Coexpression of tumor-associated alpha 2-macroglobulin and growth factors in human melanoma cell lines.

alpha 2-Macroglobulin (alpha 2M) is known as an inhibitor of various proteinases and to bind several of the growth factors. We previously demonstrated that clonal variation exists in the production of alpha 2M in a human melanoma and that this variation may be associated with growth stimulation. We have now analyzed six human melanoma cell lines for the simultaneous expression of TGF-alpha, TGF-beta, PDGF-A chain, PDGF-B chain, and tumor-associated alpha 2M. In Northern blot analysis TGF-alpha was detected in four of the cell lines, TGF-beta in all, PDGF-A chain in three, and PDGF-B chain in none of the cell lines. alpha 2M, detected by immunoblotting, varied significantly between the different melanoma cell lines and only one cell line was found to be negative. Evaluation of growth-promoting activity in conditioned media suggested that alpha 2-macroglobulin, secreted by these tumor cell lines, is a significant modulator of melanoma cell growth.