Estrogen receptor alpha and the activating protein-1 complex cooperate during insulin-like growth factor-I-induced transcriptional activation of the pS2/TFF1 gene.

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 alpha (ERalpha). However the precise molecular mechanisms involved in this process are still unclear. IGF-I treatment induces phosphorylation of the AF1 domain of ERalpha 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 ERalpha and for the activating protein-1 (AP1) complex, transcriptional activation by IGF-I requires both ERalpha 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 ERalpha. We propose a molecular mechanism with stepwise assembly of the AP1 complex and ERalpha 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 ERalpha via its interaction with c-Jun.

Ligand-induced estrogen receptor alpha degradation by the proteasome: new actors?

In this perspective we consider new aspects of ligand-induced estrogen receptor alpha (ERalpha) degradation. What are the possible roles of CSN5/Jab1 and the CSN complex in this process? We compare hormone (estrogen) or pure antagonist (fulvestrant) induced degradation of ERalpha and review the effects of kinase-inhibitors and CRM1-dependent nuclear export on ERalpha degradation and transcription activation. A model for ERalpha action integrating these new actors is proposed and the relation between hormone-induced ERalpha degradation and transcription-activation is discussed.

Protection of mammalian cell used in biosensors by coating with a polyelectrolyte shell.

In order to detect xenoestrogens which induce perturbations of mammalian cells, design of biosensor using a mammalian cell line enable to detect these compounds is necessary. MELN cell line is suitable to detect estrogen activity, since they are stably transfect with an estrogen regulated luciferase gene. To realize this biosensor, it appeared necessary to add a protection to the mamalian cell, which is devoided, of the wall protecting yeasts or plant cells. With this aim in view, MELN cells have been isolated with a polyelectrolyte shell using the layer-by-layer technique. Among several polyelectrolyte-couples, the best cell survival (>80%) was obtained by alternating the polycation poly-diallyldimethyl ammonium chloride layer and the negatively charged poly-styrene sulfonate. We observed that the composition of the buffer used for layer-deposition was crucial to preserving cell viability, e.g. potassium ions were preferred to sodium ions during the coating. Furthermore, viability was increased when cells were allowed to recover for 2 h between each bilayer deposition. The use of engineered mammalian cells that synthesize luciferase as a response to exposure to estradiol, demonstrated that coating not only permits cell survival, but also allows essential metabolic functions, such as RNA and protein synthesis to take place. Capsule formation allows free diffusion of small molecules, while it prevents internalization in the cells of proteins larger than 60 kDa.

CSN5/Jab1 is involved in ligand-dependent degradation of estrogen receptor {alpha} by the proteasome.

Here, we show that estrogen receptor alpha (ERalpha) coimmunoprecipitates with CSN5/Jab1, a subunit of the COP9 signalosome (CSN), and that overexpression of CSN5/Jab1 causes an increase in ligand-induced ERalpha degradation. Inhibition of either the kinase activity associated with the CSN complex by curcumin or of nuclear export by leptomycin B (LMB) impaired estradiol-induced ERalpha degradation by the proteasome. Degradation of ERalpha induced by the pure antagonist ICI 182,780 (ICI) was blocked by curcumin but not by LMB, indicating that in the presence of ICI, ERalpha is degraded by a nuclear fraction of the proteasome. In addition, we observed that curcumin inhibited estradiol-induced phosphorylation of ERalpha. The use of three inhibitors of ERalpha degradation that target different steps of the estrogen response pathway (inhibition of the CSN-associated kinase, nuclear export, and proteasome) suggests that a phosphorylation event inhibited by curcumin is necessary for ERalpha binding to its cognate DNA target. Our results demonstrate that transcription per se is not required for ERalpha degradation and that assembly of the transcription-initiation complex is sufficient to target ERalpha for degradation by the proteasome.

Two antiestrogens affect differently chromatin remodeling of trefoil factor 1 (pS2) gene and the fate of estrogen receptor in MCF7 cells.

We show here that the two antagonists ICI 182 780, a pure estrogen antagonist, and 4-hydroxy-tamoxifen, a selective estrogen receptor modulator (SERM) have distinct effects on TFF1 (formerly pS2) gene chromatin structure and transcription. Indeed, ICI 182 780 decreased both the intensity of the hormone-dependent DNase I hypersensitive site pS2 HS-1 and transcription of the pS2 gene whereas 4-hydroxy-tamoxifen (OH-Tam) increased the intensity of pS2-HS1 and had no effect on pS2 gene transcription. Interestingly, these differential effects are associated with different fates of ERalpha following the two treatments: The ERalpha-OH-Tam complex was retained in the nucleus more efficiently than the ERalpha-estradiol complex. In contrast, ICI 182 780 provoked a rapid relocation of ERalpha complex to an insoluble nuclear fraction, followed by its degradation. Taken together, these data suggest that regulating the amount of ERalpha in the nucleus is a major way of action of estrogen antagonists with respect to chromatin remodeling and transcriptional control.