ROLE OF CADHERINS IN THE TRANSENDOTHELIAL MIGRATION OF MELANOMA-CELLSIN CULTURE

Transmigration of cancer cells through the vascular endothelium (diape desis) is a key event in tumor metastasis. To investigate mechanisms i nvolved in diapedesis, we used laser scanning confocal microscopy to e xamine the distribution of cadherins of WM239 melanoma cells as they m igrated through a monolayer of activated human umbilical vein endothel ial cells (EC) cultured on matrigel. Cadherins, including VE-cadherin, but not N-cadherin, were enriched in contacts between EC, whereas N-c adherin, but not VE-cadherin, was found in contacts between melanoma c ells. During the early stages of diapedesis, EC located below the atta ched melanoma cells decreased in height and VE-cadherin disappeared fr om the EC contact located underneath the melanoma cell. Transendotheli al migration began with small melanoma cell processes penetrating the VE-cadherin-negative regions between the EC. Subsequently, melanoma ce lls became intercalated between EC. Despite the absence of both VE-cad herin and N-cadherin, other members of the cadherin family were presen t in the heterotypic contacts between EC and melanoma cells. EC surrou nding the intercalated melanoma cell subsequently extended processes a nd spread over the melanoma cell to re-form the endothelial monolayer. Interestingly, the leading margins of these EC processes contained hi gh levels of N-cadherin, but not VE-cadherin. VE-cadherin-rich cell-ce ll contacts, however reformed between advancing endothelial processes when they met above the melanoma cell. As the melanoma cells came into contact with the underlying matrigel, they spread out and adopted a f ibroblast-like morphology. Addition of anti-N-cadherin antibodies to t he assay resulted in a delay in the transendothelial migration of mela noma cells. Together, these results suggest that EC actively participa te in diapedesis by disassembling and reassembling VE-cadherin-rich ad herens junctions, and that N-cadherin plays an important role in the t ransmigration of melanoma cells and the reclosure of the endothelium. (C) 1997 Wiley-Liss, Inc.