The Role of Apc and beta-Catenin in Cell Regulation and

一氧化氮（NO）对PGHS-2（又名COX-2）的调节，是一种促炎信号因子，发生在几个水平上。通过条件永生化小鼠结肠上皮细胞与Apc基因型的对比，我们发现NOS II和NO供体增加了COX-2的表达，NO供体增加了β -连环蛋白：Tcf/LEF:DNA复合物的形成。这种作用的机制与e -钙粘蛋白的降解和β -连环蛋白结合在质膜上的释放有关。尽管这种no启动的β -连环蛋白依赖效应与COX-2表达增加有关，但缺乏COX-2启动子直接激活的证据。我们现在已经证明β -连环蛋白信号可以增加Ets转录因子家族成员PEA3的表达，PEA3可以激活COX-2启动子。在转染多种转录因子的COX-2启动子荧光素酶模型中，我们发现PEA3与p300协同作用可显著诱导COX-2启动子活性。一氧化氮，由NO供体外源性传递或由转染的iNOS内源性产生，增强了转染的PEA3/p300的COX-2启动子活性。c-jun、β -连环蛋白、TCF-4或各种转录因子的组合均未见NO的刺激，但仅限于PEA3/p300。这些研究表明，NO在多个水平上刺激COX-2的表达。它激活金属蛋白酶，释放β -连环蛋白，增加其信号传导，从而增加PEA3的表达。此外，NO与p300结合可提高PEA3的转录活性。我们将继续研究这种相互作用的机制，因为p300不仅作为转录因子的共同调节因子，而且还通过其组蛋白乙酰化酶活性提供表观遗传调节机制。

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.