A role for heterologous gap junctions between melanoma and endothelial cells in metastasis

F10 and BL6 sublines of B16 mouse melanoma cells are metastatic after intra venous injection, but only BLG cells are metastatic after subcutaneous inje ction. We found that connexin (Cx) 26 is unpregulated in BL6 cells. To exam ine gap junction formation, we devised a coculture system, in which an open ed vein segment was placed at the bottom ofa culture dish and then dye-labe led melanoma cells were seeded onto it. Immunohistochemistry indicated that the vein segment preserved the integrity of the endothelial monolayer. In this system, BL6 cells could transfer dye into endothelial cells but F10 ce lls could not. Transfection with wild-type Cx26 rendered F10 cells competen t for coupling with endothelial cells and as spontaneously metastatic as BL G cells. Conversely, transfection with a dominant-negative form of Cx26 ren dered BL6 cells deficient in coupling and less metastatic. In human melanom a lesions, the level of Cx26 expression was low in melanoma cells residing in the basal layer, but significantly upregulated in melanoma cells invadin g the dermis, The results suggested that Cx26 plays a role in intravasation and extravasation of tumor cells through heterologous gap junction formati on with endothelial cells.