THE BM88 ANTIGEN, A NOVEL NEURON-SPECIFIC MOLECULE, ENHANCES THE DIFFERENTIATION OF MOUSE NEUROBLASTOMA-CELLS

The BM88 antigen is a neuron-specific molecule widely distributed in t he mammalian nervous system. It is a 22-kDa, apparently not glycosylat ed, integral membrane protein, which appears early during brain develo pment and remains at high levels in the mature animal. Here, we descri be the cDNA cloning of the porcine BM88 antigen and present evidence t hat this protein is involved in neuroblastoma cell differentiation. Th e deduced protein is a novel molecule consisting of 140 amino acids an d bears a putative transmembrane domain at the COOH-terminal region. T he mRNA of this protein is expressed only in neural tissues, where it is restricted to neurons. Stably transfected Neuro-2a cells overexpres sing the BM88 antigen exhibited a significant change in morphology, re flected by enhanced process outgrowth, and a slower rate of division. Moreover, in the presence of differentiation agents, such as sucrose a nd retinoic acid, an accelerated differentiation of the transfected Ne uro-2a cells was observed. Especially in the presence of sucrose, the consequent overexpression of the BM88 antigen in the transfected cells resulted in their enhanced morphological differentiation accompanied by the induction of neurofilament protein expression. Our results sugg est that the BM88 antigen plays a role in the differentiation of neuro blastoma cells.