The high-affinity binding of laminin to cells. Assignation of a major cell-binding site to the long arm of laminin and of a latent cell-binding site to its short arms.
The laminin proteolytic fragments 1 (derived from the intersection of the short arms of the cruciform laminin molecule) and 8 (derived from the laminin long arm) bind to distinct receptors on HT-1080 human fibrosarcoma cells; both fragments are shown here to inhibit the high-affinity binding of laminin to these cells. Inhibition of binding between fragment 8 and laminin was competitive, whereas that between fragment 1 and laminin was noncompetitive. This indicates that laminin and fragment 8 most probably share the same cellular receptors, whereas laminin and fragment 1 bind to distinct receptors, inhibition being due to steric hindrance. Surprisingly, fragment 1-4 (corresponding to the complete short arms of laminin) neither bound to HT-1080 cells nor inhibited the binding of laminin or fragment 1. After treatment of fragment 1-4 with pepsin, however, the smaller subfragment 1 was liberated, which could then bind to the cells, and so was shown to block the binding of laminin and fragment 1. We conclude that native laminin bound to HT-1080 cells via the fragment-8-binding site near the end of its long arm. Although these cells also have distinct receptors for the short arm fragment 1, this receptor-binding site was not used as it appeared to be latent within the native laminin molecule.
Nurcombe
V
V
Max-Planck-Institut für Psychiatrie, Martinsried, Federal Republic of Germany.
Aumailley
M
M
Timpl
R
R
Edgar
D
D
D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D002460:Cell Line; D005354:Fibrosarcoma / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007797:Laminin / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010447:Peptide Hydrolases; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D007797:Laminin; D010446:Peptide Fragments; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic; C032193:glycoprotein receptor GPIb-IX; D010447:Peptide Hydrolases