Novel endothelial cell activation factor(s) released from activated platelets which induce E-selectin expression and...

Activation of endothelial cells (ECs) by tumor cells (TCs) to elicit expression of adhesion receptors such as selectins and intercellular adhesion molecules (ICAMs) has been considered to facilitate TC-EC adhesion, the initial step in TC metastasis. Studies reported here indicate that: (i) TC lines tested did not activate ECs; (ii) tested TCs activated native (but not inert) platelets, which in turn activated ECs to express E-selectin, leading to TC-EC adhesion; (iii) auto-aggregation of TCs eventually resulted in adhesion of large TC aggregates to ECs; (iv) process ii is inhibited by H7 and calphostin, indicating involvement of a signaling process mediated by protein kinases in expression of E-selectin.