LIGAND-INDUCED GROWTH CONE COLLAPSE - AMPLIFICATION AND BLOCKADE BY VARIANT GAP-43 PEPTIDES

Growth cones are powerful amplifiers for signals from the microenviron ment. Their collapse can be triggered by cell surface components of my elin and brain membranes, as well as by soluble ligands, including neu rotransmitters. GAP-43 is a protein concentrated on the inner surface of the growth cone membrane. Assayed in isolation, it interacts with t he heterotrimeric protein, G(o), and in oocytes it amplifies the effec ts of ligand-triggered G protein activation. We wished to examine whet her GAP-43 serves to amplify signals at the growth cone. The G(o), sti mulating region of GAP-43 is encoded in the 10 amino acids (MLCCMRRTKQ ) of the first exon. We examined the effect of this peptide upon chick dorsal root ganglion growth cone collapse and neurite retraction trig gered by brain membranes or myelin, as well as by serotonin. We find t hat application of the GAP-43 1-10 peptide amplifies the effects of al l three ligands. The amplification is greater when GAP-43 1-10 is inje cted intracellularly. Peptides with amino acid substitutions for the t wo cysteine residues manifest parallel changes in growth cone collapse and G(o) stimulation. In particular, tyrosine or methionine substitut ions cause the peptide to inhibit G(o) and to block induced growth con e collapse. The GAP-43 peptides therefore regulate the sensitivity of growth cones to extrinsic signals. The modified peptides serve as a st arting point for the design of reagents to enhance CNS regeneration.