Coexpression of tumor-associated α2-macroglobulin and growth factors in human melanoma cell lines

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Abstract
α2‐Macroglobulin (α2M) is known as an inhibitor of various proteinases and to bind several of the growth factors. We previously demonstrated that clonal variation existsin the production of α2M 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‐α TGF‐β, PDGF‐A chain, PDGF‐B chain, and tumor‐associated α2M. In Northern blot analysis TGF‐α was detected in four of the cell lines, TGF‐β in all, PDGF‐A chain in three, and PDGF‐B chain in none of the cell lines. α2M, 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 α2‐macroglobulin, secreted by these tumor cell lines, is a significant modulator of melanoma cell growth.