Endothelial IQGAP1 regulates leukocyte transmigration by directing the LBRC to the site of diapedesis

Abstract

Transendothelial migration (TEM) of leukocytes across the endothelium is critical for inflammation. In the endothelium, TEM requires the coordination of membrane movements and cytoskeletal interactions, including, prominently, recruitment of the lateral border recycling compartment (LBRC). The scaffold protein IQGAP1 was recently identified in a screen for LBRC-interacting proteins. Knockdown of endothelial IQGAP1 disrupted the directed movement of the LBRC and substantially reduced leukocyte TEM. Expression of truncated IQGAP1 constructs demonstrated that the calponin homology domain is required for IQGAP1 localization to endothelial borders and that the IQ domain, on the same IQGAP1 polypeptide, is required for its function in TEM. This is the first reported function of IQGAP1 requiring two domains to be present on the same polypeptide. Additionally, we show for the first time that IQGAP1 in the endothelium is required for efficient TEM in vivo. These findings reveal a novel function for IQGAP1 and demonstrate that IQGAP1 in endothelial cells facilitates TEM by directing the LBRC to the site of TEM.

Endothelial Cell Calcium Signaling during Barrier Function and Inflammation

“…Recently, it was found that endothelial IQ-motif containing GTPase-activating protein 1 is required for leukocyte TEM, and the actin-binding calponin homology domain and the IQ motif domains are key for mediating this function. 52,53 The IQ motif domain has been previously reported to bind CaM in other contexts, but this interaction and its role in TEM have not yet been explored. 54 Regional heterogeneity of endothelial cells and the uncertainty about which types of ion channels are present in endothelial cell subsets also affect the studies of calcium signaling in the multistep inflammatory cascade.…”

Spatiotemporal restriction of endothelial cell calcium signaling is required during leukocyte transmigration

“…It rescues the TEM defect caused by endogenous IQGAP1 knockdown; it contains both the CHD and IQ domains. Construct Δ4–6 lacks the IQ domain (domain 4) and therefore does not support TEM, even though it localizes to the cell border ( Sullivan et al, 2019 ).…”

“…Neutrophil position with respect to the endothelial cells was precisely scored according to a standard system ( Fig. 7 B ; Sullivan et al, 2019 ; Watson et al, 2015 ; Weber et al, 2015 ). Both control and CaMKIIN-expressing mice recruited similar numbers of neutrophils to the ear ( Fig.…”

“…Structurally, it is composed of six distinct domains. The role for IQGAP1 in TEM has only recently been described ( Sullivan et al, 2019 ). Specifically, both the N-terminal calponin homology domain (CHD) and the IQ domain are required for IQGAP1 function during TEM.…”

The Tumour Vasculature as a Target to Modulate Leucocyte Trafficking

“…As leucocytes transmigrate through the EC barrier, they are encapsulated by the lateral border recycling compartment (LBRC), a recently described peri-junctional network of interconnected tubulovesicular membrane in ECs [ 98 , 99 ]. Targeted trafficking of the LBRC is coordinated with remodelling of EC junctions at sites of TEM [ 100 ]. LBRC consists of molecules crucial for leucocyte TEM, such as platelet-endothelial cell adhesion molecule-1 (PECAM-1, CD31), CD99, and junctional adhesion molecule (JAM)-A. Leucocytes interact with these unligated molecules presented by the LBRC membrane on their path across the ECs [ 88 ].…”