Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 Inhibits Proximal TCR Signaling by Targeting ZAP-70

Abstract

The long cytoplasmic tail (CT) isoforms of carcinoembryonic Ag-related cell adhesion molecule 1 (CEACAM1) are expressed on activated human T cells and possess two ITIM motifs in the CT. These isoforms of CEACAM1 are inhibitory for T cell responses initiated by the TCR/CD3 complex with the inhibition dependent upon the ITIMs of CEACAM1 and Src homology 2 domain-containing phosphatase 1 (SHP-1). However, the mechanism by which this inhibition occurs in T cells is unknown. We demonstrate here that the Src family kinase, Lck, and the ability of CEACAM1 to bind homophilically are required for the ITIM phosphorylation of CEACAM1 that is a prerequisite for CEACAM1 association with SHP-1. We further show that CEACAM1 associates with and recruits SHP-1 to the TCR/CD3 complex leading to decreased phosphorylation of CD3-ζ and ZAP-70 and consequently decreased activation of the elements downstream of ZAP-70. This is physiologically relevant because extinction of SHP-1 expression or blockade of homophilic binding by CEACAM1 using a Fab that specifically recognizes the homophilic binding region of human CEACAM1 increases the cytolytic function initiated by the TCR/CD3 complex. These studies show that long CT isoforms of CEACAM1 orchestrate an inhibitory program that abrogates extremely proximal events downstream of the TCR/CD3 complex by focusing on the activation of ZAP-70.

CEACAM1: a key regulator of vascular permeability

“…This is consistent with previous observations that the tyrosines within the CEACAM1-L ITIMs are phosphorylated by c-Src kinase in epithelial cells, Lck kinase in T cells, Btk kinase in B cells, Lyn in neutrophils, and insulin receptor as well as epidermal growth factor receptor tyrosine kinases in hepatocytes (Brummer et al, 1995;Skubitz et al, 1995;Abou-Rjaily et al, 2004;Pantelic et al, 2005;Dubois et al, 2006;Chen et al, 2008;Muller et al, 2009). We have previously shown in a mouse colon tumor model that CEACAM1-L acts as a tumor growth inhibitor.…”

“…Previous studies have shown that tyrosine phosphorylation of CEACAM1-L within the ITIM motif is crucial for its function, including the regulation of signaling pathways in epithelial and immune cells (Huber et al, 1999;Izzi et al, 1999). Upon tyrosine phosphorylation, CEACAM1-L can bind SH2 domain-containing proteins, thereby activating Src-family tyrosine kinases and the protein tyrosine phosphatases SHP-1 and SHP-2 (Huber et al, 1999;Poy et al, 2002;Dubois et al, 2006;Chen et al, 2008;Klaile et al, 2009;Muller et al, 2009). We therefore evaluated whether CEACAM1-L was phosphorylated in response to VEGF treatment of endothelial cells and whether SHP-1 and the Src-like kinases played a role in CEACAM1-mediated endothelial phenotypes.…”

“…Because CEACAM1-L is phosphorylated by Src-like kinases in epithelial and immune cells (Brummer et al, 1995;Skubitz et al, 1995;Abou-Rjaily et al, 2004;Pantelic et al, 2005;Dubois et al, 2006;Chen et al, 2008;Muller et al, 2009), we looked at whether VEGF-induced CEACAM1-L phosphorylation was elicited by Src kinases in transfected BAECs. To address this, inhibition of Src activity was achieved by pretreating the transfected cells with a specific Src family kinase inhibitor, PP2, before VEGF treatment (Fig.…”

“…3A revealed that phosphorylation of the key tyrosine residues Tyr488 and Tyr515 within the ITIM motif are required for the function and association of CEACAM1-L with SHP-1 in epithelial and endothelial cells (Huber et al, 1999;Izzi et al, 1999;Dubois et al, 2006;Chen et al, 2008). To evaluate the contribution of these CEACAM1-L key phosphorylation residues in the eNOS signaling pathway, we measured NO release in VEGF-stimulated BAECs transfected with different CEACAM1 mutants (Fig.…”

CEACAM1 : modulateur central du métabolisme, de la progression tumorale,de l’angiogenèse et de l’immunité

“…Cette association faciliterait le recrutement de SHP-1 dans le complexe TCR/CD3, induisant la déphosphoryla-tion de la protéine Zap-70, kinase essentielle à l'activation du complexe. L'activation des voies de signalisation en aval de Zap-70 serait alors fortement inhibée [29]. S'ajoute à ce mécanisme l'intervention d'autres partenaires.…”