PGE(2) induces COX-2 expression in podocytes via the EP(4) receptor through a PKA-independent mechanism

Cell Signal. 2008 Nov;20(11):2156-64. doi: 10.1016/j.cellsig.2008.08.007. Epub 2008 Aug 15.

Abstract

Cyclooxygenase-2 (COX-2)-dependent prostaglandin E(2) (PGE(2)) synthesis correlates with the onset of proteinuria and increased glomerular capillary pressure (P(gc)) glomerular disease models. We previously showed that an in vitro surrogate for P(gc) (cyclical mechanical stretch) upregulates the expression of both COX-2 and the PGE(2) responsive E-Prostanoid receptor, EP(4) in cultured mouse podocytes. In the present study we further delineate the signaling pathways regulating podocyte COX-2 induction. Time course experiments carried out in conditionally-immortalized mouse podocytes revealed that PGE(2) transiently increased phosphorylated p38 MAPK levels at 10 min, and induced COX-2 protein expression at 4 h. siRNA-mediated knockdown of EP(4) receptor expression, unlike treatment with the EP(1) receptor antagonist SC 19220, completely abrogated PGE(2)-induced p38 phosphorylation and COX-2 upregulation suggesting the involvement of the EP(4) receptor subtype. PGE(2)-induced COX-2 induction was abrogated by inhibition of either p38 MAPK or AMP activated protein kinase (AMPK), and was mimicked by AICAR, a selective AMPK activator, and by the cAMP-elevating agents, forskolin (FSK) and IBMX. Surprisingly, neither PGE(2) nor FSK/IBMX-dependent p38 activation and COX-2 expression were blocked by PKA inhibitors or mimicked by 8-cPT-cAMP a selective EPAC activator, but were instead abrogated by Compound C, suggesting the involvement of AMPK. These results indicate that in addition to mechanical stretch, PGE(2) initiates a positive feedback loop in podocytes that drives p38 MAPK activity and COX-2 expression through a cAMP/AMPK-dependent, but PKA-independent signaling cascade. This PGE(2)-induced signaling network activated by increased P(gc) could be detrimental to podocyte health and glomerular filtration barrier integrity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinase Kinases
  • Animals
  • Cells, Cultured
  • Cyclic AMP / pharmacology
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cyclooxygenase 2 / biosynthesis*
  • Dinoprostone / pharmacology*
  • Dose-Response Relationship, Drug
  • Enzyme Activation / drug effects
  • Enzyme Induction / drug effects
  • Guanine Nucleotide Exchange Factors / metabolism
  • Mice
  • Phosphorylation / drug effects
  • Podocytes / drug effects*
  • Podocytes / enzymology*
  • Protein Kinases / metabolism
  • Receptors, Prostaglandin E / genetics
  • Receptors, Prostaglandin E / metabolism*
  • Receptors, Prostaglandin E, EP4 Subtype
  • Time Factors
  • Up-Regulation / drug effects
  • p38 Mitogen-Activated Protein Kinases / metabolism

Substances

  • Epac protein, mouse
  • Guanine Nucleotide Exchange Factors
  • Ptger4 protein, mouse
  • Receptors, Prostaglandin E
  • Receptors, Prostaglandin E, EP4 Subtype
  • Cyclic AMP
  • Ptgs2 protein, mouse
  • Cyclooxygenase 2
  • Protein Kinases
  • Cyclic AMP-Dependent Protein Kinases
  • p38 Mitogen-Activated Protein Kinases
  • AMP-Activated Protein Kinase Kinases
  • Dinoprostone