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Prostaglandin E₂ Induces Breast Cancer–Related Aromatase Promoters via Activation of p38 and c-Jun NH₂-Terminal Kinase in Adipose Fibroblasts

Division of Reproductive Biology Research, Department of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois

Requests for reprints: Dong Chen, Division of Reproductive Biology Research, Department of Obstetrics and Gynecology, Northwestern University, 303 East Superior Street, Chicago, IL 60611. Phone: 312-503-3761; Fax: 312-503-0095; E-mail: dong-chen{at}northwestern.edu.

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 E₂ (PGE₂), 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 PGE₂-stimulated signaling pathways essential for aromatase induction downstream of cAMP and PKC in human BAFs. Here, we show that PGE₂ or its surrogate hormonal mixture dibutyryl cAMP (Bt₂cAMP) + phorbol diacetate (PDA) stimulated the p38, c-jun NH₂-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 PGE₂- or Bt₂cAMP + PDA–induced aromatase activity and expression via PI.3/PII. Conversely, overexpression of wild-type p38 or JNK1 enhanced PGE₂-stimulated aromatase expression via PII. PGE₂ or Bt₂cAMP + 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, PGE₂ 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. [Cancer Res 2007;67(18):8914–22]

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