ANGIO-TUMORAL LAMININ IN MURINE TUMORS DERIVED FROM HUMAN MELANOMA CELL LINES. IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL OBSERVATIONS

: Cells in tissues interact with each other and with the extracellular matrix as part of a structural and informational unit. During cancer progression, tumor cells participate in the formation of a neotissue involving other cells and matrix. We recently observed in melanoma an association between tumor and endothelial cells via an amorphous matrix containing free laminin. The pericytic location of melanoma cells in this angio-tumoral complex raised the question of an intramesenchymal migration of metastatic melanoma cells promoted by free laminin along the endothelium. However the respective roles of melanoma cells and endothelial cells in laminin secretion were not clear. In an attempt to clarify the latter issue, we injected into mice three human melanoma cells lines, one secreting laminin and two that did not, in order to identify the source of laminin secretion in the subsequent interactions between tumor cells and vascular endothelium. Using immunohistochemistry and electron microscopy we observed in all three cases an amorphous matrix containing laminin between tumor and endothelial cells. The fact that two cell lines did not secrete laminin suggests that the periendothelial/peritumoral laminin could be of endothelial origin. Given the presence of laminin alone during intramesenchymal angiogenesis and embryogenesis, we propose an analogous role for endothelial laminin in facilitating the migration of melanoma cells along the abluminal surface of the endothelium.