Regulation of Hyaluronic Acid Synthesis in Pericardial Cells

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We studied the effects of growth factors (IGF-I and/or EGF) or prostaglandin E_2 (PGE_2) on hyaluronic acid (HA) synthesis in rabbit pericardial mesothelial cells, and the following results were obtained.1. Stimulation of HA synthesis by IGF-I and/or EGF(1) Combined exposure of pericardial cells to IGF-I and EGF cooperatively increased HA synthesis and the level of hyaluronic aid synthase (HASase) activity over that seen with or without IGF-I or EGF alone, but did not significantly stimulate the sulfated glycosaminoglycan synthesis. (2) Increase in the level of HA synthesis and HASase activity induced by these growth factors was blocked after pretreatment with a tyrosine-specific protein kinase inhibitor, genistein. (3)Genistein had no direct inhibitory effect on HASase activity. These results suggest that cooperative enhancement of HA synthesis induced by combined use of IGF-I and EGF could be mediated by a receptor tyrosine kinase-involved transmembrane signaling process that is resp … More onsive to IGF-I and EGF.2. Stimulation of HA synthesis by PGE_2 (1) PGE_2 (10-1000 ng/ml) stimulated HA synthesis and the level of HASase activity in a dose- and time-dependent manner, but PGF_2alpha didn't. (2) Cyclic AMP (cAMP) levels in the cells peaked (about a 7-fold increase) at 5-10 min after adding PGE_2 (1000 ng/ml). (3) Increased HA synthesis induced by PGE_2 was significantly inhibited after pretreatment with either an adenylate cyclase inhibitor (2', 5'-dideoxyadenosine) or a cAMP-dependent protein kinase (PK) inhibitor (PKI 5-24), but there was no inhibition with the PKC inhibitor (H-7). (4) When the intracellular cAMP level was raised by manipulating levels of dibutyryl cyclic AMP (Bt_2-cAMP) or forskolin, HA synthesis and the level of HASase activity were also stimulated. These results suggest that PGF_2 produced by cells stimulates HA synthesis in rabbit pericardial cells and that the stimulation mechanism involves in the cAMP-mediated protein kinase signal transduction process. Less