Pifithrin-α, an inhibitor of p53 transactivation, up-regulates COX-2 expression through an MAPK-dependent pathway.

Cyclooxygenase-2 (COX-2) has been reported to be elevated in many cancers, including breast and colorectal cancers, resulting in accumulation of prostaglandin E₂ in the cancer cell environment. In this study, we investigated the effect of pifithrin (PFT)-α, an inhibitor of p53 transactivation, on COX-2 expression in breast and fibrosarcoma cells. Our results showed that COX-2 expression was dose-dependently increased by PFT-α in MDA-MB231 breast cancer cells with mutant p53. In addition, the expression level of COX-2 was also increased by PFT-α in normal fibroblasts as well as in HT1080 fibrosarcoma cells with p53 wild-type cells. To verify the regulatory mechanism of COX-2 in response to PFT-α, we pretreated cells with a mitogen-activated protein kinase (MAPK) kinase (MEK)1/2 inhibitor (UO126) and a phosphoinositide-3 (PI-3K) inhibitor (LY294002). PFT-α-induced COX-2 expression was significantly decreased by UO126 and LY294002 in MDA-MB231 cells. However, the phosphorylation of extracellular signal-regulated kinase (ERK) was increased by PFT-α, but not Akt phosphorylation. Finally, we confirmed the correlation of the MEK and PI-3K pathway and COX-2 expression using the constitutively active (CA)-MEK and myr-Akt adenovirus systems. COX-2 expression was increased by CA-MEK transfection, but not by myr-Akt. Taken together, we have demonstrated that PFT-α-induced COX-2 expression is regulated through a MEK/ERK pathway in MDA-MB231 human breast cancer cells.