Synthetic peptides from the carboxy-terminal globular domain of the A chain of laminin: their ability to promote cell adhesion and neurite outgrowth, and interact with heparin and the beta 1 integrin subunit

The large carboxy-terminal globular domain (G domain; residues 2,110-3,060) of the A chain of murine-derived laminin has been shown to promote heparin binding, cell adhesion, and neurite outgrowth. This study was conducted to define the potential sequence(s) originating from the G domain of laminin with any of these functional activities. A series of peptides were synthesized from the G domain, termed GD peptides, each approximately 20 amino acids long and containing multiple positively charged amino acids. In direct 3H-heparin binding assays, peptides GD-1 and GD-2 bound high levels of 3H-heparin, while peptides GD-3 and GD-4 bound lower levels of 3H-heparin, and GD-5 bound essentially no 3H-heparin. The binding of 3H-heparin to peptides GD-1 and GD-2 appeared to be of high affinity, since significant binding of 3H-heparin to these two peptides was still observed even when the NaCl concentration was raised to 1.0 M. Four of the peptides, GD-1, GD-2, GD-3, and GD-4, directly promoted the adhesion and spreading of HT-1080 human fibrosarcoma cells as well as the outgrowth of neurites from chick spinal cord and dorsal root ganglia neurons. In addition, solutions of these peptides or antibodies generated against these peptides inhibited laminin-mediated HT-1080 cell adhesion. Antibodies against the beta 1 integrin subunit inhibited HT-1080 cell adhesion and neurite outgrowth on surfaces adsorbed with peptides GD-3 and GD-4. Therefore, laminin appears to have multiple, independent sequences in the G domain that serve a similar cell adhesion promoting function for different cell types. Furthermore, these results suggest that the sequences comprising peptides GD-3 and GD-4 use an integrin as a receptor, of which the beta 1 integrin subunit is a component for these various cell types.