Mechanism of sustained E-selectin expression in cultured human dermal microvascular endothelial cells

Persistent E-selectin expression has been proposed to be a unique property of dermal vascular endothelium that directs skin-specific homing of a subpopulation of circulating memory T cells. We compared the kinetics of E-selectin expression on cultured human dermal microvascular endothelial cells (HDMEC) with expression on HUVEC. Following treatment with TNF, E-selectin on HDMEC appears more slowly than on HUVEC (peak values 6-8 vs 4 h, respectively) and is sustained at significantly higher levels after 24 h. E-selectin mRNA, analyzed by S1 nuclease protection, consists of a single predominant transcript that follows a similarly transient time course in both cell types. Cell surface E-selectin is internalized more slowly on HDMEC than on HUVEC (t1/2 = 4.3 vs 1.6 h, respectively) as measured by serial FACS analyses in the presence of the protein synthesis inhibitor cycloheximide. In comparison, intercellular adhesion molecule-1 (ICAM-1) expression is not measurably reduced by either cell type under the same conditions. HDMEC are similar to HUVEC in rates of pinocytosis or receptor-mediated endocytosis. Pulse-chase analysis indicated that the degradative half-life of E-selectin protein is greater in HDMEC than in HUVEC (1.9 vs 1.5 h, respectively). E-selectin internalization in microvascular endothelial cells (EC) from lung and subcutaneous fat is slow, like HDMEC, whereas internalization in large vessel EC from saphenous vein and aorta is rapid, like HUVEC. We conclude that HDMEC sustain higher levels of expression at 24 h by slower internalization and degradation of E-selectin protein and that this may be a general property of microvascular EC.