Recruitment of a heparan sulfate subunit to the interleukin-1 receptor complex - Regulation by fibronectin attachment

In this study, we identified an adhesion-regulated subunit of the interleuk in-1 (IL-1) receptor complex. Transfection of fibroblasts with an IL-1 rece ptor-EGFP construct showed that the fusion protein was located at focal adh esions in cells attaching to fibronectin. Fibronectin attachment caused enhancement in endogenous IL-1 type I recepto r levels from on average 2500 to 4300 receptors/cell. In addition, matrix a ttachment resulted in a decrease in binding affinity (K-a) from 1.0 x 10(9) (M-1) to 5.6 x 10(8) (M-1), due to a 2-fold reduction in association rate constant. The adhesion-mediated effects were reversed by soluble heparin. Cross-linki ng experiments showed that in cells attached to fibronectin, 50-70% of the radiolabeled IL-1 was associated with a heparinase sensitive, high molecula r mass component of about 300 kDa, with a core protein of 80-90 kDa, Format ion of the complex was dependent on cell interaction with the heparin bindi ng 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 r eceptor complex, following attachment to fibronectin, which correlates with alterations in receptor function. The data suggest that the heparan sulfat e constitutes an attachment regulated component of the IL-1 receptor comple x with the role of mediating matrix regulation of IL-1 responses.