Transcription factor AP-4 contains multiple dimerization domains that regulate dimer specificity

Chromatin profiling reveals TFAP4 as a critical transcriptional regulator of bovine satellite cell differentiation

BACKGROUND

Satellite cells are myogenic precursor cells in adult skeletal muscle and play a crucial role in skeletal muscle regeneration, maintenance, and growth. Like embryonic myoblasts, satellite cells have the ability to proliferate, differentiate, and fuse to form multinucleated myofibers. In this study, we aimed to identify additional transcription factors that control gene expression during bovine satellite cell proliferation and differentiation.

RESULTS

Using chromatin immunoprecipitation followed by sequencing, we identified 56,973 and 54,470 genomic regions marked with both the histone modifications H3K4me1 and H3K27ac, which were considered active enhancers, and 50,956 and 59,174 genomic regions marked with H3K27me3, which were considered repressed enhancers, in proliferating and differentiating bovine satellite cells, respectively. In addition, we identified 1,216 and 1,171 super-enhancers in proliferating and differentiating bovine satellite cells, respectively. Analyzing these enhancers showed that in proliferating bovine satellite cells, active enhancers were associated with genes stimulating cell proliferation or inhibiting myoblast differentiation whereas repressed enhancers were associated with genes essential for myoblast differentiation, and that in differentiating satellite cells, active enhancers were associated with genes essential for myoblast differentiation or muscle contraction whereas repressed enhancers were associated with genes stimulating cell proliferation or inhibiting myoblast differentiation. Active enhancers in proliferating bovine satellite cells were enriched with binding sites for many transcription factors such as MYF5 and the AP-1 family transcription factors; active enhancers in differentiating bovine satellite cells were enriched with binding sites for many transcription factors such as MYOG and TFAP4; and repressed enhancers in both proliferating and differentiating bovine satellite cells were enriched with binding sites for NF-kB, ZEB-1, and several other transcription factors. The role of TFAP4 in satellite cell or myoblast differentiation was previously unknown, and through gene knockdown and overexpression, we experimentally validated a critical role for TFAP4 in the differentiation and fusion of bovine satellite cells into myofibers.

CONCLUSIONS

Satellite cell proliferation and differentiation are controlled by many transcription factors such as AP-1, TFAP4, NF-kB, and ZEB-1 whose roles in these processes were previously unknown in addition to those transcription factors such as MYF5 and MYOG whose roles in these processes are widely known.

Function and regulation of cis P-tau in the pathogenesis and treatment of conventional and nonconventional tauopathies

Conventional tauopathies are a group of disease characterized by tau inclusions in the brains, including Alzheimer's disease (AD), Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and certain types of frontotemporal dementia (FTD), among which AD is the most prevalent. Extensive post-translational modifications, especially hyperphosphorylation, and abnormal aggregation of tau protein underlie tauopathy. Cis-trans isomerization of protein plays an important role in protein folding, function, and degradation, which is regulated by peptidyl-proline isomerases (PPIases). Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), the only PPIase found to isomerize Pro following phosphorylated Ser or Thr residues, alters phosphorylated tau protein conformation at pT231-P motif. The cis P-tau but not trans P-tau serves as an early driver of multiple neurodegenerative disease, encompassing AD, traumatic brain injury (TBI), chronic traumatic encephalopathy (CTE), and vascular contributions to cognitive impairment and dementia (VCID). Cis but not trans P-tau is resistant to protein dephosphorylation and degradation, and also prone to protein aggregation. Cis P-tau loses its ability to stabilize microtubule, causing and spreading tauopathy mainly in axons, a pathological process called cistauosis. The conformation-specific monoclonal antibody that targets only the cis P-tau serves as a very early diagnosis method and a potential treatment of not only conventional tauopathies but also nonconventional tauopathies such as VCID, with clinical trials ongoing. Notably, cis P-tau antibody is the only clinical-stage Alzheimer's therapeutic that has shown the efficacy in animal models of not only AD but also TBI and stroke, which are very early stages of dementia. Here we review the identification and pathological consequences of cis pt231-tau, the role of its regulator Pin1, as well as the clinical implication of cis pt231-tau conformation-specific antibody in conventional and nonconventional tauopathies.

Transcriptional Mechanism of the Mouse β4-Galactosyltransferase 6 Gene in Mouse Neuroblastoma Cell Line Neuro-2a

Lactosylceramide (Lac-Cer) constitutes the backbone structure of various gangliosides whose abnormal expression is associated with malignancy of neuroblastoma. The understanding of the regulatory mechanism of Lac-Cer contributes to the development of neuroblastoma therapy. In this study, the transcriptional mechanism of mouse β4-galactosyltransferase (β4GalT) 6, which is one of Lac-Cer synthase, was analyzed using mouse neuroblastoma cell line Neuro-2a. The -226 to -13 region relative to the most downstream transcriptional start site was determined to be the promoter region by luciferase assay using the 5'-deletion constructs. The mutation into the activating protein (AP) 4-binding site -110/-101 drastically decreased the promoter activity, indicating that this site is mainly implicated in the transcription. Furthermore, the mutation into the GATA-binding site -210/-201 or another AP4-binding site -202/-193 partially decreased the promoter activity. The study suggests that the mouse β4GalT6 gene is transcriptionally regulated by AP4 in cooperation with GATA family transcription factor in neuroblastoma.

Biological impact and therapeutic perspective of targeting PI3K/Akt signaling in hepatocellular carcinoma: Promises and Challenges

Cancer progression results from activation of various signaling networks. Among these, PI3K/Akt signaling contributes to proliferation, invasion, and inhibition of apoptosis. Hepatocellular carcinoma (HCC) is a primary liver cancer with high incidence rate, especially in regions with high prevalence of viral hepatitis infection. Autoimmune disorders, diabetes mellitus, obesity, alcohol consumption, and inflammation can also lead to initiation and development of HCC. The treatment of HCC depends on the identification of oncogenic factors that lead tumor cells to develop resistance to therapy. The present review article focuses on the role of PI3K/Akt signaling in HCC progression. Activation of PI3K/Akt signaling promotes glucose uptake, favors glycolysis and increases tumor cell proliferation. It inhibits both apoptosis and autophagy while promoting HCC cell survival. PI3K/Akt stimulates epithelial-to-mesenchymal transition (EMT) and increases matrix-metalloproteinase (MMP) expression during HCC metastasis. In addition to increasing colony formation capacity and facilitating the spread of tumor cells, PI3K/Akt signaling stimulates angiogenesis. Therefore, silencing PI3K/Akt signaling prevents aggressive HCC cell behavior. Activation of PI3K/Akt signaling can confer drug resistance, particularly to sorafenib, and decreases the radio-sensitivity of HCC cells. Anti-cancer agents, like phytochemicals and small molecules can suppress PI3K/Akt signaling by limiting HCC progression. Being upregulated in tumor tissues and clinical samples, PI3K/Akt can also be used as a biomarker to predict patients' response to therapy.

LINC00520: A Potential Diagnostic and Prognostic Biomarker in Cancer

Long non-coding RNA (lncRNA) is important in the study of cancer mechanisms. LINC00520 is located on human chromosome 14q22.3 and is a highly conserved long non-coding RNA. LINC00520 is widely expressed in various tissues. The expression of LINC00520 is regulated by transcription factors such as Sp1, TFAP4, and STAT3. The high expression of LINC00520 is significantly related to the risk of 11 cancers. LINC00520 can competitively bind 10 miRNAs to promote tumor cell proliferation, invasion, and migration. In addition, LINC00520 is involved in the regulation of P13K/AKT and JAK/STAT signaling pathways. The expression of LINC00520 is significantly related to the clinicopathological characteristics and prognosis of tumor patients and is also related to the sensitivity of HNSCC to radiotherapy. Here, this article summarizes the abnormal expression pattern of LINC00520 in cancer and its potential molecular regulation mechanism and points out that LINC00520 can be used as a potential biomarker for cancer diagnosis, prognosis, and treatment.

A microRNA binding site polymorphism in the 3' UTR region of VEGF-A gene modifies colorectal cancer risk based on ethnicity: a meta-analysis

BACKGROUND

Vascular endothelial growth factor A (VEGF-A) plays an integral role in angiogenesis by contributing to growth, development, and metastasis of solid tumors. Recently, a single-nucleotide polymorphism +936C/T located in the VEGF-A 3' untranslated region (UTR) facilitated the susceptibility of colorectal cancer. The association between VEGF-A gene polymorphism +936C/T and colorectal cancer risk has been widely studied in the last decade, but presently, the results furnished remain enigmatic. Hence, the study aimed to investigate the association between VEGF-A +936C/T miRNA binding site polymorphism and the risk of developing colorectal cancer.

METHODS

This meta-analysis included 13 published case-control studies covering 3465 cases (colorectal cancer) and 3476 healthy controls. Publication bias was examined by means of Begg's funnel plots and Egger's regression tests. The quality of the studies included was evaluated using Newcastle-Ottawa scale. Subgroup analyses were performed in accordance to the various ethnicities of the study subjects and the study quality.

RESULTS

From the data obtained, it is implied that VEGF-A +936C/T polymorphism did not correlate with elevated colorectal cancer risk in all genetic models. But the results acquired from the subgroup analysis in over dominant model (CT vs. CC + TT: OR = 1.5047, 95% CI = 1.19-1.90) suggest that VEGF-A +936C/T polymorphism leads to the raise in the risk of developing CRC among the East Asian population. No association was observed in Caucasian and South Asian population.

CONCLUSIONS

Our results indicate that VEGF-A +936C/T polymorphism is not a risk factor for developing CRC in Caucasian and South Asian population. However, the East Asian population was related to an increased risk of developing colorectal cancer due to the presence of the minor allele.

Unexpected suppression of tumorigenesis by c-MYC via TFAP4-dependent restriction of stemness in B lymphocytes

The proliferative burst of B lymphocytes is essential for antigen receptor repertoire diversification during the development and selective expansion of antigen-specific clones during immune responses. High proliferative activity inevitably promotes oncogenesis, the risk of which is further elevated in B lymphocytes by endogenous gene rearrangement and somatic mutations. However, B-cell-derived cancers are rare, perhaps owing to putative intrinsic tumor-suppressive mechanisms. We show that c-MYC facilitates B-cell proliferation as a protumorigenic driver and unexpectedly coengages counteracting tumor suppression through its downstream factor TFAP4. TFAP4 is mutated in human lymphoid malignancies, particularly in >10% of Burkitt lymphomas, and reduced TFAP4 expression was associated with poor survival of patients with MYC-high B-cell acute lymphoblastic leukemia. In mice, insufficient TFAP4 expression accelerated c-MYC-driven transformation of B cells. Mechanistically, c-MYC suppresses the stemness of developing B cells by inducing TFAP4 and restricting self-renewal of proliferating B cells. Thus, the pursuant transcription factor cascade functions as a tumor suppressor module that safeguards against the transformation of developing B cells.

Transcription Factor AP4 Mediates Cell Fate Decisions: To Divide, Age, or Die

Simple Summary

Here, we review the literature on Activating Enhancer-Binding Protein 4 (AP4)/transcription factor AP4 (TFAP4) function and regulation and its role in cancer. Elevated expression of AP4 was detected in tumors of various organs and is associated with poor patient survival. AP4 is encoded by a Myc target gene and mediates cell fate decisions by regulating multiple processes, such as cell proliferation, epithelial-mesenchymal transition, stemness, apoptosis, and cellular senescence. Thereby, AP4 may be critical for tumor initiation and progression. In this review article, we summarize published evidence showing how AP4 functions as a transcriptional activator and repressor of a plethora of direct target genes in various physiological and pathological conditions. We also highlight the complex interactions of AP4 with c-Myc, N-Myc, p53, lncRNAs, and miRNAs in feed-back loops, which control AP4 levels and mediate AP4 functions. In the future, a better understanding of AP4 may contribute to improved prognosis and therapy of cancer.

Abstract

Activating Enhancer-Binding Protein 4 (AP4)/transcription factor AP4 (TFAP4) is a basic-helix-loop-helix-leucine-zipper transcription factor that was first identified as a protein bound to SV40 promoters more than 30 years ago. Almost 15 years later, AP4 was characterized as a target of the c-Myc transcription factor, which is the product of a prototypic oncogene that is activated in the majority of tumors. Interestingly, AP4 seems to represent a central hub downstream of c-Myc and N-Myc that mediates some of their functions, such as proliferation and epithelial-mesenchymal transition (EMT). Elevated AP4 expression is associated with progression of cancer and poor patient prognosis in multiple tumor types. Deletion of AP4 in mice points to roles of AP4 in the control of stemness, tumor initiation and adaptive immunity. Interestingly, ex vivo AP4 inactivation results in increased DNA damage, senescence, and apoptosis, which may be caused by defective cell cycle progression. Here, we will summarize the roles of AP4 as a transcriptional repressor and activator of target genes and the contribution of protein and non-coding RNAs encoded by these genes, in regulating the above mentioned processes. In addition, proteins interacting with or regulating AP4 and the cellular signaling pathways altered after AP4 dysregulation in tumor cells will be discussed.

HLH-11 modulates lipid metabolism in response to nutrient availability

The ability of organisms to sense nutrient availability and tailor their metabolic states to withstand nutrient deficiency is critical for survival. To identify previously unknown regulators that couple nutrient deficiency to body fat utilization, we performed a cherry-picked RNAi screen in C. elegans and found that the transcription factor HLH-11 regulates lipid metabolism in response to food availability. In well-fed worms, HLH-11 suppresses transcription of lipid catabolism genes. Upon fasting, the HLH-11 protein level is reduced through lysosome- and proteasome-mediated degradation, thus alleviating the inhibitory effect of HLH-11, activating the transcription of lipid catabolism genes, and utilizing fat. Additionally, lipid profiling revealed that reduction in the HLH-11 protein level remodels the lipid landscape in C. elegans. Moreover, TFAP4, the mammalian homolog of HLH-11, plays an evolutionarily conserved role in regulating lipid metabolism in response to starvation. Thus, TFAP4 may represent a potential therapeutic target for lipid storage disorders.

Organismal metabolism fluctuates depending on nutritional conditions. Here, the authors show that, in C. elegans, HLH-11 negatively regulates lipid metabolism genes in the presence of nutrients and that its abundance decreased in response to starvation, thereby promoting fat utilization.

Chromatin accessibility dynamics of Chlamydia-infected epithelial cells

Chlamydia are Gram-negative, obligate intracellular bacterial pathogens responsible for a broad spectrum of human and animal diseases. In humans, Chlamydia trachomatis is the most prevalent bacterial sexually transmitted infection worldwide and is the causative agent of trachoma (infectious blindness) in disadvantaged populations. Over the course of its developmental cycle, Chlamydia extensively remodels its intracellular niche and parasitises the host cell for nutrients, with substantial resulting changes to the host cell transcriptome and proteome. However, little information is available on the impact of chlamydial infection on the host cell epigenome and global gene regulation. Regions of open eukaryotic chromatin correspond to nucleosome-depleted regions, which in turn are associated with regulatory functions and transcription factor binding. We applied formaldehyde-assisted isolation of regulatory elements enrichment followed by sequencing (FAIRE-Seq) to generate temporal chromatin maps of C. trachomatis-infected human epithelial cells in vitro over the chlamydial developmental cycle. We detected both conserved and distinct temporal changes to genome-wide chromatin accessibility associated with C. trachomatis infection. The observed differentially accessible chromatin regions include temporally-enriched sets of transcription factors, which may help shape the host cell response to infection. These regions and motifs were linked to genomic features and genes associated with immune responses, re-direction of host cell nutrients, intracellular signalling, cell-cell adhesion, extracellular matrix, metabolism and apoptosis. This work provides another perspective to the complex response to chlamydial infection, and will inform further studies of transcriptional regulation and the epigenome in Chlamydia-infected human cells and tissues.

Regulation of Expression and Latency in BLV and HTLV

Human T-lymphotrophic virus type 1 (HTLV-1) and Bovine leukemia virus (BLV) belong to the Deltaretrovirus genus. HTLV-1 is the etiologic agent of the highly aggressive and currently incurable cancer adult T-cell leukemia (ATL) and a neurological disease HTLV-1-associated myelopathy (HAM)/tropical spastic paraparesis (TSP). BLV causes neoplastic proliferation of B cells in cattle: enzootic bovine leucosis (EBL). Despite the severity of these conditions, infection by HTLV-1 and BLV appear in most cases clinically asymptomatic. These viruses can undergo latency in their hosts. The silencing of proviral gene expression and maintenance of latency are central for the establishment of persistent infection, as well as for pathogenesis in vivo. In this review, we will present the mechanisms that control proviral activation and retroviral latency in deltaretroviruses, in comparison with other exogenous retroviruses. The 5′ long terminal repeats (5′-LTRs) play a main role in controlling viral gene expression. While the regulation of transcription initiation is a major mechanism of silencing, we discuss topics that include (i) the epigenetic control of the provirus, (ii) the cis-elements present in the LTR, (iii) enhancers with cell-type specific regulatory functions, (iv) the role of virally-encoded transactivator proteins, (v) the role of repressors in transcription and silencing, (vi) the effect of hormonal signaling, (vii) implications of LTR variability on transcription and latency, and (viii) the regulatory role of non-coding RNAs. Finally, we discuss how a better understanding of these mechanisms may allow for the development of more effective treatments against Deltaretroviruses.

Transcription factor AP-4 (TFAP4)-upstream ORF coding 66 aa inhibits the malignant behaviors of glioma cells by suppressing the TFAP4/long noncoding RNA 00520/microRNA-520f-3p feedback loop

Upstream ORF (uORF) is a translational initiation element located in the 5′UTR of eukaryotic mRNAs. Studies have found that uORFs play an important regulatory role in many diseases. Based on The Cancer Genome Atlas database, the results of our experiments and previous research evidence, we investigated transcription factor AP‐4 (TFAP4) and its uORF, LIM and SH3 protein 1 (LASP1), long noncoding RNA 00520 (LINC00520), and microRNA (miR)‐520f‐3p as candidates involved in glioma malignancy, which is a poorly understood process. Both TFAP4‐66aa‐uORF and miR‐520f‐3p were downregulated, and TFAP4, LASP1, and LINC00520 were highly expressed in glioma tissues and cells. TFAP4‐66aa‐uORF or miR‐520f‐3p overexpression or TFAP4, LASP1, or LINC00520 knockdown inhibited glioma cell proliferation, migration, and invasion, but promoted apoptosis. TFAP4‐66aa‐uORF inhibited the translation of TFAP4 by binding to the TFAP4 mRNA. MicroRNA‐520f‐3p inhibited TFAP4 expression by binding to its 3′UTR. However, LINC00520 could promote the expression of TFAP4 by competitively binding to miR‐520f‐3p. In addition, TFAP4 transcriptionally activated LASP1 and LINC00520 expression by binding to their promoter regions, forming a positive feedback loop of TFAP4/LINC00520/miR‐520f‐3p. Our findings together indicated that TFAP4‐66aa‐uORF inhibited the TFAP4/LINC00520/miR‐520f‐3p feedback loop by directly inhibiting TFAP4 expression, subsequently leading to inhibition of glioma malignancy. This provides a basis for developing new therapeutic approaches for glioma treatment.

Association between Vascular Endothelial Growth Factor Gene Polymorphisms and Pre-Eclampsia Susceptibility: An Updated Meta-Analysis

Objectives: The aim of this study was to assess the genetic association between vascular endothelial growth factor (VEGF) gene polymorphisms and the risk of pre-eclampsia (PE).Methods: A systematic literature search of several databases (PubMed, Embase, and the China National Knowledge Infrastructure (CNKI)) was conducted for case-control trials comparing VEGF polymorphisms (+936C/T, -634G/C, -2578C/A, and -1154G/A) with the risk of PE. Meta-analysis was performed using the Stata 12.0 software.Results: Twenty-three case-control studies on a total of 2597 PE patients and 3075 controls were included in our meta-analysis. The +936C/T polymorphism was observed to be associated with the risk of PE in the overall population (T vs. C: odds ratios (OR) = 1.434, 95% confidence interval (CI) = 1.120-1.836, P = .004). However, the -634G/C, -2578C/A, and -1154G/A polymorphisms showed no association with the risk of PE. A subgroup analysis based on ethnicity found that the +936C/T polymorphism was associated with the risk of PE in both Europeans and Asians. Furthermore, the -634G/C polymorphism was found to be associated with the risk of PE in Europeans (C vs. G: OR = 1.428, 95% CI = 1.141-1.778, P = .002). The polymorphisms at other loci were not associated with the risk of PE.Conclusion: This meta-analysis suggests that VEGF +936C/T polymorphism, rather than -634G/C, -2578C/A, or -1154G/A polymorphisms, is associated with the risk of PE in the overall study population. However, the -634G/C polymorphism may be associated with the risk of developing PE in Europeans.

TFAP4 Promotes Hepatocellular Carcinoma Invasion and Metastasis via Activating the PI3K/AKT Signaling Pathway

Transcription factor activating enhancer binding protein 4 (TFAP4) is established as a regulator of human cancer genesis and progression. Overexpression of TFAP4 indicates poor prognosis in various malignancies. The current study was performed to quantify TFAP4 expression as well as to further determine its potential prognostic value and functional role in patients with hepatocellular carcinoma (HCC). We identified that the expression of TFAP4 mRNA in 369 tumor tissues was higher than that in 160 normal liver tissues. Upregulated TFAP4 expressions were discovered in HCC cell lines compared to the healthy liver cell line, and similarly, the levels of TFAP4 were higher in tumor tissues than its expression in paratumor tissues. High mRNA and protein expression of TFAP4 was associated with worse overall survival (OS) and disease-free survival (DFS). Additionally, TFAP4 expression emerged as a risk factor independently affecting both OS and DFS of HCC patients. Functional studies demonstrated that TFAP4 increased HCC cell migration and invasion. Further investigations found that TFAP4 promotes invasion and metastasis by inducing epithelial-mesenchymal transition (EMT) and regulating MMP-9 expression via activating the PI3K/AKT signaling pathway in HCC. In conclusion, our study demonstrated that TFAP4 is a valuable prognostic biomarker in determining the likelihood of tumor metastasis and recurrence, as well as the long-term survival rates of HCC patients. Exploring the regulatory mechanism of TFAP4 will also contribute to the development of new prevention and treatment strategies for HCC.

miR-144 suppresses cell proliferation and invasion in gastric cancer through downregulation of activating enhancer-binding protein 4

Gastric cancer (GC) is the most common malignant disease and its incidence rate is increasing rapidly worldwide. The molecular mechanisms underlying GC tumorigenesis require further investigation. The expression and physiological roles of microRNA-144 (miR-144) have been investigated in numerous types of tumor. However, its biological function in GC remains largely unknown. The reverse transcription- quantitative polymerase chain reaction was used to determine the expression of miR-144 in GC cells and normal gastric epithelial cells. An miR-144 mimic was transfected into HGC-27 cells. In addition, bioinformatics analysis was performed to identify the potential targets of miR-144. Protein expression, luciferase and rescue assays were used to confirm the target of miR-144. It was identified that the expression of miR-144 was significantly downregulated in GC cells compared with in normal gastric epithelial cells. Furthermore, overexpression of miR-144 suppressed HGC-27 cell proliferation, migration and invasion. Additionally, bioinformatics analysis suggested that the activating enhancer-binding protein 4 (AP4) is a target gene of miR-144. In addition, it was determined that miR-144 suppresses the expression of AP4 by binding directly to its 3'-untranslated regions. Furthermore, restoration of AP4 partially attenuated miR-144-induced inhibition of cell proliferation, migration and invasion. Therefore, the results of the present study suggest that miR-144 serves an important role in GC progression.

MYC Oncogene Contributions to Release of Cell Cycle Brakes

Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.

TRIB2 functions as novel oncogene in colorectal cancer by blocking cellular senescence through AP4/p21 signaling

Background

Cellular senescence is a state of irreversible cell growth arrest and senescence cells permanently lose proliferation potential. Induction of cellular senescence might be a novel therapy for cancer cells. TRIB2 has been reported to participate in regulating proliferation and drug resistance of various cancer cells. However, the role of TRIB2 in cellular senescence of colorectal cancer (CRC) and its molecular mechanism remains unclear.

Methods

The expression of TRIB2 in colorectal cancer tissues and adjacent tissues was detected by immunohistochemistry and RT-PCR. The growth, cell cycle distribution and cellular senescence of colorectal cancer cells were evaluated by Cell Counting Kit-8 (CCK8) assay, flow cytometry detection and senescence-associated β-galactosidase staining, respectively. Western blot, RT-PCR and luciferase assay were performed to determine how TRIB2 regulates p21. Immunoprecipitation (IP) and chromatin-immunoprecipitation (ChIP) were used to investigate the molecular mechanisms.

Results

We found that TRIB2 expression was elevated in CRC tissues compared to normal adjacent tissues and high TRIB2 expression indicated poor prognosis of CRC patients. Functionally, depletion of TRIB2 inhibited cancer cells proliferation, induced cell cycle arrest and promoted cellular senescence, whereas overexpression of TRIB2 accelerated cell growth, cell cycle progression and blocked cellular senescence. Further studies showed that TRIB2 physically interacted with AP4 and inhibited p21 expression through enhancing transcription activities of AP4. The rescue experiments indicated that silencing of AP4 abrogated the inhibition of cellular senescence induced by TRIB2 overexpression.

Conclusion

These data demonstrate that TRIB2 suppresses cellular senescence through interaction with AP4 to down-regulate p21 expression. Therefore, TRIB2 could be a potential target for CRC treatment.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0922-x) contains supplementary material, which is available to authorized users.

Transcription factor AP-4 promotes tumorigenic capability and activates the Wnt/β-catenin pathway in hepatocellular carcinoma

It has been reported that the transcription factor activating enhancer-binding protein 4 (TFAP4) is upregulated and associated with an aggressive phenotype in several cancers. However, the precise mechanisms underlying the oncogenic role of TFAP4 remain largely unknown.

Methods: TFAP4 expression levels in hepatocellular carcinoma (HCC) cells and tissues were detected by quantitative real-time PCR (qPCR) and immunohistochemistry (IHC). In vitro and in vivo assays were performed to investigate the oncogenic function of TFAP4 in the tumor-initiating cell (TIC)-like phenotype and the tumorigenic capability of HCC cells. Luciferase reporter and chromatin immunoprecipitation (ChIP)-qPCR assays were performed to determine the underlying mechanism of TFAP4-mediated HCC aggressiveness.

Results: TFAP4 was markedly upregulated in human HCC, and was associated with significantly poorer overall and relapse-free survival in patients with HCC. Furthermore, we found that overexpression of TFAP4 significantly enhanced, whereas silencing TFAP4 inhibited, the tumor sphere formation ability and proportion of side-population cells in HCC cells in vitro, and ectopic TFAP4 enhanced the tumorigenicity of HCC cells in vivo. Mechanistically, we demonstrated that TFAP4 played an important role in activating Wnt/β-catenin signaling by directly binding to the promoters of DVL1 (dishevelled segment polarity protein 1) and LEF1 (lymphoid enhancer binding factor 1).

Conclusions: Our results provide new insight into the mechanisms underlying hyperactivation of the Wnt/β-catenin pathway in HCC, as well the oncogenic ability of TFAP4 to enhance the tumor-forming ability of HCC cells.

Evaluating the prognostic value and functional roles of transcription factor AP4 in colorectal cancer

The basic helix-loop-helix transcription factor AP4 (TFAP4) gene serves an important function in the genesis and progression of tumors. However, few studies to date have defined the role of this gene in colorectal cancer (CRC). The aim of the present study was to assess the expression of TFAP4 in CRC and its impact on the prognosis of patients with CRC. In the present study, the expression of TFAP4 was detected in 30 matched pairs of fresh CRC tissues, 187 cases of clinical paraffin-embedded CRC tissues and CRC cell lines using the reverse transcriptase-quantitative polymerase chain reaction, immunohistochemistry or western blot analysis. Survival analysis was based on TFAP4 expression. The effects of TFAP4 on CRC cell function were investigated by ectopic expression or knockdown of TFAP4 in vitro. TFAP4 expression was revealed to be increased in human CRC tissues and cell lines. The overall survival (OS) time of patients with high TFAP4 expression was significantly decreased compared with patients with low TFAP4 expression (P<0.001). In addition, TFAP4 was revealed to be an independent prognostic factor for the OS time of patients with CRC (hazard ratio, 2.607; 95% confidence interval, 1.469-4.627; P=0.001). Ectopic TFAP4 expression promoted CRC cell proliferation, migration and invasion in vitro, and the silencing of TFAP4 expression resulted in the inhibition of these events. These results demonstrated that TFAP4, which was overexpressed in CRC tissues and cell lines, increased the malignant potential of CRC cells and may serve as an indicator for poor prognosis in patients with CRC.

USP22 drives colorectal cancer invasion and metastasis via epithelial-mesenchymal transition by activating AP4

Ubiquitin specific peptidase 22 (USP22), a putative cancer stem cell marker, is overexpressed in liver metastases of colorectal cancer (CRC). However, the mechanism by which USP22 promotes CRC metastasis remains largely unknown. Here, we report that USP22 and AP4 are simultaneously overexpressed during TGF-β1-induced CRC cell epithelial-mesenchymal transition (EMT). USP22 up-regulation enhances CRC cell migration and invasion and EMT-related marker and AP4 expression, but these effects are partly blocked by AP4 knockdown. In addition, USP22 binds to the promoter region of AP4 to activate its transcription. In vivo, elevated USP22 expression promotes CRC cell metastasis to the lungs in nude mice, as evidenced by the fact that CRC metastatic nodules stain deeply positive for USP22 and AP4. In human CRC tissues, the genes encoding USP22 and AP4 are overexpressed in metastatic liver lesions compared with primary cancer tissues, and their overexpression is significantly associated with poor CRC patient survival. These findings indicate that USP22 and AP4 may serve as prognostic markers for predicting the risk of developing distant metastases in CRC.

AP4 positively regulates LAPTM4B to promote hepatocellular carcinoma growth and metastasis, while reducing chemotherapy sensitivity

Polymorphisms of the lysosomal-associated protein transmembrane-4 beta (LAPTM4B) gene are related to various forms of tumour susceptibility, which led us to hypothesize that some unique transcription factors targeting this polymorphism region may affect the biological function of LAPTM4B in tumour progression. In this study, we found that the transcription factor AP4 directly binds to the polymorphism region of the LAPTM4B gene promoter and induces its transcription. In addition, we demonstrated that AP4 promotes hepatocellular carcinoma (HCC) cell proliferation and metastasis and depresses chemotherapy sensitivity via LAPTM4B by activating the PI3K/AKT signalling pathway and caspase-dependent pathway. Interestingly, we found that AP4 could not only regulate LAPTM4B by directly binding to the promoter, but also be regulated via a positive feedback mechanism involving LAPTM4B acting on c-myc. Finally, we showed that AP4 and LAPTM4B are highly coexpressed in HCC tissues, and their coexpression may be a marker of poor prognosis. These findings provide evidence of the expression and functional coupling between AP4 and LAPTM4B and shed light on the regulation of LAPTM4B and its function in liver cancer.

MYCN promotes neuroblastoma malignancy by establishing a regulatory circuit with transcription factor AP4

Amplification of the MYCN oncogene, a member of the MYC family of transcriptional regulators, is one of the most powerful prognostic markers identified for poor outcome in neuroblastoma, the most common extracranial solid cancer in childhood. While MYCN has been established as a key driver of malignancy in neuroblastoma, the underlying molecular mechanisms are poorly understood. Transcription factor activating enhancer binding protein-4 (TFAP4) has been reported to be a direct transcriptional target of MYC. We show for the first time that high expression of TFAP4 in primary neuroblastoma patients is associated with poor clinical outcome. siRNA-mediated suppression of TFAP4 in MYCN-expressing neuroblastoma cells led to inhibition of cell proliferation and migration. Chromatin immunoprecipitation assay demonstrated that TFAP4 expression is positively regulated by MYCN. Microarray analysis identified genes regulated by both MYCN and TFAP4 in neuroblastoma cells, including Phosphoribosyl-pyrophosphate synthetase-2 (PRPS2) and Syndecan-1 (SDC1), which are involved in cancer cell proliferation and metastasis. Overall this study suggests a regulatory circuit in which MYCN by elevating TFAP4 expression, cooperates with it to control a specific set of genes involved in tumor progression. These findings highlight the existence of a MYCN-TFAP4 axis in MYCN-driven neuroblastoma as well as identifying potential therapeutic targets for aggressive forms of this disease.

Differential cellular responses by oncogenic levels of c-Myc expression in long-term confluent retinal pigment epithelial cells

c-Myc is a highly pleiotropic transcription factor known to control cell cycle progression, apoptosis, and cellular transformation. Normally, ectopic expression of c-Myc is associated with promoting cell proliferation or triggering cell death via activating p53. However, it is not clear how the levels of c-Myc lead to different cellular responses. Here, we generated a series of stable RPE cell clones expressing c-Myc at different levels, and found that consistent low level of c-Myc induced cellular senescence by activating AP4 in post-confluent RPE cells, while the cells underwent cell death at high level of c-Myc. In addition, high level of c-Myc could override the effect of AP4 on cellular senescence. Further knockdown of AP4 abrogated senescence-like phenotype in cells expressing low level of c-Myc, and accelerated cell death in cells with medium level of c-Myc, indicating that AP4 was required for cellular senescence induced by low level of c-Myc.

Current immunogenetic predisposition to tuberculosis in the Moroccan population

Tuberculosis (TB) is a serious infectious disease that kills approximately two million people per year, particularly in low- and middle-income countries. Numerous genetic epidemiology studies have been conducted of many ethnic groups worldwide and have highlighted the critical impact of the genetic environment on TB distribution. Many candidate genes associated with resistance or susceptibility to TB have been identified. In Morocco, where TB is still a major public health problem, various observations of clinical, microbiological and incidence distribution are heavily affected by genetic background and external environment. Morocco has almost the same clinical profile as do other North African countries, mainly the increase in more extrapulmonary than pulmonary forms of the diseases, when compared to European, Asian or American populations. In addition, a linkage analysis study that examined Moroccan TB patients identified a unique chromosome region that had a strong association with the risk of contracting TB. Other genes in the Moroccan population that were found to be associated seem to be involved predominantly in modulating the innate immunity. In this review, we appraise the major candidate genes that have been reported in Moroccan immunogenetic studies and discuss their updated role in TB, particularly during the first phase of the immune response to Mycobacterium tuberculosis (Mtb) infection.

AP4 modulated by the PI3K/AKT pathway promotes prostate cancer proliferation and metastasis of prostate cancer via upregulating L-plastin

The transition from androgen-dependent to metastatic castration-resistant prostate cancer (PCa) is a lethal event of uncertain molecular aetiology. Our previous studies demonstrated that L-plastin is involved in PCa invasion and metastasis and is upregulated by androgen and oestrogen in the hormone-dependent PCa cell line LNCaP. We recently found that L-plastin expression is consistently activated even after androgen deprivation, suggesting that androgen-independent transcription factors may regulate its expression. Herein, we performed sequential deletion and luciferase analysis of the L-plastin promoter and found that an androgen-independent regulatory factor prominently located in the region close to the transcription initiation site (−216 to +118) may facilitate L-plastin upregulation. AP4 was then identified as the relevant transcription activator that directly binds to the L-plastin promoter, as confirmed by EMSAs, supershift assays and CHIP-qPCR experiments. Moreover, we determined that the AP4/L-plastin axis is regulated by the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, contributing to PCa metastasis and castration resistance. Furthermore, we found that AP4 promotes PCa metastasis by upregulating L-plastin expression in vitro and in vivo. We collected a total of 136 PCa tissues and corresponding adjacent normal tissues from patients who underwent prostatectomy at Sun Yat-Sen Memorial Hospital from 2005 to 2015 and measured AP4 and L-plastin protein levels by immunohistochemistry. The results showed that AP4 levels strongly correlated with those of its downstream target gene L-plastin, were significantly upregulated in PCa tissues, were positively correlated with lymph node metastasis and Gleason scores over 7, and were an independent prognostic factor for patient survival. In summary, these findings support a plausible mechanism by which the AP4/L-plastin axis is regulated by the PI3K/AKT pathway in human PCa and may represent a novel therapeutic target in PCa treatment.

Overexpression of transcription factor activating enhancer binding protein 4 (TFAP4) predicts poor prognosis for colorectal cancer patients

Transcription factor activating enhancer binding protein 4 (TFAP4) is an important regulator in the genesis and progression of human cancers. Overexpression of TFAP4 has been found to be correlated with several malignancies. The present study assessed the clinical importance of TFAP4 in colorectal cancer (CRC). First, immunohistochemistry was used to analyze TFAP4 expression and the association of TFAP4 expression with clinicopathological features on a tissue microarray containing 208 CRC patients. The results revealed that TFAP4 protein expression was significantly upregulated in CRC tissues compared with that in normal colon tissues (P<0.001). Of note, statistical analysis revealed that TFAP4 expression was significantly correlated with a high pathological grade (P=0.034), advanced clinical stage (P=0.024), enhanced tumor invasion (P=0.002) and lymph node metastasis (P=0.041). In addition, the Cancer Genome Atlas dataset further validated that TFAP4 mRNA levels were increased in CRC with advanced clinical stage (P=0.026), lymph node metastasis (P=0.018) and vascular invasion (P=0.046). Kaplan-Meier survival analysis demonstrated that CRC patients with high TFAP4 expression had shorter overall survival compared with those with low TFAP4 expression (P=0.011). Importantly, overexpression of TFAP4 was a valuable independent prognostic factor for CRC patients (hazard ratio, 8.200; 95% confidence interval, 1.838-36.591; P=0.006). In summary, TFAP4 may have an important role in CRC progression and upregulation of TFAP4 may be a predictor of poor prognosis for CRC patients.

Genome-wide association study of prostate-specific antigen levels identifies novel loci independent of prostate cancer

Prostate-specific antigen (PSA) levels have been used for detection and surveillance of prostate cancer (PCa). However, factors other than PCa—such as genetics—can impact PSA. Here we present findings from a genome-wide association study (GWAS) of PSA in 28,503 Kaiser Permanente whites and 17,428 men from replication cohorts. We detect 40 genome-wide significant (P<5 × 10⁻⁸) single-nucleotide polymorphisms (SNPs): 19 novel, 15 previously identified for PSA (14 of which were also PCa-associated), and 6 previously identified for PCa only. Further analysis incorporating PCa cases suggests that at least half of the 40 SNPs are PSA-associated independent of PCa. The 40 SNPs explain 9.5% of PSA variation in non-Hispanic whites, and the remaining GWAS SNPs explain an additional 31.7%; this percentage is higher in younger men, supporting the genetic basis of PSA levels. These findings provide important information about genetic markers for PSA that may improve PCa screening, thereby reducing over-diagnosis and over-treatment.

Prostate-specific antigen is used as a biomarker of prostate cancer, but levels can be affected by other factors not related to cancer. Here, the authors find genes associated with prostate specific antigen levels in healthy men, which could be used to reduce over-diagnosis and over-treatment.

Prediction and validation of protein-protein interactors from genome-wide DNA-binding data using a knowledge-based machine-learning approach

The ability to accurately predict the DNA targets and interacting cofactors of transcriptional regulators from genome-wide data can significantly advance our understanding of gene regulatory networks. NKX2-5 is a homeodomain transcription factor that sits high in the cardiac gene regulatory network and is essential for normal heart development. We previously identified genomic targets for NKX2-5 in mouse HL-1 atrial cardiomyocytes using DNA-adenine methyltransferase identification (DamID). Here, we apply machine learning algorithms and propose a knowledge-based feature selection method for predicting NKX2-5 protein : protein interactions based on motif grammar in genome-wide DNA-binding data. We assessed model performance using leave-one-out cross-validation and a completely independent DamID experiment performed with replicates. In addition to identifying previously described NKX2-5-interacting proteins, including GATA, HAND and TBX family members, a number of novel interactors were identified, with direct protein : protein interactions between NKX2-5 and retinoid X receptor (RXR), paired-related homeobox (PRRX) and Ikaros zinc fingers (IKZF) validated using the yeast two-hybrid assay. We also found that the interaction of RXRα with NKX2-5 mutations found in congenital heart disease (Q187H, R189G and R190H) was altered. These findings highlight an intuitive approach to accessing protein-protein interaction information of transcription factors in DNA-binding experiments.

AP4 is required for mitogen- and c-MYC-induced cell cycle progression

AP4 represents a c-MYC-inducible bHLH-LZ transcription factor, which displays elevated expression in many types of tumors. We found that serum-starved AP4-deficient mouse embryo fibroblasts (MEFs) were unable to resume proliferation and showed a delayed S-phase entry after restimulation. Furthermore, they accumulated as tetraploid cells due to a cytokinesis defect. In addition, AP4 was required for c-MYC-induced cell cycle re-entry. AP4-deficient MEFs displayed decreased expression of CDK2 (cyclin-dependent kinase 2), which we characterized as a conserved and direct AP4 target. Activation of an AP4 estrogen receptor fusion protein (AP4-ER) enhanced proliferation of human diploid fibroblasts in a CDK2-dependent manner. However, in contrast to c-MYC-ER, AP4-ER activation was not sufficient to induce cell cycle re-entry or apoptosis in serum-starved MEFs. AP4-deficiency was accompanied by increased spontaneous and c-MYC-induced DNA damage in MEFs. Furthermore, c-MYC-induced apoptosis was decreased in AP4-deficient MEFs, suggesting that induction of apoptosis by c-MYC is linked to its ability to activate AP4 and thereby cell cycle progression. Taken together, these results indicate that AP4 is a central mediator and coordinator of cell cycle progression in response to mitogenic signals and c-MYC activation. Therefore, inhibition of AP4 function may represent a therapeutic approach to block tumor cell proliferation.

Vascular endothelial growth factor (-460 C/T, +405 G/C, and +936 C/T) polymorphisms and endometriosis risk in Tunisian population

The vascular endothelial growth factor (VEGF), a major angiogenic factor, is known to play an important role in the development of endometriosis. The aim of this study was to investigate the association of three VEGF (-460 C/T, +405 G/C, and +936 C/T) polymorphisms with the risk of endometriosis in the Tunisian population. This study includes 105 women with endometriosis and 150 women with no laparoscopic evidence of disease. Genotyping of the VEGF -460 C/T, +405 G/C, and +936 C/T polymorphisms were performed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). The distribution of genotypes (P = 0.006) and allele (P = 0.0009) frequencies of the +936 C/T polymorphism was significantly different between patients and controls. Patients with stages III-IV endometriosis showed a higher VEGF + 936T allele frequency than controls (P = 0.0001). However, the distribution of genotypes and allele frequencies of the VEGF -460 C/T and +405 G/C polymorphisms did not differ significantly between endometriosis patients and controls. These findings suggest that the VEGF +936 C/T polymorphism may be a risk factor for endometriosis development and the VEGF +936 T allele is associated with an increased risk of stages III-IV endometriosis in the Tunisian population.

Cropped, Drosophila transcription factor AP-4, controls tracheal terminal branching and cell growth

Background

Endothelial or epithelial cellular branching is vital in development and cancer progression; however, the molecular mechanisms of these processes are not clear. In Drosophila, terminal cell at the end of some tracheal tube ramifies numerous fine branches on the internal organs to supply oxygen. To discover more genes involved in terminal branching, we searched for mutants with very few terminal branches using the Kiss enhancer-trap line collection.

Results

In this analysis, we identified cropped (crp), encoding the Drosophila homolog of the transcription activator protein AP-4. Overexpressing the wild-type crp gene or a mutant that lacks the DNA-binding region in either the tracheal tissues or terminal cells led to a loss-of-function phenotype, implying that crp can affect terminal branching. Unexpectedly, the ectopic expression of cropped also led to enlarged organs, and cell-counting experiments on the salivary glands suggest that elevated levels of AP-4 increase cell size and organ size. Like its mammalian counterpart, cropped is controlled by dMyc, as ectopic expression of dMyc in terminal cells increased cellular branching and the Cropped protein levels in vivo.

Conclusions

We find that the branching morphogenesis of terminal cells of the tracheal tubes in Drosophila requires the dMyc-dependent activation of Cropped/AP-4 protein to increase the cell growth of terminal cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0069-6) contains supplementary material, which is available to authorized users.

Regulation of CD4 and CD8 coreceptor expression and CD4 versus CD8 lineage decisions

During blood cell development, hematopoietic stem cells generate diverse mature populations via several rounds of binary fate decisions. At each bifurcation, precursors adopt one fate and inactivate the alternative fate either stochastically or in response to extrinsic stimuli and stably maintain the selected fates. Studying of these processes would contribute to better understanding of etiology of immunodeficiency and leukemia, which are caused by abnormal gene regulation during the development of hematopoietic cells. The CD4(+) helper versus CD8(+) cytotoxic T-cell fate decision serves as an excellent model to study binary fate decision processes. These two cell types are derived from common precursors in the thymus. Positive selection of their TCRs by self-peptide presented on either MHC class I or class II triggers their fate decisions along with mutually exclusive retention and silencing of two coreceptors, CD4 and CD8. In the past few decades, extensive effort has been made to understand the T-cell fate decision processes by studying regulation of genes encoding the coreceptors and selection processes. These studies have identified several key transcription factors and gene regulatory networks. In this chapter, I will discuss recent advances in our understanding of the binary cell fate decision processes of T cells.

Identification of rice Di19 family reveals OsDi19-4 involved in drought resistance

The OsDi19 proteins functioned as transcription factors and played crucial roles in response to abiotic stress. Overexpression of OsDi19-4 in rice increased drought tolerance by enhancing ROS-scavenging activity. Many transcription factors play crucial roles in plant responses to abiotic stress. Here, comprehensive sequence analysis suggested that the drought-induced 19 (Di19) gene family in rice genome contain seven members, and these proteins contained a well-conserved zinc-finger Di19 domain. Most OsDi19 proteins were mainly targeted to the nucleus and have transactivation activity in yeast. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that most OsDi19 proteins could form protein dimers. Expression analysis demonstrated that the OsDi19 genes were differentially and abundantly expressed in vegetative tissues, but expressed little in reproductive tissues and some of the OsDi19 genes were markedly induced by abiotic stresses and hormones in qRT-PCR analysis and microarray data. Overexpression of one stress-responsive gene, OsDi19-4, in rice resulted in significantly increased tolerance to drought stress compared with the wild type plants. Moreover, obviously increased ROS-scavenging ability was detected in the OsDi19-4-overexpressing plants under normal and drought stress conditions. These results suggested that the increased stress tolerance of OsDi19-4-overexpressing plants may be attributable to the enhanced ROS-scavenging activity. Taken together, these studies provide a detailed overview of the rice Di19 gene family, and suggest that the OsDi19 family may play crucial roles in the plant response to abiotic stress.

C936T polymorphism of the VEGF gene in relation to the risk and the clinical and biological characteristics of sporadic colorectal adenocarcinoma

Background

One of the main glycoproteins responsible for angiogenesis is the vascular endothelial growth factor. It is believed that C936T polymorphism, located in the VEGF gene, is correlated with susceptibility towards development of sporadic colorectal adenocarcinoma. The aim of this study was to identify the frequencies of the genotypes of C936T polymorphism of the VEGF gene in patients with sporadic colorectal adenocarcinoma, in comparison with controls, and whether this correlates with the degree of tumor invasion, lymph node involvement and occurrence of metastases at the time of the diagnosis. The analysis was done on 261 patients with sporadic colorectal adenocarcinoma and 261 controls. The genotypes of C936T polymorphism were evaluated by means of the polymerase chain reaction and enzyme digestion, using peripheral blood samples.

Results

The occurrences of genotype 936CC were similar in the two groups (80.5% versus 78.5%, p = 0.2288). In relation to tumor location, lymph node involvement, infiltration and tumor metastasis, no statistically significant results were obtained (p = 0.3116, p = 0.8485, p = 0.9408 and p = 0.2861, respectively).

Conclusion

C936T polymorphism of the VEGF gene did not influence the occurrence of sporadic colorectal adenocarcinoma development and did not correlated with the degree of tumor invasion, lymph node involvement and occurrence of metastases.

c-Myc-induced transcription factor AP4 is required for host protection mediated by CD8+ T cells

Although c-Myc is essential to establish a metabolically active and proliferative state in T cells after priming, its expression is transient. It remains unknown how T cell activation is maintained after c-Myc down-regulation. Here, we identify AP4 as the transcription factor that is induced by c-Myc and sustains activation of antigen-specific CD8⁺ T cells. Despite normal priming, AP4-deficient CD8⁺ T cells fail to continue transcription of a broad range of c-Myc-dependent targets. Mice lacking AP4 specifically in CD8⁺ T cells showed enhanced susceptibility to West Nile virus infection. Genome-wide analysis suggests that many activation-induced metabolic genes are shared targets of c-Myc and AP4. Thus, AP4 maintains c-Myc-initiated cellular activation programs in CD8⁺ T cells to control microbial infections.

Vascular endothelial growth factor +936C/T polymorphism and breast cancer risk: a meta-analysis of 13 case-control studies

The association between vascular endothelial growth factor (VEGF) +936C/T polymorphism and breast cancer risk has been widely reported, but results were inconsistent. In order to derive a more precise estimation of the relationship, a meta-analysis was performed. Eligible articles were identified through search of databases including PubMed, Embase, and Chinese Biomedical Literature Database (CBM). The association between the VEGF +936C/T polymorphism and breast cancer risk was conducted by odds ratios (ORs) and 95 % confidence intervals (95 % CIs). Finally, a total of 13 studies with 6,879 cases and 7,219 controls were included in our meta-analysis. Overall, a significant association was found between VEGF +936C/T polymorphisms and the risk of breast cancer in overall populations under five models (T vs. C: OR = 0.83, 95 % CI = 0.73–0.94, P = 0.002; TT vs. CC: OR = 0.74, 95 % CI = 0.61–0.91, P = 0.004, Fig. 1a; TC vs. CC: OR = 0.83, 95 % CI = 0.71–0.96, P = 0.014; TT vs. CC/CT: OR = 0.77, 95 % CI = 0.62–0.94, P = 0.010; TT/TC vs. CC: OR = 0.82, 95 % CI = 0.72–0.95, P = 0.006). In the subgroup analysis by ethnicity, there were also significant associations found between VEGF +936C/T polymorphism and breast cancer risk in Asians and Caucasians. In conclusion, the results of our meta-analysis suggest that the VEGF +936C/T polymorphism is significantly associated with breast cancer development and the VEGF 936T allele carriers may be associated with decreased breast cancer risk.

p53-induced miR-15a/16-1 and AP4 form a double-negative feedback loop to regulate epithelial-mesenchymal transition and metastasis in colorectal cancer

The transcription factor AP4 mediates epithelial-mesenchymal transition (EMT) in colorectal cancer but its control in this setting is not fully understood. Here, we report the definition of a double-negative feedback loop involving AP4 and miR-15a/16-1 that regulates EMT and metastatic progression. In colorectal cancer cells, AP4 was downregulated by DNA damage in a p53-dependent manner. AP4 downregulation by p53 was mediated indirectly by the tumor-suppressive microRNAs miR-15a and miR-16-1, which targeted the 3' untranslated region (3'-UTR) of AP4 mRNA, induced mesenchymal-epithelial transition (MET), and inhibited colorectal cancer cell migration and invasion. The downregulation of AP4 was necessary for induction of MET and cell cycle arrest by miR-15a/16-1. In tumor xenoplants, ectopic miR-15a/16-1 suppressed formation of lung metastases. Furthermore, AP4 directly suppressed expression of miR-15a/16-1. In clinical specimens of colorectal cancer, miR-15a levels inversely correlated with AP4 protein levels shown previously to correlate with distant metastasis and poor survival. In summary, our results define a double-negative feedback loop involving miR-15a/16-1 and AP4 that stabilizes epithelial and mesenchymal states, respectively, which may determine metastatic prowess.

Vascular endothelial growth factor gene polymorphism and protein expression in the pathogenesis of pterygium

BACKGROUND AND AIMS

Vascular endothelial growth factor (VEGF) gene expression has been linked to cancer progression. Here we hypothesise that the polymorphism and protein expression of VEGF are correlated with the pathogenesis and therapy response of pterygium.

METHODS

60 pterygial and 121 normal conjunctival samples were collected to determine the genotypes and protein expression of VEGF. Primary pterygium cells (PECs) were used to confirm the effect of the VEGF polymorphism on the angiogenesis of pterygium.

RESULTS

48 (83.3%) pterygial specimens tested positive for VEGF protein expression, which was significantly higher than in the control groups (16.7%, p<0.0001). The frequency of the 936 C>T variant, but not the -2578C>A variant, was significantly higher in the pterygium group compared with the control group. VEGF protein expression was significantly higher in the 936 C/C group than in the 936 C/T and T/T groups (p=0.001). The results of our cell model showed that PECs with the C/C genotype had a higher angiogenesis ability and higher response to the antiangiogenesis drug bevacizumab than cells with the C/T and T/T genotypes.

CONCLUSIONS

We suggest that VEGF could be used as a target for pterygium therapy in patients with the 936C>T genotype.

AP4 directly downregulates p16 and p21 to suppress senescence and mediate transformation

Here we analyzed the function of the c-MYC-inducible basic helix–loop–helix leucine-zipper transcription factor AP4 in AP4-deficient mouse embryo fibroblasts (MEFs). Loss of AP4 resulted in premature senescence and resistance towards immortalization. Senescence was accompanied by induction of the cyclin-dependent kinase inhibitor-encoding genes p16, a known tumor suppressor, and p21, a previously described target for repression by AP4. Notably, AP4 directly repressed p16 expression via conserved E-box motifs in MEFs and human diploid fibroblasts. Senescence caused by AP4-deficiency was prevented by depletion of p16 and/or p21, demonstrating that these factors mediate senescence caused by AP4 loss. As senescence induced by the loss of AP4 was rescued by ectopic AP4, secondary lesions were not involved in causing premature senescence. Activation of c-MYC resulted in repression of p21 and p16 in AP4^+/+, but not in AP4^−/− MEFs. Furthermore, after combined expression of c-MYC and mutant RAS in MEFs, AP4 was required for colony formation, anchorage-independent growth and tumor formation in mice. In addition, combined ectopic expression of AP4 and mutant RAS in MEFs resulted in colony formation. However, additional loss of the p53 tumor suppressor was necessary for anchorage-independent growth and tumor formation of MEFs by combined AP4 and mutant RAS expression. In conclusion, this study identified AP4 as an oncogenic antagonist of cellular senescence. AP4 achieves this effect by direct repression of p16 and p21, and may thereby critically contribute to c-MYC function and tumor progression.

AP4 is a mediator of epithelial-mesenchymal transition and metastasis in colorectal cancer

The basic helix-loop-helix transcription factor AP4/TFAP4/AP-4 is encoded by a c-MYC target gene and displays up-regulation concomitantly with c-MYC in colorectal cancer (CRC) and numerous other tumor types. Here a genome-wide characterization of AP4 DNA binding and mRNA expression was performed using a combination of microarray, genome-wide chromatin immunoprecipitation, next-generation sequencing, and bioinformatic analyses. Thereby, hundreds of induced and repressed AP4 target genes were identified. Besides many genes involved in the control of proliferation, the AP4 target genes included markers of stemness (LGR5 and CD44) and epithelial-mesenchymal transition (EMT) such as SNAIL, E-cadherin/CDH1, OCLN, VIM, FN1, and the Claudins 1, 4, and 7. Accordingly, activation of AP4 induced EMT and enhanced migration and invasion of CRC cells. Conversely, down-regulation of AP4 resulted in mesenchymal-epithelial transition and inhibited migration and invasion. In addition, AP4 induction was required for EMT, migration, and invasion caused by ectopic expression of c-MYC. Inhibition of AP4 in CRC cells resulted in decreased lung metastasis in mice. Elevated AP4 expression in primary CRC significantly correlated with liver metastasis and poor patient survival. These findings imply AP4 as a new regulator of EMT that contributes to metastatic processes in CRC and presumably other carcinomas.

Association of the vascular endothelial growth factor gene polymorphisms (-460C/T, +405G/C and +936T/C) with endometriosis: a meta-analysis

Published data on the association between the vascular endothelial growth factor (VEGF) gene -460C/T (rs833061), +405G/C (rs2010963), +936T/C (rs3025039) polymorphisms and endometriosis risk are inconclusive. Eleven eligible case-control studies including 2690 cases and 2803 controls were included in this meta-analysis through searching the databases of PubMed and CBMdisc (up to August 1, 2011). In the overall analysis, no significant association between the -460C/T and +405G/C polymorphisms and risk of endometriosis was observed. However, significant associations were observed between endometriosis risk and VEGF+936T polymorphism with summarized odds ratio of 1.19 (95%CI, 1.02-1.37), 1.18 (95%CI, 1.03-1.37), 1.15 (95%CI, 1.01-1.30) for CT versus CC genotype, dominant mode (CT/TT vs. CC) and allele comparison (T vs. C), respectively. Furthermore, stratified analysis showed that significantly strong association between +936T/C polymorphism and endometriosis was present only in stage III-IV (OR = 1.32 for dominant mode; OR = 1.30 for T vs. C), but not in stage I-II. However, no significantly increased risk of endometriosis was found in any of the genetic models in Asians or in Caucasians. This meta-analysis supports that VEGF+936T/C polymorphism is capable of causing endometriosis susceptibility.

Associations between Vascular Endothelial Growth Factor Gene Polymorphisms and Susceptibility to Acute Mountain Sickness

Objective:

This study investigated associations between polymorphisms in the vascular endothelial growth factor (VEGF) gene and susceptibility to acute mountain sickness.

Methods:

Two hundred Han Chinese soldiers who developed acute mountain sickness after rapidly ascending to an altitude of < 3600 m and 200 control soldiers (who did not develop the condition) were enrolled in the study. Twelve single nucleotide polymorphisms (SNPs) of the VEGF gene were genotyped in all the study participants. Plasma VEGF concentrations were measured by enzyme-linked immunosorbent assay in 40 subjects with acute mountain sickness and 40 controls before and after exposure to high altitude.

Results:

The frequencies of the rs3025039 genotype and allele were significantly different between the groups. Two SNPs, rs3025039 (which involves a C→T allele variation at position 936 in the 3′ untranslated region) and rs3025030 (which involves a G→C allele variation in the intronic sequence), were associated with a decreased risk of acute mountain sickness.

Conclusion:

The SNPs rs3025039 and rs3025030 of the VEGF gene may be associated with a decreased risk of acute mountain sickness development.

High expression of AP-4 predicts poor prognosis for hepatocellular carcinoma after curative hepatectomy

The aim of this study was to evaluate the association between activating enhancer binding protein 4 (AP-4) tissue expression and patient prognosis in hepatocellular carcinoma (HCC). The levels of AP-4 mRNA and protein in tumor and para-tumor tissue were evaluated in 30 HCC cases by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Additionally, AP-4 protein expression in 112 HCC was analyzed by immunohistochemistry. The correlation of AP-4 expression and patients' clinicopathological parameters was evaluated. Survival analysis was performed using the Kaplan-Meier method and Cox's proportional hazards model. By RT-PCR and Western blot, the levels of AP-4 mRNA and protein were significantly higher in HCC, compared to that in para-tumor tissue (p < 0.001). Immunohistochemical staining revealed that AP-4 was highly expressed in 53.6 % of the HCC patients. The AP-4 expression level was closely associated with serum alpha fetoprotein elevation, tumor size, histological differentiation, tumor recurrence, tumor metastasis, and tumor stage. Kaplan-Meier survival analysis showed that a high expression level of AP-4 resulted in a significantly poor prognosis of HCC patients. Multivariate analysis revealed that AP-4 expression level was an independent prognostic parameter for the overall survival rate of HCC patients. These findings provide evidence that a high expression level of AP-4 serves as a biomarker for poor prognosis for HCC. Thus, we speculate that AP-4 may be a potential target of antiangiogenic therapy for HCC.

The single-nucleotide polymorphisms +936 C/T VEGF and -710 C/T VEGFR1 are associated with breast cancer protection in a Spanish population

Vascular endothelial growth factor (VEGF) is a potent regulator of angiogenesis and thereby involved in the development and progression of solid tumours. The association between polymorphisms of angiogenesis pathway genes and risk of breast cancer (BC) has been widely studied, but the results are not conclusive. This information is especially limited in Spanish women, so we decided to conduct a case-control study. Here, we selected four commonly studied polymorphisms in VEGF, rs3025039 (known as +936 C/T), rs1109324, rs154765 and rs833052, one polymorphism at the promoter of the VEGFR1 (-710 C/T) and another in the FGF2, rs1449683, gene to explore their association with BC susceptibility. Genotyping was performed by TaqMan SNP assays and polymerase chain reaction-restriction fragment length polymorphis (PCR-RFLP) on 453 patients and 461 controls in a population from Valencia (Spain). We observed that women carriers of +936 CT + TT VEGF genotypes have a protective effect concerning this disease (p = 0.014; OR 0.67, 95% CI 0.48-0.92) in the global group of patients. The haplotype TGAC of VEGF (rs3025039, rs1109324, rs154764 and rs833052) shows a reduction of the risk to develop BC (p = 3e-04; OR 0.48, 95% CI 0.32-0.72). Furthermore, we found that carriers of -710 CT + TT VEGFR1 genotypes have also a protective effect (p = 0.039; OR 0.55, 95% CI 0.31-0.98). When we stratified by groups of ages these associations were maintained. Our data report for the first time the association of the polymorphism -710 C/T VEGFR1 with BC. Additional experiments focused on VEGF-A, VEGFR1 and sVEGFR1 gene expression demonstrated that carriers of T allele at -710 C/T VEGFR1 genotype have higher levels of sVEGFR1/VEGF-A than the C/C genotype carriers. This was consistent with the hypothesis that this polymorphism may act as low penetrance risk factor. The data provided suggest that +936 C/T VEGF and -710 C/T VEGFR1 genotypes are likely important genetic markers of susceptibility to BC.

Down-regulation of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human gastric cancer cells

Background

AP-4 belongs to the basic helix-loop-helix leucine-zipper subgroup; it controls target gene expression, regulates growth, development and cell apoptosis and has been implicated in tumorigenesis. Our previous studies indicated that AP-4 was frequently overexpressed in gastric cancers and may be associated with the poor prognosis. The purpose of this study is to examine whether silencing of AP-4 can alter biological characteristics of gastric cancer cells.

Methods

Two specific siRNAs targeting AP-4 were designed, synthesized, and transfected into gastric cancer cell lines and human normal mucosa cells. AP-4 expression was measured with real-time quantitative PCR and Western blot. Cell proliferation and chemo-sensitivity were detected by CCK-8 assay. Cell cycle assay and apoptosis assay were performed by flow cytometer, and relative expression of cell cycle regulators were detected by real-time quantitative PCR and Western blot, expression of the factors involved in the apoptosis pathway were examined in mRNA and protein level.

Results

The expression of AP-4 was silenced by the siRNAs transfection and the effects of AP-4 knockdown lasted 24 to 96 hrs. The siRNA-mediated silencing of AP-4 suppressed the cellular proliferation, induced apoptosis and sensitized cancer cells to anticancer drugs. In addition, the expression level of p21, p53 and Caspase-9 were increased when AP-4 was knockdown, but the expression of cyclin D1, Bcl-2 and Bcl-x_L was inhibited. It didn't induce cell cycle arrest when AP-4 was knockdown in p53 defect gastric cancer cell line Kato-III.

Conclusions

These results illustrated that gene silencing of AP-4 can efficiently inhibited cell proliferation, triggered apoptosis and sensitized cancer cells to anticancer drugs in vitro, suggesting that AP-4 siRNAs mediated silencing has a potential value in the treatment of human gastric cancer.

Prevalence, distribution and functional significance of the -237C to T polymorphism in the IL-12Rβ2 promoter in Indian tuberculosis patients

Cytokine/cytokine receptor gene polymorphisms related to structure/expression could impact immune response. Hence, the −237 polymorphic site in the 5′ promoter region of the IL-12Rβ2 (SNP ID: rs11810249) gene associated with the AP-4 transcription motif GAGCTG, was examined. Amplicons encompassing the polymorphism were generated from 46 pulmonary tuberculosis patients, 35 family contacts and 28 miscellaneous volunteers and sequenced. The C allele predominated among patients, (93.4%, 43/46), and in all volunteers and contacts screened, but the T allele was exclusively limited to patients, (6.5%, 3/46). The functional impact of this polymorphism on transcriptional activity was assessed by Luciferase-reporter and electrophoretic mobility shift assays (EMSA). Luciferase-reporter assays showed a significant reduction in transcriptional efficiency with T compared to C allele. The reduction in transcriptional efficiency with the T allele construct (pGIL-12Rb2-T), in U-87MG, THP-1 and Jurkat cell lines, were 53, 37.6, and 49.8% respectively, compared to the C allele construct (pGIL-12Rb2-C). Similarly, densitometric analysis of the EMSA assay showed reduced binding of the AP-4 transcription factor, to T compared to the C nucleotide probe. Reduced mRNA expression in all patients (3/3) harboring the T allele was seen, whereas individuals with the C allele exhibited high mRNA expression (17/25; 68%, p = 0.05). These observations were in agreement with the in vitro assessment of the promoter activity by Luciferase-reporter and EMSA assays. The reduced expression of IL-12Rβ2 transcripts in 8 patients despite having the C allele was attributed to the predominant over expression of the suppressors (IL-4 and GATA-3) and reduced expression of enhancers (IFN-α) of IL-12Rβ2 transcripts. The 17 high IL-12Rβ2 mRNA expressers had significantly elevated IFN-α mRNA levels compared to low expressers and volunteers. Notwithstanding the presence of high levels of IL-12Rβ2 mRNA in these patients elevated IFN-α expression could modulate their immune responses to Mycobacterium tuberculosis.

Transcription factor AP4 modulates reversible and epigenetic silencing of the Cd4 gene

CD4 coreceptor expression is negatively regulated through activity of the Cd4 silencer in CD4(-)CD8(-) double-negative (DN) thymocytes and CD8(+) cytotoxic lineage T cells. Whereas Cd4 silencing is reversed during transition from DN to CD4(+)CD8(+) double-positive stages, it is maintained through heritable epigenetic processes following its establishment in mature CD8(+) T cells. We previously demonstrated that the Runx family of transcription factors is required for Cd4 silencing both in DN thymocytes and CD8(+) T cells. However, additional factors that cooperate with Runx proteins in the process of Cd4 silencing remain unknown. To identify collaborating factors, we used microarray and RNAi-based approaches and found the basic helix-loop-helix ZIP transcription factor AP4 to have an important role in Cd4 regulation. AP4 interacts with Runx1 in cells in which Cd4 is silenced, and is required for Cd4 silencing in immature DN thymocytes through binding to the proximal enhancer. Furthermore, although AP4-deficient CD8(+) T cells appeared to normally down-regulate CD4 expression, AP4 deficiency significantly increased the frequency of CD4-expressing effector/memory CD8(+) T cells in mice harboring point mutations in the Cd4 silencer. Our results suggest that AP4 contributes to Cd4 silencing both in DN and CD8(+) T cells by enforcing checkpoints for appropriate timing of CD4 expression and its epigenetic silencing.

Identification and functional analysis of a second RBF-2 binding site within the HIV-1 promoter

Transcription from the HIV-1 long terminal repeat (LTR) is mediated by numerous host transcription factors. In this study we characterized an E-box motif (RBE1) within the core promoter that was previously implicated in both transcriptional activation and repression. We show that RBE1 is a binding site for the RBF-2 transcription factor complex (USF1, USF2, and TFII-I), previously shown to bind an upstream viral element, RBE3. The RBE1 and RBE3 elements formed complexes of identical mobility and protein constituents in gel shift assays, both with Jurkat T-cell nuclear extracts and recombinant USF/TFII-I. Furthermore, both elements are regulators of HIV-1 expression; mutations in LTR-luciferase reporters and in HIV-1 molecular clones resulted in decreased transcription, virion production, and proviral expression in infected cells. Collectively, our data indicate that RBE1 is a bona fide RBF-2 binding site and that the RBE1 and RBE3 elements are necessary for mediating proper transcription from the HIV-1 LTR.