Vinculin is one of the major endogenous substrates for intrinsic tyrosine kinases in neuronal growth cones isolated from fetal rat brain

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Abstract
Neuronal growth cones, the motile tips of growing neuronal processes, are responsible for the exact guidance of extending neurites. To elucidate the mechanisms of their biochemical signal transduction in growth cones, the growth‐cone‐enriched fraction was isolated biochemically from fetal rat brain and the endogenous protein phosphorylation in the fraction was analyzed under the conditions where tyrosine residues were preferentially phosphorylated. One of the major phosphoproteins was a 130‐kDa slightly acidic protein which reacted with anti‐phosphotyrosine antibody. Its phosphoryl residues were alkali‐stable. Thus, the 130‐kDa protein was concluded to be susceptible to tyrosine phosphorylation. This protein was a component of cytoskeletal proteins thought to be associated indirectly with membranes. All the behavior of the 130‐kDa protein was compatible with the properties of vinculin, a component of focal contacts which are responsible for the stable or motile adhesion between cells or between a cell and the substratum. Immunochemical analyses showed that the 130‐kDa protein was specifically recognized by anti‐vinculin antibody. Therefore, the 130‐kDa protein was concluded to be vinculin. Tyrosine phosphorylation of the protein appeared to be relatively more pronounced in the growth‐cone‐enriched fraction than in adult synaptosomes. The results suggest that tyrosine phosphorylation of vinculin may be regulated developmentally and it may be involved in the functions of growth cones.