Myeloid DAP12-associating lectin (MDL)-1 is a cell surface receptor involved in the activation of myeloid cells

Abstract

Crosslinking of immunoreceptor tyrosinebased activation motif (ITAM)-containing receptor complexes on a variety of cells leads to their activation through the sequential triggering of protein tyrosine kinases. Recently, DAP12 has been identified as an ITAM-bearing signaling molecule that is noncovalently associated with activating isoforms of MHC class I receptors on natural killer cells. In addition to natural killer cells, DAP12 is expressed in peripheral blood monocytes, macrophages, and dendritic cells, suggesting association with other receptors present in these cell types. In the present study, we report the molecular cloning of the myeloid DAP12-associating lectin-1 (MDL-1), a DAP12-associating membrane receptor expressed exclusively in monocytes and macrophages. MDL-1 is a type II transmembrane protein belonging to the C type lectin superfamily and contains a charged residue in the transmembrane region that enables it to pair with DAP12. Crosslinking of MDL-1͞DAP12 complexes in J774 mouse macrophage cells resulted in calcium mobilization. These findings suggest that signaling via MDL-1͞DAP12 complexes may constitute a significant activation pathway in myeloid cells.Crosslinking of immune receptors, such as the B or T cell receptor (BCR or TCR) or Fc receptors, on a variety of cells leads to their activation through the sequential activation of protein tyrosine kinases (PTKs) (1). These receptor complexes have in common that ligand binding and signal transduction occur in distinct receptor subunits. In their signal-transducing subunits (e.g., CD3 in the TCR), these complexes contain one or more immunoreceptor tyrosine-based activation motifs (ITAMs). Upon engagement of the ligand-binding subunit, the cytoplasmic ITAMs in the signaling subunits are tyrosinephosphorylated by src-family PTKs. This leads to the recruitment of syk-family PTKs, which, in turn, triggers a cascade of intracellular phosphorylation that results in cellular activation.A number of receptor complexes that recognize MHC class I molecules have been identified on natural killer (NK) cells (2-5). Although many of these receptors possess immunoreceptor tyrosine-based inhibition motifs (ITIMs) that recruit protein tyrosine phosphatases and inhibit NK cell activation, several of these MHC class I receptors lack intrinsic signaling sequences. These receptors express a charged residue in their transmembrane domain, suggesting the association with an adapter molecule that is capable of signaling. Recently, we identified DAP12, a type I glycoprotein containing an ITAM (6). DAP12 is expressed at the cell surface of NK cells noncovalently associated with the human KIR2DS receptor for HLA-C (6, 7), the mouse Ly49D and Ly49H receptors (8, 9), and the human heterodimer CD94͞NKG2C receptor complex recognizing HLA-E (10).In addition to NK cells, DAP12 is expressed in peripheral blood granulocytes, monocytes, and dendritic cells, suggesting association with other receptors present in these cell types. In the present study, we report the cloning ...

Structural Flexibility of the Macrophage Dengue Virus Receptor CLEC5A

“…DAP12 has no extracellular domain and interacts with CLEC5A through an ionic interaction between polar residues in the transmembrane regions of both proteins (a lysine in CLEC5A and an aspartate in DAP12). The presence of this transmembrane ionic interaction has been shown to be critical for both DAP12 and DAP10 signaling (4,7,34). However, it is unclear how this charge-mediated association within the membrane could transmit information about ligand binding from the extracellular domain of CLEC5A to the intracellular signaling domain of DAP12 as there are no structural studies of the transmembrane interactions of DAP12 or DAP10 with CLEC5A.…”

“…CLEC5A plays an important role in the activation of macrophages; CLEC5A stimulation of mouse myeloid cells up-regulates expression of the inflammatory mediator CD11b, inducing significant chemokine production and concurrent signaling through Toll-like receptors (4,8). Both human and mouse CLEC5A have been reported to bind to dengue virions, and the interaction is inhibited in vitro by fucose and mannan (3).…”

“…Signal transmission occurs through the interaction with DAP12, which has a cytoplasmic immunoreceptor tyrosine-based activation motif (4,5). The CLEC5A-DAP12 interaction depends upon a chargecharge interaction between a lysine residue and an aspartate residue in the transmembrane domains of CLEC5A and DAP12, respectively (4,6). Ligand binding by CLEC5A induces the phosphorylation of DAP12 by Src kinases and an interaction with Syk, which triggers further downstream signaling events (6).…”

“…CLEC5A contains a C-type lectin-like domain in its C-terminal extracellular region and has only four amino acids in its predicted N-terminal cytoplasmic region. Signal transmission occurs through the interaction with DAP12, which has a cytoplasmic immunoreceptor tyrosine-based activation motif (4,5). The CLEC5A-DAP12 interaction depends upon a chargecharge interaction between a lysine residue and an aspartate residue in the transmembrane domains of CLEC5A and DAP12, respectively (4,6).…”

The centromeric part of the human NK gene complex: linkage of LOX-1 and LY49L with the CD94/NKG2 region

“…Recently, the lectin-type LLT1 receptor was reported to be broadly expressed in lymphocytes. 28 Furthermore, a member of another lectin-type receptor class, LOX-1, has been implicated as a receptor for oxidized low-density lipoprotein on endothelial cells and monocytes. 29 In order to establish the basis to search for novel forms of lectin-type receptor genes, to link the NKG2 and CD94 NK cell receptor genes 13,23 with the region containing the LY49L and other potentially related genes and to get some clues to the evolution of the locus, we have now constructed a physical map based on PAC and BAC clones of the centromeric part of the NK complex region.…”