Interrelation of motility, cytoskeletal organization and gap junctional communication with invasiveness of melanocytic cells in vitro.

Intercellular communication and the active movement of malignant cells into and through host tissue barriers play a critical role during the complex process of tumor invasion. Motile activity, cytoskeletal actin and vinculin organization as well as gap junctional communication of in vivo benign and malignant melanocytes were compared and related to in vitro invasiveness. Normal melanocytes, Melan-a, showed significantly less motile activity, a higher organization of the actin cytoskeleton and more vinculin-containing cell-substratum adhesion plaques than highly metastatic melanoma cells, K1735-M2. There was no pronounced difference in gap junctional communication under comparable culture conditions. However, cultivation of Melan-a cells in a conventional melanocyte growth medium containing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) enhanced intercellular communication. Melanocytes were less invasive than melanoma cells both in the embryonic chick heart model and in the Matrigel invasion assay. The least invasive activity was determined for melanocytes cultivated in TPA-deficient medium indicating that the medium supplement TPA stimulates invasion. The comparison of certain in vitro properties of both melanocytic cell lines revealed a positive correlation of motility with in vitro invasion, whereas an inverse correlation was found for the degree of actin filament organization as well as for the number of vinculin plaques. Gap junctional communication was not directly related to in vitro invasiveness.