IDENTIFICATION AND CHARACTERIZATION OF A NOVEL SURFACE-ANTIGEN GENE INDUCED IN MAST-CELLS ACTIVATED THROUGH THE HIGH-AFFINITY IGE RECEPTOR

In an effort to isolate novel genes involved in inflammation and/or ma st cell activation, we have used a combination of differential screeni ng and subtractive hybridization to isolate genes whose expression are induced upon activation of a transformed rat mast cell line. One of t he isolated clones, pMCA-32, contained an open reading frame of 278 am ino acids that included a putative hydrophobic transmembrane domain, a cysteine rich Ig-like extracellular domain, and a cytoplasmic domain containing three consensus SH2-domain phosphotyrosine binding sites. T he MCA-32 gene is also highly conserved between rat and mouse, with th e two coding regions being 73% identical. Although the MCA-32 coding r egion did not contain an obvious signal peptide, MCA-32 protein was de tected on the surface of rat mast cells, and the cloned cDNA produced a cell surface protein when expressed in COS-7 cells. MCA-32 RNA from both mouse and rat undergoes alternative splicing, producing an mRNA c ontaining an in-frame deletion of the TM domain, suggesting that a for m of MCA-32 protein may be secreted. MCA-32 mRNA expression was up-reg ulated upon activation of RBL-2H3 cells and was highly abundant in pri mary peritoneal mast cells. Expression of MCA-32 RNA was only observed in primary and transformed mast cells from rat, while in the mouse MC A-32, RNA was also produced in significant amounts by a number of tran sformed monocyte cell lines. Thus, MCA-32 is a novel surface protein w hose structure and expression suggest roles in the development and/or activation of mast cells and monocytes.