INTERACTION OF INTEGRIN ALPHA-7-BETA-1 IN C2C12 MYOTUBES AND IN SOLUTION WITH LAMININ

The dimer of integrin alpha 7 and beta 1 is a major laminin-binding re ceptor in skeletal. muscle. We studied interactions of integrity alpha 7 beta 1 with the extracellular matrix protein laminin in solution an d in intact cells. Integrin alpha 7 beta 1 bound to EHS laminin (lamin in-1, composed of alpha 1, beta 1, and gamma 1 chains), but not to end ogenous laminin expressed in C2C12 myotubes. Northern blot analysis de monstrated that C2C12 myotubes synthesized laminin-1 alpha, beta, and gamma subunits mRNAs, C2C12 laminin was, however, immunologically dist inct from EHS laminin; it was not recognized by 5D3 anti-laminin-1 mon oclonal. antibody, whereas 5A2 and LT3 antibodies reacted equally swel l with C2C12 and EHS laminins, Following deglycosylation of ENS lamini n, separation of the subunits by SDS-PAGE, Western blotting, and parti al amino acid sequencing of the protein bands, the epitope recognized by 5D3 antibody was localized to the gamma 1 laminin chain. Following binding in vitro the complex of EHS laminin and integrin alpha 7 beta 1 was subject to chemical cross-linking. The two proteins did not unde rgo cross-linking at the cell surface, consistent with the fact that i n intact, resting myotubes integrin alpha 7 beta 1 interacted poorly w ith EHS laminin, which may reflect a limited accessibility of integrin alpha 7 beta 1 in the membrane to laminin or an inactive state of the integrin. (C) 1998 Academic Press.