Adhesion of epithelial basal cells to the basement membrane (BM) is required for maintenance of a proliferative, undifferentiated phenotype. To understand the mechanism of this adhesion requirement, we characterized ligands, receptors, and signaling proteins involved in adhesion of cultured human foreskin keratinocytes (HFKs) to the BM: (I) Laminin 5 (epiligrin) is the primary adhesive ligand in epithelial BMs of both homeostatic tissue and wound sites. It is synthesized by HFKs in wound sites. (ii) Integrin alpha-6-beta-4 in hemidesmosome-like stable anchoring contacts (SACs) and integrin alpha-3-beta-1 in focal adhesions (FAs) are adhesion receptors for laminin-5. Epithelial cells anchor to laminin 5 via alpha-6-beta-4 in homeostatic epidermis and migrate via alpha-3-beta-1 in wound sites. Integrin alpha-2-beta-1 also functions in wound repair by interacting with collagen exposed in wound sites. (iii) Phosphorylation of a tyrosine residue(s) on a new membrane-associated signaling protein, p80, is the first detectable signaling event resulting from de-attachment of HFKs from laminin 5 via alpha-6-beta-4. In contrast, ligation of alpha-2-beta-1 and alpha-3-beta-1 regulates phosphorylation of FA kinase (FAK). Synchronization of the anchorage and migratory functions to avoid interference in wound activation is regulated by receptor cross-talk. We hypothesize, that differences in cell adhesion induced by laminin 5 verses collagen results in altered phosphorylation of p80 and FAK, DNA synthesis and differentiation. We propose to: characterize p80 and its role in cell adhesion, define the mechanisms of regulatory cross-talk between the beta-1 and beta-4 receptors, and analyze the promoter of the LAMA3 gene to identify sequences responsible for transcriptional control in response to cell adhesion. these results will define the molecular mechanism through which cell adhesion regulates gene expression and wound repair in epithelium.
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