Analysis of the DNA-binding and activation properties of the human transcription factor AP-2

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.

Intronic polymorphisms within TFAP2B regulate transcriptional activity and affect adipocytokine gene expression in differentiated adipocytes

We have identified a gene encoding transcription factor activating enhancer binding protein-2beta (TFAP2B) as a candidate for conferring susceptibility to type 2 diabetes. Although we have also found that TFAP2B was preferentially expressed in adipose cells in a differentiation-dependent manner, the mechanisms by which the gene and gene polymorphisms contribute to conferring susceptibility to the disease have not yet been elucidated. The aim of this study was to evaluate the impact of the polymorphisms within the TFAP2B gene on conferring susceptibility to type 2 diabetes. We identified that a 300-bp DNA fragment in intron 1 of TFAP2B had significant enhancer activity, and the variations of this region affected this enhancer activity in differentiated adipocytes. In an experiment using adenovirus vectors encoding TFAP2B, the expression of TNF-alpha gene was shown to be elevated in the TFAP2B overexpressing cells compared with those in control cells. Furthermore, we demonstrated that the expression of TFAP2B was increased in the adipose tissues of subjects with the disease-susceptibility allele, and the plasma levels of TNF-alpha and high sensitivity C-reactive peptide were significantly elevated in the patients with the disease-susceptibility allele. These results suggest that TFAP2B may contribute to the pathogenesis of type 2 diabetes through regulation of adipocytokine gene expression, and that TFAP2B may be a promising target for treatment or prevention of this disease.

The polymorphic nature of the human dopamine D4 receptor gene: a comparative analysis of known variants and a novel 27 bp deletion in the promoter region

BACKGROUND

The human dopamine D4 receptor (DRD4) is a candidate gene of great interest in molecular studies of human personality and psychiatric disorders. This gene is unique in having an exceptionally high amount of polymorphic sites both in the coding and in the promoter region.

RESULTS

We report the identification of a new 27 bp deletion starting 524 bp upstream of the initiation codon (27 bp del) of the dopamine D4 receptor (DRD4) gene, in the close vicinity of the -521C>T SNP. The presence of the 27 bp deletion leads to the misgenotyping of the -616C>G SNP by the Sau96 I RFLP method, thus the genotype determination of the mutation is of additional importance. The frequency of this novel sequence variation is considerably low (allele frequency is = 0.16%), as no homozygotes, and only 3 heterozygote carriers were found in a healthy, unrelated Caucasian sample (N = 955).

CONCLUSION

Remarkably, the deleted region contains consensus sequences of binding sites for several known transcription factors, suggesting that the different alleles may affect the transcriptional regulation of the gene. A comparison of methods and results for the allelic variations of the DRD4 gene in various ethnic groups is also discussed, which has a high impact in psychiatric genetic studies.

Transcription factor AP-2 and monoaminergic functions in the central nervous system

In the central nervous system, transcription factor AP-2 family is one of the critical regulatory factors for neural gene expression and neuronal development. Several genes in the monoaminergic systems display AP-2 binding sites in regulatory regions. In addition, brainstem levels of transcription factor AP-2alpha and AP-2beta are positively correlated to monoamine measures in rat forebrain, suggesting a regulatory role of AP-2 also in the adult brain. Great changes in psychiatric phenotypes due to genetic factors are seldom the result of a single gene polymorphism. Recently, identification of combinations of candidate genes that are all linked to one disease or psychiatric phenotype has been discussed. The expression of these candidate genes might be regulated by the same transcription factors, e.g. AP-2. Recent data on transcription factor AP-2 family in relation to monoaminergic functions are described in this paper. Transcription factor AP-2beta genotype has been studied in relation to personality, platelet monoamine oxidase (MAO) activity, CSF-levels of monoamine metabolites, binge-eating disorder, premenstrual dysphoric disorder, and schizophrenia. Furthermore, the involvement of AP-2 in the molecular mechanism of antidepressant drugs is discussed. Altogether, this paper discusses data supporting a notion that the transcription factor AP-2 family is involved in the regulation of the monoaminergic systems both pre- and postnatally, and, therefore, might be involved in the pathophysiology of neuropsychiatric disorders.

AP-2alpha selectively regulates fragile X mental retardation-1 gene transcription during embryonic development

Fragile X syndrome (FXS) is almost always caused by silencing of the FMR1 gene. The defects observed in FXS indicate that the normal FMR1 gene has a range of functions and plays a particularly prominent role during development. However, the mechanisms regulating FMR1 expression in vivo are not known. Here, we have tested the role of the transcription factor AP-2alpha in regulating Fmr1 expression. Chromatin immunoprecipitation showed that AP-2alpha associates with the Fmr1 promoter in vivo. Furthermore, Fmr1 transcript levels are reduced >4-fold in homozygous null AP-2alpha mutant mice at embryonic day 18.5 when compared with normal littermates. Notably, AP-2alpha exhibits a strong gene dosage effect, with heterozygous mice showing approximately 2-fold reduction in Fmr1 levels. Examination of conditional AP-2alpha mutant mice indicates that this transcription factor plays a major role in regulating Fmr1 expression in embryos, but not in adults. We further investigated the role of AP-2alpha in the developmental regulation of Fmr1 expression using the Xenopus animal cap assay. Over-expression of a dominant-negative AP-2alpha in Xenopus embryos led to reduced Fmr1 levels. Moreover, exogenous wild-type AP-2alpha rescued Fmr1 expression in embryos where endogenous AP-2alpha had been suppressed. We conclude that AP-2alpha associates with the Fmr1 promoter in vivo and selectively regulates Fmr1 transcription during embryonic development.

Preliminary array analysis reveals novel genes regulated by ovarian steroids in the monkey raphe region

We hypothesize that ovarian hormones may improve serotonin neuron survival. We sought the effect of estradiol (E) and progesterone (P) on novel gene expression in the macaque dorsal raphe region with Affymetrix array analysis. Nine spayed rhesus macaques were treated with either placebo, E or E+P via Silastic implant for 1 month prior to euthanasia (n=3 per treatment). RNA was extracted from a small block of midbrain containing the dorsal raphe and examined on an Agilent Bioanalyzer. The RNA from each monkey was labeled and hybridized to an Affymetrix HG_U95AV Human GeneChip Array. After filtering and sorting, 25 named genes remained that were regulated by E, and 24 named genes remained that were regulated by supplemental P. These genes further sorted into functional categories that would promote neuronal plasticity, transmitter synthesis, and trafficking, as well as reduce apoptosis. The relative abundance of four pivotal genes was examined in all nine animals with quantitative RT-PCR and normalized by glyceraldehyde 3-phosphate dehydrogenase (GAPDH). E+/-P caused a significant threefold reduction in JNK-1 (a pro-apoptosis gene, p<0.007); and a significant sixfold decrease in kynurenine mono-oxygenase (produces neurotoxic quinolones, p<0.05). GABA-A receptor (alpha3 subunit; benzodiazepine site) and E2F1 (interferes with cytokine signaling) were unaffected by E, but increased sevenfold (p<0.02) and fourfold (p<0.009), respectively, upon treatment with P. In summary, subsets of genes related to tissue remodeling or apoptosis were up- or down-regulated by E and P in a tissue block containing the dorsal raphe. These changes could promote cellular resilience in the region where serotonin neurons originate.

Transcription of brain creatine kinase in U87-MG glioblastoma is modulated by factor AP2

Our previous studies established in U87-MG glioblastoma cells that elevated cAMP increased transcription of the endogenous as well as a transiently-transfected brain creatine kinase (CKB) gene, despite the absence of a cAMP response element (CRE) in the CKB proximal promoter. This report employed transfection to show that the transcription of CKB in U87 cells is induced by transcription factor AP2alpha, which is known to be activated by cAMP. Dominant-negative forms of AP2alpha not only prevented the AP2alpha-mediated activation of CKB but also blocked the cAMP-mediated increase in CKB transcription caused by forskolin treatment. The mutation of the four potential AP2 elements within the CKB proximal promoter showed that induction of CKB by AP2 was mediated principally through the AP2 element located at -50 bp in the promoter. Electromobility shift assays revealed a protein in U87 nuclear extracts that bound to a consensus AP2alpha element as well as to the (-50) AP2 element in CKB. Interestingly, the CKB (-50) AP2 element contains GCCAATGGG which also bound NF-Y, the CCAAT-binding protein, suggesting that interplay between AP2 and NF-Y may modulate CKB transcription. This is the first report of a role for AP2 in the regulation of CKB transcription and of an AP2 element within which an NF-Y site is located.

Sumoylation of internally initiated Sp3 isoforms regulates transcriptional repression via a Trichostatin A-insensitive mechanism

Sp3 is a ubiquitously expressed member of the Sp family of transcription factors that encodes three proteins, Sp3, M1 and M2, with differing capacities to stimulate or repress transcription. As part of ongoing efforts to study the functions of Sp3 isoforms, we employed a yeast "two-hybrid" screen to identify Sp3-binding proteins. This screen resulted in the identification of Ubc9, a SUMO-1 conjugating enzyme, as an M2-binding protein, and consistent with these results sequence analyses identified consensus sumoylation motifs within several Sp family members. Western blots probed with anti-Sp3 detected a high molecular weight Sp3 isoform that is stabilized by a SUMO-1 hydrolase inhibitor, and this protein is also bound by anti-SUMO-1 antiserum. Transient transfection assays with epitope-tagged-SUMO-1 and GFP-SUMO-1 fusion proteins confirmed that Sp3, M1 and M2 proteins are sumoylated in vivo. Substitution of arginine for lysine at one putative site of sumoylation, lysine(551), blocked sumoylation of all Sp3 isoforms in vivo and led to a marginal increase in Sp3-mediated trans-activation in insect and mammalian cells. In contrast, introduction of this amino acid substitution within M1 converted it into a potent transcriptional trans-activator. We conclude that Sp3 isoforms are sumoylated in vivo and this post-translational modification plays an important role in the regulation of Sp3-mediated transcription.

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.

Genotyping and haplotyping of the dopamine D4 receptor gene by capillary electrophoresis

In this paper we report on simultaneous genotyping of adjacent polymorphisms (referred to as haplotyping) by combining double-tube allele-specific polymerase chain reaction, restriction fragment length polymorphism and capillary gel electrophoresis analysis of the resulting fragments. Direct molecular haplotyping is of particular importance in the case of double heterozygote samples, since in these instances the haplotype structure cannot be constructed based on genotype data. Our approach provided a powerful tool for coincidental genotype analysis of the 48 base pair (bp) variable number of tandem repeats of the third exon and haplotype investigation of the -616CG and -521CT single nucleotide polymorphisms of the dopamine D4 receptor (DRD4) gene. The linear polyacrylamide sieving matrix was optimized for the size range of the double-stranded DNA fragments of interest varying from 35 to 763 bp. We demonstrated that capillary gel electrophoresis in combination with laser induced fluorescence detection offers a sensitive and accurate tool for automated haplotyping in clinical settings.

Distinct spatial expression patterns of AP-2alpha and AP-2gamma in non-neoplastic human breast and breast cancer

Although transcription factors AP-2alpha and AP-2gamma have been implicated in the control of estrogen receptor (ER) and ErbB-2, their impact for breast cancer is still controversial. To better understand the role of AP-2 proteins in mammary neoplasia, the analysis of their spatial expression pattern in normal breast and breast cancer is required. A total of 51 specimens of female breast cancer patients and a tissue microarray containing 93 additional female breast cancer cases were immunohistochemically stained for AP-2alpha, AP-2gamma, ER and ErbB-2. In 70 cases of the tissue microarray, survival data comprising a period of up to 30 years were present. In non-neoplastic breast tissue, AP-2alpha was expressed in the inner glandular cell layer while AP-2gamma was expressed in the outer myoepithelial cell layer. Ductal carcinoma in situ revealed strongly AP-2alpha-positive tumor cells surrounded by a layer of AP-2gamma-positive myoepithelial cells. In invasive carcinoma, expression of AP-2alpha and AP-2gamma was variable. High expression of ER and AP-2alpha showed better survival rates than low expression of these markers. AP-2gamma expression had no effect on survival. These results for the first time reveal a distinct spatial expression pattern of AP-2alpha and AP-2gamma in normal breast and in ductal carcinoma in situ with specific AP-2gamma expression in myoepithelium. High ER and AP-2alpha expression in invasive breast cancer showed favorable survival rates. Therefore, AP-2alpha expression seems to be associated with better prognosis of breast cancer. AP-2gamma expression has no influence on survival reflecting that myoepithelial cells are not involved in the neoplastic process.

Identification and embryonic expression of a new AP-2 transcription factor, AP-2 epsilon

AP-2 proteins comprise a family of highly related transcription factors, which are expressed during mouse embryogenesis in a variety of ectodermal, neuroectodermal, and mesenchymal tissues. AP-2 transcription factors were shown to be involved in morphogenesis of craniofacial, urogenital, neural crest-derived, and placental tissues. By means of a partial cDNA fragment identified during an expressed sequence tag search for AP-2 genes, we identified a fifth, previously unknown AP-2-related gene, AP-2 epsilon. AP-2 epsilon encodes an open reading frame of 434 amino acids, which reveals the typical modular structure of AP-2 transcription factors with highly conserved C-terminal DNA binding and dimerization domains. Although the N-terminally localized activation domain is less homologous, position and identity of amino acids essential for transcriptional transactivation are conserved. Reverse transcriptase-polymerase chain reaction analyses of murine embryos revealed AP-2 epsilon expression from gestational stage embryonic day 7.5 throughout all later embryonic stages until birth. Whole-mount in situ hybridization using a specific AP-2 epsilon cDNA fragment demonstrated that during embryogenesis, expression of AP-2 epsilon is mainly restricted to neural tissue, especially the midbrain, hindbrain, and olfactory bulb. This expression pattern was confirmed by immunohistochemistry with an AP-2 epsilon-specific antiserum. By using this antiserum, we could further localize AP-2 epsilon expression in a hypothalamic nucleus and the neuroepithelium of the vomeronasal organ, suggesting an important function of AP-2 epsilon for the development of the olfactory system.

Loss of the AP-2α Transcription Factor Is Associated with the Grade of Human Gliomas

Purpose: The activator protein (AP)-2α transcription factor plays a crucial role in the progression of several human tumors, including malignant melanoma, prostate, and breast cancer. Loss of AP-2α results in deregulation of several genes with AP-2α binding motifs such as E-cadherin, p21WAF1, MMP-2, MCAM/MUC18, VEGF, and c-KIT. The purpose of our study was to determine AP-2α expression distribution among grades of gliomas and any possible effect on prognosis.

Experimental Design: A tissue microarray was assembled from all surgical glioma cases with available tissue samples at M.D. Anderson Cancer Center since 1986 to include 72 glioblastomas, 49 anaplastic astrocytomas, 9 low-grade astrocytoma, 37 oligodendrogliomas, 37 anaplastic oligodendrogliomas, 15 mixed oligoastrocytomas, 20 anaplastic mixed oligoastrocytomas, and 7 gliosarcomas. The microarray included normal brain tissue, and AP-2α expression was determined by immunohistochemistry.

Results: AP-2α expression was lost on 99% (P &lt; 0.001) and 98% (P &lt; 0.001) of glioblastomas and anaplastic astrocytomas, respectively, compared with grade 2 astrocytomas and normal brain, all of which (100%) maintained expression of AP-2α. The loss of AP-2α was a negative prognostic indicator within the overall category of gliomas by univariate analysis (rate ratio, 4.30; 95% confidence interval, 2.60-7.10; P &lt; 0.001). However, there was no significant effect of loss of AP-2α expression on survival observed after adjustment for patient age, Karnofsky Performance Scale score, tumor grade, and extent of resection (rate ratio, 1.2; 95% confidence interval, 0.6-2.2; P = 0.6).

Conclusions: AP-2α expression correlates inversely with glioma grade, suggesting a direct role in glioma tumorigenicity, possibly through subsequent deregulation of target genes. Of all the previously characterized markers of progression, the loss of AP-2α would be the most common (96.2%) molecular marker as an astrocytic tumor evolves from grade 2 to 3.

Multiple marker analysis at the promoter region of the DRD4 gene and ADHD: evidence of linkage and association with the SNP -616

Abnormalities of dopamine neurotransmission have been hypothesized to play an important role in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Support for this has come from numerous association studies on candidate genes including the dopamine D4 receptor gene (DRD4). One of the most replicated associations between ADHD and the dopaminergic system is the 7-repeat allele of the VNTR polymorphism of this gene. A lack of association between this marker and ADHD has also been reported in several investigations. In the absence of a firm link between the number of the VNTR repeats and the function of the gene, we sought to investigate several additional markers at the 5'-end of the gene with potential influence on the expression of the DRD4. We observed a significant over transmission of single nucleotide polymorphism (SNP) (chi(2) = 7.45, P = 0.008, OR = 1.63). In addition, an excess transmission of the A allele of the -521 SNP was observed, although it did not attain statistical significance (chi(2) = 2.14, P = 0.17, OR = 1.25). Linkage disequilibrium (LD) analysis demonstrated a weak level of D' between any of the tested markers implying that this may be a region of high recombination. It also raises the possibility that the new association with ADHD may be independent of the 7-repeat allele. Further analyses, preferably in samples demonstrating association with the VNTR, or in other ethnic groups, are required to confirm these observations.

Association between single nucleotide polymorphisms in deoxycytidine kinase and treatment response among acute myeloid leukaemia patients

Development of resistance to 1-beta-arabinofuranosylcytosine (AraC) is a major obstacle in the treatment of patients with acute myeloid leukaemia (AML). Deficiency of functional deoxycytidine kinase (dCK) plays an important role in AraC resistance in vitro. We screened 5378 bp sequences of the dCK gene, including all exons and the 5' flanking region, and identified two single nucleotide polymorphisms (SNPs) in the regulatory region (rSNPs) with high allele frequencies. These two rSNPs (-201C>T and -360C>G) formed two major haplotypes. Genotyping with sequencing and MassARRAY system among 122 AML patients showed that those with -360CG/-201CT and -360GG/-201TT compound genotypes (n = 41) displayed a favourable response to chemotherapy whereas those with -360CC/-201CC (n = 81) tended to have a poor response (P = 0.025). Moreover, real-time quantitative reverse transcriptase-polymerase chain reaction showed that patients with -360CG/-201CT and -360GG/-201TT genotypes expressed higher level of dCK mRNA compared to those with the -360CC/-201CC genotype (P = 0.0034). Luciferase-reporter assay showed that dCK 5' regulatory region bearing -360G/-201T genotype alone had an eight-fold greater transcriptional activation activity compared to that with -360C/-201C genotype, whereas co-transfection of both -360G/-201T and -360C/-201C constructs mimicked the heterozygous genotype, which exhibited a four-fold greater activity compared to that with -360C/-201C. These results indicate that rSNP haplotypes of dCK gene may serve as a genetic marker for predicting drug responsiveness, which will be beneficial in establishing more effective AML chemotherapeutic regimens.

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.

Control of the rat angiotensin I converting enzyme gene by CRE-like sequences

We characterized the role of potential cAMP-responsive elements (CRE) in basal and in induced angiotensin converting enzyme (ACE) gene promoter activity in order to shed light on the regulation of somatic ACE expression. We identified stimulators and repressors of basal expression between 122 and 288 bp and between 415 and 1303 bp upstream from the transcription start site, respectively, using a rabbit endothelial cell (REC) line. These regions also contained elements associated with the response to 8BrcAMP. When screening for CRE motifs we found pCRE, a proximal sequence between 209 and 222 bp. dCRE, a distal tandem of two CRE-like sequences conserved between rats, mice and humans, was detected between 834 and 846 bp. Gel retardation analysis of nuclear extracts of REC indicated that pCRE and dCRE bind to the same protein complexes as bound by a canonical CRE. Mutation of pCRE and dCRE in REC established the former as a positive element and the latter as a negative element. In 293 cells, a renal cell line, pCRE and dCRE are negative regulators. Co-transfection of ATF-2 or ATF-2 plus c-Jun repressed ACE promoter activity, suggesting that the ACE gene is controlled by cellular stress. Although mapping of cAMP responsiveness was consistent with roles for pCRE and dCRE, mutation analysis indicated that they were not required for cAMP responsiveness. We conclude that the basal activity of the somatic ACE promoter is controlled by proximal and distal CREs that can act as enhancers or repressors depending on the cell context.

Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells

In most human colorectal cancers, mutations in the adenomatous polyposis coli gene (APC) or CTNNB1 constitutively activate the beta-catenin/T-cell factor (TCF)/lymphoid enhancer factor (LEF) signaling pathway. Here, we show that the transcription factor activator protein (AP)-2alpha inhibited a beta-catenin/TCF-responsive reporter in human embryonic kidney 293 cells and in two human colorectal cancer lines, despite the fact that beta-catenin and TCF-4 protein levels were unchanged in the nucleus. Co-immunoprecipitation studies revealed that AP-2alpha formed a complex with APC and beta-catenin and that AP-2alpha disrupted beta-catenin/TCF-4 interactions in the nucleus. Thus, AP-2alpha.APC.beta-catenin complex formation appears to suppress beta-catenin transactivation by shifting the pool of nuclear beta-catenin toward an inactive form, having reduced binding to TCF/LEF transcription factors. Glutathione S-transferase pull-down assays showed that AP-2alpha physically associated with APC rather than with beta-catenin, and the AP-2alpha binding site was identified in the N terminus of APC, involving both the heptad and armadillo repeat domains, whereas the APC binding site in AP-2alpha was in the basic region of the C-terminal DNA binding domain. These findings provide the first evidence for a specific interaction between the tumor suppressor protein APC and the transcription factor AP-2alpha, and they suggest a link between the Wnt signaling pathway and various other pathways of development and differentiation associated with AP-2alpha.

Suppression of invasion and peritoneal carcinomatosis of ovarian cancer cells by overexpression of AP-2alpha

A previous report demonstrated that AP-2alpha favors the survival of ovarian cancer patients by clinical findings. However, the functional roles of AP-2alpha in human ovarian cancers have not been determined. To clarify the roles, we overexpressed AP-2alpha in SKOV3 human ovarian cancer cells, which originally possess little AP-2alpha. AP-2alpha overexpression changed cell morphology from spindle to epithelioid type and suppressed cell proliferation and invasion, which would be partially correlated with decreased phosphorylation levels of the erbB2, Akt and ERK pathways, increased E-cadherin and reduced pro-matrix metalloproteinase-2 levels. Moreover, nude mice intraperitoneally injected with AP-2alpha-overexpressing cells survived longer than those with neo-transfected cells. The present data represent the first direct evidence that AP-2alpha plays a tumor suppressive role in ovarian cancer.

Endogenous GATA Factors Bind the Core Sequence of the tetO and Influence Gene Regulation with the Tetracycline System

The tetracycline-regulated eukaryotic gene expression systems have been applied in numerous areas of bioscience. The systems utilize a tetracycline-responsive promoter (P(tet)) and synthetic transactivators (tTA or rtTA) that bind to the promoter in the presence or absence of doxycycline, regulating gene expression. Both the basal activity of the P(tet) and the magnitude of regulation by the system vary between cell types. In this investigation we have mapped the positions of endogenous transcription factor binding sites within the P(tet) and through deletion studies determined the portion of the promoter that contributes to basal activity. The tetracycline operator (tetO) repeats appear to be the source of basal activity and they were shown to harbor motifs for GATA transcription factors. The GATA motif is located within the central core of the tetO and so has the potential to compete with tTA and rtTA binding. The molecular interactions of endogenous and overexpressed GATA factors with the GATA motif in the tetO were demonstrated and effects on function of the tetracycline-regulated gene expression system investigated. GATA factors are widespread in embryonic tissues, are expressed within several adult cell types, and display altered expression in disease states. We suggest that endogenous GATA factor expression may influence the degree of gene regulation by the tetracycline system between different cell types. The findings of this study may have implications for the application of the tetracycline system in gene therapy.

Critical role for transcription factor AP-2alpha in human trophoblast differentiation

To examine whether AP-2alpha is a critical component of the genetic program that directs human trophoblast differentiation, we used DNA microarray analyses to characterize the effects of a dominant-negative form of the AP-2 protein upon in vitro differentiating cytotrophoblast cells. Human cytotrophoblast cells (>95% pure) were cultured for 3 days in the presence of control medium or medium containing an adenovirus that expresses a dominant-negative mutant of AP-2 (Ad2.AP-2D/N) or an adenovirus lacking the AP-2 mutant gene (Ad.WT). DNA microarray analyses using Affymetrix human U95Av2 GeneChips were performed on RNA extracted from the three groups of cells immediately prior to and after 3 days of cell culture. Cells infected with Ad2.AP-2D/N or Ad2.WT underwent morphological differentiation similar to that of uninfected cells, with greater than 90% of the cells in each group fusing to form multinucleated syncytiotrophoblast cells. However, Ad2.AP-2D/N markedly inhibited the induction or repression of many genes that were regulated in the noninfected and Ad2.WT-infected cells during differentiation. Eighteen of the 25 most induced genes and 17 of the 20 most repressed genes during differentiation were AP-2 dependent, with the majority of these related to extracellular organization, cellular communication, and signal transduction. Taken together, these findings strongly suggest that AP-2 plays a critical role for both the induction and repression of genes that comprise postsyncytialization gene expression programs of trophoblast differentiation and maturation. AP-2, however, is not required for the fusion of cytotrophoblast cells to form a syncytium or the expression of syncytin.

Wnt1-Cre-mediated deletion of AP-2alpha causes multiple neural crest-related defects

The AP-2alpha transcription factor is required for multiple aspects of vertebrate development and mice lacking the AP-2alpha gene (tcfap2a) die at birth from severe defects affecting the head and trunk. Several of the defects associated with the tcfap2a-null mutation affect neural crest cell (NCC) derivatives including the craniofacial skeleton, cranial ganglia, and heart outflow tract. Consequently, there is considerable interest in the role of AP-2alpha in neural crest cell function in development and evolution. In addition, the expression of the AP-2alpha gene is utilized as a marker for premigratory and migratory neural crest cells in many vertebrate species. Here, we have specifically addressed how the presence of AP-2alpha in neural crest cells affects development by creating a conditional (floxed) version of tcfap2a which has subsequently been intercrossed with mice expressing Cre recombinase under the control of Wnt1 cis-regulatory sequences. Neural crest-specific disruption of tcfap2a results in frequent perinatal lethality associated with neural tube closure defects and cleft secondary palate. A small but significant fraction of mutant mice can survive into adulthood, but have retarded craniofacial growth, abnormal middle ear development, and defects in pigmentation. The phenotypes obtained confirm that AP-2alpha directs important aspects of neural crest cell function. At the same time, we did not observe several neurocristopathies affecting the head and heart that might be expected based on the phenotype of the AP-2alpha-null mouse. These results have important implications for the evolution and function of the AP-2 gene family in both the neural crest and the vertebrate embryo.

Frontonasal process-specific disruption of AP-2alpha results in postnatal midfacial hypoplasia, vascular anomalies, and nasal cavity defects

A majority of the bones of the vertebrate cranial vault and craniofacial complex develop via intramembranous ossification, and are separated by fibrous sutures that undergo osteogenic differentiation in response to growth stimuli. Craniosynostosis is a common human birth defect that results from the premature bony fusion within skull sutures, and causes a myriad of complications including mental retardation and craniofacial anomalies. Synostosis of facial sutures has been reported to cause midfacial hypoplasia in some craniosynostosis cases, but most studies focus on cranial vault sutures. In this study, we have generated a mouse model of frontonasal suture synostosis and midfacial hypoplasia through the tissue-specific elimination of the AP-2alpha transcription factor. We report here the generation AP-2CRE, a frontonasal process (FNP)- and limb-specific CRE recombinase allele that is directed by human AP-2alpha promoter and enhancer elements. We used the AP-2CRE line in combination with the conditional AP-2alpha line to produce a new frontonasal knockout (FKO) mutant that lacks AP-2alpha in the FNP and limbs. FKO mice exhibit shortened snouts and wide-set eyes that become apparent at postnatal day 15. The most prominent defects in FKO snouts are (1) a lack of growth within the frontonasal sutures, and (2) a reduction in the snout vasculature. Additional defects are observed in the FKO nasal bones and sutures, the nasal cavity cartilage and bony projections, and the olfactory epithelium. The characteristics of the FKO mouse model are a unique combination of midfacial growth anomalies, and provide the first evidence that AP-2alpha is essential for appropriate postnatal craniofacial morphogenesis.

An ENU-induced mutation in AP-2α leads to middle earand ocular defects in Doarad mice

One of the advantages of N-ethyl- N-nitrosourea (ENU)-induced mutagenesis is that, after randomly causing point mutations, a variety of alleles can be generated in genes leading to diverse phenotypes. For example, transcription factor AP-2alpha ( Tcfap2a) null homozygote mice show a large spectrum of developmental defects, among them missing middle ear bones and tympanic ring. This is the usual occurrence, where mutations causing middle ear anomalies usually coincide with other abnormalities. Using ENU-induced mutagenesis, we discovered a new dominant Tcfap2a mutant named Doarad ( Dor) that has a missense mutation in the PY motif of its transactivation domain, leading to a misshapen malleus, incus, and stapes without any other observable phenotype. Dor homozygous mice die perinatally, showing prominent abnormal facial structures and ocular defects. In vitro assays suggest that this mutation causes a "gain of function" in the transcriptional activation of AP-2alpha. These mice enable us to address more specifically the developmental role of Tcfap2a in the eye and middle ear and are the first report of a mutation in a gene specifically causing middle ear abnormalities, leading to conductive hearing loss.

AP-2 transcription factor family member expression, activity, and regulation in human epidermal keratinocytes in vitro

The AP-2 transcription factor family is presumed to play an important role in the regulation of the keratinocyte squamous differentiation program; however, limited functional data are available to support this. In the present study, the activity and regulation of AP-2 were examined in differentiating human epidermal keratinocytes. We report that (1) AP-2 transcriptional activity decreases in differentiated keratinocytes but remains unchanged in differentiation-insensitive squamous cell carcinoma cell lines, (2) diminished AP-2 transcriptional activity is associated with a loss of specific DNA-bound AP-2 complexes, and (3) there is an increase in the ability of cytoplasmic extracts, derived from differentiated keratinocytes, to phosphorylate AP-2 alpha and AP-2 beta when cells differentiate. In contrast, extracts from differentiation-insensitive squamous cell carcinoma cells are unable to phosphorylate AP-2 proteins. Finally, the phosphorylation of recombinant AP-2 alpha by cytosolic extracts from differentiated keratinocytes is associated with decreased AP-2 DNA-binding activity. Combined, these data indicate that AP-2 trans-activation and DNA-binding activity decrease as keratinocytes differentiate, and that this decreased activity is associated with an enhanced ability to phosphorylate AP-2 alpha and beta.

Human potassium chloride cotransporter 1 (SLC12A4) promoter is regulated by AP-2 and contains a functional downstream promoter element

Most K-Cl cotransport in the erythrocyte is attributed to potassium chloride cotransporter 1 (KCC1). K-Cl cotransport is elevated in sickle erythrocytes, and the KCC1 gene has been proposed as a modifier gene in sickle cell disease. To provide insight into our understanding of the regulation of the human KCC1 gene, we mapped the 5' end of the KCC1 cDNA, cloned the corresponding genomic DNA, and identified the KCC1 gene promoter. The core promoter lacks a TATA box and is composed of an initiator element (InR) and a downstream promoter element (DPE), a combination found primarily in Drosophila gene promoters and rarely observed in mammalian gene promoters. Mutational analyses demonstrated that both the InR and DPE sites were critical for full promoter activity. In vitro DNase I footprinting, electrophoretic mobility shift assays, and reporter gene assays identified functional AP-2 and Sp1 sites in this region. The KCC1 promoter was transactivated by forced expression of AP-2 in heterologous cells. Sequences encoding the InR, DPE, AP-2, and Sp1 sites were 100% conserved between human and murine KCC1 genes. In vivo studies using chromatin immunoprecipitation assays with antihistone H3 and antihistone H4 antibodies demonstrated hyperacetylation of this core promoter region.

Activator protein 2alpha inhibits tumorigenicity and represses vascular endothelial growth factor transcription in prostate cancer cells

Activator protein-2alpha (AP-2) is a transcription factor that regulates proliferation and differentiation in mammalian cells. We have shown previously that although AP-2 is expressed highly in normal prostatic epithelium, its expression is lost in high-grade prostatic intraepithelial neoplasia and prostate cancer, suggesting that loss of AP-2 plays a role in prostate cancer development. We demonstrate that forced AP-2 expression in the prostate cancer cell line LNCaP-LN3 (AP-2 negative) inhibited dramatically tumor incidence in nude mice. To identify the genes that might have been responsible for this effect, we used microchip expression array. We found several genes known to be involved in malignancy were deregulated, including the vascular endothelial growth factor (VEGF) gene. Because VEGF was down-regulated by 14.7-fold in the AP-2-transfected cells and because it is a major angiogenic factor in prostate cancer development and progression, we chose to examine the AP-2-VEGF interaction. Our evidence suggests that AP-2 repressed transcriptionally the VEGF promoter by competing with the transcriptional activator Sp3. Loss of AP-2 in prostate cancer cells reduced the AP-2:Sp3 ratio and activated VEGF expression. AP-2 acts as a tumor-suppressor gene in prostate cancer. Elucidating the molecular events resulting from loss of AP-2 in the prostate epithelium has implications for the understanding and prevention of the onset of prostate cancer.

Neural crest survival and differentiation in zebrafish depends on mont blanc/tfap2a gene function

Neural crest progenitor cells are the main contributors to craniofacial cartilage and connective tissue of the vertebrate head. These progenitor cells also give rise to the pigment, neuronal and glial cell lineages. To study the molecular basis of neural crest differentiation, we have cloned the gene disrupted in the mont blanc (mobm610) mutation,which affects all neural crest derivatives. Using a positional candidate cloning approach we identified an A to G transition within the 3′ splice site of the sixth intron of the tfap2a gene that abolishes the last exon encoding the crucial protein dimerization and DNA-binding domains. Neural crest induction and specification are not hindered in mobm610 mutant embryos, as revealed by normal expression of early neural crest specific genes such as snail2, foxd3and sox10. In addition, the initial stages of cranial neural crest migration appear undisturbed, while at a later phase the craniofacial primordia in pharyngeal arches two to seven fail to express their typical set of genes (sox9a, wnt5a, dlx2, hoxa2/b2). In mobm610 mutant embryos, the cell number of neuronal and glial derivatives of neural crest is greatly reduced, suggesting that tfap2a is required for their normal development. By tracing the fate of neural crest progenitors in live mont blanc(mobm610) embryos, we found that at 24 hpf neural crest cells migrate normally in the first pharyngeal arch while the preotic and postotic neural crest cells begin migration but fail to descend to the pharyngeal region of the head. TUNEL assay and Acridine Orange staining revealed that in the absence of tfap2a a subset of neural crest cells are unable to undergo terminal differentiation and die by apoptosis. Furthermore, surviving neural crest cells in tfap2a/mobm610 mutant embryos proliferate normally and later differentiate to individual derivatives. Our results indicate that tfap2a is essential to turn on the normal developmental program in arches 2-7 and in trunk neural crest. Thus, tfap2a does not appear to be involved in early specification and cell proliferation of neural crest, but it is a key regulator of an early differentiation phase and is required for cell survival in neural crest derived cell lineages.

Transcription Factors Pax6 and AP-2alpha Interact To Coordinate Corneal Epithelial Repair by Controlling Expression of Matrix Metalloproteinase Gelatinase B

Pax6 is a paired box containing transcription factor that resides at the top of a genetic hierarchy controlling eye development. It continues to be expressed in tissues of the adult eye, but its role in this capacity is unclear. Pax6 is present in the adult corneal epithelium, and we showed that the amount of Pax6 is increased at the migrating front as the epithelium resurfaces the cornea after injury. We also showed that Pax6 controls activity of the transcriptional promoter for the matrix metalloproteinase, gelatinase B (gelB; MMP-9) in cell culture transfection studies. gelB expression is turned on at the migrating epithelial front in the cornea, and it coordinates and effects aspects of epithelial regeneration. We define here two positively acting Pax6 response elements in the gelB promoter. Pax6 binds directly to one of these sites through the paired DNA-binding domain. It binds the second site indirectly by interaction with AP-2alpha, a transcription factor that also exerts control over eye development. Pax6 control of gelB expression was examined in vivo by using a corneal reepithelialization model in mice heterozygous for a Pax6 paired-domain mutation (Sey(+/-)). A reduced Pax6 dosage in these mice resulted in a loss of gelB expression at the migrating epithelial front. This effect was correlated with an increase in inflammation and the rate of reepithelialization, a finding consistent with the phenotype of gelB knockout mice. Together, these data indicate that Pax6 controls activity of the gelB promoter through cooperative interactions with AP-2alpha and support an active role for Pax6 in maintenance and repair of the adult corneal epithelium.

lockjawencodes a zebrafishtfap2arequired for early neural crest development

The neural crest is a uniquely vertebrate cell type that gives rise to much of the craniofacial skeleton, pigment cells and peripheral nervous system, yet its specification and diversification during embryogenesis are poorly understood. Zebrafish homozygous for the lockjaw (low)mutation show defects in all of these derivatives and we show that low (allelic with montblanc) encodes a zebrafish tfap2a, one of a small family of transcription factors implicated in epidermal and neural crest development. A point mutation in lowtruncates the DNA binding and dimerization domains of tfap2a, causing a loss of function. Consistent with this, injection of antisense morpholino oligonucleotides directed against splice sites in tfap2a into wild-type embryos produces a phenotype identical to low. Analysis of early ectodermal markers revealed that neural crest specification and migration are disrupted in low mutant embryos. TUNEL labeling of dying cells in mutants revealed a transient period of apoptosis in crest cells prior to and during their migration. In the cranial neural crest, gene expression in the mandibular arch is unaffected in low mutants, in contrast to the hyoid arch, which shows severe reductions in dlx2 and hoxa2 expression. Mosaic analysis, using cell transplantation,demonstrated that neural crest defects in low are cell autonomous and secondarily cause disruptions in surrounding mesoderm. These studies demonstrate that low is required for early steps in neural crest development and suggest that tfap2a is essential for the survival of a subset of neural crest derivatives.

Cell cycle arrest and apoptosis induction by activator protein 2alpha (AP-2alpha) and the role of p53 and p21WAF1/CIP1 in AP-2alpha-mediated growth inhibition

Activator protein 2alpha (AP-2alpha) is a sequence-specific DNA-binding transcription factor implicated in differentiation and transformation. In this study, we have made a replication-deficient recombinant adenovirus that expresses functional AP-2alpha (Ad-AP2). Cells infected with Ad-AP2 expressed induced levels of AP-2alpha protein, which bound to DNA in a sequence-specific manner and activated the AP-2-specific reporter 3X-AP2. Expression of AP-2alpha from Ad-AP2 inhibited cellular DNA synthesis and induced apoptosis. Ad-AP2 infection resulted in efficient inhibition of growth of cancer cells of six different types. In addition, prior expression of AP-2alpha increased the chemosensitivity of H460, a lung carcinoma cell line, to adriamycin (2.5-fold) and cisplatin (5-fold). Furthermore, the growth inhibition by AP-2alpha was found to be less efficient in the absence of p53 or p21, which correlated with reduced apoptosis in p53 null cells and lack of DNA synthesis inhibition in p21WAF1/CIP1 null cells by AP-2alpha, respectively. These results suggest that AP-2alpha inhibits the growth of cells by inducing cell cycle arrest and apoptosis and that the use of AP-2alpha should be explored as a therapeutic strategy either alone or in combination with chemotherapy.

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.

Cellular retinoic acid-binding protein II gene expression is directly induced by estrogen, but not retinoic acid, in rat uterus

It has been suggested that cellular retinoic acid-binding protein (II) (CRABP(II)) may have a role in the movement of retinoic acid (RA) to its nuclear receptors, thereby enhancing the action of RA in the cells in which it is expressed. RA has also been shown to increase expression of CRABP(II). Previous work from our laboratory has shown that 17 beta-estradiol (E2) administration to prepubertal female rats leads to acquisition of the ability of the lining epithelium to synthesize RA as well as to express CRABP(II). To determine whether this appearance of CRABP(II) was dependent on the production of RA, both E2 and RA were administered to ovariectomized rats. E2 administration induced expression of the CRABP(II) gene in the uterus within 4 h, and this induction was not inhibited by prior administration of puromycin, indicating that the induction was direct. In contrast, RA caused no change in CRABP(II) message level, even at times as late as 48 h after administration. Isolation and analysis of 4.5 kb of the 5'-flanking region of the gene revealed no apparent E2-response element. Using this portion of the gene to drive expression of the luciferase gene in transfected cells allowed identification of a region containing an imperfect estrogen-response element and estrogen-response element half-site, necessary for E2-driven induction. A possible Sp1 binding site in the 5'-flanking region of the CRABP(II) gene was also required for this induction. The ability of E2 to induce expression of CRABP(II) suggests that it can enhance the activity of RA, directly affecting expression of retinoid-responsive genes.

Expression patterns of the transcription factor AP-2alpha during hair follicle morphogenesis and cycling

AP-2alpha is a member of a family of transcription factors expressed in cells of the epithelial and neural crest lineage. AP-2alpha plays an essential role in embryonic development and in regulation of epithelial gene transcription. To further characterize the role of AP-2alpha in skin biology, we assessed its expression in the skin of C57BL/6J mice during defined stages of hair follicle morphogenesis and cycling. During early hair follicle morphogenesis, AP-2alpha was upregulated in the epidermal placode, in the basal keratinocytes of the hair follicle bud, and then in the inner root sheath. The follicular papilla cells underwent a brief upregulation of AP-2alpha expression during the initiation of hair shaft formation and active hair follicle downward growth. Completion of hair follicle morphogenesis was associated with a marked reduction of AP-2alpha immunoreactivity in the lower portion of the hair follicle including both epithelial and mesenchymal compartments. In adolescent mouse skin, consistently strong AP-2alpha expression was found in the basal keratinocytes of the epidermis, in the hair follicle infundibulum, and in the sebocytes. In the follicular papilla, AP-2alpha was weakly expressed in telogen, significantly upregulated in early anagen, then gradually declined, and reappeared again in middle catagen. In the inner root sheaths, AP-2alpha expression was detected during early and middle anagen and during middle catagen stages. Prominent AP-2alpha expression was also seen in the zone of club hair formation. Therefore, AP-2alpha upregulation in both epithelial and mesenchymal hair follicle compartments was coordinated with initiation of major remodeling processes. Our findings support the use of the hair follicle as a model to explore the role of AP-2alpha in physiologic remodeling of developing organs and in reciprocal ectodermal-mesenchymal interactions.

Cloning and embryonic expression analysis of the mouse Gbx1 gene

We report the cloning of a cDNA encoding the complete mouse Gbx1 coding region as well as a comparative expression analysis of Gbx1 and Gbx2 during murine development. Gbx1 is expressed first during gastrulation and later in a dynamic pattern in the central nervous system, including rhombomeres 3 and 5, optic vesicles, and the medial ganglionic eminence. Gbx1 expression is not upregulated in Gbx2 null homozygotes. Therefore, the only regions of potential genetic redundancy are where Gbx1 and 2 are normally coexpressed: the primitive streak, regions of the ventricular zone of the neural tube and the medial ganglionic eminence. Finally, we demonstrate that neither Gbx1 nor Gbx2 require FGF8 for expression during gastrulation, contrary to previous published reports.

Physical and functional interactions among AP-2 transcription factors, p300/CREB-binding protein, and CITED2

The transcriptional co-activators and histone acetyltransferases p300/CREB-binding protein (CBP) interact with CITED2, a transcription factor AP-2 (TFAP2) co-activator. p300/CBP, CITED2, and TFAP2A are essential for normal neural tube and cardiac development. Here we show that p300 and CBP co-activate TFAP2A in the presence of CITED2. TFAP2A transcriptional activity was modestly impaired in p300(+/-) and CBP(+/-) mouse embryonic fibroblasts; this was rescued by ectopic expression of p300/CBP. p300, TFAP2A, and endogenous CITED2 could be co-immunoprecipitated from transfected U2-OS cells indicating that they can interact physically in vivo. CITED2 interacted with the dimerization domain of TFAP2C, which is highly conserved in TFAP2A/B. In mammalian two-hybrid experiments, full-length p300 and TFAP2A interacted only when CITED2 was co-transfected. N-terminal residues of TFAP2A, containing the transactivation domain, are both necessary and sufficient for interaction with p300, and this interaction was independent of CITED2. Consistent with this, N-terminal residues of TFAP2A were required for p300- and CITED2-dependent co-activation. A histone acetyltransferase-deficient p300 mutant (D1399Y) did not co-activate TFAP2A and did not affect the expression or cellular localization of TFAP2A or CITED2. In mammalian two-hybrid experiments p300D1399Y failed to interact with TFAP2A, explaining, at least in part, its failure to function as a co-activator. Our results suggest a model wherein interactions among TFAP2A, CITED2, and p300/CBP are necessary for TFAP2A-mediated transcriptional activation and for normal neural tube and cardiac development.

Overexpression of transcription factor AP-2alpha suppresses mammary gland growth and morphogenesis

AP-2 transcription factors are key regulators of mouse embryonic development. Aberrant expression of these genes has also been linked to the progression of human breast cancer. Here, we have investigated the role of the AP-2 gene family in the postnatal maturation of the mouse mammary gland. Analysis of AP-2 RNA and protein levels demonstrates that these genes are expressed in the mammary glands of virgin and pregnant mice. Subsequently, AP-2 expression declines during lactation and then is reactivated during involution. The AP-2alpha and AP-2gamma proteins are localized in the ductal epithelium, as well as in the terminal end buds, suggesting that they may influence growth of the ductal network. We have tested this hypothesis by targeting AP-2alpha expression to the mouse mammary gland using the MMTV promoter. Our studies indicate that overexpression of AP-2alpha inhibits mammary gland growth and morphogenesis, and this coincides with a rise in PTHrP expression. Alveolar budding is severely curtailed in transgenic virgin mice, while lobuloalveolar development and functional differentiation are inhibited during pregnancy and lactation, respectively. Our studies strongly support a role for the AP-2 proteins in regulating the proliferation and differentiation of mammary gland epithelial cells in both mouse and human.

Terminal renal failure in mice lacking transcription factor AP-2 beta

Inactivation of the transcription factor AP-2 beta in a genetically mixed C57BL/6/129S1 mouse strain resulted in perinatal lethality as a consequence of massively enhanced apoptotic death of renal epithelial cells (Genes Dev 1997;11:1938-1948). Recently, we observed that the phenotype is modulated by genetic background because AP-2 beta mutant mice, backcrossed onto 129P2 background, survive approximately 2 weeks after birth, allowing for a detailed analysis of kidney function. Here we show that kidneys reveal varying amounts of cysts derived from all tubular structures (proximal and distal tubuli, collecting ducts). However, all mice died irrespective of the degree of cyst formation. Serum analysis of AP-2 beta mutant animals revealed defective tubular secretory function and ion homeostasis including severe hypocalcemia, hyperphosphatemia, and hyperuremia. Because hormonal calcium regulation was not impaired, the mice developed secondary renal hyperparathyroidism as typically observed in patients with terminal renal failure. We further demonstrate that molecular defects in the collecting duct system lead to insufficient water retention and urinary concentration. In summary, our studies reveal essential, nonredundant roles of AP-2 beta in renal tubular functions.

Follicle-stimulating hormone increases testicular Anti-Mullerian hormone (AMH) production through sertoli cell proliferation and a nonclassical cyclic adenosine 5'-monophosphate-mediated activation of the AMH Gene

Anti-Müllerian hormone (AMH) production by testicular Sertoli cells is high before puberty and can be further induced by FSH. Our objective was to delineate the mechanisms by which FSH stimulates AMH production. Assay of serum AMH levels and histological morphometric analysis in prepubertal FSH-deficient transgenic mice showed that serum AMH and testicular mass were decreased owing to reduced Sertoli cell number. All parameters resumed normal values in mice treated with recombinant FSH. We also analyzed the ability of FSH and the factors involved in its signaling pathway to activate AMH transcription by transfecting AMH promoter-luc reporter constructs of different lengths in a prepubertal Sertoli cell line. Our results showed that FSH activates AMH transcription via adenylate cyclase, cAMP, and protein kinase A but involving a nonclassical cAMP-response pathway requiring nuclear factor-kappaB and activating protein 2 binding sites, which lie more than 1.9 kb upstream of the AMH transcription start site. This is the first report showing the importance of distant sequences in the regulation of AMH expression. We conclude that prepubertal testicular AMH production is increased by FSH stimulation through Sertoli cell proliferation and an enhancement of AMH gene transcription.

Positive influence of AP-2alpha transcription factor on cadherin gene expression and differentiation of the ocular surface

The family of transcription factors Activating protein-2 (AP-2) are known to play important roles in numerous developmental events, including those associated with differentiation of stratified epithelia. However, to date, the influence of the AP-2 genes on endogenous gene expression in the stratified epithelia and how this affects differentiation has not been well defined. The following study examines the detailed expression of the AP-2alpha and AP-2beta proteins in the stratified epithelia of the ocular surface, including that in the cornea and developing eyelids. The effect of altered levels of the AP-2alpha gene on ocular surface differentiation was also examined using a corneal epithelial cell line and AP-2alpha chimeric mice. Immunolocalization studies revealed that, while AP-2beta was broadly expressed throughout all cell layers of the stratified corneal epithelium, AP-2alpha expression was confined to cell compartments more basally located. AP-2alpha was also highly expressed in the less differentiated cell layers of the eyelid epidermis. Overexpression of the AP-2alpha gene in the corneal cell line, SIRC, resulted in a dramatic change in cell phenotype including a clumping growth behavior that was distinct from the smooth monolayer of the parent cell line. Accompanying this change was an up-regulation in levels of the cell adhesion molecule, N-cadherin. Examination of the ocular surface of AP-2alpha chimeric mice, derived from a mixed population of AP-2alpha-/- and AP-2alpha+/+, revealed that a down-regulation in E-cadherin expression is correlated with location of the AP-2alpha-/- null cells. Together, these findings demonstrate that AP-2alpha participates in regulating differentiation of the ocular surface through induction in cadherin expression.

Identification of HTF (HER2 transcription factor) as an AP-2 (activator protein-2) transcription factor and contribution of the HTF binding site to ERBB2 gene overexpression

The ERBB2 gene is overexpressed in 30% of human breast cancers and this is correlated with poor prognosis. Overexpression of the ERBB2 gene is due to increased transcription and gene amplification. Our previous studies have identified a new cis element in the ERBB2 promoter which is involved in the gene's overexpression. This cis element, located 501 bp upstream from the main ERBB2 transcription initiation site, binds a transcription factor called HTF (HER2 transcription factor). We report here the identification of HTF as an AP-2 (activator protein-2) transcription factor. The new cis element is bound by AP-2 with high affinity, compared with a previously described AP-2 binding site located 284 bp downstream. Co-transfection of an AP-2alpha expression vector with a reporter vector containing the newly identified AP-2 binding site in front of a minimal ERBB2 promoter induced a dose-dependent increase in transcriptional activity. We examined the contribution of the new AP-2 binding site to ERBB2 overexpression. For this purpose we abolished the new and/or the previously described AP-2 binding sequence by site-directed mutagenesis. The results show that the two functional AP-2 sites in the first 700 bp of the ERBB2 promoter co-operate to achieve maximal transcriptional activity.

Chronic citalopram treatment induces time-dependent changes in the expression and DNA-binding activity of transcription factor AP-2 in rat brain

Imbalances in the midbrain monoaminergic systems have been implicated to play a role in neuropsychiatric conditions. Several genes in these systems have binding sites for transcription factor activating protein-2 (AP-2) in their regulatory regions. Thus, AP-2 may be a factor controlling the expression of genes in the monoaminergic systems important for maintaining normal psychiatric functions. The present study indicates that subchronic treatment with the antidepressant citalopram induces time-dependent changes in DNA-binding activity and levels of transcription factor AP-2 in rat whole brain. Rats were treated with citalopram (10 mg/kg) for 1, 3, 7 and 21 days. Animals treated for 7 days had significantly decreased DNA-binding activity and levels of AP-2 alpha and AP-2 beta isoforms when compared to saline-treated animals. There was no observed difference between citalopram- and saline-treated animals after 21 days. Elucidation of the molecular mechanisms underlying mental disorders is important for future drug development, where transcription factors might be important drug targets.

A novel gene, GliH1, with homology to the Gli zinc finger domain not required for mouse development

The Sonic hedgehog (Shh)-Gli signaling pathway regulates development of many organs, including teeth. We cloned a novel gene encoding a transcription factor that contains a zinc finger domain with highest homology to the Gli family of proteins (61-64% amino acid sequence identity) from incisor pulp. Consistent with this sequence conservation, gel mobility shift assays demonstrated that this new Gli homologous protein, GliH1, could bind previously characterized Gli DNA binding sites. Furthermore, transfection assays in dental pulp cells showed that whereas Gli1 induces a nearly 50-fold increase in activity of a luciferase reporter containing Gli DNA binding sites, coexpression of Gli1 with Gli3 and/or GliH1 results in inhibition of the Gli1-stimulated luciferase activity. In situ hybridization analysis of mouse embryos demonstrated that GliH1 expression is initiated later than the three Gli genes and has a more restricted expression pattern. GliH1 is first detected diffusely in the limb buds at 10.0 days post coitus and later is expressed in the branchial arches, craniofacial interface, ventral part of the tail, whisker follicles and hair, intervertebral discs, teeth, eyes and kidney. LacZ was inserted into the GliH1 allele in embryonic stem cells to produce mice lacking GliH1 function. While this produced indicator mice for GliH1-expression, analysis of mutant mice revealed no discernible phenotype or required function for GliH1. A search of the Celera Genomics and associated databases identified possible gene sequences encoding a zinc finger domain with approximately 90% homology to that of GliH1, indicating there is a family of GliH genes and raising the possibility of overlapping functions during development.

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.

AP2-like cis element is required for calretinin gene promoter activity in cells of neuronal phenotype differentiated from multipotent human cell line DEV

Calretinin (CR) is an EF-hand calcium binding protein expressed at high level in neurons. To identify regulatory elements in CR gene promoter, cultured rat cortical cells were transfected with constructs containing its 5'-end deletion mutants and the luciferase reporter gene. A fragment ending at -115 bp upstream of the transcription start site had high promoter activity and was able to induce expression of luciferase specifically in neuronal cells of cortical cultures. The wild type sequence of -115/+54 CR promoter fragment preferentially drove the expression of green fluorescent protein analog in cells of neuronal phenotype differentiated from multipotent human cell line DEV. Electrophoretic mobility shift assays (EMSA) revealed that the -115/-71 CR gene promoter region contains a binding site for a factor present in brain nuclear extract. Among oligonucleotides containing consensus binding sites for transcription factors within this region, the one representing AP2 binding site was able to compete formation of a protein complex. Mutations of this site prevented the binding between brain protein(s) and the -115/+54 CR gene promoter region and abolished the preferential expression of reporter gene in neuronal cells of DEV line. Thus, the AP2-like element seems to be essential for the neuron-specific activity of the CR gene promoter.

Transcription factor AP-2 interacts with the SUMO-conjugating enzyme UBC9 and is sumolated in vivo

The members of the AP-2 family of transcription factors are developmentally regulated and have distinct yet overlapping functions in the regulation of many genes governing growth and differentiation. All AP-2 factors appear to be capable of binding very similar DNA recognition sites, and the determinants of functional specificity remain to be elucidated. AP-2 transcription factors have been shown to act both as transcriptional activators and repressors in a promoter-specific manner. Although several mediators of their activation function have been suggested, few mechanisms for the repression or down-regulation of transactivation have been described. In a two-hybrid screen for proteins interacting with AP-2 factors, we have identified the UBC9 gene that encodes the E2 (ubiquitin carrier protein)-conjugating enzyme for the small ubiquitin-like modifier, SUMO. The interaction domain resides in the C-terminal half of AP-2, which contains the conserved DNA binding and dimerization domains. We have detected sumolated forms of endogenous AP-2 in mammalian cells and have further mapped the in vivo sumolation site to conserved lysine 10. Transient transfection studies indicate that sumolation of AP-2 decreases its transcription activation potential, and we discuss the possible mechanisms for the observed suppression of AP-2 transactivation.

Risk factors for the neurohumoral alterations underlying personality disturbances

Numerous studies have shown that MAO-B activity in platelets correlates with specific personality characteristics such as sensation seeking and impulsiveness. Low levels of platelet MAO as well as the personality traits associated with these low levels have been associated with type 2 alcoholism, recurrent criminality and antisocial violent behavior. Platelet MAO has a high degree of heritability and regulation of MAOB gene expression seems to explain most of the inter-individual differences in activity. The transcription factor family AP-2 is an important regulatory factor for neural gene expression and neural development, especially in midbrain structures, including the monoaminergic nuclei. In man, the gene encoding AP-2beta contains a polymorphic region in the second intron, consisting of a variable number of tandem repeats [CAAA](4-5). The long AP-2beta allele has previously been associated with specific personality traits as well as with binge-eating disorder characterized by an impulsive temperament. We have shown that males and females homozygous for the long AP-2beta allele display significantly lower platelet MAO activity compared to subjects with one or two short alleles. Thus, we find it likely that the personality disturbances previously linked to low platelet MAO activity could be associated with the presence of two long alleles of the AP-2beta gene. We suggest that the molecular mechanisms underlying the association between platelet MAO and vulnerability, e.g. substance abuse, may involve specific transcription factors that regulate the expression of midbrain monoamine structures as well as that of platelet MAO.

AP-2alpha modulates human corticotropin-releasing hormone gene expression in the placenta by direct protein-protein interaction

Since AP-2alpha induces the expression of hPL, hCG and other syncytiotrophoblast-specific marker genes in cytotrophoblast cells during in vitro differentiation, we have examined whether AP-2alpha also induces hCRH gene expression during differentiation of cytotrophoblast cells. Infection of human cytotrophoblast cells in vitro with an adenovirus expressing AP-2alpha resulted in a twofold increase in hCRH mRNA levels, while infection with an adenovirus expressing a dominant/negative mutant of AP-2alpha inhibited basal hCRH mRNA levels by 40% and completely blocked the induction of hCRH mRNA by AP-2alpha. Transient transfection studies in AtT-20 and HepG2 cells indicated that the induction of hCRH mRNA levels was due, at least in part, to transcriptional activation of the hCRH gene. Gel mobility shift and immunoprecipitation assays strongly suggest that AP-2alpha induces hCRH gene expression by interacting with CREB and not by binding directly to the hCRH promoter.

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.

Glucocorticoid responsiveness of the rat phenylethanolamine N-methyltransferase gene

Two newly identified, overlapping (1 bp) glucocorticoid response elements (GREs) at -759 and -773 bp in the promoter of the rat phenylethanolamine N-methyltransferase (PNMT; EC 2.1.1.28) gene are primarily responsible for its glucocorticoid sensitivity, rather than the originally identified -533-bp GRE. A dose-dependent increase in PNMT promoter activity was observed in RS1 cells transfected with a wild-type PNMT promoter-luciferase reporter gene construct and treated with dexamethasone (maximum activation at 0.1 microM). The type II glucocorticoid receptor antagonist RU38486 (10 microM) fully inhibited dexamethasone (1 microM) activation of the PNMT promoter, consistent with classical glucocorticoid receptors mediating corticosteroid-stimulated transcriptional activity. Relative IC(50) values from gel mobility shift competition assays showed that the -759-bp GRE has a 2-fold greater affinity for the glucocorticoid receptor than the -773-bp GRE. Site-directed mutation of the -533-, -759-, and -773-bp GREs alone or in tandem demonstrated that the -759-bp GRE was also functionally more important, but both the -759- and -773-bp GREs are required for maximum glucocorticoid responses. Moreover, the -533-bp GRE, rather than increasing glucocorticoid sensitivity of the promoter, may limit corticosteroid responsiveness mediated via the -759- and -773-bp GREs. Finally, the glucocorticoid receptor bound to the -759- and -773-bp GREs interacts cooperatively with Egr-1 and/or AP-2 to stimulate PNMT promoter activity in RS1 cells treated with dexamethasone. In contrast, glucocorticoid receptors bound to the -533-bp GRE only seem to participate in synergistic activation of the PNMT promoter through interaction with activator protein 2.