Regulation of CS1 fibronectin expression and function by IL-1 in endothelial cells

VLA-4 is a critical adhesion molecule that regulates mononuclear cell traff icking to sites of inflammation. VCAM-1 is a primary ligand of VLA-4, altho ugh alternatively spliced fibronectin (FN) containing the CS1 region (CS1 F N) also binds to VLA-4. CS1 FN is expressed by rheumatoid arthritis (RA) sy novial endothelial cells, but the factors that regulate CS1 FN expression a re not known. We incubated human umbilical vein endothelial cells (HUVEC) w ith 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 Weste rn blot analysis. An adhesion assay using Cr-51-labeled Jurkat cells and IL -1-stimulated HUVEC was used to determine if IL-1-induced CS1 FN mediates c ell binding. Cyclic CS1 peptide (10 mu g/ml) blocked 49 +/- 5% of IL-1-indu ced Jurkat cell adhesion to HUVEC (P < 0.01), whereas anti-VCAM-1 antibody inhibited binding by only 35 +/- 58 (P < 0.01). CSI peptide and anti-VCAM a ntibody treatment were not additive (50 +/- 7% inhibition), and 38 +/- 6% o f new VLA-4-mediated adhesion to IL-1-treated HUVEC was due to an increase in CSI FN. These data show that IL-1 increases CS1 FN expression by HUVEC a nd increases CS1-mediated cell adhesion. CS1 mimetics might have therapeuti c efficacy by blocking recruitment of VLA-4-bearing cells. (C) 2000 Academi c Press.