Paracrine and autocrine regulation of human melanocyte and melanoma cell growth by transforming growth factor beta in vitro.

It has been considered that the growth of human melanoma cells is positively and negatively regulated by transforming growth factors. To investigate further the role of transforming growth factor beta (TGF-beta) in melanoma biology, we analysed paracrine and autocrine growth regulatory properties of TGF-beta in normal human melanocytes and malignant melanoma cell lines in vitro. Exogenously added TGF-beta 1 potently inhibited normal melanocyte proliferation and DNA-synthesis in all cultures examined; in contrast, TGF-beta 1 inhibited only moderately or not at all the growth of cultured melanoma cells. Melanoma cell lines established from metastatic lesions were found to be less sensitive to TGF-beta 1 than those derived from primary melanomas. TGF-beta 1 resistance correlated with high levels of active TGF-beta secreted by metastatic cell lines. Inactivation of endogenously produced TGF-beta by neutralizing anti-TGF-beta antibody resulted in the stimulation of cell proliferation of a TGF-beta-sensitive primary melanoma cell line but not of a resistant metastatic one. These findings suggest that TGF-beta may function as a paracrine and autocrine growth inhibiting factor in the growth regulation of human melanocytic cells. The gradual loss of response of melanocytic cells to TGF-beta during malignant progression suggests that escape of melanoma cells from growth regulation by TGF-beta could be involved in melanoma oncogenesis.