The 43-kDa neuronal growth-associated protein (GAP-43) is present in plasma membranes of rat astrocytes

One of the neuronal growth-associated proteins, GAP-43 (molecular mass, approximately 43 kDa; pI 4.3), is abundant in growth-cone membranes and corresponds to a major protein kinase C substrate, the 46-kDa phosphoprotein (pp46), of a growth-cone-enriched subcellular fraction. This protein has the following additional designations (depending on context): B-50 (phospholipid metabolism), F1 (synaptic plasticity), and p57 (calmodulin binding). We show that a protein with the same molecular mass and isoelectric point as GAP-43, which interacts with anti-GAP-43 antibodies on immunoblots, is present in the plasma membranes of cultured neonatal rat cortical astrocytes. Double-immunofluorescence labeling of cells with a serum against glial fibrillary acidic protein and anti-GAP-43 antibody was observed. Furthermore, astrocytic protein was phosphorylated in vitro by protein kinase C and comigrated in two-dimensional PAGE with GAP-43. The data indicate that GAP-43, heretofore believed to be neuron-specific, is present in at least one class of glial cells.