TYROSINE PHOSPHORYLATION-INDUCED BY INTEGRIN-MEDIATED ADHESION OF RETINAL NEURONS TO LAMININ

Integrin alpha 6 beta 1 is a laminin receptor involved in adhesion and neurite extension of retinal neurons on laminin. The present study wa s carried out to understand some of the intracellular mechanisms which allow integrin-mediated neurite extension on laminin in primary neuro nal cultures. Both integrin-mediated adhesion to laminin and antibody- induced integrin clustering resulted in the increased tyrosine phospho rylation of a 120 kDa polypeptide which was identified as the focal ad hesion kinase. The kinetics of phosphorylation and dephopsphorylation of this kinase were dramatically different in neurons plated on lamini n, than in neurons in which the receptors were clustered with anti-int egrin antibodies. To look at possible interactions of the focal adhesi on kinase with integrins, we made use of sucrose velocity gradients, w hich have allowed the identification of a large complex containing the alpha 6 beta 1 laminin receptor. Analysis of the gradients showed tha t the focal adhesion kinase was not associated with the integrin recep tors under these experimental conditions, while about 26% of the c-Src kinase codistributed with the integrin receptor complex, and showed a molecular size and a distribution similar to that of a 59 kDa phospho protein co-migrating with the alpha 6 beta 1 receptor. Our results sug gest that integrin-induced tyrosine phosphorylation is an early intrac ellular event during neuronal adhesion, and that the integrin-mediated increase in tyrosine phosphorylation of the focal adhesion kinase is not sufficient per se for the induction of neurite outgrowth. Furtherm ore, our data indicate that Src kinase may be involved in integrin-med iated neuronal interactions with laminin. Copyright (C) 1996 ISDN.