br Materials and methods br Results
Materials and methods
Discussion COX-2-mediated production of PGE2 is involved in cell growth and metastasis of many cancers. Previous studies indicated that COX-2 was overexpressed in many cancer tissues and that PGE2 increased cancer cell growth, a process that could be suppressed by several COX-2 inhibitors (Leng et al., 2003, Wendum et al., 2004, Smith and Langenbach, 2001, Zha et al., 2004). Studies have also demonstrated that PGE2 induces angiogenesis (Zhao et al., 2007, Hussain et al., 2003) and promotes tumor cell migration and invasion (Bai et al., 2009, Mayoral et al., 2005). PGE2-mediated cell growth and metastasis are coordinated by a number of proteins, including CD44 (Dohadwala et al. 2001), EGFR (Han et al., 2006, Buchanan et al., 2003), MMP (Mayoral et al. 2005), Akt (Leng et al., 2003, Wu et al., 2004), and MAPK (Zhang et al., 2007, Martineau et al., 2004). The survivin protein has also been implicated in cell growth in many cancers. Pathological evidence has shown a significant correlation between survivin expression and tumor stage, prognosis, and recurrence (Barnes et al., 2006, Atikcan et al., 2006, Ye et al., 2007, Lee et al., 2005). Downregulation of survivin expression by drugs or RNA interference sensitizes tumor cells to chemotherapy and induces cell apoptosis (Nakao et al., 2006, Yonesaka et al., 2006). Previous studies have suggested that survivin is expressed in the G2/M phase of the DLPC in a cycle-regulated manner, and is essential for cell survival during mitosis (Li et al. 1998). In addition, survivin appears to be a component of the chromosomal passenger protein complex, a structure that participates in multiple facets of cell mitosis. Depletion of survivin causes defects in cell division, followed by an arrest of DNA synthesis due to activation of checkpoints, such as the tumor suppressor protein p53 (Li et al., 1998, Yang et al., 2004). Survivin and COX-2 are often co-expressed in many cancers (Barnes et al., 2006, Mori et al., 2007, Erkanli et al., 2007). Several selective COX-2 inhibitors have been reported to induce cell apoptosis by decreasing expression of survivin (Konturek et al., 2006, Nakamura et al., 2006, Sakoguchi-Okada et al., 2007). Krysan et al. (Krysan et al., 2004, Krysan et al., 2003) demonstrated that COX-2-dependent expression of survivin is critical for resistance to apoptosis in non-small cell lung cancer. Further, the stabilization of the survivin protein is modulated by PGE2. Other reports have shown that treatment with 10µM PGE2 significantly increases expression of survivin mRNA and protein, and that the treated cells exhibited increased cell viability compared with controls in human monocyte-derived dendritic cells. Additionally, this effect is inversely correlated with caspase-3 activation (Baratelli et al. 2005). However, the mechanism involved in PGE2-mediated expression of survivin remains unclear. Here, we report that PGE2 strongly induces survivin expression by activating the EP1/EGFR/PI3K pathway in hepatocellular carcinoma cells. In general, PGE2 has been shown to exert diverse effects in a variety of liver cancer cells. Our previous studies have shown that the expression level of COX-2 and the production of PGE2 were both higher in hepatoma cells than in normal liver cells. Endogenous production of PGE2 increased in hepatocellular carcinoma cells following transfection with the COX-2-pcDNA3 plasmid (Leng et al. 2003). Celecoxib, a selective COX-2 inhibitor, suppressed PGE2 production in HUH-7 cells and other cell types. Treatment with 10μM celecoxib triggered a less than 20% reduction in PGE2 production in cholangiocarcinoma cells. However, treatment with 50μM celecoxib decreased PGE2 production up to 80% in HUH-7 cells (Wu et al., 2004, Cui et al., 2005). The current study focuses on the impact of PGE2 on expression of survivin. Treatment with PGE2 at 5µM was sufficient to induce upregulation of the survivin protein in HUH-7 cells. COX-2 overexpression mimicked the effects of PGE2, and these effects were totally inhibited by treatment with 50μM celecoxib. These findings suggest that survivin may play a role in PGE2-mediated cell proliferation.