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A natural cytotoxicity receptor (NCR) NKp46 has been shown to represent a novel NK cell-specific molecule involved in human NK cell activation. The natural cytotoxicity receptors (NCRs) are a recently characterized family of Ig-like activation receptors that appear to be major triggering receptors in tumor cell recognition. The three known NCRs include NKp46 and NKp30, which are expressed on circulating NKcells, and NKp44, which is expressed only on activating NK cells. NKp46 has been implicated in NK cell-mediated lysis of several autologous tumor cells, pathogen-infected cell lines and mononuclear phagocytes infected with an intracellular bacterium. The Lysis of tumor cells by NK-cells involves recognition by NKp46 of heparan sulfate moieties of membrane heparan sulfate proteoglycans. Furthermore, NKp46 is a surface receptor involved in NK-cell cell death by apoptosis. NKp46 has two extracellular Ig-like domains followed by a ~40 residue stalk region, a type I transmembrane domain, and a short cytoplasmic tail. The extracellular Ig-like domain of NKp46 (22-255aa) is purified by FPLC gel-filtration chromatography, after refolding of the isolated inclusion bodies in a redox buffer. In addition, engagement of the antigen with the monoclonal antibody stimulates intracellular calcium levels and the synthesis of cytokines. CD59 is an NKp46 coreceptor (by physical association) together they activate cytotoxicity of human NK-cells, their engagement results in tyrosine phosphorylation of CD3-zeta chains associated with NKp46. Reduced cell surface expression of NKp46 and other NK-cell receptors is linked to the impaired NK-cell cytolytic function in viremic HIV-1 infection.

The Fas receptor (CD95) mediates apoptotic signaling by Fas-ligand expressed on the surface of other cells. The Fas-FasL interaction plays an important role in the immune system and lack of this system leads to autoimmunity, indicating that Fas-mediated apoptosis removes self-reactive lymphocytes. Fas signaling is also involved in immune surveillance to remove transformed cells and virus infected cells. Binding of FAS to oligimerized FasL on another cell activates apoptotic signaling through a cytoplasmic domain termed the death domain that interacts with signaling adaptors including FAF, FADD and DAX to activate the caspase proteolytic cascade. Caspase-8 and caspase-10 are first activated, to then cleave and activate downstream caspases, and a variety of cellular substrates that lead to cell death. Caspases cleave nuclear lamins, causing the nucleus to break down and lose its normal structure and another caspase substrate is DFF, inducing cleavage and degradation of the genome. Other caspase substrates are involved in cytoskeletal structure, cell cycle regulation and signaling pathways. Activation of JNK kinase, activation of Jun, and production of ceramide may also play roles in Fas-mediated apoptosis. Activation of fas-mediated apoptosis is opposed by I-FLICE and FAP. Viruses and tumors may escape immune surveillance in part through suppression of fas-mediated apoptosis using similar mechanisms.

Bcl-2-like protein 11 (BCL2L11) is a member of the Bcl-2 family and contains a Bcl-2 homology domain 3 (BH3). BCL2L11 expression can be stimulated by nerve growth factor (NGF), in addition to the forkhead transcription factor (FKHR-L1) which proposes a role of the BCL2L11 gene in neuronal and lymphocyte apoptosis. BCL2L11 interacts with other members of the BCL-2 protein family, including BCL2, BCL2L1/BCL-X(L), and MCL1, and acts as an apoptotic activator. BimEL, BimL and BimS are the main isoforms which are ubiquitously expressed with a tissue-specific variation. The Isoform Bim-gamma, on the other hand, is most abundantly expressed in the small intestine and colon, and in lower levels in spleen, prostate, testis, heart, liver and kidney.

KLRD1, also known as Killer Cell Lectin Like Receptor D1, is expressed on the surface of natural killer cells in the innate immune system. KLRD1 functions as a receptor for the recognition of MHC class I HLA-E molecules by NK cells and some cytotoxic T-cells. KLRD1 can create disulfide-bonded heterodimer with NKG2 family members. CD94 & NKG2 complex interacts with (HLA)-E, Human Leukocyte Antigen on target cells on the surface of natural killer cells.

CRADD is a 22kDa, widely-expressed cytosolic adaptor/signaling protein that induces cell apoptosis/cell death in numerous tissues. CRADD is a death domain (CARD) that recruits, caspase 2/ICH1 to the cell death signal transduction complex that includes TNFR1A, RIPK1/RIP kinase, and numbers of other CARD domain-containing proteins.

CDC123 is a member of the CDC123 family. CDC123is required for S phase entry of the cell cycle. It is also broadly expressed in spleen,thymus, prostate, testis, ovary, small intestine, colon and leukocytes with the uppermost expression in testis.

BCL2 gene encodes an integral outer mitochondrial membrane protein that blocks the apoptotic death of some cells such as lymphocytes. Constitutive expression of BCL2, such as in the case of translocation of BCL2 to Ig heavy chain locus, is thought to be the cause of follicular lymphoma. Two transcript variants, produced by alternate splicing, differ in their C-terminal ends.

BCL2 gene encodes an integral outer mitochondrial membrane protein that blocks the apoptotic death of some cells such as lymphocytes. Constitutive expression of BCL2, such as in the case of translocation of BCL2 to Ig heavy chain locus, is thought to be the cause of follicular lymphoma. Two transcript variants, produced by alternate splicing, differ in their C-terminal ends.

Death-Associated Protein (DAP) is a proline-rich protein. DAP, which is a negative regulator of autophagy, takes part in the mediation of IFN-gamma-induced cell death.

NKp30 is a natural cytotoxicity receptor (NCR) that may assist NK cells in the lysis of tumor cells. NKp30 interacts with CD3-zeta (CD247), a T-cell receptor. A single nucleotide polymorphism in the 5'' untranslated region of the NKp30 gene has been linked to mild malaria susceptibility.

PTB domain-containing engulfment adapter protein 1 (GULP1) is an evolutionarily conserved adaptor protein essential for efficient phagocytosis of apoptotic cells by phagocytes. Furthermore, GULP1 helps modulate cellular glycosphingolipid and cholesterol transport. In addition, GULP1 may have a role in the internalization and endosomal trafficking of various LRP1 ligands, such as PSAP. Increased cytoplasmic levels of GULP1 are linked with increases in cellular levels of GTP-bound ARF6.

Killer Cell lectin-Like Receptor Subfamily K, Member 1 (KLRK1) is an activating receptor which has recently generated considerable interest. The most fascinating of these, are a couple of closely related proteins known as MICA and MICB. These are cell-surface molecules distantly related to MHC class I proteins, and their genes have elements of heat shock promoters. Thus, MICA and MICB are expressed in the course of cell stress and are up-regulated in tumor cells and during viral infections. This receptor-ligand combination has a crucial role in the immune response to various pathologies.

BCL2-Like 1 (BCL2L1) belongs to the BCL-2 protein family. BCL2L1 is found at the outer mitochondrial membrane controls outer mitochondrial membrane channel (VDAC) opening. In addition, BCL2L1 regulate s a switch between cell death modes during mitotic arrest.

NCR2 (NKp44) belongs to the natural cytotoxicity receptor (NCR) family which is expressed on activated human NK cells. NKp44 exhibits a single extracellular Ig-like V domain and a transmembrane portion containing the charged residue (Lysine), possibly involved in the association with KARAP/DAP12 molecules. The gene coding for NKp44 maps on human chromosome 6p21.1.

Killer-cell immunoglobulin-like receptors (KIRs), are a family of cell surface glycoproteins found on Natural Killer (NK) Cells, which are important cells of the immune system. They control the killing function of these cells by interacting with MHC class I molecules, which are expressed on all cell types. This interaction allows them to identify virally infected cells or tumor cells that have a distinctive low level of Class I MHC on their surface. The majority of KIRs are inhibitory, which means that their recognition of MHC suppresses the cytotoxic activity of their NK cell. Only a limited number of KIRs have the capacity to activate cells.
The KIR genes are found in a cluster on chromosome 19q13.4 within the 1 Mb leukocyte receptor complex (LRC). KIR molecules are extremely polymorphic, meaning their gene sequences differ significantly between individuals, so that different individuals have different arrays/repertoires of KIR genes.
The KIR proteins are categorized by the number of extracellular immunoglobulin domains (2D or 3D) and by whether they have a long (L) or short (S) cytoplasmic domain. KIR proteins with the long cytoplasmic domain transduce inhibitory signals upon ligand binding via an immune tyrosine-based inhibitory motif (ITIM). Whereas KIR proteins with the short cytoplasmic domain lack the ITIM motif and instead associate with the TYRO protein tyrosine kinase binding protein to transduce activating signals.
The three Ig-domain from of inhibitory killer cell Ig-like receptor 1(KIR3DL1, NKB1, nkat3, p70KIR) is a NK cell receptor for polymorphic HLA-B determinant. KIR3DLl recognizes the Bw4 determinant defined by sequence motifs at positions 77-83 of the HLA-B heavy chain. The cytoplasmic tail of KIR, which contains two immunoreceptor tyrosine-based inhibition motifs (ITIMs), mediates inhibitory signal transduction that prevents killer cell-mediated cytotoxicity. A His-tag fusion protein of KIR3DL1 cytoplasmic tail (361-444aa) was overexpressed as insoluble protein aggregates (inclusion bodies).

BCL2 gene encodes an integral outer mitochondrial membrane protein that blocks the apoptotic death of some cells such as lymphocytes. Constitutive expression of BCL2, such as in the case of translocation of BCL2 to Ig heavy chain locus, is thought to be the cause of follicular lymphoma. Two transcript variants, produced by alternate splicing, differ in their C-terminal ends.

BAK1 is a member of the BCL2 protein family. The BCL2 family members form oligomers or heterodimers and act as anti- or pro-apoptotic regulators which are involved in a wide variety of cellular activities. The BAK1 gene encodes a receptor-like kinase (RLK) with a putative extracellular domain, a single transmembrane domain, an intracellular-juxtamembrane domain, and a kinase domain. BAK1 localizes to mitochondria, and functions to induce apoptosis. BAK1 interacts with and accelerates the opening of the mitochondrial voltage-dependent anion channel, leading to a loss in membrane potential and the release of cytochrome c. Furthermore, BAK1 interacts with the tumor suppressor P53 after exposure to cell stress. BAK1 expression is linked to the progression of Prostate cancer.

Killer-cell immunoglobulin-like receptors (KIRs), are a family of cell surface glycoproteins found on Natural Killer (NK) Cells, which are important cells of the immune system. They control the killing function of these cells by interacting with MHC class I molecules, which are expressed on all cell types. This interaction allows them to identify virally infected cells or tumor cells that have a distinctive low level of Class I MHC on their surface. The majority of KIRs are inhibitory, which means that their recognition of MHC suppresses the cytotoxic activity of their NK cell. Only a limited number of KIRs have the capacity to activate cells.
The KIR genes are found in a cluster on chromosome 19q13.4 within the 1 Mb leukocyte receptor complex (LRC). KIR molecules are extremely polymorphic, meaning their gene sequences differ significantly between individuals, so that different individuals have different arrays/repertoires of KIR genes.
The KIR proteins are categorized by the number of extracellular immunoglobulin domains (2D or 3D) and by whether they have a long (L) or short (S) cytoplasmic domain. KIR proteins with the long cytoplasmic domain transduce inhibitory signals upon ligand binding via an immune tyrosine-based inhibitory motif (ITIM). Whereas KIR proteins with the short cytoplasmic domain lack the ITIM motif and instead associate with the TYRO protein tyrosine kinase binding protein to transduce activating signals.
KIR2DL1 is an inhibitory Killer Cell Ig-like Receptor (KIR, previously called p58 KIR, p58.1, cl-42, NKAT1, or KIR-K6), which recognizes class I MHC molecules (HLA-Cw2, -Cw4, -Cw5, and Cw6). The extracellular domain of KIR2DL1 was over expressed as insoluble protein aggregates (inclusion bodies).

BCL2 gene encodes an integral outer mitochondrial membrane protein that blocks the apoptotic death of some cells such as lymphocytes. Constitutive expression of BCL2, such as in the case of translocation of BCL2 to Ig heavy chain locus, is thought to be the cause of follicular lymphoma. Two transcript variants, produced by alternate splicing, differ in their C-terminal ends.

KLRC3 belongs to the NKG2 group that can be found mostly in natural killer (NK) cells and encodes a family of transmembrane proteins known for their C-type lectin domain and their type II membrane orientation (extracellular C terminus). The NKG2 gene family is situated inside the NK complex, a region which has quite a few C-type lectin genes mostly expressed on NK cells.

Human TNFRSF10A is a type 1 transmembrane protein in the TNF R superfamily. TNFRSF10A is not expressed in rodents. The trimeric ligand Trail binds TNFRSF10A and induces apoptosis, and recombinant, soluble forms of the receptor inhibit Trail-induced apoptosis. TNFRSF10A is expressed generally in damaged, infected, and malignant cells. TNFRSF10A functions in immune surveillance, inducing apoptosis in cancer cells but not normal cells.

TNF-related apoptosis-inducing ligand (TRAIL) is a ligand molecule which induces apoptosis. It is a type II transmembrane protein with homology to other members of the tumor necrosis factor family.
In humans, the gene that encodes for TRAIL is located at chromosome 3q26.
TRAIL binds to the death receptors, DR4 and DR5. The process of apoptosis is caspase-8-dependent. This protein preferentially induces apoptosis in transformed and tumor cells, but does not appear to kill normal cells although it is expressed at a significant level in most normal tissues.

GADD45B is part of the nuclear proteins to interact with various proteins whose transcript levels are raised after stressful growth arrest conditions and treatment with DNA-damaging agents. GADD45B reacts to environmental stresses by mediating activation of the p38/JNK pathway which is mediated through their protein binding and activating MTK1/MEKK4 kinase, which is an upstream activator of both p38 and JNK MAPKs. GADD45B is involved in the regulation of growth and apoptosis. GADD45b takes part during chondrocyte terminal differentiation and mediates MMP-13 gene expression. GADD45 in B cells is induced by CD40 via a mechanism that involves NF-kappa B and that induction suppresses Fas-mediated killing. GADD45b is down-regulated in most cases of hepatocellular carcinoma (HCC), and is a molecular marker in the diagnosis of HCC and as a possible therapeutic target.

FADD is an adaptor protein that cooperates with a variety of cell surface receptors and mediates cell apoptotic signals. Using its C-terminal death domain, FADD is recruited by TNFRSF6/Fas-receptor, tumor necrosis factor receptor, TNFRSF25, and TNFSF10/TRAIL-receptor, and consequently it take parts in the death signaling initiated by these receptors. FADD interaction with the receptors reviels the N-terminal effector domain of, which allows it to recruit caspase-8, and thus initiate the cysteine protease cascade. Knockout studies in mice furthermore propose the significance of FADD in premature T cell development. FADD plays a role in survival/proliferation and cell cycle development. FADD also takes part in cellular sublocalization, protein phosphorylation, and inhibitory molecules.