Characterization of PGE2 receptors (EP) and their role as mediators of 1α,25-(OH)2D3 effects on growth zone chondrocytes

V. L. Sylvia, Jr Del Toro, R. Hardin, D. D. Dean, B. D. Boyan, Z. Schwartz

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

Growth plate chondrocyte function is modulated by the vitamin D metabolite 1α,25-(OH)2D3 via activation of protein kinase C (PKC). In previous studies with cells derived from prehypertrophic and upper hypertrophic zones of rat costochondral cartilage (growth zone cells), inhibition of prostaglandin production with indomethacin caused a decrease in the stimulation of PKC activity, suggesting that changes in prostaglandin levels mediate the 1α,25-(OH)2D3-dependent response in these cells. Growth zone cells also respond to PGE2 directly, indicating that prostaglandins act as autocrine or paracrine regulators of chondrocyte metabolism in the growth plate. The aim of the present study was to identify which PGE2 receptor subtypes (EP) mediate the effects of PGE2 on growth zone cells. Using primers specific for EP1-EP4, reverse transcription-polymerase chain reaction (RT-PCR) amplified EP1 and EP2 cDNA in a RT-dependent manner. In parallel experiments, we used EP subtype-specific agonists to examine the role of EP receptors in 1α,25-(OH)2D3-mediated cell proliferation and differentiation. 17-Phenyl-trinor-PGE2 (PTPGE2), an EP1 agonist, decreased [3H]-thymidine incorporation in a dose-dependent manner and augmented the 1α,25-(OH)2D2-induced inhibition of [3H]-thymidine incorporation. PTPGE2 also caused significant increases in proteoglycan production, as measured by [35S]-sulfate incorporation, and alkaline phosphatase specific activity. 1α,25-(OH)2D3-induced alkaline phosphatase activity was only slightly stimulated by PTPGE2. In contrast, 1α,25-(OH)2D3-induced PKC activity was synergistically increased by PTPGE2, whereas EP1 antagonists SC-19220 and AH6809 inhibited PKC activity in a dose-dependent manner. The EP2, EP3 and EP4 agonists had no effect on the various cell-induced responses measured. EP1 receptor-induced responses were blocked by the phospholipase C inhibitor U73122, and reduced by PKA inhibitors. EP1 receptor-induced PKC activity was insensitive to pertussis toxin or choleratoxin but blocked by the G-protein inhibitor GDPβS, suggesting the involvement of Gq. These results suggest that the EP1 receptor subtype mediates various PGE2-induced cellular responses in growth zone chondrocytes leading to decreased proliferation and enhanced differentiation, as well as the effect of 1α,25-(OH)2D3 on cellular maturation.

Original languageEnglish (US)
Pages (from-to)261-274
Number of pages14
JournalJournal of Steroid Biochemistry and Molecular Biology
Volume78
Issue number3
DOIs
StatePublished - Oct 22 2001

Keywords

  • 1α,25-(OH)D
  • Chondrocytes
  • Costochondral cartilage
  • EP receptors
  • Growth plate
  • PGE

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Endocrinology
  • Clinical Biochemistry
  • Cell Biology

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