Estrogens induce cell proliferation in target tissues by stimulating progression through the G 1 phase of the cell cycle. Induction of cyclin D1 expression is a critical feature of the mitogenic action of estrogen. We have determined a region between ؊96 and ؊29 in the cyclin D1 promoter that confers regulation by estrogens in the human mammary carcinoma cells MCF-7. This region encompasses a unique known transcription factor binding site with a sequence of a potential cAMP response element (CRE-D1). The induction is strictly hormone dependent and requires the DNA binding domain as well as both AF-1 and AF-2 domains of the estrogen receptor (ER) ␣. Destruction of the CRE-D1 motif caused complete loss of estrogen responsiveness. Both c-Jun and ATF-2 transactivated the cyclin D1 promoter in transient transfection experiments, and a clear additional increase was detected when ER was cotransfected with either c-Jun or with c-Jun and ATF-2 but not with ATF-2 alone. Furthermore, the expression of a dominant negative variant of c-Jun, TAM67, completely abolished the induction of the cyclin D1 promoter both in the absence and presence of ER. We show that ATF-2 homodimers and ATF-2͞c-Jun heterodimers, but not c-Jun homodimers, were able to bind the CRE of the cyclin D1 promoter. To interpret these results, we propose a mechanism in which ATF-2͞c-Jun heterodimers bind to the CRE-D1 element and mediate the activation of cyclin D1 promoter by the ER. This mechanism represents a pathway by which estrogens control the proliferation of target cells.Estrogens are decisive actors responsible for the proliferation of normal mammary epithelial cells and the development and progression of breast cancer (1). They act in early G 1 phase of the cell cycle, and both steroidal and nonsteroidal antiestrogens arrest estrogen-dependent breast cancer cells in the G 0 ͞G 1 phases (2, 3). Several studies have suggested that cyclin D1 may be involved in mediating the steroid-dependent growth of both normal and malignant mammary epithelial cells. Cyclin D1-deficient mice have a defect in steroid hormone-responsive proliferation of breast epithelium during pregnancy (4). Estrogens reinitiate the cell cycle in simvastatin-arrested MCF-7 breast cancer cells as well as the expression of cyclin D1 and phosphorylation of the retinoblastoma protein even under conditions where mitogen-activated protein kinase activity is inhibited by the continuous presence of simvastatin in the culture medium (5). Moreover, a strong correlation of increased levels of cyclin D1 mRNA with estrogen receptor (ER) overexpression in breast cancer cells has been noted (6). These results suggest a direct regulation of cyclin D1 expression by estrogens even in the absence of peptide growth factors. Thus, cell cycle control by estrogen differs from that by growth factors.Estrogens act primarily through binding to their receptor, which belongs to the steroid͞thyroid nuclear receptor superfamily (7). Like other members of the superfamily, ER␣ (NR3A1; ref. 32) exhibits a m...

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Reduction of epithelial cell-cell adhesion via the transcriptional repression of cadherins in combination with the acquisition of mesenchymal properties are key determinants of epithelial-mesenchymal transition (EMT). EMT is associated with early stages of carcinogenesis, cancer invasion and recurrence. Furthermore, the tumor stroma dictates EMT through intensive bidirectional communication. The pathological analysis of EMT signatures is critically, especially to determine the presence of cancer cells at the resection margins of a tumor. When diVusion barriers disappear, EMT markers may be detected in sera from cancer patients. The detection of EMT signatures is not only important for diagnosis but can also be exploited to enhance classical chemotherapy treatments. In conclusion, further detailed understanding of the contextual cues and molecular mediators that control EMT will be required in order to develop diagnostic tools and small molecule inhibitors with potential clinical implications.

WISP-2/CCN5 is an estrogen-regulated member of the "connective tissue growth factor/cysteine-rich 61/ nephroblastoma overexpressed" (CCN) family of the cell growth and differentiation regulators. The WISP-2/ CCN5 mRNA transcript is undetectable in normal human mammary cells, as well as in highly aggressive breast cancer cell lines, in contrast with its higher level in the breast cancer cell lines characterized by a more differentiated phenotype. We report here that knockdown of WISP-2/CCN5 by RNA interference in estrogen receptor alpha (ER␣)-positive MCF-7 breast cancer cells induced an estradiol-independent growth linked to a loss of ER␣ expression and promoted epithelial-to-mesenchymal transdifferentiation. In contrast, forced expression of WISP-2/CCN5 directed MCF-7 cells toward a more differentiated phenotype. When introduced into the poorly differentiated, estrogen-independent, and invasive MDA-MB-231 breast cancer cells, WISP-2/ CCN5 was able to reduce their proliferative and invasive phenotypes. In a series of ER␣-positive tumor biopsies, we found a positive correlation between the expression of WISP-2/CCN5 and ID2, a transcriptional regulator of differentiation in normal and transformed breast cells. We propose that WISP-2/CCN5 is an important regulator involved in the maintenance of a differentiated phenotype in breast tumor epithelial cells and may play a role in tumor cell invasion and metastasis.