Role of cadherins in the transendothelial migration of melanoma cells in culture.

Transmigration of cancer cells through the vascular endothelium (diapedesis) is a key event in tumor metastasis. To investigate mechanisms involved in diapedesis, we used laser scanning confocal microscopy to examine the distribution of cadherins of WM239 melanoma cells as they migrated through a monolayer of activated human umbilical vein endothelial cells (EC) cultured on matrigel. Cadherins, including VE-cadherin, but not N-cadherin, were enriched in contacts between EC, whereas N-cadherin, but not VE-cadherin, was found in contacts between melanoma cells. During the early stages of diapedesis, EC located below the attached melanoma cells decreased in height and VE-cadherin disappeared from the EC contact located underneath the melanoma cell. Transendothelial migration began with small melanoma cell processes penetrating the VE-cadherin-negative regions between the EC. Subsequently, melanoma cells became intercalated between EC. Despite the absence of both VE-cadherin and N-cadherin, other members of the cadherin family were present in the heterotypic contacts between EC and melanoma cells. EC surrounding the intercalated melanoma cell subsequently extended processes and spread over the melanoma cell to re-form the endothelial monolayer. Interestingly, the leading margins of these EC processes contained high levels of N-cadherin, but not VE-cadherin. VE-cadherin-rich cell-cell 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 fibroblast-like morphology. Addition of anti-N-cadherin antibodies to the assay resulted in a delay in the transendothelial migration of melanoma cells. Together, these results suggest that EC actively participate in diapedesis by disassembling and reassembling VE-cadherin-rich adherens junctions, and that N-cadherin plays an important role in the transmigration of melanoma cells and the reclosure of the endothelium.