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

TFAP2E is implicated in central nervous system, orofacial and maxillofacial anomalies

BACKGROUND

Previous studies in mouse, Xenopus and zebrafish embryos show strong tfap2e expression in progenitor cells of neuronal and neural crest tissues suggesting its involvement in neural crest specification. However, the role of human transcription factor activator protein 2 (TFAP2E) in human embryonic central nervous system (CNS), orofacial and maxillofacial development is unknown.

METHODS

Through a collaborative work, exome survey was performed in families with congenital CNS, orofacial and maxillofacial anomalies. Exome variant prioritisation prompted TFAP2E gene for functional analysis in zebrafish embryos. Embryonic morphology and development were assessed after antisense morpholino (MO) knockdown (KD), CRISPR/Cas9 knockout and overexpression of tfap2e in fluorescent zebrafish reporter lines using in vivo microscopy. Computational structural protein modelling of the identified human variants was performed.

RESULTS

In total, exome survey identified novel or ultra-rare heterozygous missense variants in TFAP2E in seven individuals from five independent families with predominantly CNS, orofacial and maxillofacial anomalies. One variant was found de novo and another variant segregated in an affected multiplex family. Protein modelling of the identified variants indicated potential distortion of TFAP2E in the transactivation or dimerisation domain. MO KD and CRISPR/Cas9 knockout of tfap2e in zebrafish revealed hydrocephalus and a significant reduction of brain volume, consistent with a microencephaly phenotype. Furthermore, mRNA overexpression of TFAP2E indicates dosage-sensitive phenotype expression. In addition, zebrafish showed orofacial and maxillofacial anomalies following tfap2e KD, recapitulating the human phenotype.

CONCLUSION

Our human genetic data and analysis of Tfap2e manipulation in zebrafish indicate a potential role of TFAP2E in human CNS, orofacial and maxillofacial anomalies.

Knockdown of TFAP2E results in rapid G2/M transition in oral squamous cell carcinoma cells

TFAP2E is a member of the activator protein-2 transcription factor family and acts as a tumor suppressor in several types of cancer. Downregulation of TFAP2E expression is significantly associated with a shorter overall survival period in patients with oral squamous cell carcinoma (OSCC). To evaluate the molecular mechanisms by which TFAP2E suppresses the development or progression of OSCC, the present study investigated the effects of TFAP2E downregulation on OSCC-derived Ca9-22 and HSC-4 cells. The present study demonstrated that small interfering RNA mediated-knockdown of TFAP2E accelerated the proliferation of these OSCC cell lines compared with that in the control group, as determined by the standard water-soluble tetrazolium salt-8 assay. To analyze the cell cycle progression rate, the cell cycle distribution patterns of TFAP2E-knockdown and control cells cultured in the presence of nocodazole, which prevents the completion of mitosis, were analyzed by fluorescence-activated cell sorting at different time points. When analyzing cellular DNA contents, no major differences in cell cycle profiles were observed; however, the rate of increase in cells positive for histone H3 Serine 28 phosphorylation, a standard molecular marker of early M phase, was significantly higher in TFAP2E-knockdown cells than in the control cells. Collectively, these results suggested that TFAP2E may attenuate the proliferation of OSCC cells by regulating G2/M transition.

Ap-2β regulates cranial osteogenic potential via the activation of Wnt/β-catenin signaling pathway

The skull is a fundamental bone that protects the development of brain and consists of several bony elements, such as the frontal and parietal bones. Frontal bone exhibited superior in osteogenic potential and regeneration of cranial defects compared to parietal bone. However, how this regional difference is regulated remains largely unknown. In this study, we identified an Ap-2β transcriptional factor with a higher expression in frontal bone, but its molecular function in osteoblasts needs to be elucidated. We found that Ap-2β knockdown in preosteoblasts leads to reduced proliferation, increased cell death and impaired differentiation. Through RNA-seq analysis, we found that Ap-2β influences multiple signaling pathways including the Wnt pathway, and overexpression of Ap-2β showed increased nuclear β-catenin and its target genes expressions in osteoblasts. Pharmacological activation of Wnt/β-catenin signaling using LiCl treatment cannot rescue the reduced luciferase activities of the β-catenin/TCF/LEF reporter in Ap-2β knockdown preosteoblasts. Besides, transient expression of Ap-2β via the lentivirus system could sufficiently rescue the inferior osteogenic potential in parietal osteoblasts, while Ap-2β knockdown in frontal osteoblasts resulted in reduced osteoblast activity, reduced active β-catenin and target genes expressions. Taken together, our data demonstrated that Ap-2β modulates osteoblast proliferation and differentiation through the regulation of Wnt/β-catenin signaling pathway and plays an important role in regulating regional osteogenic potential in frontal and parietal bone.

Roles of activator protein-2 gamma in breast cancer: A narrative review (SANRA)

Activator protein-2 gamma (AP-2γ) is a crucial transcription factor involved in breast cancer development. Abnormal expression and activity of AP-2γ have also been identified as important markers of malignancy. In the last decade, the importance of AP-2γ in breast cancer progression has been widely studied. In this review, we summarize the current knowledge on the regulatory roles of AP-2γ in breast cancer oncogenesis and progression and its potential as a diagnostic biomarker and drug target in breast cancer treatment.

The regulatory role of AP-2β in monoaminergic neurotransmitter systems: insights on its signalling pathway, linked disorders and theragnostic potential

Monoaminergic neurotransmitter systems play a central role in neuronal function and behaviour. Dysregulation of these systems gives rise to neuropsychiatric and neurodegenerative disorders with high prevalence and societal burden, collectively termed monoamine neurotransmitter disorders (MNDs). Despite extensive research, the transcriptional regulation of monoaminergic neurotransmitter systems is not fully explored. Interestingly, certain drugs that act on these systems have been shown to modulate central levels of the transcription factor AP-2 beta (AP-2β, gene: TFAP2Β). AP-2β regulates multiple key genes within these systems and thereby its levels correlate with monoamine neurotransmitters measures; yet, its signalling pathways are not well understood. Moreover, although dysregulation of TFAP2Β has been associated with MNDs, the underlying mechanisms for these associations remain elusive. In this context, this review addresses AP-2β, considering its basic structural aspects, regulation and signalling pathways in the controlling of monoaminergic neurotransmitter systems, and possible mechanisms underpinning associated MNDS. It also underscores the significance of AP-2β as a potential diagnostic biomarker and its potential and limitations as a therapeutic target for specific MNDs as well as possible pharmaceutical interventions for targeting it. In essence, this review emphasizes the role of AP-2β as a key regulator of the monoaminergic neurotransmitter systems and its importance for understanding the pathogenesis and improving the management of MNDs.

METTL3 contributes to renal ischemia-reperfusion injury by regulating Foxd1 methylation

To investigate the mechanism of renal ischemia-reperfusion injury (IRI) via regulation of N⁶-methyl-adenosine (m6A) and relevant genes, IRI was induced in Sprague-Dawley rats, and urine and serum creatinine levels and tissue structure changes were observed. m6A and methyltransferase-like 3 (METTL3) protein levels were assessed via dot-blot and Western blot analyses, respectively. The hypoxia/reoxygenation (H/R) cell model was constructed using NRK-52E cells, and METTL3 protein levels were assessed. METTL3 was inhibited to observe its impact on NRK-52E cell apoptosis and m6A expression in H/R processes. Methylated RNA immunoprecipitation (MeRIP) sequencing was conducted followed by MeRIP-quantitative RT-PCR and quantitative RT-PCR validation. Our results indicated that urine and serum creatinine levels increased and that renal injury and cell apoptosis were both observed in the IRI model. In additon, m6A expression increased in the IRI model, and METTL3 protein levels significantly increased in the IRI and H/R models. When METTL3 was inhibited, m6A levels were accordingly decreased and cell apoptosis was suppressed in the H/R in vitro model. Based on MeRIP sequencing, transcription factor activating enhancer binding protein 2α (tfap2a), cytochrome P-450 1B1 (cyp1b1), and forkhead box D1 (foxd1) were significantly differentially expressed, as was m6A, which is involved in the negative regulation of cell proliferation and kidney development. We confirmed that foxd1 mRNA and its methylation levels contributed to IRI and H/R.

AP-2ε Expression in Developing Retina: Contributing to the Molecular Diversity of Amacrine Cells

AP-2 transcription factors play important roles in the regulation of gene expression during development. Four of the five members of the AP-2 family (AP-2α, AP-2β, AP-2γ and AP-2δ) have previously been shown to be expressed in developing retina. Mouse knockouts have revealed roles for AP-2α, AP-2β and AP-2δ in retinal cell specification and function. Here, we show that the fifth member of the AP-2 family, AP-2ε, is also expressed in amacrine cells in developing mammalian and chicken retina. Our data indicate that there are considerably fewer AP-2ε-positive cells in the developing mouse retina compared to AP-2α, AP-2β and AP-2γ-positive cells, suggesting a specialized role for AP-2ε in a subset of amacrine cells. AP-2ε, which is restricted to the GABAergic amacrine lineage, is most commonly co-expressed with AP-2α and AP-2β, especially at early stages of retinal development. Co-expression of AP-2ε and AP-2γ increases with differentiation. Analysis of previously published Drop-seq data from single retinal cells supports co-expression of multiple AP-2s in the same cell. Since AP-2s bind to their target sequences as either homodimers or heterodimers, our work suggests spatially- and temporally-coordinated roles for combinations of AP-2 transcription factors in amacrine cells during retinal development.

The AP-2 Transcription Factor APTF-2 Is Required for Neuroblast and Epidermal Morphogenesis in Caenorhabditis elegans Embryogenesis

The evolutionarily conserved family of AP-2 transcription factors (TF) regulates proliferation, differentiation, and apoptosis. Mutations in human AP-2 TF have been linked with bronchio-occular-facial syndrome and Char Syndrome, congenital birth defects characterized by craniofacial deformities and patent ductus arteriosus, respectively. How mutations in AP-2 TF cause the disease phenotypes is not well understood. Here, we characterize the aptf-2(qm27) allele in Caenorhabditis elegans, which carries a point mutation in the conserved DNA binding region of AP-2 TF. We show that compromised APTF-2 activity leads to defects in dorsal intercalation, aberrant ventral enclosure and elongation defects, ultimately culminating in the formation of morphologically deformed larvae or complete arrest during epidermal morphogenesis. Using cell lineaging, we demonstrate that APTF-2 regulates the timing of cell division, primarily in ABarp, D and C cell lineages to control the number of neuroblasts, muscle and epidermal cells. Live imaging revealed nuclear enrichment of APTF-2 in lineages affected by the qm27 mutation preceding the relevant morphogenetic events. Finally, we found that another AP-2 TF, APTF-4, is also essential for epidermal morphogenesis, in a similar yet independent manner. Thus, our study provides novel insight on the cellular-level functions of an AP-2 transcription factor in development.

Mutations in the evolutionarily conserved family of AP-2 transcription factors are associated with multiple birth defects in Char syndrome and Brancio-oculo-facial syndrome. These DNA-binding proteins are known to regulate the proliferation, differentiation and death of specific cells during embryonic development but how point mutations in the AP-2 DNA-binding domain lead to these diseases during development is currently unknown. We have identified a mutation in one of the AP-2 orthologs of the nematode Caenorhabditis elegans, APTF-2, which falls in the same mutation hotspot as in human Char syndrome and Brancio-oculo-facial syndrome patients. Compromised APTF-2 activity in C. elegans results in embryonic lethality and embryos that survive to hatching displays body morphological defects, reminiscent of the aforementioned human diseases. Using time-lapse microscopy, we found that misregulation of cell division in the skin, muscle and neuronal cell lineages is the primary cause of developmental arrest. Our study provides insight into the regulation of cell division timing by AP-2 transcription factors and provides a model to study human diseases associated with AP-2 mutations.

Transcription Factor AP2ε: A Potential Predictor of Chemoresistance in Patients With Gastric Cancer

Chemotherapy is a mainstay of therapy for advanced gastric cancer (GC); however, owing to drug resistances, the effectiveness of chemotherapy is not satisfactory for some patients with GC. Therefore, identification of a marker that predicts treatment response is beneficial to patients. Hypermethylation of transcription factor activating enhancer-binding protein 2∊ (TFAP2E) has been implicated in chemotherapy resistance to fluorouracil-based chemotherapy in patients with colorectal cancer, but its role in GC is still unknown. In this study, we investigated TFAP2E as a predictor of treatment response in GC. We used methylation-sensitive high-resolution melting analysis to study the methylation of TFAP2E in 141 GC tissue specimens and 45 adjacent nontumor tissue specimens. In vitro experiments, we analyzed the expression and methylation of TFAP2E and to examine the sensitivity of GC cell lines to 5-fluorouracil (5-FU). The TFAP2E methylation occurred at a significantly higher incidence rate in tumor tissues compared to adjacent nontumor tissues (chi-square [χ2] = 38.919, P < .001). Hypermethylation of TFAP2E occurred more frequently in tumors with lower differentiation grades (P < .001) and was significantly associated with nonresponse to fluorouracil-based chemotherapy (P = .010). Hypermethylation was also associated with decreased expression of TFAP2E (P < .01) and nonresponse to 5-FU exposure in vitro (P < .001). Hypermethylation of TFAP2E was associated with lack of response to fluorouracil-based chemotherapy, indicating that it might be a potential predictor of treatment response in patients with GC.

TFAP2B overexpression contributes to tumor growth and a poor prognosis of human lung adenocarcinoma through modulation of ERK and VEGF/PEDF signaling

BACKGROUND

TFAP2B is a member of the AP2 transcription factor family, which orchestrates a variety of cell processes. However, the roles of TFAP2B in regulating carcinogenesis remain largely unknown. Here, we investigated the regulatory effects of TFAP2B on lung adenocarcinomas growth and identified the underlying mechanisms of actions in non-small cell lung cancer (NSCLC) cells.

METHODS

We first examined the expression of TFAP2B in lung cancer cell lines and tumor tissues. We also analyzed the prognostic predicting value of TFAP2B in lung adenocarcinomas. Then we investigated the molecular mechanisms by which TFAP2B knockdown or overexpression regulated lung cancer cell growth, angiogenesis and apoptosis, and further confirmed the role of TFAP2B in tumor growth in a lung cancer xenograft mouse model.

RESULTS

TFAP2B was highly expressed in NSCLC cell lines and tumor tissues. Strong TFAP2B expression showed a positive correlation with the poor prognoses of patients with lung adenocarcinomas (P < 0.001). TFAP2B knockdown by siRNA significantly inhibited cell growth and induced apoptosis in NSCLC cells in vitro and in a lung cancer subcutaneous xenograft model, whereas TFAP2B overexpression promoted cell growth. The observed regulation of cell growth was accompanied by the TFAP2B-mediated modulation of the ERK/p38, caspase/cytochrome-c and VEGF/PEDF-dependent signaling pathways in NSCLC cells.

CONCLUSIONS

These results indicate that TFAP2B plays a critical role in regulating lung adenocarcinomas growth and could serve as a promising therapeutic target for lung cancer treatment.

Genome-wide screening of aberrant DNA methylation which associated with gene expression in mouse skin cancers

Epigenetic alteration of genomic DNA is a common and key process in carcinogenesis. There is considerable evidence indicating that some of the somatic alterations occurring during carcinogenesis in humans also involve the same processes as those observed in mice. Therefore, we analyzed mouse skin cancer tissues induced by the 2-stage carcinogenesis model to identify skin tumor-specific differentially methylated regions (ST-DMRs) during the multistep carcinogenesis process. We have previously identified ST-DMRs using the restriction landmark genomic scanning (RLGS) technique and reported that some of the mouse ST-DMRs were also epigenetically modified in human cancers, such as melanoma, neuroblastoma, and brain tumor. These results encouraged us to pursue global methylation screening in mouse skin carcinogenesis. Using the methylated DNA immunoprecipitation (MeDIP) method combined with the NimbleGen promoter plus CpG island (CpGi) array, we identified 615 ST-DMRs. In combination with global gene expression analysis, 91 of these ST-DMRs were shown to be located on or around the genes differentially expressed between normal skin and tumor tissues, including a candidate human tumor suppressor gene Tfap2e. As observed in human colorectal cancers, Tfap2e was methylated at a CpGi located in intron 3 and downregulated in skin tumors. Our results identified aberrant methylated regions that were associated with gene expression regulation during carcinogenesis, which may indicate critical genetic regions also involved in human carcinogenesis. © 2013 Wiley Periodicals, Inc.

The transcription factor activating enhancer-binding protein epsilon (AP-2ε) regulates the core promoter of type II collagen (COL2A1)

The transcription factor activating enhancer-binding protein epsilon (AP-2ε) was recently shown to be expressed during late chondrocyte differentiation, especially in hypertrophic chondrocytes. In this study, we were able to reveal that the promoter of the type II collagen (COL2A1) gene, encoding the extracellular matrix protein type II collagen, is specifically regulated by AP-2ε. Expression of COL2A1 is downregulated at the transition of chondroblasts into hypertrophic chondrocytes and our data provide evidence that AP-2ε is involved in this process. In reporter gene assays, overexpression of AP-2ε in cartilaginous cell lines resulted in a significant reduction in COL2A1 core promoter activity of ~ 45%. Furthermore, we found that this process is dose-dependent and highly specific for the epsilon isoform. Computational analysis offered only a single putative AP-2-binding motif within the chosen promoter fragment but site-directed mutagenesis revealed this motif to be regulatory inactive. After expanding our screening to motifs containing minor differences from the classical AP-2 consensus sequence (5'-GCCN3 GGC-3'), we determined the sequence 5'-GCCCAGGC-3' ranging from position -128 to -135 bp as an important regulatory site and responsible for COL2A1 downregulation through AP-2ε. Interaction of AP-2ε with the COL2A1 promoter at this site was confirmed by chromatin immunoprecipitation and electromobility shift assay. Further, our experiments suggest that at least one additional factor is involved in this process. This is the first study to prove regulation of COL2A1 by AP-2ε highlighting the role of the transcription factor as a modulator of cartilage development.

Identification of transcription factors regulating CTNNAL1 expression in human bronchial epithelial cells

Adhesion molecules play important roles in airway hyperresponsiveness or airway inflammation. Our previous study indicated catenin alpha-like 1 (CTNNAL1), an alpha-catenin-related protein, was downregulated in asthma patients and animal model. In this study, we observed that the expression of CTNNAL1 was increased in lung tissue of the ozone-stressed Balb/c mice model and in acute ozone stressed human bronchial epithelial cells (HBEC). In order to identify the possible DNA-binding proteins regulating the transcription of CTNNAL1 gene in HBEC, we designed 8 oligo- nucleotide probes corresponding to various regions of the CTNNAL1 promoter in electrophoretic mobility shift assays (EMSA). We detected 5 putative transcription factors binding sites within CTNNAL1 promoter region that can recruit LEF-1, AP-2α and CREB respectively by EMSA and antibody supershift assay. Chromatin immunoprecipitation (ChIP) assay verified that AP-2 α and LEF-1 could be recruited to the CTNNAL1 promoter. Therefore we further analyzed the functions of putative AP-2 and LEF-1 sites within CTNNAL1 promoter by site-directed mutagenesis of those sites within pGL3/FR/luc. We observed a reduction in human CTNNAL1 promoter activity of mutants of both AP-2α and LEF-1 sites. Pre-treatment with ASOs targeting LEF-1and AP-2α yielded significant reduction of ozone-stress-induced CTNNAL1 expression. The activation of AP-2α and LEF-1, followed by CTNNAL1 expression, showed a correlation during a 16-hour time course. Our data suggest that a robust transcriptional CTNNAL1 up-regulation occurs during acute ozone-induced stress and is mediated at least in part by ozone-induced recruitments of LEF-1 and AP-2α to the human CTNNAL1 promoter.

AP-2δ is a crucial transcriptional regulator of the posterior midbrain

Ap-2 transcription factors comprise a family of 5 closely related sequence-specific DNA binding proteins that play pivotal and non-redundant roles in embryonic organogenesis. To investigate the function of Ap-2δ, wδe analyzed its expression during embryogenesis and generated Ap-2δ-deficient mice. In line with the specific expression pattern of Ap-2δ in the mesencephalic tectum and the dorsal midbrain, Ap-2δ-deficient mice failed to maintain the colliculus inferior, a derivative of the dorsal midbrain, as a consequence of increased apoptotic cell death. To identify specific Ap-2δ target genes in cells of the developing dorsal midbrain, we performed whole genome analysis of cDNA expression levels. This approach identified a set of 12 putative target genes being expressed in the developing midbrain, including the transcription factors Pitx2, Mef2c, Bhlhb4 and Pou4f3. Using chromatin immunoprecipitation (CHIP) we showed that some of these genes are direct targets of Ap-2δ. Consistently, we demonstrate that Ap-2δ occupies and activates the Pou4f3 and Bhlhb4 promoters. In addition, known Pou4f3 target genes were downregulated in the posterior midbrain of Ap-2δ-deficient mice. Despite the absence of a central part of the auditory pathway, the presence of neuronal responses to sounds in the neocortex of Ap-2δ-deficient mice indicates that auditory information from the brainstem still reaches the neocortex. In summary, our data define Ap-2δ as an important transcription factor, specifying gene expression patterns required for the development of the posterior midbrain.

A heart-hand syndrome gene: Tfap2b plays a critical role in the development and remodeling of mouse ductus arteriosus and limb patterning

BACKGROUND

Patent ductus arteriosus (PDA) is one of the most common forms of congenital heart disease. Mutations in transcription factor TFAP2B cause Char syndrome, a human disorder characterized by PDA, facial dysmorphysm and hand anomalies. Animal research data are needed to understand the mechanisms. The aim of our study was to elucidate the pathogenesis of Char syndrome at the molecular level.

METHODOLOGY/PRINCIPAL FINDINGS

Gene expression of Tfap2b during mouse development was studied, and newborns of Tfap2b-deficient mice were examined to identify phenotypes. Gel shift assays had been carried out to search for Tfap2 downstream genes. Promoters of candidate genes were cloned into a reporter construct and used to demonstrate their regulation by Tfap2b in cell transfection. In situ hybridizations showed that the murine transcription factor Tfap2b was expressed during the entire development of mouse ductus arteriosus. Histological examination of ductus arteriosus from Tfap2b knockout mice 6 hours after birth revealed that they were not closed. Consequently, the lungs of Tfap2b(-/-) mice demonstrated progressive congestion of the pulmonary capillaries, which was postulated to result secondarily from PDA. In addition, Tfap2b was expressed in the limb buds, particularly in the posterior limb field during development. Lack of Tfap2b resulted in bilateral postaxial accessory digits. Further study indicated that expressions of bone morphogenetic protein (Bmp) genes, which are reported to be involved in the limb patterning and ductal development, were altered in limb buds of Tfap2b-deficient embryos, due to direct control of Bmp2 and Bmp4 promoter activity by Tfap2b.

CONCLUSIONS/SIGNIFICANCE

Tfap2b plays important roles in the development of mouse ductus arteriosus and limb patterning. Loss of Tfap2b results in altered Bmp expression that may cause the heart-limb defects observed in Tfap2b mouse mutants and Char syndrome patients. The Tfap2b knockout mouse may add to the very limited available animal models of PDA.

α5β1 integrin-mediated adhesion to fibronectin is required for axis elongation and somitogenesis in mice

The arginine-glycine-aspartate (RGD) motif in fibronectin (FN) represents the major binding site for α5β1 and αvβ3 integrins. Mice lacking a functional RGD motif in FN (FN^RGE/RGE) or α5 integrin develop identical phenotypes characterized by embryonic lethality and a severely shortened posterior trunk with kinked neural tubes. Here we show that the FN^RGE/RGE embryos arrest both segmentation and axis elongation. The arrest is evident at about E9.0, corresponding to a stage when gastrulation ceases and the tail bud-derived presomitic mesoderm (PSM) induces α5 integrin expression and assumes axis elongation. At this stage cells of the posterior part of the PSM in wild type embryos are tightly coordinated, express somitic oscillator and cyclic genes required for segmentation, and form a tapered tail bud that extends caudally. In contrast, the posterior PSM cells in FN^RGE/RGE embryos lost their tight associations, formed a blunt tail bud unable to extend the body axis, failed to induce the synchronised expression of Notch1 and cyclic genes and cease the formation of new somites. Mechanistically, the interaction of PSM cells with the RGD motif of FN is required for dynamic formation of lamellipodia allowing motility and cell-cell contact formation, as these processes fail when wild type PSM cells are seeded into a FN matrix derived from FN^RGE/RGE fibroblasts. Thus, α5β1-mediated adhesion to FN in the PSM regulates the dynamics of membrane protrusions and cell-to-cell communication essential for elongation and segmentation of the body axis.

The transcription factor AP-2ɛ regulates CXCL1 during cartilage development and in osteoarthritis

OBJECTIVE

Recently, the transcription factor AP-2ɛ was shown to be a regulator of hypertrophy in cartilage and to be differentially expressed in osteoarthritis (OA). However, the only known target gene of AP-2ɛ up to date is integrin alpha10. To better characterize the function of AP-2ɛ in cartilage we screened for additional target genes.

DESIGN

Promoter analysis, ChIP-assays and electrophoretic mobility shift assay were used to characterize the regulation of a new AP-2ɛ target gene in detail.

RESULTS

In this study, we determined the chemokine CXCL1, already known to be important in osteoarthritis (OA), as a new target gene of AP-2ɛ. We could confirm that CXCL1 is expressed in chondrocytes and significantly over-expressed in OA-chondrocytes. Transient transfection of chondrocytes with an AP-2ɛ expression construct led to a significant increase of the CXCL1 mRNA level in these cells. We identified three potential AP-2 binding sites within the CXCL1 promoter and performed luciferase assays, indicating that an AP-2 binding motif (AP-2.2) ranging from position -135 to -144 bp relative to the translation start is responsive to AP-2ɛ. This result was further addressed by site-directed mutagenesis demonstrating that activation of the CXCL1 promoter by AP-2ɛ is exclusively dependent on AP-2.2. Chromatin immunoprecipitation and electromobility shift assays confirmed the direct binding of AP-2ɛ to the CXCL1 promoter in OA-chondrocytes at this site.

CONCLUSION

These findings revealed CXCL1 as a novel target gene of AP-2ɛ in chondrocytes and support the important role of AP-2ɛ in cartilage.

Transcription factor AP-2β regulates the neurotransmitter phenotype and maturation of chromaffin cells

During development, sympathetic neurons and chromaffin cells originate from bipotential sympathoadrenal (SA) progenitors arising from neural crests (NC) in the trunk regions. Recently, we showed that AP-2β, a member of the AP2 family, plays a critical role in the development of sympathetic neurons and locus coeruleus and their norepinephrine (NE) neurotransmitter phenotype. In the present study, we investigated the potential role of AP-2β in the development of NC-derived neuroendocrine chromaffin cells of the adrenal medulla and the epinephrine (EPI) phenotype determination. In support of its role in chromaffin cell development, AP-2β is prominently expressed in both embryonic and adult adrenal medulla. In adrenal chromaffin cells of the AP-2β(-/-) mouse, the expression levels of catecholamine biosynthesizing enzymes, dopamine β-hydroxylase (DBH) and phenylethanolamine-N-methyl-transferase (PNMT), as well as the SA-specific transcription factor, Phox2b, are significantly reduced compared to wild type. In addition, ultrastructural analysis demonstrated that the formation of large secretory vesicles, a hallmark of differentiated chromaffin cells, is defective in AP-2β(-/-) mice. Furthermore, the level of EPI content is largely diminished (>80%) in the adrenal gland of AP-2β(-/-) mice. Chromatin immunoprecipitation (ChIP) assays of rat adrenal gland showed that AP-2β binds to the upstream promoter of the PNMT gene in vivo; strongly suggesting that it is a direct target gene. Overall, our data suggest that AP-2β plays critical roles in the epinephrine phenotype and maturation of adrenal chromaffin cells.

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

Background

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

Results

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

Conclusions

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

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

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

Identification of target genes of transcription factor activator protein 2 gamma in breast cancer cells

Background

Activator protein 2 gamma (AP-2γ) is a member of the transcription factor activator protein-2 (AP-2) family, which is developmentally regulated and plays a role in human neoplasia. AP-2γ has been found to be overexpressed in most breast cancers, and have a dual role to inhibit tumor initiation and promote tumor progression afterwards during mammary tumorigensis.

Methods

To identify the gene targets that mediate its effects, we performed chromatin immunoprecipitation (ChIP) to isolate AP-2γ binding sites on genomic DNA from human breast cancer cell line MDA-MB-453.

Results

20 novel DNA fragments proximal to potential AP-2γ targets were obtained. They are categorized into functional groups of carcinogenesis, metabolism and others. A combination of sequence analysis, reporter gene assays, quantitative real-time PCR, electrophoretic gel mobility shift assays and immunoblot analysis further confirmed the four AP-2γ target genes in carcinogenesis group: ErbB2, CDH2, HPSE and IGSF11. Our results were consistent with the previous reports that ErbB2 was the target gene of AP-2γ. Decreased expression and overexpression of AP-2γ in human breast cancer cells significantly altered the expression of these four genes, indicating that AP-2γ directly regulates them.

Conclusion

This suggested that AP-2γ can coordinate the expression of a network of genes, involving in carcinogenesis, especially in breast cancer. They could serve as therapeutic targets against breast cancers in the future.

Disorganized olfactory bulb lamination in mice deficient for transcription factor AP-2epsilon

Within the olfactory bulb, neurons and their axonal connections are organized into distinct layers corresponding to different functionalities. Here we demonstrate that transcription factor AP-2epsilon is required for olfactory bulb development, specifically the establishment of appropriate neuronal lamination. During normal mouse embryogenesis, AP-2epsilon transcripts are one of the earliest markers of olfactory bulb formation, and expression eventually becomes refined to the projection neurons, the mitral and tufted cells. To assess the function of AP-2epsilon in olfaction, we generated a null allele (the "AK" allele) by inserting a Cre recombinase transgene into the endogenous AP-2epsilon genomic locus. AP-2epsilon-null mice exhibited defective olfactory bulb architecture. The mitral cell layer was disorganized, typified by misoriented and aberrantly positioned projection neurons, and the adjacent internal plexiform layer was absent. Despite the significant disruption of olfactory bulb organization, AP-2epsilon null mice were viable and could discriminate a variety of odors. AP-2epsilon-null mice thus provide compelling evidence for the robust nature of the mouse olfactory system, and serve as a model system to probe both the regulation of neuronal lamination and the functional circuitry of the olfactory bulb. We also show that Cre recombinase expression directed by the AP-2epsilon locus can specifically target floxed genes within the olfactory bulb, extending the utility of this AK allele.

Regulation of the noradrenaline neurotransmitter phenotype by the transcription factor AP-2beta

AP-2 family transcription factors are essential for development and morphogenesis of diverse tissues and organs, but their precise roles in specification of neural crest stem cell (NCSC)-derived cell types have not been determined. Among three members known to be expressed in the NCSC (i.e. AP-2alpha, AP-2beta, and AP-2gamma), we found that only AP-2beta is predominantly expressed in the sympathetic ganglia of developing mouse embryos, supporting its role in sympathetic development. Indeed, AP-2beta null mice expressed significantly reduced levels of both noradrenaline (NA) and NA-synthesizing dopamine beta-hydroxylase in the peripheral nervous system. Strikingly, we also found that NA neuron development was significantly compromised in the locus coeruleus as well. Pharmacological treatment with an NA intermediate during pregnancy significantly rescues the neonatal lethality of AP-2beta(-/-) mice, indicating that NA deficiency is one of the main causes for lethality found in AP-2beta(-/-) mice. We also showed that forced expression of AP-2beta, but not other AP-2 factors, in NCSC favors their differentiation into NA neurons. In summary, we propose that AP-2beta plays critical and distinctive roles in the NA phenotype specification in both the peripheral and central nervous system during development.

PPARalpha and AP-2alpha regulate bombesin receptor subtype 3 expression in ozone-stressed bronchial epithelial cells

Previously, we found that bombesin receptor subtype 3 (BRS-3) significantly increased in an ozone-stressed airway hyperresponsiveness animal model and resulted in induced wound repair and protection from acute lung injury. In the present study, we determined molecular mechanisms of BRS-3 regulation in human BECs (bronchial epithelial cells) in response to ozone stress. Ten oligonucleotide probes corresponding to various regions of the BRS-3 promoter were used in EMSA (electrophoretic mobilityshift assays). Four were found to have an enhanced mobility shift with extracts from ozone-stressed cells. On the basis of the assay of mutated probes binding with extracts and antibody supershift, they were verified as MTF-1 (metal-regulatory-element-binding transcription factor-1), PPARalpha (peroxisome-proliferator-activated receptor alpha), AP-2alpha (activator protein 2alpha) and HSF-1 (heat-shock factor 1). Next, ChIP (chromatin immunoprecipitation) assay, site-directed mutagenesis technology and antisense oligonucleotide technology were used to observe these transcription factors associated with the BRS-3 promoter. Only AP-2alpha and PPARalpha increased ozone-inducible DNA binding on the BRS-3 promoter and BRS-3 expression. The time courses of AP-2alpha and PPARalpha activation, followed by BRS-3 expression, were also examined. It was shown that ozone-inducible BRS-3 expression and AP-2alpha- and PPARalpha-binding activity correlated over a 48 h period. The translocation of PPARalpha was observed by immunofluorescence assay, which showed that PPARalpha nuclear translocation increased after ozone exposure. Our data suggest that AP-2alpha and PPARalpha may be especially involved in this ozone-inducible up-regulation mechanism of BRS-3 expression.

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

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

Regulation of integrin α10 expression in chondrocytes by the transcription factors AP-2ε and Ets-1

Expression of integrin alpha10 is initiated at the beginning of chondrogenesis and continues throughout cartilage development in adult cartilage. In our study, we aim to identify regulatory sequences that control the cell-type specific expression of the human integrin alpha10 gene. Therefore, promoter constructs harboring 1139bp 5' of the transcriptional start site of the human integrin alpha10 gene were analyzed. Our experiments localized a promoter region that directs high levels of expression specifically in chondrocytes. A sequence analysis detected three consensus AP-2 binding sites within this functional domain. Functionality of these sites was tested and confirmed by cotransfection of AP-2 in a luciferase reporter assay. Interestingly, EMSA identified AP-2epsilon as the major AP-2 protein binding to the AP-2 consensus sequences. Additionally, Ets-1 was shown to be a positive regulator of the integrin alpha10 expression whereas Sox9 was irrelevant. Taken together, these results suggest that AP-2epsilon and Ets-1 are involved in the regulation of integrin alpha10 transcription in chondrocytes.

GAS41 interacts with transcription factor AP-2beta and stimulates AP-2beta-mediated transactivation

Transcription factor AP-2 regulates transcription of a number of genes involving mammalian development, differentiation and carcinogenesis. Recent studies have shown that interaction partners can modulate the transcriptional activity of AP-2 over the downstream targets. In this study, we reported the identification of GAS41 as an interaction partner of AP-2β. We documented the interaction both in vivo by co-immunoprecipitation as well as in vitro through glutathione S-transferase (GST) pull-down assays. We also showed that the two proteins are co-localized in the nuclei of mammalian cells. We further mapped the interaction domains between the two proteins to the C-termini of both AP-2β and GAS41, respectively. Furthermore, we have identified three critical residues of GAS41 that are important for the interaction between the two proteins. In addition, by transient co-expression experiments using reporter containing three AP-2 consensus binding sites in the promoter region, we found that GAS41 stimulates the transcriptional activity of AP-2β over the reporter. Finally, electrophoretic mobility shift assay (EMSA) suggested that GAS41 enhances the DNA-binding activity of AP-2β. Our data provide evidence for a novel cellular function of GAS41 as a transcriptional co-activator for AP-2β.

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.

TAp63alpha induces AP-2gamma as an early event in epidermal morphogenesis

Epidermal morphogenesis begins with the commitment of the single-layered surface ectoderm to initiate a stratification program, a process that requires the expression of the transcription factor TAp63alpha. To determine the molecular mechanism by which TAp63alpha induces genes associated with the commitment to stratification, such as K14, we have used a combination of in vitro and in vivo approaches. Our initial gene expression profiling studies suggested that TAp63alpha could regulate one or more AP-2 genes, which have been implicated in development and maintenance of the epidermis. We now demonstrate that TAp63alpha directly induces AP-2gamma expression in embryonic epidermis, when commitment to stratification occurs. Furthermore, we show that, in the absence of AP-2gamma, TAp63alpha fails to induce K14 expression in vitro. Our data identify AP-2gamma as the first in vivo target gene of TAp63alpha, and provide novel insights into the molecular mechanisms associated with early events in epidermal morphogenesis.

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.

Brainstem levels of transcription factor AP-2 in rat are changed after treatment with phenelzine, but not with citalopram

BACKGROUND

Before therapeutic effect is obtained after treatment with antidepressant drugs, like serotonin selective reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAO-Is) there is an initial lag-period of a few weeks. Neuronal adaptations on a molecular level are supposed to be involved in the initiation of the antidepressant effect. Transcription factor AP-2 is essential for neuronal development and many genes involved in the brainstem monoaminergic systems have binding sites for AP-2 in their regulatory regions. The genotype of the AP-2beta isoform has been associated with e.g. anxiety-related personality traits and with platelet MAO activity. In addition, previous studies have shown that the levels of AP-2alpha and AP-2beta in rat whole brain were decreased after 10 days of treatment with citalopram (SSRI) and imipramine (TCA), and were increased with phenelzine (MAO-I).

RESULTS

In the present study, we report that treatment with citalopram for 1, 7 or 21 days did not have effect on the AP-2 levels in rat brainstem. However, after treatment with phenelzine for 1, 7 or 21 days the levels of AP-2alpha and AP-2beta had increased after 7 days, but had returned to control levels at day 21.

CONCLUSION

The decrease in AP-2 levels in rat whole brain previously seen after treatment with citalopram does not seem to be localised to the brainstem, it may rather occur in the monoaminergic terminal projection areas. The present data suggest that the increase in AP-2 levels previously seen in rat whole brain after subchronic treatment with phenelzine is located in the brainstem. It cannot, however, be excluded that other brain regions are involved.

Cell type-specific and sexually dimorphic expression of transcription factor AP-2 in the adult mouse brain

Expression of transcription factor AP-2 family genes in adult mouse brain regions was examined at RNA and protein levels and in tissue sections. AP-2 family RNA transcripts, nuclear AP-2 DNA binding activity, and AP-2 immunoreactivity were greatest in hindbrain and midbrain regions. Cells expressing AP-2 were predominantly differentiated neurons and were abundant in the solitary tract nucleus, hypoglossal nucleus, locus coeruleus, cerebellar molecular layer, superior colliculus, mitral cell layers of the main and accessory olfactory bulbs, and in some divisions of the bed nucleus of the stria terminalis. Sexually dimorphic expression of AP-2 was seen in the bed nucleus of the stria terminalis, a forebrain region required for regulation of gender-specific reproductive and social behaviors. In males, AP-2 expressing neurons were present in supracapsular, lateral ventral, and medial ventral divisions of the bed nucleus of the stria terminalis. In contrast, females had AP-2 expressing neurons in the lateral ventral division, but not the supracapsular division, and AP-2 expression in medial ventral division neurons oscillated during the estrus cycle. With the exception of the bed nucleus of the stria terminalis, forebrain regions generally lacked cells with high levels of AP-2. However, a small population of cells co-expressing low levels of AP-2 and Notch1 was sparsely distributed in the cerebral cortex and hippocampal dentate gyrus subgranular zone. Based on their variable levels of NeuN, a marker for differentiated neurons, these cells may include nascent neurons. A subset of cerebellar Purkinje cells also co-expressed low levels of AP-2 and Notch1. Together, the adult brain regions with AP-2 expressing neurons are notable for their importance in pathways that integrate sensory and neuroendocrine information for regulation of reproductive, social, and feeding behaviors. Our data suggest that AP-2 transcription factors contribute at multiple levels to adult brain function including regulation of gender-specific behavior.