Monocytic thrombomodulin promotes cell adhesion through interacting with its ligand, Lewis^y

Abstract

The leukocyte adhesion cascade involves multiple events that efficiently localize circulating leukocytes into the injured sites to mediate inflammatory responses. From rolling to firm adhesion, the interactions between adhesion molecules have pivotal roles in increasing the avidity of leukocytes to endothelial cells. Thrombomodulin (TM), an essential anticoagulant protein in the vasculature, is also expressed on leukocytes. We previously demonstrated that Lewisy (Ley), a specific ligand of TM, is upregulated in inflamed endothelium and is involved in leukocyte adhesion. The current study aimed to investigate whether leukocyte-expressed TM promotes cell adhesion by interacting with Ley. Using human monocytic THP-1 cells as an in vitro cell model, we showed that TM increases THP-1 cell adhesion to inflamed endothelium as well as to Ley-immobilized surface. When THP-1 adhered to activated endothelium and Ley-immobilized surface, the TM distribution became polarized. Addition of soluble Ley to a suspension of THP-1 cells with TM expression triggered an increase in the level of phosphorylated p38 mitogen-activated protein kinase (MAPK), which enabled THP-1 to adhere firmly to intercellular adhesion molecule (ICAM)-1 by activating β2 integrins. In vivo, macrophage infiltration and neointima formation following arterial ligation-induced vascular injury were higher in wild-type TM (TMflox/flox) than in myeloid-specific TM-deficient (LysMcre/TMflox/flox) mice. Taken together, these results suggest a novel function for TM as an adhesion molecule in monocytes, where it enhances cell adhesion by binding Ley, leading to β2 integrin activation via p38 MAPK.

Blood group‐related antigen Ley on human platelets and its involvement in platelet aggregation via a possible interaction with CD61

“…Many studies have suggested a role for Le y in inflammation, as it is expressed as a carbohydrate ligand for cell adhesion. 1,21,22 Thus, the expression of Le y on platelets may also contribute to adhesion and platelet aggregation. However, we found no correlation between the intrinsic Le y expression level and the aggregation rate in random Figure S1).…”

“…Wu et al demonstrated that leukocyte-expressed thrombomodulin (TM) is a ligand for Le y on the endothelium. 1 Thus, TM on the endothelium is also likely to be a ligand for platelet Le y . If so, this may also contribute to the adhesion of platelets to the endothelial matrix.…”

“…Le y (Fucα1-2Galβ1-4(Fucα1-3)GlcNAcβ1-R)) is a carbohydrate moiety that modifies various glycoproteins to regulate cellular functions. 1 Le y is a member of the Lewis antigen family and is structurally related to ABH blood group antigens. For example, Le y is an isomer of the Le b antigen.…”

Thrombomodulin Regulation of Mitogen-Activated Protein Kinases

“…Interaction of PKCδ with TM in the monocytic THP-1 cells leads to inhibition of the cell cycle and subsequent differentiation through ERK1/2 mediated cytoskeletal remodeling [67]. Moreover, monocytic TM is reported to bind Lewis-Y (LeY) on the inflamed endothelium, thereby triggering an increase in activation of p38 MAPK signaling [68]. This facilitates firm binding of THP-1 to ICAM-1 on the endothelium by activating β2 integrins on THP-1 cells [68].…”

“…Moreover, monocytic TM is reported to bind Lewis-Y (LeY) on the inflamed endothelium, thereby triggering an increase in activation of p38 MAPK signaling [68]. This facilitates firm binding of THP-1 to ICAM-1 on the endothelium by activating β2 integrins on THP-1 cells [68]. However, this process seems to operate under localized inflammatory conditions since systemic inflammatory molecules like LPS decreases the TM expression on THP-1 cells [69]…”