Colon Carcinoma Cell Growth Is Associated with Prostaglandin E2/EP4 Receptor-evoked ERK Activation

Abstract

Cyclooxygenase (COX) and its prostanoid metabolites have been implicated in the control of cell survival; however, their role as mitogens remains undefined. To better understand the role of prostanoids on cell growth, we used mouse colon adenocarcinoma (CT26) cells to investigate the role of prostaglandin E 2 (PGE 2 ) in cell proliferation. CT26 cells express both COX1 and COX2 and metabolize arachidonic acid to PGE 2. Treatment with indomethacin, or COXselective inhibitors, prevents PGE 2 biosynthesis and CT26 cell proliferation. The anti-proliferative effects of COX inhibition are rescued specifically by treatment with PGE 2 or the EP4 receptor-selective agonist PGE 1 -OH via phosphatidylinositol 3-kinase/extracellular signal-regulated kinase (ERK) activation, thus providing a functional link between PGE 2 -induced cell proliferation and EP4-mediated ERK signaling. Indomethacin or COX2 inhibitors, but not COX1 inhibitors, reduced the size and number of CT26-derived tumors in vivo. These inhibitory effects are paralleled by marked declines in the levels of tumor PGE 2 , suggesting that their anti-tumor effects are directly associated with the inhibition of COX2 enzymatic activity. The described anti-tumor effects of indomethacin are evident whether it is administered at the time of, or 7 days after, tumor cell injection, suggesting that it has tumor preventive and therapeutic actions. Furthermore, the observation that indomethacin increases the survival rates of tumor-bearing mice, even after withdrawal of the drug, indicates that its effects are long lasting and that it may be potentially useful for the prevention and the clinical management of human cancers.The identification of cyclooxygenase (COX) 1 as the target for non-steroidal anti-inflammatory drugs (NSAIDs) led to new understandings of its pathophysiological role and of the mechanisms of action of these drugs (1, 2). The discovery of COX2, an isoform that, although catalytically identical to COX1, shows inducible tissue-selective expression, suggested physiological and pathophysiological roles for the constitutively expressed (COX1) and inducible (COX2) isoforms, respectively (1-4). Studies showing a correlation between NSAIDs and decreased colon cancer incidence, and the demonstration of up-regulated COX2 expression in colon carcinoma, suggested a role for COX2 in the pathophysiology of colon cancer and created new paradigms for the study of the role of prostanoids in cancer (1-3). Nevertheless, despite extensive supporting evidence, direct links between the anti-tumor effects of NSAIDs and COX inhibition are yet to be established (4 -9). The potential for non-COX-dependent anti-tumor effects of NSAIDs (6 -9), as well as limited evidence available identifying a specific prostanoid(s) as the mediator responsible for the anti-tumor effects of the COX inhibitors (5), raised questions regarding the mechanism of action of NSAIDs and of the role of arachidonic acid, prostanoids, and COXs in human cancer (4 -9).During studies of arachidonic acid metabolism ...

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

“…Although recent studies suggest a role for the EP2 receptor in PGE 2 -induced cellular response, a caveat with these studies is the use of cell culture systems in which the EP2 receptor is ectopically expressed [40]. Our studies, which are in agreement with several other reports [36], indicate an important role for the EP4 receptor for the following reasons: 1) PGE1-OH (relatively selective EP4 agonist), but not 17-phenyltrinor PGE 2 (EP1/EP3 agonist) induced ERK phosphorylation; 2) pretreatment of HCA-7 cells with AH6809 (EP1/EP2 antagonist) did not have any effect on PGE 2 -induced ERK phosphorylation; 3) L-161,982 at concentrations that does not bind to either EP1 or EP2 receptors [18] abrogated PGE 2 -induced ERK phosphorylation. Nevertheless, the relative contribution of the EP2 and EP4 receptors to human colon cancer will require further study.…”

“…For example, PGE 2 has been reported to stimulate the proliferation and motility of LS174T colorectal cancer cells via EP4 dependent stimulation of PI-3-K/AKT signaling [10]. In addition Pozzi et al [36] demonstrated EP4 mediated PI-3-K/ ERK signaling pathway in mouse colon carcinoma cells. Furthermore, Chell et al [17] demonstrated increased EP4 receptor expression in human colon cancer progression and increased proliferation of EP4 expressing cells in response to PGE 2 .…”

Ets-1 and Runx2 Regulate Transcription of a Metastatic Gene, Osteopontin, in Murine Colorectal Cancer Cells

“…YAMC cells were grown in monolayer in RPMI 1640 (Invitrogen) supplemented with 5% FBS, 1 g/ml insulin, 5 IU/ml mouse interferon-, 100 IU/ml penicillin, and 100 g/ml streptomycin in a 33°C incubator with 5% CO 2 in humidified air. The utilization by established investigators of the metastatic and nonmetastatic companion cell lines CT26 and YAMC in studying colon cancer is well described in the literature (20,21).…”

Multiple Signaling Pathways Are Responsible for Prostaglandin E2–Induced Murine Keratinocyte Proliferation

“…Multiple intracellular signaling pathways can be activated after prostanoid receptor binding (25,49,50). The different signal transduction pathways induced by PGE 2 seem to depend on the type of cells and on the subtype of G-protein coupled receptors involved in signaling (49).…”