Blockade of β1 integrin-laminin-5 interaction affects spreading and insulin secretion of rat β-cells attached on extracellular matrix

When attached on a matrix produced by a rat bladder carcinoma cell line (804G matrix), rat pancreatic beta-cells spread in response to glucose and secrete more insulin compared with cells attached on poly-L-lysine. The aim of this study was to determine whether laminin-5 and,its corresponding cell receptor beta 1 integrin are implicated in these phenomena. By using specific blocking antibodies, we demonstrated that laminin-5 is the component present in 804G matrix responsible for the effect of 804G matrix on beta-cell function and spreading. When expression of two well-known laminin-5 ligands, beta 1 and beta 4 integrin, was assessed by Western blot and RT-PCR, only the beta 1 integrin was detected in beta-cells. Anti-beta I integrin antibody reduced the spreading of beta-cells on 804G matrix. Blockade of the interaction between beta 1 integrins and laminin-5 resulted in a reduction in glucose-stimulated insulin secretion. Blocking anti-beta 1 integrin antibody also inhibited focal adhesion kinase phosphorylation induced by 804G matrix. In conclusion, anti-beta 1 integrin and -laminin-5 antibodies interfere with spreading of beta-cells, resulting in decreased insulin secretion in response to glucose. Our findings indicate that outside-in signaling via engagement of beta 1 integrins by laminin-5 is an important component of normal beta-cell function.