Epithelium-specific ets transcription factor 2 upregulates cytokeratin 18 expression in pulmonary epithelial cells through an interaction with cytokeratin 18 intron 1

Normal and Cystic Fibrosis Human Bronchial Epithelial Cells Infected with Pseudomonas aeruginosa Exhibit Distinct Gene Activation Patterns

BACKGROUND AND AIMS

In cystic fibrosis (CF), Pseudomonas aeruginosa is not eradicated from the lower respiratory tract and is associated with epithelial inflammation that eventually causes tissue damage. To identify the molecular determinants of an effective response to P. aeruginosa infection, we performed a transcriptomic analysis of primary human bronchial epithelial cells from healthy donors (CTRL) 2, 4, and 6 h after induced P. aeruginosa infection. Compared to noninfected cells, infected cells showed changes in gene activity, which were most marked 6 h postinfection and usually consisted in upregulation.

RESULTS

By comparing for each time point of infection, the transcriptomic response of epithelial cells from CF patients and healthy donors, we identified 851, 638, 667, and 980 differentially expressed genes 0, 2, 4, and 6 h postinfection, respectively. Gene selection followed by bioinformatic analysis showed that most of the differentially expressed genes, either up- or downregulated, were in the protein-binding and catalytic gene-ontology categories. Finally, we established that the protein products of the genes exhibiting the greatest differential upregulation (CSF2, CCL2, TNF, CSF3, MMP1, and MMP10) between CF patients and CTRL were produced in higher amounts by infected cells from CF patients versus CTRL.

CONCLUSIONS

The differentially expressed genes in CF patients may constitute a signature for a detrimental inflammatory response and for an inefficient P. aeruginosa host-cell response.

ELF5, normal mammary development and the heterogeneous phenotypes of breast cancer

SUMMARY The ETS transcription factor ELF5 specifies the formation of the secretory cell lineage of the mammary gland during pregnancy, by directing cell fate decisions of the mammary progenitor cells. The decision-making activity continues in breast cancer, where in luminal breast cancer cells forced ELF5 expression suppresses estrogen sensitivity and shifts gene expression toward the basal molecular subtype. The development of anti-estrogen resistance in luminal breast cancer is accompanied by increased expression of ELF5 and acquired dependence on ELF5 for continued proliferation, providing a potential new therapeutic target or prognostic marker to improve the treatment of this stage of the disease. Forced ELF5 expression suppresses the mesenchymal phenotype, making cells more epithelial and producing lower rates of invasion and motility. Conversely, loss of ELF5 promotes metastasis, with a clear corollary in the claudin-low subtype of breast cancer, which does not express ELF5 and is highly metastatic, or during the final stages of tumor progression, where loss of ELF5 expression may be involved in the acquisition of the lethal phenotype. In circumstances where ELF5 expression increases in parallel with metastatic potential, such as anti-estrogen resistant luminal breast cancers and basal breast cancer, there is much more to be understood about ELF5 and metastasis.

Elf5, hormones and cell fate

Recent elucidation of the stem and progenitor cell hierarchies that operate during normal tissue and organ development has provided a foundation for the development of new insights into the disease process. These hierarchies are established by genetic mechanisms, which specify and determine cell fate and act as cell-clade gatekeepers, upon which all multicellular organisms depend for viability. Perturbation of this gatekeeper function characterizes developmentally based diseases, such as cancer. Here, the emerging gatekeeper and master regulatory roles of the ETS transcription factor Elf5 in several diverse developmental scenarios is reviewed, and how this function intersects with hormonal and growth factor mediated regulation of these processes is shown.

Transcript profiling of Elf5+/- mammary glands during pregnancy identifies novel targets of Elf5

Background

Elf5, an epithelial specific Ets transcription factor, plays a crucial role in the pregnancy-associated development of the mouse mammary gland. Elf5^−/− embryos do not survive, however the Elf5^+/− mammary gland displays a severe pregnancy-associated developmental defect. While it is known that Elf5 is crucial for correct mammary development and lactation, the molecular mechanisms employed by Elf5 to exert its effects on the mammary gland are largely unknown.

Principal Findings

Transcript profiling was used to investigate the transcriptional changes that occur as a result of Elf5 haploinsufficiency in the Elf5^+/− mouse model. We show that the development of the mouse Elf5^+/− mammary gland is delayed at a transcriptional and morphological level, due to the delayed increase in Elf5 protein in these glands. We also identify a number of potential Elf5 target genes, including Mucin 4, whose expression, is directly regulated by the binding of Elf5 to an Ets binding site within its promoter.

Conclusion

We identify novel transcriptional targets of Elf5 and show that Muc4 is a direct target of Elf5, further elucidating the mechanisms through which Elf5 regulates proliferation and differentiation in the mammary gland.

Genome-wide search identifies Ccnd2 as a direct transcriptional target of Elf5 in mouse mammary gland

Background

The ETS transcription factor Elf5 (also known as ESE-2) is highly expressed in the mammary gland and plays an important role in its development and differentiation. Indeed studies in mice have illustrated an essential role for Elf5 in directing alveologenesis during pregnancy. Although the molecular mechanisms that underlie the developmental block in Elf5 null mammary glands are beginning to be unraveled, this investigation has been hampered by limited information about the identity of Elf5-target genes. To address this shortcoming, in this study we have performed ChIP-cloning experiments to identify the specific genomic segments that are occupied by Elf5 in pregnant mouse mammary glands.

Results

Sequencing and genomic localization of cis-regulatory regions bound by Elf5 in vivo has identified several potential target genes covering broad functional categories. A subset of these target genes demonstrates higher expression levels in Elf5-null mammary glands suggesting a repressive functional role for this transcription factor. Here we focus on one putative target of Elf5, the Ccnd2 gene that appeared in our screen. We identify a novel Elf5-binding segment upstream of the Ccnd2 gene and demonstrate that Elf5 can transcriptionally repress Ccnd2 by directly binding to the proximal promoter region. Finally, using Elf5-null mammary epithelial cells and mammary glands, we show that loss of Elf5 in vivo leads to up regulation of Ccnd2 and an altered expression pattern in luminal cells.

Conclusions

Identification of Elf5-targets is an essential first step in elucidating the transcriptional landscape that is shaped by this important regulator. Our studies offer new toolbox in examining the biological role of Elf5 in mammary gland development and differentiation.

Elf5 conditional knockout mice reveal its role as a master regulator in mammary alveolar development: failure of Stat5 activation and functional differentiation in the absence of Elf5

The transcription factor Elf5 plays an important role in mammary gland development. However, because of the embryonic lethality of Elf5 straight knockout mice, prior studies have been limited to experiments with Elf5 haploinsufficient animals, overexpression systems or transplants. Here, we have utilized K14-Cre to generate mammary-gland specific Elf5 conditional knockout mice. During pregnancy, Elf5-null mammary epithelium completely failed to initiate alveologenesis, and a characteristic of virgin ductal epithelial cells persisted postpartum. We demonstrate that the loss of Elf5 leads to the absence of alveolar secretory markers confirming previous published data. Interestingly, the developmental block due to a lack of Elf5 could not be restored by multiple gestations. Elf5-null mammary epithelial cells also display disorganized cell structures as evident by altered cell polarities, which might be the cause for collapsed lumina. We observe reduced levels of Stat5 and attenuated Stat5 activity as measured by p-Stat5 levels both in Elf5-null mammary glands as well as cultured mammary epithelial cells. This data suggests that the failure of alveolar and lactogenic differentiation due to the loss of Elf5 is mediated in part due to impaired Stat5 activity. In support of this hypothesis, we show by ChIP experiments that Stat5a promoter contains a conserved Elf5-binding site that is occupied by Elf5 in mammary glands. Mammary epithelia lacking Elf5 exhibited downregulation of several other critical genes involved in alveologenesis, suggesting Elf5 as a master regulator in alveolar development. We propose a model for Elf5-mediated alveolar development, in which Elf5 regulates the expression of key mediators of the PrlR/Jak2/Stat5 signaling pathway.

Elf5 is an epithelium-specific, fibroblast growth factor-sensitive transcription factor in the embryonic lung

Fibroblast growth factor (FGF) signaling has been shown to be essential for many aspects of normal lung development. To determine epithelial targets of FGF signaling, we cultured embryonic day (E) 11.5 mouse lungs for 24 hr in the presence or absence of the FGF receptor antagonist SU5402, which inhibited branching morphogenesis. Affymetrix gene chip analysis of treated and control epithelia identified several genes regulated by FGF signaling, including Elf5, a member of the Epithelial-specific Ets family of transcription factors. SU5402 reduced Elf5 expression in mesenchyme-free cultures of E12.5 epithelium, demonstrating that the inhibition was direct. In situ hybridization revealed that Elf5 had a dynamic pattern of expression during lung development. We found that expression of Elf5 was induced by FGF7 and FGF10, ligands that primarily bind FGFR2b. To further define the pathways by which FGFs activate Elf5 expression, we cultured E11.5 lung tips in the presence of compounds to inhibit FGF receptors (SU5402), PI3-Kinase/Akt-mediated signaling (LY294002), and MAP Kinase/Erk-mediated signaling (U0126). We found that SU5402 and LY294002 significantly reduced Elf5 expression, whereas U0126 had no effect. LY294002 also reduced Elf5 expression in cultures of purified epithelium. Finally, pAkt was coexpressed with Elf5 in the proximal epithelial airways of E17.5 lungs. These results demonstrate that Elf5 is an FGF-sensitive transcription factor in the lung with a dynamic pattern of expression and that FGF regulation of Elf5 by means of FGFR2b occurs through the PI3-Kinase/Akt pathway.

Determination of the consensus DNA-binding sequence and a transcriptional activation domain for ESE-2

The ESE (epithelium-specific Ets) subfamily of Ets transcription factors plays an important role in regulating gene expression in a variety of epithelial cell types. Although ESE proteins have been shown to bind to regulatory elements of some epithelial genes, the optimal DNA-binding sequence has not been experimentally ascertained for any member of the ESE subfamily of transcription factors. This has made the identification and validation of their targets difficult. We are studying ESE-2 (Elf5), which is highly expressed in epithelial cells of many tissues including skin keratinocytes. Here, we identify the preferred DNA-binding site of ESE-2 by performing CASTing (cyclic amplification and selection of targets) experiments. Our analysis shows that the optimal ESE-2 consensus motif consists of a GGA core and an AT-rich 5'- and 3'-flanking sequences. Mutational and competition experiments demonstrate that the flanking sequences that confer high DNA-binding affinity for ESE-2 show considerable differences from the known consensus DNA-binding sites of other Ets proteins, thus reinforcing the idea that the flanking sequences may impart recognition specificity for Ets proteins. In addition, we have identified a novel isoform of murine ESE-2, ESE-2L, that is generated by use of a hitherto unreported new exon and an alternate promoter. Interestingly, transient transfection assays with an optimal ESE-2 responsive reporter show that both ESE-2 and ESE-2L are weak transactivators. However, similar studies utilizing GAL4 chimaeras of ESE-2 demonstrate that while the DNA-binding ETS (E twenty-six) domain functions as a repressor, the PNT (pointed domain) of ESE-2 can act as a potent transcriptional activation domain. This novel transactivating property of PNT is also shared by ESE-3, another ESE family member. Identification of the ESE-2 consensus site and characterization of the transcriptional activation properties of ESE-2 shed new light on its potential as a regulator of target genes.

Differential role of FGF9 on epithelium and mesenchyme in mouse embryonic lung

Mesothelial Fibroblast Growth Factor 9 (Fgf9) has been demonstrated by inactivation studies in mouse to be critical for the proliferation of the mesenchyme. We now show that Fgf9 is also expressed at significant levels in the distal epithelium from the mid-pseudoglandular stages. Using mesenchymal-free lung endoderm culture, we show that FGF9 triggers the proliferation of the distal epithelium leading to the formation of a cyst-like structure. On embryonic Fgfr2b-/- lungs, FGF9 induces proliferation of the mesenchyme but fails to trigger a similar effect on the epithelium, therefore involving the FGFR2b receptor in the proliferative response of the epithelium to FGF9. While FGF9 inhibits the differentiation of the mesenchyme, the epithelium appears to differentiate normally. At the molecular level, FGF9 up-regulates Fgf10 expression in the mesenchyme likely via increased expression of Tbx4 and 5 and controls the transcription of Hedgehog targets Ptc and Gli-1 in a Hedgehog-independent manner. We also show that FGF9 inhibits the activation of the canonical Wnt pathway in the epithelium by increasing Dkk1 expression, a canonical Wnt antagonist. Our work shows for the first time that FGF9 acts on the epithelium involving FGFR2b to control its proliferation but not its differentiation and contributes to the regulation of canonical Wnt signaling in the epithelium.