The regulation of PGHS-2 (aka COX-2) by nitric oxide (NO), a proinflammatory signaling factor, occurs at several levels. Using conditionally immortalized murine colonic epithelial cells contrasting in Apc genotype, we have shown that NOS II and NO donors increased COX-2 expression and NO donors increased the formation of beta-catenin: Tcf/LEF:DNA complexes. The mechanism of this effect is linked to the degradation of E-cadherin and release of beta-catenin bound to plasma membranes. Although this NO-initiated, beta-catenin-dependent effect was associated with increased expression of COX-2, evidence of direct activation of the COX-2 promoter was lacking. We now have shown that beta-catenin signaling increases the expression of PEA3, a member of the Ets family of transcriptional factors and that PEA3 activates the COX-2 promoter. In a COX-2 promoter luciferase model transfected with a variety of transcriptional factors, we showed that PEA3 acting synergistically with p300 markedly induced COX-2 promoter activity. Nitric oxide, delivered exogenously from NO donors or produced endogenously from transfected iNOS, augmented COX-2 promoter activity of transfected PEA3/p300. The stimulation by NO was not seen with c-jun, beta-catenin, TCF-4, or with various combinations of transcriptional factors, but was limited to PEA3/p300. These studies suggest that NO acts at several levels to stimulate COX-2 expression. It activates metalloproteinases which releases beta-catenin, increases its signaling and thereby increases the expression of PEA3. Furthermore, NO increases the transcriptional activity of PEA3 in combination with p300. We will pursue the mechanisms of this interaction because p300 not only acts as a co-regulator with transcriptional factors but also provides a mechanism for epigenetic modulation through its histone acetylase activity.
