Inhibition of EP2/EP4 prostanoid receptor-mediated signaling suppresses IGF-1-induced proliferation of pancreatic cancer BxPC-3 cells via upregulating γ-glutamyl cyclotransferase expression

Abstract Inhibition of prostaglandin E 2 signaling via EP2/EP4 prostanoid receptors suppresses Insulin-like growth factor (IGF)-1-induced proliferation of pancreatic cancer BxPC-3 cells. To better understand the mechanism of EP2/EP4 signaling for controlling cell proliferation, we performed metabolome analyses in BxPC-3 cells treated with IGF-1 alone or IGF-1 plus EP2/EP4 inhibitors. These analyses revealed increased g-aminobutyric acid and 5-oxoproline production following the addition of EP2/EP4 inhibitors to IGF-1-treated cells. The expression of a 5-oxoproline-catalyzing enzyme, γ-glutamylcyclotransferase (GGCT), was also upregulated by IGF-1 treatment and further enhanced by the addition of EP2/EP4 inhibitors. Knockdown of GGCT expression resulted in the loss of suppressive effects of EP2/EP4 inhibitors on IGF-1-induced BxPC-3 cell proliferation, whereas GGCT overexpression repressed the basal proliferation of BxPC-3 cells but did not affect the suppressive effects of EP2/EP4 inhibitors. To summarize, we propose a role for EP2/EP4 signaling in regulating IGF-1-induced cell proliferation, in which EP2/EP4 signaling represses IGF-1-induced GGCT expression, which mediates and whose amount controls a branch of IGF-1 signaling to promote cell proliferation via extracellular signal-regulated kinase phosphorylation.