The EP4 receptor antagonist, L-161,982, blocks prostaglandin E2-induced signal transduction and cell proliferation in HCA-7 colon cancer cells

Abstract

Accumulating evidence indicates that elevated levels of prostaglandin E 2 (PGE 2 ) can increase intestinal epithelial cell proliferation, and thus play a role in colorectal tumorigenesis. PGE 2 exerts its effects through four G-protein coupled PGE receptor (EP) subtypes, named the EP1, EP2, EP3, and EP4. Increased phosphorylation of extracellular regulated kinases (ERK1/2) is required for PGE 2 to stimulate cell proliferation of human colon cancer cells. However, the EP receptor(s) that are involved in this process remain unknown. We provide evidence that L-161,982, a selective EP4 receptor antagonist, completely blocks PGE 2 -induced ERK phosphorylation and cell proliferation of HCA-7 cells. In order to identify downstream target genes of ERK1/2 signaling, we found that PGE 2 induces expression of early growth response gene-1 (EGR-1) downstream of ERK1/2 and regulates its expression at the level of transcription. PGE 2 treatment induces phosphorylation of cyclic AMP response element binding protein (CREB) at Ser133 residue and CRE-mediated luciferase activity in HCA-7 cells. Studies with dominant negative CREB mutant (ACREB) provide clear evidence for the involvement of CREB in PGE 2 driven egr-1 transcription in HCA-7 cells. In conclusion, this study reveals that egr-1 is a target gene of PGE 2 in HCA-7 cells and is regulated via the newly identified EP4/ERK/CREB pathway. Finally our results support the notion that antagonizing EP4 receptors may provide a novel therapeutic approach to the treatment of colon cancer.

The Prostanoid EP4 Receptor and Its Signaling Pathway

“…PGE 2 stimulates cell proliferation in colorectal cancer cells via cAMP signaling (Loffler et al, 2008). EP4 involvement in proliferation of colorectal cancer cells was also demonstrated in several reports (Sheng et al, 2001;Mutoh et al, 2002;Cherukuri et al, 2007). Pozzi et al (2004) demonstrated that indomethacin, a nonspecific COX inhibitor, and COX-1 or -2 selective inhibitors prevented PGE 2 biosynthesis and proliferation of mouse colon adenocarcinoma cells.…”

“…PGE 2 increased expression of early growth response gene-1 (EGR-1), a downstream molecule of ERK, at the level of transcription. Cherukuri et al (2007) demonstrated that PGE 2 increased EGR-1 expression via CREB. They also showed that the EP4 receptor agonist PGE 1 -OH phosphorylated ERK in human colon adenocarcinoma cells, whereas the EP4 receptor antagonist L-161,982 blocked PGE 2 -induced ERK and CREB phosphorylation.…”

“…The importance of EP4 has been most clearly shown in colorectal cancer. It has been reported that EP4 is the predominant PGE 2 receptor subtype in HT-29 and HCA-7 human colon cancer cell lines (Cherukuri et al, 2007;Doherty et al, 2009). Mutoh et al (2002) have reported similar results in colon cancer tissues in mice.…”

E Series of Prostaglandin Receptor 2-Mediated Activation of Extracellular Signal-Regulated Kinase/Activator Protein-1 Signaling Is Required for the Mitogenic Action of Prostaglandin E2in Esophageal Squamous-Cell Carcinoma

“…PGE 2 or Butaprost Increased Erk1/2 Phosphorylation. Because phosphorylation of Akt and Erk1/2 has been suggested to mediate the growth-promoting effect of PGE 2 in other cancer cell types (Leng et al, 2003;Han and Wu, 2005;Krysan et al, 2005;Cherukuri et al, 2007), we examined the direct effects with PGE 2 on the phosphorylation of these proteins. As shown in Fig.…”

“…L-748706, a selective COX-2 inhibitor, has also been found to reduce tumor multiplicity in carcinogen-induced esophageal tumor in rats by reducing PGE 2 levels (Stoner et al, 2005). In relation to the signaling mechanism, emerging evidence suggests that increased phosphorylation of extracellular signal-regulated kinases (Erk) 1/2 and protein kinase B (Akt) may be required for the stimulatory effect of PGE 2 on cell proliferation (Leng et al, 2003;Han and Wu, 2005;Krysan et al, 2005;Cherukuri et al, 2007).…”