Chen Dong, Reierstad Scott, Lin Zhihong, Lu Meiling, Brooks Chris, Li Newton, Innes Joy, Bulun Serdar E
Division of Reproductive Biology Research, Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois 60611, USA.
Cancer Res. 2007 Sep 15;67(18):8914-22. doi: 10.1158/0008-5472.CAN-06-4751.
Aromatase is the key enzyme for estrogen biosynthesis. A distal promoter, PI.4, maintains baseline levels of aromatase in normal breast adipose tissue. In contrast, malignant breast epithelial cells secrete prostaglandin E(2) (PGE(2)), which stimulates aromatase expression via proximal promoters PI.3/PII in a cyclic AMP (cAMP)- and protein kinase C (PKC)-dependent manner in adjacent breast adipose fibroblasts (BAF), leading to increased local concentrations of estrogen. Although an effective treatment for breast cancer, aromatase inhibitors indiscriminately abolish estrogen synthesis in all tissues, causing major side effects. To identify drug targets to selectively block aromatase and estrogen production in breast cancer, we investigated PGE(2)-stimulated signaling pathways essential for aromatase induction downstream of cAMP and PKC in human BAFs. Here, we show that PGE(2) or its surrogate hormonal mixture dibutyryl cAMP (Bt(2)cAMP) + phorbol diacetate (PDA) stimulated the p38, c-jun NH(2)-terminal kinase (JNK)-1, and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase pathways. Inhibition or small interfering RNA-mediated knockdown of p38 or JNK1, but not ERK, inhibited PGE(2)- or Bt(2)cAMP + PDA-induced aromatase activity and expression via PI.3/PII. Conversely, overexpression of wild-type p38alpha or JNK1 enhanced PGE(2)-stimulated aromatase expression via PII. PGE(2) or Bt(2)cAMP + PDA stimulated c-Jun and activating transcription factor-2 (ATF2) phosphorylation and binding to the PI.3/PII region. Specific activation of protein kinase A (PKA) or EPAC with cAMP analogues stimulated p38 and JNK1; however, only PKA-activating cAMP analogues induced aromatase expression. The PKC activator PDA effectively stimulated p38 and JNK1 phosphorylation but not aromatase expression. Taken together, PGE(2) activation of p38 and JNK1 via PKA and PKC is necessary for aromatase induction in BAFs, and p38 and JNK1 are potential new drug targets for tissue-specific ablation of aromatase expression in breast cancer.
芳香化酶是雌激素生物合成的关键酶。一个远端启动子PI.4维持正常乳腺脂肪组织中芳香化酶的基础水平。相比之下，恶性乳腺上皮细胞分泌前列腺素E2（PGE2），其通过近端启动子PI.3/PII以环磷酸腺苷（cAMP）和蛋白激酶C（PKC）依赖的方式刺激相邻乳腺脂肪成纤维细胞（BAF）中芳香化酶的表达，导致局部雌激素浓度升高。尽管芳香化酶抑制剂是治疗乳腺癌的有效药物，但它会不加区分地消除所有组织中的雌激素合成，从而产生严重的副作用。为了确定在乳腺癌中选择性阻断芳香化酶和雌激素产生的药物靶点，我们研究了PGE2刺激的信号通路，该通路对于人BAF中cAMP和PKC下游的芳香化酶诱导至关重要。在此，我们表明PGE2或其替代激素混合物二丁酰cAMP（Bt2cAMP）+佛波酯（PDA）刺激了p38、c-Jun氨基末端激酶（JNK）-1和细胞外信号调节激酶（ERK）丝裂原活化蛋白激酶通路。抑制或小干扰RNA介导的p38或JNK1敲低（而非ERK）可抑制PGE2或Bt2cAMP + PDA诱导的芳香化酶活性及通过PI.3/PII的表达。相反，野生型p38α或JNK1的过表达增强了PGE2通过PII刺激的芳香化酶表达。PGE2或Bt2cAMP + PDA刺激了c-Jun和活化转录因子-2（ATF2）的磷酸化以及与PI.3/PII区域的结合。用cAMP类似物特异性激活蛋白激酶A（PKA）或交换蛋白直接激活剂（EPAC）可刺激p38和JNK1；然而，只有激活PKA的cAMP类似物可诱导芳香化酶表达。PKC激活剂PDA有效刺激了p38和JNK1的磷酸化，但未刺激芳香化酶表达。综上所述，PGE2通过PKA和PKC激活p38和JNK1对于BAF中芳香化酶诱导是必需的，并且p38和JNK1是乳腺癌中组织特异性消除芳香化酶表达的潜在新药物靶点。
