Abstract
Epidermal growth factor (EGF) is essential to heal gastric ulcers, whereas glucocorticoid delays rat gastric ulcer healing. We found that dexamethasone inhibited EGF-stimulated rat gastric epithelial cell (RGM-1) proliferation by cell count and DNA synthesis analysis of flow cytometry and attempted to elucidate the possible mechanistic pathway via Western blot analysis. EGF (10 ng/ml) treatment for 24 h significantly increased RGM-1 cell proliferation, and dexamethasone (10–8 and 10–6 M) markedly suppressed EGF-stimulated cell proliferation. Western blotting results demonstrated that the phosphorylated extracellular signal-regulated kinase (pERK) (pERK1/pERK2) significantly increased at 10 min after EGF treatment. This was followed by increase of cyclooxygenase (COX)-2 expression at 3 h after EGF treatment. The continued increase of COX-2 (up to 18 h) resulted in increased intracellular prostaglandin E2 and cyclin D1 expression significantly after 8 and 12 h of EGF treatment. Dexamethasone substantially reduced EGF-stimulated COX-2 expression at 3 and 6 h and cyclin D1 expression at 8 and 12 h. Pretreatment of RGM-1 cells with dexamethasone or 2′-amino-3′-methoxyflavone (PD98059)-mitogen-activated protein kinase kinase inhibitor (5 × 10–5 M) significantly reduced EGF-stimulated pERK1/pERK2 expression. Simultaneous treatment of RGM-1 cells with PD98059 and EGF also markedly decreased EGF-stimulated COX-2 expression at 6 h. These findings indicate that dexamethasone significantly suppresses EGF-stimulated gastric epithelial cell proliferation, and one of the pathways involved is via inhibiting activation of ERK1/ERK2, followed by inhibition of COX-2, cyclin D1 expression, and finally DNA synthesis.
Footnotes
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This study is supported by National Science Council of Taiwan Grant NSC 94-2314-B-075-087, Yen Tjing Ling Medical Foundation Grant CI-93-13, and Taipei Veteran General Hospital Grant VGH94-170. J.-C.L. is the recipient of the Physician Scientist Award from the National Health Research Institutes of Taiwan.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.113035.
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ABBREVIATIONS: EGF, epidermal growth factor; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; COX, cyclooxygenase; PG, prostaglandin; NS-398, N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methane sulfonamide; MEK, mitogen-activated protein kinase kinase; PD98059, 2′-amino-3′-methoxyflavone; BSA, bovine serum albumin; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; pERK, phosphorylated extracellular signal-regulated kinase; JNK, c-Jun NH2-terminal kinase; pJNK, phosphorylated c-Jun NH2-terminal kinase; cPLA2, cytosolic phospholipase A2; Dexa, dexamethasone; Mif, mifepristone.
- Received September 3, 2006.
- Accepted October 30, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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