Laminin-mediated adhesion in metastatic rat rhabdomyosarcoma cell lines involves prominent interactions with the laminin E8 fragment.

In vitro attachment assays were carried out to assess adhesion between two basement membrane proteins, type IV collagen and laminin, and rat rhabdomyosarcoma (RMS) cell lines with different metastatic potentials. Whereas cells did not adhere to type IV collagen, adhesion to laminin appeared to be very sensitive as maximal adhesion was achieved in dose-response assays with only nanograms of laminin. Adhesion was mediated by interactions between coated laminin and cell surface components, probably receptors, but not endogenous laminin. Laminin-mediated adhesion of RMS cell lines was compared with that of the MCF-7 (human mammary carcinoma) and the L6 (rat myoblast) cell lines. In dose-response assays, RMS cell lines required 10 times less laminin to reach half-maximal attachment rates than MCF-7 and L6 cell lines. Two laminin fragments, P1 and E8, which are structurally and immunologically distinct as shown by alpha-helix content, SDS-PAGE and monoclonal antibody mapping, supported adhesion by RMS cells and L6 myoblasts, but MCF-7 adhered only to P1. This fragment was 10 times less active than laminin in RMS cell lines. Attachment in dose-response assays and adhesion inhibition studies by antibodies revealed that E8 accounted for the activity of laminin in RMS cell adhesion. Adhesion in the RMS cell lines was dominated by interaction with E8 regardless of metastatic potential.