Different integrins mediate cell spreading, haptotaxis and lateral migration of HaCaT keratinocytes on fibronectin

Collaborative role of various fibronectin-binding integrins (alpha 5 beta 1 , alpha v beta 1 and alpha v beta 6) as mediators of cell adhesion and migr ation on fibronectin was studied using cultured HaCaT keratinocytes. This c ell line spontaneously expressed all three fibronectin-binding integrins. I n addition, the expression of alpha v beta 6 integrin was strongly and spec ifically upregulated by transforming growth factor-beta 1 (TGF beta 1) wher eas the amount of other integrins remained practically unchanged on the cel l surface. Adhesion, spreading and motility of HaCaT keratinocytes on fibro nectin were promoted by TGF beta 1. Based on antibody blocking experiments, both untreated and TGF beta 1-treated HaCaT cells used alpha v beta 6 inte grin as their main fibronectin receptor for cell spreading. In contrast to TGF beta 1-treated cells, the untreated cells also needed alpha 5 beta 1 in tegrin for maximal cell spreading on fibronectin. Combinations of antibodie s blocking both of these receptors totally prevented spreading of both untr eated and TGF beta 1-treated cells. Haptotactic motility of individual HaCa T cells through fibronectin-coated membranes was again mainly dependent on alpha v beta 6 integrin, while alpha v beta 1 and alpha 5 beta 1 integrins played a lesser role both in untreated and TGF beta 1-treated HaCaT cells. However, unlike haptotaxis, lateral migration of HaCaT cell sheet was mainl y mediated by beta 1 integrins, and alpha v beta 6 integrin showed a minor role. The migration process appeared to involve a number of beta 1 integrin s that could adaptively replace each other when blocking antibodies were pr esent. Thus, keratinocytes appear to use different fibronectin receptors fo r different functions, such as cell spreading, haptotaxis and lateral migra tion. The cells can also adapt to a situation where one receptor is unfunct ional by switching to another receptor of the same ligand.