LAK cells release a novel form of directly acting TGF beta, tightly bound to a high molecular weight carrier(s).

We showed in previous work that LAK cell supernatants contain a large molecular weight factor with toxic activity for A375 melanoma and other cell lines. The factor, Fr1, was identified tentatively as TGF beta-related, since its activity was abolished by anti-TGF beta serum. This relatedness is further confirmed in the present work, which demonstrates that, like TGF beta, Fr1 stimulates the release and deposition of fibronectin and induces morphological changes indistinguishable from those induced by TGF beta. The TGF beta derived from LAK cells, although associated with a large carrier molecule, is directly acting and does not dissociate from its carrier following gel filtration in acetic acid. Its carrier is different from alpha-2 macroglobulin. SDS-PAGE and immunoblotting showed that FR1 contains TGF beta complexed with large molecules (150 and > 200 kDa), which dissociate in reduced gels to molecules of 60-67 kDa. We interpret these data as showing that TGF beta secreted by LAK cells is, presumably, covalently linked to monomeric carrier molecules of approximately 60 kDa, which, in turn, are S-S bonded to form multimeric molecules of 150 kDa and > 200 kDa.