Chen Dong, Reierstad Scott, Fang Feng, Bulun Serdar E
Division of Reproductive Biology Research, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
Mol Endocrinol. 2011 May;25(5):767-75. doi: 10.1210/me.2010-0368. Epub 2011 Mar 10.
Aromatase is the key enzyme in estrogen biosynthesis. Normal breast adipose tissue expresses low levels of aromatase via the distal promoter I.4. Breast adipose tissue surrounding a tumor exhibits excessive aromatase expression controlled by proximal aromatase promoters I.3/II, leading to high local levels of estrogen and breast cancer progression. Prostaglandin E(2) (PGE(2)) secreted by malignant breast epithelial cells activates breast cancer-associated aromatase promoters I.3/II, but silences promoter I.4, in cultured human breast adipose fibroblasts (BAF). The c-Jun N-terminal kinase 1 and p38α mitogen activated protein kinases are necessary for PGE(2) activation of aromatase promoters I.3/II; thus, we examined the roles of downstream targets, c-Jun, JunB, JunD, and activating transcription factor 2, in PGE(2)-mediated regulation of aromatase expression in BAF. PGE(2) induced JunB and JunD protein expression through protein kinase A and protein kinase C, respectively. JunB or JunD knockdown by small interfering RNA markedly reduced PGE(2)-induced total aromatase mRNA level and enzyme activity via promoters I.3/II. JunB knockdown also abrogated JunD expression. JunB stimulated, whereas JunD inhibited, aromatase promoter I.4 activity. Activating transcription factor 2 knockdown did not affect promoter-specific or total aromatase mRNA levels. c-Jun knockdown increased promoter I.4-specific and PGE(2)-induced promoters I.3/II-specific aromatase mRNA levels, leading to enhanced PGE(2)-induced total aromatase mRNA level and enzyme activity. JunD, c-Jun, and JunB bound to a CRE(-211/-199) essential for PGE(2) induction of aromatase promoters I.3/II. Taken together, JunD and c-Jun repress aromatase promoter I.4. JunD mediates, whereas c-Jun modulates, PGE(2) activation of aromatase promoters I.3/II via CRE(-211/-199). JunB also activates aromatase promoters I.3/II by maintaining JunD expression. Targeting JunD may abolish aromatase expression selectively in breast cancer tissue.
芳香化酶是雌激素生物合成中的关键酶。正常乳腺脂肪组织通过远端启动子I.4表达低水平的芳香化酶。肿瘤周围的乳腺脂肪组织表现出由近端芳香化酶启动子I.3/II控制的过度芳香化酶表达，导致局部高水平的雌激素和乳腺癌进展。恶性乳腺上皮细胞分泌的前列腺素E(2)（PGE(2)）在培养的人乳腺脂肪成纤维细胞（BAF）中激活与乳腺癌相关的芳香化酶启动子I.3/II，但使启动子I.4沉默。c-Jun氨基末端激酶1和p38α丝裂原活化蛋白激酶是PGE(2)激活芳香化酶启动子I.3/II所必需的；因此，我们研究了下游靶点c-Jun、JunB、JunD和激活转录因子2在PGE(2)介导的BAF中芳香化酶表达调控中的作用。PGE(2)分别通过蛋白激酶A和蛋白激酶C诱导JunB和JunD蛋白表达。通过小干扰RNA敲低JunB或JunD可显著降低PGE(2)通过启动子I.3/II诱导的总芳香化酶mRNA水平和酶活性。敲低JunB也消除了JunD的表达。JunB刺激而JunD抑制芳香化酶启动子I.4的活性。敲低激活转录因子2不影响启动子特异性或总芳香化酶mRNA水平。敲低c-Jun增加了启动子I.4特异性和PGE(2)诱导的启动子I.3/II特异性芳香化酶mRNA水平，导致PGE(2)诱导的总芳香化酶mRNA水平和酶活性增强。JunD、c-Jun和JunB与PGE(2)诱导芳香化酶启动子I.3/II所必需的CRE(-211/-199)结合。综上所述，JunD和c-Jun抑制芳香化酶启动子I.4。JunD介导而c-Jun调节PGE(2)通过CRE(-211/-199)对芳香化酶启动子I.3/II的激活。JunB也通过维持JunD的表达来激活芳香化酶启动子I.3/II。靶向JunD可能会选择性地消除乳腺癌组织中的芳香化酶表达。
