Activator protein-2 mediates transcriptional activation of the CYP11A1 gene by interaction with Sp1 rather than binding to DNA

Transcription factor AP-2α activates RNA polymerase III-directed transcription and tumor cell proliferation by controlling expression of c-MYC and p53

Deregulation of transcription factor AP2 alpha (TFAP2A) and RNA polymerase III (Pol III) products is associated with tumorigenesis. However, the mechanism underlying this event is not fully understood and the connection between TFAP2A and Pol III-directed transcription has not been investigated. Here, we report that TFAP2A functions as a positive factor in the regulation of Pol III-directed transcription and cell proliferation. We found TFAP2A is also required for the activation of Pol III transcription induced by the silencing of filamin A, a well-known cytoskeletal protein and an inhibitor in Pol III-dependent transcription identified previously. Using a chromatin immunoprecipitation technique, we showed TFAP2A positively modulates the assembly of Pol III transcription machinery factors at Pol III-transcribed gene loci. We found TFAP2A can activate the expression of Pol III transcription-related factors, including BRF1, GTF3C2, and c-MYC. Furthermore, we demonstrate TFAP2A enhances expression of MDM2, a negative regulator of tumor suppressor p53, and also inhibits p53 expression. Finally, we found MDM2 overexpression can rescue the inhibition of Pol III-directed transcription and cell proliferation caused by TFAP2A silencing. In summary, we identified that TFAP2A can activate Pol III-directed transcription by controlling multiple pathways, including general transcription factors, c-MYC and MDM2/p53. The findings from this study provide novel insights into the regulatory mechanisms of Pol III-dependent transcription and cancer cell proliferation.

O-GlcNAc transferase contributes to sex-specific placental deregulation in gestational diabetes

INTRODUCTION

Gestational diabetes (GDM) is traditionally thought to emerge from placental endocrine dysregulations, but recent evidence suggests that fetal sex can also impact GDM development. Understanding the molecular mechanisms through which sex modulates placenta physiology can help identify novel molecular targets for future clinical care. Thus, we investigated the nutrient-sensing O-GlcNAc pathway as a potential mediator of sex-specific placenta dysfunction in GDM.

METHODS

Expression levels of O-GlcNAc enzymes were measured in male and female (n = 9+/gender) human placentas based on the maternal diagnosis of GDM. We then simulated the observed differences in both BeWo cells and human syncytiotrophoblasts primary cells (SCT) from male and female origins (n = 6/gender). RNA sequencing and targeted qPCR were performed to characterize the subsequent changes in the placenta transcriptome related to gestational diabetes.

RESULTS

O-GlcNAc transferase (OGT) expression was significantly reduced only in male placenta collected from mothers with GDM compared to healthy controls. Similar downregulation of OGT in trophoblast-like BeWo male cells demonstrated significant gene expression deregulations that overlapped with known GDM-related genes. Notably, placental growth hormone (GH) production was significantly elevated, while compensatory factors against GH-related insulin resistance were diminished. Inflammatory and immunologic factors with toxic effects on pancreatic β cell mass were also increased, altogether leaning toward a decompensatory diabetic profile. Similar changes in hormone expression were confirmed in male human primary SCTs transfected with siOGT. However, down-regulating OGT in female primary SCTs did not impact hormone production.

CONCLUSION

Our study demonstrated the significant deregulation of placental OGT levels in mothers with GDM carrying a male fetus. When simulated in vitro, such deregulation impacted hormonal production in BeWo trophoblast cells and primary SCTs purified from male placentas. Interestingly, female placentas were only modestly impacted by OGT downregulation, suggesting that the sex-specific presentation observed in gestational diabetes could be related to O-GlcNAc-mediated regulation of placental hormone production.

BCI, an inhibitor of the DUSP1 and DUSP6 dual specificity phosphatases, enhances P2X7 receptor expression in neuroblastoma cells

P2X7 receptor (P2RX7) is expressed strongly by most human cancers, including neuroblastoma, where high levels of P2RX7 are correlated with a poor prognosis for patients. Tonic activation of P2X7 receptor favors cell metabolism and angiogenesis, thereby promoting cancer cell proliferation, immunosuppression, and metastasis. Although understanding the mechanisms that control P2X7 receptor levels in neuroblastoma cells could be biologically and clinically relevant, the intracellular signaling pathways involved in this regulation remain poorly understood. Here we show that (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one (BCI), an allosteric inhibitor of dual specificity phosphatases (DUSP) 1 and 6, enhances the expression of P2X7 receptor in N2a neuroblastoma cells. We found that exposure to BCI induces the phosphorylation of mitogen-activated protein kinases p38 and JNK, while it prevents the phosphorylation of ERK1/2. BCI enhanced dual specificity phosphatase 1 expression, whereas it induced a decrease in the dual specificity phosphatase 6 transcripts, suggesting that BCI-dependent inhibition of dual specificity phosphatase 1 may be responsible for the increase in p38 and JNK phosphorylation. The weaker ERK phosphorylation induced by BCI was reversed by p38 inhibition, indicating that this MAPK is involved in the regulatory loop that dampens ERK activity. The PP2A phosphatase appears to be implicated in the p38-dependent dephosphorylation of ERK1/2. In addition, the PTEN phosphatase inhibition also prevented ERK1/2 dephosphorylation, probably through p38 downregulation. By contrast, inhibition of the p53 nuclear factor decreased ERK phosphorylation, probably enhancing the activity of p38. Finally, the inhibition of either p38 or Sp1-dependent transcription halved the increase in P2X7 receptor expression induced by BCI. Moreover, the combined inhibition of both p38 and Sp1 completely prevented the effect exerted by BCI. Together, our results indicate that dual specificity phosphatase 1 acts as a novel negative regulator of P2X7 receptor expression in neuroblastoma cells due to the downregulation of the p38 pathway.

The adiponectin receptor agonist, AdipoRon, promotes reproductive hormone secretion and gonadal development via the hypothalamic-pituitary-gonadal axis in chickens

Adiponectin is a key hormone secreted by fat tissues that has multiple biological functions, including regulating the energy balance and reproductive system by binding to its receptors AdipoR1 and AdipoR2. This study investigated the correlation between the levels of adiponectin and reproductive hormones in the hypothalamic-pituitary-ovarian (HPO) axis of laying hens at 4 different developmental stages (15, 20, 30, and 68 wk) and explored the effects of AdipoRon (an activator of adiponectin receptors) on the hypothalamic-pituitary-gonadal (HPG) axis and follicle and testicular Leydig cells in vitro and in vivo. The results demonstrated that the adiponectin level was significantly correlated with that of reproductive hormones in the HPO axis (e.g., GnRH, FSH, LH, and E2) in laying hens at 4 different ages. Moreover, AdipoRon could promote the expression of AdipoR1 and AdipoR2 and the secretion of reproductive hormones in the HPG axis, including GnRH, FSH, LH, P4, and T. AdipoRon could also upregulate the expression of genes related to follicular steroidogenesis (STAR, CYP19A1, CYP17A1, and CYP11A1), hepatic lipid synthesis (OVR, MTP), follicular lipid uptake (PPAR-g), and follicular angiogenesis (VEGFA1, VEGFA2, VEGFR1, ANGPT1, ANGPT2, TEK) in the oviposition period, and all of these findings were consistent with the results obtained from in vitro experiments after the transfection of small white follicles (SWFs) with AdipoRon. Furthermore, the results suggest that AdipoRon increases the diameter of testicular seminiferous tubules, the number of spermatogenic cells and sperm production in vivo and enhances the expression of AdipoR1, AdipoR2 and steroid hormones in vitro. Collectively, the findings suggest that AdipoRon could facilitate the expression and secretion of reproductive hormones in the HPG axis by activating its receptors and then improve the growth and development of follicles and testes in chickens.

How trophoblasts fuse: an in-depth look into placental syncytiotrophoblast formation

In humans, cell fusion is restricted to only a few cell types under normal conditions. In the placenta, cell fusion is a critical process for generating syncytiotrophoblast: the giant multinucleated trophoblast lineage containing billions of nuclei within an interconnected cytoplasm that forms the primary interface separating maternal blood from fetal tissue. The unique morphology of syncytiotrophoblast ensures that nutrients and gases can be efficiently transferred between maternal and fetal tissue while simultaneously restricting entry of potentially damaging substances and maternal immune cells through intercellular junctions. To maintain integrity of the syncytiotrophoblast layer, underlying cytotrophoblast progenitor cells terminate their capability for self-renewal, upregulate expression of genes needed for differentiation, and then fuse into the overlying syncytium. These processes are disrupted in a variety of obstetric complications, underscoring the importance of proper syncytiotrophoblast formation for pregnancy health. Herein, an overview of key mechanisms underlying human trophoblast fusion and syncytiotrophoblast development is discussed.

Upregulation of CYP17A1 by Sp1-mediated DNA demethylation confers temozolomide resistance through DHEA-mediated protection in glioma

Steroidogenesis-mediated production of neurosteroids is important for brain homeostasis. Cytochrome P450 17A1 (CYP17A1), which converts pregnenolone to dehydroepiandrosterone (DHEA) in endocrine organs and the brain, is required for prostate cancer progression and acquired chemotherapeutic resistance. However, whether CYP17A1-mediated DHEA synthesis is involved in brain tumor malignancy, especially in glioma, the most prevalent brain tumor, is unknown. To investigate the role of CYP17A1 in glioma, we determined that CYP17A1 expression is significantly increased in gliomas, which secrete more DHEA than normal astrocytes. We found that as gliomas became more malignant, both CYP17A1 and DHEA were significantly upregulated in temozolomide (TMZ)-resistant cells and highly invasive cells. In particular, the increase of CYP17A1 was caused by Sp1-mediated DNA demethylation, whereby Sp1 competed with DNMT3a for binding to the CYP17A1 promoter in TMZ-resistant glioma cells. CYP17A1 was required for the development of glioma cell invasiveness and resistance to TMZ-induced cytotoxicity. In addition, DHEA markedly attenuated TMZ-induced DNA damage and apoptosis. Together, our results suggest that components of the Sp1-CYP17A1-DHEA axis, which promotes the development of TMZ resistance, may serve as potential biomarkers and therapeutic targets in recurrent glioma.

AP-2α downregulation by cigarette smoke condensate is counteracted by p53 in human lung cancer cells

Cumulative findings have demonstrated that the dysregulation of tumor suppressor genes may be implicated in cigarette smoke-induced carcinogenesis. Activating enhancer-binding protein 2 (AP-2) is a eukaryotic transcriptional factor that plays a significant role in embryonic development and tumorigenesis. The vertebrate AP-2 family consists of AP-2α, AP-2β, AP-2γ, AP-2δ and AP-2ε. Previous studies have suggested that cigarette smoking disrupts AP-2 regulation. In the present study, we investigated the effects of cigarette smoke condensate (CSC) on AP-2α expression in human lung cancer cell lines (NCI-H1299, NCI-H446 and A549), as well as the potential mechanisms involved. Using RT-qPCR, we found that CSC decreased AP-2α expression by suppressing its transcription in human lung cancer cell lines, particularly in p53-deficient NCI-H1299 cells. Western blotting and luciferase assays were implemented and we found that the restoration of p53 expression rescued the NCI-H1299 cells from CSC-induced AP-2α loss, while the silencing of p53 resulted in increased AP-2α loss induced by CSC, suggesting an antagonizing role of p53 in the regulation of AP-2α by CSC. Our results indicate that AP-2α downregulation may be involved in smoke-induced lung carcinogenesis.

Implications of adiponectin in linking metabolism to testicular function

Obesity is a major health problem, contributing to the development of various diseases with aging. In humans, obesity has been associated with reduced testosterone production and subfertility. Adipose tissue is an important source of hormones having influences on both metabolism and reproduction. Among them, the production and secretion of adiponectin is inversely correlated to the severity of obesity. The purpose of this review of literature is to present the current state of knowledge on adiponectin research to determine whether this hormone affects reproduction in men. Surprisingly, evidences show negative influences of adiponectin on GnRH secretion from the hypothalamus, LH and FSH secretion from the pituitary and testosterone at the testicular level. Thus far, the involvement of adiponectin in the influence of metabolism on reproduction in men is limited. However, adiponectin and its receptors are expressed by different cell types of the male gonad, including Leydig cells, spermatozoa, and epididymis. In addition, actions of adiponectin at the testicular level have been shown to promote spermatogenesis and sperm maturation. Therefore, autocrine/paracrine actions of adiponectin in the testis may contribute to support male reproductive function.

Detection of interacting transcription factors in human tissues using predicted DNA binding affinity

Background

Tissue-specific gene expression is generally regulated by combinatorial interactions among transcription factors (TFs) which bind to the DNA. Despite this known fact, previous discoveries of the mechanism that controls gene expression usually consider only a single TF.

Results

We provide a prediction of interacting TFs in 22 human tissues based on their DNA-binding affinity in promoter regions. We analyze all possible pairs of 130 vertebrate TFs from the JASPAR database. First, all human promoter regions are scanned for single TF-DNA binding affinities with TRAP and for each TF a ranked list of all promoters ordered by the binding affinity is created. We then study the similarity of the ranked lists and detect candidates for TF-TF interaction by applying a partial independence test for multiway contingency tables. Our candidates are validated by both known protein-protein interactions (PPIs) and known gene regulation mechanisms in the selected tissue. We find that the known PPIs are significantly enriched in the groups of our predicted TF-TF interactions (2 and 7 times more common than expected by chance). In addition, the predicted interacting TFs for studied tissues (liver, muscle, hematopoietic stem cell) are supported in literature to be active regulators or to be expressed in the corresponding tissue.

Conclusions

The findings from this study indicate that tissue-specific gene expression is regulated by one or two central regulators and a large number of TFs interacting with these central hubs. Our results are in agreement with recent experimental studies.

Reversal of epigenetic silencing of AP-2alpha results in increased zinc uptake in DU-145 and LNCaP prostate cancer cells

Zinc accumulation is lost during prostate carcinogenesis. Recent studies reveal a strong association between prostate cancer progression and the downregulation of the zinc uptake transporters hZip1 and hZip3. The aim of this work was to assess the involvement of epigenetic processes in the disruption of zinc uptake homeostasis in prostate adenocarcinoma. In this report, we demonstrate an increase in hZip1 and hZip3 zinc transporters' expression and zinc uptake by the prostate cancer cells DU-145 and LNCaP in response to 5-aza-2'-deoxycytidine. This effect is due to demethylation of the promoter region of the activator protein (AP)-2alpha protein, which is crucial for hZip1 and hZip3 genes expression. Loss of AP-2alpha expression in DU-145 and LNCaP prostate cancer cells is due to hypermethylation of its promoter region. Similarly, we found higher AP-2alpha promoter methylation levels in clinical samples of early-stage prostate adenocarcinoma when compared with adjacent non-malignant prostate tissue. Taken together, our findings provide a better understanding of the epigenetic mechanisms that are involved in the loss of AP-2alpha protein in prostate cancer cells which lead to decreased cellular zinc uptake-a sine qua non of prostate cancer development.

Regulation of steroid production: analysis of Cyp11a1 promoter

CYP11A1 is a key enzyme in steroid synthesis abundantly expressed in the adrenal, testis, ovary, and placenta. This article reviews recent studies on cis-regulatory elements and trans-regulators of the CYP11A1 promoter, with special focus on their tissue-specific regulation. Trans-regulators include tissue-specific factors such as SF-1, DAX-1, TReP-132, LBP, and GATA that regulate tissue-specific expression of CYP11A1. These tissue-specific factors interact with factors commonly present in most cells like AP-1, Sp1, and AP-2 to bring CYP11A1 transcription to full potential. These transcription factors stimulate CYP11A1 transcriptional activity through interaction with their specific cis-elements or through protein-protein interaction. The cis-element on the Cyp11a1 promoter was further characterized in vitro and in vivo. Mutation of the proximal SF-1-binding site results in down regulation of CYP11A1 in the adrenal and testis but not in the ovary and placenta, leading to attenuated corticosterone circadian rhythms and blunted stress response.

Identification of functional TFAP2A and SP1 binding sites in new TFAP2A-modulated genes

Background

Different approaches have been developed to dissect the interplay between transcription factors (TFs) and their cis-acting sequences on DNA in order to identify TF target genes. Here we used a combination of computational and experimental approaches to identify novel direct targets of TFAP2A, a key TF for a variety of physiological and pathological cellular processes. Gene expression profiles of HeLa cells either silenced for TFAP2A by RNA interference or not were previously compared and a set of differentially expressed genes was revealed.

Results

The regulatory regions of 494 TFAP2A-modulated genes were analyzed for the presence of TFAP2A binding sites, employing the canonical TFAP2A Positional Weight Matrix (PWM) reported in Jaspar http://jaspar.genereg.net/. 264 genes containing at least 2 high score TFAP2A binding sites were identified, showing a central role in "Cellular Movement" and "Cellular Development". In an attempt to identify TFs that could cooperate with TFAP2A, a statistically significant enrichment for SP1 binding sites was found for TFAP2A-activated but not repressed genes. The direct binding of TFAP2A or SP1 to a random subset of TFAP2A-modulated genes was demonstrated by Chromatin ImmunoPrecipitation (ChIP) assay and the TFAP2A-driven regulation of DCBLD2/ESDN/CLCP1 gene studied in details.

Conclusions

We proved that our computational approaches applied to microarray selected genes are valid tools to identify functional TF binding sites in gene regulatory regions as confirmed by experimental validations. In addition, we demonstrated a fine-tuned regulation of DCBLD2/ESDN transcription by TFAP2A.

WWOX gene and gene product: tumor suppression through specific protein interactions

The WWOX gene, an archetypal fragile gene, encompasses a chromosomal fragile site at 16q23.2, and encodes the approximately 46-kDa Wwox protein, with WW domains that interact with a growing list of interesting proteins. If the function of a protein is defined by the company it keeps, then Wwox is involved in numerous important signal pathways for bone and germ-cell development, cellular and animal growth and death, transcriptional control and suppression of cancer development. Because alterations to genes at fragile sites are exquisitely sensitive to replication stress-induced DNA damage, there has been an ongoing scientific discussion questioning whether such gene expression alterations provide a selective advantage for clonal expansion of neoplastic cells, and a parallel discussion on why important genes would be present at sites that are susceptible to inactivation. We offer some answers through a description of known WWOX functions.

Activator protein-2 overexpression accounts for increased insulin receptor expression in human breast cancer

Various studies have shown that the insulin receptor (IR) is increased in most human breast cancers, and both ligand-dependent malignant transformation and increased cell growth occur in cultured breast cells overexpressing the IR. However, although numerous in vivo and in vitro observations have indicated an important contributory role for the IR in breast cancer cell biology, the molecular mechanisms accounting for increased IR expression in breast tumors have not previously been elucidated. Herein, we did immunoblot analyses of nuclear protein from cultured breast cancer cells and normal and tumoral tissues from breast cancer patients combined with promoter studies by using a series of human wild-type and mutant IR promoter constructs. We provide evidence that IR overexpression in breast cancer is dependent on the assembly of a transcriptionally active multiprotein-DNA complex, which includes the high-mobility group A1 (HMGA1) protein, the developmentally regulated activator protein-2 (AP-2) transcription factor and the ubiquitously expressed transcription factor Sp1. In cultured breast cancer cells and human breast cancer specimens, the expression of AP-2 was significantly higher than that observed in cells and tissues derived from normal breast, and this overexpression paralleled the increase in IR expression. However, AP-2 DNA-binding activity was undetectable with the IR gene promoter, suggesting that transactivation of this gene by AP-2 might occur indirectly through physical and functional cooperation with HMGA1 and Sp1. Our findings support this hypothesis and suggest that in affected individuals, hyperactivation of the AP-2 gene through the overexpression of IR may play a key role in breast carcinogenesis.

A Novel Functional Interaction between the Sp1-like Protein KLF13 and SREBP-Sp1 Activation Complex Underlies Regulation of Low Density Lipoprotein Receptor Promoter Function

Cholesterol homeostasis is regulated by a family of transcription factors designated sterol regulatory element-binding proteins (SREBPs). Precise control of SREBP-targeted genes requires additional interactions with co-regulatory transcription factors. In the case of the low density lipoprotein receptor (LDLR), SREBP cooperates with the specificity protein Sp1 to activate the promoter. In this report, we describe a novel pathway in LDLR transcriptional regulation distinct from the SREBP-Sp1 activation complex involving the Sp1-like protein Krueppel-like factor 13 (KLF13). Using a combination of RNA interference, electrophoretic mobility shift, chromatin immunoprecipitation, and reporter assays, deletion, and site-directed mutagenesis, we demonstrated that KLF13 mediates repression in a DNA context-selective manner. KLF13 repression of LDLR promoter activity appears to be needed to keep the receptor silent, a state that can be antagonized by Sp1, SREBP, and inhibitors of histone deacetylase activity. Chromatin immunoprecipitation assay confirmed that KLF13 binds proximal LDLR DNA sequences in vivo and that exogenous oxysterol up-regulates such binding. Together these studies identify a novel regulatory pathway in which gene repression by KLF13 must be overcome by the Sp1-SREBP complex to activate the LDLR promoter. Therefore, these data should replace a pre-existent and more simple paradigm that takes into consideration only the induction of the activator proteins Sp1-SREBP as necessary for LDLR promoter drive without including default repression, such as that by KLF13, of the LDLR gene.

The AP-2 family of transcription factors

AP-2 transcription factors are involved in cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development. Members of the family are found in mammals (with five different proteins in human and mice), frogs and fish, as well as protochordates, insects and nematodes.

The AP-2 family of transcription factors consists of five different proteins in humans and mice: AP-2α, AP-2β, AP-2γ, AP-2δ and AP-2ε. Frogs and fish have known orthologs of some but not all of these proteins, and homologs of the family are also found in protochordates, insects and nematodes. The proteins have a characteristic helix-span-helix motif at the carboxyl terminus, which, together with a central basic region, mediates dimerization and DNA binding. The amino terminus contains the transactivation domain. AP-2 proteins are first expressed in primitive ectoderm of invertebrates and vertebrates; in vertebrates, they are also expressed in the emerging neural-crest cells, and AP-2α^-/- animals have impairments in neural-crest-derived facial structures. AP-2β is indispensable for kidney development and AP-2γ is necessary for the formation of trophectoderm cells shortly after implantation; AP-2α and AP-2γ levels are elevated in human mammary carcinoma and seminoma. The general functions of the family appear to be the cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development.

Cited2 controls left-right patterning and heart development through a Nodal-Pitx2c pathway

Malformations of the septum, outflow tract and aortic arch are the most common congenital cardiovascular defects and occur in mice lacking Cited2, a transcriptional coactivator of TFAP2. Here we show that Cited2(-/-) mice also develop laterality defects, including right isomerism, abnormal cardiac looping and hyposplenia, which are suppressed on a mixed genetic background. Cited2(-/-) mice lack expression of the Nodal target genes Pitx2c, Nodal and Ebaf in the left lateral plate mesoderm, where they are required for establishing laterality and cardiovascular development. CITED2 and TFAP2 were detected at the Pitx2c promoter in embryonic hearts, and they activate Pitx2c transcription in transient transfection assays. We propose that an abnormal Nodal-Pitx2c pathway represents a unifying mechanism for the cardiovascular malformations observed in Cited2(-/-) mice, and that such malformations may be the sole manifestation of a laterality defect.

Insulin drives transcriptional activity of the CYP17 gene in primary cultures of swine theca cells

Insulin stimulates androgen biosynthesis and the accumulation of CYP17 mRNA and heterogeneous nuclear (hn) RNA in primary cultures of immature swine theca cells. To further assess insulinomimetic transcriptional control, we subcloned 1.007 kilobases (kb) of the 5'-upstream region of the CYP17 gene (-976 to +31 base pairs [bp] to the transcriptional start site) into a firefly-luciferase reporter construct. Insulin drove transcriptional activity of this probe in a time- and dose-dependent fashion, with maximal stimulation of 2.7- to 3.2-fold after insulin exposure (100 ng/ml) for 6 h. Progressive deletional constructs -839, -473, -174, and -75/+31 bp delineated expected reduction in responsiveness, except paradoxical gain of basal CYP17 promoter activity by the -473/+31-bp sequence. The latter suggests a possible intervening inhibitory sequence. Elimination of all sequences 5'-upstream to -174 bp markedly reduced basal transcriptional activity and abolished insulin action. Point mutation of a presumptive Sp1-like element located within -193/-180 bp inhibited basal and insulin-stimulated luciferase activity of the full-length promoter fragment by 40% and 67%, respectively. Disruption of a contiguous presumptive AP-2 site produced a comparable outcome. Combined mutation of the Sp1 and AP-2-like elements eliminated basal and insulin-potentiated CYP17 promoter activity. By Western analysis, insulin augmented cognate receptor phosphoprotein concentrations by 31-fold within 10 min. Chemical inhibitors of MEK-activated ERK1/2 attenuated insulin-enhanced CYP17 transcriptional activity by 76-80%. In summary, insulin drives transcriptional activity of a 5'-upstream regulatory sequence (-976 to +31 bp) of the swine CYP17 gene in primary cultures of theca cells, under a minimal requirement for combined activity of proximal (-193/180 bp) Sp1 and AP-2-like elements.

Adrenocorticotropin/3',5'-cyclic AMP-mediated transcription of the scavenger akr1-b7 gene in adrenocortical cells is dependent on three functionally distinct steroidogenic factor-1-responsive elements

The akr1-b7 gene encodes a scavenger enzyme expressed in steroidogenic glands under pituitary control. In the zona fasciculata of the adrenal cortex where its expression is controlled by ACTH, AKR1-B7 detoxifies isocaproaldehyde produced during the first step of steroidogenesis. Three steroidogenic factor-1 (SF-1)-responsive elements (SFREs) are contained within the -510/+41 promoter region, which was previously demonstrated to drive gene expression in transgenic mice adrenal cortex. All these sequences bind at least SF-1 in Y1 adrenocortical cell nuclear extracts and can be activated by overexpression of this factor in HeLa cells. However, the three SFREs show distinct properties regarding akr1-b7 promoter activity in Y1 cells. Whereas the proximal -102 SFRE supports basal promoter activity, the -458 bona fide SFRE is essential for both basal promoter activity and cAMP responsiveness, although it is unresponsive to cAMP when isolated from its promoter context. This suggests that SF-1 is not a cAMP-responsive factor per se. The neighboring SFRE at -503 is a palindromic sequence that binds monomeric and heteromeric SF-1 as well as an adrenal-specific complex. Using MA-10 Leydig cells and Y1-10r9 mutant cells, we provide evidence that its activity in adrenocortical cells depends on the binding of the adrenal-specific factor, which is required for basal and cAMP-induced promoter activity. Furthermore, the -503 site has intrinsic cAMP-sensing ability in Y1 cells, which is correlated with increased adrenal-specific complex binding. Collectively, our results suggest that cAMP responsiveness of the akr1-b7 promoter is achieved through cooperation between the adrenal-specific factor bound to the -503 site and SF-1 bound to the -458 site.

Transcriptional activation by AP-2alpha is modulated by the oncogene DEK

Cell differentiation and development are highly regulated processes at the transcriptional level. One of the main transcription factors that regulate these processes is AP-2alpha, a cell-type specific protein required for vertebrate development and embryogenesis. AP-2alpha also regulates apoptosis and cell-cycle specific events by interacting with the oncogene c-Myc. In searching for novel AP-2alpha- interacting factors, using an affinity chromatography approach, we have observed that oncoprotein DEK interacts with AP-2alpha in vitro. The existence of an interaction between AP-2alpha and DEK in cellular cultures was demonstrated by expression of a tagged AP-2alpha form followed by immunodetection. By transient co-expression experiments using a reporter for APOE promoter activity we have found that DEK stimulates the transactivation activity of AP-2alpha over APOE promoter. Finally, electrophoretic mobility shift assays suggested that DEK enhances the DNA-binding activity of AP-2alpha. Our data suggest a novel cellular function of DEK as a transcriptional co-activator.

Role of three SF-1 binding sites in the expression of the mvdp/akr1-b7 isocaproaldehyde reductase in Y1 cells

Mvdp/akr1-b7 encodes an aldose-reductase-like enzyme expressed in the zona fasciculata of the adrenal cortex, the function of which is essential for the detoxification of the cholesterol side chain cleavage product, isocaproaldehyde. The -510/+41 akr1-b7 promoter fragment is able to reproduce the endogenous gene zona fasciculata restricted, ACTH-controlled expression, in transgenic mice adrenals. Here, we report that three response elements contained within this promoter (positions -102, -458, -503) are able to bind SF-1, the essential regulator of steroidogenesis, although the low affinity site at -503 retains some other specific proteins present in Y1 nuclear extracts. Mutation of the -102 site results in a lowering of the activity of the -510/+41 promoter in Y1 cells, whereas mutation of the -458 site induces a reduction both in the global activity and forskolin sensitivity of the promoter. Interestingly, differential mutations of the -503 site nucleotides either induce an increase or a decrease in the basal and forskolin-induced activity.

Sp1 and AP2 regulate but do not constitute TATA-less human TAF(II)55 core promoter activity

Human TAF(II)55 (hTAF(II)55), a component of the general transcription factor TFIID, is the only general transcription factor encoded by an intronless gene identified thus far. Analysis of the TATA-less hTAF(II)55 promoter-proximal sequence reveals putative binding sites for STAT-1, MEF2, E2F, Sp1, AP2, AREB6 and E47. Using chromatin immunoprecipitation, DNase I footprinting and electrophoretic mobility shift assays, we demonstrate that Sp1 and AP2 can bind simultaneously to juxtaposed Sp1- and AP2-binding sites in the hTAF(II)55 promoter-proximal region and functionally modulate hTAF(II)55 promoter activity, as evidenced by reporter gene assays performed in transiently transfected human C-33A and insect SL2 cell lines. Interestingly, removal of all the promoter-proximal Sp1-binding sites does not impair the function of the hTAF(II)55 core promoter. Moreover, a 52-bp DNA fragment containing only the hTAF(II)55 initiator (Inr) and downstream promoter element (DPE) is able to support Gal4-VP16-mediated activation in vivo and in vitro. Our data suggest that Sp1, although it plays an enhancing role in hTAF(II)55 gene expression, is not essential for hTAF(II)55 core promoter activity. Interestingly, mutations introduced at the Inr and DPE differentially affect the selection of transcription start sites, suggesting that these two core promoter elements play a non-redundant role in the function of TATA-less promoters.

Transcription of cholesterol side-chain cleavage cytochrome P450 in the placenta: activating protein-2 assumes the role of steroidogenic factor-1 by binding to an overlapping promoter element

Progesterone is essential to the sustenance of pregnancy in humans and other mammals. From the second trimester on, the human placenta is the sole origin of de novo synthesized steroid hormones. In mice, placentation at midgestation is accompanied by a temporal rise of steroid hormone synthesis commencing in the giant cells of the mouse trophoblast. In doing so, the giant trophoblasts, as any other steroidogenic cell, express high levels of the key steroidogenic enzyme, cholesterol side-chain cleavage cytochrome P450 (P450scc). Because steroidogenic factor 1 (SF-1), the transcription factor required for expression of P450scc in the adrenals and the gonads, is not expressed in the placenta, we hypothesized that placenta-specific nuclear factor(s) (PNF) assumes the role of SF-1 by binding to the same promoter region that harbors the SF-1 recognition site in the P450scc gene. To address this possibility, we used SCC1, a well conserved proximal region in the P450scc genes (-60/-32 in the rat gene) to purify PNF from human term placenta. Sequencing of the purified PNF revealed that it is the alpha isoform of the human activating protein-2 (AP-2alpha). Specific antibodies tested in EMSA confirmed that AP-2alpha is the predominant isoform that binds SCC1 in the human placenta, whereas AP-2gamma is the only mouse placental protein that binds this oligonucleotide. Functional studies showed that coexpression of the rat P450scc promoter (-378/+8 CAT) and AP-2 isoforms (alpha or gamma) in human embryonic kidney 293 cells results in a marked activation of chloramphenicol acetyltransferase (CAT) transcription that is dependent on an intact AP-2 motif, GCCTTGAGC. This motif conforms with consensus sequences previously determined for binding of the AP-2 alpha and gamma isoforms. Mutations of the AP-2 element ablated binding of AP-2 to SCC1, as well as severely diminished the promoter activity in primary mouse giant trophoblasts and human choriocarcinoma JAR cells. Collectively, these studies suggest that expression of placental P450scc is governed by AP-2 factors that bind to a cis-element that largely overlaps the sequence required for recognition of SF-1 in other steroidogenic tissues.

Transcription factor AP-2γ is essential in the extra-embryonic lineages for early postimplantation development

The members of the AP-2 family of transcription factors play important roles during mammalian development and morphogenesis. AP-2γ (Tcfap2c – Mouse Genome Informatics) is a retinoic acid-responsive gene implicated in placental development and the progression of human breast cancer. We show that AP-2γ is present in all cells of preimplantation embryos and becomes restricted to the extra-embryonic lineages at the time of implantation. To study further the biological function of AP-2γ, we have generated Tcfap2c-deficient mice by gene disruption. The majority of Tcfap2c–/– mice failed to survive beyond 8.5 days post coitum (d.p.c.). At 7.5 d.p.c., Tcfap2c–/– mutants were typically arrested or retarded in their embryonic development in comparison to controls. Morphological and molecular analyses of mutants revealed that gastrulation could be initiated and that anterior-posterior patterning of the epiblast remained intact. However, the Tcfap2c mutants failed to establish a normal maternal-embryonic interface, and the extra-embryonic tissues were malformed. Moreover, the trophoblast-specific expression of eomesodermin and Cdx2, two genes implicated in FGF-responsive trophoblast stem cell maintenance, was significantly reduced. Chimera studies demonstrated that AP-2γ plays no major autonomous role in the development of the embryo proper. By contrast, the presence of AP-2γ in the extra-embryonic membranes is required for normal development of this compartment and also for survival of the mouse embryo.

Androgen receptor acetylation governs trans activation and MEKK1-induced apoptosis without affecting in vitro sumoylation and trans-repression function

The androgen receptor (AR) is a nuclear hormone receptor superfamily member that conveys both trans repression and ligand-dependent trans-activation function. Activation of the AR by dihydrotestosterone (DHT) regulates diverse physiological functions including secondary sexual differentiation in the male and the induction of apoptosis by the JNK kinase, MEKK1. The AR is posttranslationally modified on lysine residues by acetylation and sumoylation. The histone acetylases p300 and P/CAF directly acetylate the AR in vitro at a conserved KLKK motif. To determine the functional properties governed by AR acetylation, point mutations of the KLKK motif that abrogated acetylation were engineered and examined in vitro and in vivo. The AR acetylation site point mutants showed wild-type trans repression of NF-kappa B, AP-1, and Sp1 activity; wild-type sumoylation in vitro; wild-type ligand binding; and ligand-induced conformational changes. However, acetylation-deficient AR mutants were selectively defective in DHT-induced trans activation of androgen-responsive reporter genes and coactivation by SRC1, Ubc9, TIP60, and p300. The AR acetylation site mutant showed 10-fold increased binding of the N-CoR corepressor compared with the AR wild type in the presence of ligand. Furthermore, histone deacetylase 1 (HDAC1) bound the AR both in vivo and in cultured cells and HDAC1 binding to the AR was disengaged in a DHT-dependent manner. MEKK1 induced AR-dependent apoptosis in prostate cancer cells. The AR acetylation mutant was defective in MEKK1-induced apoptosis, suggesting that the conserved AR acetylation site contributes to a pathway governing prostate cancer cellular survival. As AR lysine residue mutations that abrogate acetylation correlate with enhanced binding of the N-CoR repressor in cultured cells, the conserved AR motif may directly or indirectly regulate ligand-dependent corepressor disengagement and, thereby, ligand-dependent trans activation.

Sp3 represses gene expression via the titration of promoter-specific transcription factors

We have determined previously that Sp3 encodes three distinct gene products as follows: a full-length protein (Sp3) that is an activator of transcription and two isoforms (M1 and M2) derived via internal translational initiation that function as transcriptional repressors. To identify amino acids and functions required for transcriptional repression, we employed PCR-directed mutagenesis to create a panel of mutated M2 proteins. Biochemical and functional analyses of these mutated proteins indicate that functions encoded by the M2 carboxyl terminus, such as DNA binding activity and the capacity to form multimeric complexes, are not required or sufficient for transcriptional repression. Instead, a 93-amino acid portion of the trans-activation domain was shown to be the minimal portion of M2 required to block Sp-dependent gene expression. Transcriptional analysis of three Sp-dependent promoters showed that mutations sustained by many M2 proteins result in promoter-specific effects. Regions of M2 required for physical interactions with five TATA box-associated factors (TAF(II)s) were mapped, and mutations that disrupt the interaction of M2 with two of these proteins, TAF(II)70 and TAF(II)40, were identified. We conclude that Sp3- mediated transcriptional repression is due, at least in part, to competition for promoter-specific transcription factors.

Transcriptional regulation of the human manganese superoxide dismutase gene: the role of specificity protein 1 (Sp1) and activating protein-2 (AP-2)

Manganese superoxide dismutase (MnSOD) plays an important role in regulating cellular redox conditions. Expression of MnSOD has been shown to protect against damage by oxidative stress and to suppress the malignant phenotype of human cancer cells. We have previously cloned the human MnSOD (SOD2) gene and analysed its 5' proximal promoter, which has been characterized by a lack of a TATA or CAAT box and the presence of multiple GC boxes. To define further the molecular mechanisms for the regulation of MnSOD expression, multiple transcription factor-binding motifs containing overlapping specificity protein 1 (Sp1)- and activator protein (AP)-2-binding sites were identified by DNase I footprinting analysis. Functional studies in three cell lines with different levels of Sp1 and AP-2 proteins suggested that the cellular levels of these proteins may differentially regulate transcription via GC-binding motifs in the human SOD2 promoter. Co-transfection of an Sp1 expression vector resulted in an increase in the transcription of the promoter-driven reporter gene. In contrast, co-transfection of the AP-2 expression vector caused a decrease in transcription. Direct mutagenesis analysis of Sp1- and AP-2-binding sites showed that Sp1 is essential for transcription of the human SOD2 gene, whereas AP-2 plays a negative role in the transcription. Immunoprecipitation of Sp1 and AP-2 proteins demonstrated that Sp1 interacts with AP-2 in vivo. Two-hybrid analysis revealed that interaction between Sp1 and AP-2 plays both a positive and negative role in the transcription of the reporter gene in vivo. Taken together, our data indicate that AP-2 down-regulates transcription of the human SOD2 gene via its interaction with Sp1 within the promoter region. These findings, coupled with our previous observation that several cancer cell lines have mutations in the promoter region of the human MnSOD gene, which lead to an increase in an AP-2-binding site and a decrease in the promoter activity, signal the importance of understanding the promoter structure and the regulation of the human SOD2 gene by Sp1 and AP-2.

Induction of cPLA2 in lung epithelial cells and non-small cell lung cancer is mediated by Sp1 and c-Jun

Activating mutations in ras genes are frequently associated with non-small cell lung cancer cells (NSCLC) and contribute to transformed growth in these cells. Expression of oncogenic forms of Ras in these cells is associated with increased expression and activity of cytosolic phospholipase A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2), leading to constitutively elevated levels of prostaglandin production. Expression of oncogenic Ras is sufficient to induce these enzymes in normal lung epithelial cells. We have previously reported that the JNK and ERK pathways are necessary for induction of cPLA(2) and have defined a minimal region of the cPLA(2) promoter from -58 to -12 that is required for Ha-Ras-mediated induction. To further characterize the cis-regulatory elements within this region involved in this response, site-directed mutagenesis was used to make mutations at various sites. Three cis-regulatory elements were identified: regions -21/-18, -37/-30, and -55/-53. Mutations in any of these elements decreased basal and Ha-Ras-induced cPLA(2) promoter activity in both normal lung epithelial cells, as well as steady state promoter activity in A549 cells, with a mutation in element -21/-18 completely eliminating all promoter activity. Overexpression studies and gel shift assays indicated that Sp1 may serve as a transcription factor functionally regulating promoter activity by directly interacting with two of the cis-regulatory elements, -21/-18 and -37/-30. Expression of Ha-Ras led to induction of c-Jun protein, which showed functional cooperation with Sp1 in driving promoter activity. Additional unidentified transcription factors bound to the regions from -55/-53 and -37/-34.

Sp1 and krüppel-like factor family of transcription factors in cell growth regulation and cancer

The Sp/KLF family contains at least twenty identified members which include Sp1-4 and numerous krüppel-like factors. Members of the family bind with varying affinities to sequences designated as 'Sp1 sites' (e.g., GC-boxes, CACCC-boxes, and basic transcription elements). Family members have different transcriptional properties and can modulate each other's activity by a variety of mechanisms. Since cells can express multiple family members, Sp/KLF factors are likely to make up a transcriptional network through which gene expression can be fine-tuned. 'Sp1 site'-dependent transcription can be growth-regulated, and the activity, expression, and/or post-translational modification of multiple family members is altered with cell growth. Furthermore, Sp/KLF factors are involved in many growth-related signal transduction pathways and their overexpression can have positive or negative effects on proliferation. In addition to growth control, Sp/KLF factors have been implicated in apoptosis and angiogenesis; thus, the family is involved in several aspects of tumorigenesis. Consistent with a role in cancer, Sp/KLF factors interact with oncogenes and tumor suppressors, they can be oncogenic themselves, and altered expression of family members has been detected in tumors. Effects of changes in Sp/KLF factors are context-dependent and can appear contradictory. Since these factors act within a network, this diversity of effects may arise from differences in the expression profile of family members in various cells. Thus, it is likely that the properties of the overall network of Sp/KLF factors play a determining role in regulation of cell growth and tumor progression.

Induction of AP-2α Expression by Adenoviral Infection Involves Inactivation of the AP-2rep Transcriptional Corepressor CtBP1

AP-2 transcription factors execute important functions during embryonic development and malignant transformation. Recently, we have isolated a transcriptional repressor of AP-2alpha expression, the novel Krüppel-related zinc finger protein AP-2rep (Klf12). Here, we show that repression of AP-2alpha transcription by AP-2rep is dependent on an N-terminal PVDLS motif that interacts specifically with the corepressor CtBP1 both in vivo and in vitro. This interaction motif was previously identified in the C-terminal region of the adenoviral oncoprotein E1A. Infection of both HeLa and PA-1 cells with adenovirus type 5 strongly induced AP-2alpha mRNA. Consistently, E1A was necessary and sufficient to mediate up-regulation of AP-2alpha. Transiently transfected wild-type E1A protein activated an AP-2rep sensitive cis-regulatory element of the AP-2alpha promoter, but E1A protein harboring a mutation in the PVDLS motif failed to activate. In summary, we conclude that the adenoviral oncoprotein E1A activates transcription from the endogenous AP-2alpha gene, an effect that involves transcriptional derepression of the AP-2alpha promoter by interaction of E1A with the AP-2rep corepressor CtBP1.

Transcription factor AP-2 functions as a repressor that contributes to the liver-specific expression of serum amyloid A1 gene

We previously identified transcription factor AP-2 as the nuclear factor that interacts with the tissue-specific repressor element in the rat serum amyloid A1 (SAA1) promoter. In this report, we provide evidence for a second AP-2-binding site and show that both AP-2 sites participate in mediating the transcription repression of SAA1 promoter. This proximal AP-2 site overlaps with the NFkappaB-binding site known to be essential for SAA1 promoter activity. Protein binding competition experiments demonstrated that AP-2 and NFkappaB binding to these overlapping sites were mutually exclusive. Furthermore, the addition of AP-2 easily displaced prebound NFkappaB, whereas NFkappaB could not displace AP-2. These results thus suggest that one mechanism by which AP-2 negatively regulates SAA1 promoter activity may be by antagonizing the function of NFkappaB. Consistent with a repression function, transient expression of AP-2 in HepG2 cells inhibited conditioned medium-induced SAA1 promoter activation. This inhibition was dependent on functional AP-2-binding sites, since mutation of AP-2-binding sites abolished inhibitory effects of AP-2 in HepG2 cells as well as resulted in derepression of the SAA1 promoter in HeLa cells. In addition to SAA1, we found that several other liver gene promoters also contain putative AP-2-binding sites. Some of these sequences could specifically inhibit AP-2.DNA complex formation, and for the human complement C3 promoter, overexpression of AP-2 also could repress its cytokine-mediated activation. Finally, stable expression of AP-2 in hepatoma cells significantly reduced the expression of endogenous SAA, albumin, and alpha-fetoprotein genes. Taken together, our results suggest that AP-2 may function as a transcription repressor to inhibit the expression of not only SAA1 gene but also other liver genes in nonhepatic cells.

The minimal promoter of the human alpha 3 nicotinic receptor subunit gene. Molecular and functional characterization

The minimal promoter of the human alpha(3) nicotinic receptor subunit gene has been mapped to a region of 60 base pairs and found to contain two Sp1 sites, one of which is essential for promoter activity. DNase footprinting has revealed the presence of another region of interaction with nuclear factors (named F2) immediately downstream of the Sp1 sites. This region has been found to be functional since it is capable of stimulating the minimal promoter. The F2 protection is completely and specifically competed by an AP2 consensus oligonucleotide that has been proved to bind AP2alpha exclusively. However, the AP2alpha recombinant protein was unable to bind the F2 region directly, thus suggesting that AP2alpha may participate in F2 protection by protein-protein interactions with other nuclear factors. The minimal promoter has been shown to be stimulated by two additional regions, one located downstream of F2 and the other upstream of the minimal promoter itself. In neuronal cells, the combined stimulatory activities of these three regions have synergistic effects, whereas in non-neuronal cells, there is a negative interference between the upstream and downstream regions. These opposite transcriptional effects may account for at least part of the neuro-specific expression profile of the alpha(3) gene.

Tau promoter confers neuronal specificity and binds Sp1 and AP-2

Tau, a microtubule-associated protein, is encoded by a single gene, whose expression is primarily neuronal. In this work, we defined an 80-bp region of the tau promoter that confers tau protein with neuronal expression. This fragment works in conjunction with an endogenous initiation region to activate neuronal precursor-specific transcription of the tau promoter and works independently of this initiation region to confer nerve growth factor inducibility. Furthermore, this 80-bp fragment binds both Sp1 and AP-2 proteins. DNase I foot-print analysis revealed a third protein binding region at the center of this 80-bp fragment in neuronal cells. Mutation within any of these three protein binding sites decreases transcriptional activation of the tau gene. Comprehension of the interactions that occur between cis- and trans-regulatory elements of the tau promoter is important to understand the regulation of tau expression during normal development and changes that may occur in many cases of dementia, including Alzheimer's disease.

Differential expression of retinoic acid-inducible (Stra) genes during mouse placentation

Several retinoid binding proteins and nuclear receptors are specifically expressed in murine placenta. However, little is known about molecular events and target genes regulated by retinoids during placentation. Here, we report that several retinoic acid-inducible (Stra) genes, originally isolated by a differential screening procedure, exhibit specific expression patterns in mouse placental tissues. Three Stra genes, including the ephrinB1 receptor tyrosine kinase ligand, are prominently expressed in the regions of exchanges between maternal and embryonic circulations, i.e. the yolk sac and/or the labyrinthine zone of the mature placenta. The Meis2 homeobox gene appears to be specifically expressed in maternally-derived cell populations. Three other Stra genes, including the AP-2-related gene AP-2gamma, are differentially expressed in the trophoblastic cell lineage. Thus, retinoids may regulate various signaling pathways in specific placental cell-types.

Sp1-like proteins function in the transcription of human ferredoxin genes

We characterized a regulatory element located in the -76 to -62 region of the human ferredoxin gene. This region bound to Sp1-like proteins with low affinity, as shown using electrophoretic mobility shift, competition, antibody binding, and Southwestern experiments. The similarity of the regulatory element to Sp1 extends beyond its DNA-binding domain, as cloned Sp1 functioned equally well when fused to a peptide that bound to an irrelevant site. The function of these Sp1-binding sites is mediated through the cAMP-dependent protein kinase (PKA) signaling pathway, because reporter genes downstream of the Sp1-binding sites were not activated in a PKA-deficient cell line. Transfection of the catalytic subunit of PKA restored activated transcription. Similar Sp1-binding sites identified in the CYP11A1 and CYP21 genes also controlled cAMP-dependent transcription of the reporter gene. Our finding of the function of Sp1-like proteins in steroidogenic gene transcription adds one more role Sp1 plays in controlling physiological events.