Regulation of CS1 Fibronectin Expression and Function by IL-1 in Endothelial Cells

VLA-4 is a critical adhesion molecule that regulates mononuclear cell trafficking to sites of inflammation. VCAM-1 is a primary ligand of VLA-4, although alternatively spliced fibronectin (FN) containing the CS1 region (CS1 FN) also binds to VLA-4. CS1 FN is expressed by rheumatoid arthritis (RA) synovial endothelial cells, but the factors that regulate CS1 FN expression are not known. We incubated human umbilical vein endothelial cells (HUVEC) with IL-1 (0.1–10 ng/ml) for 8–48 h and determined total FN and CS1 FN mRNA by Northern blot analysis. Both were constitutively expressed by HUVEC, and IL-1 increased total FN mRNA and the CS1-containing isoform (P < 0.05). IL-1 also increased CS1 FN protein expression on HUVEC as determined by Western blot analysis. An adhesion assay using 51Cr-labeled Jurkat cells and IL-1-stimulated HUVEC was used to determine if IL-1-induced CS1 FN mediates cell binding. Cyclic CS1 peptide (10 μg/ml) blocked 49 ± 5% of IL-1-induced Jurkat cell adhesion to HUVEC (P < 0.01), whereas anti-VCAM-1 antibody inhibited binding by only 35 ± 5% (P < 0.01). CS1 peptide and anti-VCAM antibody treatment were not additive (50 ± 7% inhibition), and 38 ± 6% of new VLA-4-mediated adhesion to IL-1-treated HUVEC was due to an increase in CS1 FN. These data show that IL-1 increases CS1 FN expression by HUVEC and increases CS1-mediated cell adhesion. CS1 mimetics might have therapeutic efficacy by blocking recruitment of VLA-4-bearing cells.