Role of tyrosine phosphorylation in matrix-induced neurite outgrowth in human neuroblastoma cells

Adhesion of human neuroblastoma cells (SK-N-SH clone SY5Y) to laminin or collagen type IV promotes tyrosine phosphorylation of a group of proteins with molecular mass ranging from 100 to 130 kDa and of a protein of 180 kDa. The same pattern of tyrosine phosphorylation was observed when SY5Y cells were allowed to adhere to culture dishes coated with monoclonal antibodies directed to the integrin subunits expressed in the cells, α₁, α₃, and β₁, indicating that these receptors are responsible for this signaling mechanism. Using specific antibodies we identified the focal adhesion kinase p125(FAK) as a component of the 100- to 130-kDa phosphoproteins. Treatment with genistein or herbimycin A, two specific tyrosine kinase inhibitors, greatly reduced the tyrosine phosphorylation of the 100- to 130- and the 180-kDa proteins in response to laminin or collagen IV. Concomitantly, neurite outgrowth on the matrix proteins was strongly inhibited. This effect was observed in two distinct neuroblastoma cell lines, SY5Y and SK-N-BE. Genistein and herbimycin A treatment did not affect cell viability nor cause retraction of preformed neurites. These data suggest that matrix-induced tyrosine phosphorylation events are involved in neurite extension.