Biology of the interleukin-1 receptor.

The biological effects of the two interleukin-1s on cells of connective tissue origin are mediated by specific cell-surface receptors. Molecular cloning studies have revealed that these receptors are identical in protein sequence to the IL-1 receptors on cells of the T-lymphocyte lineage. The functional interleukin-1 receptor on T-cells and fibroblasts is composed of a single polypeptide chain that binds both IL-1 alpha and IL-1 beta. The single chain appears to be all that is required to transduce a signal to cells. While the nature of the signal is unknown, the structure of the receptor is inconsistent with its possessing any protein tyrosine kinase activity. It is therefore not surprising that the mitogenic activity of IL-1 for fibroblasts is mediated by IL-1 induction of PDGF-A gene transcription. Finally, IL-1 is known to modulate fibroblast-matrix interactions in several ways. It is interesting therefore, that the majority of the IL-1 receptors on cultured fibroblasts are clustered into focal adhesions.