Estrogen Receptor α and the Activating Protein-1 Complex Cooperate during Insulin-like Growth Factor-I-induced Transcriptional Activation of the pS2/TFF1 Gene

Abstract

Insulin like growth factor I (IGF-I) displays estrogenic activity in breast cancer cells. This activity is strictly dependent on the presence of estrogen receptor ␣ (ER␣). However the precise molecular mechanisms involved in this process are still unclear. IGF-I treatment induces phosphorylation of the AF1 domain of ER␣ and activation of estrogen regulated genes. These genes are characterized by important differences in promoter architecture and response element composition. We show that promoter structure is crucial for IGF-I-induced transcription activation. We demonstrate that on a complex promoter such as the pS2/TFF1 promoter, which contains binding sites for ER␣ and for the activating protein-1 (AP1) complex, transcriptional activation by IGF-I requires both ER␣ and the AP1 complex. IGF-I is unable to stimulate transcription of an estrogen-regulated gene under the control of a minimal promoter containing only a binding site for ER␣. We propose a molecular mechanism with stepwise assembly of the AP1 complex and ER␣ during transcription activation of pS2/TFF1 by IGF-I. IGF-I stimulation induces rapid phosphorylation and an increase in protein levels of the AP1 complex. Binding of the phosphorylated AP1 complex to the pS2/TFF1 promoter allows recruitment of the chromatin remodeling factor Brg1 followed by binding of ER␣ via its interaction with c-Jun.Control of breast cancer cell proliferation is a complex, multifactorial, and interactive process. Estradiol, a steroid hormone, which acts via its nuclear receptors (ER␣ 2 and -␤ for estrogen receptor ␣ and ␤) and growth factors such as insulinlike growth factor I (IGF-I) or IGF-II, epidermal growth factor, or transforming growth factor ␣, whose action is mediated by tyrosine kinase transmembrane receptors, controls gene expression and cellular proliferation of breast cancer cells (1). Although it was discovered more than 10 years ago that ER␣ could be activated in a ligand-independent fashion by growth factors like epidermal growth factor or IGF (2), the cross-talk between estrogens and growth factor pathways remains to be elucidated.In the classical model of ER action, the receptor binds as a homodimer (3) or a heterodimer (4 -7) to estrogen response elements (EREs) within the promoters of estrogen-responsive genes. Once present on the promoter of estrogen responsive genes, ER recruits an array of transcriptional cofactors (coactivators and corepressors) that bind to the receptor and interact with other transcription factors, including components of the general transcription machinery. Some of these cofactors possess chromatin-remodeling activities or histone modifying activities or recruit additional proteins to the complex to mediate transcription (for review, see Ref. 8). ER␣ may also modulate transcription without receptor-DNA interaction by functional interference with other transcription factors such as activating protein-1 (AP1) (for review, see Refs. 9 -12).The AP1 complex, which is implicated in diverse cellular processes, including differentiation, c...

Eliminating epigenetic barriers induces transient hormone-regulated gene expression in estrogen receptor negative breast cancer cells

“…The interplay between ERa and other transcription activators that modulate the ability of ERa to activate gene expression as shown recently for the pS2/TFF1 promoter (Baron et al, 2007) could be altered in ERa-negative breast cancer cells. We postulate that a distinct chromatin environment that surrounds ERa target genes in their silent conformation may translate into distinct requirements for cofactors that are necessary to overcome the repressive chromatin structure during gene activation.…”

“…qRT-PCR experiments qRT-PCR experiments were performed as described in Baron et al (2007). The following primer pairs were used to amplify cDNAs after reverse transcription experiments: for GAPDH, 5 0 -ACAGCAACAGGGTGGTGGAC-3 0 and 5 0 -GACCATT GCTGGGGCTGGTG-3 0 ; for pS2/TFF1, 5 0 -GTACACG GAGGCCCAGACAGA-3 0 and 5 0 -AGGGCGTGACACCAG GAAA-3 0 ; for PR, 5 0 -GGCCATACCTATCTCCCTGGA-3 0 and 5 0 -CTCCACGTCCGACAGCGACT-3 0 ; for b-actin, 5 0 -GGTGACAGCAGTCGGTTGGA-3 0 and 5 0 -CACAATAGT CCTCGGCCACATT-3 0 ; for ANXA9, 5 0 -CCGCTGTACT TTGCTGACAA-3 0 and 5 0 -GTTCAGCCAAACACGGAA AT-3 0 ; for BMP6 5 0 -CCCTCTTCATGCTGGATCTG-3 0 and 5 0 -AGGGGAGAACTCCTTGTCGT-3 0 ; for TPD52L1 5 0 -AA CCGTTGCAAGGAACAGAC-3 0 and 5 0 -ATGCCAGCTTT TGCTGAAGT-3 0 ; for ret 5 0 -TCCTGGGAGAAGCTCAGT GT-3 0 and 5 0 -GATGTTGGGGCACAAGAACT-3 0 ; for GREB1 5 0 -GTGGTAGCCGAGTGGACAAT-3 0 and 5 0 -AAACCCGTC TGTGGTACAGC-3 0 .…”

Sex-related differences in left ventricular remodeling in severe aortic stenosis and reverse remodeling after aortic valve replacement: A cardiovascular magnetic resonance study

“…This pattern of remodeling is seen despite similar valvular gradients between groups but may be in part related to differing degrees of baseline aortic regurgitation. Hormonal influences may also be involved, with oestrogen limiting hypertrophy up to the menopause and its subsequent lack leading to accelerated (and possibly therefore different) patterns of hypertrophy in post-menopausal women compared to men 23 .…”

The Effects of Biological Sex and Diet on the Development of Heart Failure

“…Although these mechanisms largely depend on estrogen binding to ERs, a recent study shows that ERs can be recruited in the absence of estrogen to transactivate estrogen-responsive genes. 182 In the study by Baron et al, 182 insulin-like growth factor 1-induced transcription is dependent on the recruitment of ER␣ to the activator protein 1 complex but does not require estrogen to be present. Moreover, tamoxifen (a mixed ER agonist/antagonist) or ICI 182780 (an ER antagonist), agents traditionally thought to act through ERs, negatively influence cell growth and proliferation in neonatal rat cardiomyocytes through an ER-independent mechanism.…”