The interaction of TIGIT with PVR and PVRL2 inhibits human NK cell cytotoxicity

Abstract

NK cell cytotoxicity is controlled by numerous NK inhibitory and activating receptors. Most of the inhibitory receptors bind MHC class I proteins and are expressed in a variegated fashion. It was recently shown that TIGIT, a new protein expressed by T and NK cells binds to PVR and PVR-like receptors and inhibits T cell activity indirectly through the manipulation of DC activity. Here, we show that TIGIT is expressed by all human NK cells, that it binds PVR and PVRL2 but not PVRL3 and that it inhibits NK cytotoxicity directly through its ITIM. Finally, we show that TIGIT counter inhibits the NK-mediated killing of tumor cells and protects normal cells from NK-mediated cytoxicity thus providing an ''alternative self'' mechanism for MHC class I inhibition.inhibitory receptors ͉ natural killers I n contrast to T cells, that possess a single dominant antigen receptor (1), NK cells rely on a vast combinatorial array of receptors to initiate effector functions (2). Both activating and inhibitory receptors expressed on NK cells regulate their activity when interacting with tumors, virus infected cells and bacteria, as well as normal self-cells (2). MHC class I-expressing cells are protected from NK-mediated lysis due to the recognition of various MHC class I proteins by the inhibitory receptors KIR, LIR and CD94-NKG2A (3). Other NK inhibitory receptors which do not interact with MHC class I also exist, such as CEACAM1 and IRp60 (4-8). The significance, however, of these non-MHC class I inhibitory receptors in normal conditions is still unclear. All of the inhibitory receptors share a common immune receptor tyrosinebased inhibitory motif (ITIM) in their cytoplasmic regions, which delivers the inhibitory signal (3).The NK cell-mediated killing is extracted by specific receptors, among which are the natural cytotoxicity receptors (NCRs), which include the NKp30 that interacts with pp65 of human cytomegalovirus (CMV), BAT3 and the recently identified B7-family member B7-H6 (9-11), and the NKp46/NKp44 receptors, which interact with various viral hemagglutinins (12, 13). The NKG2D receptor interacts with MICA, MICB and ULBP 1-5 (14) and NKp80 interacts with AICL (15). In addition, two other receptors, DNAM-1 and CD96, enhance NK cytotoxicity (16,17). Both DNAM-1 and CD96 recognize PVR (CD155), whereas DNAM-1 also recognizes PVRL2 (CD112) (16,17). It was recently shown that a new receptor, named TIGIT, for T cell Ig and ITIM domain, interacts with PVR and its related proteins and that TIGIT inhibits T cell activity indirectly through the manipulation of DC activity (18). Here, we show that TIGIT, through its ITIM, can directly inhibit NK cytotoxicity. ResultsTIGIT Inhibits YTS Killing Through Its ITIM Motif. While searching for new CD28 family-like receptors, based on bioinformatics analysis, we observed that a protein named VSIG9 or VSTM3 in the databases expresses an ITIM motif. We continued to work on this protein and found that it interacts with PVR (CD155) but not with any other NK ligands tested (supporting information (...

Recruitment of Grb2 and SHIP1 by the ITT-like motif of TIGIT suppresses granule polarization and cytotoxicity of NK cells

“…We used the NK cell line YTS cells as effector killers and the 721.221 cells as targets, which execute a restricted killing mainly through the interaction between the 2B4 receptor on YTS cells and its ligand CD48 on the target cells. 11 Additionally, Stanietsky et al 11 showed that CD226 and CD96 are expressed on YTS cells, but they are unable to enhance the killing ability mediated by PVR for an unknown reason. Actually, YTS cells did not express TIGIT, and 721.221 cells did not have PVR.…”

“…Moreover, TIGIT/PVR ligation almost completely blocked NK cell-mediated cytolysis (Figure 1b), which is in agreement with a recent report. 11 TIGIT is phosphorylated at its cytoplasmic tail after its ligation with PVR. It was shown that the first step of the inhibitory signaling pathway is phosphorylation of ITIM in the inhibitory receptors.…”

“…[10][11][12] However, it is not clear about how TIGIT mediates an inhibitory signaling pathway in T and NK cells. Herein we demonstrate that TIGIT/PVR engagement disrupts granule polarization leading to loss of killing activity of NK cells.…”

“…11 TIGIT-deficient mice are more susceptible to autoimmune diseases. 14,15 However, the inhibitory mechanism mediated by TIGIT has not been elucidated.…”

“…[10][11][12] TIGIT harbors one extracellular immunoglobulin domain, a type 1 transmembrane region, and an immunoglobulin tail tyrosine (ITT)-like phosphorylation motif followed by an ITIM (immunoreceptor tyrosine-based inhibition motif) of the cytoplasmic tail. 13 The physical ligands of TIGIT were identified as the poliovirus receptor (PVR, or CD155) and the PVRL2 (Nectin2, or CD112).…”