Function of laminins and laminin binding integrins in gingival epithelial cell adhesion

Background: In human gingiva, epithelial cells attach to their adjacent tissues by means of specialized molecular adhesion complexes and a basement membrane. Little is known about the synthesis of adhesion proteins by gingival keratinocytes; we, therefore, studied how cultured immortalized gingival epithelial cells produce laminins and express laminin-binding integrins. We presumed that different laminins and integrins would be involved in the adhesion of gingival epithelial cells. Methods: We cultured gingival keratinocytes and studied their production of laminins and expression of integrins using immunofluorescence microscopy, immunoprecipitation, and immunoblotting methods and by quantitative cell adhesion experiments. We also studied how gingival tissue expresses these adhesion proteins in vivo by using immunofluorescence microscopy. Results: In immunofluorescence microscopy, the cells were seen to organize chains of laminin-5 (alpha3X3gamma2) to extracellular patches, whereas the alpha5 chain of laminin-10 (alpha5beta1gamma1) could only be seen intracellularly. Of the laminin-binding integrin subunits, integrin alpha(6) subunit was organized to dotted arrays, typical of prehemidesmosomal adhesions, whereas integrin alpha(3) subunit was located at cell-cell junctions, in prehemidesmosomal structures, and at some locations also in small focal-contact like patches. Integrin beta1 subunit was found at cell-cell junctions and in focal contacts. Immunoprecipitation experiments showed that the cells synthesize and secrete chains of laminin-5 and laminin-10. In quantitative cell adhesion experiments, the cells adhered efficiently to these laminins by using cooperatively integrin alpha(3)beta(1) and alpha(6)beta(1) integrin complexes. None of the other known laminin-binding integrin subunits appeared to be significantly involved in cell adhesion to these laminin isoforms. Conclusions: Our results provide new information on gingival epithelial cell adhesion and extracellular matrix production and may thus aid in the understanding of periodontal physiology.