Le cancer du sein (de nouvelles pistes de recherche, de nouveaux espoirs thérapeutiques)

MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF

Etude du rôle et de la régulation des récepteurs des oestrogènes dans les cancers du sein

Les œstrogènes sont impliqués dans la différenciation et la prolifération des cellules épithéliales du sein normal et augmentent le risque de développement de cancer du sein. Les médiateurs clés de l'action des œstrogènes sont leurs récepteurs ERalpha et ERbêta. Le but de ma thèse a été l'étude du rôle et de la régulation de ces récepteurs dans le développement des cancers du sein. Nous avons montré que certains gènes impliqués dans la croissance de cellules de cancer du sein pouvaient être régulés par ERalpha exprimé de manière exogène. Dans la deuxième partie de ma thèse, nous avons identifié deux mécanismes de régulation de l'expression protéique et de l activité de ERbêta: la voie du protéasome et la balance entre les activités histones acétyltransférases et déacétylases. La compréhension des mécanismes fondamentaux de l'action de ces récepteurs dans le cancer du sein constitue l étape préliminaire indispensable à l'identification de nouvelles cibles thérapeutiques.MONTPELLIER-BU Pharmacie (341722105) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Phosphorylation of activation function-1 regulates proteasome-dependent nuclear mobility and E6-associated protein ubiquitin ligase recruitment to the estrogen receptor beta.

International audienceThe ubiquitin-proteasome pathway has been recognized as an important regulator in the hormonal response by estrogen receptor (ER) alpha, but its impact on ERbeta function is poorly characterized. In the current study, we investigated the role of the ubiquitin-proteasome pathway in regulating ERbeta activity and identified regulatory sites within the activation function (AF)-1 domain that modulate ERbeta ubiquitination and nuclear dynamics in a hormone-independent manner. Although both ERalpha and ERbeta were dependent on proteasome function for their maximal response to estrogen, they were regulated differently by proteasome inhibition in the absence of hormone, an effect shown to be dependent on their respective AF-1 domain. Given the role of AF-1 phosphorylation to regulate ER activity, we found that sequential substitutions of specific serine residues contained in MAPK consensus sites conferred transcriptional activation of ERbeta in a proteasome-dependent manner through reduced ubiquitination and enhanced accumulation of mutant receptors. Specifically, serines 94 and 106 within ERbeta AF-1 domain were found to modulate subnuclear mobility of the receptor to transit between inactive clusters and a more mobile state in a proteasome-dependent manner. In addition, cellular levels of ERbeta were regulated through these sites by facilitating the recruitment of the ubiquitin ligase E6-associated protein in a phosphorylation-dependent manner. These findings suggest a role for ERbeta AF-1 in contributing to the activation-degradation cycling of the receptor through a functional clustering of phosphorylated serine residues that cooperate in generating signals to the ubiquitin-proteasome pathway

IL-8 expression and its possible relationship with estrogen-receptor-negative status of breast cancer cells.

Estrogen-receptor (ER) status is an important parameter in breast cancer management as ER-positive breast cancers have a better prognosis than ER-negative tumors. This difference comes essentially from the lower aggressiveness and invasiveness of ER-positive tumors. Here, we demonstrate, that interleukin-8 (IL-8) was clearly overexpressed in most ER-negative breast, ovary cell lines and breast tumor samples tested, whereas no significant IL-8 level could be detected in ER-positive breast or ovarian cell lines. We have also cloned human IL-8 from ER-negative MDA-MB-231 cells, and we show that IL-8 produced by breast cancer cells is identical to monocyte-derived IL-8. Interestingly, the invasion potential of ER-negative breast cancer cells is associated at least in part with expression of IL-8, but not with IL-8 receptor levels. Moreover, IL-8 increases the invasiveness of ER-positive breast cancer cells by two fold, thus confirming the invasion-promoting role of IL-8. On the other hand, exogenous expression of estrogen receptors in ER-negative cells led to a decrease of IL-8 levels. In summary, our data show that IL-8 expression is negatively linked to ER status of breast and ovarian cancer cells. We also support the idea that IL-8 expression is associated with a higher invasiveness potential of cancer cells in vitro, which suggests that IL-8 could be a novel marker of tumor aggressiveness

ERalpha and ERbeta expression and transcriptional activity are differentially regulated by HDAC inhibitors.

The proliferative action of ERalpha largely accounts for the carcinogenic activity of estrogens. By contrast, recent data show that ERbeta displays tumor-suppressor properties, thus supporting the interest to identify compounds that could increase its activity. Here, we show that histone deacetylase inhibitors (HDI) upregulated ERbeta protein levels, whereas it decreased ERalpha expression. Part of this regulation took place at the mRNA level through a mechanism independent of de novo protein synthesis. In addition, we found that, in various cancer cells, the treatment with different HDI enhanced the ligand-dependent activity of ERbeta more strongly than that of ERalpha. On the other hand, in MDA-MB231 and HeLa cells, the expression of ERs modified the transcriptional response to HDI. The use of deletion mutants of both receptors demonstrated that AF1 domain of the receptors was required. Finally, we show that ERbeta expression led to a dramatic increased in the antiproliferative activity of HDI, which correlated with a modification of the transcription of genes involved in cell cycle control by HDI. Altogether, these data demonstrate that the interference of ERbeta and HDAC on the control of transcription and cell proliferation constitute a promising approach for cancer therapy

The nuclear receptor liver receptor homolog-1 is an estrogen receptor target gene.

International audienceLiver receptor homolog-1 (LRH-1) is a nuclear receptor previously known to have distinct functions during mouse development and essential roles in cholesterol homeostasis. Recently, a new role for LRH-1 has been discovered in tumor progression, giving LRH-1 potential transforming functions. In order to identify critical factors stimulating LRH-1 expression leading to deregulated cellular proliferation, we studied its expression and its regulation in several breast cancer cell lines. We observed that LRH-1 expression was increased in estrogen receptor (ER) alpha expressing cell lines, whereas weak-to-no expression was found in nonexpressing ERalpha cell lines. In MCF7, LRH-1 expression was highly induced after treatment with 17beta-estradiol (E2). This transcriptional regulation was the result of a direct binding of the ER to the LRH-1 promoter, as demonstrated by gelshift and chromatin immunoprecipitation assays. Interestingly, siRNA-mediated inactivation of LRH-1 decreased the E2-dependent proliferation of MCF7 cells. Finally, LRH-1 protein expression was detected by immunohistochemistry in tumor cells of human mammary ductal carcinomas. Altogether, these data demonstrate that LRH-1 is transcriptionally regulated by the ER alpha and reinforce the hypothesis that LRH-1 could exert potential oncogenic effects during breast cancer formation

Identification of genes involved in growth inhibition of breast cancer cells transduced with estrogen receptor.

Estrogen receptor alpha (ERalpha)-negative breast cancer cells display an aggressive phenotype. We previously showed that adenoviral expression of ERalpha in ER-negative breast cancer cells leads to an estrogen-dependent down-regulation of the proliferation, which could be of interest to control the growth of such cells. In this study, we observed an increase in protein levels of p21 and p27 cyclin-dependent kinase inhibitors, whereas pRb phosphorylation is strongly decreased. Flow cytometry experiments showed a slower transit of cells in G1 (hormone-independent), a hormone-induced accelerated transit through S phase and a possible arrest in G2/M phase. In addition, ERalpha-expressing cells were undergoing apoptosis. By using cDNA macroarrays, we identified a novel collection of genes regulated by liganded ERalpha potentially regulating cell cycle, apoptosis, cell signalling, stress response and DNA repair