Received for publication September 5, 2006.
Revised October 15, 2006.
Accepted for publication October 30, 2006.

Dexamethasone inhibits epidermal growth factor-stimulated gastric epithelial cell proliferation

Abstract

Epidermal growth factor (EGF) is essential to heal gastric ulcer, whereas glucocorticoid delays rat gastric ulcer healing. We found dexamethasone inhibited EGF-stimulated rat gastric epithelial cell (RGM-1 cell) proliferation by cell count and DNA synthesis analysis of flowcytometry and attempted to elucidate the possible mechanistic pathway via Western blot analysis. EGF 10 ng/mL treatment for 24 hr significantly increased RGM-1 cell proliferation and dexamethasone (10^-8 M and 10^-6 M) markedly suppressed EGF-stimulated cell proliferation. Western blotting results demonstrated that the expression of phosphorylated extracellular signal-regulated kinase (pERK1/pERK2) significantly increased at 10 min after EGF treatment. This was followed by increase of cyclooxygenase (COX)-2 expression at 3 hr after EGF treatment. The continued increase of COX-2 (up to 18 hr) resulted in increased intracellular prostaglandin E₂ and cyclin D1 expression significantly after 8 and 12 hr of EGF treatment. Dexamethasone substantially reduced EGF-stimulated COX-2 expression at 3 and 6 hr and cyclin D1 expression at 8 and 12 hr. Pretreatment of RGM-1 cells with dexamethasone or PD98059-MEK inhibitor (5x10^-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 hr. 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.

Key words: RGM-1 cell, cell proliferation, cyclooxygenase, dexamethasone, epidermal growth factor, extracellular signal-regulated kinase (ERK)