LEUKOREGULIN IS A POTENT INDUCER OF HYALURONAN SYNTHESIS IN CULTURED HUMAN ORBITAL FIBROBLASTS

Leukoregulin, a 50-kDa glycoprotein lymphokine, can regulate the extracellular matrix in dermal fibroblasts. Here we investigate the effects of leukoregulin on the synthesis of glycosaminoglycans in human orbital fibroblasts. We demonstrate that leukoregulin enhances the incorporation of [H-3]glucosamine into glycosaminoglycans. The effect is dose dependent in the concentration range tested (0.1-2 U/ml), is maximal at 1 U/ml, and is time dependent. [H-3]glycosaminoglycan accumulation is enhanced 7.67 +/- 1.23-fold (SE, n = 7) in orbital fibroblast strains. Pulse-chase studies indicate that this enhanced accumulation is not a result of a decreased rate of macromolecular degradation. Radiolabeled material induced by leukoregulin is sensitive to Streptomyces hyaluronidase digestion. Dexamethasone (10(-8) M) and cycloheximide (10 mu g/ml) can block the cytokine's stimulation of hyaluronan synthesis. [S-35]sulfate incorporation into glycosaminoglycan is unaffected by leukoregulin. In dermal fibroblasts, leukoregulin increased hyaluronan synthesis 3.66 +/- 0.37-fold (n = 5 strains, P < 0.02 compared with orbit). The increase in hyaluronan synthesis in orbital fibroblasts is substantially greater than that observed previously with other cytokines, making leukoregulin a candidate molecular trigger in Graves' ophthalmopathy.