Expression of integrin and organization of F-actin in epithelial cells depends on the underlying surface.

Purpose: To evaluate the role of ionic interactions in the cell surface expression of integrins and the organization of F-actin. Understanding these interactions will allow the development of surfaces for prosthetic purposes that will promote the normal expression of adhesion proteins.
Methods: Hema (hydroxyethylmethacrylate) hydrogels were used to mimic the charges present on extracellular matrix proteins. The surfaces were modified by the addition of amines (N,N-dimethylaminoethylmethacrylate; NDAM) or carboxyl moieties (methacrylic acid). The effects of ionic interactions on cellular spreading and on the expression of proteins were examined by modification of the stoichiometrically defined amounts of positive and negative charges on the Hemas. Changes in intracellular pH and the distribution and localization of protein were monitored using fluorescent markers, spectrofluorometry, and confocal laser scanning microscopy, respectively. The immunohistochemical studies were confirmed by flow cytometric analysis.
Results: The data indicate that although cells adhered to all the surfaces, the number of cells possessing adhesion receptors is significantly greater on surfaces with amine functionalities. Cell seeding and plating efficiency after 2 hours were identical on all surfaces. The intracellular pH of epithelial cells grown on surfaces containing NDAM, a tertiary amine, was higher than that of cells grown on Hemas containing only methacrylic acid. Lamellipodial extensions and an extensive actin network were present on surfaces containing 5% NDAM. The alpha 6 subunit was localized along the lateral cell membranes. The alpha 2 and 3 subunits were present along cell membranes and at lamellipodial extensions. Cells cultured on surfaces containing only methacrylic acid did not spread. Actin filaments were not detected, and alpha 6 was negligible on these surfaces.
Conclusions: This is a novel approach to understanding cell-substrate interactions, and one that allows quantitative evaluation of the response of cells to defined surfaces. The organization of F-actin is altered by the substrates containing only carboxyl moieties. The distribution of integrin subunits is also altered by the substrate. These results indicate that epithelial cell spreading and protein expression may be regulated by ionic interactions.