Role for Protein Kinase C in the Mediation of Increased Fibronectin Accumulation by Mesangial Cells Grown in High-glucose Medium

The fibronectin content of RMC cultures grown for 8-14 days in medium containing 30 mM (540 mg/dl) D-glucose was increased 30-60% relative to that of control cells cultured in 10 mM (180 mg/dl) glucose. Addition of equiosmolar concentrations (20 mM, 360 mg/dl) of L-glucose, 3-O-methylglucose, or mannitol to 10 mM glucose media did not alter fibronectin accumulation compared with values observed in 10 mM glucose alone. The basal phosphorylation of the 80,000-M(r) MARKS protein, which is a substrate for PKC, and the phosphorylation induced by acute (15-min) exposure of cells to 15% FCS or to 0.1 microM (50 ng/ml) PDBu were all increased in cells grown in 30 mM compared with 10 mM glucose. By contrast, phosphorylation of the 80,000-M(r) protein in response to a maximal concentration of PDBu (1 microM, 500 ng/ml) was not different in cells grown in 30 mM compared with 10 mM glucose. The acute increases in phosphorylation of the 80,000-M(r) protein were blocked by the PKC inhibitor calphostin C. Chronic (7-day) exposure of mesangial cells grown in 10 mM glucose to 0.1 microM of the PKC agonist PDBu also resulted in a sustained 40% increase in 80,000-M(r) phosphorylation and a 20-30% increase in fibronectin accumulation. As assessed by [35S]methionine incorporation, mesangial cell fibronectin synthesis was increased by exposure to PDBu, a finding consistent with earlier observations with 30 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)