Integrins as a primary signal transduction molecule regulating monocyte immediate-early gene induction

Integrins are cell surface receptors found on monocytes that facilitate adhesion to both cellular and extracellular substrates. These integrins are thought to be involved in the selective gene induction observed after monocyte adhesion to various extracellular matrices. To investigate this hypothesis, we stimulated monocytes with monoclonal antibodies to different integrin receptors to specifically mimic the integrin receptor-ligand interactions. Engagement of the common beta chain of the beta 1 subfamily of integrins resulted in expression of the inflammatory mediator genes, interleukin 1 beta, interleukin 1 receptor antagonist, and monocyte adherence-derived inflammatory gene 6 (MAD-6), whereas engagement of the common beta chain of the beta 2 family did not. Furthermore, to characterize integrin-mediated gene induction, we examined the ability of antibodies to the alpha chain of integrin receptors to regulate gene expression. Engagement of the very late antigen 4 (VLA-4) receptor resulted in induction of all the mediator genes. Receptor crosslinking was required because individual Fab fragments were unable to stimulate gene induction whereas the divalent F(ab')2 fragment and the whole IgG molecule could. Interleukin 1 beta secretion was dependent on the anti-integrin antibody used. Some antibodies required a second signal and, for others, direct engagement was sufficient for protein production. In conclusion, engagement of integrin receptors regulated the production of both inflammatory mediator mRNA and protein. These results suggest that integrin-dependent recognition and adherence may provide the key signals for initiation of the inflammatory response during monocyte diapedesis.