The genomic structure of the human AP-2 transcription factor

Novel TFAP2A mutation in a Japanese family with Branchio-oculo-facial syndrome

Branchio-oculo-facial syndrome (BOFS) is a rare autosomal dominant disorder characterized by craniofacial, ocular, and ectodermal anomalies. BOFS is caused by mutation of the transcription factor AP2-alpha gene (TFAP2A). We performed detailed genetic analysis of a Japanese family with clinically suspected BOFS and identified a novel missense mutation resulting in a predicted amino-acid substitution in the highly conserved basic DNA-binding domain of TFAP2A (NM_003220.2:c.699A>C).

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

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

Human Melanoma cells over-express extracellular matrix 1 (ECM1) which is regulated by TFAP2C

Extracellular matrix 1 (ECM1) is over-expressed in multiple epithelial malignancies. However, knowledge regarding the expression of ECM1 in melanomas and the mechanisms of ECM1 regulation is limited. In this study, we found that ECM1 is over-expressed in several melanoma cell lines, when compared to primary melanocytes, and furthermore, that ECM1 expression paralleled that of TFAP2C levels in multiple cell lines. Knockdown of TFAP2C in the A375 cell line with siRNA led to a reduction in ECM1 expression, and upregulation of TFAP2C with adenoviral vectors in the WM793 cell line resulted in ECM1 upregulation. Utilizing 5’ RACE to identify transcription start sites (TSS) and luciferase reporter assays in the ECM1-overexpressing A375 cell line, we identified the minimal promoter region of human ECM1 and demonstrate that an approximately 100bp fragment upstream of the TSS containing a TATA box and binding sites for AP1, SP1 and Ets is sufficient for promoter activity. Chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in the A375 cell line identified an AP2 regulatory region in the promoter of the ECM1 gene. Gelshift assays further confirmed binding of TFAP2C to this site. ECM1 knockdown reduces melanoma cell attachment and is consistent with findings that ECM1 overexpression has been associated with a poor prognosis. Our investigations show an as yet unrecognized role for TFAP2C in melanoma via its regulation of ECM1.

miR-214 coordinates melanoma progression by upregulating ALCAM through TFAP2 and miR-148b downmodulation

Malignant melanoma is one of the most aggressive human cancers, but the mechanisms governing its metastatic dissemination are not fully understood. Upregulation of miR-214 and ALCAM and the loss of TFAP2 expression have been implicated in this process, with TFAP2 a direct target of miR-214. Here, we link miR-214 and ALCAM as well as identify a core role for miR-214 in organizing melanoma metastasis. miR-214 upregulated ALCAM, acting transcriptionally through TFAP2 and also posttranscriptionally through miR-148b (itself controlled by TFAP2), both negative regulators of ALCAM. We also identified several miR-214-mediated prometastatic functions directly promoted by ALCAM. Silencing ALCAM in miR-214-overexpressing melanoma cells reduced cell migration and invasion without affecting growth or anoikis in vitro, and it also impaired extravasation and metastasis formation in vivo. Conversely, cell migration and extravasation was reduced in miR-214-overexpressing cells by upregulation of either miR-148b or TFAP2. These findings were consistent with patterns of expression of miR-214, ALCAM, and miR-148b in human melanoma specimens. Overall, our results define a pathway involving miR-214, miR-148b, TFAP2, and ALCAM that is critical for establishing distant metastases in melanoma.

Protein-binding microarray analysis of tumor suppressor AP2α target gene specificity

Cheap and massively parallel methods to assess the DNA-binding specificity of transcription factors are actively sought, given their prominent regulatory role in cellular processes and diseases. Here we evaluated the use of protein-binding microarrays (PBM) to probe the association of the tumor suppressor AP2α with 6000 human genomic DNA regulatory sequences. We show that the PBM provides accurate relative binding affinities when compared to quantitative surface plasmon resonance assays. A PBM-based study of human healthy and breast tumor tissue extracts allowed the identification of previously unknown AP2α target genes and it revealed genes whose direct or indirect interactions with AP2α are affected in the diseased tissues. AP2α binding and regulation was confirmed experimentally in human carcinoma cells for novel target genes involved in tumor progression and resistance to chemotherapeutics, providing a molecular interpretation of AP2α role in cancer chemoresistance. Overall, we conclude that this approach provides quantitative and accurate assays of the specificity and activity of tumor suppressor and oncogenic proteins in clinical samples, interfacing genomic and proteomic assays.

A novel TFAP2A mutation in familial Branchio-Oculo-Facial Syndrome with predominant ocular phenotype

INTRODUCTION

Branchio-Oculo-Facial Syndrome (BOFS) is a rare autosomal dominant congenital disorder defined by branchial defects, ocular anomalies and craniofacial malformations, including variable degrees of cleft lip with or without cleft palate. In addition, temporal bone anomalies, renal and ectodermal manifestations can be present. Mutations in the TFAP2A gene have been reported in patients with BOFS, prompting phenotype-genotype studies because of the variable clinical spectrum.

MATERIALS AND METHODS

We report on a family (a mother, her daughter and son) with BOFS and significant variability in clinical expression. The daughter presents predominantly with an ocular phenotype of unilateral microphthalmia and bilateral chorioretinal colobomas, whereas her brother is more severely affected contrasting with the paucisymptomatic mother. TFAP2A molecular analysis revealed a novel frameshift mutation.

DISCUSSION

We confirm the wide clinical spectrum of BOFS. The importance of upper lip examination in mild and paucisymptomatic cases is underlined. TFAP2A mutation spectrum is discussed and broadened by the report of the second frameshift mutation in this gene.

CONCLUSION

Patients with BOFS and predominant ocular phenotypes can be underdiagnosed. In such cases, upper lip examination can be of important diagnostic value. TFAP2A analysis provides diagnostic confirmation and improves genetic counselling.

microRNA-214 contributes to melanoma tumour progression through suppression of TFAP2C

Malignant melanoma is fatal in its metastatic stage. It is therefore essential to unravel the molecular mechanisms that govern disease progression to metastasis. MicroRNAs (miRs) are endogenous non-coding RNAs involved in tumourigenesis. Using a melanoma progression model, we identified a novel pathway controlled by miR-214 that coordinates metastatic capability. Pathway components include TFAP2C, homologue of a well-established melanoma tumour suppressor, the adhesion receptor ITGA3 and multiple surface molecules. Modulation of miR-214 influences in vitro tumour cell movement and survival to anoikis as well as extravasation from blood vessels and lung metastasis formation in vivo. Considering that miR-214 is known to be highly expressed in human melanomas, our data suggest a critical role for this miRNA in disease progression and the establishment of distant metastases.

CREB inhibits AP-2alpha expression to regulate the malignant phenotype of melanoma

BACKGROUND

The loss of AP-2alpha and increased activity of cAMP-responsive element binding (CREB) protein are two hallmarks of malignant progression of cutaneous melanoma. However, the molecular mechanism responsible for the loss of AP-2alpha during melanoma progression remains unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Herein, we demonstrate that both inhibition of PKA-dependent CREB phosphorylation, as well as silencing of CREB expression by shRNA, restored AP-2alpha protein expression in two metastatic melanoma cell lines. Moreover, rescue of CREB expression in CREB-silenced cell lines downregulates expression of AP-2alpha. Loss of AP-2alpha expression in metastatic melanoma occurs via a dual mechanism involving binding of CREB to the AP-2alpha promoter and CREB-induced overexpression of another oncogenic transcription factor, E2F-1. Upregulation of AP-2alpha expression following CREB silencing increases endogenous p21(Waf1) and decreases MCAM/MUC18, both known to be downstream target genes of AP-2alpha involved in melanoma progression.

CONCLUSIONS/SIGNIFICANCE

Since AP-2alpha regulates several genes associated with the metastatic potential of melanoma including c-KIT, VEGF, PAR-1, MCAM/MUC18, and p21(Waf1), our data identified CREB as a major regulator of the malignant melanoma phenotype.

Tfap2 transcription factors in zebrafish neural crest development and ectodermal evolution

Transcription factor AP2 (Tfap2) genes play essential roles in development of the epidermis and migratory cells of the neural crest (NC) in vertebrate embryos. These transcriptional activators are among the earliest genes expressed in the ectoderm and specify fates within the epidermis/crest through both direct and indirect mechanisms. The Tfap2 family arose from a single ancestral gene in a chordate ancestor that underwent gene duplication to give up to five family members in living vertebrates. This coincided with the acquisition of important roles in NC development by Tfap2 genes suggesting that this gene family was important in ectodermal evolution and possibly in the origin of NC. Here, we show that a zebrafish tfap2c is expressed in the nonneural ectoderm during early development and functions redundantly with tfap2a in NC specification. In zebrafish embryos depleted of both tfap2a and tfap2c, NC cells are virtually eliminated. Cell transplantation experiments indicate that tfap2c functions cell-autonomously in NC specification. Cells of the enveloping layer, which forms a temporary skin layer surrounding the ectoderm, also fail to differentiate or to express appropriate keratins in tfap2c deficient embryos. The role of Tfap2 genes in epidermal and NC development is considered here in the broader context of ectodermal evolution. Distinct, tissue-specific functions for Tfap2 genes in different vertebrates may reflect subfunctionalisation of an ancestral gene that consequently led to the gain of novel roles for different subfamily members in patterning the epidermis and NC.

Inefficient proteasomal-degradation pathway stabilizes AP-2alpha and activates HER-2/neu gene in breast cancer

HER-2/neu proto-oncogene is overexpressed in about one fourth of human breast cancers. AP-2 transcription factors bind to the HER-2/neu gene promoter and activate its expression. In a striking concurrence, anomalous abundance of AP-2alpha protein or its homolog AP-2gamma is also detected with HER-2/neu protein in mammary tumor-derived cell lines. This suggests that the deregulation of AP-2 is the preceding pathogenic event and probably the pivotal one in this type of mammary carcinogenesis. We examined the process of AP-2alpha gene expression in mammary carcinoma cell lines to identify where the aberration had occurred. We found no amplification of the AP-2alpha gene. Its promoter was marginally upregulated; however, it did not significantly increase the mRNA levels. When the AP-2alpha protein was examined, a remarkable stability was seen in breast cancer cell lines MDA-MB-453 and SK-BR-3, with a half-life of over 30 hr. This is sharply higher than the approximate 1 hr observed in mammary epithelial cell line MCF-10A and murine cell line NIH 3T3. Treatment of MCF-10A and NIH 3T3 cells with the proteasome inhibitor MG-132 showed that AP-2alpha was ubiquitinated and its level significantly increased. Moreover, this increase was accompanied by elevated levels HER-2/neu protein. In contrast, weaker ubiquitination of AP-2alpha was seen in MDA-MB-453 and SK-BR-3 cancer cells, and MG-132 treatment did not raise the AP-2alpha level any further. These results uncover that unusual stability is the main mechanism that raises the levels of AP-2 proteins, and in addition, provide the first clue that defective ubiquitin-dependent proteasomal-degradation pathway is possibly the prime cause that affects the HER-2/neu gene and culminates in breast cancer.

Dopamine-D1 and -D2 receptors differentially regulate synapsin II expression in the rat brain

We previously demonstrated that chronic treatment with the dopamine-D2 receptor antagonist, haloperidol, increases mRNA and protein content of the phosphoprotein, synapsin II, in the rat striatum. Since dopamine-D2 receptor antagonism and dopamine-D1 receptor blockade can have opposing effects on gene expression, the present investigation compared the effects of haloperidol with those of the dopamine-D1 receptor antagonist, R-[+]-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH23390), on the expression of synapsin II protein. Haloperidol and SCH23390 respectively elevated and reduced concentrations of the molecule in mouse primary midbrain cell cultures. Additional experiments revealed that the dopamine-D1 receptor agonist, R-[+]-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzapezine-7,8-diol (SKF38393), upregulated the phosphoprotein in these cells. Furthermore, in vivo rat studies demonstrated that chronic haloperidol treatment increases synapsin II protein expression in the medial prefrontal cortex and nucleus accumbens, as was observed in the striatum. In contrast, chronic SCH23390 administration reduced concentrations of this protein in all of these regions, although the reductions seen in the medial prefrontal cortex were insignificant. Neither haloperidol nor the dopamine-D1 receptor antagonist affected synapsin I protein expression in any of the studied brain areas. Based on these findings, we propose dopamine receptors may specifically regulate synapsin II expression through a cyclic AMP-dependent pathway. Since synapsin II is involved in neurotransmitter release and synaptogenesis, and changes in synaptic efficacy and structure are suggested in schizophrenia as well as in haloperidol treatment, our findings offer insight into the mechanistic actions of the antipsychotic agent at the synaptic level.

Regulation of KiSS-1 metastasis suppressor gene expression in breast cancer cells by direct interaction of transcription factors activator protein-2alpha and specificity protein-1

KiSS-1 has been shown to function as a tumor metastasis suppressor gene and reduce the number of metastases in different cancers. The expression of KiSS-1 or KiSS1, like other tumor suppressor, is commonly reduced or completely ablated in a variety of cancers via an unknown mechanism. Here we show that the loss of KiSS-1 expression in highly metastatic breast cancer cell lines correlates directly with the expression levels of two transcription factors, activator protein-2alpha (AP-2alpha) and specificity protein 1 (Sp1), which synergistically activate the transcriptional regulation of KiSS-1 in breast cancer cells. Although the KiSS-1 promoter contains multiple AP-2alpha binding elements, AP-2alpha-mediated regulation occurs indirectly through Sp1 sites, as determined by deletion and mutation analysis. Overexpression of AP-2alpha into highly metastatic breast cell lines did not alter KiSS-1 promoter-driven luciferase gene activity. However, co-transfection of AP-2alpha wild-type or the dominant negative form of AP-2 lacking its C-terminal DNA-binding domain, AP-2B, together with Sp1, increased KiSS-1 promoter activity dramatically, suggesting that AP-2alpha regulation of KiSS-1 transcription does not require direct binding to the KiSS-1 promoter. Furthermore, we demonstrated that AP-2alpha directly interacted with Sp1 to form transcription complexes at two tandem Sp1-binding sites of the promoter to activate KiSS-1 transcription. Together, our results indicate that AP-2alpha and Sp1 are strong transcriptional regulators of KiSS-1 and that loss or decreased expression of AP-2alpha in breast cancer may account for the loss of tumor metastasis suppressor KiSS-1 expression and thus increased cancer metastasis.

Molecular cloning and characterization of AP-2 epsilon, a fifth member of the AP-2 family

The mammalian AP-2 family of transcription factors consists of four members, AP-2 alpha, AP-2 beta, AP-2 gamma and AP-2 delta, which play an important role in regulating gene expression during development and differentiation of multiple organs and tissues. The defining feature of the AP-2 family is a highly conserved carboxy-terminal basic helix-turn-helix domain that is involved in dimerization and sequence-specific DNA-binding. In this report, we use bioinformatics to identify both the mouse and human AP-2 epsilon, a fifth member of the AP-2 family. The predicted mouse and human AP-2 epsilon proteins consist of 442 amino acids and show a high level of sequence similarity with other AP-2 proteins in the DNA-binding and dimerization domain and weak similarity in the N-terminal activation domain. Northern blot analysis reveals that among the adult mouse tissues examined, AP-2 epsilon is highly expressed in skin tissue. The human AP-2 epsilon gene maps to chromosome 1p42, consists of seven exons spanning 23 kb and exhibits a genomic structure similar to other AP-2 family members. Human AP-2 epsilon mRNA is expressed in human skin and keratinocytes grown in culture. Finally, we show that recombinant AP-2 epsilon can bind to AP-2 binding sequences from keratin promoters in electrophoretic mobility shift assays. Our study establishes AP-2 epsilon as a novel member of the AP-2 family, and suggests that it may play an important role in skin biology.

Functional characterization of the interacting domains of the positive coactivator PC4 with the transcription factor AP-2α

The transcriptional positive cofactor 4 (PC4) physically interacts with the transcription factor, activator protein-2 (AP-2) alpha, and overexpression of PC4 results in a relief of the AP-2 transcriptional self-interference, which is induced by high levels of AP-2alpha expression. PC4 was initially described as a DNA-binding protein that enhances the activator-dependent transcription of class II genes in vitro, but it was later shown that PC4 could also act as a potent repressor of transcription on specific DNA structures such as single-stranded (ss) DNA, DNA ends and heteroduplex DNA. To further explore the functional domains of PC4 and its ssDNA-binding effect in the interaction with AP-2alpha and on AP-2 transcriptional activity, we investigated the C-terminal domain of PC4 (PC4-CTD) and several PC4 mutants in which the ssDNA binding function was interrupted. We found that the C-terminal domain of PC4 physically interacts with AP-2alpha and retains the function of full-length protein in relieving transcription self-interference of AP-2. A point-mutated form of PC4 within the C-terminal domain beta-ridge, PC4 W89A, or a triple mutant in the beta2-beta3 loop of PC4, F77A/K78G/K80G, inactivate the ability of PC4 to bind AP-2alpha and to relieve the transcription self-interference of AP-2alpha. In addition, point-mutated forms of AP-2alpha within the activation domain (AD) that inactivate AP-2 transcription activity also lose their self-interference function. Our data suggest that the C-terminal domain of the transcription cofactor PC4 is critical for AP-2alpha transcriptional interference that is mediated by the activation domain of AP-2alpha.

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.

Characterization of the human activator protein-2gamma (AP-2gamma) gene: control of expression by Sp1/Sp3 in breast tumour cells

The activator protein-2 (AP-2) family of DNA-binding transcription factors are developmentally regulated and also play a role in human neoplasia. In particular, the AP-2gamma protein has been shown to be overexpressed in a high percentage of breast tumours. In the present study, we report the complete sequence determination of the human TFAP2C gene encoding the AP-2gamma transcription factor plus the mapping of the transcription start site used in breast tumour-derived cells. The 5'-end of the gene lies within a CpG island and transcription is initiated at a single site within a classical initiator motif. We have gone on to investigate why some breast tumour-derived cell lines readily express AP-2gamma, whereas others do not, and show that the proximal promoter (+191 to -312) is differentially active in the two cell phenotypes. DNase footprinting led to the identification of three Sp1/Sp3-binding sites within this region, two of which are absolutely required both for promoter function and cell-type-specific activity. By Western blotting a panel of expressing and non-expressing breast tumour lines we show that the latter have higher levels of Sp3. Furthermore, increasing Sp3 levels in AP-2gamma-expressing cells led to the repression of AP-2gamma promoter activity, particularly when Sp3 inhibitory function was maximized through sumoylation. We propose that differences in the level and activity of Sp3 between breast tumour lines can determine the expression level of their AP-2gamma gene.

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.

Expression of AP-2?, c-kit, and cleaved caspase-6 and -3 in naevi and malignant melanomas of the skin. A possible role for caspases in melanoma progression?

Progression of melanoma is associated with loss of the transcription factor AP-2alpha and tyrosine-kinase receptor c-kit. However, the mechanisms by which these two proteins are down-regulated have not been fully elucidated. Fifty non-selected melanomas comprising ten superficial spreading melanomas (five exhibiting a radial growth phase and five a vertical growth phase), ten primary nodular melanomas, 30 melanoma metastases, and 16 naevi were investigated by direct sequencing analysis of the AP-2alpha and c-kit genes and by immunohistochemistry for the respective proteins. Because it has recently been demonstrated that AP-2alpha is preferentially cleaved by caspase-6 and to a lesser extent by caspase-3, immunohistochemistry for the cleaved (activated) forms of caspase-6 (c-casp-6) and caspase-3 (c-casp-3) was carried out. No mutations were identified in the c-kit gene, but three different point mutations were demonstrated in the activation motif of AP-2alpha in four tumours: one vertical growth phase superficial spreading melanoma, one nodular melanoma, and two metastases. Immunohistochemistry revealed progressive loss of the AP-2alpha and c-kit proteins in primary melanomas and metastases when compared with naevi. The decrease of both markers was more accentuated in the dermal component of all primary tumours, with c-kit more affected than AP-2alpha. All invasive melanomas and metastases expressed c-casp-6. c-casp-3 was expressed by 83% of the metastases and in the dermal component of one nodular melanoma. These findings suggest that the loss of AP-2alpha protein expression during the progression of melanoma could be related to mutation of the gene in only a small number of tumours, whereas the expression and activation of caspases, most prominently caspase-6, may be an important factor for the down-regulation of AP-2alpha protein. Furthermore, this study supports recent data that the activation of caspases does not inevitably result in apoptosis, but may also contribute to tumour progression in melanomas.

The human transcription factor activation protein-2 gamma (AP-2gamma): gene structure, promoter, and expression in mammary carcinoma cell lines

Human activation protein-2 gamma (hAP-2gamma) is a key developmental transcription factor. It has been implicated in mammary carcinogenesis through its regulation of HER-2/neu proto-oncogene and estrogen receptor gene The hAP-2gamma gene is located on human chromosome 20q13.2. We cloned this gene, deduced its genomic structure, and mapped and analyzed its promoter. The hAP-2gamma gene contains seven exons. Primer extension analysis and 5'-rapid amplification of complementary DNA ends studies show that there is a single transcription start site 232 nt upstream of the translational start codon. The promoter lacks canonical binding sites for basal transcription factors such as TATA and CCAAT boxes, but contains a cluster of CpG islands and may rely on an initiator element for transcription. Deletion analyses of the promoter and chloramphenicol acetyl transferase reporter gene assays indicate that the sequence between -746 and -575 is important for its expression in mammary carcinoma cell lines. The hAP-2gamma gene is marginally activated in these cells suggesting that increased transcription partly contributes to its abundance. Architecture of the gene and promoter strikingly resembles that of hAP-2alpha, which is located on a different chromosome, suggesting a cognate origin. hAP-2alpha and hAP-2gamma have some common and some distinct roles in cells, and are likely the remarkable results of gene duplication, translocation and functional divergence through evolution.

Amphioxus and lamprey AP-2 genes: implications for neural crest evolution and migration patterns

The neural crest is a uniquely vertebrate cell type present in the most basal vertebrates, but not in cephalochordates. We have studied differences in regulation of the neural crest marker AP-2 across two evolutionary transitions: invertebrate to vertebrate, and agnathan to gnathostome. Isolation and comparison of amphioxus, lamprey and axolotl AP-2 reveals its extensive expansion in the vertebrate dorsal neural tube and pharyngeal arches, implying co-option of AP-2 genes by neural crest cells early in vertebrate evolution. Expression in non-neural ectoderm is a conserved feature in amphioxus and vertebrates, suggesting an ancient role for AP-2 genes in this tissue. There is also common expression in subsets of ventrolateral neurons in the anterior neural tube, consistent with a primitive role in brain development. Comparison of AP-2 expression in axolotl and lamprey suggests an elaboration of cranial neural crest patterning in gnathostomes. However,migration of AP-2-expressing neural crest cells medial to the pharyngeal arch mesoderm appears to be a primitive feature retained in all vertebrates. Because AP-2 has essential roles in cranial neural crest differentiation and proliferation, the co-option of AP-2 by neural crest cells in the vertebrate lineage was a potentially crucial event in vertebrate evolution.

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

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

Dominant-negative transcription factor AP-2 augments SB-2 melanoma tumor growth in vivo

We have previously demonstrated that the transition of melanoma to the metastatic phenotype is associated with a loss of expression of the transcription factor AP-2. To further investigate the role of AP-2 in the progression of human melanoma, we attempted to inactivate AP-2 in primary cutaneous SB-2 melanoma cells by using a dominant-negative AP-2, or AP-2B, gene. AP-2B is an alternatively spliced AP-2 variant capable of inhibiting AP-2 trans-activator function. Stable transfection of primary cutaneous melanoma SB-2 cells with the dominant-negative AP-2B gene was confirmed by RT--PCR and Northern blot analyses. Electromobility shift assay using nuclear extracts from these cell lines demonstrated decreased functional binding of AP-2B-transfected cells to the AP-2 consensus binding sequence compared with neo-transfected controls. In addition, CAT activity driven by a construct containing the AP-2 consensus binding sequence was downregulated in the AP-2B transfected cells, indicating AP-2 activity was quenched in the transfected cells. Orthotopic (subcutaneous) injection of the dominant-negative (AP-2B)-transfected cell lines into nude mice increased their tumorigenicity compared to control neo-transfected cells. The AP-2B-transfected cells displayed an increase in MMP-2 expression (by Northern blot) and MMP-2 activity (by zymography), which resulted in an increase in invasiveness through Matrigel-coated filters. The AP-2B-transfected tumors also displayed an increase in MMP-2 expression, microvessel density, and angiogenesis in vivo. These results demonstrate that inactivation of AP-2 contributes to the progression of melanoma, at least partially via deregulation of the MMP-2 gene.

Expression of AP-2 alpha in SV40 immortalized human lung fibroblasts is associated with a distinct pattern of cytosine methylation in the AP-2 alpha promoter

Activator protein-2 alpha (AP-2 alpha) is a cell type-specific, developmentally regulated, transcription factor that has been implicated as a critical regulator of gene expression during vertebrate development and carcinogenesis. We found that AP-2 alpha was differentially expressed in the normal human lung fibroblast cell strains WI38, MRC-5 and their respective SV40-transformed cell counterparts WI38-VA, MRC-5VA. Since CpG methylation within genetic regulatory regions has been implicated as a mechanism of gene regulation, we investigated the CpG methylation status of the AP-2 alpha gene promoter in these cells. High resolution mapping of methylated cytosines revealed that differential expression of the AP-2 alpha gene in normal human lung fibroblasts and their SV40-transformed counterparts was associated with distinct patterns of cytosine methylation in the AP-2 alpha promoter just 5' to the transcription initiation site. Site-specific methylation was positively correlated with increased AP-2 alpha gene expression in both transformed cell lines investigated. Interestingly, one of the two major centers of hypermethylation in the transformed cells encompassed the cis-element for the AP-2 repressing transcription factor AP-2rep (KLF12). Finally, a sequence variation in human lung fibroblasts relative to the published sequence revealed a previously unidentified AP-2 binding site at position -528 with respect to the transcription initiation site that overlapped the AP-2rep site. Our results suggest that transcriptional activation of AP-2 alpha in the SV40-transformed cells is mediated, at least in part, by site-specific methylation of a negative regulatory cis-element in the AP-2 alpha promoter.

Novel activator protein-2alpha splice-variants function as transactivators of the ovine placental lactogen gene

Activator protein-2 (AP-2) has been implicated as a transactivator of the human and ovine placental lactogen (oPL) genes. Transcriptional enhancement through an AP-2 cis-acting element has been described for other genes expressed in the placenta, but the AP-2 isoform enhancing expression is species dependent. Transactivation of the oPL minimal promoter (-124 bp to +16 bp) by AP-2 was confirmed by mutational analysis in transiently transfected human choriocarcinoma cells (BeWo). AP-2alpha was localized in ovine chorionic epithelial cells by immunohistochemistry and a 3-kb transcript was identified by Northern hybridization. Four nearly full-length AP-2 cDNAs were isolated from an ovine placenta cDNA library. Nucleotide sequencing these cDNAs revealed that the AP-2 mRNA expressed in the ovine placenta shares identity with human AP-2alpha, but variations in the predicted N-terminus were observed, and three unique AP-2alpha splice-variants were identified. Expression of AP-2alpha variants in HepG2 cells, devoid of endogenous AP-2, indicates that enhancement through the AP-2 element in the oPL gene minimal promoter was variant dependent. RNA transcripts for all of the ovine AP-2alpha splice-variants were confirmed in ovine placenta by RT-PCR, and homologs for two variants were found in human placenta. However, only one AP-2alpha transcript, which shares identity to Xenopus AP-2alpha, was expressed in BeWo cells. Immunoblot analysis confirmed AP-2alpha variants in ovine chorionic binucleate cell nuclear extracts, one of which migrates similar to the AP-2alpha variant identified in BeWo cell nuclear extracts. These data indicate the presence of new mammalian AP-2alpha splice-variants that augment transactivation of the oPL gene in ovine chorionic binucleate cells.

Regulatory roles of AP-2 transcription factors in vertebrate development, apoptosis and cell-cycle control

AP-2 transcription factors represent a family of three closely related and evolutionarily conserved sequence-specific DNA-binding proteins, AP-2alpha, -beta and -gamma. Subsequent studies have identified spatially and temporally regulated embryonic expression patterns in a number of different tissues including neural crest derivatives, neural, epidermal and urogenital tissues. Here, we review the current understanding of developmental defects in AP-2-deficient mice and consider regulatory functions of AP-2 in control of apoptosis, cell cycle, and gene expression. Recently, the first inherited human disorder, Char syndrome, was identified to be caused by AP-2beta missense mutations. In light of the manifold and essential functions of AP-2 proteins in cell growth, differentiation and programmed death, mutations or changes in precisely programmed expression patterns are likely to contribute to other congenital malformations or neoplastic diseases.

Genomic structure and DNA binding properties of the human zinc finger transcriptional repressor AP-2rep (KLF12)

We recently cloned a novel murine transcriptional repressor, the Krüppel-like zinc finger protein AP-2rep (HGMW-approved symbol KLF12), that binds to a regulatory element in the AP-2alpha gene promoter. In the present study, we characterize the human AP-2rep homolog and describe expression patterns in human urogenital and lymphoma cell lines. The predicted human protein of 402 amino acids exhibits 95.8% identity and 98.5% similarity to the murine AP-2rep peptide. The genomic locus of human AP-2rep consists of seven exons and was assigned to chromosome 13q22 by fluorescence in situ hybridization to metaphase chromosomes. Human AP-2rep repressed both reporter expression from a transiently transfected AP-2alpha promoter and the endogenous AP-2alpha gene and inversely was negatively regulated by AP-2alpha. The consensus motif CAGTGGG was identified by an in vitro binding site selection assay. In summary, our data further point to an important role of AP-2rep as a transcriptional silencer and reveal reciprocal regulation of AP-2alpha and AP-2rep.

Transcriptional regulation of the AP-2alpha promoter by BTEB-1 and AP-2rep, a novel wt-1/egr-related zinc finger repressor

AP-2 transcription factors have been suggested to exert key regulatory functions in vertebrate embryonic development, in tumorigenicity of various cancer cell types, and in controlling cell cycle and apoptotic effector genes. In this study, we investigated transcriptional regulation of the AP-2alpha gene promoter mediated by an autoregulatory element (referred to as A32) with a core consensus AP-2 binding site at position -336 relative to the mRNA initiation site. AP-2 and multiple different nuclear proteins in HeLa and Neuro2A cell extracts form specific bandshifts with the A32 element. By screening a mouse brain cDNA expression library, we isolated two different cDNAs encoding the transcription factor BTEB-1 and a novel zinc finger protein, AP-2rep. AP-2rep reveals a modular structure with homology to transcription factors of the wt-1/egr-1-family. AP-2rep, BTEB-1, and AP-2 interact in a mutually exclusive manner with overlapping binding sites in the A32 element. Transfection studies revealed that BTEB-1 is a strong activator of AP-2alpha promoter activity, whereas cotransfected AP-2alpha resulted in moderate autoactivation of promoter activity. In contrast, AP-2rep confers strong transcriptional repression to the AP-2alpha gene, and we observed an excellent correlation between induction of AP-2rep mRNA expression and downregulation of AP-2alpha mRNA during development of the kidney. In summary, we have identified multiple transcription factors and cloned from an expression library a novel zinc finger silencing factor, AP-2rep, mediating positive and negative regulation of AP-2alpha expression through a set of overlapping cis-regulatory promoter elements.

A synergistic interaction of transcription factors AP2 and YB-1 regulates gelatinase A enhancer-dependent transcription

The matrix metalloproteinase gelatinase A plays a central role in several critical physiologic processes, including angiogenesis, tumor invasion/metastasis, and chronic inflammation. We demonstrate that high level gelatinase A expression is mediated by a unique interaction of two developmentally regulated transcription factors, AP2 and YB-1, within a discrete 40-base pair enhancer element (RE-1) located in the 5'-flanking region of the gelatinase A gene. Electrophoretic mobility shift assay studies and immunoprecipitation experiments confirmed a direct interaction of AP2 with this binding sequence in the form of AP2.YB-1 heteromeric complexes. Binding of AP2.YB-1 complexes to the RE-1 sequence results in the formation of extended single-stranded DNA regions and may stabilize DNA conformational changes. Overexpression of YB-1 and AP2 proteins by gelatinase A synthesizing hepatoma HepG2 cells induced a synergistic increase in the RE-1-mediated transcription of nearly 160-fold. Thus, the transcription of gelatinase A is subject to a previously unrecognized interplay of double (AP2) and single-stranded (YB-1) DNA binding transcription factors to yield a highly regulated pattern of gene expression.

A novel alternative spliced variant of the transcription factor AP2alpha is expressed in the murine ocular lens

The AP2alpha gene encodes a transcription factor containing a basic, helix-span-helix DNA-binding/dimerization domain, which is developmentally regulated and retinoic acid inducible. Recent reports about AP2alpha null mice indicate that AP2alpha plays an important role in embryogenesis, especially in craniofacial development and midline fusion. Ocular development is also affected in these null mice. As AP2alpha may be involved in transcriptional regulation in the lens, it was important to examine the expression of the AP2alpha gene in the lens. Four AP2alpha mRNA variants have been previously isolated from whole mouse embryos. Variants 1, 3, and 4 are transcriptional activators that are transcribed from different promoters and variant 2 is a repressor lacking the activation domain encoded by exon 2. Using in situ-PCR, we found that AP2alpha is expressed in the lens epithelia but not in the lens fibers. RT-PCR analysis of lens mRNA with amplimers specific for each variant revealed that AP2alpha variants 1, 2, and 3 are expressed in newborn mouse lenses. However, variant 4 is not expressed in the lens. In this report we characterized a novel isoform, which we named variant 5, expressed in the lens and kidney. Variant 5, which is generated by alternative splicing, may function as a repressor due to the partial deletion of the proline-rich transactivation domain encoded by exon 2. This is the first molecular characterization of AP2alpha gene expression in the lens. Our results indicate that two activator and two repressor AP2alpha isoforms may play a role in regulating gene expression in the lens.

Redox modulation of AP-2 DNA binding activity in vitro

Transcription factor AP-2 plays a critical role in regulating gene expression during vertebrate development and cellular differentiation. We report here that AP-2 DNA binding in vitro can be reversibly modulated by redox conditions and that thioredoxin is a potent stimulator of AP-2 DNA binding. Our studies indicate that oxidation of recombinant human AP-2 with diamide or hydrogen peroxide inhibits its DNA binding activity to synthetic AP-2 oligodeoxynucleotides. The inhibitory effect of diamide on AP-2 DNA binding was dose-dependent and was reversible by addition of reducing agents beta-mercaptoethanol, dithiothreitol, and thioredoxin. Immunoblot assays indicated that treatment with oxidants caused a change in migration of the AP-2 protein in nonreducing gels and that this effect was also reversible by treatment of the oxidized AP-2 with reducing agents. These data suggest a mechanism by which the oxidation state of conserved cysteine residues in the AP-2 DNA binding domain may contribute to its DNA binding activity. AP-2 joins a group of other transcription factors whose functions are regulated in part by their redox states.

Loss of AP-2 results in downregulation of c-KIT and enhancement of melanoma tumorigenicity and metastasis

Expression of the tyrosine kinase receptor, c-KIT, progressively decreases during local tumor growth and invasion of human melanomas. We have previously shown that enforced c-KIT expression in highly metastatic cells inhibited tumor growth and metastasis in nude mice. Furthermore, the ligand for c-KIT, SCF, induces apoptosis in human melanoma cells expressing c-KIT under both in vitro and in vivo conditions. Here we show that loss of c-KIT expression in highly metastatic cells correlates with loss of expression of the transcription factor AP-2. The c-KIT promoter contains three binding sites for AP-2 and EMSA gels demonstrated that AP-2 protein binds directly to the c-KIT promoter. Transfection of wild-type AP-2 into c-KIT-negative A375SM melanoma cells activated a c-KIT promoter-driven luciferase reporter gene, while expression of a dominant-negative AP-2B in c-KIT-positive Mel-501 cells inhibited its activation. Endogenous c-KIT mRNA and expression of proteins were upregulated in AP-2-transfected cells, but not in control cells. In addition, re-expression of AP-2 in A375SM cells suppressed their tumorigenicity and metastatic potential in nude mice. These results indicate that the expression of c-KIT is highly regulated by AP-2 and that enforced AP-2 expression suppresses tumorigenicity and metastatic potential of human melanoma cells, possibly through c-KIT transactivation and SCF-induced apoptosis. Therefore, loss of AP-2 expression might be a crucial event in the development of malignant melanoma.

RB and c-Myc activate expression of the E-cadherin gene in epithelial cells through interaction with transcription factor AP-2

E-cadherin plays a pivotal role in the biogenesis of the first epithelium during development, and its down-regulation is associated with metastasis of carcinomas. We recently reported that inactivation of RB family proteins by simian virus 40 large T antigen (LT) in MDCK epithelial cells results in a mesenchymal conversion associated with invasiveness and a down-regulation of c-Myc. Reexpression of RB or c-Myc in such cells allows the reexpression of epithelial markers including E-cadherin. Here we show that both RB and c-Myc specifically activate transcription of the E-cadherin promoter in epithelial cells but not in NIH 3T3 mesenchymal cells. This transcriptional activity is mediated in both cases by the transcription factor AP-2. In vitro AP-2 and RB interaction involves the N-terminal domain of AP-2 and the oncoprotein binding domain and C-terminal domain of RB. In vivo physical interaction between RB and AP-2 was demonstrated in MDCK and HaCat cells. In LT-transformed MDCK cells, LT, RB, and AP-2 were all coimmunoprecipitated by each of the corresponding antibodies, and a mutation of the RB binding domain of the oncoprotein inhibited its binding to both RB and AP-2. Taken together, our results suggest that there is a tripartite complex between LT, RB, and AP-2 and that the physical and functional interactions between LT and AP-2 are mediated by RB. Moreover, they define RB and c-Myc as coactivators of AP-2 in epithelial cells and shed new light on the significance of the LT-RB complex, linking it to the dedifferentiation processes occurring during tumor progression. These data confirm the important role for RB and c-Myc in the maintenance of the epithelial phenotype and reveal a novel mechanism of gene activation by c-Myc.

Loss of AP-2 results in up-regulation of MCAM/MUC18 and an increase in tumor growth and metastasis of human melanoma cells

MCAM/MUC18 is a cell-surface glycoprotein of 113 kDa, originally identified as a melanoma antigen, whose expression is associated with tumor progression and the development of metastatic potential. We have previously shown that enforced expression of MCAM/MUC18 in primary cutaneous melanoma led to increased tumor growth and metastatic potential in nude mice. The mechanism for up-regulation of MCAM/MUC18 during melanoma progression is unknown. Here we show that up-regulation of MCAM/MUC18 expression in highly metastatic cells correlates with loss of expression of the transcription factor AP-2. The MCAM/MUC18 promoter contains four binding sites for AP-2, and electrophoretic mobility shift assay gels demonstrated that the AP-2 protein bound directly to the MCAM/MUC18 promoter. Transfection of AP-2 into highly metastatic A375SM melanoma cells (AP-2-negative and MCAM/MUC18-positive) inhibited MCAM/MUC18 promoter-driven chloramphenicol acetyltransferase reporter gene in a dose-dependent manner. MCAM/MUC18 mRNA and protein expression were down-regulated in AP-2-transfected but not in control cells. In addition, re-expression of AP-2 in A375SM cells inhibited their tumorigenicity and metastatic potential in nude mice. These results indicate that the expression of MCAM/MUC18 is regulated by AP-2 and that enforced AP-2 expression suppresses tumorigenicity and metastatic potential of human melanoma cells, possibly by down-regulating MCAM/MUC18 gene expression. Since AP-2 also regulates other genes that are involved in the progression of human melanoma such as c-KIT, E-cadherin, MMP-2, and p21(WAF-1), we propose that loss of AP-2 is a crucial event in the development of malignant melanoma.

Genomic cloning and characterization of the mouse POZ/zinc-finger protein ZF5

We isolated genomic DNA containing the entire sequence of ZF5, which was originally identified by its ability to repress the mouse c-myc promoter and which was characterized as one of the POZ (Poxvirus and zinc finger) proteins. The POZ motif is a protein-protein interaction interface found at the N-terminal region of zinc finger proteins. Sequence analysis demonstrated that the ATG translation initiation codon was separately located from the remainder of the coding sequence. Using both RNase protection and primer extension assay, a single major transcription start site was determined. Promoter analysis by transient transfection assay suggested positive autoregulation by ZF5 itself. The ZF5 N-terminal region, including the POZ domain, was required for this regulation. Sp1 also activated the ZF5 promoter and this activity was repressed by addition of ZF5. ZF5 expression was stronger in mouse ovary, lung and brain than in other organs.

Autoregulation of eukaryotic transcription factors

The structures of several promoters regulating the expression of eukaryotic transcription factors have in recent years been examined. In many cases there is good evidence for autoregulation, in which a given factor binds to its own promoter and either activates or represses transcription. Autoregulation occurs in all eukaryotes and is an important component in controlling expression of basal, cell cycle specific, inducible response and cell type-specific factors. The basal factors are autoregulatory, being strictly necessary for their own expression, and as such must be epigenetically inherited. Autoregulation of stimulus response factors typically serves to amplify cellular signals transiently and also to attenuate the response whether or not a given inducer remains. Cell cycle-specific transcription factors are positively and negatively autoregulatory, but this frequently depends on interlocking circuits among family members. Autoregulation of cell type-specific factors results in a form of cellular memory that can contribute, or define, a determined state. Autoregulation of transcription factors provides a simple circuitry, useful in many cellular circumstances, that does not require the involvement of additional factors, which, in turn, would need to be subject to another hierarchy of regulation. Autoregulation additionally can provide a direct means to sense and control the cellular conce]ntration of a given factor. However, autoregulatory loops are often dependent on cellular pathways that create the circumstances under which autoregulation occurs.

CCAAT/enhancer-binding protein delta gene expression is mediated by autoregulation through downstream binding sites

CCAAT/enhancer-binding protein delta (C/EBP delta) transcription factor is sharply induced at the early stage of the acute phase response. We previously reported that the C/EBP delta gene expression is induced by the acute-phase response factor/signal transducers and activators of transcription 3 (APRF/STAT3). However, the expression level of the C/EBP delta gene is relatively high up to several hours after the stimulation, whereas APRF/STAT3 is inactivated within one hour. In this report, we identified the two C/EBP delta binding sites at the downstream region of this gene. The binding analysis revealed that both of these sites bound recombinant C/EBP delta protein. A cotransfection analysis identified these sites as the cis-elements for the autoregulation. We conclude that the C/EBP delta gene is activated by APRF/STAT3, and the expression level is then maintained by an autoregulation mechanism.

Nuclear and non-nuclear targets of genotoxic agents in the induction of gene expression. Shared principles in yeast, rodents, man and plants

The interplay between environmental cues and the genetic response is decisive for the development, health and well-being of an organism. For some environmental factors a narrow margin separates beneficial and toxic impacts. With the increasing exposure to UV-B this dichotomy has reached public attention. This review will be concerned with the mechanisms that mediate a cellular genetic response to noxious agents. The toxic stimuli find access to the regulatory network inside cells by interacting at several points with cellular molecules - a process that converts the 'outside information' into 'cellular language'. As a consequence of such interactions, many adverse agents cause massive signal transduction and changes of gene expression. There is an interesting conservation of the mechanisms from yeast to man. An understanding of the genetic programs and of their phenotypic consequences is lagging behind.

Chicken transcription factor AP-2: cloning, expression and its role in outgrowth of facial prominences and limb buds

Embryonic facial development in chick embryos involves a sequential activation of genes that control differential growth and patterning of the beak. In the present study we isolate one such gene, the transcription factor, AP-2, that is known to be expressed in the face of mouse embryos. The protein sequence of chick AP-2alpha is 94% homologous to human and mouse AP-2. Wholemount in situ hybridization with a probe for chick AP-2 identifies expression from primitive streak stages up to stage 28. The most striking expression patterns in the head are during neural crest cell migration when AP-2 transcripts follow closely the tracts previously mapped for neural crest cells. Later, expression in the facial mesenchyme is strongest in the frontonasal mass and lateral nasal prominences and is downregulated in the maxillary and mandibular prominences. Once limb buds are visible, high expression is seen in the distal mesenchyme but not in the apical ectodermal ridge. The expression patterns of AP-2 in stage 20 embryos suggested that the gene may be important in "budding out" of facial prominences and limb buds. We implanted beads soaked in retinoic acid in the right nasal pit of stage 20 embryos resulting in a specific inhibition of outgrowth of the frontonasal mass and lateral nasal prominences. AP-2 expression was completely down-regulated in the lateral nasal within 8 hr of bead application. In addition, the normal up-regulation of AP-2 in the frontonasal mass did not occur following retinoic-acid treatment. There was an increase in programmed cell death around the right nasal pit that accompanied the down-regulation of AP-2. Prominences whose morphogenesis were not affected by retinoic acid did not have altered expression patterns. We removed the apical ectodermal ridge in stage 20 limb buds and found that AP-2 expression was partially downregulated 4 hr following ridge removal and completely downregulated 8 hr following stripping. Application of an FGF-4 soaked bead to the apex of the limb bud maintained AP-2 expression. Thus AP-2 is involved in outgrowth and could be regulated by factors such as FGFs that are present in the ectoderm of both the face and limb.

Enhanced apoptotic cell death of renal epithelial cells in mice lacking transcription factor AP-2beta

Expression of AP-2 transcription factors has been detected previously in embryonic renal tissues. We show here that AP-2beta -/- mice complete embryonic development and die at postnatal days 1 and 2 because of polycystic kidney disease. Analyses of kidney development revealed that induction of epithelial conversion, mesenchyme condensation, and further glomerular and tubular differentiation occur normally in AP-2beta-deficient mice. At the end of embryonic development expression of bcl-X(L), bcl-w, and bcl-2 is down-regulated in parallel to massive apoptotic death of collecting duct and distal tubular epithelia. Addressing the molecular mechanism we show that transfection of AP-2 into cell lines in vitro strongly suppresses c-myc-induced apoptosis pointing to a function of AP-2 in programming cell survival during embryogenesis. The position of the human AP-2beta gene was identified at chromosome 6p12-p21.1, within a region that has been mapped for autosomal recessive polycystic kidney disease (ARPKD). Sequence analyses of ARPKD patients and linkage analyses using intragenic polymorphic markers indicate that the AP-2beta gene is located in close proximity to but distinct from the ARPKD gene.

Comparative analysis of AP-2 alpha and AP-2 beta gene expression during murine embryogenesis

Transcription factor AP-2 has been identified as playing important roles during embryonic development of the neural tube, neural crest derivatives, skin, and urogenital tissues. Recently, we isolated a second AP-2 transcription factor, AP-2 beta, which is 76% homologous to the previously known AP-2 alpha gene, and showed that both genes are coexpressed in murine embryos at day 13.5 and 15.5 post coitum (pc). In the current study, we used specific cRNA probes to study comparatively AP-2 alpha and AP-2 beta expression by in situ hybridization of murine embryonic tissue sections. Our results reveal that expression of both genes starts at day 8 pc in the lateral head mesenchyme and extraembryonic trophoblast. The expression pattern was identical until day 10 pc but diverged significantly during later stages of development. From day 11 forward, specific expression patterns of AP-2 alpha and AP-2 beta mRNA were observed. Specific AP-2 beta signals were detected in the midbrain, sympathetic ganglia, adrenal medulla, and cornea. Specific AP-2 alpha signals were present in the limb buds, dorsal root ganglia, tooth germs, and Moll's and Meibom's glands. In contrast, expression of both genes occurred in skin, facial mesenchyme, spinal cord, cerebellum, and renal tubular epithelia. Our results indicate that both genes are expressed with different temporal and spatial patterns during embryonic development.

Selective transcription factor induction in retinal pigment epithelial cells during photoreceptor phagocytosis

Expression of early response genes during rod outer segment phagocytosis by normal Long Evans and Royal College of Surgeons-rdy+p+ rats and by dystrophic Royal College of Surgeons-p+ rat retinal pigment epithelial cells was studied in primary cell culture. Northern analysis revealed that the abundance of zif-268 (egr-1), c-fos, and tis-1 (NGF1-B) mRNA was rapidly and transiently increased in normal retinal pigment epithelial cells during rod outer segment phagocytosis but not during phagocytosis of latex particles. No increase in gene expression was found in Royal College of Surgeons-p+ dystrophic retinal pigment epithelial cells challenged with rod outer segments. As shown by electrophoretic mobility shift assay, a prominent short term increase in the intensity of the gel-shifted band was detected using nuclear protein extracts derived from rod outer segment-challenged, control retinal pigment epithelial cells and zif-268, AP-1, AP-2, or tis-1 consensus oligonucleotides. No such increase was detected when using nuclear factor kappaB consensus oligonucleotide or when the early response gene prostaglandin H synthase-2 mRNA was measured over the time course studied. The results suggest that in retinal pigment epithelial cells, rod outer segment-specific phagocytosis is accompanied by the selective expression of early response genes coding for transcription factors. The specific pattern of the induction of these transcription factors is predicted to modulate the expression of gene cascades.

Transcriptional activation of the Cu,Zn-superoxide dismutase gene through the AP2 site by ginsenoside Rb2 extracted from a medicinal plant, Panax ginseng

We report here that the ginseng saponins induce the transcription of Cu,Zn-superoxide dismutase gene (SOD1), which is one of the major antioxidant enzymes. Total saponins and panaxatriol did not elevate the level of SOD1, but panaxadiol significantly increased SOD1. Among the panaxadiol fractions, ginsenoside Rb2 was a more specific and more remarkable inducer of the SOD1 gene than ginsenoside Rb1. Deletion analyses of the SOD1 promoter revealed that the proximal promoter is responsible for this induction. Mobility shift assays with cis-elements in the proximal promoter region showed that specific binding of the AP2 transcription factor was significantly increased by treatment with ginsenoside Rb2. Mutations of the AP2 binding sites in the heterologous promoter and natural context systems abolished the transcriptional activation by ginsenoside Rb2. These results suggest that the SOD1 gene was greatly activated by ginsenoside Rb2 through transcription factor AP2 binding sites and its induction.

Craniofacial defects in AP-2 null mutant mice

AP-2 is a recent significant addition to the list of transcription factors that have been demonstrated by targeted gene disruption to be essential for normal development. Two recent reports of AP-2 null mutant mice indicate that AP-2 holds a key position in the network of genes and proteins controlling developmental pattern and morphogenesis, and that it is particularly important for development of the cranial region and for midline fusions.

Comparative and functional analysis of the AP2 promoter indicates that conserved octamer and initiator elements are critical for activity

AP-2 is a developmentally-regulated transcription factor expressed in ectodermal cell lineages. The AP-2 protein is essential for neural tube, craniofacial and body wall morphogenesis and has been implicated in oncogenesis. Here we report the isolation of the AP-2 promoter from human, mouse and chicken. The initiation sites for the human gene have been mapped in a variety of cell lines, including several derived from breast tumours. Initiation occurs just upstream of an IR3-like repetitive element, present in the human and mouse genes, but absent in chicken. The cis-acting elements responsible for promoter activity in human HeLa cells have been mapped both in vivo and in vitro. The proximal promoter contains binding sites for transcription factors AP-2, NF-1 and octamer proteins, but lacks a TATA box motif. Functional analysis demonstrates that the octamer binding site is the critical component of basal promoter activity. In addition, the promoter relies on an initiator element for efficient start site utilization. There is an excellent correlation between the requirement for the initiator and octamer elements in transcription assays and the conservation of these cis-acting sequences between chicken, mouse and human.

Structure and promoter analysis of the gene encoding the human melanoma-inhibiting protein MIA

We have recently described the isolation of a novel protein, MIA, which is secreted from malignant melanoma cells and elicits growth inhibition on melanoma cells in vitro (Blesch, A., Bosserhoff, A. K., Apfel, R., Behl, C., Hessdörfer, B., Schmitt, A., Jachimczak, P., Lottspeich, F., Schlingensiepen, H., Buettner, R., and Bogdahn, U. (1994) Cancer Res. 54, 5695-5701). Here, we report the structure of the human MIA gene locus, describe its expression pattern in melanocytic tumors in vivo, and provide an initial characterization of the MIA promoter. The MIA gene is encoded by four exons, and the mRNA initiation site was identified 70 base pairs upstream from the translation start codon. MIA mRNA expression in vivo correlated with progressive malignancy of melanocytic lesions and was inducible in other cells by phorbol esters. To investigate mechanisms mediating this melanoma-associated expression pattern, we analyzed the promoter activity of the 1.3-kilobase genomic sequences located 5'-upstream of the MIA gene. The MIA promoter conferred high levels of gene activation specifically in human and murine melanoma cells, and its activity was further enhanced by treatment with phorbol esters. Site-directed mutation of an NF-kB site within the MIA promoter did reduce the basal promoter activity in melanoma cells but did not change significantly enhancement by phorbol esters.

Cloning and characterization of a second AP-2 transcription factor: AP-2 beta

AP-2 has been characterized previously as a unique 52 × 10(3) M(r) transcription activator encoded by a single gene that is expressed in a restricted pattern during embryonic morphogenesis of the peripheral nervous system, face, skin and nephric tissues. Here we report the isolation of genomic and cDNA clones encoding for a second AP-2 related transcription factor, designated AP-2 beta. AP-2 beta binds specifically to a series of well-characterized AP-2 binding sites, consensus to the sequence G/CCCN3GGC, and transactivates transcription from a reporter plasmid under the control of an AP-2-dependent promoter. A C-terminal domain known to mediate homodimerization of the previously cloned AP-2 alpha transcription activator is highly conserved and sufficient to mediate interaction between the two proteins. Northern blot and in situ hybridizations revealed that the two genes are expressed in murine embryos between days 9.5 and 19.5 p.c. Coexpression of both mRNAs was detected in many tissues at day 13.5 and 15.5 of embryogenesis but some regions of the developing brain and face including the primordium of midbrain and the facial mesenchyme differed in their expression pattern of AP-2 genes. AP-2 alpha and AP-2 beta signals in the central and peripheral nervous system overlapped with regions of developing sensory neurons. In adult tissues AP-2 alpha expression was found mainly in the skin, eye and prostate and AP-2 beta expression in the kidney. In summary, our analyses of embryonic and adult mice demonstrate that two different AP-2 transcription factors are specifically expressed during differentiation of many neural, epidermal and urogenital tissues.

The developmentally regulated transcription factor AP-2 is involved in c-erbB-2 overexpression in human mammary carcinoma

Overexpression of the c-erbB-2/HER2 protooncogene in breast carcinoma is controlled not only by the degree of amplification of the gene but also at the level of gene transcription. Thus, whether or not the gene is amplified, the activity of the c-erbB-2 promoter is enhanced in overexpressing cells through the binding of an additional transcription factor, OB2-1, whose activity is increased in these lines. Here we describe further characterization of OB2-1 and show that it is identical to the developmentally regulated transcription factor AP-2. Functional assays confirm that AP-2 is able to regulate c-erbB-2 expression in mammary-derived cell lines. Furthermore, although AP-2 is barely detectable in cells with the low c-erbB-2 expression phenotype, protein levels are clearly elevated in a panel of c-erbB-2-overexpressing lines. These findings demonstrate an important role for this transcription factor in human cancer.

N-ras oncogene causes AP-2 transcriptional self-interference, which leads to transformation

Genetic alterations in elements of normal signal transduction mechanisms are known to be oncogenic events often resulting in aberrant activation of programs of gene transcription. We have investigated the effect of N-ras oncogene-induced tumorigenic transformation on the transcription factor AP-2. N-ras oncogene-induced transformation of human teratocarcinoma cells PA-1 results in sixfold elevated AP-2 mRNA levels. However, the level of AP-2-mediated trans-activation is dramatically inhibited in these cells. We show here that the high-level expression of AP-2 ultimately results in transcriptional "self-interference". The activation domain of AP-2, when fused to the DNA-binding domain of GAL4, is sufficient for self-interference. Non-N-ras PA-1 cells constitutively expressing AP-2 or GAL4-AP-2 fusion protein from an SV40 promoter exhibit reduced AP-2-mediated transcriptional activation, inhibition of differentiation, and promotion of anchorage-independent growth, properties that are similar to N-ras-transformed PA-1 cells. Thus, AP-2 is placed in the N-ras signal transduction pathway, and many of the biological effects of N-ras can be accomplished by overexpression of AP-2. This is the first evidence that inhibition of the activity of a transcription factor by self-interference contributes to a physiological process.