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.