The colocalization of integrins α2β1 and α3β1 at intercellular contact sites of keratinocytes in culture and in epidermis suggests that these integrins may mediate intercellular adhesion (ICA). P1B5, an anti-α3β1 mAb previously reported to inhibit keratinocyte adhesion to epiligrin, was also found to induce ICA. Evidence that P1B5-induced ICA was mediated by α2β1 and α3β1 was obtained using both ICA assays and assays with purified, mAb-immobilized integrins. Selective binding of α2β1-coated beads to epidermal cells or plate-bound α3β1 was observed. This binding was inhibited by mAbs to integrin α3, α2, or β1 subunits and could be stimulated by P1B5. We also demonstrate a selective and inhibitable interaction between affinity-purified integrins α2β1 and α3β1. Finally, we show that expression of α2β1 by CHO fibroblasts results in the acquisition of collagen and α3β1binding. Binding to both of these ligands is inhibited by P1H5, an anti-α2β1 specific mAb. Results of these in vitro experiments suggest that integrins α2β1 and α3β1 can interact and may do so to mediate ICA in vivo. Thus, α3β1 mediates keratinocyte adhesion to epiligrin and plays a second role in ICA via α2β1.
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