CORTACTIN-SRC KINASE SIGNALING PATHWAY IS INVOLVED IN N-SYNDECAN-DEPENDENT NEURITE OUTGROWTH

N-syndecan (syndecan-3) was previously isolated as a cell surface rece ptor for heparin-binding growth-associated molecule (HB-GAM) and sugge sted to mediate the neurite growth-promoting signal from cell matrix-b ound HB-GAM to the cytoskeleton of neurites, However, it is unclear wh ether N-syndecan would possess independent signaling capacity in neuri te growth or in related cell differentiation phenomena. In the present study, we have transfected N18 neuroblastoma cells with a rat N-synde can cDNA and show that N-syndecan transfection clearly enhances HB-GAM -dependent neurite growth and that the transfected N-syndecan distribu tes to the growth cones and the filopodia of the neurites. The N-synde can-dependent neurite outgrowth is inhibited by the tyrosine kinase in hibitors herbimycin A and PP1, Biochemical studies show that a kinase activity, together with its substrate(s), binds specifically to the cy tosolic moiety of N-syndecan immobilized to an affinity column. Wester n blotting reveals both c-Src and Fyn in the active fractions. In addi tion, cortactin, tubulin, and a 30-kDa protein are identified in the k inase-active fractions that bind to the cytosolic moiety of N-syndecan , Ligation of N-syndecan in the transfected cells by HB-GARI increases phosphorylation of c-Src and cortactin, We suggest that N-syndecan bi nds a protein complex containing Src family tyrosine kinases and their substrates and that N-syndecan acts as a neurite outgrowth receptor v ia the Src kinase-cortactin pathway.