EVIDENCE THAT BETA(1) INTEGRINS IN KERATINOCYTE CELL-CELL JUNCTIONS ARE NOT IN THE LIGAND-OCCUPIED CONFORMATION

Integrins are a family of heterodimeric cell surface molecules that fu nction as adhesion receptors in cell-cell and cell-extracellular matri x contact, Integrins of the beta(1) family are found on keratinocytes clustered at sites of cell-cell junctions both in culture and in norma l skin, The possibility that these integrins function in cell-cell adh esion has been both supported and refuted in recent conflicting public ations, Rather than testing further for the presence or absence of an interaction, we present evidence to show that beta(1) integrins in ker atinocyte cell-cell junctions are in the non-ligand-occupied conformat ion, We transfected keratinocytes with a construct that expresses a ch imeric cell surface molecule containing the integrin beta(1) cytoplasm ic tail, This chimera is thought to mimic the ligand-occupied receptor and has previously been shown to be actively localized to focal adhes ions in fibroblasts. We find that keratinocytes are also able to local ize this chimera in focal adhesions but do not localize it to areas of cell-cell junctions, A monoclonal anti-beta(1) antibody that has been previously shown to preferentially recognize ligand-occupied beta(1) receptors was used to stain keratinocytes, This antibody showed staini ng of focal adhesions, with little or no staining of cell-cell junctio ns, In contrast, four other anti-beta(1) antibodies showed strong, pre ferential staining at cell-cell junctions, Double staining confirmed t hat both the conformation-specific monoclonal antibody and a pan-beta( 1) antibody were capable of recognizing the same focal adhesions, Take n together, these data indicate that integrins in cell-cell junctions of keratinocytes are in the non-ligand-occupied conformation, Although we do not directly prove the absence of an integrin-integrin interact ion at this site, we show that any such interaction does not induce th e ligand-occupied conformation and, therefore, is less likely to play a major role in cytoskeletal re-organization or signal transduction.