Mechanisms of MAdCAM-1 gene expression in human intestinal microvascular endothelial cells

1 Division of Gastroenterology and Hepatology, 2 Division of Pediatric Surgery, 3 Department of Surgery, 4 Digestive Disease Center, and 5 Free Radical Research Center, Froedtert Memorial Lutheran Hospital, Milwaukee Veterans Administration Medical Center, Children's Hospital of Wisconsin, Medical College of Wisconsin, Milwaukee, Wisconsin Submitted 22 September 2003 ; accepted in final form 29 September 2004 Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is a homing receptor preferentially expressed on gut-associated endothelial cells that plays a central role in leukocyte traffic into the mucosal immune compartment. Although the molecular mechanisms underlying endothelial ICAM-1 or E-selectin expression have been intensively investigated, the mechanisms that regulate human MAdCAM-1 expression have not been defined. We report MAdCAM-1 gene and protein expression in primary cultures of human intestinal microvascular endothelial cells (HIMEC) that was not demonstrated in human umbilical vein endothelial cells. Similar to ICAM-1 and E-selectin expression, MAdCAM-1 gene expression in HIMEC was inducible with TNF- , IL-1 , or LPS activation. However, in striking contrast to ICAM-1 and E-selectin expression, MAdCAM-1 mRNA and protein expression in HIMEC was heavily dependent on culture duration and/or cellular density, suggesting a prominent role for cell-cell interaction among these endothelial cells in the expression of the mucosal addressin. MAdCAM-1 expression was inhibited by both SN-50 (NF- B inhibitor) and LY-294002 [phosphatidylinositol 3-kinase (PI3-K) inhibitor], whereas ICAM-1 and E-selectin expression was inhibited by SN-50 but not by LY-294002. The Akt phosphorylation by TNF- or LPS was greater at higher cell density, demonstrating a pattern similar to that of MAdCAM-1 expression. NF- B activation was not affected by cellular density in HIMEC. MAdCAM-1 expression in human gut endothelial cells is regulated by distinct signaling mechanisms involving both NF- B and PI3-K/Akt. These data also suggest that PI3-K/Akt is involved in the gut-specific differentiation of HIMEC, which results in expression of the mucosal addressin MAdCAM-1. cell adhesion molecules; nuclear factor- B; phosphatidylinositol 3-kinase Address for reprint requests and other correspondence: P. Rafiee, Division of Pediatric Surgery, Children's Hospital of Wisconsin, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226 (E-mail: prafiee{at}mcw.edu )