Chronic NKG2D Engagement In Vivo Differentially Impacts NK Cell Responsiveness by Activating NK Receptors

Abstract

Immunosuppression is a typical hallmark of cancer and frequently includes perturbations of the NKG2D tumor recognition system as well as impaired signaling by other activating NK cell receptors. Several in vitro studies suggested that sustained engagement of the NKG2D receptor, as it is occurring in the tumor microenvironment, not only impairs expression and function of NKG2D but also impacts signaling by other activating NK receptors. Here, we made use of a transgenic mouse model of ubiquitous NKG2D ligand expression (H2-Kb-MICA mice) to investigate consequences of chronic NKG2D engagement in vivo for functional responsiveness by other activating NK receptors such as NKp46 and Ly49D. Unexpectedly, we found no evidence for an impairment of NKp46 expression and function in H2-Kb-MICA mice, as anticipated from previous in vitro experiments. However, we observed a marked downregulation and dysfunction of the activating receptor Ly49D in activated NK cells from H2-Kb-MICA mice. Ly49D shares the adaptor proteins DAP10 and DAP12 with NKG2D possibly explaining the collateral impairment of Ly49D function in situations of chronic NKG2D engagement. Altogether, our results demonstrate that persistent engagement of NKG2D in vivo, as often observed in tumors, can selectively impair functions of unrelated NK receptors and thereby compromise NK responsiveness to third-party antigens.

MICAgen Mice Recapitulate the Highly Restricted but Activation-Inducible Expression of the Paradigmatic Human NKG2D Ligand MICA

“…In accord with the high abundance of MICA transcripts in hematopoietic organs of H2-K b -MICA mice and our previous reports on MICA expression by H2-K b -MICA hematopoietic cells (27,28), we readily detected MICA expression by leukocytes in tissue sections of lymph nodes, thymus, and the large and small intestines of H2-K b -MICA mice ( Figure 3A). In contrast, MICA molecules could be or not be unambiguously detected in sections of the corresponding organs of MICAgen mice, which presented alike the negative controls from nontransgenic littermates (nontgLM) ( Figure 3A).…”

“…The cosmid MB24/1 had also been transfected into mouse L-tk cells with MICA-expressing L-tk transfectants being used for cloning of the corresponding MICA cDNA by reverse transcription-PCR (RT-PCR). Transgenic mice expressing this human MICA cDNA (MICA * 00701 allele; GenBank accession number AY750850.1) under control of the H2-K b promoter have been termed H2-K b -MICA and been described elsewhere (27,28). Litters were tested transgenes by PCR using genomic DNA or for MICA surface expression on peripheral blood lymphocytes (PBL) by flow cytometry using anti-MICA mAb AMO1-AlexaFluor647.…”

“…B16F10-mock and B16F10-MICA * 001 transductants were previously described (27). B16F10 transductants were cultured in Dulbecco's modified Eagle medium (DMEM) (Sigma-Aldrich, Steinheim, Germany) supplemented with 10% fetal calf serum (FCS) (Biochrom, Berlin, Germany), 2 mM L-glutamine (Sigma-Aldrich), 100 U/ml penicillin, 100 µg/ml streptomycin (Sigma-Aldrich), 1 mM sodium pyruvate (Life Technologies, Darmstadt, Germany), and non-essential amino acids (Sigma-Aldrich).…”

NKG2D Ligands–Critical Targets for Cancer Immune Escape and Therapy

“…Whereas, a diverse array of stresses can be recognized by a functional receptor, the shedding of a single ligand is sufficient to render immune cells blind to the entire ligand family. On top, chronic engagement of the NKG2D receptor was shown to downmodulate also the activity of other NK cell receptors ( 60 , 61 ) which may be in part connected to the degradation of the CD3ζ signaling molecule that also impairs T cell activity ( 62 ). Therefore, shedding is a very powerful way to overcome NKG2D-mediated immune surveillance.…”

Cytoplasmic Citrate Flux Modulates the Immune Stimulatory NKG2D Ligand MICA in Cancer Cells

“…Upregulation of NKG2DLs on cancer cells enhance NK cell infiltration and promote cancer cytotoxicity (2,3). Conversely, numerous cancer cells maintain chronic NKG2DL expression and evade immune elimination by down-modulating and impairing NKG2D receptor signaling (4)(5)(6)(7).…”