Prostaglandin E2 inhibits the interleukin-2 promoter activity through down-regulation of the Oct-dependent transcription of the octamer motif

Prostaglandins, mainly those of the E series (PGE), are modulators of immune responses. Indeed PGE₂ inhibits T cell activation and the transcription of the interleukin 2 (IL-2) gene, the major T cell growth factor. We observed that PGE₂ inhibits IL-2 promoter transcription activity by interfering with signals activating the (-96 to -66 bp) octamer motif. This motif binds Oct-1 and Oct-2 as well as the phorbol ester and calcium ionophore-inducible jun and fos AP-1 factors. The PGE₂-dependent down-modulation is observed in the presence of either the endogenous transacting factor Oct-1 or the exogenously expressed Oct-2. PGE₂ does not regulate octamer function by influencing the jun and fos mRNA or Oct-1 protein levels or their DNA-binding abilities. Functional dissection of the octamer motif, through mutations of either the AP-1 or the octamer sites, revealed that the AP-1 site is dispensable for PGE₂-dependent inhibition which instead may occur through the interference with the Oct-mediated transactivation of the octamer element. Our data suggest that the Oct-octamer interaction is a novel target of the PGE₂-induced down-regulation of the IL-2 promoter.