Platelet factor 4 selectively inhibits binding of TGF‐β₁ to the type I TGF‐β₁ receptor

Abstract

A low molecular weight inhibitor of TGF-beta 1 binding was detected in partially purified human platelet extracts by using Hep 3B hepatoma cells in the binding assays. The inhibitory protein was purified to homogeneity and was identified as platelet factor 4 on the basis of its amino acid sequence. TGF-beta 1 binding to Hep 3B cells was almost completely inhibited by 100 nM concentrations of platelet factor 4, but TGF-beta 1 binding to NRK 49F fibroblasts was inhibited only slightly. Affinity cross-linking experiments revealed that these differences in the inhibition of TGF-beta 1 binding by platelet factor 4 were due to differences in the complements of TGF-beta 1 binding proteins present on these two cell types. In Hep 3B cells the majority of bound TGF-beta 1 was cross-linked to a complex which had an apparent molecular weight of 70 kDa. TGF-beta 1 binding to this protein was the most sensitive to inhibition by platelet factor 4. Based on its size and TGF-beta 1 binding properties, we believe this protein is the type I TGF-beta 1 receptor. Hep 3B cells also had a high-affinity TGF-beta 1 binding protein which appeared as an 80 kDa complex, and which we believe to be the type II TGF-beta 1 receptor. TGF-beta 1 binding to this protein was not inhibited by platelet factor 4. TGF-beta 1 was also cross-linked to complexes of higher molecular weights in Hep 3B cells, but it was not clear whether any of them represented the type III TGF-beta 1 receptor. In NRK 49F cells, the majority of bound TGF-beta 1 was cross-linked to a high molecular weight complex which probably represented the type III TGF-beta 1 receptor. NRK 49F cells also had type I TGF-beta 1 receptors and platelet factor 4 inhibited binding to these receptors in the NRK cells. Since the type I receptor contributed only a small percentage of total TGF-beta 1 binding, however, the overall effects of platelet factor 4 on TGF-beta 1 binding to NRK 49F cells were negligible. We were unable to demonstrate specific or saturable binding of platelet factor 4 to Hep 3B cells using either direct binding or affinity cross-linking assays. Thus, it is not clear whether platelet factor 4 inhibits TGF-beta 1 binding by competition for binding to the type I receptor. Modest concentrations of TGF-beta 1 reduced the adherence of Hep 3B cells to tissue culture dishes.(ABSTRACT TRUNCATED AT 400 WORDS)

TGF‐β1 inhibits DNA synthesis and phosphorylation of the retinoblastoma gene product in a rat liver epithelial cell line

“…It remains a possibility that TGF-P, inhibits cell growth differently in different cell types. We have shown that TGF-6, inhibits the growth of human Hep 3B hepatoma cells in a novel manner that causes them to lose attachment to tissue culture flasks [27]. TGF-P, does not appear to inhibit pRb phosphorylation in this cell type (Whitson, unpublished results).…”

Autocrine transforming growth factor β1 blocks colony formation and progenitor cell generation by hemopoietic stem cells stimulated with steel factor

“…Although essentially all cells have high affinity receptors that specifically bind TGF-P, it remains uncertain to what extent binding proteins on the cell surface contribute in neutralizing TGF-P but without receptor-mediated intracellular signaling. Such constituents could be a subspecies of heparin molecules or related proteoglycans as betaglycan [35, 361, or proteins as platelet factor 4 that inhibit TGF-Pl binding to its type I TGF-P1 receptor [37]. It has been reported that the presence of serum is a requirement for the ability of SF + IL-I 1 to initiate colony formation in bone marrow cells from post-5-FU mice [ 1 11.…”

Specific Binding of the Chemokine Platelet Factor 4 to Heparan Sulfate

“…PF4 has been proposed to exert procoagulant activity by preventing the formation of the stable heparin-antithrombin III-thrombin ternary complex (2). It also inhibits binding of heparin-binding growth factors such as basic fibroblast growth factor, vascular endothelial growth factor (splice variant 165), and transforming growth factor ␤1 to their receptors (3)(4)(5) and is antiangiogenic, having been shown to inhibit proliferation and migration of endothelial cells in vitro (6). Subsequent studies demonstrated the ability of PF4 in vivo to specifically bind to areas of active angiogenesis (7) and to inhibit the growth of murine melanoma and colon carcinoma, probably as a result of suppressing tumor-induced neovascularization (8,9).…”