ENDOTHELIAL-CELL INTRACELLULAR CA2-TUMOR CELL CONTACT AND MEDIATES TUMOR-CELL TRANSENDOTHELIAL MIGRATION( CONCENTRATION IS INCREASED UPON BREAST)

Tumor cell extravasation is a determinant step in the process of hemat ogenous metastasis. The signal transduction pathways involved in the i nteractions between tumor cells and the vascular endothelium during tr ansendothelial migration are still undefined. In the present study, we have investigated the influence of human breast adenocarcinoma cells (MCF7) on human umbilical vein endothelial cell (HUVEC) intracellular Ca2+ concentration ([Ca2+](i)). We show that the contact between MCF7 cells and a confluent HUVEC monolayer induces an immediate and transie nt increase in HUVEC [Ca2+](i). This [Ca2+](i) rise could not be elici ted by tumor cell-conditioned medium, isolated tumor cell membranes, i nert beads or normal breast epithelial cells, demonstrating the involv ement of specific recognition mechanisms between MCF7 cells and HUVEC. Depletion of HUVEC intracellular Ca2+ stores by the endoplasmic retic ulum Ca2+-ATPase inhibitor thapsigargin as well as the selective deple tion of inositol 1,4,5-triphosphate (IP3)-sensitive Ca2+ stores by pri or activation of HUVEC using histamine resulted in a complete inhibiti on of tumor cell-induced [Ca2+](i) elevation. Similar results were obt ained when HUVEC monolayers were treated with the tyrosine kinase inhi bitor herbimycin A, suggesting a role for tyrosine kinase-associated c ell surface receptors in tumor cell-endothelial cell interactions. The depletion of HUVEC intracellular Ca2+ stores by thapsigargin was also shown to delay MCF7-induced endothelial cell disjunction, to prevent their spreading on the subendothelial extracellular matrix and transen dothelial migration in vitro. These results suggest that transient cha nges in endothelial [Ca2+](i) may govern multiple steps of tumor cell extravasation.