PROSTAGLANDIN E2 stimulates cancer-related phenotypes in prostate cancer PC3 cells through cyclooxygenase-2

6 Cyclooxygenase (COX)-derived prostaglandin E2 (PGE(2)) affects many mechanisms that have been shown to play roles in carcinogenesis. Recently, we found that, in androgen-independent prostate cancer PC3 cells, PGE(2) acts through an intracrine mechanism by which its uptake by the prostaglandin transporter (PGT) results in increased intracellular PGE(2) (iPGE(2)), leading to enhanced cell proliferation, migration, invasion, angiogenesis, and loss of cell adhesion to collagen I. These iPGE(2)-mediated effects were dependent on hypoxia-inducible factor 1-alpha (HIF-1 alpha), whose expression increased upon epidermal growth factor receptor (EGFR) transactivation by a subset of intracellular PGE(2) receptors. Here, we aimed to study the role of COX in PGE(2) protumoral effects in PC3 cells and found that the effects were prevented by inhibition of COX-2, which highlights its crucial role amplifying the levels of iPGE(2). Treatment with exogenous PGE(2) determined a transcriptional increase in COX-2 expression, which was abolished by genetic or pharmacologic inhibition of PGT. PGE(2)-induced increase in COX-2 expression and, thereby, in transcriptional increase in HIF-1 alpha expression was due to EGFR activation, leading to the activation of Phosphoinositide 3-kinase/Akt, Extracellular signal -regulated kinases 1/2, p38 and Mitogen- and stress-activated protein kinase-1 (PI3K/Akt, Erk1/2, p38 and MSK-1). Collectively, the data suggest that EGFR-dependent COX-2 upregulation by a novel positive feedback loop triggered by iPGE(2) underlies the intracrine pro-tumoral effects of PGE(2) in PC3 cells. Therefore, this feedback loop may be relevant in prostate cancer for the maintenance of PGE(2)-dependent cancer cell growth through amplifying the activity of the COX-2 pathway.