Cellular heparan sulfate negatively modulates transforming growth factor-β1 (TGF-β1) responsiveness in epithelial cells

Cell-surface proteoglycans have been shown to modulate transforming growth factor ( TGF)-beta responsiveness in epithelial cells and other cell types. However, the proteoglycan ( heparan sulfate or chondroitin sulfate) involved in modulation of TGF-beta responsiveness and the mechanism by which it modulates TGF-beta responsiveness remain unknown. Here we demonstrate that TGF-beta(1) induces transcriptional activation of plasminogen activator inhibitor-1 ( PAI-1) and growth inhibition more potently in CHO cell mutants deficient in heparan sulfate ( CHO-677 cells) than in wild-type CHO-K1 cells. I-125-TGF-beta(1) affinity labeling analysis of cell-surface TGF-beta receptors reveals that CHO-K1 and CHO-677 cells exhibit low (<1) and high (>1) ratios of I-125-TGF-beta(1) binding to T beta R-II and T beta R-I, respectively. Receptor-bound I-125-TGF-beta(1) undergoes nystatin-inhibitable rapid degradation in CHO-K1 cells but not in CHO-677 cells. In Mv1Lu cells ( which, like CHO-K1 cells, exhibit nystatin-inhibitable rapid degradation of receptor-bound I-125-TGF-beta(1)), treatment with heparitinase or a heparan sulfate biosynthesis inhibitor results in a change from a low (< 1) to a high (>1) ratio of I-125-TGF-beta(1) binding to T beta R-II and T beta R-I and enhanced TGF-beta(1)-induced transcriptional activation of PAI-1. Sucrose density gradient analysis indicates that a significant fraction of T beta R-I and T beta R-II is localized in caveolae/lipid-raft fractions in CHO-K1 and Mv1Lu cells whereas the majority of the TGF-beta receptors are localized in non-lipid-raft fractions in CHO-677 cells. These results suggest that heparan sulfate negatively modulates TGF-beta 1 responsiveness by decreasing the ratio of TGF-beta 1 binding to T beta R-II and T beta R-I, facilitating caveolae/lipid-raft-mediated endocytosis and rapid degradation of TGF-beta 1, thus diminishing non-lipid-raft-mediated endocytosis and signaling of TGF-beta 1 in these epithelial cells.