[Restoration of growth contact inhibition in malignant melanocytes from man, mice, and hamsters].

Contact inhibition of growth is the in vitro property whose loss is most closely correlated with in vivo tumorigenicity. A contact inhibited line of hamster melanocytes produces a diffusible high molecular weight protein (melanocyte contact inhibitory factor, MCIF) which restores contact inhibition of growth to hamster malignant melanocytes. MCIF, extracted from culture medium of confluent contact-inhibited cultures, is now shown to restore the same capacity for in vitro growth regulation to malignant melanocytes of human and murine origins. In all 3 species MCIF produces characteristic changes in growth and morphology of cultures, with significant reductions of saturation densities. MCIF, the first protein identified which restores contact inhibition of growth to malignant cells, may be the prototype for a closely related class of surface-associated proteins concerned with regulation of normal cell-cell interactions leading to feedback inhibition of growth.