Beta-catenin and ZO-1: shuttle molecules involved in tumor invasion-associated epithelial-mesenchymal transition processes.

The cytoplasmic/nuclear relocalization of beta-catenin and ZO-1 from the adherens and tight junctions are common processes of the epithelial-mesenchymal transition (EMT) associated with tumor invasion. Data are now accumulating to demonstrate that these molecules, which shuttle between the plasma membrane and the nucleus or the cytosol, are involved in signaling pathways, and contribute to the regulation of genes such as vimentin or matrix metalloproteinase-14 which are turned on during EMT.

Transactivation of vimentin by beta-catenin in human breast cancer cells.

The cytoplasmic and nuclear redistribution of beta-catenin and the de novo expression of vimentin are frequently involved in the epithelial-to-mesenchymal transition associated with increased invasive/migratory properties of epithelial cells. Because beta-catenin can act as a coactivator of transcription through its binding to the T-cell factor (TCF)/lymphoid enhancer factor 1 transcription factor family, we have explored the possibility that beta-catenin/TCF could directly transactivate vimentin. We first compared vimentin expression in relation with the localization of beta-catenin in eight breast cancer cell lines displaying various degrees of invasiveness and in a model of cell migration using human mammary MCF10A cells. We could thus show a cytoplasmic and/or nuclear distribution of beta-catenin in invasive/migratory cells expressing vimentin, but not in noninvasive/stationary vimentin-negative cell lines. In addition, the human vimentin promoter was found to be up-regulated by beta-catenin and TCF-4 cotransfection. Varying with the cellular background, a diminution of this up-regulation was observed when the putative beta-catenin/TCF binding site of the vimentin promoter was mutated. Our results therefore demonstrate that the vimentin promoter is a target of the beta-catenin/TCF pathway and strongly suggest an implication of this regulation in epithelial cell migration/invasion.

Combined estrogenic and anti-estrogenic properties of estetrol on breast cancer may provide a safe therapeutic window for the treatment of menopausal symptoms.

Increased risk of breast cancer is a critical side effect associated with the use of a menopausal hormone therapy (MHT). Estetrol (E4) is a natural estrogen produced by the human fetal liver and is a promising compound for clinical use in MHT. However, its impact on breast cancer is controversial and poorly defined. In this preclinical study, we show that E4 acts as a weak estrogen by stimulating the growth of hormone-dependent breast cancer only at concentrations exceeding menopausal therapeutic needs. E4 presents also an antitumor activity by decreasing the strong proliferative effect of estradiol (E2). While estrogen receptor alpha (ERα) is the predominant receptor mediating its effects, the dual weak-estrogenic/anti-estrogenic feature of E4 results from differential signaling pathways activation. Both nuclear and rapid extra-nuclear signaling pathway are necessary for a complete estrogenic effect of E4. However, the antitumor action of E4 is not due to a capacity to antagonize E2-induced nuclear activity. Altogether, our results highlight that E4 has a limited impact on breast cancer and may offer a safe therapeutic window for the treatment of menopausal symptoms.

The uterine and vascular actions of estetrol delineate a distinctive profile of estrogen receptor α modulation, uncoupling nuclear and membrane activation.

Estetrol (E4) is a natural estrogen with a long half-life produced only by the human fetal liver during pregnancy. The crystal structures of the estrogen receptor α (ERα) ligand-binding domain bound to 17ß-estradiol (E2) and E4 are very similar, as well as their capacity to activate the two activation functions AF-1 and AF-2 and to recruit the coactivator SRC3. In vivo administration of high doses of E4 stimulated uterine gene expression, epithelial proliferation, and prevented atheroma, three recognized nuclear ERα actions. However, E4 failed to promote endothelial NO synthase activation and acceleration of endothelial healing, two processes clearly dependent on membrane-initiated steroid signaling (MISS). Furthermore, E4 antagonized E2 MISS-dependent effects in endothelium but also in MCF-7 breast cancer cell line. This profile of ERα activation by E4, uncoupling nuclear and membrane activation, characterizes E4 as a selective ER modulator which could have medical applications that should now be considered further.

Regulation of CXCL8/IL-8 expression by zonula occludens-1 in human breast cancer cells.

Accumulating data now suggest that ZO-1, once delocalized from tight junctions, could be implicated in the regulation of tumor-promoting genes. Because of their major implication in different steps of tumor progression, we investigated here the influence of ZO-1 on chemokines expression in breast cancer cells. Using GeneArray analysis to compare chemokine mRNA expression in breast tumor cells transfected with a siRNA against ZO-1, we identified CXCL-8IL-8 as a major potential target of ZO-1 signaling, being strongly downregulated following ZO-1 siRNA transfection. Examining further the relationship between ZO-1 and interleukin-8 (CXCL8/IL-8), we first showed that CXCL8/IL-8 expression correlates with a relocalization of ZO-1 in several breast cancer cell lines. Moreover, CXCL8/IL-8 is downregulated in invasive BT549 cells transfected with three different ZO-1 siRNA and overexpressed in noninvasive BT20 and SKBR3 cells transfected with vectors expressing ZO-1. We also provide evidence for an activation of the CXCL8/IL-8 promoter by ZO-1. Finally, we show that the regulation of CXCL8/IL-8 by ZO-1 is independent of the ß-catenin pathway. Our results thus clearly show an implication of ZO-1 in CXCL8/IL-8 regulation. Because of the major implications of CXCL8/IL-8 in tumor invasion, such a regulation could play an important role in breast cancer progression.

Is the baboon model appropriate for endometriosis studies?

OBJECTIVE: To determinethe prevalence of spontaneous endometriosis andthe incidence of induced endometriosis after endocervical canal resection in baboons. DESIGN: Induction and follow-up of endometriosis in baboons, which is one of the primate species that develop spontaneous endometriosis. Forty-one baboons were checked for the presence of spontaneous endometriosis. We then attempted to induce endometriosis in 30 of them by endocervical canal resection. SETTING: Institute of Primate Research, Nairobi, Kenya, and Catholic University of Louvain, Brussels, Belgium. ANIMAL(S): Forty-one baboons were checked for spontaneous endometriosis and 30 of them were used to develop a model of induced endometriosis. INTERVENTION(S): A total of 41 baboons underwent diagnostic laparoscopy for 10 months. In a first step, 30 of this number subsequently underwent endocervical canal resection. In a second step, 20 of the 30 underwent uterine horn resection. MAIN OUTCOME MEASURE(S): Follow-up by laparoscopy. RESULT(S): Two of the 41 baboons were diagnosed with spontaneous endometriosis (4.8%). Twelve months after the surgical procedure to induce endometriosis, 8 of 29 animals presented with endometriotic lesions diagnosed by using laparoscopy and confirmed by histologic examination. The incidence of induced endometriosis in our model was thus 27.6%. In 2 baboons, endometriosis disappeared over time, resulting in a final rate of 20.7% (6/29). CONCLUSION(S): The rate of spontaneous endometriosis is very low (4.8%). Endometriosis can be induced (with a rate of just 27.6%) by endocervical canal resection to stimulate retrograde menstruation.

Transactivation of MCP-1/CCL2 by beta-catenin/TCF-4 in human breast cancer cells.

The loss of E-cadherin expression and the translocation of beta-catenin to the nucleus are frequently associated with the metastatic conversion of epithelial cells. In the nucleus, beta-catenin binds to the TCF/LEF-1 (T-cell factor/ lymphoid enhancer factor) transcription factor family resulting in the activation of several genes, some of them having important implications in tumour progression. In our study, we investigated the potential regulation of monocyte chemotactic protein-1 (MCP-1/CCL2) expression by the beta-catenin/TCF pathway. This CC-chemokine has been implicated in tumour progression events such as angiogenesis or tumour associated macrophage (TAM) infiltration. We thus demonstrated that MCP-1 expression correlates with the reorganization of the E-cadherin/beta-catenin complexes. Indeed, MCP-1 was expressed by invasive breast cancer cells (MDA-MB-231, BT549 and Hs578T), which do not express E-cadherin but was not produced by noninvasive breast cancer cell lines (MCF7 and T47D) expressing high level of E-cadherin. In addition, the MCP-1 promoter was activated in BT549 breast cancer cells transfected with beta-catenin and TCF-4 cDNAs. The MCP-1 mRNA level was similarly upregulated. Moreover, we showed that MCP-1 mRNA was downregulated after transfection with a siRNA against beta-catenin in both BT549 and Hs578T cells. Our results therefore identify MCP-1 as a target of the beta-catenin/TCF/LEF pathway in breast tumour cells, a regulation which could play a key role in breast tumour progression.