Heparan sulphate recruitment to the IL-1 receptor complex

Abstract

Localization of IL-1 receptors at focal adhesions was demonstrated by transfection of an EGFP containing construct and confocal microscopy. IL-1/IL-1R binding at these sites was shown to be regulated by cell matrix interaction. In addition, fibronectin binding resulted in recruitment of a novel attachment-induced component to the IL-1 receptor complex, constituting a heparan sulfate. Fibronectin attachment caused a pronounced enhancement in IL-1 receptor binding (from 2500 to 4300 receptor/cell). In addition cell–matrix interaction resulted in a decrease in binding affinity (from 1.0 × 109 to 5.6 × 108m−1) resulting from a 2 fold reduction in association rate constant. These effects could be reversed by the addition of soluble heparin. Crosslinking experiments showed that in cells on fibronectin, 75% of the radiolabeled IL-1 was associated with a highly glycosytaled high molecular weight component of about 300 kD. Enzyme digestion demonstrated the presence of a heparin sulfate with a core protein of about 90 kD. The interaction was demonstrated to involve specifically the type I IL-1 receptor and to require IL-1 binding. Further, using a mutant fibronectin, formation of the complex was shown to be dependent on cell interaction with the heparin binding region. The attachment induced involvement of heparin sulfate in regulation of IL-1/Il–1 receptor interaction correlates with data on matrix effects on signal transduction suggesting a significant role of this interaction in inflammatory responses.