Noninflammatory expression of E-selectin is regulated by cell growth.

E-selectin, an endothelial-specific adhesion molecule best known for its role in leukocyte adhesion, is not detected in quiescent endothelial cells, but is induced by inflammatory stimuli. However, E-selectin is also expressed in proliferating endothelial cells under noninflammatory conditions in vivo and in vitro, suggesting that E-selectin is also regulated by growth signals. To investigate E-selectin expression in lipopolysaccharide-stimulated versus nonstimulated proliferating cells, we analyzed the distribution of E-selectin-positive human microvascular endothelial cells in G0/G1, S, and G2/M phases of the cell cycle under both conditions. Lipopolysaccharide treatment resulted in uniformly increased E-selectin expression in cells in G0/G1, S, and G2/M. In contrast, levels of E-selectin in nonstimulated proliferating cells showed a linear correlation with the percentage of cells in G2/M. E-selectin in proliferating endothelial cells was not reduced by addition of soluble tumor necrosis factor-alpha-receptor or soluble interleukin-1-receptor indicating that its expression was not due to endogenous production of either cytokine. In addition, E-selectin was increased in cells stimulated with basic fibroblast growth factor, a well-known mitogen for endothelial cells. E-selectin in proliferating endothelial cells is functional, as shown by E-selectin-dependent adhesion of the promyelocytic leukemia cell line HL-60 to subconfluent human microvascular endothelial cells. In summary, these studies indicate that E-selectin can be regulated by a non-inflammatory pathway that is related to the proliferative state of the endothelium.