Dexamethasone Inhibits Epidermal Growth Factor-Stimulated Gastric Epithelial Cell Proliferation

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 Ϫ8and 10 Ϫ6 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 E 2 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 2Ј-amino-3Ј-methoxyflavone (PD98059)-mitogen-activated protein kinase kinase inhibitor (5 ϫ 10 Ϫ5 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.

Fasting differentially regulates plasma corticosterone-binding globulin, glucocorticoid receptor, and cell cycle in the gastric mucosa of pups and adult rats

“…Together with cyclin D and CDKs, p21 waf1 and p27 kip1 (hereafter referred to as p21 and p27) constitute targets of GR (5,45,50). Conversely, the activity of this receptor is also influenced by the phosphorylation promoted by cell cycle proteins (25,53).Throughout development, the administration of glucocorticoids exerts early inhibitory effects on gastric epithelial cell proliferation either in vivo or in vitro (20,21,35), besides inducing apoptosis (21). …”

“…In the absence of glucocorticoids, GR is found in cytoplasm as part of a large multiprotein complex, which contains heat shock proteins (HSPs), specifically HSP 70 and HSP 90 that allow the proper folding of the receptor and control entrance to the nucleus (23). After glucocorticoids bind GR, a conformational change releases the receptor from the complex, and it translocates into the nucleus to bind glucocorticoid-responsive elements at regulatory regions of target genes, to which repression is the most common response (23).GR arrests cell cycle through induction of antimitogenic factors and inhibition of proliferative molecules (35,45,50). Progression through cell cycle is accomplished by the formation of complexes between cyclins and cyclin-dependent kinases (CDKs), which are regulated by CDK-inhibitory proteins.…”

“…GR arrests cell cycle through induction of antimitogenic factors and inhibition of proliferative molecules (35,45,50). Progression through cell cycle is accomplished by the formation of complexes between cyclins and cyclin-dependent kinases (CDKs), which are regulated by CDK-inhibitory proteins.…”

Gastroduodenal defense

“…[58]. Luo et al [55,56] found that EGF activates extracellular signal-regulated kinase-1/2, then increases COX-2 expression and prostaglandin E 2 synthesis, increasing cyclin D1 expression, which promotes RGM-1 cell proliferation. This was reversed with dexamethasone, which may interfere with EGF binding to its receptor or EGF activation of extracellular signalregulated kinase-1/2, thereby delaying ulcer repair.…”

“…Previously, it was discovered that dexamethasone delayed rat gastric ulcer healing by inhibiting epithelial cell proliferation and angiogenesis at the ulcer margin and base, via COX-2 and prostaglandin E 2 inhibition [55]. A recent study demonstrated that dexamethasone strongly inhibits epidermal growth factor (EGF)-stimulated gastric epithelial cell proliferation [56]. EGF promotes gastric ulcer healing by upregulating gastric epithelial COX-2 expression [57] and by activating the Ras/Raf/mitogen-activated Methionine, an essential amino acid, is obtained by dietary intake and transported to the liver mainly by the System L. Methionine adenosyltransferase (MAT) catalyzes the ATP-dependent conversion of methionine to S-adenosylmethionine, which is converted to S-adenosylhomocysteine by the glycine N-methyltransferase (GNMT) and then hydrolyzed to homocysteine.…”