Molecular cloning of transmembrane and soluble forms of a novel rat natural killer cell receptor related to 2B4

Natural killer (NK)-cell recognition of target cells and cytolytic function are controlled by multiple receptor-ligand interactions. These receptors c an transmit either positive or negative signals and belong to the lectin su perfamily or immunoglobulin superfamily (IgSF). One member of the IgSF, 2B4 , is expressed on the surface of all mouse and human NK cells and the subse t of T cells that mediate NK-like killing. In both mouse and human, 2B4 is a transmembrane protein and is the counter-receptor for CD48. Northern blot analysis had indicated the existence of 2B4-related genes. Here we report the cloning of novel cDNAs (r2B4R) closely related to the rat 2B4. Unlike 2 B4, rat NK cells express mRNA corresponding to both transmembrane (r2B4R-tm ) and soluble (r2B4R-se) forms of r2B4R. r2B4R-tm contains an open reading frame encoding a polypeptide of 311 amino acid residues. The encoded protei n has characteristics of type I transmembrane proteins with a 20-amino acid leader sequence, a 203-amino acid extracellular domain, a 23-amino acid tr ansmembrane domain, and a 65-amino acid cytoplasmic domain. r2B4R-se encode s a protein of 205 amino acid residues without a putative transmembrane dom ain. Northern blot analysis and reverse transcriptase-PCR analysis revealed that both transmembrane and soluble forms of r2B4R are expressed in interl eukin-2-activated NK cells.