Abstract 98: Cell membrane cholesterol modulates lung cancer cell adhesion and rolling on E-selectin

Despite numerous advances in cancer research, lung cancer has remained the major cause of cancer-related mortality worldwide, mainly because of metastasis and the lack of curative systemic therapy. It has been well established that lipid rafts, the membrane microdomains containing cholesterol and glycosphingolipids, play an important role in cell adhesion and spreading. Notably, there are elevated levels of cholesterol-rich lipid rafts observed in cancer cells relative to normal ones. Thus, alterations in lipid rafts, such as through cholesterol depletion, have been considered as a strategy for cancer metastasis prevention. In this study three different treatments - methyl-beta-cyclodextrin (mβCD), sphingomyelinase (smase), and simvastatin (simva) - were used to investigate the effects of cholesterol depletion on the mechanics of adhesion and rolling velocities of multiple non-small cell lung cancer (NSCLC) cell lines (H1299, H23, H460, and A569) and a small cell lung cancer (SCLC) cell line (SHP-77) on E-selectin, a vascular endothelial molecule hypothesized to initiate recruitment of circulating tumor cells at metastatic sites. Under physiological conditions in a parallel plate chamber, it was observed that the number of adherent NSCLC cells significantly decreased through mβCD and simva treatments, while smase treatment did not show significant effect on those cells. In addition, only for NSCLC cells, significant increases in rolling velocities were detected after treatments with mβCD and simva, but not via smase. In contrast, cholesterol depletion did not affect the number of attached cells and rolling velocity of the SCLC cells. Our results show that cholesterol might regulate E-selectin-mediated adhesion of NSCLC cells to endothelium, most likely by disturbing functional E-selectin ligands expressed on the surface of the cancer cells. We have previously reported that CD44 expressed on colon cancer and breast cancer cells are functional E-selectin ligands that mediate cell adhesion and rolling on endothelium. Protein structure analysis by flow cytometry and western blot showed that all NSCLC cell lines strongly expressed CD44. After the cholesterol depletion through the various treatments, the molecular surface expression of CD44 was down regulated for all these cells. In contrast, the SCLC line did not show any expression of CD44. Although further studies must be performed to verify CD44 function as an E-selectin ligand, the data in total imply prote