T3-activation of the rat growth hormone gene is inhibited by a zinc finger/homeodomain protein

PKCα Modulates Epithelial-to-Mesenchymal Transition and Invasiveness of Breast Cancer Cells Through ZEB1

ZEB1 is a master regulator of the Epithelial-to-Mesenchymal Transition (EMT) program. While extensive evidence confirmed the importance of ZEB1 as an EMT transcription factor that promotes tumor invasiveness and metastasis, little is known about its regulation. In this work, we screened for potential regulatory links between ZEB1 and multiple cellular kinases. Exploratory in silico analysis aided by phospho-substrate antibodies and ZEB1 deletion mutants led us to identify several potential phospho-sites for the family of PKC kinases in the N-terminus of ZEB1. The analysis of breast cancer cell lines panels with different degrees of aggressiveness, together with the evaluation of a battery of kinase inhibitors, allowed us to expose a robust correlation between ZEB1 and PKCα both at mRNA and protein levels. Subsequent validation experiments using siRNAs against PKCα revealed that its knockdown leads to a concomitant decrease in ZEB1 levels, while ZEB1 knockdown had no impact on PKCα levels. Remarkably, PKCα-mediated downregulation of ZEB1 recapitulates the inhibition of mesenchymal phenotypes, including inhibition in cell migration and invasiveness. These findings were extended to an in vivo model, by demonstrating that the stable knockdown of PKCα using lentiviral shRNAs markedly impaired the metastatic potential of MDA-MB-231 breast cancer cells. Taken together, our findings unveil an unforeseen regulatory pathway comprising PKCα and ZEB1 that promotes the activation of the EMT in breast cancer cells.

Glypican-3 induces a mesenchymal to epithelial transition in human breast cancer cells

Breast cancer is the disease with the highest impact on global health, being metastasis the main cause of death. To metastasize, carcinoma cells must reactivate a latent program called epithelial-mesenchymal transition (EMT), through which epithelial cancer cells acquire mesenchymal-like traits.Glypican-3 (GPC3), a proteoglycan involved in the regulation of proliferation and survival, has been associated with cancer. In this study we observed that the expression of GPC3 is opposite to the invasive/metastatic ability of Hs578T, MDA-MB231, ZR-75-1 and MCF-7 human breast cancer cell lines. GPC3 silencing activated growth, cell death resistance, migration, and invasive/metastatic capacity of MCF-7 cancer cells, while GPC3 overexpression inhibited these properties in MDA-MB231 tumor cell line. Moreover, silencing of GPC3 deepened the MCF-7 breast cancer cells mesenchymal characteristics, decreasing the expression of the epithelial marker E-Cadherin. On the other side, GPC3 overexpression induced the mesenchymal-epithelial transition (MET) of MDA-MB231 breast cancer cells, which re-expressed E-Cadherin and reduced the expression of vimentin and N-Cadherin. While GPC3 inhibited the canonical Wnt/β-Catenin pathway in the breast cancer cells, this inhibition did not have effect on E-Cadherin expression. We demonstrated that the transcriptional repressor of E-Cadherin - ZEB1 - is upregulated in GPC3 silenced MCF-7 cells, while it is downregulated when GPC3 was overexpressed in MDA-MB231 cells. We presented experimental evidences showing that GPC3 induces the E-Cadherin re-expression in MDA-MB231 cells through the downregulation of ZEB1.Our data indicate that GPC3 is an important regulator of EMT in breast cancer, and a potential target for procedures against breast cancer metastasis.

Phosphorylation Regulates Functions of ZEB1 Transcription Factor

ZEB1 transcription factor is important in both development and disease, including many TGFβ-induced responses, and the epithelial-to-mesenchymal transition (EMT) by which many tumors undergo metastasis. ZEB1 is differentially phosphorylated in different cell types; however the role of phosphorylation in ZEB1 activity is unknown. Luciferase reporter studies and electrophoresis mobility shift assays (EMSA) show that a decrease in phosphorylation of ZEB1 increases both DNA-binding and transcriptional repression of ZEB1 target genes. Functional analysis of ZEB1 phosphorylation site mutants near the second zinc finger domain (termed ZD2) show that increased phosphorylation (due to either PMA plus ionomycin, or IGF-1) can inhibit transcriptional repression by either a ZEB1-ZD2 domain clone, or full-length ZEB1. This approach identifies phosphosites that have a substantial effect regulating the transcriptional and DNA-binding activity of ZEB1. Immunoprecipitation with anti-ZEB1 antibodies followed by western analysis with a phospho-Threonine-Proline-specific antibody indicates that the ERK consensus site at Thr-867 is phosphorylated in ZEB1. In addition to disrupting in vitro DNA-binding measured by EMSA, IGF-1-induced MEK/ERK phosphorylation is sufficient to disrupt nuclear localization of GFP-ZEB1 fusion clones. These data suggest that phosphorylation of ZEB1 integrates TGFβ signaling with other signaling pathways such as IGF-1. J. Cell. Physiol. 231: 2205-2217, 2016. © 2016 Wiley Periodicals, Inc.

CCN6 (WISP3) decreases ZEB1-mediated EMT and invasion by attenuation of IGF-1 receptor signaling in breast cancer

During progression of breast cancer, CCN6 protein exerts tumor inhibitory functions. CCN6 is a secreted protein that modulates the insulin-like growth factor-1 (IGF-1) signaling pathway. Knockdown of CCN6 in benign mammary epithelial cells triggers an epithelial to mesenchymal transition (EMT), with upregulation of the transcription factor ZEB1/δEF1. How CCN6 regulates ZEB1 expression is unknown. We hypothesized that CCN6 might regulate ZEB1, EMT and breast cancer invasion by modulating IGF-1 signaling. Exogenously added human recombinant CCN6 protein was sufficient to downregulate ZEB1 mRNA and protein levels in CCN6-deficient (CCN6 KD) HME cells and MDA-MB-231 breast cancer cells. Recombinant CCN6 protein decreased invasion of CCN6 KD cells compared with controls. We discovered that knockdown of CCN6 induced IGF-1 secretion in HME cells cultivated in serum-free medium to higher concentrations than found in MDA-MB-231 cells. Treatment with recombinant CCN6 protein was sufficient to decrease IGF-1 protein and mRNA to control levels, rescuing the effect of CCN6 knockdown. Specific inhibition of IGF-1 receptors using the pharmacological inhibitor NVP-AE541 or short hairpin shRNAs revealed that ZEB1 upregulation due to knockdown of CCN6 requires activation of IGF-1 receptor signaling. Recombinant CCN6 blunted IGF-1-induced ZEB1 upregulation in MDA-MB-231 cells. Our data define a pathway in which CCN6 attenuates IGF-1 signaling to decrease ZEB1 expression and invasion in breast cancer. These results suggest that CCN6 could be a target to prevent or halt breast cancer invasion.

Polychlorinated biphenyls 105 and 118 form thyroid hormone receptor agonists after cytochrome P4501A1 activation in rat pituitary GH3 cells

BACKGROUND

Polychlorinated biphenyls (PCBs) may interfere with thyroid hormone (TH) signaling by reducing TH levels in blood, by exerting direct effects on TH receptors (TRs), or both.

OBJECTIVE

Our objective was to identify individual PCBs that directly affect TH signaling by acting on the TR.

METHODS

We administered a mixture of six PCB congeners based on their ortho substitution pattern, including PCBs 77 and 126 (non-ortho), PCBs 105 and 118 (mono-ortho), and PCBs 138 and 153 (di-ortho), to pregnant Sprague-Dawley rats from gestational days (G) 6 to 16. This mixture, or various combinations of the components, was also evaluated in a transient transfection system using GH3 cells.

RESULTS

The mixture reduced serum TH levels in pregnant rats on G16 but simultaneously up-regulated the expression of malic enzyme in liver. It also functioned as a TR agonist in vitro; however, none of the individual PCB congeners comprising this mixture were active in this system. Using the aryl hydrocarbon receptor (AhR) antagonist alpha-naphthoflavone, and the cytochrome P450 (CYP)1A1 antagonist ellipticine, we show that the effect of the mixture on the thyroid hormone response element required AhR and CYP1A1.

CONCLUSIONS

We propose that PCB 126 induces CYP1A1 through the AhR in GH3 cells, and that CYP1A1 activates PCB 105 and/or 118 to a form a compound that acts as a TR agonist. These data suggest that some tissues may be especially vulnerable to PCBs interfering directly with TH signaling due to their capacity to express CYP1A1 in response to coplanar PCBs (or other dioxin-like molecules) if sufficient mono-ortho PCBs are present.

Molecular physiology of pituitary development: signaling and transcriptional networks

The pituitary gland is a central endocrine organ regulating basic physiological functions, including growth, the stress response, reproduction, metabolic homeostasis, and lactation. Distinct hormone-producing cell types in the anterior pituitary arise from a common ectodermal primordium during development by extrinsic and intrinsic mechanisms, providing a powerful model system for elucidating general principles in mammalian organogenesis. The central purpose of this review is to inspect the integrated signaling and transcriptional events that affect precursor proliferation, cell lineage commitment, terminal differentiation, and physiological regulation by hypothalamic tropic factors.

The ZFHX1A gene is differentially autoregulated by its isoforms

The Zfhx1a gene expresses two different isoforms; the full length Zfhx1a-1 and a truncated isoform termed Zfhx1a-2 lacking the first exon. Deletion analysis of the Zfhx1a-1 promoter localized cell-specific repressors, and a proximal G-string that is critically required for transactivation. Transfection of Zfhx1a-1 cDNA, but not Zfhx1a-2, downregulates Zfhx1a-1 promoter activity. Mutation of an E2-box disrupted the binding of both Zfhx1a isoforms. Consistent with this, transfected Zfhx1a-1 does not regulate the transcriptional activity of the E-box mutated Zfhx1a-1 promoter. Competitive EMSAs and transfection assays show that Zfhx1a-2 can function as a dominant negative isoform since it is able to compete and displace Zfhx1a-1 from its binding site and overcome Zfhx1a-1 induced repression of the Zfhx1a-1 promoter in cells. Hence, the Zfhx1a-1 gene is autoregulated in part by negative feedback on its own promoter which is, in turn, modified by the availability of the negative dominant isoform Zfhx1a-2.

4-Hydroxy-PCB106 acts as a direct thyroid hormone receptor agonist in rat GH3 cells

Polychlorinated biphenyls (PCBs) may interfere with thyroid hormone (TH) action by interacting directly with the TH receptor (TR). We found that the hydroxylated PCB metabolite, 4-OH-CB106, bound to the human TRbeta1 and significantly elevated endogenous growth hormone (GH) expression in GH3 cells in a manner similar to that of T(3) itself. This effect was also observed using a consensus TH response element (TRE) in a luciferase expression system, and was blocked by a single base-pair substitution in this TRE. In addition, we found that 4-OH-CB106 did not alter the ability of TRbeta1 to physically interact with the TRE in the GH promoter, or with SRC1 or NCoR. These effects were directly parallel to effects of T(3), indicating that 4-OH-CB106 exerts a direct agonistic effect on the TRbeta1.

The transcription factor ZEB1 is aberrantly expressed in aggressive uterine cancers

The transcription factor ZEB1 (deltaEF1 in mice) has been implicated in cellular processes during development and tumor progression including epithelial to mesenchymal transition. deltaEF1 null mice die at birth, but heterozygotes expressing a LacZ reporter inserted into the deltaEF1 gene live and reproduce. Using these mice, we observed ZEB1 promoter activity in the virgin myometrium, and stroma and myometrium of the pregnant uterus. ZEB1 protein is up-regulated in the myometrium and endometrial stroma after progesterone or estrogen treatment of ovariectomized mice. In the normal human uterus, ZEB1 protein is increased in the myometrium and stroma during the secretory stage of the menstrual cycle. ZEB1 is not expressed in the normal endometrial epithelium. In malignancies of the uterus, we find that ZEB1 (a) is overexpressed in malignant tumors derived from the myometrium (leiomyosarcomas), (b) is overexpressed in tumor-associated stroma of low-grade endometrioid adenocarcinomas, and (c) is aberrantly expressed in the tumor epithelial cells of aggressive endometrial cancers. Specifically, in grade 3 endometrioid adenocarcinomas and uterine papillary serous carcinomas, ZEB1 could be expressed in the epithelial-derived carcinoma cells as well as in the stroma. In malignant mixed Müllerian tumors, the sarcomatous component always expresses ZEB1, and the carcinomatous component can also be positive. In summary, ZEB1 is normally regulated by both estrogen and progesterone receptors, but in uterine cancers, it is likely no longer under control of steroid hormone receptors and becomes aberrantly expressed in epithelial-derived tumor cells, supporting a role for ZEB1 in epithelial to mesenchymal transitions associated with aggressive tumors.

Expression of Zfhep/deltaEF1 protein in palate, neural progenitors, and differentiated neurons

Zfhep/deltaEF1 is essential for embryonic development. We have investigated the expression pattern of Zfhep protein during mouse embryogenesis. We show expression of Zfhep in the mesenchyme of the palatal shelves, establishing concordance of expression with the reported cleft palate of the deltaEF1-null mice. Zfhep protein is strongly expressed in proliferating progenitors of the nervous system. In most regions of the brain, post-mitotic cells stop expressing Zfhep when they migrate out of the ventricular zone (VZ) and differentiate. However, in the hindbrain, Zfhep protein is also highly expressed in post-mitotic migratory neuronal cells of the precerebellar extramural stream that arise from the neuroepithelium adjacent to the lower rhombic lip. Also, Zfhep is expressed as cells migrate from a narrow region of the pons VZ towards the trigeminal nucleus. Co-expression with Islet1 shows that Zfhep is expressed in motor neurons of the trigeminal nucleus of the pons, but not in the inferior olive motor neurons at E12.5. Therefore, Zfhep is strongly expressed in a tightly regulated pattern in proliferating neural stem cells and a subset of neurons. Zfhep protein is also strongly expressed in trigeminal ganglia, and is moderately expressed in other cranial ganglia. In vitro studies have implicated Zfhep as a repressor of myogenesis, however, we find that Zfhep protein expression increases during muscle differentiation.

Transcriptional control during mammalian anterior pituitary development

The mammalian anterior pituitary gland is a compound endocrine organ that regulates reproductive development and fitness, growth, metabolic homeostasis, the response to stress, and lactation, by actions on target organs such as the gonads, the liver, the thyroid, the adrenals, and the mammary gland. The protein and peptide hormones that control these physiological parameters are secreted by specialized pituitary cell types that derive from a common origin in the early ectoderm. Collectively, the broad physiological importance of the pituitary gland, its intriguing organogenesis, and the clinical and agricultural significance of its actions, have established pituitary development as an excellent model system for the study of the gene-regulatory cascades that guide vertebrate cell determination and differentiation. We review the transcriptional pathways that regulate the commitment of the individual pituitary cell lineages and that subsequently modulate trophic hormone gene activity in the differentiated cells of the mature gland.

Cell-specific phosphorylation of Zfhep transcription factor

Zinc finger homeodomain enhancer-binding protein (Zfhep/Zfhx1a) is a transcription factor essential for immune system development, skeletal patterning, and life. Regulation of the interleukin-2 gene in T cells has been suggested to depend on post-translational processing of Zfhep, however, no modifications of Zfhep are known. Here we demonstrate that Zfhep is present in both hyperphosphorylated and hypophosphorylated forms. Western blot analysis demonstrates two forms of Zfhep with different mobilities. Differences in phosphorylation are sufficient to explain the difference in mobilities. Zfhep is primarily phosphorylated on Ser and Thr residues since PP2A dephosphorylates the slower mobility band. Treatment of nuclear extract with O-GlcNAcase did not detect O-linked sugar. Importantly, post-translational processing is cell-specific. Doublets of Zfhep were detected in five cell lines, whereas 6 cell lines contain only, or predominantly, non-phosphorylated Zfhep, and Saos-2 cells contain predominantly the phosphorylated form. These data provide the first demonstration that Zfhep is post-translationally modified.