Estrogen Induces c-myc Gene Expression via an Upstream Enhancer Activated by the Estrogen Receptor and the AP-1 Transcription Factor

Abstract

c-myc oncogene is implicated in tumorigenesis of many cancers, including breast cancer. Although c-myc is a well-known estrogen-induced gene, its promoter has no estrogen-response element, and the underlying mechanism by which estrogen induces its expression remains obscure. Recent genome-wide studies by us and others suggested that distant elements may mediate estrogen induction of gene expression. In this study, we investigated the molecular mechanism by which estrogen induces c-myc expression with a focus on these distal elements. Estrogen rapidly induced c-myc expression in estrogen receptor (ER)-positive breast cancer cells. Although estrogen had little effect on c-myc proximal promoter activity, it did stimulate the activity of a luciferase reporter containing a distal 67-kb enhancer. Estrogen induction of this luciferase reporter was dependent upon both a half-estrogen response element and an activator protein 1 (AP-1) site within this enhancer, which are conserved across 11 different mammalian species. Small interfering RNA experiments and chromatin immunoprecipitation assays demonstrated the necessity of ER and AP-1 cross talk for estrogen to induce c-myc expression. TAM67, the AP-1 dominant negative, partially inhibited estrogen induction of c-myc expression and suppressed estrogen-induced cell cycle progression. Together, these results demonstrate a novel pathway of estrogen regulation of gene expression by cooperation between ER and AP-1 at the distal enhancer element and that AP-1 is involved in estrogen induction of the c-myc oncogene. These results solve the long-standing question in the field of endocrinology of how estrogen induces c-myc expression.

Estrogen Receptor Alpha Mediates Progestin-Induced Mammary Tumor Growth by Interacting with Progesterone Receptors at the Cyclin D1/MYC Promoters

“…Moreover, it has recently been reported that ERE half sites at the MYC proximal promoter (Fig. 6B) are not responsive to estrogens (41). It may be possible that after progestin treatment, these sites might also bind ERa in complexes with PR.…”

GC skew defines distinct RNA polymerase pause sites in CpG island promoters

“…We used chromatin conformation capture (3C) to probe the relationship between enhancer-promoter looping interactions and pausing class in MCF7 cells transiently exposed to estradiol (E2). Upon estrogen stimulation, well-characterized distal enhancers for the MYC, P2RY2, and SIAH2 genes are bound by the estrogen receptor alpha, resulting in the looping between the enhancer and promoter and rapid induction of gene expression (Fullwood et al 2009;Wang et al 2011;). The MYC, P2RY2, and SIAH2 genes were chosen for this assay because they are rapidly induced in response to estrogen exposure, ensuring a direct transcriptional effect, and because their promoter-associated CGIs are sufficiently large that the TSS and 3 ′ CGI edge can be readily resolved, allowing us to determine the spatial relationship between enhancer contacts and the paused Pol II (Hah et al 2011Danko et al 2013).…”

Insight into the mechanisms of action of estrogen receptor β in the breast, prostate, colon, and CNS

“…ERa interacts with a distal half-ERE and an AP1 site in the enhancer of c-myc and transcriptionally upregulates c-myc expression (Dubik & Shiu 1992, Wang et al 2011. Inhibition of ERa with tamoxifen causes a decrease in cyclin D1 and c-myc expression, which represses downstream targets such as Bcl2 and increases cell death (Butt et al 2005, Nehra et al 2010.…”