J Biol Chem, Vol. 274, Issue 29, 20103-20109, July 16, 1999

Recruitment of a Heparan Sulfate Subunit to the Interleukin-1 Receptor Complex
REGULATION BY FIBRONECTIN ATTACHMENT

Soraya Vallés, Christina Tsoi^§, Wen-Yan Huang, David Wyllie, Franco Carlotti, Janet A. Askari^¶, Martin J. Humphries^¶, Steven K. Dower, and Eva E. Qwarnström^§

From the  Functional Genomics Group, Division of Molecular and Genetic Medicine, Royal Hallamshire Hospital, University of Sheffield, Glossop Rd., Sheffield S10 2JF, United Kingdom, the ^§ Department of Pathology, University of Washington, Seattle, Washington, and the ^¶ Wellcome Trust Center for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom

In this study, we identified an adhesion-regulated subunit of the interleukin-1 (IL-1) receptor complex. Transfection of fibroblasts with an IL-1 receptor-EGFP construct showed that the fusion protein was located at focal adhesions in cells attaching to fibronectin.

Fibronectin attachment caused enhancement in endogenous IL-1 type I receptor levels from on average 2500 to 4300 receptors/cell. In addition, matrix attachment resulted in a decrease in binding affinity (K_a) from 1.0 × 10⁹ (M¹) to 5.6 × 10⁸ (M¹), due to a 2-fold reduction in association rate constant.

The adhesion-mediated effects were reversed by soluble heparin. Cross-linking experiments showed that in cells attached to fibronectin, 50-70% of the radiolabeled IL-1 was associated with a heparinase sensitive, high molecular mass component of about 300 kDa, with a core protein of 80-90 kDa. Formation of the complex was dependent on cell interaction with the heparin binding region in fibronectin and required IL-1/type I IL-1 receptor binding.

This report demonstrates the recruitment of a heparan sulfate to the IL-1 receptor complex, following attachment to fibronectin, which correlates with alterations in receptor function. The data suggest that the heparan sulfate constitutes an attachment regulated component of the IL-1 receptor complex with the role of mediating matrix regulation of IL-1 responses.