Connective tissue activation. XVIII. Stimulation of hyaluronic acid synthetase activity.

Human synovial fibroblasts synthesize hyaluronic acid, a process that can be stimulated by a number of agents. Several steps in the synthetic pathway could be the locus at which these stimulators act; the final step, promoted by hyaluronic acid synthetase, was selectd for study. Hyaluronic acid synthetase is an enzyme system that transfers monosaccharide units to nascent hyaluronic acid chains. Activities of the enzyme were determined in lysates of cultured synovial fibroblasts by measuring incorporation of 14C-UDP-glucuronic acid into hyaluronic acid. Rates of hyaluronic acid synthesis were increased by adding CTAP-I or CTAP-III, DbcAMP, or prostaglandin E2 to the cultures. In each instance, hyaluronic acid synthetase activity was enhanced in a manner comparable to that seen in hyaluronic acid synthesis. The changes in enzyme and product were observed as early as 6 hr after cultures were exposed to CTAP-III, and both indices declined when this stimulator was withdrawn for 24 hr. Although DbcAMP incrased the hyaluronic acid synthetase activity of intact fibroblasts, it had no effect on the enzyme in lysates of cells. In the cultured cells, cycloheximide reduced basal levels of synthetase activity and hyaluronic acid synthesis of hyaluronic acid may do so by inducing hyaluronic acid synthetase.