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C Bottino

Publications and source records attributed to C Bottino.

At least 37 records · Page 2Linked to original sources
PubMed2000

Surface receptors delivering opposite signals regulate the function of human NK cells.

The effector function of NK cells is regulated by a number of positive and negative signals. The receptors involved in the negative regulation of NK cells are known since several years: they are represented by different families of MHC-specific receptors characterized by ITIM sequences in their cytoplasmic tail. In contrast, the surface molecules responsible for NK cell activation in the process of natural cytotoxicity and tumor cell lysis have remained elusive until recently. Three distinct NK-specific molecules termed 'natural cytotoxicity receptors' (NCR) have recently been identified and cloned. They play a complementary role in mediating NK cell activation in the interaction and lysis of most tumor cells. They are associated with different ITAM-containing adaptor proteins mediating signal transduction. Molecular cloning revealed novel members of the Ig superfamily displaying a limited homology with known human receptors.

Cytotoxicity, Immunologic↗
PubMed2000

Human natural killer cell activating receptors.

Natural killer (NK) cells were poorly characterized until 10 years ago and few molecules expressed on their cell surface were known. Now the situation has changed dramatically, since a plethora of receptors characterized by opposite functions have been functionally and molecularly defined. NK cells express clonally distributed inhibitory receptors specific for different groups of HLA class I alleles, thus protecting normal cells from NK-mediated lysis. On the contrary, various activating receptors are involved in triggering of NK-mediated natural cytotoxicity. Their engagement induces human NK cells to kill target cells that are either HLA class I-negative or -deficient. Here a brief description of the activating receptors and coreceptor and of their ligand(s) is given.

Cytotoxicity, Immunologic↗
PubMed2000

Natural cytotoxicity receptors that trigger human NK-cell-mediated cytolysis.

Natural killer (NK) cells can detect whether cells have undergone tumour transformation or viral infection. The discovery of specific inhibitory receptors for major histocompatibility complex class I molecules clarified the basis of this discrimination. However, the receptors responsible for NK-cell triggering in the process of natural cytotoxicity remained elusive until recently. Here, Alessandro Moretta and colleagues describe the identification and characterization of several such receptors.

Animals↗
PubMed2000

Triggering receptors involved in natural killer cell-mediated cytotoxicity against choriocarcinoma cell lines.

The lack of classical HLA-class I molecules on trophoblast is necessary to prevent allorecognition by maternal CTL, but may induce activation of NK cells. A protective role against NK cells equipped of suitable inhibitory receptors has been proposed for nonclassical HLA-class I molecules including HLA-E and HLA-G. In the present study we show that the NK-mediated killing of two choriocarcinoma cell lines, JAR and JEG3, is induced upon engagement of natural cytotoxicity receptors (NCR) with their specific ligands. In particular, we show that NKp44, a triggering receptor expressed at the NK cell surface only after in vitro culture in the presence of IL-2, plays a central role in triggering NK cytotoxicity against trophoblast cells. Also NKp46 appear to contribute to this function by cooperating with NKp44. On the other hand, other triggering receptors such as NKp30, 2B4, and NKG2D are not involved in killing of choriocarcinoma. Our findings suggest that resistance of trophoblast to NK-mediated cytotoxicity is the result of insufficient activating interactions between the various triggering NK receptors and their target cell ligands. On the other hand, the interaction of nonclassical HLA class I molecules with inhibitory NK receptors appears to play only a marginal role in regulating the susceptibility of choriocarcinoma to NK mediated cytotoxicity.

Antibodies, Monoclonal↗
PubMed2000

The human natural cytotoxicity receptors (NCR) that induce HLA class I-independent NK cell triggering.

The cytolytic activity mediated by human natural killer (NK) cells is the result of a balance between signals delivered by inhibitory and activating receptors. The inhibitory receptors are represented by different families of HLA-specific receptors characterized by immunoreceptor tyrosine-based inhibiting motif(ITIM) sequences in their cytoplasmic portion. The function and the specificity of the inhibitory receptors imply the existence of triggering receptors specific for non-HLA ligands that are responsible for the induction of the cytolytic activity against HLA class I-deficient target cells. These receptors have remained elusive until recently when three distinct NK-specific molecules, termed natural cytotoxicity receptors (NCR), were identified and cloned. The different members of this novel family of receptors play a complementary role in the recognition and lysis of target cells. The NCR family is composed by a heterogeneous group of molecules belonging to the Ig superfamily that associate to different immunoreceptor tyrosine-based activating motif (ITAM)-containing signal transducing polypeptides.

Cytotoxicity, Immunologic↗
PubMed1999

Identification and molecular characterization of NKp30, a novel triggering receptor involved in natural cytotoxicity mediated by human natural killer cells.

Two major receptors involved in human natural cytotoxicity, NKp46 and NKp44, have recently been identified. However, experimental evidence suggested the existence of additional such receptor(s). In this study, by the generation of monoclonal antibodies (mAbs), we identified NKp30, a novel 30-kD triggering receptor selectively expressed by all resting and activated human natural killer (NK) cells. Although mAb-mediated cross-linking of NKp30 induces strong NK cell activation, mAb-mediated masking inhibits the NK cytotoxicity against normal or tumor target cells. NKp30 cooperates with NKp46 and/or NKp44 in the induction of NK-mediated cytotoxicity against the majority of target cells, whereas it represents the major triggering receptor in the killing of certain tumors. This novel receptor is associated with CD3zeta chains that become tyrosine phosphorylated upon sodium pervanadate treatment of NK cells. Molecular cloning of NKp30 cDNA revealed a member of the immunoglobulin superfamily, characterized by a single V-type domain and a charged residue in the transmembrane portion. Moreover, we show that NKp30 is encoded by the previously identified 1C7 gene, for which the function and the cellular distribution of the putative product were not identified in previous studies.

Animals↗
PubMed1999

Identification and molecular cloning of p75/AIRM1, a novel member of the sialoadhesin family that functions as an inhibitory receptor in human natural killer cells.

In this study, by the generation of a specific monoclonal antibody, we identified p75/AIRM1 (for adhesion inhibitory receptor molecule 1), a novel inhibitory receptor that is mostly confined to human natural killer cells. p75/AIRM1 is a 75-kD glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates to src homology 2 domain-bearing protein tyrosine phosphatase (SHP)-1. The p75/AIRM1 gene is located on human chromosome 19 and encodes a novel member of the sialoadhesin family characterized by three immunoglobulin-like extracellular domains (one NH(2)-terminal V-type and two C2-type) and a classical immunoreceptor tyrosine-based inhibitory motif (ITIM) in the cytoplasmic portion. The highest amino acid sequence similarity has been found with the myeloid-specific CD33 molecule and the placental CD33L1 protein. Similar to other sialoadhesin molecules, p75/AIRM1 appears to mediate sialic acid-dependent ligand recognition.

Amino Acid Sequence↗
PubMed1999

NKp44, a triggering receptor involved in tumor cell lysis by activated human natural killer cells, is a novel member of the immunoglobulin superfamily.

Surface receptors involved in natural killer (NK) cell triggering during the process of tumor cell lysis have recently been identified. Of these receptors, NKp44 is selectively expressed by IL-2- activated NK cells and may contribute to the increased efficiency of activated NK cells to mediate tumor cell lysis. Here we describe the molecular cloning of NKp44. Analysis of the cloned cDNA indicated that NKp44 is a novel transmembrane glycoprotein belonging to the Immunoglobulin superfamily characterized by a single extracellular V-type domain. The charged amino acid lysine in the transmembrane region may be involved in the association of NKp44 with the signal transducing molecule killer activating receptor-associated polypeptide (KARAP)/DAP12. These molecules were found to be crucial for the surface expression of NKp44. In agreement with data of NKp44 surface expression, the NKp44 transcripts were strictly confined to activated NK cells and to a minor subset of TCR-gamma/delta+ T lymphocytes. Unlike genes coding for other receptors involved in NK cell triggering or inhibition, the NKp44 gene is on human chromosome 6.

Adaptor Proteins, Signal Transducing↗
PubMed1999

The murine homologue of the human NKp46, a triggering receptor involved in the induction of natural cytotoxicity.

The NKp46 molecule has been proposed to play the role of triggering receptor in the natural cytotoxicity mediated by human NK cells. In this study we have identified the gene encoding the murine NKp46 homologue that we termed MAR-1. The MAR-1 gene is localized on chromosome 7 that is synthenic to the human chromosome 19 where the NKp46 gene is located. MAR-1 encodes a type I transmembrane glycoprotein belonging to the immunoglobulin (Ig) superfamily that, like human NKp46, is characterized by two C2-type Ig-like domains, a transmembrane portion containing a positively charged residue and a cytoplasmic tail lacking the immunoreceptor tyrosine-based activation motif (ITAM). The MAR-1 protein is expressed on the surface of cell transfectants and displays a molecular mass of approximately 46 kDa similar to that of its human counterpart. Semiquantitative RT-PCR analysis showed that MAR-1, similar to the human NKp46, is selectively expressed by NK cells. The MAR-1 protein displays 58 % identity with the human NKp46 receptor. This high homology together with the presence of a charged amino acid (Arg) in the transmembrane portion suggest that MAR-1 may associate at the cell membrane into a multimeric complex with ITAM containing polypeptides.

Amino Acid Sequence↗
PubMed1999

NKp46 is the major triggering receptor involved in the natural cytotoxicity of fresh or cultured human NK cells. Correlation between surface density of NKp46 and natural cytotoxicity against autologous, allogeneic or xenogeneic target cells.

NKp46 is a novel triggering receptor expressed by all human NK cells that is involved in natural cytotoxicity. In this study we show that the surface density of NKp46 may vary in different NK cells and that a precise correlation exists between the NKp46 phenotype of NK clones and their natural cytotoxicity against HLA-class I-unprotected allogeneic or xenogeneic cells. Thus, NKp46bright clones efficiently lysed human and murine tumor cells while NKp46dull clones were poorly cytolytic against both types of target cells. We also show that the NKp46 phenotype of NK clones correlates with their ability to lyse HLA-class I-unprotected autologous cells. Finally, NKp46 was found to be deeply involved in the natural cytotoxicity mediated by freshly derived NK cells. This was indicated both by the inhibition of cytolysis after monoclonal antibody-mediated masking of NKp46 and by the correlation existing between the natural cytotoxicity of fresh NK cells derived from different donors and their NKp46 phenotype. In conclusion, these studies strongly support the concept that NKp46 plays a central role in the physiological triggering of NK cells and, as a consequence (in concert with killer inhibitory receptors), in the NK-mediated clearance of abnormal cells expressing inadequate amounts of HLA-class I molecules.

Cells, Cultured↗
PubMed1999

Molecular and functional characterization of IRp60, a member of the immunoglobulin superfamily that functions as an inhibitory receptor in human NK cells.

In this study we describe the functional and molecular characterization of IRp60 (inhibitory receptor protein 60), an inhibitory receptor expressed on all human NK cells. The IRp60 molecule has been identified by the generation of three novel monoclonal antibodies (mAb). Cross-linking of IRp60 by specific mAb strongly inhibits the spontaneous cytotoxicity of NK cells as well as the NK-mediated cytolytic activity induced via different non-HLA-specific or HLA-specific activating receptors. IRp60 is a 60-kDa glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates with the SH2-containing phosphatases SHP-1 and SHP-2. The IRp60 gene is located on human chromosome 17 and encodes a molecule belonging to the immunoglobulin (Ig) superfamily characterized by a single V-type Ig-like domain in the extracellular portion. The cytoplasmic tail contains three classical immunoreceptor tyrosine-based inhibitory motifs. Southern blot analysis revealed cross-hybridization with monkey and mouse genomic DNA, thus suggesting that IRp60 may be conserved among different species. Moreover, based on the use of different anti-IRp60 mAb, we could identify two IRp60 allelic variants. Since IRp60 is also expressed by other cell types, including T cell subsets, monocytes and granulocytes, it may play a more general role in the negative regulation of different leukocyte populations.

Amino Acid Sequence↗
PubMed1999

Natural killer cell-mediated recognition of human trophoblast.

Large numbers of natural killer cells are present within the maternal decidua close to the extravillous trophoblast cells. Most of these natural killer cells express high levels of inhibitory NK receptors (KIR) specific for HLA class I molecules. Since trophoblast cells only express HLA-C and HLA-G, the KIR expressed by decidual NK cells can only recognize these HLA class I molecules in order to avoid NK-mediated rejection of fetal tissues. We show that HLA-C recognition by decidual NK cells can be mediated by p58, LIR-1 and (indirectly) by CD94/NKG2A receptors. On the other hand, HLA-G recognition is not only mediated by LIR-1 and (indirectly) by CD94/NKG2A but also by a newly identified receptor termed p49. The p49 receptor, unlike the other KIR, appears to be selectively expressed by decidual NK cells.

Alleles↗
PubMed1998

Molecular cloning of NKp46: a novel member of the immunoglobulin superfamily involved in triggering of natural cytotoxicity.

NKp46 has been shown to represent a novel, natural killer (NK) cell-specific surface molecule, involved in human NK cell activation. In this study, we further analyzed the role of NKp46 in natural cytotoxicity against different tumor target cells. We provide direct evidence that NKp46 represents a major activating receptor involved in the recognition and lysis of both human and murine tumor cells. Although NKp46 may cooperate with other activating receptors (including the recently identified NKp44 molecule) in the induction of NK-mediated lysis of human tumor cells, it may represent the only human NK receptor involved in recognition of murine target cells. Molecular cloning of the cDNA encoding the NKp46 molecule revealed a novel member of the immunoglobulin (Ig) superfamily, characterized by two C2-type Ig-like domains in the extracellular portion. The transmembrane region contains the positively charged amino acid Arg, which is possibly involved in stabilizing the association with CD3zeta chain. The cytoplasmic portion, spanning 30 amino acids, does not contain immunoreceptor tyrosine-based activating motifs. Analysis of a panel of human/hamster somatic cell hybrids revealed segregation of the NKp46 gene on human chromosome 19. Assessment of the NKp46 mRNA expression in different tissues and cell types unambiguously confirmed the strict NK cell specificity of the NKp46 molecule. Remarkably, in line with the ability of NKp46 to recognize ligand(s) on murine target cells, the cDNA encoding NKp46 was found to be homologous to a cDNA expressed in murine spleen. In conclusion, this study reports the first characterization of the molecular structure of a NK-specific receptor involved in the mechanism of NK cell activation during natural cytotoxicity.

Amino Acid Sequence↗
PubMed1998

NKp44, a novel triggering surface molecule specifically expressed by activated natural killer cells, is involved in non-major histocompatibility complex-restricted tumor cell lysis.

After culture in interleukin (IL)-2, natural killer (NK) cells acquire an increased capability of mediating non-major histocompatibility complex (MHC)-restricted tumor cell lysis. This may reflect, at least in part, the de novo expression by NK cells of triggering receptors involved in cytolysis. In this study we identified a novel 44-kD surface molecule (NKp44) that is absent in freshly isolated peripheral blood lymphocytes but is progressively expressed by all NK cells in vitro after culture in IL-2. Different from other markers of cell activation such as CD69 or VLA.2, NKp44 is absent in activated T lymphocytes or T cell clones. Since NKp44 was not detected in any of the other cell lineages analyzed, it appears as the first marker specific for activated human NK cells. Monoclonal antibody (mAb)-mediated cross-linking of NKp44 in cloned NK cells resulted in strong activation of target cell lysis in a redirected killing assay. This data indicated that NKp44 can mediate triggering of NK cell cytotoxicity. mAb-mediated masking of NKp44 resulted in partial inhibition of cytolytic activity against certain (FcgammaR-negative) NK-susceptible target cells. This inhibition was greatly increased by the simultaneous masking of p46, another recently identified NK-specific triggering surface molecule. These data strongly suggest that NKp44 functions as a triggering receptor selectively expressed by activated NK cells that, together with p46, may be involved in the process of non-MHC-restricted lysis. Finally, we show that p46 and NKp44 are coupled to the intracytoplasmic transduction machinery via the association with CD3zeta or KARAP/DAP12, respectively; these associated molecules are tyrosine phosphorylated upon NK cell stimulation.

Biomarkers↗
PubMed1998

The activating form of CD94 receptor complex: CD94 covalently associates with the Kp39 protein that represents the product of the NKG2-C gene.

Inhibitory receptor complexes formed by CD94 and NKG2-A (Kp43) molecules have been implicated in HLA class I recognition by human natural killer (NK) cells. Additional forms of CD94 receptors have recently been described in NK cells characterized by the lack of NKG2-A expression. These CD94 receptors were shown to display activating functions. Immunoprecipitation with anti-CD94 monoclonal antibodies (mAb) led to the identification, in these cells, of a 39-kDa (Kp39) molecule that was originally believed to represent an activating isoform of the CD94 molecules. In the present study we show that the Kp39 molecule is covalently associated with CD94 and displays a protein backbone (26 kDa) similar to that of NKG2-A (Kp43) glycoproteins. Peptide mapping analysis indicates that Kp39 and NKG2-A glycoproteins belong to the same molecular family. A novel NKG2-specific mAb (termed P25) has been generated that specifically reacts with both NKG2-A and NKG2-C molecules, but fails to recognize NKG2-E molecules. Analysis of polyclonal and clonal NK cells shows that P25 mAb reacts with all NKG2-A+ cells and with a fraction of CD94+ cells lacking the expression of NKG2-A. These data indicate that NKG2-C molecules are indeed expressed only in a subset of cells lacking the expression of NKG2-A. The CD94-associated Kp39 molecule can be detected only in NKG2-A- P25+ cells, i.e. cells expressing NKG2-C molecules. Indeed, reverse transcription-polymerase chain reaction analysis performed on a large panel of NK clones indicates that NKG2-A- P25+ NK clones express the NKG2-C transcript. Notably, the cytolytic activity of these clones can be triggered by the P25 mAb in redirected killing analysis. Finally, biochemical analysis of COS7 cells cotransfected with CD94 and NKG2-C demonstrates the identity between Kp39 and NKG2-C molecules. Altogether, our data demonstrate that NKG2-C molecules associate with CD94 to form an activating receptor complex in a subset of human NK cells.

Amino Acid Sequence↗