Activation of protein kinase C by tumor necrosis factor-alpha in human non-pigmented ciliary epithelium

J Ocul Pharmacol Ther. 1998 Oct;14(5):401-12. doi: 10.1089/jop.1998.14.401.


Previously, we have shown that tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, increases the synthesis and release of endothelin-1 (ET-1), a potent vasoactive peptide from human non-pigmented ciliary epithelial (HNPE) cells, in a protein kinase C (PKC)-dependent manner. Diacylglycerol (DAG) and intracellular calcium ([Ca2+]i) are well known activators of PKC. Some cytokines induce PKC activation by stimulating phospholipase C that hydrolyzes phosphatidylinositol bisphosphate (PIP2) into IP3 (intracellular calcium mobilizer) and DAG. In this study, the existence of a similar pathway was evaluated in HNPE cells treated with TNF-alpha, using intracellular calcium ([Ca2+]i) measurements, PKC translocation assays and thin-layer chromatography (TLC) for quantification of DAG. Incubation times for agonists and inhibitors ranged from 1-30 minutes. The increase in DAG levels with TNF-alpha treatment was consistent with the observed translocation of the calcium-dependent PKC alpha isoform from the cytosol to the plasma membrane. However, these observations were not accompanied by a concomitant increase in [Ca2+]i. Similar translocation responses were observed with phorbol ester (phorbol 12-myristate 13-acetate) treatment. Our results indicate that TNF-alpha-induced PKC activation in HNPE cells occurs as a result of elevated DAG levels and is not due to an increase in intracellular calcium. Activated PKC, could enhance the pro-inflammatory responses of TNF-alpha in part by increasing the production of endothelins in the eye.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism
  • Cell Line
  • Ciliary Body / drug effects*
  • Ciliary Body / enzymology
  • Diglycerides / metabolism
  • Endothelin-1 / pharmacology
  • Enzyme Activation
  • Humans
  • Isoenzymes / metabolism
  • Protein Kinase C / metabolism*
  • Protein Kinase C-alpha
  • Tumor Necrosis Factor-alpha / pharmacology*


  • Diglycerides
  • Endothelin-1
  • Isoenzymes
  • Tumor Necrosis Factor-alpha
  • PRKCA protein, human
  • Protein Kinase C
  • Protein Kinase C-alpha
  • Calcium