Crossing the endothelium: E-selectin regulates tumor cell migration under flow conditions.

Diapedesis is a vital part of tumor metastasis, whereby tumor cells attach to and cross the endothelium to enter the circulation. Specific adhesion molecules, expressed by both the tumor and endothelial cells, mediate this process. This review summarizes recent findings regarding the mechanisms by which colon cancer cells migrate through the endothelium under flow conditions mediated by E-selectin. Using a laminar flow chamber and a tissue engineered human blood vessel, E-selectin was found to regulate initial attachment and rolling of colon cancer cells and also the subsequent diapedesis through the endothelium. Three different mechanisms of diapedesis were reported to be regulated by E-selectin; the formation of a mosaic chimeric layer of tissue, paracellular diapedesis between endothelial cells and transcellular diapedesis, in which tumor cells were transported via large vacuoles within the endothelial cells. Moreover activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase by E-selectin was further required for paracellular diapedesis. This study is the first to report these observations under dynamic and shear stress conditions.