Activation of protein kinase C reduces thromboxane receptors in glomeruli and mesangial cells

• Published in: Kidney international Vol. 44; no. 1; pp. 58 - 64
• Main Authors: Studer, Rebecca K., Craven, Patricia A., DeRubertis, Frederick R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 01-07-1993; Nature Publishing
• Subjects: Animals; Biological and medical sciences; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; Enzyme Activation - drug effects; Fatty Acids, Unsaturated; Female; Fundamental and applied biological sciences. Psychology; Glomerular Mesangium - drug effects; Glomerular Mesangium - metabolism; Glucose - pharmacology; Hydrazines - metabolism; In Vitro Techniques; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus - drug effects; Kidney Glomerulus - metabolism; Membrane Proteins; Myristoylated Alanine-Rich C Kinase Substrate; Phorbol 12,13-Dibutyrate - pharmacology; Phosphorylation; Protein Kinase C - metabolism; Proteins - metabolism; Rats; Rats, Sprague-Dawley; Receptors, Thromboxane - metabolism; Vertebrates: urinary system; Cell culture; Protein kinase C; Rat; Enzyme; Mesangial cell; Thromboxane A2; Rodentia; Activation; Renal glomerulus; Vertebrata; Membrane receptor; Mammalia; Animal
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1038/ki.1993.213

Activation of protein kinase C reduces thromboxane receptors in glomeruli and mesangial cells. The potential role of protein kinase C (PKC) in the modulation of thromboxane A2 (TX) receptor density was evaluated in intact glomeruli and cultured renal mesangial cells (MC) from the rat. Incubation of glomeruli with 0.1 µM phorbol dibutyrate (PDBu) or 30 mM glucose for four hours activated PKC as reflected by increased in situ phosphorylation of the 80 kDa MARCKS protein, a specific endogenous substrate for PKC. High affinity binding to TX receptors, as assessed from the binding of the stable TX antagonist [3H]-Sq-29548 (Sq), was decreased 30% in glomeruli exposed to PDBu and 28% in glomeruli incubated in 30 mM D-glucose for four hours. Concurrent incubation with 0.05 µM of the PKC inhibitor staurosporine blocked both MARCKS protein phosphorylation and the decrease in TX receptor sites in response to either PDBu or 30 mM glucose. Neither 30 mM L-glucose nor 30 mM mannitol altered glomerular PKC activity or TX receptor density, thus excluding an osmotic effect of D-glucose, and implicating cellular metabolism of glucose in the expression of these actions. Inhibition of endogenous production of TX with indomethacin during exposure of glomeruli to 30 mM glucose did not prevent the decrease in TX binding. Homologous down-regulation of TX receptors mediated by endogenous TX was therefore not implicated in this action of glucose. The affinity of the glomerular receptor sites for [3H]-Sq was not affected by PKC activation. MC in passages 3 to 7 also demonstrated high affinity sites for [3H]-Sq (Kd, 2.8 nM). Culture of MC with PDBu (0.05 or 0.1 µM) for four hours decreased TX receptor density. In response to 0.1 µM PDBu, TX receptor density declined from 15 to 10 fmol/106 cells. These studies demonstrate that PKC activation is linked to down-regulation of TX receptor sites in both glomeruli and MC. They suggest that the down-regulation in glomerular TX receptor sites observed in early diabetes in the rat may likewise be related to the concurrent activation of glomerular PKC previously demonstrated in that model.