Autocrine prostaglandin E2signaling promotes promonocytic leukemia cell survival via COX-2 expression and MAPK pathway

The COX-2/PGE₂ pathway has been implicated in the occurrence and progression of cancer. The underlying mechanisms facilitating the production of COX-2 and its mediator, PGE₂, in cancer survival remain unknown. Herein, we investigated PGE₂-induced COX-2 expression and signaling in HL-60 cells following menadione treatment. Treatment with PGE₂ activated anti-apoptotic proteins such as Bcl-2 and Bcl-xL while reducing pro-apoptotic proteins, thereby enhancing cell survival. PGE₂ not only induced COX-2 expression, but also prevented casapse-3, PARP, and lamin B cleavage. Silencing and inhibition of COX-2 with siRNA transfection or treatment with indomethacin led to a pronounced reduction of the extracellular levels of PGEv, and restored the menadione- induced cell death. In addition, pretreatment of cells with the MEK inhibitor PD98059 and the PKA inhibitor H89 abrogated the PGE₂-induced expression of COX-2, suggesting involvement of the MAPK and PKA pathways. These results demonstrate that PGE₂ signaling acts in an autocrine manner, and specific inhibition of PGE₂ will provide a novel approach for the treatment of leukemia.