Purpose: COX-2 overexpression and elevated levels of prostaglandin E2 (PGE2) play an important role in breast cancer carcinogenesis. Recently, expression of the PGE2 receptor EP3 has been shown to be a positive prognostic factor in breast cancer. This study analyzes the functional aspects of targeting EP3 in breast cancer cell lines. Material and methods: EP3 and EP1 expressions were determined in five breast cancer cell lines on the mRNA- and the protein-level. The selected cell lines were subsequently stimulated for 24-72 hrs with 10-1,000 nM of PGE2, the EP1/EP3 agonist sulprostone and the EP3 antagonist L798,106. Cell proliferation was determined via BrdU-assay, migration via scratch assay, EP3, Gi-protein and p-ERK1/2 expressions via Western blot and cAMP concentrations via ELISA. The Mann-Whitney-U-test was used to test for statistical significance. Results: The cell lines T-47D (EP3 expression 77.7%) and SK-BR-3 (EP3 expression 48.7%) were chosen. EP3 antagonism reduced its expression on SK-BR-3 significantly, while no effect was observed on T-47D. The proliferation and migration of SK-BR-3 cells were significantly reduced due to treatment with the EP1/3 agonist, the EP3 antagonist or a combination of both. Neither agonism nor antagonism influenced cell proliferation or migration in T-47D. In SK-BR-3, EP3 antagonism showed a significant decrease in Gi-protein levels, an increase in cAMP levels, and no significant change in p-ERK1/2 expression. Conclusion: Antagonism of the EP3 receptor results in a reduced proliferation and migration of SK-BR-3 breast cancer cells, potentially mediated via a Gi-protein-cAMP pathway. The results suggest that EP3 plays a role in tumorigenesis. This is in accordance with the cell culture data of other gynecological tumors, but it is conflicting in so far, as positive EP3 expression is clinically a positive prognostic marker in breast cancer. Therefore, other factors may be important in explaining this contradiction.
Keywords: carcinoma of the breast; cell growth; cell traffic; in vitro experiments; prostaglandin E2 receptor 3; signal transduction.