Regulatory role of tetraspanin CD9 in tumor-endothelial cell interaction during transendothelial invasion of melanoma cells

Heterotypic interaction among tumor cells (TCs) and endothelial cells (ECs) may play a critical role during the vascular dissemination of neoplastic c ells and during pathologic angiogenesis in tumors. To identify molecules in volved in these processes, the distribution of vascular junctional proteins was first studied by immunofluorescence at sites of heterologous intercell ular contact using TC-EC mosaic monolayers grown on 2-dimensional collagen. Several members of the tetraspanin superfamily, including CD9, CD81, and C D151, were found to localize at the TC-EC contact area. The localization of tetraspanins to the TC-EC heterologous contact area was also observed duri ng the active transmigration of TCs across EC monolayers grown onto 3-dimen sional collagen matrices. Dynamic studies by time-lapse immunofluorescence confocal microscopy showed an active redistribution of endothelial CD9 to p oints of melanoma insertion. Anti-CD9 monoclonal antibodies were found to s pecifically inhibit the transendothelial migration of melanoma cells; the i nhibitory effect was likely caused by a strengthening of CD9-mediated heter otypic interactions of TCs to the EC monolayer. These data support a novel mechanism of tetraspanin-mediated regulation of TC transcellular migration independent of TC motility and growth during metastasis and a role for thes e molecules in the formation of TC-EC mosaic monolayers during tumor angiog enesis. (C) 2001 by The American Society of Hematology.