V-REL INDUCES ECTOPIC EXPRESSION OF AN ADHESION MOLECULE, DM-GRASP, DURING B-LYMPHOMA DEVELOPMENT

In an effort to identify aberrantly expressed genes in v-rel-induced t umors, monoclonal antibodies were developed that reacted selectively w ith avian B-cell tumors. One antibody, HY78, immunoprecipitated a 120- kDa glycoprotein (p120) from cells that express v-rel. N-terminal amin o acid sequencing of p120 identified a 27-amino-acid sequence that is also present in DM-GRASP, an adhesion molecule belonging to the immuno globulin superfamily. Evidence from tissue distribution, immunological cross-reaction, PCR amplification, cDNA cloning, and DNA sequence sho ws that p120 is indeed DM-GRASP. Northern (RNA) analysis using a probe from the DM-GRASP gene identified a 5.3-kb transcript in mRNA from bu rsa, thymus, and brain as well as from v-rel-induced B-cell lymphomas but not from bursal B cells. The induction of this protein by v-rel du ring the development of bursal B-cell lymphomas appears, therefore, to be ectopic in nature. Overexpression of v-rel or c-rel in chicken emb ryonic fibroblasts, B-cell lines, and spleen mononuclear cells induces the expression of DM-GRASP. The ratio of DM-GRASP to v-Rel was fivefo ld higher than that of DM-GRASP/c-Rel in a B-cell line, DT95. Interest ingly, the presence of HY78 antibody inhibits the in vitro proliferati on of v-rel-transformed cells but not cells that immortalized by myc. These data suggest that DM-GRASP is one of the genes induced during v- rel-mediated tumor development and that DM-GRASP may be involved in th e growth of v-rel tumor cells.