Chamutal Gur

Human microRNAs regulate stress-induced immune responses mediated by the receptor NKG2D

MICA and MICB are stress-induced ligands recognized by the activating receptor NKG2D. A microRNA encoded by human cytomegalovirus downregulates MICB expression by targeting a specific site in the MICB 3′ untranslated region. As this site is conserved among different MICB alleles and a similar site exists in the MICA 3′ untranslated region, we speculated that these sites are targeted by cellular microRNAs. Here we identified microRNAs that bound to these MICA and MICB 3′ untranslated region sequences and obtained data suggesting that these microRNAs maintain expression of MICA and MICB protein under a certain threshold and facilitate acute upregulation of MICA and MICB during cellular stress. These microRNAs were overexpressed in various tumors and we demonstrate here that they aided tumor avoidance of immune recognition.

Binding of the Fap2 Protein of Fusobacterium nucleatum to Human Inhibitory Receptor TIGIT Protects Tumors from Immune Cell Attack

Bacteria, such as Fusobacterium nucleatum, are present in the tumor microenvironment. However, the immunological consequences of intra-tumoral bacteria remain unclear. Here, we have shown that natural killer (NK) cell killing of various tumors is inhibited in the presence of various F. nucleatum strains. Our data support that this F. nucleatum-mediated inhibition is mediated by human, but not by mouse TIGIT, an inhibitory receptor present on all human NK cells and on various T cells. Using a library of F. nucleatum mutants, we found that the Fap2 protein of F. nucleatum directly interacted with TIGIT, leading to the inhibition of NK cell cytotoxicity. We have further demonstrated that tumor-infiltrating lymphocytes expressed TIGIT and that T cell activities were also inhibited by F. nucleatum via Fap2. Our results identify a bacterium-dependent, tumor-immune evasion mechanism in which tumors exploit the Fap2 protein of F. nucleatum to inhibit immune cell activity via TIGIT.

The activating receptor NKp46 is essential for the development of type 1 diabetes.

The mechanism of action of natural killer (NK) cells in type 1 diabetes is still unknown. Here we show that the activating receptor NKp46 recognizes mouse and human ligands on pancreatic beta cells. NK cells appeared in the pancreas when insulitis progressed to type 1 diabetes, and NKp46 engagement by beta cells led to degranulation of NK cells. NKp46-deficient mice had less development of type 1 diabetes induced by injection of a low dose of streptozotocin. Injection of soluble NKp46 proteins into nonobese diabetic mice during the early phase of insulitis and the prediabetic stage prevented the development of type 1 diabetes. Our findings demonstrate that NKp46 is essential for the development of type 1 diabetes and highlight potential new therapeutic modalities for this disease.

Enhanced In Vivo Growth of Lymphoma Tumors in the Absence of the NK-Activating Receptor NKp46/NCR1

The in vitro elimination of virus-infected and tumor cells by NK cells is regulated by a balance between signals conveyed via specific inhibitory and activating receptors. Whether NK cells and specifically the NK-activating receptor NKp46 (NCR1 in mice) are directly involved in tumor eradication in vivo is still largely unknown. Since the NKp46/NCR1 tumor ligands have not been identified yet, we use a screening technique to identify functional ligands for NKp46/NCR1 which is based on a cell reporter assay and discover a NCR1 ligand in the PD1.6 lymphoma line. To study whether NKp46/NCR1 is important for the eradication of PD1.6 lymphoma in vivo, we used the Ncr1 knockout Ncr1gfp/gfp mice generated by our group. Strikingly, all Ncr1 knockout mice developed growing PD1.6 tumors, whereas initial tumor growth was observed in the wild-type mice and tumors were completely rejected as time progressed. The growth of other lymphoma cell lines such as B10 and EL4 was equivalent between the Ncr1 knockout and wild-type mice. Finally, we show that PD1.6 lymphoma cells are less killed both in vitro and in vivo in the absence of NKp46/NCR1. Our results therefore reveal a crucial role for NKp46/NCR1 in the in vivo eradication of some lymphoma cells.

NKp46-mediated killing of human and mouse hepatic stellate cells attenuates liver fibrosis

Background Liver fibrosis, which involves activation of hepatic stellate cells (HSC), is a major health problem and is the end outcome of all chronic liver diseases. The liver is populated with lymphocytes, among which are natural killer (NK) cells, whose activity is controlled by inhibitory and activating receptors. NKp46, one of the major NK activating receptors expressed by NK cells, is also a specific NK marker that discriminates NK cells from all other lymphocyte subsets. It recognises viral haemagglutinins and unknown cellular ligands. Methods The anti-fibrotic activity of the NKp46 receptor was assessed in vivo and in vitro using NKp46-deficient mice (NCR1gfp/gfp), the carbon tetrachloride model and in vitro NK killing assays. Primary murine and human HSC were stained for the expression of the NKp46 ligand using fusion proteins composed of the extracellular portions of the murine and human NKp46 receptors fused to human IgG1. Results It was shown that murine HSC express a ligand for the murine orthologue of the NKp46 receptor, NCR1. NCR1 inhibited liver fibrosis in vivo; in vitro, murine HSC were killed in an NCR1-dependent manner. In humans it was shown that human HSC also express a ligand for the human NKp46 receptor and that the killing of human HSC is NKp46 dependent. Conclusions In addition to NKG2D, NKp46/NCR1 play an important role in inhibition of liver fibrosis. This suggests that fibrosis can be better controlled through the manipulation of NKp46 activity.

Recognition and Prevention of Tumor Metastasis by the NK Receptor NKp46/NCR1

NK cells employ a variety of activating receptors to kill virally infected and tumor cells. Prominent among these receptors are the natural cytotoxicity receptors (NCRs) (NKp30, NKp44, and NKp46), of which only NKp46 has a mouse ortholog (NCR1). The tumor ligand(s) of NKp46/NCR1 is still unknown, but it was shown that the human NKp46 and the mouse NCR1 are involved in tumor eradication both in vitro and in vivo. Whether any of the NK activating receptors is involved in the prevention of tumor metastasis is unknown. To address this question, we studied the activity of the NK cell receptor NKp46/NCR1 in two spontaneous metastasis models, the B16F10.9 melanoma (B16) and the Lewis lung carcinoma (D122) in the NCR1 knockout mouse that was generated by our group, in various in vitro and in vivo assays. We demonstrated that all B16 and D122 tumors, including those generated in vivo, express an unknown ligand(s) for NKp46/NCR1. We have characterized the properties of the NKp46/NCR1 ligand(s) and demonstrated that NKp46/NCR1 is directly involved in the killing of B16 and D122 cells. Importantly, we showed in vivo that NKp46/NCR1 plays an important role in controlling B16 and D122 metastasis. Thus, to our knowledge, in this study we provide the first evidence for the direct involvement of a specific NK killer receptor in preventing tumor metastasis.

Direct Recognition of Fusobacterium nucleatum by the NK Cell Natural Cytotoxicity Receptor NKp46 Aggravates Periodontal Disease

Periodontitis is a common human chronic inflammatory disease that results in the destruction of the tooth attachment apparatus and tooth loss. Although infections with periopathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) are essential for inducing periodontitis, the nature and magnitude of the disease is determined by the hosts immune response. Here, we investigate the role played by the NK killer receptor NKp46 (NCR1 in mice), in the pathogenesis of periodontitis. Using an oral infection periodontitis model we demonstrate that following F. nucleatum infection no alveolar bone loss is observed in mice deficient for NCR1 expression, whereas around 20% bone loss is observed in wild type mice and in mice infected with P. gingivalis. By using subcutaneous chambers inoculated with F. nucleatum we demonstrate that immune cells, including NK cells, rapidly accumulate in the chambers and that this leads to a fast and transient, NCR1-dependant TNF-α secretion. We further show that both the mouse NCR1 and the human NKp46 bind directly to F. nucleatum and we demonstrate that this binding is sensitive to heat, to proteinase K and to pronase treatments. Finally, we show in vitro that the interaction of NK cells with F. nucleatum leads to an NCR1-dependent secretion of TNF-α. Thus, the present study provides the first evidence that NCR1 and NKp46 directly recognize a periodontal pathogen and that this interaction influences the outcome of F. nucleatum-mediated periodontitis.

Tumor Immunoediting by NKp46

NK cells interact with a wide variety of hazardous cells including pathogen-infected and tumor cells. NKp46 is a specific NK killer receptor that recognizes various influenza hemagglutinins and unknown tumor ligands. It was recently shown that NKp46 plays a significant role in the in vivo eradication of tumor cells; however, the role played by NKp46 in vivo with regard to tumor development is still unclear. In this study, we used the 3-methylcholanthrene (MCA)-induced fibrosarcoma model in NKp46-deficient mice to test the NKp46 recognition of carcinogen-induced tumors. We show that although the rate of MCA-induced tumor formation was similar in the presence and in the absence of NKp46, the expression of its unknown ligands was NKp46 dependent. The unknown NKp46 ligands were nearly absent in tumors that originated in wild-type mice, whereas they were detected in tumors that originated in the NKp46-deficient mice. We demonstrate that the interactions between NKp46 and its MCA tumor-derived ligands lead to the secretion of IFN-γ but not to the elimination of the MCA-derived tumor cells. In addition, we show that the in vivo growth of MCA-derived tumor cells expressing high levels of the NKp46 ligands is NKp46 and IFN-γ dependent. Thus, we present in this study a novel NKp46-mediated mechanism of tumor editing.

Killing of Avian and Swine Influenza Virus by Natural Killer Cells

ABSTRACT Today, global attention is focused on two influenza virus strains: the current pandemic strain, swine origin influenza virus (H1N1-2009), and the highly pathogenic avian influenza virus, H5N1. At present, the infection caused by the H1N1-2009 is moderate, with mortality rates of less <1%. In contrast, infection with the H5N1 virus resulted in high mortality rates, and ca. 60% of the infected patients succumb to the infection. Thus, one of the world greatest concerns is that the H5N1 virus will evolve to allow an efficient human infection and human-to-human transmission. Natural killer (NK) cells are one of the innate immune components playing an important role in fighting against influenza viruses. One of the major NK activating receptors involved in NK cell cytotoxicity is NKp46. We previously demonstrated that NKp46 recognizes the hemagglutinin proteins of B and A influenza virus strains. Whether NKp46 could also interact with H1N1-2009 virus or with the avian influenza virus is still unknown. We analyzed the immunological properties of both the avian and the H1N1-2009 influenza viruses. We show that NKp46 recognizes the hemagglutinins of H1N1-2009 and H5 and that this recognition leads to virus killing both in vitro and in vivo. However, importantly, while the swine H1-NKp46 interactions lead to the direct killing of the infected cells, the H5-NKp46 interactions were unable to elicit direct killing, probably because the NKp46 binding sites for these two viruses are different.

LONG ACTING SOMATOSTATIN ANALOGUES ARE AN EFFECTIVE TREATMENT FOR TYPE 1 GASTRIC CARCINOID TUMOURS

BACKGROUND Gastric carcinoid tumours type 1 (GCA1) originate from hyperplastic enterochromaffin-like (ECL) cells secondary to hypergastrinaemia. Treatment with somatostatin analogues (SSA) might impede ECL-cell hyperplasia by suppressing gastrin secretion and/or by a direct anti-proliferative effect on ECL cells. We conducted a multicentre prospective study to assess the effects of long-acting SSA on hypergastrinaemia and ECL-cell proliferation in patients with GCA1. METHODS We studied 15 patients with GCA1 treated with monthly long-acting release octreotide (LAR) (20-30 mg; n=14) or Lanreotide 90 mg (n=1) for at least 6 months. Patients had serum gastrin and chromogranin A measurements performed and biopsies taken from both tumours and surrounding mucosa before, and every 6-12 months following treatment. Sections were immunostained for neuroendocrine markers. The cell proliferation index Ki-67, intensity of staining before and after treatment and the degree of gastric wall invasion were also assessed. RESULTS All patients tolerated treatment well (mean follow-up of 18 months). In 11 patients (73%), a complete disappearance of the tumours at 1 year of treatment was observed on endoscopy, while in three patients (20%), the tumours decreased significantly in number and size. Gastrin levels normalized in 25% of patients, and were reduced by more than 80% in the remaining 75%. CONCLUSIONS Treatment with SSAs in GCA1 leads to a substantial tumour load reduction, with a concomitant decrease of serum gastrin levels. Our data indicate an important anti-proliferative effect of SSA on ECL cells, providing clinical benefit and obviating, at least temporarily, the need for invasive therapies for GCA1.