Localization and activity of calmodulin is involved in cell-cell adhesion of tumor cells and endothelial cells in response to hypoxic stress

Adhesion of tumor cells to endothelial cells is known to be involved in the hematogenous metastasis of cancer, which is regulated by hypoxia. Hypoxia is able to induce a significant increase in free intracellular Ca2+ levels in both tumor cells and endothelial cells. Here, we investigate the regulatory effects of calmodulin (CaM), an intracellular calcium mediator, on tumor cell-endothelial cell adhesion under hypoxic conditions. Hypoxia facilitates HeLa cell-ECV304 endothelial cell adhesion, and results in actin cytoskeleton rearrangement in both endothelial cells and tumor cells. Suppression of CaM activation by CaM inhibitor W-7 disrupts actin cytoskeleton organization and CaM distribution in the cell-cell contact region, and thus inhibits cell-cell adhesion. CaM inhibitor also downregulates hypoxia-induced HIF-1-dependent gene expression. These results suggest that the Ca2+-CaM signaling pathway might be involved in tumor cell-endothelial cell adhesion, and that co-localization of CaM and actin at cell-cell contact regions might be essential for this process under hypoxic stress.