GAP-43 AMINO-TERMINAL PEPTIDES MODULATE GROWTH CONE MORPHOLOGY AND NEURITE OUTGROWTH

The neuronal growth-associated protein GAP-43 is expressed maximally d uring development and regeneration, and is enriched at the cytosolic s urface of the growth cone membrane. GAP-43 can activate the GTP-bindin g protein G(o), which is also a major component of the growth cone mem brane. These findings have led to the hypothesis that GAP-43 might mod ulate neurite outgrowth by altering G-protein activity. Here we define the sequence requirements for GAP-43 amino terminal peptide stimulati on of G(o), and test these peptides as potential modulators of neurite outgrowth. The first 10 amino acids of GAP-43, Met-Leu-Cys-Cys-Met-Ar g-ArgThr-Lys-Gln, stimulate G(o). Substitutions at particular residues reveal that cys3, cys4, arg6, and lys9 are critical, but arg7 is not. Both the GAP-43(1-10) peptide and the G-protein-activating peptide ma stoparan induce growth cone collapse and inhibit neurite extension fro m embryonic chick dorsal root ganglion and retinal neurons. This is li kely to be mediated by G-proteins: pertussis toxin blocks the inhibiti on, and mutant peptides that do not activate G(o) do not alter outgrow th. In contrast to the case with embryonic chick dorsal root ganglion cells, neurite outgrowth from N1E-115 neuroblastoma cells is stimulate d by GAP-43(1-10). This is probably also a G-protein-mediated event be cause it is blocked by pertussis toxin, because the sequence requireme nts match those for G(o) stimulation, and because mastoparan stimulate s outgrowth from these cells. The longer GAP-43(1-25) peptide does not alter neurite outgrowth unless the cells are permeabilized, suggestin g an intracellular site of action. These data identify a novel set of compounds that modulate neurite outgrowth, and also support the notion that GAP-43 can alter neurite extension by modulating pertussis toxin -sensitive G-protein activity in the growth cone.