Regulation of transcription factor AP-2 by the morphogen retinoic acid and by second messengers

TFAP2 paralogs regulate midfacial development in part through a conserved ALX genetic pathway

Cranial neural crest development is governed by positional gene regulatory networks (GRNs). Fine-tuning of the GRN components underlies facial shape variation, yet how those networks in the midface are connected and activated remain poorly understood. Here, we show that concerted inactivation of Tfap2a and Tfap2b in the murine neural crest, even during the late migratory phase, results in a midfacial cleft and skeletal abnormalities. Bulk and single-cell RNA-seq profiling reveal that loss of both TFAP2 family members dysregulates numerous midface GRN components involved in midface morphogenesis, patterning and differentiation. Notably, Alx1, Alx3 and Alx4 (ALX) transcript levels are reduced, whereas ChIP-seq analyses suggest TFAP2 family members directly and positively regulate ALX gene expression. Tfap2a, Tfap2b and ALX co-expression in midfacial neural crest cells of both mouse and zebrafish implies conservation of this regulatory axis across vertebrates. Consistent with this notion, tfap2a zebrafish mutants present with abnormal alx3 expression patterns, Tfap2a binds ALX loci and tfap2a-alx3 genetic interactions are observed. Together, these data demonstrate TFAP2 paralogs regulate vertebrate midfacial development in part by activating expression of ALX transcription factor genes.

TFAP2 paralogs regulate midfacial development in part through a conserved ALX genetic pathway

Cranial neural crest development is governed by positional gene regulatory networks (GRNs). Fine-tuning of the GRN components underly facial shape variation, yet how those in the midface are connected and activated remain poorly understood. Here, we show that concerted inactivation of Tfap2a and Tfap2b in the murine neural crest even during the late migratory phase results in a midfacial cleft and skeletal abnormalities. Bulk and single-cell RNA-seq profiling reveal that loss of both Tfap2 members dysregulated numerous midface GRN components involved in midface fusion, patterning, and differentiation. Notably, Alx1/3/4 (Alx) transcript levels are reduced, while ChIP-seq analyses suggest TFAP2 directly and positively regulates Alx gene expression. TFAP2 and ALX co-expression in midfacial neural crest cells of both mouse and zebrafish further implies conservation of this regulatory axis across vertebrates. Consistent with this notion, tfap2a mutant zebrafish present abnormal alx3 expression patterns, and the two genes display a genetic interaction in this species. Together, these data demonstrate a critical role for TFAP2 in regulating vertebrate midfacial development in part through ALX transcription factor gene expression.

Overexpression of Tfap2a in Mouse Oocytes Impaired Spindle and Chromosome Organization

Transcription factor AP-2-alpha (Tfap2a) is an important sequence-specific DNA-binding protein that can regulate the transcription of multiple genes by collaborating with inducible viral and cellular enhancer elements. In this experiment, the expression, localization, and functions of Tfap2a were investigated in mouse oocytes during maturation. Overexpression via microinjection of Myc-Tfap2a mRNA into the ooplasm, immunofluorescence, and immunoblotting were used to study the role of Tfap2a in mouse oocyte meiosis. According to our results, Tfap2a plays a vital role in mouse oocyte maturation. Levels of Tfap2a in GV oocytes of mice suffering from type 2 diabetes increased considerably. Tfap2a was distributed in both the ooplasm and nucleoplasm, and its level gradually increased as meiosis resumption progressed. The overexpression of Tfap2a loosened the chromatin, accelerated germinal vesicle breakdown (GVBD), and blocked the first polar body extrusion 14 h after maturation in vitro. The width of the metaphase plate at metaphase I stage increased, and the spindle and chromosome organization at metaphase II stage were disrupted in the oocytes by overexpressed Tfap2a. Furthermore, Tfap2a overexpression dramatically boosted the expression of p300 in mouse GV oocytes. Additionally, the levels of pan histone lysine acetylation (Pan Kac), histone H4 lysine 12 acetylation (H4K12ac), and H4 lysine 16 acetylation (H4K16ac), as well as pan histone lysine lactylation (Pan Kla), histone H3 lysine18 lactylation (H3K18la), and H4 lysine12 lactylation (H4K12la), were all increased in GV oocytes after Tfap2a overexpression. Collectively, Tfap2a overexpression upregulated p300, increased the levels of histone acetylation and lactylation, impeded spindle assembly and chromosome alignment, and ultimately hindered mouse oocyte meiosis.

Allele-specific expression reveals genes with recurrent cis-regulatory alterations in high-risk neuroblastoma

BACKGROUND

Neuroblastoma is a pediatric malignancy with a high frequency of metastatic disease at initial diagnosis. Neuroblastoma tumors have few recurrent protein-coding mutations but contain extensive somatic copy number alterations (SCNAs) suggesting that mutations that alter gene dosage are important drivers of tumorigenesis. Here, we analyze allele-specific expression in 96 high-risk neuroblastoma tumors to discover genes impacted by cis-acting mutations that alter dosage.

RESULTS

We identify 1043 genes with recurrent, neuroblastoma-specific allele-specific expression. While most of these genes lie within common SCNA regions, many of them exhibit allele-specific expression in copy neutral samples and these samples are enriched for mutations that are predicted to cause nonsense-mediated decay. Thus, both SCNA and non-SCNA mutations frequently alter gene expression in neuroblastoma. We focus on genes with neuroblastoma-specific allele-specific expression in the absence of SCNAs and find 26 such genes that have reduced expression in stage 4 disease. At least two of these genes have evidence for tumor suppressor activity including the transcription factor TFAP2B and the protein tyrosine phosphatase PTPRH.

CONCLUSIONS

In summary, our allele-specific expression analysis discovers genes that are recurrently dysregulated by both large SCNAs and other cis-acting mutations in high-risk neuroblastoma.

Isotretinoin and Thalidomide Down-Regulate c-MYC Gene Expression and Modify Proteins Associated with Cancer in Hepatic Cells

Hepatocellular carcinoma (HCC) is the most common form of liver cancer. The number of cases is increasing and the trend for the next few years is not encouraging. HCC is usually detected in the advanced stages of the disease, and pharmacological therapies are not entirely effective. For this reason, it is necessary to search for new therapeutic options. The objective of this work was to evaluate the effect of the drugs isotretinoin and thalidomide on c-MYC expression and cancer-related proteins in an HCC cellular model. The expression of c-MYC was measured using RT-qPCR and western blot assays. In addition, luciferase activity assays were performed for the c-MYC promoters P1 and P2 using recombinant plasmids. Dose-response-time analyses were performed for isotretinoin or thalidomide in cells transfected with the c-MYC promoters. Finally, a proteome profile analysis of cells exposed to these two drugs was performed and the results were validated by western blot. We demonstrated that in HepG2 cells, isotretinoin and thalidomide reduced c-MYC mRNA expression levels, but this decrease in expression was linked to the regulation of P1 and P1-P2 c-MYC promoter activity in isotretinoin only. Thalidomide did not exert any effect on c-MYC promoters. Also, isotretinoin and thalidomide were capable of inducing and repressing proteins associated with cancer. In conclusion, isotretinoin and thalidomide down-regulate c-MYC mRNA expression and this is partially due to P1 or P2 promoter activity, suggesting that these drugs could be promising options for modulating the expression of oncogenes and tumor suppressor genes in HCC.

miR-142-5p promotes renal cell tumorigenesis by targeting TFAP2B

The transcription factor AP-2 β (TFAP2B) serves an important role in kidney development. MicroRNAs (miRNAs) regulate carcinogenic pathways and have gained increasing attention owing to their association with human clear cell renal cell carcinoma (ccRCC) tumorigenesis. However, whether miRNAs could affect renal cell tumorigenesis by regulating TFAP2B expression has not been identified. The aim of this study was to investigate the effects of miRNA on TFAP2B and its potential role in cell growth, invasion and migration. PCR, western blot and dual luciferase reporter assays were performed to analyze the effects of miR-142-5p on TFAP2B. Furthermore, MTT, flow cytometry, wound healing and Transwell migration assays were used to analyze the effect of miR-142-5p on cell proliferation and migration. The results demonstrated that miR-142-5p targeted TFAP2B and downregulated the expression of TFAP2B at the mRNA and protein levels, promoting cell proliferation and migration in two ccRCC cell lines, 786-O and A-498. This phenomenon supported the theory that miR-142-5p may function as an oncogene in ccRCC. The potential clinical significance of miR-142-5p as a biomarker and a therapeutic target provides rationale for further investigation into miR-142-5p-mediated molecular pathways and how these may be associated with ccRCC development.

HIPSTR and thousands of lncRNAs are heterogeneously expressed in human embryos, primordial germ cells and stable cell lines

Eukaryotic genomes are transcribed into numerous regulatory long non-coding RNAs (lncRNAs). Compared to mRNAs, lncRNAs display higher developmental stage-, tissue-, and cell-subtype-specificity of expression, and are generally less abundant in a population of cells. Despite the progress in single-cell-focused research, the origins of low population-level expression of lncRNAs in homogeneous populations of cells are poorly understood. Here, we identify HIPSTR (Heterogeneously expressed from the Intronic Plus Strand of the TFAP2A-locus RNA), a novel lncRNA gene in the developmentally regulated TFAP2A locus. HIPSTR has evolutionarily conserved expression patterns, its promoter is most active in undifferentiated cells, and depletion of HIPSTR in HEK293 and in pluripotent H1_BP cells predominantly affects the genes involved in early organismal development and cell differentiation. Most importantly, we find that HIPSTR is specifically induced and heterogeneously expressed in the 8-cell-stage human embryos during the major wave of embryonic genome activation. We systematically explore the phenomenon of cell-to-cell variation of gene expression and link it to low population-level expression of lncRNAs, showing that, similar to HIPSTR, the expression of thousands of lncRNAs is more highly heterogeneous than the expression of mRNAs in the individual, otherwise indistinguishable cells of totipotent human embryos, primordial germ cells, and stable cell lines.

Transcription factor activating protein 2 beta (TFAP2B) mediates noradrenergic neuronal differentiation in neuroblastoma

Neuroblastoma is an embryonal pediatric tumor that originates from the developing sympathetic nervous system and shows a broad range of clinical behavior, ranging from fatal progression to differentiation into benign ganglioneuroma. In experimental neuroblastoma systems, retinoic acid (RA) effectively induces neuronal differentiation, and RA treatment has been therefore integrated in current therapies. However, the molecular mechanisms underlying differentiation are still poorly understood. We here investigated the role of transcription factor activating protein 2 beta (TFAP2B), a key factor in sympathetic nervous system development, in neuroblastoma pathogenesis and differentiation. Microarray analyses of primary neuroblastomas (n = 649) demonstrated that low TFAP2B expression was significantly associated with unfavorable prognostic markers as well as adverse patient outcome. We also found that low TFAP2B expression was strongly associated with CpG methylation of the TFAP2B locus in primary neuroblastomas (n = 105) and demethylation with 5-aza-2'-deoxycytidine resulted in induction of TFAP2B expression in vitro, suggesting that TFAP2B is silenced by genomic methylation. Tetracycline inducible re-expression of TFAP2B in IMR-32 and SH-EP neuroblastoma cells significantly impaired proliferation and cell cycle progression. In IMR-32 cells, TFAP2B induced neuronal differentiation, which was accompanied by up-regulation of the catecholamine biosynthesizing enzyme genes DBH and TH, and down-regulation of MYCN and REST, a master repressor of neuronal genes. By contrast, knockdown of TFAP2B by lentiviral transduction of shRNAs abrogated RA-induced neuronal differentiation of SH-SY5Y and SK-N-BE(2)c neuroblastoma cells almost completely. Taken together, our results suggest that TFAP2B is playing a vital role in retaining RA responsiveness and mediating noradrenergic neuronal differentiation in neuroblastoma.

CRABP1 is associated with a poor prognosis in breast cancer: adding to the complexity of breast cancer cell response to retinoic acid

Background

Clinical trials designed to test the efficacy of retinoic acid (RA) as an adjuvant for the treatment of solid cancers have been disappointing, primarily due to RA resistance. Estrogen receptor (ER)-negative breast cancer cells are more resistant to RA than ER-positive cells. The expression and subcellular distribution of two RA-binding proteins, FABP5 and CRABP2, has already been shown to play critical roles in breast cancer cell response to RA. CRABP1, a third member of the RA-binding protein family, has not previously been investigated as a possible mediator of RA action in breast cancer.

Methods

CRABP1 and CRABP2 expression in primary breast tumor tissues was analyzed using gene expression and tissue microarrays. CRABP1 levels were manipulated using siRNAs and by transient overexpression. RA-induced subcellular translocation of CRABPs was examined by immunofluorescence microscopy and immunoblotting. RA-induced transactivation of RAR was analyzed using a RA response element (RARE)-driven luciferase reporter system. Effects of CRABP1 expression and RA treatment on downstream gene expression were investigated by semi-quantitative RT-PCR analysis.

Results

Compared to normal mammary tissues, CRABP1 expression is significantly down-regulated in ER+ breast tumors, but maintained in triple-negative breast cancers. Elevated CRABP1 levels are associated with poor patient prognosis, high Ki67 immunoreactivity and high tumor grade in breast cancer. The prognostic significance of CRABP1 is attributed to its cytoplasmic localization. We demonstrate that CRABP1 expression attenuates RA-induced cell growth arrest and inhibits RA signalling in breast cancer cells by sequestering RA in the cytoplasm. We also show that CRABP1 affects the expression of genes involved in RA biosynthesis, trafficking and metabolism.

Conclusions

CRABP1 is an adverse factor for clinical outcome in triple-negative breast cancer and a potent inhibitor of RA signalling in breast cancer cells. Our data indicate that CRABP1, in conjunction with previously identified CRABP2 and FABP5, plays a key role in breast cancer cell response to RA. We propose that these three RA-binding proteins can serve as biomarkers for predicting triple-negative breast cancer response to RA, with elevated levels of either cytoplasmic CRABP1 or FABP5 associated with RA resistance, and elevated levels of nuclear CRABP2 associated with sensitivity to RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0380-7) contains supplementary material, which is available to authorized users.

Transcriptional regulation and its misregulation in Alzheimer's disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by loss of memory and cognitive function. A key neuropathological event in AD is the accumulation of amyloid-β (Aβ) peptide. The production and clearance of Aβ in the brain are regulated by a large group of genes. The expression levels of these genes must be fine-tuned in the brain to keep Aβ at a balanced amount under physiological condition. Misregulation of AD genes has been found to either increase AD risk or accelerate the disease progression. In recent years, important progress has been made in uncovering the regulatory elements and transcriptional factors that guide the expression of these genes. In this review, we describe the mechanisms of transcriptional regulation for the known AD genes and the misregualtion that leads to AD susceptibility.

Analyses of GATA4, NKX2.5, and TFAP2B genes in subjects from southern China with sporadic congenital heart disease

BACKGROUND

Congenital heart disease is the most common birth defect in newborns in southern China. The germline mutations in GATA4, NKX2.5, and TFAP2B genes have been identified to be responsible for congenital heart disease. The frequency of GATA4, NKX2.5, and TFAP2B mutations in subjects with congenital heart disease in southern China and the correlation between their genotype and congenital heart disease phenotype are not known.

METHODS

We screened germline mutations in the coding exons and the flanking intron sequences of the GATA4, NKX2.5, and TFAP2B genes in 224 congenital heart disease patients located in southern China by denaturing high-performance liquid chromatography and DNA sequencing.

RESULTS

Fifteen heterozygous mutations in the GATA4 gene were identified in 30 congenital heart disease patients, including a novel heterozygous missense mutation (c.788 C>G) of GATA4 in one patient with ventricular septal defect. A novel TFAP2B mutation (c.31 A>G) in a patient with endocardial cushion defect and an unreported novel TFAP2B variant (c.1006 G>A) in six patients suffering from tetralogy of Fallot (one patient), persistent truncus arteriosus (two patients) and patent ductus arteriosus (three patients) was found. There were no reported NKX2.5 mutations except for several single nucleotide polymorphisms in the patients.

CONCLUSION

These results suggest that genomic GATA4 and TFAP2B missense mutations may be associated with nonfamilial congenital heart disease with diverse clinical phenotypes in patients with congenital heart disease from southern China. They also revealed that the variation of the NKX2.5 gene may not be a risk factor for sporadic patients with congenital heart disease in this population.

Transcriptional repression of the α7 nicotinic acetylcholine receptor subunit gene (CHRNA7) by activating protein-2α (AP-2α)

The CHRNA7 gene, which encodes the α7 nicotinic acetylcholine receptor (α7*nAChR), has been implicated as a candidate gene in schizophrenia. Expression of the α7*nAChR mRNA and protein are reduced in multiple regions of post-mortem brain from patients diagnosed with schizophrenia. Transcriptional regulation may therefore be an important mechanism for the regulation of this gene. A 230-bp proximal promoter fragment, necessary for transcription in cultured neuroblastoma cells, was used to study a putative AP-2α binding site. Mutation of the site indicates that AP-2α plays a negative role in regulating CHRNA7 transcription. This was confirmed through knockdown and overexpression of AP-2α. Electrophoretic mobility shift assays (EMSAs) identified positive DNA-protein interaction at this same site, and supershift assays indicate that the complex includes AP-2α. The interaction was confirmed in cells using chromatin immunoprecipitation (ChIP). DNA methylation was discovered as an anomalous mechanism for CHRNA7 regulation in one cell line. These studies suggest a role for AP-2α regulation of CHRNA7 mRNA expression in multiple tissues during development.

SOX10 directly modulates ERBB3 transcription via an intronic neural crest enhancer

Background

The ERBB3 gene is essential for the proper development of the neural crest (NC) and its derivative populations such as Schwann cells. As with all cell fate decisions, transcriptional regulatory control plays a significant role in the progressive restriction and specification of NC derived lineages during development. However, little is known about the sequences mediating transcriptional regulation of ERBB3 or the factors that bind them.

Results

In this study we identified three transcriptional enhancers at the ERBB3 locus and evaluated their regulatory potential in vitro in NC-derived cell types and in vivo in transgenic zebrafish. One enhancer, termed ERBB3_MCS6, which lies within the first intron of ERBB3, directs the highest reporter expression in vitro and also demonstrates epigenetic marks consistent with enhancer activity. We identify a consensus SOX10 binding site within ERBB3_MCS6 and demonstrate, in vitro, its necessity and sufficiency for the activity of this enhancer. Additionally, we demonstrate that transcription from the endogenous Erbb3 locus is dependent on Sox10. Further we demonstrate in vitro that Sox10 physically interacts with that ERBB3_MCS6. Consistent with its in vitro activity, we also show that ERBB3_MCS6 drives reporter expression in NC cells and a subset of its derivative lineages in vivo in zebrafish in a manner consistent with erbb3b expression. We also demonstrate, using morpholino analysis, that Sox10 is necessary for ERBB3_MCS6 expression in vivo in zebrafish.

Conclusions

Taken collectively, our data suggest that ERBB3 may be directly regulated by SOX10, and that this control may in part be facilitated by ERBB3_MCS6.

AP2alpha is essential for MUC8 gene expression in human airway epithelial cells

Mucins are high molecular weight proteins that make up the major components of mucus. Hypersecretion of mucus is a feature of several chronic inflammatory airway diseases. MUC8 is an important component of airway mucus, and its gene expression is upregulated in nasal polyp epithelium. Little is known about the molecular mechanisms of MUC8 gene expression. We first observed overexpression of activator protein-2 alpha (AP2 alpha) in human nasal polyp epithelium. We hypothesized that AP2 alpha overexpression in nasal polyp epithelium correlates closely with MUC8 gene expression. We demonstrated that phorbol 12-myristate 13-acetate (PMA) treatment of the airway epithelial cell line NCI-H292 increases MUC8 gene and AP2 alpha expression. In this study, we sought to determine which signal pathway is involved in PMA-induced MUC8 gene expression. The results show that the protein kinase C and mitogen-activating protein/ERK kinase (MAPK) pathways modulate MUC8 gene expression. PD98059 or ERK1/2 siRNA and RO-31-8220 or PKC siRNA significantly suppress AP2 alpha as well as MUC8 gene expression in PMA-treated cells. To verify the role of AP2 alpha, we specifically knocked down AP2 alpha expression with siRNA. A significant AP2 alpha knock-down inhibited PMA-induced MUC8 gene expression. While dominant negative AP2 alpha decreased PMA-induced MUC8 gene expression, overexpressing wildtype AP2 alpha increased MUC8 gene expression. Furthermore, using lentiviral vectors for RNA interference in human nasal polyp epithelial cells, we confirmed an essential role for AP2 alpha in MUC8 gene expression. From these results, we concluded that PMA induces MUC8 gene expression through a mechanism involving PKC, ERK1/2, and AP2 alpha activation in human airway epithelial cells.

Involvement of transcription factor NR2F2 in human trophoblast differentiation

Background

During the in vitro differentiation of human villous cytotrophoblast (CTB) cells to a syncytiotrophoblast (STB) phenotype, mRNA levels for the nuclear hormone receptor NR2F2 (ARP-1, COUP-TFII) increase rapidly, reaching a peak at day 1 of differentiation that is 8.8-fold greater than that in undifferentiated CTB cells. To examine whether NR2F2 is involved in the regulation of villous CTB cell differentiation, studies were performed to determine whether NR2F2 regulates the expression of TFAP2A (AP-2α), a transcription factor that is critical for the terminal differentiation of these cells to a STB phenotype.

Methodology/Primary Findings

Overexpression of NR2F2 in primary cultures of human CTB cells and JEG-3 human choriocarcinoma cells induced dose-dependent increases in TFAP2A promoter activity. Conversely, siRNA mediated silencing of the NR2F2 gene in villous CTB undergoing spontaneous differentiation blocked the induction of the mRNAs for TFAP2A and several STB cell specific marker genes, including human placental lactogen (hPL), pregnancy specific glycoprotein 1 (PSG1) and corticotropin releasing hormone (CRH) by 51–59%. The induction of TFAP2A promoter activity by NR2F2 was potentiated by the nuclear hormone receptors retinoic acid receptor alpha (RARA) and retinoid X receptor alpha (RXRA).

Conclusions/Significance

Taken together, these results strongly suggest that NR2F2 is involved in villous CTB cell differentiation and that NR2F2 acts, at least in part, by directly activating TFAP2A gene expression and by potentiating the transactivation of TFAP2A by RARA and RXRA.

Roles of AP-2 transcription factors in the regulation of cartilage and skeletal development

During embryogenesis, most of the mammalian skeletal system is preformed as cartilaginous structures that ossify later. The different stages of cartilage and skeletal development are well described, and several molecular factors are known to influence the events of this enchondral ossification, especially transcription factors. Members of the AP-2 family of transcription factors play important roles in several cellular processes, such as apoptosis, migration and differentiation. Studies with knockout mice demonstrate that a main function of AP-2s is the suppression of terminal differentiation during embryonic development. Additionally, the specific role of these molecules as regulators during chondrogenesis has been characterized. This review gives an overview of AP-2s, and discusses the recent findings on the AP-2 family, in particular AP-2alpha, AP-2beta, and AP-2epsilon, as regulators of cartilage and skeletal development.

The transcriptional regulation and cell-specific expression of the MAPK-activated protein kinase MK5

The mitogen-activated protein kinase (MAPK) cascades regulate important cellular processes, including growth, differentiation, apoptosis, embryogenesis, motility and gene expression. Although MAPKs mostly appear to be constitutively expressed, the transcript levels of some MAPK-encoding genes increase upon treatment with specific stimuli. This applies to the MAPKactivated protein kinases MK2 and MK3. By contrast, the transcriptional regulation of the related MK5 has not yet been studied. The MK5 promoters of mouse, rat and human contain a plethora of putative transcription factor sites, and the spatio-temporal expression of MK5 suggests inducible transcription of the gene. We examined the transcription pattern of MK5 in different tissues, and studied the kinetics of MK5 expression at the transcriptional and/or translation level in PC12 cells exposed to arsenite, forskolin, KCl, lipopolysaccharide, spermine NONOate, retinoic acid, serum, phorbol ester, temperature shock, and vanadate. Cells exposed to forskolin display a transient increase in MK5 mRNA, despite their unaltered MK5 protein levels. The MK5 promoters of human, mouse and rat contain a cAMP-responsive element that binds the cAMPresponsive element-binding protein (CREB) in vitro. Luciferase reporter constructs containing an 850-base pair human MK5 promoter fragment encompassing the CRE showed a basal activity that was 10-fold higher than the corresponding construct in which the CRE motif was deleted. siRNA-mediated depletion of CREB had no effect on the endogenous MK5 protein levels. Several binding motifs for heat shock factor are dispersed in the mouse and rat promoter, and temperature shock transiently enhanced the MK5 transcript levels. None of the other tested stimuli had an effect on the MK5 mRNA or protein levels. Our results indicate an inducible regulation of MK5 transcription in response to specific stimuli. However, the MK5 protein levels remained unaffected by all the stimuli tested. There is still no explanation for the discrepancy between the increased mRNA and unchanged MK5 protein levels.

Disruption of epidermal specific gene expression and delayed skin development in AP-2 gamma mutant mice

Summary Sentence: Conditional ablation of AP-2 gamma results in a delay in skin development and abnormal expression of p63, K14, K1, filaggrin, repetin and secreted Ly6/Plaur domain containing 1, key genes required for epidermal development and differentiation. The development of the epidermis, a stratified squamous epithelium, is dependent on the regulated differentiation of keratinocytes. Differentiation begins with the initiation of stratification, a process tightly controlled through proper gene expression. AP-2 gamma is expressed in skin and previous research suggested a pathway where p63 gene induction results in increased expression of AP-2 gamma, which in turn is responsible for induction of K14. This study uses a conditional gene ablation model to further explore the role of AP-2 gamma in skin development. Mice deficient for AP-2 gamma exhibited delayed expression of p63, K14, and K1, key genes required for development and differentiation of the epidermis. In addition, microarray analysis of E16.5 skin revealed delayed expression of additional late epidermal differentiation genes: filaggrin, repetin and secreted Ly6/Plaur domain containing 1, in mutant mice. The genetic delay in skin development was further confirmed by a functional delay in the formation of an epidermal barrier. These results document an important role for AP-2 gamma in skin development, and reveal the existence of regulatory factors that can compensate for AP-2 gamma in its absence.

Activator protein-2 in carcinogenesis with a special reference to breast cancer-A mini review

Activator protein-2 (AP-2) transcription factors are involved in the regulation of cell proliferation, differentiation, apoptosis and carcinogenesis. AP-2alpha has been suggested to function as a tumor suppressor in many cancers and AP-2gamma to be a marker of testicular and germ cell malignancies. At least 3 of the 5 AP-2 family members identified to date, AP-2alpha, AP-2beta and AP-2gamma, are known to be expressed in breast tissue and thought to coordinate the growth and development of the breast via regulation of several breast-related genes such as human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER). The function of AP-2alpha seems to be tumor suppressive in breast tissue, whereas the role of the other AP-2 family members is less well known. In this review, we summarize the current knowledge of AP-2 in carcinogenesis, especially in breast cancer.

Nucleophosmin acts as a novel AP2alpha-binding transcriptional corepressor during cell differentiation

Nucleophosmin (NPM) is an important nucleolar phosphoprotein with pleiotropic functions in various cellular processes. In this study, we have further examined the largely uncharacterized role of NPM in transcriptional regulation by uncovering novel NPM-binding transcriptional factors. Among potential interactors, we found that activating protein transcription factor 2 (AP2)alpha forms a complex with NPM during retinoic-acid-induced cell differentiation. We show that this complex is recruited to the promoters of certain retinoic-acid-responsive genes, including NPM itself. Such binding of AP2alpha, and consequent recruitment of NPM, is selective and dependent on a consensus AP2alpha-binding sequence. Remarkably, suppression of NPM by RNA interference alleviates the repression of gene expression mediated by retinoic acid and AP2alpha. Our findings further show that, on promoter binding, NPM probably exerts its repressive effect by inducing a change in local chromatin structure that also engages histone deacetylases. This study unveils a hitherto unrecognized transcriptional corepressor function of the NPM protein, and highlights a novel mechanism by which NPM regulates cell growth and differentiation.

Frontal nasal prominence expression driven by Tcfap2a relies on a conserved binding site for STAT proteins

The AP-2 transcription factor family is linked with development of the head and limbs in both vertebrate and invertebrate species. Recent evidence has also implicated this gene family in the evolution of the neural crest in chordates, a critical step that allowed the development and elaboration of the vertebrate craniofacial skeleton. In mice, the inappropriate embryonic expression of one particular AP-2 gene, Tcfap2a, encoding AP-2alpha, results in multiple developmental abnormalities, including craniofacial and limb defects. Thus, Tcfap2a provides a valuable genetic resource to analyze the regulatory hierarchy responsible for the evolution and development of the face and limbs. Previous studies have identified a 2-kilobase intronic region of both the mouse and human AP-2alpha locus that directs expression of a linked LacZ transgene to the facial processes and the distal mesenchyme of the limb bud in transgenic mice. Further analysis identified two highly conserved regions of approximately 200-400 bp within this tissue-specific enhancer. We have now initiated a transgenic and biochemical analysis of the most important of these highly conserved regions. Our analysis indicates that although the sequences regulating face and limb expression have been integrated into a single enhancer, different cis-acting sequences ultimately control these two expression domains. Moreover, these studies demonstrate that a conserved STAT binding site provides a major contribution to the expression of Tcfap2a in the facial prominences.

Apoptosis induction by activator protein 2alpha involves transcriptional repression of Bcl-2

Activator protein 2alpha (AP-2alpha) induces cytotoxicity by inducing cell cycle arrest and apoptosis. In this study we investigated the mechanism of apoptosis induction by AP-2alpha. We found that AP-2alpha induced apoptosis efficiently in cells treated with benzyloxycar-bonyl-IETD-fluoromethyl ketone or FADD-silenced cells but failed to do so in benzyloxycarbonyl-LEHD-fluoromethyl ketone-treated or apoptosis protease activation factor-1 (Apaf1)-silenced cells, suggesting the central role of mitochondria in AP-2alpha-induced apoptosis. In good correlation, cells overexpressing AP-2alpha showed a reduction in mitochondrial membrane potential (Deltapsi(m)), cytochrome c and Smac/DIABLO release into cytosol, and Bax translocation into mitochondria. We found that the pro-apoptotic protein Bax is important for AP-2alpha-induced apoptosis as adenovirus AP2 failed to induce apoptosis in HCT116 Bax(-/-) cells. However, we found the IAP (inhibitor of apoptosis) inhibitor Smac/DIABLO may have a limited role in AP-2alpha-induced apoptosis as we found the IAP member Survivin down-regulated by AP-2alpha. Although the total Bax level remains unaltered, we found a time-dependent increase in the activated form of Bax in adenovirus AP2-infected cells. In addition, we show that AP-2alpha transcriptionally represses Bcl-2 by binding to its promoter both in vitro and in vivo and that this is essential for AP-2alpha-induced apoptosis as ectopic expression of Bcl-2 efficiently inhibited apoptosis induced by AP-2alpha. Furthermore, we show that chemotherapy-induced endogenous AP-2alpha down-regulates Bcl-2 and induces apoptosis in an AP-2alpha-dependent manner. Moreover, we demonstrate that inhibition of okadaic acid or staurosporine-sensitive pathways in AP-2alpha overexpressing breast cancer cells resulted in AP-2alpha-dependent apoptosis induction. These results suggest that AP-2alpha induces apoptosis by down-regulating Bcl-2 and utilizing a bax/cytochrome c/Apaf1/caspase 9-dependent mitochondrial pathway.

PTHrP promotes murine secondary trophoblast giant cell differentiation through induction of endocycle, upregulation of giant-cell-promoting transcription factors and suppression of other trophoblast cell types

The murine trophoblast cell lineage represents an intriguing experimental cell model as it is composed of four trophoblast stem (TS)-derived cell types: trophoblast giant cells (TGCs), spongiotrophoblast, syncytotrophoblast, and glycogen trophoblast cells. To investigate the role of parathyroid hormone-related protein (PTHrP) in TGC differentiation, we analyzed the effect of exogenous PTHrP on secondary TGCs of day 8.5 p.c. ectoplacental cone explant culture. Secondary TGCs expressed PTHrP and PTHR1 receptor in vivo and in vitro. TGCs treated with PTHrP had reduced proliferation and decreased apoptosis starting from day 2 in culture, and enhanced properties of giant cell differentiation: increased DNA synthesis, number of cells with giant nuclei and expression of placental lactogen-II (PL-II). The induction of TGC formation by PTHrP correlated with downregulation of cyclin B1 and mSNA expression, but upregulation of cyclin D1, thus allowing mitotic-endocycle transition. Moreover, PTHrP treatment influenced TGC differentiation by inducing the expression of transcription factors known to stimulate giant cell formation: Stra13 and AP-2gamma, and inhibiting the formation of other trophoblast cell types by suppressing trophoblast progenitors and spongiotrophoblast-promoting factors, Eomes, Mash-2, and mSNA. Taken together with the spatial and temporal patterns of TGC formation and PTHrP synthesis in vivo, these findings indicate an important role for PTHrP in the differentiation of secondary TGCs during placentation.

Transcription factor AP-2alpha triggers apoptosis in cardiac myocytes

Idiopathic-dilated cardiomyopathy (IDC) is a common primary myocardial disease of unknown etiology associated with apoptosis, cardiac dilatation, progressive heart failure and increased mortality. An elevation of the transcription factor activator protein 2alpha (AP-2alpha) is involved in vertebrate embryonic development and oncogenesis. Here, we show that AP-2alpha protein is expressed in the human heart and increased in human failing myocardium with IDC. Adenovirus-mediated overexpression of human AP-2alpha triggered apoptosis and increased mRNA levels of Bcl-2 family members Bax and Bcl-x in rat cardiomyocytes. Immunohistological analysis of human myocardium revealed an increased percentage of AP-2alpha-positive nuclei in IDC and, interestingly, a colocalization of AP-2alpha-positive but not -negative cells with a caspase-cleaved fragment of poly(ADP-ribose)polymerase. We suggest AP-2alpha as a novel cardiac regulator implicated in the activation of apoptosis in IDC.

Regulating fragile X gene transcription in the brain and beyond

The past several years have seen remarkable growth in our understanding of the molecular processes underlying fragile X syndrome (FXS). Many studies have provided new insights into the regulation of Fmr1 gene expression and the potential function of its protein product. It is now known that the promoter elements modulating Fmr1 transcription involve a complex array of both cis and trans factors. Moreover, recent studies of epigenetic modification of chromatin have provided novel clues to unlocking the mysteries behind the regulation of Fmr1 expression. Here, we review the latest findings on the regulation of Fmr1 transcription.

Involvement of AP-2 binding sites in regulation of human beta-glucuronidase

The lysosomal hydrolase beta-glucuronidase (beta-gluc) can be used for the bioactivation of non-toxic glucuronide prodrugs of anticancer agents. The enzyme is present at high levels in many tumours and hence may lead to an enhanced drug targeting by tumour-selective release of the active anticancer drug. Individual expression and regulation of this enzyme is one factor modulating the bioactivation of glucuronide prodrugs. Nevertheless, in contrast to murine beta-gluc, which is inducible by androgens, the human enzyme has been regarded as an unregulated housekeeping gene due to a lacking TATA box and high G+C contents within the putative promotor sequence. Despite these facts, we were able to demonstrate downregulation of human beta-gluc expression by the calcium ionophore A23187 and the calcium ATPase inhibitor thapsigargin in the human hepatoma cell line HepG2. However, cis-acting elements responsible for this regulation have not yet been identified. We therefore characterised the 5'-untranslated region of the human beta-gluc gene using transient transfection assays with promotor-luciferase constructs in HepG2 cells and cloned fragments between 3,770 bp and 107 bp. A23187 reduced the beta-gluc promotor activity. This effect disappeared using fragments smaller than 356 bp. Using site-directed in vitro mutagenesis and gel-electrophoretic-mobility shift assays, we found evidence of an involvement of transcription factor activating protein-2 (AP-2) binding sites on the regulation of human beta-glucuronidase by A23187. Our studies provide a basis for the understanding of the transcriptional regulation of the human beta-glucuronidase gene and could be useful for the optimisation of glucuronide prodrug therapy.

Transcriptional regulation by cAMP and Ca2+ links the Na+/Ca2+ exchanger 3 to memory and sensory pathways

The signaling cascades triggered by neurotrophins such as BDNF and by several neurotransmitters and hormones lead to the rapid induction of gene transcription by increasing the intracellular concentration of cAMP and Ca2+. This review examines the mechanisms by which these second messengers control transcriptional initiation at CRE promoters via transcription factor CREB, as well as at DRE sites via transcriptional repressor DREAM. The regulation of the SLC8A3 gene encoding the Na+/Ca2+ exchanger 3 (NCX3) is taken as an example to illustrate both mechanisms since it includes a CRE site in the promoter and several DRE sites in the exon 1 sequence. The upregulation of the NCX3 by Ca2+ signals may be specifically required to establish the Ca2+ balance that regulates several physiological and pathological processes in neurons. The regulatory features and the expression pattern of SLC8A3 gene suggest that NCX3 activity could be crucial in neuronal functions such as memory formation and sensory processing.

Ah receptor signals cross-talk with multiple developmental pathways

For many years, the Ah receptor (AHR) has been a favorite of toxicologists and molecular biologists studying the connections between genes and the changes in the control of gene expression resulting from environmental exposures. Much of the attention given to the Ah receptor has focused on the nature of its ligands, many of which are known or suspected carcinogens, and on the role that its best studied regulatory product, the CYP1A1 enzyme, plays in toxic responses and carcinogen activation. This understandable bias has resulted in a disproportionate amount of Ah receptor research being directed at toxicological or adaptive end points. In recent times, it has become evident that Ah receptor functions are also involved in molecular cascades that lead to inhibition of proliferation, promotion of differentiation, or apoptosis, with an important bearing in development. Developmental and toxicological AHR functions may not always be related. The ancestral AHR protein in invertebrates directs the developmental fate of a few specific neurons and does not bind xenobiotic ligands. The mammalian AHR maintains normal liver function in the absence of exogenous ligands and, when activated by dioxin, cross-talks with morphogenetic and developmental signals. Toxic end points, such as the induction of cleft palate by dioxin in mice embryos, might be at the crossroads of these signals and provide important clues as to the developmental role of the AHR.

Identification of retinoid-modulated proteins in squamous carcinoma cells using high-throughput immunoblotting

Retinoids have shown clinical efficacy in cancer chemoprevention and therapy presumably by modulating the growth, differentiation, and apoptosis of normal, premalignant, and malignant cells. To better understand the mechanisms by which retinoids exert their effects, we used a high-throughput Western blotting method (Becton-Dickinson PowerBlot) to evaluate changes in the levels of cellular signaling proteins in head and neck squamous cell carcinoma cells treated with the cytostatic all-trans-retinoic acid or with the proapoptotic retinoids 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid or N-(4-hydroxyphenyl)retinamide. Treatments of the head and neck squamous cell carcinoma cells with these retinoids for 24 h resulted in increased levels of 14, 22, and 22 proteins and decreased levels of 5, 10, and 7 proteins, respectively. The changes in the levels of the following proteins were confirmed by conventional western immunoblotting: all-trans-retinoic acid increased ELF3, topoisomerase II alpha, RB2/p130, RIG-G, and EMAPII and decreased MEF2D and cathepsin L. N-(4-Hydroxyphenyl)retinamide up-regulated ELF3, c-Jun, Rb2/p130, JAK1, p67phox, Grb2, O(6)-methylguanine-DNA methyltransferase, and Ercc-1. 6-[3-(1-Adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid increased Rb2/p130, c-Jun, Sp1, Sin, and tomosyn and decreased cathepsin L, Mre11, and topoisomerase II alpha. Some of these proteins were also modulated by these retinoids in other human cancer cell lines. A subset of the proteins were modulated similarly by the different retinoids, whereas changes in other proteins were unique for each retinoid. These results suggest that the mechanisms by which these retinoids modulate proteins are distinct but may overlap. Some of the retinoid-modulated proteins identified in this study may be novel candidates for mediating different responses to retinoids.

AP-2 and HNK-1 define distinct populations of cranial neural crest cells

OBJECTIVE

To determine if distinct populations of cranial neural crest cells (CNCC) exist by characterization of their divergent gene expression patterns.

DESIGN

Identification of unique populations of CNCC was determined by a combination of lineage and immunohistochemical analyses.

SETTING

Department of Pathology, Children's Hospital of Philadelphia and the University of Pennsylvania School of Medicine, Philadelphia, PA 19104.

RESULTS

We found antibodies of two proteins previously described as identifying all CNCC, label three populations of CNCC at specific time-points. Furthermore, the activating protein 2 (AP-2) expressing CNCC become neural or mesenchymal NCC derivatives whereas the HNK-1 labeled cells do not participate in the mesenchymal lineage.

CONCLUSION

These data provide molecular markers for unique CNCC fates and thus will be invaluable in the characterizing of craniofacial anomalies related to defects in NCCS. In addition, our data suggest AP-2 may function in determining the unique mesenchymal fate of CNCCs.

Differential regulation of chondrogenic differentiation by the serotonin2B receptor and retinoic acid in the embryonic mouse hindlimb

Retinoic acid (RA) synthesizing and metabolizing enzymes are coordinately expressed with serotonin 2B (5-HT2B) receptors at sites of epithelial-mesenchymal (E-M) interaction in the mouse embryo (Bhasin et al., 1999). The promoter of the 5-HT2B receptor contains potential RA response element (RAREs) as well as an AP-2 site. Because both retinoid and serotonergic signaling have been implicated in the regulation of chondrogenic differentiation, the present study investigated whether these signals may work together to regulate this morphogenetic process in hindlimb bud micromass cultures. Results indicate that 5-HT promotes [35S]sulfate incorporation (chondrogenic differentiation) by activation of 5-HT2B receptors, which use the mitogen activated protein kinase (p42 MAPK) signal transduction pathway, whereas RA dose-dependently inhibits sulfate incorporation and promotes expression of RARbeta, which could lead to inhibition of p38 MAPK. No evidence was found to support the possibility that RA negatively regulates expression of 5-HT2B receptors. Taken together, these results suggest that 5-HT and RA may act as opposing signals to regulate chondrogenic differentiation in the developing hindlimb, possibly mediated by different MAPK signal transduction pathways.

Noradrenergic neurons in the zebrafish hindbrain are induced by retinoic acid and require tfap2a for expression of the neurotransmitter phenotype

Tfap2a is a transcriptional activator expressed in many different cell types, including neurons, neural crest derivatives and epidermis. We show that mutations at the zebrafish locus previously called mont blanc (mob) or lockjaw (low) encode tfap2a. The mutant phenotype reveals that tfap2a is essential for the development of hindbrain noradrenergic (NA) neurons of the locus coeruleus, medulla and area postrema, as well as for sympathetic NA neurons, epibranchial placode derived visceral sensory ganglia, and craniofacial and trunk crest derivatives. We focus our analysis on the role of tfap2a NA differentiation in the CNS. In the locus coeruleus, Phox2a and Tfap2a are co-expressed and are both required for NA development. By contrast, in the medulla Phox2a and Tfap2a are expressed in adjacent overlapping domains, but only tfap2a activity is required for NA differentiation, as NA neurons develop normally in soulless/phox2a mutant medulla. phox2a and tfap2a do not appear to affect each others expression. Our studies show that two distinct inductive mechanisms control NA development in the zebrafish hindbrain. For the posterior hindbrain, we identify retinoic acid as an important signal to induce NA differentiation in the medulla oblongata and area postrema, where it expands the tfap2a expression domain and thus acts upstream of tfap2a. By contrast, previous work revealed Fgf8 to be involved in specification of NA neurons in the locus coeruleus. Thus, although the inductive signals may be distinct, hindbrain NA neurons of the locus coeruleus and the posterior groups both require Tfap2a to establish their noradrenergic identity.

Identification and regulation of tissue-specificcis-acting elements associated with the human AP-2? gene

Mice lacking transcription factor AP-2alpha exhibit defects in the formation of the head, body wall, heart, neural tube, eye, and limbs, reflecting important sites of AP-2alpha expression in the developing embryo. AP-2alpha is also expressed in the postnatal mammary gland and has been linked to tumor progression and defects in growth regulation in the breast. We have used a transgenic mouse approach to identify tissue-specific cis-acting sequences associated with expression of the human AP-2alpha gene. Our analysis indicates that multiple elements located throughout the gene contribute to expression in the trigeminal ganglia, spinal cord, mammary gland, and epidermis. A discrete cis-element located within the fifth intron is required for expression in the face and limbs, and we have derived a permanent line of AP-2alpha::lacZ transgenic mice to assess expression of this latter enhancer throughout morphogenesis. We also introduced this transgene into an AP-2alpha-null mouse background and detected subtle alterations of its expression within the progress zone and apical ectodermal ridge of the forelimbs. Similar changes in lacZ expression were observed within the zeugopod, and these correlated with defects in radius condensation in AP-2alpha-knockout mice. Taken together, these findings indicate that cell:cell communication within the forelimb is altered in the absence of AP-2alpha and reveal novel regulatory potential for AP-2alpha in limb development.

Role and regulation of the thrombin receptor (PAR-1) in human melanoma

To determine treatment strategies and predict the clinical outcome of patients with melanoma it is important to understand the etiology of this disease. Recently, there has been some insight into molecular basis of melanoma including identification of a few of the regulatory factors and genes involved in this disease. For instance, the transcription factor AP-2 plays a tumor suppressor-like role in melanoma progression by regulating genes involved in tumor growth and metastasis. Previously, we have shown that the progression of human melanoma to the metastatic phenotype is associated with loss of AP-2 expression and deregulation of target genes such as MUC18/MCAM, c-KIT, and MMP-2. Increasing evidence demonstrates that the thrombin receptor (protease-activated receptor-1, PAR-1) plays a major role in tumor invasion and contributes to the metastatic phenotype of human melanoma. This review focuses on the role of the thrombin receptor in melanoma and its regulation by AP-2. We show that loss of AP-2 expression in metastatic melanoma cells correlates with overexpression of the thrombin receptor. Our analysis of AP-2/Sp1 complexes within the regulatory region of the thrombin receptor demonstrates that AP-2 binds the proximal 3' region of the promoter and diminishes PAR-1 expression. Levels of AP-2 and Sp1 proteins in a panel of melanoma cell lines demonstrated a marked decrease in the ratio of AP-2/Sp1, a decrease that correlated with overexpression of PAR-1 in metastatic melanoma cells. We propose that loss of AP-2 results in increased expression of the thrombin receptor, which subsequently contributes to the metastatic phenotype of melanoma by upregulating the expression of adhesion molecules, proteases, and angiogenic molecules.

Regulation of lipocalin-type prostaglandin D synthase gene expression by Hes-1 through E-box and interleukin-1 beta via two NF-kappa B elements in rat leptomeningeal cells

The promoter function of the rat lipocalin-type prostaglandin D synthase (L-PGDS) gene was characterized in primary cultures of leptomeningeal cells prepared from the neonatal rat brain. Luciferase reporter assays with deletion and site-directed mutation of the promoter region (-1250 to +77) showed that an AP-2 element at -109 was required for activation and an E-box at +57, for repression. Binding of nuclear factors to each of these cis-elements was demonstrated by an electrophoretic mobility shift assay. Several components of the Notch-Hes signaling pathway, Jagged, Notch1, Notch3, and Hes-1, were expressed in the leptomeningeal cells. Human Hes-1 co-expressed in the leptomeningeal cells bound to the E-box of the rat L-PGDS gene, and repressed the promoter activity of the rat L-PGDS gene in a dose-dependent manner. The L-PGDS gene expression was up-regulated slowly by interleukin-1 beta to the maximum level at 24 h. The reporter assay with deletion and mutation revealed that two NF-kappa B elements at -1106 and -291 were essential for this up-regulation. Binding of two NF-kappa B subunits, p65 and c-Rel, to these two NF-kappa B elements occurred after the interleukin-1 beta treatment. Therefore, the L-PGDS gene is the first gene identified as the target for the Notch-Hes signal through the E-box among a variety of genes involved in the prostanoid biosynthesis, classified to the lipocalin family, and expressed in the leptomeninges. Moreover, the L-PGDS gene is a unique gene that is activated slowly by the NF-kappa B system.

Control of the Na+/Ca2+ exchanger 3 promoter by cyclic adenosine monophosphate and Ca2+ in differentiating neurons

The human gene for member 3 of solute carrier family 8 (SLC8A3), encoding the Na+/Ca2+ exchanger isoform 3 (NCX3), was identified on chromosome 14q24.2. The minimal promoter region was predicted 250 bp upstream of exon 1. This was confirmed by luciferase reporter assays of pGL3-promoter constructs in transfected SH-SY5Y cells. The promoter activity was monitored during the differentiation of this cell line elicited by the sequential treatment with retinoic acid and brain-derived neurotrophic factor (BDNF). The activity was induced by cyclic AMP (cAMP) via the CRE (cAMP response element) and was stimulated by retinoic acid. The increase of intracellular Ca2+ induced by the partial depolarization of the plasma membrane with KCl down-regulated both the basal and the cAMP-stimulated transcription. The down-regulation of the latter may be mediated by the phosphorylation of the CRE-binding protein by a calmodulin-dependent kinase (CaMKII). The exposure of cells to BDNF after treatment with retinoic acid rapidly induced promoter activity during the initial five hours and phosphorylation of CRE-binding protein during the first two hours. The promoter activity was further enhanced by cAMP, but became insensitive to Ca2+. In BDNF-stimulated cells cAMP elevation caused the preferential phosphorylation of ATF1 instead of that of CRE-binding protein.

Male-enhanced antigen-1 gene flanked by two overlapping genes is expressed in late spermatogenesis

The male-enhanced antigen-1 gene (Mea1) was originally isolated from a murine testicular cDNA library using anti-H-Y antigen antisera and was assigned to chromosome 17. On analysis of its structure and expression, we found that the Mea1 genomic sequence is flanked by two other genes: Ppp2r5d present in its 3'-terminus in a tail-to-tail orientation and a novel gene called Peas in its 5'-terminus in a head-to-head orientation. The coding sequences of the two genes embedded in the Mea1 sequence are located on the opposite DNA strands of Mea1. Cap-site analysis of Mea1 revealed that it is transcribed from at least seven sites. Most splice variants of Mea1 were abundantly expressed in the testis; the d-type was weakly expressed in the other tissues. AP-2-binding motifs were detected in the transcription-initiation sites. In situ hybridization and immunohistochemical studies revealed Mea1 expression in pachytene spermatocytes. This expression was most prominent in spermatids and residual bodies. The Mea1 protein was also localized in the cytoplasm of elongated spermatids and residual bodies. Localization of the Mea1 suggests that it may function in the very late stages of spermiogenesis. The possibility that Mea1 is one of the serologically detectable male antigens is discussed.

The role of Sp1 and AP-2 in basal and protein kinase A--induced expression of mitochondrial serine:pyruvate aminotransferase in hepatocytes

Transcription of mitochondrial serine:pyruvate aminotransferase (SPT) mRNA (SPTm-mRNA) in rat liver is unique in that it occurs from the upstream site of the two transcription start sites within the first exon of the SPT gene and is selectively enhanced by cAMP via the protein kinase A (PKA) signaling pathway. In this study, we identified the DNA elements and nuclear factors responsible for the basal and PKA-induced activities of the upstream promoter. By using a luciferase reporter assay with HepG2 cells, DNase I footprinting analysis, and gel shift experiments, we identified the binding sites for Sp1 and AP-2 within the regions -125 to -89 and -14 to +10, respectively. Mutational analyses indicated that these regions are essential for the transcription factor binding and the SPT promoter activity. Expression of AP-2 caused a marked increase in the basal promoter activity to about the same level as that achieved by PKA. On the other hand, both the basal and PKA-induced activities were elevated by overexpression of Sp1, its effect on PKA-induced activity being more pronounced with coexpression of CBP and repressed by E1A oncoprotein. These results suggest that AP-2 and Sp1 regulate basal promoter activity, and Sp1 is also involved in PKA-mediated expression of the rat SPT gene in concert with the transcriptional coactivator CBP.

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.

Transcriptional regulation of the human polymeric Ig receptor gene: analysis of basal promoter elements

Secretory Igs provide the first line of adaptive immune defense against ingested, inhaled, and sexually transmitted pathogens at mucosal surfaces. The polymeric Ig receptor regulates transport of dimeric IgA and pentameric IgM into external secretions. The level of expression of polymeric Ig receptor is controlled to a large extent by transcription of the PIGR gene in mucosal epithelial cells. Here we present a detailed analysis of the promoter of the PIGR gene by transient transfection of luciferase reporter plasmids into cultured cell lines. Comparisons of the human and mouse PIGR promoters in human and mouse intestinal and liver cell lines demonstrated that the human PIGR promoter was 4- to 5-fold more active than the mouse PIGR promoter in all cell types, and that both the human and mouse PIGR promoters were more active in intestinal than in liver cell lines. Targeted deletions of 22-bp segments of the human PIGR promoter revealed that the region from nt -63 to -84 is crucial for basal transcription, and that two upstream regions can act as positive or negative regulators. Point mutations within the region from nt -63 to -84 demonstrated that an E box motif, which binds the basic helix-loop-helix protein upstream stimulatory factor, is required for PIGR promoter activity. Two additional regulatory motifs were identified in the proximal promoter region: a binding site for AP2, and an inverted repeat motif that binds an unidentified protein. These findings suggest that cooperative binding of multiple transcription factors regulates basal activity of the human PIGR promoter.

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.

Distribution of the transcription factors Sox9, AP-2, and [delta]EF1 in adult murine articular and meniscal cartilage and growth plate

The control of extracellular matrix (ECM) production is important for the development, maintenance, and repair of cartilage tissues. Matrix molecule synthesis is generally regulated by the rate of gene transcription determined by DNA transcription factors. We have shown that transcription factors Sox9, AP-2, and [delta]EF1 are able to alter the rate of CD-RAP transcription in vitro: Sox9 upregulates, AP-2 exhibits biphasic effects, and [delta]EF1 represses expression of the CD-RAP gene. To correlate these in vitro activities in vivo, transcription factors were co-immunolocalized with ECM proteins in three different cartilage tissues in which the rates of biosynthesis are quite different: articular, meniscal, and growth plate. Immunoreactivities of type II collagen and CD-RAP were higher in growth plate than in either the articular or meniscal cartilages and correlated positively with Sox9 protein. Sox9 staining decreased with hypertrophy and was low in articular and meniscal cartilages. In contrast, AP-2 and [delta]EF1 were low in proliferating chondrocytes but high in lower growth plate, articular, and meniscal cartilages. This increase was also accompanied by intense nuclear staining. These immunohistochemical results are the first to localize both [delta]EF1 and AP-2 to adult articular, meniscal, and growth plate cartilages and provide in vivo correlation of previous molecular biological studies.

Development of gonadotropin-releasing hormone-1 neurons

Gonadotropin releasing hormone-1 (GnRH-1) neurons, critical for reproduction, are derived from the nasal placode and migrate into the brain during prenatal development. Once within the brain, GnRH-1 cells become integral components of the CNS-pituitary-gonadal axis, essential for reproductive maturation and maintenance of reproductive function in adults. This review focuses on the lineage and development of the GnRH-1 neuroendocrine system. Although the migration of these cells from nose to brain has been well documented in a variety of species, many questions remain concerning the melecules and cues directing GnRH-1 cell differentiation, migration, axon targeting, and establishment and control of GnRH-1 secretion. These process most likely involve multiple and redundant cues because if these mechanisms fail, reproduction dysfunction will ensue and guarantee that this defect does not remain in the gene pool.

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.

Regulation of the murine alpha(2)(I) collagen promoter by retinoic acid and retinoid X receptors

Retinoic acid decreases collagen production by hepatic stellate cells. This study investigated the effects of retinoic acid receptor beta (RARbeta) and retinoid X receptor alpha (RXRalpha) on the regulation of the alpha(2)(I) collagen promoter. Retinoic acid and the RARbeta and RXRalpha expression vectors suppressed the promoter in transfected stellate cells with maximal suppression obtained when combined. Mutation of the retinoic acid response element (RARE) at -879 to -874 (site 1) enhanced promoter activity and diminished but did not eliminate the suppression by RARbeta and RXRalpha. Mutation of another RARE site (site 2), at -930 to -911, resulted in low activity that was inhibited by retinoic acid. Mutation of the AP-2-binding site enhanced promoter activity that was inhibited by retinoic acid. This study shows that the suppressive effect of retinoic acid on the promoter is maximal with a combination of RARbeta and RXRalpha and occurs at more than one RARE site. The effect of retinoic acid is not mediated by AP-2.

Increased MMP-2 expression in connective tissue growth factor over-expression vascular smooth muscle cells

Connective tissue growth factor (CTGF) is abundantly expressed in the vascular smooth muscle cells (VSMC) of atherosclerotic lesions but not in normal vessels. CTGF is able to promote VSMC proliferation and migration and influences the composition of extracellular matrix. The mechanisms for controlling these events remain unclear. We studied the effects of CTGF on matrix metalloproteinases (MMPs) by introducing a CTGF over-expression construct into VSMC. We found that the over-expression of CTGF significantly increased the activity of MMP-2 in VSMC conditioned medium. MMP-2 activity was similarly increased by exogenous CTGF treatment, and this effect could be blocked by an anti-CTGF antibody. We also showed that the increased MMP-2 activity was due to an increase in MMP-2 mRNA levels in VSMC. We further studied the mechanisms involved in the regulation of MMP-2 mRNA levels and found that the AP-2 transcription factor is responsible for most of the CTGF-induced MMP-2 transcription. Because MMP-2 is an important factor directly involved in controlling cell movement and the turnover of extracellular matrix, our study may provide a mechanism for CTGF-promoted VSMC migration.