the 60-kD protein was also found in a human colon c
arcinoma (HT-29) cell line but not in rat kidney (NRK-49F) or human fi
broblast (HUT-12) cell lines. The 60-kD protein could be extracted fro
m cells containing it and transferred to the surface of previously neg
ative cells. The 60-kD protein may serve to regulate the binding of TG
F-beta to its signal transducing receptors by targeting TGF-beta to ap
propriate locations in the microenvironment of cells.