Disease relevance of NCR2

• The low surface density of NKp46, NKp30 and NKp44 was also confirmed in in-vitro-activated NK cell populations and NK cell clones derived from HIV-1 patients compared with uninfected donors [1].
• ANIMALS AND INTERVENTIONS: 31 male Sprague Dawley rats randomised into four groups: controls, given vehicle alone (n = 6), LPS 6 mg/kg body weight alone (n = 12), and LPS 6 mg/kg but pretreated with the retinoic acid receptor-alpha (RAR-alpha) agonists CD336 (n = 6) and CD2081 (n = 7) [2].

High impact information on NCR2

• Three novel, NK-specific, triggering surface molecules (NKp46, NKp30, and NKp44) have been identified [3].
• 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 [4].
• Unlike genes coding for other receptors involved in NK cell triggering or inhibition, the NKp44 gene is on human chromosome 6 [5].
• 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 [5].
• 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 [5].

Biological context of NCR2

• In gel mobility shift assay, we observed that HMG proteins 1 and 2 could bind to both negative regulatory regions (NCR1 and NCR2) [6].
• Searching for NKp44 orthologs, we found similarity to ESTs from a novel rodent TREM family member, which we termed TREM6, and not to any possible NKp44 ortholog [7].
• Here, we present activated polyclonal gammadelta T cells from healthy donors with an NK T cell-like phenotype expressing the natural cytotoxicity receptor NKp44 [8].
• Furthermore, using the technique of the in vitro reconstitution of nucleosome, the mono- and di- nucleosomes were assembled in vitro with both HS2core (-10681 to -10970 bp) and NCR2 (-372 to -194 bp) DNA sequences in the 5 flanking sequence of human b-globin gene [9].
• 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 [10].

Anatomical context of NCR2

• NKp44 (NCR2) is a member of the natural cytotoxicity receptor (NCR) family that is expressed on activated human NK cells [11].
• By expressing a chimeric receptor in an NK-like cell line, we found that this ITIM-like motif from NKp44 lacks inhibitory capacity in a redirected cytotoxicity assay [11].
• To our knowledge, this is the first description of the expression of NKp44 on polyclonal gammadelta T cells [8].
• Here, we show that one of these receptors, NKp44, is present on a subset of natural interferon-producing cells (IPCs) in tonsils [12].
• 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 [10].

Associations of NCR2 with chemical compounds

• The NKp44 cytoplasmic tyrosine was efficiently phosphorylated in the chimeric receptor upon treating the cells with pervanadate, but it was unable to recruit ITIM-binding negative effector phosphatases [11].
• 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 [5].
• NCR-1 and NCR-2, the C. elegans homologs of the human Niemann-Pick type C1 disease protein, function upstream of DAF-9 in the dauer formation pathways [13].
• To determine the role of retinoic acid receptors (RARs) in the regulation of epithelial differentiation, we tested the effect of the synthetic retinoids CD336, CD2019, and CD666, selective agonists for RARalpha, RARbeta, and RARgamma, respectively, during differentiation of human nasal epithelial (HNE) cells in vitro [14].
• When pregnant hamsters were given an oral bolus of CD 336 or CD 135 during the early primitive streak stage of gestation, these retinoids proved 60-100 times more potent teratogens than all-trans-retinoic acid [15].

Regulatory relationships of NCR2

• NKp44 triggers NK cell activation through DAP12 association that is not influenced by a putative cytoplasmic inhibitory sequence [11].
• The human TREM gene cluster at 6p21.1 encodes both activating and inhibitory single IgV domain receptors and includes NKp44 [16].

Other interactions of NCR2

• Physical linkage to DAP12 requires lysine-183 in the NKp44 transmembrane domain [11].
• Isolated polyclonal gammadelta T cells cultured for 7 days according to the cytokine-induced killer cell (CIK) protocol with additional IL-15 revealed a surface expression of NKp44 of 8+/-7% (n=22) [8].
• We also generated NK-like cell lines expressing epitope-tagged wild-type or tyrosine to phenylalanine mutant (Y238F) versions of NKp44 and compared their capacities to induce activation marker expression, promote IFN-gamma production, or stimulate target cell cytotoxicity [11].
• Freshly isolated NK cells are NKp44 negative and lysed pEC exclusively in an NKG2D-dependent fashion [17].
• Crosslinking of NKp44 does not trigger IPC-mediated cytotoxicity but, paradoxically, inhibits interferon alpha (IFN-alpha) production by IPCs in response to cytosine-phosphate-guanosine (CpG) oligonucleotides [12].

Analytical, diagnostic and therapeutic context of NCR2

• Gel mobility shift assays showed that the nuclear extracts from JEG-3 cells contained proteins that form three complexes with NCR1, two with NCR2, and six with NCR3 [18].
• This could be confirmed by detection of NKp 44 mRNA by reverse transcription-polymerase chain reaction (RT-PCR). gammadelta T cells exhibited a marked cytotoxic activity against myeloma cells, which could be reduced by inhibition of NKp44 [8].
• In conclusion, strategies aimed to inhibit interactions between NKp44 and NKG2D on human NK cells and so far unknown ligands on pEC may prevent direct NK responses against xenografts but not xenogeneic Ab-dependent cell-mediated cytotoxicity [17].
• Here we describe the molecular cloning of NKp44 [5].
• Crystallization and preliminary crystallographic characterization of the extracellular Ig-like domain of human natural killer cell activating receptor NKp44 [19].

References