Direct action of a protein-bound polysaccharide, PSK, on transforming growth factor-beta.

We investigated the action of a protein-bound polysaccharide, PSK, on transforming growth factor-beta (TGF-beta). (1) In in vitro-mixed culture of peripheral blood mononuclear cells (PBMC) from healthy human and mitomycin C-treated human colon cancer cells, PSK or polyclonal antibody to TGF-beta significantly enhanced incorporation of 3H-thymidine into PBMC, and apparently decreased TGF-beta1 levels of acid-treated culture supernatant. (2) PSK or the antibody interfered with the quantitation by enzyme immunoassay of TGF-beta1 in acid-treated supernatant of the mixed culture. (3) PSK was suggested to form a complex with 125I-human recombinant TGF-beta1 standard, when changes in molecular weight of radioactivities were assessed by gel filtration. Recombinant human TGF-beta1 inhibited growth of mink lung epithelial cell line Mv1Lu and promoted collagen synthesis in rat kidney fibroblast cell line NRK49F, but the complex did not have such activities. (4) In addition to TGF-beta1, PSK bound with TGF-beta2 and platelet-derived growth factor; however, PSK did not bind with 22 other species of cytokines and growth factors. (5) Protein moiety of PSK is suggested to play an important role in the expression of the activity. These results suggest that PSK modulates the biological activity of TGF-beta1 by binding to its active form.