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Activation of protein kinase C attenuates prostaglandin E2 responses in a colonic cell line
G Warhurst1, N B Higgs, M Lees
1Department of Medicine, University of Manchester School of Medicine, Hope Hospital, Salford, United Kingdom.
Abstract:
We examined the possibility that the protein kinase C pathway may interact with the adenosine 3',5'-cyclic monophosphate (cAMP) pathway in intestinal epithelium by studying the influence of phorbol esters on the response to prostaglandin E2 (PGE2) in a colonic epithelial cell line. Pretreatment of T84 cells with 4 beta-phorbol 12,13-dibutyrate (PDB) markedly attenuated the rise in short-circuit current provoked by PGE2, a receptor-mediated cAMP agonist. The EC50 of this effect was 52 nM PDB with a half time of 4-6 min. The responses to nonreceptor-mediated agonists, forskolin and dibutyryl cAMP, were unaffected by phorbol ester. PDB also reduced the ability of PGE2 to stimulate adenylate cyclase activity in these cells. The accumulation of cAMP in response to PGE2 was inhibited by PDB (EC50 38 nM), an effect mimicked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol. In addition, PGE2 stimulation of adenylate cyclase in membranes from PDB-treated cells was reduced by 30-40%. Inhibition was not mediated via the catalytic or regulatory subunit of the adenylate cyclase, implying an action involving desensitization of PGE2 receptors. These results provide evidence of a complex interrelationship between protein kinase C- and cAMP-mediated pathways that might be important in regulating the cellular response to secretagogues.
Insights
Protein kinase C activation inhibits prostaglandin E2 (PGE2)-induced responses in intestinal cells by desensitizing PGE2 receptors. This interaction between protein kinase C and cyclic adenosine monophosphate (cAMP) pathways regulates cellular responses to secretagogues.
Area of Science:
- Cellular biology
- Gastroenterology
- Molecular pharmacology
Background:
- The protein kinase C (PKC) and cyclic adenosine monophosphate (cAMP) signaling pathways play crucial roles in intestinal epithelial function.
- Understanding the interplay between these pathways is vital for comprehending cellular responses to secretagogues.
Purpose of the Study:
- To investigate the potential interaction between the PKC and cAMP pathways in the intestinal epithelium.
- To determine the effect of PKC activation on the cellular response to prostaglandin E2 (PGE2), a cAMP-mediated agonist.
Main Methods:
- Utilized T84 colonic epithelial cells.
- Administered phorbol ester (phorbol 12,13-dibutyrate, PDB) to activate PKC.
- Measured short-circuit current, adenylate cyclase activity, and cAMP accumulation in response to PGE2 and other agonists (forskolin, dibutyryl cAMP).
Main Results:
- PKC activation by PDB significantly attenuated PGE2-induced short-circuit current and cAMP accumulation.
- PDB reduced PGE2-stimulated adenylate cyclase activity, suggesting desensitization of PGE2 receptors.
- Responses to non-receptor-mediated cAMP agonists were unaffected, indicating a specific interaction at the receptor or early signaling level.
Conclusions:
- PKC activation interferes with PGE2-mediated cAMP signaling in intestinal epithelial cells.
- Evidence suggests PKC acts via desensitization of PGE2 receptors, not directly on adenylate cyclase components.
- A complex interplay exists between PKC and cAMP pathways, potentially regulating intestinal epithelial responses to secretagogues.