Molecular and pathological signatures of epithelial–mesenchymal transitions at the cancer invasion front

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 diffusion 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

p21(WAF1/CIP1) Selectively Controls the Transcriptional Activity of Estrogen Receptor α

Estrogen receptors (ER) are ligand-dependent transcription factors that regulate growth, differentiation, and maintenance of cellular functions in a wide variety of tissues. We report here that p21(WAF1/CIP1), a cyclin-dependent kinase (Cdk) inhibitor, cooperates with CBP to regulate the ERα-mediated transcription of endogenous target genes in a promoter-specific manner. The estrogen-induced expression of the progesterone receptor and WISP-2 mRNA transcripts in MCF-7 cells was enhanced by p21(WAF1/CIP1), whereas that of the cyclin D1 mRNA was reduced and the pS2 mRNA was not affected. Chromatin immunoprecipitation assays revealed that p21(WAF1/CIP1) was recruited simultaneously with ERα and CBP to the endogenous progesterone receptor gene promoter in an estrogen-dependent manner. Experiments in which the p21(WAF1/CIP1) protein was knocked down by RNA interference showed that the induction of the expression of the gene encoding the progesterone receptor required p21(WAF1/CIP1), in contrast with that of the cyclin D1 and pS2 genes. p21(WAF1/CIP1) induced not only cell cycle arrest in breast cancer cells but also milk fat globule protein and lipid droplets, indicators of the differentiated phenotype, as well as cell flattening and increase of the volume of the cytoplasm. These results indicate that p21(WAF1/CIP1), in addition to its Cdk-regulatory role, behaves as a transcriptional coactivator in a gene-specific manner implicated in cell differentiation

Ligand-free estrogen receptor activity complements IGF1R to induce the proliferation of the MCF-7 breast cancer cells

<p>Abstract</p> <p>Background</p> <p>Ligand-dependent activation of the estrogen receptor (ER) as well as of the insulin-like growth factor type 1 (IGF1R) induces the proliferation of luminal breast cancer cells. These two pathways cooperate and are interdependent. We addressed the question of the mechanisms of crosstalk between the ER and IGF1R.</p> <p>Methods</p> <p>We evaluated the mitogenic effects of estradiol (E2; agonist ligand of ER) and of insulin (a ligand of IGF1R) in the MCF-7 cells by flow cytometry and by analyzing the cell levels of cell cycle-related proteins (immunoblotting) and mRNA (RT-QPCR). To verify the requirement for the kinase activity of Akt (a downstream target of IGF1R) in the mitogenic action of estradiol, we used shRNA strategy and shRNA-resistant expression vectors.</p> <p>Results</p> <p>The activation of the ER by E2 is unable to induce the cell cycle progression when the phosphatidyl inositol-3 kinase (PI3K)/Akt signaling is blocked by a chemical inhibitor (LY 294002) or by shRNA targeting Akt1 and Akt2. shRNA-resistant Akt wild-type constructs efficiently complemented the mitogenic signaling activity of E2 whereas constructs with inactivated kinase function did not. In growth factor-starved cells, the residual PI3K/Akt activity is sufficient to complement the mitogenic action of E2. Conversely, when ER function is blocked by the antiestrogen ICI 182780, IGF1R signaling is intact but does not lead to efficient reinitiation of the cell cycle in quiescent, growth factor-starved MCF-7 cells. The basal transcription-promoting activity of ligand-free ER in growth factor-starved cells is sufficient to complement the mitogenic action of the IGF1R-dependent signaling.</p> <p>Conclusions</p> <p>The basal ER activity in the absence of ligand is sufficient to allow efficient mitogenic action of IGF1R agonists and needs to be blocked to prevent the cell cycle progression.</p

Loss of WISP2/CCN5 in estrogen-dependent MCF7 human breast cancer cells promotes a stem-like cell phenotype.

It has been proposed that the epithelial-mesenchymal transition (EMT) in mammary epithelial cells and breast cancer cells generates stem cell features. WISP2 (Wnt-1-induced signaling protein-2) plays an important role in maintenance of the differentiated phenotype of estrogen receptor-positive breast cancer cells and loss of WISP2 is associated with EMT. We now report that loss of WISP2 in MCF7 breast cancer cells can also promote the emergence of a cancer stem-like cell phenotype characterized by high expression of CD44, increased aldehyde dehydrogenase activity and mammosphere formation. Higher levels of the stem cell markers Nanog and Oct3/4 were observed in those mammospheres. In addition we show that low-cell inoculums are capable of tumor formation in the mammary fat pad of immunodeficient mice. Gene expression analysis show an enrichment of markers linked to stem cell function such as SOX9 and IGFBP7 which is linked to TGF-β inducible, SMAD3-dependent transcription. Taken together, our data demonstrate that WISP2 loss promotes both EMT and the stem-like cell phenotype

Cell Cycle Arrest in G(2) Induces Human Immunodeficiency Virus Type 1 Transcriptional Activation through Histone Acetylation and Recruitment of CBP, NF-κB, and c-Jun to the Long Terminal Repeat Promoter

In human immunodeficiency virus type 1 (HIV-1)-infected cells, a cell cycle arrest in G(2) increases viral expression and may represent a strategy for the virus to optimize its expression. In latently infected cells, balance between viral silencing and reactivation relies on the nucleosomal organization of the integrated long terminal repeat (LTR). It is shown here that nucleosome nuc-1, which is located downstream of the TATA box, is specifically modified when latently infected cells are arrested in G(2) by chemical inducers. Notably, histones H3 and H4 are hyperacetylated, and this modification is associated with an increased LTR-driven transcription. nuc-1 hyperacetylation is also associated with the recruitment of histone acetyltransferase CBP and transcription factors NF-κB and c-Jun. NF-κB and/or c-Jun binding to the LTR in G(2)-arrested cells appears to be required for CBP recruitment as well as for nuc-1 remodeling and viral reactivation