Molecular Cloning of NKp46: A Novel Member of the Immunoglobulin Superfamily Involved in Triggering of Natural Cytotoxicity

Abstract

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 CD3ζ 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.

The CD16−CD56bright NK Cell Subset Is Resistant to Reactive Oxygen Species Produced by Activated Granulocytes and Has Higher Antioxidative Capacity Than the CD16+CD56dim Subset

“…Down-regulation of NKp46 occurs in a manner that closely parallels that of mitochondrial membrane depolarization, several hours before cell death. Because NKp46 is downregulated very early, this seems to be an active process that would presumably quickly limit CD56 dim NK cells' ability to lyse NKp46 ligand-expressing targets, such as tumor cells (34,35). H 2 O 2 exposure has been shown to inhibit NK cytotoxic ability against K562 cells (31,33,36), and signaling through NKp46 is very important for lysis of K562 cells by freshly isolated NK cells (35).…”

NKp46 and NKG2D Recognition of Infected Dendritic Cells Is Necessary for NK Cell Activation in the Human Response to Influenza Infection

“…Anti-NKp30 (F252, IgM) and anti-NKp46 (KL247, IgM,), which were from hybridoma supernatants were used at 1/2 dilutions. All Ab concentrations for blocking studies were chosen based on published information (34,36,38). F(abЈ) 2 of the NKG2D mAb (clone 1D11) were prepared using immobilized ficin (Pierce) according to the manufacturer's instructions.…”

Back to the future –defining NK cells and T cells

“…However, human NK cell clones established from fetal liver, which do not rearrange TCRb, TCRc, or TCRd genes, expressed CD3d, CD3c, and CD3e proteins in their cytoplasm, but not on their cell surface, and CD3e is transcribed by IL-2 activated human peripheral blood NK cells [7]. Both mouse and human NK cells express CD3f, which associates with NKp46 [8], and in humans with CD16 (FccRIII) [9] and NKp30 [10]. Collectively, these prior studies have established that NK cells that do not rearrange their TCR genes can express germline TCR transcripts and can express CD3 subunit proteins.…”