Phosphorylation of myelin-associated glycoprotein in cultured oligodendrocytes.

The myelin-associated glycoprotein (MAG) in primary cultures of oligodendrocytes is subject to phosphorylation in the absence of neurons. The positive response of this phosphorylation to vanadate suggests that one of the modified sites in MAG is phosphotyrosine. We found that phosphorylation was enhanced by brief treatment of the cells with insulin-like growth factor I and active phorbol ester, agents that stimulate oligodendrocyte differentiation. Preliminary observations suggest that phosphorylation enhances the association of MAG with the cytoskeleton.