ruthenium red weight It has been reported that PGE increases
It has been reported that PGE2 increases expression of the survivin mRNA (Baratelli et al. 2005) and promotes the stabilization of the survivin protein in some tumor ruthenium red weight (Krysan et al. 2003). However, it is unclear whether PGE2 affects the expression of survivin mRNA or promotes the stabilization of the survivin protein in hepatocellular carcinoma cells. In this study, we examined the level of survivin mRNA by realtime PCR. This experiment showed no increase in the mRNA levels in HUH-7 cells treated with PGE2. Thus, we suggest that PGE2 may modulate survivin expression through post-transcriptional, translational, or post-translational mechanisms. PGE2 mediates its effects by binding to and activating 4 different G-protein-coupled receptors, EP1, EP2, EP3 and EP4. Previous studies have expressed these 4 EP receptors in hepatocellular carcinoma cells (Wu 2006). Because EP1, EP2 and EP4 have previously been reported to play a role in liver carcinogenesis (Perez et al., 2004, Han et al., 2006), we investigated whether these receptors were involved in PGE2-induced expression of survivin. We found that treatment with an EP1 agonist, but not EP2 or EP4 agonists, showed marked effects on survivin upregulation. Only the EP1 antagonist suppressed PGE2-induced upregulation of survivin expression in HUH-7 cells. This finding suggests that the EP1 signaling pathway is the predominant pathway that mediates PGE2-induced expression of survivin. Transfection and RNA interference of the EP1 receptor were used in our study to eliminate false results caused by the low affinity of 17-phenyl-trinor-PGE2, the EP1 receptor agonist, to other EP receptors (Kiriyama et al. 1997). Transfection of the EP1 receptor sensitized cells to PGE2-induced cell proliferation and survivin expression. In contrast, RNA interference targeting the EP1 receptor interfered with the upregulation of survivin expression in response to PGE2 treatment. The EP1 receptor has previously been shown to play an important role in the development of various carcinomas, including skin cancer and colon cancer (Sugimoto and Narumiya, 2007, Ushikubi et al., 2000, O\'Callaghan et al., 2008). It is also involved in the progression of cholangiocarcinoma through activation of Akt (Han and Wu 2005). In hepatocellular carcinoma cells, the EP1 receptor has been implicated in PGE2-mediated cell invasion (Han et al. 2006). Our data show that the EP1 receptor plays an important role in PGE2-mediated expression of survivin. Because survivin has been widely proved to promote cell proliferation in hepatocellular carcinomas (Fields et al., 2004, Ye et al., 2007, Ito et al., 2000), our findings suggest that exploration of the possibility of the EP1 receptor as a drug target may aid in the prevention and treatment of liver cancer through prevention of the upregulation of survivin in tumor cells. Recently, several studies have shown that the EP1 receptor pathway also modulates the activation of the epidermal growth factor receptor (EGFR) (Buchanan et al. 2003). The EGFR family consists of 4 receptor tyrosine kinases, ErbB1, ErbB2, ErbB3 and ErbB4. EGFR controls a wide variety of biological responses such as cell proliferation, migration and modulation of apoptosis. These effects are mediated through activation of downstream molecules, including the phosphoinositide 3-kinase/Akt pathway (Fischer et al. 2003). In 2005, Han et al. (Han and Wu 2005) revealed a novel crosstalk between the EP1 and EGFR signaling pathways that synergistically promotes cancer cell growth and invasion. Treatment with PGE2 or EP1 receptor agonist induced an increase in the phosphorylation of EGFR, a process that was inhibited by treatment with the siRNA against the EP1 receptor or treatment with the EP1 antagonist. Treatment of cholangiocarcinoma cells with PGE2 enhanced the binding of EGFR to EP1 and c-Src. In 2006, a cross-talk between the COX-2/PGE2/EP1 and EGFR/c-Met signaling pathways was identified in hepatocellular carcinoma (Han et al. 2006). Because EGFR has been found to regulate survivin expression via the PI3K/Akt pathway in breast cancer cells (Asanuma et al. 2005), we hypothesized that the PGE2/EP1/EGFR/PI3K pathway may be implicated in mediating survivin expression in hepatocellular carcinoma cells.