Vascular endothelial growth factor (VEGF) plays a pivotal role in the regulation of microvascular permeability and angiogenesis, processes essential for normal endometrial growth and implantation. Estrogen [17beta-estradiol (E2)], via its receptor (ER alpha), rapidly stimulates VEGF expression in the uterus at the transcriptional level. The VEGF gene promoter, however, lacks a consensus estrogen response element (ERE), and attempts to identify the site through which E2 induces VEGF expression have yielded contradictory results. To address this question, we modified the chromatin immunoprecipitation method to identify transcription factors that interact with the VEGF promoter in the rat uterus in response to E2. Chromatin immunoprecipitation showed that both Sp1 and Sp3 were associated with a proximal, GC-rich region of the promoter before E2 treatment. E2 induced an increase in Sp1 binding and the recruitment of ER alpha, and the coactivator p300 to this region. The association of ER alpha persisted, however, after VEGF mRNA levels had declined again (at 4 h), indicating that other factors might be involved in that expression. Western analysis showed that both the alpha- and beta-subunits of the transcription factor hypoxia-inducible factor 1 (HIF-1), which regulates VEGF expression in response to hypoxia and several hormones and growth factors, were present in the uterus. Furthermore, E2 rapidly induced their recruitment to the -944 to -611 bp region of the VEGF promoter, which contains the hypoxia response element to which HIF-1 binds. This binding was transient, matching the pattern of E2-induced VEGF expression. These results indicate that HIF-1 is an important mediator of E2-induced VEGF expression in the uterus. In addition, E2 also induced a later increase in HIF-1alpha mRNA and protein expression in the uterus, suggesting that it may be required for longer term effects of E2 on the uterus as well. In contrast to the uterus, HEC1A cells cultured in 95% air-5% CO2 (and therefore 20% O2) contained no HIF-1alpha, consistent with the inability of E2 to stimulate the expression of VEGF by these and other cell types in vitro.

Vascular endothelial growth factor (VEGF) plays an essential role in normal uterine physiology and function as well as endometrial cancer and other uterine disorders. Recently we showed that estrogen regulation of VEGF expression in the rat uterus involves rapid recruitment of both estrogen receptor (ER)-alpha and hypoxia-inducible factor (HIF)-1alpha to the VEGF promoter. Estrogen is known to stimulate both the MAPK and phosphatidylinositol 3-kinase (PI3K) pathways, which have been linked to the activation of both of these transcription factors. Therefore, the involvement of these pathways in estrogen-induced VEGF expression was investigated. Inhibitors of the MAPK (U0126) or PI3K pathways (wortmannin or LY294002) were administered ip to immature female rats 1 h before 17beta-estradiol (E(2)) treatment. E(2) activation of both pathways occurred and was completely inhibited by the appropriate antagonist. Only PI3K inhibitors, however, blocked E(2) stimulation of VEGF mRNA expression and E(2)-induced uterine edema. In vivo chromatin immunoprecipitation analysis showed that this was associated with a failure of both HIF-1alpha and ERalpha to bind to the VEGF promoter. To determine whether inhibiting the PI3K pathway affected ERalpha induction of other estrogen target genes, the expression of creatine kinase B and progesterone receptor A/B was also examined. The expression of each was also inhibited by wortmannin, as was ERalpha binding to the creatine kinase B promoter. In conclusion, although estrogen activates both the MAPK and PI3K pathways in the rat uterus, activation of HIF-1alpha and ERalpha, and therefore regulation of VEGF gene expression is dependent only on the PI3K/Akt pathway. Furthermore, activation of the PI3K pathway appears to be a common requirement for the expression of estrogen-induced genes. These findings not only shed light on estrogen action in normal target tissues but also have important implications for cancer biology because excessive PI3K, HIF-1alpha, and VEGF activity are common in estrogen-dependent tumors.

Mortality following breast cancer diagnosis is mainly due to the development of distant metastasis. To escape from the primary site, tumor cells undergo the epithelial-to-mesenchymal transition (EMT), which helps them acquire a more motile and invasive phenotype. In our previous study, we showed that class I selective HDAC inhibitor entinostat reverses the EMT phenotype through reversal of epigenetic repression of E-cadherin. Recent evidence suggests that a subset of cells within a breast tumor may drive the metastatic outgrowth following escape from the primary site. These cells, termed tumor-initiating cells (TIC), represent a great threat to overall prognosis. They are critical in terms of drug resistance and tumor initiation at metastatic sites. Acquisition of EMT traits has also been shown to impart TIC phenotype to the cells, making EMT a "dual-threat" for prognosis. In the current study, we show that entinostat treatment can reduce the percentage of TIC cells from triple-negative breast cancer (TNBC) cells. Entinostat treatment was able to reduce the CD44 high / CD24 low cell population, ALDH-1 activity, as well as protein and mRNA expression of known TIC markers such as Bmi-1, Nanog, and Oct-4. Next, we inoculated MDA-MB-231 cells transfected with firefly luciferase (231/Luc) in mammary fat pad of NSG mice. The mice were then treated with entinostat (2.5 mg/kg/d), and tumor development and formation of metastasis were assessed by bioluminescence imaging. Treatment with entinostat significantly reduced tumor formation at the primary site as well as lung metastasis. As such, entinostat may help prevent development of distant metastasis.

We have previously shown that 17beta-estradiol (E(2)) increases vascular endothelial growth factor A (Vegfa) gene expression in the rat uterus, resulting in increased microvascular permeability, and that this involves the simultaneous recruitment of hypoxia-inducible factor 1 (HIF1) and estrogen receptor alpha (ESR1) to the Vegfa gene promoter. Both events require the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. However, those studies were carried out using whole uterine tissue, and while most evidence indicates that the likely site of E(2)-induced Vegfa expression is luminal epithelial (LE) cells, other studies have identified stromal cells as the site of that expression. To address this question, the pathway regulating Vegfa expression was reexamined using LE cells rapidly isolated after E(2) treatment. In addition, we further characterized the nature of the receptor through which E(2) triggers the signaling events that lead to Vegfa expression using the specific ESR1 antagonist ICI 182,780. In agreement with previous results in the whole uterus, E(2) stimulated Vegfa mRNA expression in LE cells, peaking at 1 h (4- to 14-fold) and returning to basal levels by 4 h. Treatment with E(2) also increased phosphorylation of AKT in LE cells, as well as of the downstream mediators FRAP1 (mTOR), GSK3B, and MDM2. The alpha subunit of HIF1 (HIF1A) was present in LE cells before E(2) treatment, was unchanged 1 h after E(2), but was >2-fold higher by 4 h. Chromatin immunoprecipitation analysis showed that HIF1A was recruited to the Vegfa promoter by 1 h and was absent again by 4 h. The E(2) activation of the PI3K/AKT pathway, HIF1A recruitment to the Vegfa promoter, and Vegfa expression were all blocked by ICI 182,780. In summary, the rapid E(2)-induced signaling events that lead to the expression of Vegfa observed previously using the whole uterus occur in LE cells and appear to be initiated via a membrane form of ESR1.