In SCID mice with tumor xenografts, mPGES-1 overexpression accelerated tumor formation and increased tumor weight (P<.01), whereas mPGES-1 knockdown delayed tumor formation and reduced tumor weight (P<.01). mPGES-1 inhibited the expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), leading to activation of the epidermal growth factor/phosphoinositide 3-kinase/AKT/mammalian target of rapamycin signaling pathways in cholangiocarcinoma cells. mPGES-1-mediated inhibition of PTEN is regulated through blocking of early growth response-1 sumoylation and binding to the 5'-untranslated region of the PTEN gene.