The high‐affinity binding of laminin to cells

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Abstract
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.