Regulation of EP4 expression via the Sp-1 transcription factor: inhibition of expression by anti-cancer agents

Biochim Biophys Acta. 2008 Jun;1783(6):1211-9. doi: 10.1016/j.bbamcr.2008.01.032. Epub 2008 Feb 20.

Abstract

For glioblastomas, COX-2 expression is linked to poor survival. COX-2 effects are mediated by the receptors EP2 and EP4, whose regulation is poorly understood. The expression of EP4, and activation or inhibition of EP4 activity in human glioblastoma T98G cells, was found to correlate with growth on soft agar. Chemoprevention drugs, troglitazone (TGZ) and some COX inhibitors, significantly suppressed EP4 expression in T98G cells in a dose dependant manner. Specificity protein 1 (Sp-1) binding sites, located within region -197 to -160 of the human EP4 promoter, are important for the transcription initiation of the human EP4 gene and are responsible for the EP4 suppression by TGZ. Mutation in the Sp-1 sites altered the promoter activity of luciferase constructs and TGZ effects on the promoter. The inhibitory effect of TGZ on EP4 expression was reversed by PD98059, a MEK-1/Erk inhibitor. Immunoprecipitation-Western blot analysis detected Sp-1 phosphorylation that was dependent on TGZ-induced Erks activation. ChIP assay confirmed that Sp-1 phosphorylation decreases its binding to DNA and as a result, leads to the suppression of EP4 expression. Thus, we propose that the expression of EP4 is regulated by Sp-1, but phosphorylation of Sp-1 induced by TGZ suppresses this expression. This represents a new and unique mechanism for the regulation of the EP4 receptor expression.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Astrocytoma / drug therapy
  • Astrocytoma / genetics
  • Astrocytoma / metabolism
  • Blotting, Western
  • Calcium-Calmodulin-Dependent Protein Kinases / antagonists & inhibitors
  • Chromans / pharmacology*
  • Chromatin Immunoprecipitation
  • Colony-Forming Units Assay
  • Cyclooxygenase 2 Inhibitors / pharmacology
  • DNA Primers / chemistry
  • DNA Primers / genetics
  • Flavonoids / pharmacology
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Glioblastoma / drug therapy
  • Glioblastoma / genetics
  • Glioblastoma / metabolism
  • Humans
  • Immunoprecipitation
  • Luciferases / metabolism
  • Phosphorylation / drug effects
  • Promoter Regions, Genetic
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / pharmacology
  • Receptors, Prostaglandin E / antagonists & inhibitors
  • Receptors, Prostaglandin E / genetics*
  • Receptors, Prostaglandin E / metabolism
  • Receptors, Prostaglandin E, EP2 Subtype
  • Receptors, Prostaglandin E, EP4 Subtype
  • Sp1 Transcription Factor / antagonists & inhibitors
  • Sp1 Transcription Factor / genetics
  • Sp1 Transcription Factor / metabolism*
  • Thiazolidinediones / pharmacology*
  • Transcription, Genetic
  • Transfection
  • Troglitazone
  • Tumor Cells, Cultured

Substances

  • Antineoplastic Agents
  • Chromans
  • Cyclooxygenase 2 Inhibitors
  • DNA Primers
  • Flavonoids
  • PTGER2 protein, human
  • PTGER4 protein, human
  • RNA, Messenger
  • RNA, Small Interfering
  • Receptors, Prostaglandin E
  • Receptors, Prostaglandin E, EP2 Subtype
  • Receptors, Prostaglandin E, EP4 Subtype
  • Sp1 Transcription Factor
  • Thiazolidinediones
  • Luciferases
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Troglitazone
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one