(145g) Influence of CD151 Expression and Endothelial Cell Phenotype On Selectivity of Cancer Cell Adhesion to Endothelial Monolayers

Though cancer has been widely studied for some time, it continues to be the second leading cause of death in the United States.  In the majority of cases, it is not the primary tumor that results in fatality, but a secondary tumor resulting from the dissemination of circulating tumor cells (CTCs) to other tissues and organs throughout the body.  The basic steps of the metastatic cascade, from initial tumor formation to growth at a secondary site, are a linear sequence of steps composed of a network of mechanisms that are not well understood.  One of these steps, the adhesion of the cancer cells to the endothelial cells during dissemination is the focus of this research.  Two main hypotheses have been suggested to explain the mechanism of cancer cell adhesion to endothelial cells.  Honn and Tang proposed a "docking and locking" mechanism, which describes the ligand-receptor interactions that take place as the tumor cells roll along the endothelium.  Alternatively, other investigators have proposed that the cancer cells must first lodge in small microvessels before firmly attaching to the endothelium.   In this study, a parallel plate flow chamber was employed to investigate the role of initial adhesion vs. lodging in the ability of cancer cells to attach to endothelial cells.  This system allows us to test the "docking and locking" mechanism by visualizing initial adhesion of cancer cells to the endothelial cell monolayer as the cells roll along the monolayer at controlled shear stresses.  Detachment of cells under controlled shear stresses after the cancer cells are allowed to settle on the monolayer can also be observed, hence simulating the lodging mechanism.  In addition, the role of endothelial cell phenotype was studied by investigating the interactions of the cancer cells with endothelial cells originating from veins and arteries.  Specifically, the “docking and locking” and lodging mechanisms were investigated and compared in both human umbilical vein endothelial cells (HUVECs) and human umbilical arterial endothelial cells (HUAECs).  Finally, the influence of the gene CD151 on these interactions was quantified.  CD151 is a gene that encodes a cell-surface glycoprotein that is known to complex with integrins and enhance cancer cell motility, invasion and metastasis.  This was accomplished by comparing adhesion assays using human breast and prostate cancer lines (sum149 and PC3, respectively) as well as sum149 and PC3 lines in which CD151 expression was lowered using shRNA.  Preliminary results have suggested that lodging plays a larger role than initial attachment in the interactions between breast cancer cells and HUVECs.  Other results presented will include a comparison of the initial attachment and lodging of these cells on HUVECs vs. HUAECs as well as the effects of CD151 expression in these adhesion assays.