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 E2 (PGE2) 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 PGE2 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 PGE2-mediated regulation of aromatase expression in BAF. PGE2 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 PGE2-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 PGE2-induced promoters I.3/II-specific aromatase mRNA levels, leading to enhanced PGE2-induced total aromatase mRNA level and enzyme activity.JunD,c-Jun,and JunB bound to a CRE(-211/-199) essential for PGE2 induction of aromatase promoters I.3/II. Taken together, JunD and c-Jun repress aromatase promoter I.4. JunD mediates, whereas c-Jun modulates, PGE2 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.
ASJC Scopus subject areas
- Molecular Biology