Endothelial cell IQGAP1 is an important regulator of the transendothelial migration of leukocytes (146.1)

Abstract

In order to mount an appropriate inflammatory response, leukocytes must cross the endothelium to gain access to the target tissue and carry out their essential role. During this process (referred to as transendothelial migration, TEM) membrane from a novel endothelial cell compartment, the Lateral Border Recycling Compartment (LBRC), is delivered to the migrating leukocyte to supply it with several requisite proteins. In a proteomic screen, we discovered that IQGAP1 is associated with the LBRC and is required for its function during TEM. IQGAP1 is a large soluble scaffolding protein that integrates signals from diverse pathways to regulate cytoskeletal remodeling, Rho family GTPase activity, and other downstream readouts. Although it has been implicated in a variety of processes in other systems, its role in TEM remains unclear. In addition to being localized to the cytoplasm, in endothelial cells it is also enriched at lateral borders. Genetic ablation of IQGAP1 expression arrests leukocytes on the apical side of endothelial cells and prevents the targeted delivery of the LBRC similar to the phenotype of blocking PECAM. Expression of a full length GFP‐tagged IQGAP1 construct completely restores this defect and also shows that endothelial IQGAP1 is enriched around the leukocyte during TEM. Furthermore, using fluorescently tagged IQGAP1 truncation constructs, we have identified the domains of IQGAP that are required for its localization and function under resting conditions and during TEM. These data suggest that IQGAP1 is an important factor in the regulation of LBRC function. Preliminary studies in IQGAP1 knockout mice support a role for IQGAP in TEM in vivo.Grant Funding Source: Supported by F32 AI084454 to DPS and R21 HL102519, R01 HL046849, and R37 HL064774 to WAM