PROTECTION OF TRANSFORMING GROWTH-FACTOR-BETA-1 ACTIVITY BY HEPARIN AND FUCOIDAN

The transforming growth factor-beta (TGF-beta) family of proteins exer t diverse and potent effects on proliferation, differentiation, and ex tracellular matrix synthesis. However, relatively little is known abou t the stability or processing of endogenous TGF-beta activity in vitro or in vivo. Our previous work indicated that 1) TGF-beta1 has strong heparin-binding properties that were not previously recognized because of neutralization by iodination, and 2) heparin, and certain other po lyanions, could block the binding of TGF-beta1 to alpha2-macroglobulin (alpha2-M). The present studies investigated the influence of heparin -like molecules on the stability of the TGF-beta1 signal in the perice llular environment. The results indicate that heparin and fucoidan, a naturally occurring sulfated L-fucose polymer, suppress the formation of an initial non-covalent interaction between I-125-TGF-beta1 and act ivated alpha2-M. Electrophoresis of I-125-TGF-beta1 showed that fucoid an protects TGF-beta1 from proteolytic degradation by plasmin and tryp sin. While plasmin caused little, if any, activation of latent TGF-bet a derived from vascular smooth muscle cells (SMC), plasmin degraded ac id-activated TGF-beta, and purified TGF-beta1, and this degradation wa s inhibited by fucoidan. In vitro, heparin and fucoidan tripled the ha lf-life of I-125-beta1 and doubled the amount of cell-associated I-125 -TGF-beta1. Consistent with this protective effect, heparin- and fucoi dan-treated SMC demonstrated elevated levels of active, but not latent , TGF-beta activity. (C) 1994 Wiley-Liss, Inc.