A complex consisting of pp60c-src/pp60c-srcN and a 38 kDa protein is highly enriched in growth cones from differentiated SH-SY5Y neuroblastoma cells

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Abstract
Nerve growth cones of primary neurons are highly enriched in the proto-oncogene product pp60c-src. In order to investigate this molecule further in growing neuronal cells, growth cone and cell body fractions were prepared from human SH-SY5Y neuroblastoma cells differentiated neuronally in vitro under the influence of phorbol ester. The fractions were characterized ultra-structurally and by biochemical criteria. The neuronal (pp60c-srcN) and the fibroblastic (pp60c-src) forms of pp60src are slightly enriched and activated in the growth cones relative to the perikarya. Immunoprecipitates of pp60src from differentiated SH-SY5Y growth cones contain at least four phosphoproteins in addition to pp60src One of these, pp38, migrates as a 100-140 kDa complex with pp60src under non-reducing conditions of gel electrophoresis. The pp38/pp60src complex is not easily detected in non-differentiated SH-SY5Y cells or perikarya of differentiated SH-SY5Y cells, but it is highly enriched in the growth cone preparation. These data suggest that growth-cone pp60src exists in a disulfide-linked oligomeric complex. The complex appears to be assembled only in the cell periphery and may be dependent upon neuronal differentiation.