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

Deletion of the transcriptional regulator TFAP4 accelerates c-MYC-driven lymphomagenesis

Many lymphoid malignancies arise from deregulated c-MYC expression in cooperation with additional genetic lesions. While many of these cooperative genetic lesions have been discovered and their functions characterised, DNA sequence data of primary patient samples suggest that many more do exist. However, the nature of their contributions to c-MYC driven lymphomagenesis have not yet been investigated. We identified TFAP4 as a potent suppressor of c-MYC driven lymphoma development in a previous genome-wide CRISPR knockout screen in primary cells in vivo [1]. CRISPR deletion of TFAP4 in Eµ-MYC transgenic haematopoietic stem and progenitor cells (HSPCs) and transplantation of these manipulated HSPCs into lethally irradiated animals significantly accelerated c-MYC-driven lymphoma development. Interestingly, TFAP4 deficient Eµ-MYC lymphomas all arose at the pre-B cell stage of B cell development. This observation prompted us to characterise the transcriptional profile of pre-B cells from pre-leukaemic mice transplanted with Eµ-MYC/Cas9 HSPCs that had been transduced with sgRNAs targeting TFAP4. This analysis revealed that TFAP4 deletion reduced expression of several master regulators of B cell differentiation, such as Spi1, SpiB and Pax5, which are direct target genes of both TFAP4 and MYC. We therefore conclude that loss of TFAP4 leads to a block in differentiation during early B cell development, thereby accelerating c-MYC-driven lymphoma development.

Propranolol suppresses infantile hemangioma cell proliferation and promotes apoptosis by upregulating miR-125b expression

Propranolol could repress infantile hemangioma cell growth and induce apoptosis. miR-125b could inhibit cell proliferation in some tumors. However, whether propranolol exerts its proliferation inhibition and apoptosis-promoting effect by regulating the expression of miR-125b needs to be further investigated. In tumor tissue and endothelial cells isolated from infantile hemangioma patients, we found that the expression levels of miR-125b were significantly decreased. In-vitro analysis revealed that propranolol increased the expression of miR-125b in hemangioma cells in a dose-dependent and time-dependent manner. Interestingly, it was observed that regression of miR-125b expression by its inhibitor could abrogate the effect of propranolol on hemangioma cell growth and apoptosis. In addition, our data further identified TFAP4 as a direct target of miR-125b. Collectively, our data provided evidence that propranolol may repress infantile hemangioma cell growth and promote apoptosis through upregulating the miR-125b expression, which exerted its suppression of tumor development by targeting TFAP4.

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.

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.

The Transcription Factor AP4 Promotes Oncogenic Phenotypes and Cisplatin Resistance by Regulating LAPTM4B Expression

Lysosomal-associated protein transmembrane-4 beta (LAPTM4B) is a novel oncogene, whose overexpression is involved in cancer occurrence and progression. However, the mechanism of LAPTM4B transcriptional regulation remains unclear. In this study, the results of transcription factor (TF) profiling plate arrays indicated that AP4 was a potential transcription factor regulating LAPTM4B expression. LAPTM4B was positively correlated with AP4 and they were both associated with poor overall and disease-free survival. Luciferase and electrophoretic mobility shift assay assays confirmed that AP4 directly bound to the polymorphism region of LAPTM4B promoter and modulated its transcription. Functionally, AP4 promoted cell proliferation, migration, invasion, and assisted drug resistance in part through upregulation of LAPTM4B. Taken together, these findings identify LAPTM4B as a direct AP4 target gene and the interaction of AP4 and LAPTM4B plays an important role in breast cancer progression.Implications: This study demonstrates that AP4 promotes cell growth, migration, invasion, and cisplatin resistance through upregulation of LAPTM4B expression, thus representing an attractive therapeutic target for breast cancer. Mol Cancer Res; 16(5); 857-68. ©2018 AACR.

Integrative microRNA and mRNA deep-sequencing expression profiling in endemic Burkitt lymphoma

BACKGROUND

Burkitt lymphoma (BL) is characterized by overexpression of the c-myc oncogene, which in the vast majority of cases is a consequence of an IGH/MYC translocation. While myc is the seminal event, BL is a complex amalgam of genetic and epigenetic changes causing dysregulation of both coding and non-coding transcripts. Emerging evidence suggest that abnormal modulation of mRNA transcription via miRNAs might be a significant factor in lymphomagenesis. However, the alterations in these miRNAs and their correlations to their putative mRNA targets have not been extensively studied relative to normal germinal center (GC) B cells.

METHODS

Using more sensitive and specific transcriptome deep sequencing, we compared previously published small miRNA and long mRNA of a set of GC B cells and eBL tumors. MiRWalk2.0 was used to identify the validated target genes for the deregulated miRNAs, which would be important for understanding the regulatory networks associated with eBL development.

RESULTS

We found 211 differentially expressed (DE) genes (79 upregulated and 132 downregulated) and 49 DE miRNAs (22 up-regulated and 27 down-regulated). Gene Set enrichment analysis identified the enrichment of a set of MYC regulated genes. Network propagation-based method and correlated miRNA-mRNA expression analysis identified dysregulated miRNAs, including miR-17~95 cluster members and their target genes, which have diverse oncogenic properties to be critical to eBL lymphomagenesis. Central to all these findings, we observed the downregulation of ATM and NLK genes, which represent important regulators in response to DNA damage in eBL tumor cells. These tumor suppressors were targeted by multiple upregulated miRNAs (miR-19b-3p, miR-26a-5p, miR-30b-5p, miR-92a-5p and miR-27b-3p) which could account for their aberrant expression in eBL.

CONCLUSION

Combined loss of p53 induction and function due to miRNA-mediated regulation of ATM and NLK, together with the upregulation of TFAP4, may be a central role for human miRNAs in eBL oncogenesis. This facilitates survival of eBL tumor cells with the IGH/MYC chromosomal translocation and promotes MYC-induced cell cycle progression, initiating eBL lymphomagenesis. This characterization of miRNA-mRNA interactions in eBL relative to GC B cells provides new insights on miRNA-mediated transcript regulation in eBL, which are potentially useful for new improved therapeutic strategies.

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.

Chemical-agnostic hazard prediction: statistical inference of in vitro toxicity pathways from proteomics responses to chemical mixtures

Toxicity pathways have been defined as normal cellular pathways that, when sufficiently perturbed as a consequence of chemical exposure, lead to an adverse outcome. If an exposure alters one or more normal biological pathways to an extent that leads to an adverse toxicity outcome, a significant correlation must exist between the exposure, the extent of pathway alteration, and the degree of adverse outcome. Biological pathways are regulated at multiple levels, including transcriptional, post-transcriptional, post-translational, and targeted degradation, each of which can affect the levels and extents of modification of proteins involved in the pathways. Significant alterations of toxicity pathways resulting from changes in regulation at any of these levels therefore are likely to be detectable as alterations in the proteome. We hypothesize that significant correlations between exposures, adverse outcomes, and changes in the proteome have the potential to identify putative toxicity pathways, facilitating selection of candidate targets for high throughput screening, even in the absence of a priori knowledge of either the specific pathways involved or the specific agents inducing the pathway alterations. We explored this hypothesis in vitro in BEAS-2B human airway epithelial cells exposed to different concentrations of Ni²⁺, Cd²⁺, and Cr⁶⁺, alone and in defined mixtures. Levels and phosphorylation status of a variety of signaling pathway proteins and cytokines were measured after 48 hours exposure, together with cytotoxicity. Least Absolute Shrinkage and Selection Operator (LASSO) multiple regression was used to identify a subset of these proteins that constitute a putative toxicity pathway capable of predicting cytotoxicity. The putative toxicity pathway for cytotoxicity of these metals and metal mixtures identified by LASSO is composed of phospho-RPS6KB1, phospho-p53, cleaved CASP3, phospho-MAPK8, IL-10, and Hif-1α. As this approach does not depend on knowledge of the chemical composition of the mixtures, it may be generally useful for identifying sets of proteins predictive of adverse effects for a variety of mixtures, including complex environmental mixtures of unknown composition.

Silencing of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human lung cancer cells

Activating enhancer-binding protein (AP)-4 is a member of the basic helix-loop-helix transcription factors, and is involved in tumor biology. However, the role of AP-4 in human lung cancer remains to be fully elucidated. In the present study, the expression of AP-4 in human lung cancer tissues and cells was investigated by reverse transcription-quantitative polymerase chain reaction, and it was observed that the level of AP-4 was increased in tumor tissues and cells compared with their normal counterparts. AP-4 expression was knocked down by transfection with a specific small interfering RNA (siRNA) in lung cancer cells, and this indicated that siRNA-mediated silencing of AP-4 inhibited cell proliferation, arrested the cell cycle at the G0/G1 phase and induced apoptosis by modulating the expression of p21 and cyclin D1. The results of the present study suggest that AP-4 may be an oncoprotein that has a significant role in lung cancer, and that siRNA-mediated silencing of AP-4 may have therapeutic potential as a strategy for the treatment of lung cancer.

Downregulation of betaine homocysteine methyltransferase (BHMT) in hepatocellular carcinoma associates with poor prognosis

Betaine homocysteine methyltransferase (BHMT) catalyzes the synthesis of methionine using betaine and homocysteine (Hcy), which is restricted to the liver and kidney. Impaired BHMT pathway has been associated with hepatocellular carcinogenesis in Bhmt-/- mice model, and decreased BHMT was observed in a small sample of human hepatocellular carcinoma (HCC) patients. However, the prognostic significance of BHMT in HCC has not been elucidated. This study aimed to examine the expression of BHMT in HCC and investigate the relationship between its expression and prognosis of HCC patients. BHMT expression was analyzed in 68 paired HCC samples (HCC tissues vs matched adjacent non-cancerous liver tissues), 115 paraffin-embedded HCC sections (primary cohort), and 65 paraffin-embedded HCC sections (validation cohort) using immunohistochemistry (IHC). The results of IHC analysis showed that BHMT was decreased in tumorous tissues in 85.2 % (58/68) of cases compared to the corresponding adjacent non-tumorous liver tissues. Further correlation analyses indicated that the decreased BHMT expression was closely correlated with serum α-fetoprotein (AFP) (p = 0.011), tumor size (p = 0.039), and vascular invasion (p = 0.017). Moreover, HCC patients with low BHMT expression had shorter overall survival (OS) and time to recurrence (TTR) than those with high BHMT expression in both primary cohort (p < 0.0001) and validation cohort (p < 0.05) assessed by the Kaplan-Meier method. In addition, multivariate analysis showed that BHMT was an independent prognostic factor for OS and TTR in the two cohorts (all p < 0.005). Collectively, our study demonstrated that BHMT could be served as a potential prognostic marker for HCC patients.

Expressional profiles of transcription factors in the progression of Helicobacter pylori-associated gastric carcinoma based on protein/DNA array analysis

Transcription factors (TFs) are crucial modulators of gene expression during the development and progression of gastric carcinoma. Helicobacter pylori (H. pylori) is one of the most significant risk factors of gastric carcinoma, and it is widely known that chronic inflammation with H. pylori infection triggers gastric carcinogenesis through inflammation-carcinoma chain [gastric carcinogenesis stages: non-atrophic gastritis, chronic atrophic gastritis, intestinal metaplasia, dysplasia and gastric carcinoma (GC)], but its mechanism regarding changed TFs remains unknown. In this study, we investigated the expressional profiles of 345 transcription factors in gastric mucosa of healthy volunteers and patients at different gastric carcinogenesis stages using protein/DNA array-based approach. The data demonstrated the up-regulated TFs such as GATA-3, AP4, c-Myc and Pbx1 in the gastric mucosa of GC patients compared with the healthy volunteers, while other TFs, particularly CCAAT and CACC, showed the consistently decreasing trend along the gastric carcinogenesis. The increased expressions of AP4, Pbx1 and C/EBPα were further validated by quantitative real-time PCR and Western blot in various H. pylori-infected models such as clinical gastric tissues, gastric epithelial cell lines and Mongolian gerbils. This study provides insights into and potential laws for gene transcriptional regulation by identifying potential TFs targets against the development of H. pylori-associated gastric carcinoma.

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.

AP4 activates cell migration and EMT mediated by p53 in MDA-MB-231 breast carcinoma cells

Tumor metastasis is the primary cause of mortality in most cancer patients. Before disassociation from the tumors, most of malignant tumor cells undergo the epithelial-mesenchymal transition to break away from the adhesions between the cells and the surrounding extracellular matrix. Recently, activating enhancer-binding protein (AP4) has been shown to be a mediator of EMT in colorectal cancer and high level of AP4 correlates with poor prognosis in cancer patients. It has been found that AP4 upregulates the genes involved in EMT and cell proliferation in colorectal cancer cells and that the aggressive human breast cancer cells MDA-MB-231 are highly metastatic. Therefore, we tested the hypothesis that AP4 may also affect cell migration and EMT in this cell type. Three different assays, including the wound-healing assay, the Boyden chamber assay, and the cell tracking assay, were employed to confirm that AP4 activated both cell migration and invasion. Immunofluorescence staining and Western blot analysis revealed that the cells underwent EMT when AP4 was upregulated. In contrast, overexpression of dominant-negative AP4, lacking the DNA-binding domain, inactivated the DNA-binding ability of endogenous AP4 and led to lower cell motility. Furthermore, we found that AP4 enhanced p53 expression at both transcriptional and translational levels. Knockdown of p53 by siRNA significantly diminished the activation of cell migration by AP4, indicating that AP4 can regulate cell migration via the activity of p53.

Proteasome-dependent degradation of transcription factor activating enhancer-binding protein 4 (TFAP4) controls mitotic division

TFAP4, a basic helix-loop-helix transcription factor that regulates the expression of a multitude of genes involved in the regulation of cellular proliferation, stemness, and epithelial-mesenchymal transition, is up-regulated in colorectal cancer and a number of other human malignancies. We have found that, during the G2 phase of the cell division cycle, TFAP4 is targeted for proteasome-dependent degradation by the SCF(βTrCP) ubiquitin ligase. This event requires phosphorylation of TFAP4 on a conserved degron. Expression of a stable TFAP4 mutant unable to interact with βTrCP results in a number of mitotic defects, including chromosome missegregation and multipolar spindles, which eventually lead to the activation of the DNA damage response. Our findings reveal that βTrCP-dependent degradation of TFAP4 is required for the fidelity of mitotic division.

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.