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 surfac e expression of integrins and the organization of F-actin. Understandi ng these interactions will allow the development of surfaces for prost hetic purposes that will promote the normal expression of adhesion pro teins. Methods. Hema (hydroxyethylmethacrylate) hydrogels were used to mimic the charges present on extracellular matrix proteins. The surfa ces were modified by the addition of amines (N,N-dimethylaminoethylmet hacrylate; NDAM) or carboxyl moieties (methacrylic acid). The effects of ionic interactions on cellular spreading and on the expression of p roteins were examined by modification of the stoichiometrically define d amounts of positive and negative charges on the Hemas. Changes in in tracellular pH and the distribution and localization of protein were m onitored using fluorescent markers, spectrofluorometry, and confocal l aser scanning microscopy, respectively. The immunohistochemical studie s were confirmed by flow cytometric analysis. Results. The data indica te that although cells adhered to all the surfaces, the number of cell s possessing adhesion receptors is significantly greater on surfaces w ith amine functionalities. Cell seeding and plating efficiency after 2 hours were identical on all surfaces. The intracellular pH of epithel ial cells grown on surfaces containing NDAM, a tertiary amine, was hig her 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 alpha6 subunit was localized alon g the lateral cell membranes. The alpha2 and 3 subunits were present a long cell membranes and at lamellipodial extensions. Cells cultured an surfaces containing only methacrylic acid did not spread. Actin filam ents were not detected, and alpha6 was negligible on these surfaces. C onclusions. This is a novel approach to understanding cell-substrate i nteractions, and one that allows quantitative evaluation of the respon se of cells to defined surfaces. The organization of F-actin is altere d by the substrates containing only carboxyl moieties. The distributio n 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.