Overexpression of activating transcription factor-2 is required for tumor growth and progression in mouse skin tumors

MLLT6/ATF2 Axis Restrains Breast Cancer Progression by Driving DDIT3/4 Expression

Epigenetic deregulation is strongly associated with tumor progression. The identification of natural tumor suppressors to overcome cancer metastasis is urgent for cancer therapy. We investigate whether myeloid/lymphoid or mixed-lineage leukemia translocated (MLLT) family members contribute to breast cancer progression and found that high MLLT6 expression predicted a better prognosis and that gradually decreased MLLT6 expression was accompanied by breast cancer malignancy. MLLT6 was downregulated by hypoxia-induced enrichment of DNMT1 at the MLLT6 promoter. The results of in vitro functional experiments indicated that MLLT6 depletion promoted colony formation and cell migration, probably by hampering apoptosis. RNA profiling revealed that the apoptotic pathway was downregulated following stable knockdown of MLLT6. DNA damage-inducible transcript 3/4 (DDIT3/4) were among the top 10 downregulated genes and may have expression patterns similar to that of MLLT6. Restoring DDIT3/4 expression in cells with MLLT6 depletion blocked colony formation and cell migration and attenuated the successful colonization of breast cancer cells in vivo. We also determined that the transcription factor activating transcription factor 2 is a binding partner of MLLT6 and participates in the MLLT6/ATF2 axis, which was reinforced by inhibition of AKT signaling, in turn inducing DDIT3/4 expression by establishing an active chromatin structure at the DDIT3/4 gene promoters. As MLLT6 promotes breast cancer cell apoptosis by inducing DDIT3/4 expression during metastasis, it could be a novel tumor suppressor. Implications: Control of MLLT6 expression via inhibition of PI3K/AKT kinase activity is a potential therapeutic approach for the management of metastatic breast cancer.

NRAS Mutant Dictates AHCYL1-Governed ER Calcium Homeostasis for Melanoma Tumor Growth

Calcium homeostasis is critical for cell proliferation, and emerging evidence shows that cancer cells exhibit altered calcium signals to fulfill their need for proliferation. However, it remains unclear whether there are oncogene-specific calcium homeostasis regulations that can expose novel therapeutic targets. Here, from RNAi screen, we report that adenosylhomocysteinase like protein 1 (AHCYL1), a suppressor of the endoplasmic reticulum (ER) calcium channel protein inositol trisphosphate receptor (IP3R), is selectively upregulated and critical for cell proliferation and tumor growth potential of human NRAS-mutated melanoma, but not for melanoma expressing BRAF V600E. Mechanistically, AHCYL1 deficiency results in decreased ER calcium levels, activates the unfolded protein response (UPR), and triggers downstream apoptosis. In addition, we show that AHCYL1 transcription is regulated by activating transcription factor 2 (ATF2) in NRAS-mutated melanoma. Our work provides evidence for oncogene-specific calcium regulations and suggests AHCYL1 as a novel therapeutic target for RAS mutant-expressing human cancers, including melanoma.

IMPLICATIONS

Our findings suggest that targeting the AHCYL1-IP3R axis presents a novel therapeutic approach for NRAS-mutated melanomas, with potential applicability to all cancers harboring RAS mutations, such as KRAS-mutated human colorectal cancers.

Macrophage lncRNAs in cancer development: Long-awaited therapeutic targets

In the tumor microenvironment, the interplay among macrophages, cancer cells, and endothelial cells is multifaceted. Tumor-associated macrophages (TAMs), which often exhibit an M2 phenotype, contribute to tumor growth and angiogenesis, while cancer cells and endothelial cells reciprocally influence macrophage behavior. This complex interrelationship highlights the importance of targeting these interactions for the development of novel cancer therapies aimed at disrupting tumor progression and angiogenesis. Accumulating evidence underscores the indispensable involvement of lncRNAs in shaping macrophage functionality and contributing to the development of cancer. Animal studies have further validated the therapeutic potential of manipulating macrophage lncRNA activity to ameliorate disease severity and reduce morbidity rates. This review provides a survey of our current understanding of macrophage-associated lncRNAs, with a specific emphasis on their molecular targets and their regulatory impact on cancer progression. These lncRNAs predominantly govern macrophage polarization, favoring the dominance of M2 macrophages or TAMs. Exosomes or extracellular vesicles mediate lncRNA transfer between macrophages and cancer cells, affecting cellular functions of each other. Moreover, this review presents therapeutic strategies targeting cancer-associated lncRNAs. The insights and findings presented in this review pertaining to macrophage lncRNAs can offer valuable information for the development of treatments against cancer.

The activating transcription factor 2: an influencer of cancer progression

In contrast to the continuous increase in survival rates for many cancer entities, colorectal cancer (CRC) and pancreatic cancer are predicted to be ranked among the top 3 cancer-related deaths in the European Union by 2025. Especially, fighting metastasis still constitutes an obstacle to be overcome in CRC and pancreatic cancer. As described by Fearon and Vogelstein, the development of CRC is based on sequential mutations leading to the activation of proto-oncogenes and the inactivation of tumour suppressor genes. In pancreatic cancer, genetic alterations also attribute to tumour development and progression. Recent findings have identified new potentially important transcription factors in CRC, among those the activating transcription factor 2 (ATF2). ATF2 is a basic leucine zipper protein and is involved in physiological and developmental processes, as well as in tumorigenesis. The mutation burden of ATF2 in CRC and pancreatic cancer is rather negligible; however, previous studies in other tumours indicated that ATF2 expression level and subcellular localisation impact tumour progression and patient prognosis. In a tissue- and stimulus-dependent manner, ATF2 is activated by upstream kinases, dimerises and induces target gene expression. Dependent on its dimerisation partner, ATF2 homodimers or heterodimers bind to cAMP-response elements or activator protein 1 consensus motifs. Pioneering work has been performed in melanoma in which the dual role of ATF2 is best understood. Even though there is increasing interest in ATF2 recently, only little is known about its involvement in CRC and pancreatic cancer. In this review, we summarise the current understanding of the underestimated ‘cancer gene chameleon’ ATF2 in apoptosis, epithelial-to-mesenchymal transition and microRNA regulation and highlight its functions in CRC and pancreatic cancer. We further provide a novel ATF2 3D structure with key phosphorylation sites and an updated overview of all so-far available mouse models to study ATF2 in vivo.

Genome-Wide Tiling Array Analysis of HPV-Induced Warts Reveals Aberrant Methylation of Protein-Coding and Non-Coding Regions

The human papillomaviruses (HPV) are a group of double-stranded DNA viruses that exhibit an exclusive tropism for squamous epithelia. HPV can either be low- or high-risk depending on its ability to cause benign lesions or cancer, respectively. Unsurprisingly, the majority of epigenetic research has focused on the high-risk HPV types, neglecting the low-risk types in the process. Therefore, the main objective of this study is to better understand the epigenetics of wart formation by investigating the differences in methylation between HPV-induced cutaneous warts and normal skin. A number of clear and very significant differences in methylation patterns were found between cutaneous warts and normal skin. Around 55% of the top-ranking 100 differentially methylated genes in warts were protein coding, including the EXOC4, KCNU, RTN1, LGI1, IRF2, and NRG1 genes. Additionally, non-coding RNA genes, such as the AZIN1-AS1, LINC02008, and MGC27382 genes, constituted 11% of the top-ranking 100 differentially methylated genes. Warts exhibited a unique pattern of methylation that is a possible explanation for their transient nature. Since the genetics of cutaneous wart formation are not completely known, the findings of the present study could contribute to a better understanding of how HPV infection modulates host methylation to give rise to warts in the skin.

Positive selection in Europeans and East-Asians at the ABCA12 gene

Natural selection acts on genetic variants by increasing the frequency of alleles responsible for a cellular function that is favorable in a certain environment. In a previous genome-wide scan for positive selection in contemporary humans, we identified a signal of positive selection in European and Asians at the genetic variant rs10180970. The variant is located in the second intron of the ABCA12 gene, which is implicated in the lipid barrier formation and down-regulated by UVB radiation. We studied the signal of selection in the genomic region surrounding rs10180970 in a larger dataset that includes DNA sequences from ancient samples. We also investigated the functional consequences of gene expression of the alleles of rs10180970 and another genetic variant in its proximity in healthy volunteers exposed to similar UV radiation. We confirmed the selection signal and refine its location that extends over 35 kb and includes the first intron, the first two exons and the transcription starting site of ABCA12. We found no obvious effect of rs10180970 alleles on ABCA12 gene expression. We reconstructed the trajectory of the T allele over the last 80,000 years to discover that it was specific to H. sapiens and present in non-Africans 45,000 years ago.

ATF2 promotes urothelial cancer outgrowth via cooperation with androgen receptor signaling

We investigated the functional role of ATF2, a transcription factor normally activated via its phosphorylation in response to phospho-ERK/MAPK signals, in the outgrowth of urothelial cancer. In both neoplastic and non-neoplastic urothelial cells, the expression levels of androgen receptor (AR) correlated with those of phospho-ATF2. Dihydrotestosterone treatment in AR-positive bladder cancer cells also induced the expression of phospho-ATF2 and phospho-ERK as well as nuclear translocation and transcriptional activity of ATF2. Meanwhile, ATF2 knockdown via shRNA resulted in significant decreases in cell viability, migration and invasion of AR-positive bladder cancer lines, but not AR-negative lines, as well as significant increases and decreases in apoptosis or G0/G1 cell cycle phase and S or G2/M phase, respectively. Additionally, the growth of AR-positive tumors expressing ATF2-shRNA in xenograft-bearing mice was retarded, compared with that of control tumors. ATF2 knockdown also resulted in significant inhibition of neoplastic transformation induced by a chemical carcinogen 3-methylcholanthrene, as well as the expression of Bcl-2/cyclin-A2/cyclin-D1/JUN/MMP-2, in immortalized human normal urothelial SVHUC cells stably expressing AR, but not AR-negative SVHUC cells. Finally, immunohistochemistry in surgical specimens demonstrated significant elevation of ATF2/phospho-ATF2/phospho-ERK expression in bladder tumors, compared with non-neoplastic urothelial tissues. Multivariate analysis further showed that moderate/strong ATF2 expression and phospho-ATF2 positivity were independent predictors for recurrence of low-grade tumors (hazard ratio (HR) = 2.956, P = 0.045) and cancer-specific mortality of muscle-invasive tumors (HR = 5.317, P = 0.012), respectively. Thus, ATF2 appears to be activated in urothelial cells through the AR pathway and promotes the development and progression of urothelial cancer.

ATF2 partly mediated the expressions of proliferative factors and inhibited pro-inflammatory factors' secretion in arsenite-treated human uroepithelial cells

Inorganic arsenic (iAs) could induce the expression of activating transcription factor-2 (ATF2) in the human urinary bladder epithelial cell line (SV-HUC-1 cells). ATF2, as a member of the bZIP transcription factor family, has been implicated in a transcriptional response leading to cell growth, migration and malignant tumor progression. However, little is known about the effects of ATF2 on proliferative factors in iAs treated human urothelial cells. In this study, ATF2 siRNA was employed to investigate the relationship between ATF2 activation and the expressions of proliferative factors, such as BCL2, cyclin D1, COX-2, MMP1 and PCNA, and pro-inflammatory factors (TNFα, TGFα and IL-8) in SV-HUC-1 cells. The results showed that low concentration arsenite increased the expressions of proliferative factors BCL2, cyclin D1, COX-2, MMP1 and PCNA in SV-HUC-1 cells, and ATF2 siRNA partly decreased the expressions of BCL2, cyclin D1, and COX-2. A neutralizing antibody of IL-8 was used for attenuating the levels of IL-8 and neutralizing antibody of IL-8 did not relieve the expressions of ATF2 and proliferative factors induced by arsenite in SV-HUC-1 cells. In addition, ATF2 knockdown did not decrease the expressions of pro-inflammatory cytokines induced by arsenite in SV-HUC-1 cells, but dramatically increased mRNA expressions of TNFα, TGFα and IL-8 under arsenite and non-arsenite conditions. In conclusion, our present study indicated that ATF2, but not IL-8, played a partial role in the expressions of proliferative factors induced by arsenite in human uroepithelial cells.

Epithelial-mesenchymal transition in cancer: Role of the IL-8/IL-8R axis

Epithelial-mesenchymal transition (EMT) is a biological process that is associated with cancer metastasis and invasion. In cancer, EMT promotes cell motility, invasion and distant metastasis. Interleukin (IL)-8 is highly expressed in tumors and may induce EMT. The IL-8/IL-8R axis has a vital role in EMT in carcinoma, which is regulated by several signaling pathways, including the transforming growth factor β-spleen associated tyrosine kinase/Src-AKT/extracellular signal-regulated kinase, p38/Jun N-terminal kinase-activating transcription factor-2, phosphoinositide 3-kinase/AKT, nuclear factor-κB and Wnt signaling pathways. Blocking the IL-8/IL-8R signaling pathway may be a novel strategy to reduce metastasis and improve patient survival rates. This review will cover IL-8-IL-8R signaling pathway in tumor epithelial-mesenchymal transition.

Inactivation of KLF4 promotes T-cell acute lymphoblastic leukemia and activates the MAP2K7 pathway

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with a high incidence of relapse in pediatric ALL. Although most T-ALL patients exhibit activating mutations in NOTCH1, the cooperating genetic events required to accelerate the onset of leukemia and worsen disease progression are largely unknown. Here, we show that the gene encoding the transcription factor KLF4 is inactivated by DNA methylation in children with T-ALL. In mice, loss of KLF4 accelerated the development of NOTCH1-induced T-ALL by enhancing the G1-to-S transition in leukemic cells and promoting the expansion of leukemia-initiating cells. Mechanistically, KLF4 represses the gene encoding the kinase MAP2K7. Our results showed that in murine and pediatric T-ALL, loss of KLF4 leads to aberrant activation of MAP2K7 and of the downstream effectors JNK and ATF2. As a proof-of-concept for the development of a targeted therapy, administration of JNK inhibitors reduced the expansion of leukemia cells in cell-based and patient-derived xenograft models. Collectively, these data uncover a novel function for KLF4 in regulating the MAP2K7 pathway in T-ALL cells, which can be targeted to eradicate leukemia-initiating cells in T-ALL patients.

ATF2 translation is induced under chemotherapeutic drug-mediated cellular stress via an IRES-dependent mechanism in human hepatic cancer Bel7402 cells

Activating transcription factor (ATF) 2 is a member of the ATF/cyclic AMP-responsive element binding protein family, which exhibits both oncogenic and tumor-suppressor functions. In our preliminary experiments, it was observed that the expression of the ATF2 protein was induced following treatment with adriamycin (ADR) and paclitaxel (PTX), which may be regulated by internal ribosome entry segment (IRES)-mediated translation. By constructing a bicistronic vector containing the ATF2 5'-untranslated region (UTR), it was demonstrated that the ATF2 5'-UTR contains an IRES and maps a 30-nucleotide (nt) sequence (from nt 299 to nt ~269), which was essential for the IRES activity. The ATF2 IRES activity exhibited significant variation in different cell lines. In addition, it was observed that ADR and PTX also induced ATF2 IRES activity in Bel7402 cells. The present study has demonstrated that ATF2 translation is initiated via IRES, which is upregulated by ADR and PTX, thus suggesting that the regulation of the IRES-dependent translation of ATF2 may be involved in effecting the cancer cell response to chemotherapeutic drugs-mediated cellular stress.

N-bromotaurine surrogates for loss of antiproliferative response and enhances cisplatin efficacy in cancer cells with impaired glucocorticoid receptor

Glucocorticoids (GCs) are frequently used in anticancer combination regimens; however, their continuous use adds selective pressure on cancer cells to develop GC-resistance via impairment of the glucocorticoid receptor (GR), therefore creating a need for GC-alternatives. Based on the drug repurposing approach and the commonalities between inflammation and neoplasia, drugs that are either in late-stage clinical trials and/or already marketed for GC-refractory inflammatory diseases could be evaluated as GC-substitutes in the context of cancer. Advantageously, unlike new molecular entities currently being de novo developed to restore GC-responsiveness of cancer cells, such drugs have documented safety and efficacy profile, which overall simplifies their introduction in clinical cancer trials. In this study, we estimated the potential of a well-established, multistage, cell line-based, mouse skin carcinogenesis model to be exploited as an initial screening tool for unveiling covert GC-substitutes. First, we categorized the cell lines of this model to GC-sensitive and GC-resistant, in correlation with their corresponding GR status, localization, and functionality. We found that GC-resistance starts in papilloma stages, due to a dysfunctional GR, which is overexpressed, DNA binding-competent, but transactivation-incompetent in papilloma, squamous, and spindle stages of the model. Then, aided by this tool, we evaluated the ability of N-bromotaurine, a naturally occurring, small-molecule, nonsteroid anti-inflammatory drug which is under consideration for use interchangeably/in replacement to GCs in skin inflammations, to restore antiproliferative response of GC-resistant cancer cells. Unlike GCs, N-bromotaurine inhibited cell-cycle progression in GC-resistant cancer cells and efficiently synergized with cisplatin, thus indicating a potential to be exploited instead of GCs against cancer.

Progression of mouse skin carcinogenesis is associated with the orchestrated deregulation of mir-200 family members, mir-205 and their common targets

MicroRNAs are small, non-coding RNAs which regulate post-transcriptionally hundreds of target mRNAs. Given that their expression is deregulated in several cancer types, they represent potential diagnostic, prognostic, and predictive biomarkers, as well as next-generation therapeutic targets. Nevertheless, the involvement of miRNAs in non-melanoma skin cancer, a cancer type with increasing prevalence, is not extensively studied, and their comprehensive characterization as regard to the initiation, promotion, and progression stages is missing. To this end, we exploited a well-established multistage mouse skin carcinogenesis model in order to identify miRNAs consistently implicated in different stages of skin carcinogenesis. The cell lines comprising this model were subjected to miRNA expression profiling using microarrays, followed by bioinformatics analysis and validation with Q-PCR, as well as treatment with miRNA modulators. We showed that among all deregulated miRNAs in our system, only a functionally coherent group consisting of the miR-200 family members and miR-205-5p displays a pattern of progressive co-downregulation from the early toward the most aggressive stages of carcinogenesis. Their overlapping, co-regulated putative targets are potentially inter-associated and, of these, the EMT-related Rap1a is overexpressed toward aggressive stages. Ectopic expression of miR-205-5p in spindle cancer cells reduces Rap1a, mitigates cell invasiveness, decreases proliferation, and delays tumor onset. We conclude that deregulation of this miRNA group is primarily associated with aggressive phenotypes of skin cancer cells. Restoration of the miR-205-5p member of this group in spindle cells reduces the expression of critical, co-regulated targets that favor cancer progression, thus reversing the EMT characteristics. © 2015 Wiley Periodicals, Inc.

Shikonin Suppresses Skin Carcinogenesis via Inhibiting Cell Proliferation

The M2 isoform of pyruvate kinase M2 (PKM2) has been shown to be up-regulated in human skin cancers. To test whether PKM2 may be a target for chemoprevention, shikonin, a natural product from the root of Lithospermum erythrorhizon and a specific inhibitor of PKM2, was used in a chemically-induced mouse skin carcinogenesis study. The results revealed that shikonin treatment suppressed skin tumor formation. Morphological examinations and immunohistochemical staining of the skin epidermal tissues suggested that shikonin inhibited cell proliferation without inducing apoptosis. Although shikonin alone suppressed PKM2 activity, it did not suppress tumor promoter-induced PKM2 activation in the skin epidermal tissues at the end of the skin carcinogenesis study. To reveal the potential chemopreventive mechanism of shikonin, an antibody microarray analysis was performed, and the results showed that the transcription factor ATF2 and its downstream target Cdk4 were up-regulated by chemical carcinogen treatment; whereas these up-regulations were suppressed by shikonin. In a promotable skin cell model, the nuclear levels of ATF2 were increased during tumor promotion, whereas this increase was inhibited by shikonin. Furthermore, knockdown of ATF2 decreased the expression levels of Cdk4 and Fra-1 (a key subunit of the activator protein 1. In summary, these results suggest that shikonin, rather than inhibiting PKM2 in vivo, suppresses the ATF2 pathway in skin carcinogenesis.

EGF-induced expression of Fused Toes Homolog (FTS) facilitates epithelial-mesenchymal transition and promotes cell migration in ME180 cervical cancer cells

The role of Fused Toes Homolog (FTS) in epidermal growth factor (EGF) induced epithelial-mesenchymal transition (EMT) in cervical cancer cells was studied. EGF treatment induced the change of EMT markers and increased cell migration. EGF treatment also increased phosphorylated EGFR and ERK and nuclear level of ATF-2. The binding of ATF-2 to the promoter region of FTS was evidenced after EGF treatment. Pretreatment with PD98059 and gefitinib prevented EGF-induced FTS expression. FTS silencing reduced EMT and cell migration by EGF treatment. These results demonstrate a novel function for FTS in EGF-mediated EMT process.

The basic leucine zipper domain transcription factor Atf1 directly controls Cdc13 expression and regulates mitotic entry independently of Wee1 and Cdc25 in Schizosaccharomyces pombe

Progression into mitosis is a major point of regulation in the Schizosaccharomyces pombe cell cycle, and its proper control is essential for maintenance of genomic stability. Investigation of the G(2)/M progression event in S. pombe has revealed the existence of a complex regulatory process that is responsible for making the decision to enter mitosis. Newer aspects of this regulation are still being revealed. In this paper, we report the discovery of a novel mode of regulation of G(2)/M progression in S. pombe. We show that the mitogen-activated protein kinase (MAPK)-regulated transcription factor Atf1 is a regulator of Cdc13 (mitotic cyclin) transcription and is therefore a prominent player in the regulation of mitosis in S. pombe. We have used genetic approaches to study the effect of overexpression or deletion of Atf1 on the cell length and G(2)/M progression of S. pombe cells. Our results clearly show that Atf1 overexpression accelerates mitosis, leading to an accumulation of cells with shorter lengths. The previously known major regulators of entry into mitosis are the Cdc25 phosphatase and the Wee1 kinase, which modulate cyclin-dependent kinase (CDK) activity. The significantly striking aspect of our discovery is that Atf1-mediated G(2)/M progression is independent of both Cdc25 and Wee1. We have shown that Atf1 binds to the Cdc13 promoter, leading to activation of Cdc13 expression. This leads to enhanced nuclear localization of CDK Cdc2, thereby promoting the G(2)/M transition.

Synthetic phosphorylation of p38α recapitulates protein kinase activity

Through a “tag-and-modify” protein chemical modification strategy, we site-selectively phosphorylated the activation loop of protein kinase p38α. Phosphorylation at natural (180) and unnatural (172) sites created two pure phospho-forms. p38α bearing only a single phosphocysteine (pCys) as a mimic of pThr at 180 was sufficient to switch the kinase to an active state, capable of processing natural protein substrate ATF2; 172 site phosphorylation did not. In this way, we chemically recapitulated triggering of a relevant segment of the MAPK-signaling pathway in vitro. This allowed detailed kinetic analysis of global and stoichiometric phosphorylation events catalyzed by p38α and revealed that site 180 is a sufficient activator alone and engenders dominant mono-phosphorylation activity. Moreover, a survey of kinase inhibition using inhibitors with different (Type I/II) modes (including therapeutically relevant) revealed unambiguously that Type II inhibitors inhibit phosphorylated p38α and allowed discovery of a predictive kinetic analysis based on cooperativity to distinguish Type I vs II.

Photodynamic agents with anti-metastatic activities

A new concept in multifunctional anticancer agents is demonstrated. Tetrakis-(diisopropyl-guanidino) zinc phthalocyanine (Zn-DIGP) exhibits excellent properties as a photodynamic therapy (PDT) agent, as well as potential anti-metastatic activities in vivo. Zn-DIGP exhibits good cellular uptake and low toxicity in the dark (EC50 > 80 μM) and is well tolerated upon its intravenous injection into mice at 8 mg/kg. Upon photoexcitation with red laser light (660 nm), Zn-DIGP exhibits a high quantum yield for singlet oxygen formation (Φ ≈ 0.51) that results in potent phototoxicity to cell cultures (EC50 ≈ 0.16 μM). Zn-DIGP is also capable of inhibiting the formation of tumor colonies in the lungs of C57BL/6 mice injected with B16F10 cells. Zn-DIGP therefore inhibits cancer growth by both light-dependent and light-independent pathways. The anti-metastatic activities of Zn-DIGP possibly result from its ability to interfere with the signaling between chemokine CXCL10 and the G protein-coupled receptor CXCR3. Zn-DIGP is a competitive inhibitor of CXCR3 activation (IC50 = 3.8 μM) and selectively inhibits downstream events such as CXCL10-activated cell migration. Consistent with the presence of feedback regulation between CXCR3 binding and CXCL10 expression, Zn-DIGP causes overexpression of CXCL10. Interestingly, Zn-DIGP binds to CXCR3 without activating the receptor yet is able to cause endocytosis and degradation of this GPCR. To the best of our knowledge, Zn-DIGP is the first PDT agent that can facilitate the photodynamic treatment of primary tumors while simultaneously inhibiting the formation of metastatic tumor colonies by a light-independent mode of action.

Network motifs in the transcriptional regulation network of cervical carcinoma cells respond to EGF

PURPOSE

Cervical carcinoma is the second most prevalent and the fifth most deadly malignancy seen in women worldwide. Dysregulated activation of EGF ErbB system has been implicated in diverse types of human cancer; however, it is elusive how it is regulated in human cervical cancer cells. We herein aimed to explore the mechanisms of cervical carcinoma response to epidermal growth factor (EGF), with a view of the pathways activated by EGF.

METHODS

Using the GSE6783 affymetrix microarray data accessible from gene expression omnibus database, we first identified the differentially expressed genes between EGF-stimulated and -unstimulated samples. Then we constructed a regulation network and identified the network motifs. We also performed biological process and pathway enrichment analyses to functionally classify the genes in the regulation network.

RESULTS

A total of 11 network motifs were identified in the regulation network. EGF treatment could increase the risk of cancer via dysregulation of cancer-related pathways and immune response pathways.

CONCLUSIONS

Network motif analysis is useful in mining the useful information underlying the network. We hope our work could serve as a basis for further experimentation.

Activating transcription factor 1 is a prognostic marker of colorectal cancer

OBJECTIVE

Identifying cancer-related genes or proteins is critical in preventing and controlling colorectal cancer (CRC). This study was to investigate the clinicopathological and prognostic value of activating transcription factor 1 (ATF1) in CRC.

METHODS

Protein expression of ATF1 was detected using immunohistochemistry in 66 CRC tissues. Clinicopathological association of ATF1 in CRC was analyzed with chi-square test or Fisher's exact test. The prognostic value of ATF1 in CRC is estimated using the Kaplan-Meier analysis and Cox regression models.

RESULTS

The ATF1 protein expression was significantly lower in tumor tissues than corresponding normal tissues (51.5% and 71.1%, respectively, P = 0.038). No correlation was found between ATF1 expression and the investigated clinicopathological parameters, including gender, age, depth of invasion, lymph node status, metastasis, pathological stage, vascular tumoral emboli, peritumoral deposits, chemotherapy and original tumor site (all with P > 0.05). Patients with higher ATF1 expression levels have a significantly higher survival rate than that with lower expression (P = 0.026 for overall survival, P = 0.008 for progress free survival). Multivariate Cox regression model revealed that ATF1 expression and depth of invasion were the predictors of the overall survival (P = 0.008 and P = 0.028) and progress free survival (P = 0.002 and P = 0.005) in CRC.

CONCLUSIONS

Higher ATF1 expression is a predictor of a favorable outcome for the overall survival and progress free survival in CRC.

ATF2, a novel factor promoting epithelial-mesenchymal transition in human pancreatic cancer cells

AIM: To investigate whether ATF2 together with TGF-β1 can induce epithelial-mesenchymal transition (EMT) in human pancreatic cancer cell line Capan2.

METHODS: Capan2 cells were induced with TGF-β1 after transfection with PGEX-ATF2, and the negative control group was treated with DMSO. Cell morphological alternations were examined by phase contrast microscopy. The expression of mesenchymal marker vimentin and epithelial markers E-cadherin and ATF2 were detected by Western blot. Cell migration was determined by Transwell motility assay.

RESULTS: Compare to the negative control group, cells transfected with ATF2 and treated with TGF-β1 showed loss of cell-cell contacts, fibroblastic morphology, decreased expression of E-cadherin, up-regulated expression of vimentin and ATF2, and increased migration ability (P = 0.008).

CONCLUSION: ATF2 together with TGF-β1 can induce EMT in human pancreatic cancer cell line Capan2. ATF2 may be a new molecular target for therapy of pancreatic cancer.

Progression of mouse skin carcinogenesis is associated with increased ERα levels and is repressed by a dominant negative form of ERα

Estrogen receptors (ER), namely ERα and ERβ, are hormone-activated transcription factors with an important role in carcinogenesis. In the present study, we aimed at elucidating the implication of ERα in skin cancer, using chemically-induced mouse skin tumours, as well as cell lines representing distinct stages of mouse skin oncogenesis. First, using immunohistochemical staining we showed that ERα is markedly increased in aggressive mouse skin tumours in vivo as compared to the papilloma tumours, whereas ERβ levels are low and become even lower in the aggressive spindle tumours of carcinogen-treated mice. Then, using the multistage mouse skin carcinogenesis model, we showed that ERα gradually increases during promotion and progression stages of mouse skin carcinogenesis, peaking at the most aggressive stage, whereas ERβ levels only slightly change throughout skin carcinogenesis. Stable transfection of the aggressive, spindle CarB cells with a dominant negative form of ERα (dnERα) resulted in reduced ERα levels and reduced binding to estrogen responsive elements (ERE)-containing sequences. We characterized two highly conserved EREs on the mouse ERα promoter through which dnERα decreased endogenous ERα levels. The dnERα-transfected CarB cells presented altered protein levels of cytoskeletal and cell adhesion molecules, slower growth rate and impaired anchorage-independent growth in vitro, whereas they gave smaller tumours with extended latency period of tumour onset in vivo. Our findings suggest an implication of ERα in the aggressiveness of spindle mouse skin cancer cells, possibly through regulation of genes affecting cell shape and adhesion, and they also provide hints for the effective targeting of spindle cancer cells by dnERα.

Protective effects of (-)-epigallocatechin-3-gallate against TNF-α-induced lung inflammation via ROS-dependent ICAM-1 inhibition

Oxidative stresses are considered to play an important role in the induction of cell adhesion molecules and proinflammatory cytokines implicated in inflammatory processes. Heme oxygenase (HO)-1 and suppressors of cytokine signaling (SOCS)-3 exert several biological functions, including antiapoptotic and anti-inflammatory effects. Here, we report that HO-1 and SOCS-3 were induced in A549 cells and human pulmonary alveolar epithelial cells (HPAEpiCs) treated with (-)-epigallocatechin-3-gallate (EGCG). EGCG protected against tumor necrosis factor (TNF)-α-mediated lung inflammation by down-regulation of oxidative stress and intercellular adhesion molecule (ICAM)-1 expression in A549 cells or HPAEpiCs and the lungs of mice. EGCG inhibited TNF-α-induced ICAM-1 expression, THP-1 cells adherence, pulmonary hematoma and leukocyte (eosinophils and neutrophils) count in bronchoalveolar lavage fluid in mice. In addition, EGCG also attenuated TNF-α-induced oxidative stress, p47(phox) translocation, MAPKs activation, and STAT-3 and activating transcription factor (ATF)2 phosphorylation. EGCG also reduced the formation of a TNFR1/TRAF2/Rac1/p47(phox) complex. Moreover, in this study, the observed suppression of TNF-α-stimulated ICAM-1 expression and reactive oxygen species (ROS) generation by EGCG was abrogated by transfection with siRNA of SOCS-3 or HO-1. These results suggested that HO-1 or SOCS-3 functions as a suppressor of TNF-α signaling, not only by inhibiting adhesion molecules expression but also by diminishing intracellular ROS production and STAT-3 and ATF2 activation in A549 cells or HPAEpiCs and the lungs of mice.

The roles of ATF2 (activating transcription factor 2) in tumorigenesis

MAPK (mitogen-activated protein kinase) pathways are among the most frequently deregulated signalling events in cancer. Among the critical targets of MAPK activities are members of the AP-1 (activator protein 1) transcription factor, a dimeric complex consisting of Jun, Fos, Maf and ATF (activating transcription factor) family DNA-binding proteins. Depending on the cellular context, the composition of the dimeric complexes determines the regulation of growth, survival or apoptosis. JNK (c-Jun N-terminal kinase), p38 and a number of Jun and Fos family proteins have been analysed for their involvement in oncogenic transformation and tumour formation. These data are also emerging for the ATF components of the AP-1 factor. The aim of the present review is to provide an overview of the functions of two ATF family proteins, ATF2 and ATF7, in mammalian development and their potential functions in tumour formation.

JDP2 suppresses transforming growth factor-β1-induced epithelial-mesenchymal transition in human pancreatic cancer cell line Panc-1

AIM: To determine the correlation between overexpression of Jun dimerization protein 2 (JDP2) and epithelial-mesenchymal transition (EMT) in human pancreatic cancer cell line Panc-1.

METHODS: Panc-1 cells were divided into three groups: negative control group, JDP2-transfected group, and empty vector-transfected group. The JDP2-transfected group and empty vector-transfected group were transiently transfected with PCEFL-HA-JDP2 vector and pCEFL vector, respectively. Untreated Panc-1 cells were used as normal controls. Forty-eight hours after transfection, cells were treated with TGF-β1 (10 ng/mL). Cell morphological alternations were examined by phase-contrast microscopy. The expression of mesenchymal marker vimentin and epithelial marker E-cadherin was detected by RT-PCR and Western blot. Cell migration was determined by Transwell motility assay.

RESULTS: TGF-β1-induced EMT was inhibited in the JDP2-transfected group. Compare to the negative control group, cells in the JDP2-transfected group showed no fibroblastic morphology and no significant changes in the levels of E-cadherin and vimentin and in migration ability (48.0 ± 5.3 vs 52.0 ± 7.2). However, cells in the vector-transfected group showed loss of cell-cell contacts, fibroblastic morphology, decreased expression of E-cadherin (mRNA: P < 0.01; protein: P < 0.05), increased expression of vimentin (P < 0.01) and migration ability (48.0 ± 5.3 vs 81.0 ± 10.7, P < 0.01) when compared to the negative control group.

CONCLUSION: JDP2 can inhibit TGF-β1-induced EMT in Panc-1 cells and may be a molecular target for pancreatic carcinoma therapy.

STRAP regulates c-Jun ubiquitin-mediated proteolysis and cellular proliferation

STRAP is a ubiquitous WD40 protein that has been implicated in tumorigenesis. Previous studies suggest that STRAP imparts oncogenic characteristics to cells by promoting ERK and pRb phosphorylation. While these findings suggest that STRAP can activate mitogenic signaling pathways, the effects of STRAP on other MAPK pathways have not been investigated. Herein, we report that STRAP regulates the expression of the c-Jun proto-oncogene in mouse embryonic fibroblasts. Loss of STRAP expression results in reduced phospho-c-Jun and total c-Jun but does not significantly reduce the level of two other early response genes, c-Myc and c-Fos. STRAP knockout also decreases expression of the AP-1 target gene, cyclin D1, which is accompanied by a reduction in cell growth. No significant differences in JNK activity or basal c-Jun mRNA levels were observed between wild type and STRAP null fibroblasts. However, proteasomal inhibition markedly increases c-Jun expression in STRAP knockout MEFs and STRAP over-expression decreases the ubiquitylation of c-Jun in 293T cells. Loss of STRAP accelerates c-Jun turnover in fibroblasts and ectopic over-expression of STRAP in STRAP null fibroblasts increases c-Jun expression. Collectively, our findings indicate that STRAP regulates c-Jun stability by decreasing the ubiquitylation and proteosomal degradation of c-Jun.

Emerging roles of ATF2 and the dynamic AP1 network in cancer

Cooperation among transcription factors is central for their ability to execute specific transcriptional programmes. The AP1 complex exemplifies a network of transcription factors that function in unison under normal circumstances and during the course of tumour development and progression. This Perspective summarizes our current understanding of the changes in members of the AP1 complex and the role of ATF2 as part of this complex in tumorigenesis.

Neurodegenerative, with expression ATF-2 by p38 in cortical neurons

DNA damage, as an important initiator of neuronal cell death, has been implicated in numerous neurodegenerative conditions. We previously delineated several pathways that control embryonic cortical neuronal cell death evoked by the DNA-damaging agent, camptothecin. The topisomerase-1 inhibitor, camptothecin, has been shown to induce cortical neuronal cell death in a reproducible and synchronistic manner. Primary embryonic neuronal cell culture cortical neurons were prepared. In the study, the survival % of neurons in camptothecin P38 group, after 6 hours (85%), 24 hours (64%) and 48 hours (50%), compared to camptothecin ATF-2 and P38 group after 4 hours (97 and 95%), have been significantly lower, and the expression % of neurons in camptothecin P38 group , after 6 hours (20%), 24 hours (40%) and 48 hours (55%), compared to camptothecin ATF-2 and P38 group after 4 hours (5 and 3%) have been significant lower (p<0.05). The expression % of neurons in camptothecin P38 group, after 24 hours (40%), compared to camptothecin ATF-2 group after 24hours (30%), have been significant lower (p<0.05). This study revealed that camptothecin induces P38 expression and P38 in embryonic cortical neurons to determine the importance of the P38 pathway in neuronal death following DNA damage, and P38 is induce phosphorylation of ATF-2 in embryonic cortical neurons following DNA damage.

Activating transcription factor 2 increases transactivation and protein stability of hypoxia-inducible factor 1alpha in hepatocytes

HIF-1 (hypoxia inducible factor 1) performs a crucial role in mediating the response to hypoxia. However, other transcription factors are also capable of regulating hypoxia-induced target-gene transcription. In a previous report, we demonstrated that the transcription factor ATF-2 (activating transcription factor 2) regulates hypoxia-induced gene transcription, along with HIF-1alpha. In the present study, we show that the protein stability of ATF-2 is induced by hypoxia and the hypoxia-mimic CoCl2 (cobalt chloride), and that ATF-2 induction enhances HIF-1alpha protein stability via direct protein interaction. The knockdown of ATF-2 using small interfering RNA and translation-inhibition experiments demonstrated that ATF-2 plays a key role in the maintenance of the expression level and transcriptional activity of HIF-1alpha. Furthermore, we determined that ATF-2 interacts directly with HIF-1alpha both in vivo and in vitro and competes with the tumour suppressor protein p53 for HIF-1alpha binding. Collectively, these results show that protein stabilization of ATF-2 under hypoxic conditions is required for the induction of the protein stability and transactivation activity of HIF-1alpha for efficient hypoxia-associated gene expression.

The links between transcription, beta-catenin/JNK signaling, and carcinogenesis

Interactions between transcription and signaling are fundamentally important for understanding both the structure and function of genetic pathways and their role in diseases such as cancer. The finding that beta-catenin/TCF4 and JNK/c-Jun cooperate has important implications in carcinogenesis. Previously, we found that binding of c-Jun and beta-catenin/TCF4 to the c-jun promoter is dependent upon JNK activity, thus one role for this complex is to contribute to the repression and/or activation of genes that may mediate cell maintenance, proliferation, differentiation, and death, whereas deregulation of these signals may contribute to carcinogenesis. Here we address the functional links reported between activated beta-catenin/JNK signaling pathways, their component genes, and their common targets, and discuss how alterations in the properties of these genes lead to the development of cancer.

Concordant overexpression of phosphorylated ATF2 and STAT3 in extramammary Paget's disease

BACKGROUND

Activating transcription factor 2 (ATF2) and signal transducer and activator of transcription 3 (STAT3) play important roles in the pathogenesis of various tumors, but ATF2 expression/activation and the relationship with STAT3 activation have not yet been investigated in extramammary Paget's disease (EMPD).

OBJECTIVE

To investigate potential contributions of ATF2 and STAT3 pathways to the pathogenesis of EMPD.

METHOD

Paraffin-embedded 45 EMPD specimens (43 primary EMPD and 2 nodal metastases) were subjected to immunohistochemical staining for ATF2, phosphorylated (p)-ATF2 and p-STAT3.

RESULTS

P-ATF2 expression in advanced EMPD, non-invasive EMPD and normal skin (NS) controls were 97.9 +/- 1.8%, 82.0 +/- 23.4% and 45.8 +/- 3.2%, respectively, and p-STAT3 expression in advanced EMPD, non-invasive EMPD and NS were 97.0 +/- 2.9%, 83.2 +/- 23.3% and 50.1 +/- 6.7%, respectively. P-ATF2 and p-STAT3 expressions in EMPD were significantly higher than those in NS, indicating a possible contribution of these pathways to the tumor development. P-ATF2 and p-STAT3 expressions in advanced EMPD were significantly higher than those in non-invasive EMPD, possibly indicating that these pathways might also contribute to the tumor invasion and/or metastasis. We also found an exceptionally high positive correlation between p-ATF2 and p-STAT3 expressions in EMPD.

CONCLUSIONS

P-ATF2 and p-STAT3 are concordantly overexpressed in EMPD and their expressions may possibly be associated with the tumor stage.

Overexpression of phosphorylated-ATF2 and STAT3 in cutaneous angiosarcoma and pyogenic granuloma

BACKGROUND

Activating transcription factor-2/Activator protein-1 (AP-1), Signal transducer and activator of transcription-3 and p53 are important regulators of cellular proliferation, apoptosis, differentiation in the pathogenesis of many human tumors, but the expression of phosphorylated (p)-activating transcription factor-2 (p-ATF2), phosphorylated (p)-signal transducer and activator of transcription-3 (p-STAT3) and p53 family (p63 and p73) has not been investigated in cutaneous angiosarcoma (CAS) and pyogenic granuloma (PG) so far.

OBJECTIVES

To investigate the expression of p-ATF2, p-STAT3 and p53 and its family in cutaneous vascular tumors (CAS and PG).

METHODS

Paraffin-embedded specimens of 14 CAS and 19 PG were subjected to immunohistochemical staining for p-ATF2, p-STAT3, p53, p63 and p73.

RESULTS

P-ATF2 was expressed in 13 out of 14 CAS and in all of 19 PG. P-STAT3 was expressed in all of 14 CAS and 19 PG. P53 was expressed in all of 14 CAS and 19 PG, while both p63 and p73 were negative in CAS and PG. The p-ATF2-, p-STAT3- and p53 expression (% positive cells) in CAS and PG were significantly higher than in normal dermal vessels, but none of these transcription factors distinguished malignant (CAS)- from benign (PG) vascular tumor.

CONCLUSIONS

The present study suggests that overexpression of p-ATF2, p-STAT3 and possibly p53, but not p63 or p73, may contribute to the tumorigenesis of cutaneous vascular tumors.

Differential gene expression in murine large cell B-cell lymphoma metastatic variants

Previous studies from this laboratory have characterized RAW117-P murine large cell B-cell lymphoma and its in vivo selected highly malignant and liver metastatic RAW117-H10 subline for their biological and biochemical properties. In this study, to understand the molecular basis of low and high metastatic behavior of these variant sublines, we have investigated the molecular phenotypes of these cells using differential display techniques and cDNA array analysis. Differential display analysis indicated a significant difference in expression of several genes between these two metastatic variant lymphoma cells. Further analyses of these cells using microarray showed an increased expression of several genes including uPAR1, CRE-BP1, Chop-10, IGF, insulin-like growth factor-IA, STAT6, Cyclin-D1, Cyclin-E, ERBB-3, Alpha NGF, Kruppel-like factor LKLF, (P)19INK4 in metastatic RAW117-H10 cells compared to parental RAW117-P cells. On the other hand, MIP1beta, CD14 antigen, Cathepsin B and MOD are expressed more in RAW117-P cells compared to RAW117-H10 cells. Differential expression of the selected genes was confirmed using semiquantitative RT-PCR techniques. The combination of plasminogen activator and its receptor and IGF-like growth factors, cell cycle regulatory molecules and transcription factors might provide an ideal environment for RAW117-H10 cells to metastasize to distant organs and colonize. Thus these results identify certain differentially expressed genes that are involved in the metastatic properties of these lymphoma cells and lay foundation for further in depth analyses to use this information to develop therapy for metastatic lymphoma.

The role of ATF-2 in oncogenesis

Activating Transcription Factor-2 is a sequence-specific DNA-binding protein that belongs to the bZIP family of proteins and plays diverse roles in the mammalian cells. In response to stress stimuli, it activates a variety of gene targets including cyclin A, cyclin D and c-jun, which are involved in oncogenesis in various tissue types. ATF-2 expression has been correlated with maintenance of a cancer cell phenotype. However, other studies demonstrate an antiproliferative or apoptotic role for ATF-2. In this review, we summarize the signaling pathways that activate ATF-2, as well as its downstream targets. We examine the role of ATF-2 in carcinogenesis with respect to other bZIP proteins, using data from studies in human cancer cell lines, human tumours and mouse models, and we propose a potential model for its function in carcinogenesis, as well as a theoretical basis for its utility in anticancer drug design.

Fyn is a novel target of (-)-epigallocatechin gallate in the inhibition of JB6 Cl41 cell transformation

The cancer preventive action of (-)-epigallocatechin gallate (EGCG), found in green tea, is strongly supported by epidemiology and laboratory research data. However, the mechanism by which EGCG inhibits carcinogenesis and cell transformation is not clear. In this study, we report that EGCG suppressed epidermal growth factor (EGF)-induced cell transformation in JB6 cells. We also found that EGCG inhibited EGF-induced Fyn kinase activity and phosphorylation in vitro and in vivo. Fyn was implicated in the process because EGF-induced JB6 cell transformation was inhibited by small interfering RNA (siRNA)-Fyn-JB6 cells. With an in vitro protein-binding assay, we found that EGCG directly bound with the GST-Fyn-SH2 domain but not the GST-Fyn-SH3 domain. The K(d) value for EGCG binding to the Fyn SH2 domain was 0.367 +/- 0.122 microM and B(max) was 1.35 +/- 0.128 nmol/mg. Compared with control JB6 Cl41 cells, EGF-induced phosphorylation of p38 MAP kinase (p38 MAPK) (Thr180/Tyr182), ATF-2 (Thr71) and signal transducer and activator of transcription 1 (STAT1) (Thr727) was decreased in siRNA-Fyn-JB6 cells. EGCG could inhibit the phosphorylation of p38 MAPK, ATF-2, and STAT1. The DNA binding ability of AP-1, STAT1, and ATF-2 was also decreased in siRNA-Fyn-JB6 cells. Overall, these results demonstrated that EGCG interacted with Fyn and inhibited Fyn kinase activity and thereby regulated EGF-induced cell transformation. Inhibition of Fyn kinase activity is a novel and important mechanism that may be involved in EGCG-induced inhibition of cell transformation.

Piperonyl butoxide activates c-Jun and ATF-2 in the hepatocytes of mice

In order to clarify the possible mechanism of hepatocarcinogenesis induced by piperonyl butoxide, we attempted to identify the transcription factor activated by piperonyl butoxide in the male ICR mouse liver. Administration of 0.6% piperonyl butoxide for 24 h elevated the level of liver nuclear proteins that bind to an AP-1 consensus oligonucleotide, and these proteins demonstrated a supershift with the anti-c-Jun antibody. Additionally, immunoblot analysis revealed that piperonyl butoxide induced c-Jun phosphorylation within 8 h of administration, and phosphorylated ATF-2 was detected after 24 h of piperonyl butoxide treatment. Immunohistochemical analysis also demonstrated the presence of phosphorylated ATF-2 in the hepatocyte nuclei of mice fed with 0.6% piperonyl butoxide for 24 h. Furthermore, piperonyl butoxide induced ATF-2 phosphorylation in TLR-3, a mouse immortalized hepatocyte cell line. These results indicated that piperonyl butoxide activated c-Jun and ATF-2 in mouse hepatocytes during the early stage of hepatocarcinogenesis.

Attenuation of p38 MAPK activity upon contact inhibition in fibroblasts

The molecular events, which govern growth control upon contact inhibition have not yet been clearly defined. Previous work has indicated that there is an increase in the expression of mitogen-activated protein kinase phosphatases (MKPs) upon the attainment of contact inhibition in normal fibroblasts, concurrently with a decrease in ERK activity. To investigate the potential role of p38 and JNK in the transition to a contact-inhibited state, normal human fibroblasts (BJ) were grown to subconfluent and confluent densities. The total levels and phosphorylation states of p38 and JNK were assayed, and were compared to protein levels seen in HT-1080 fibrosarcoma cells, which lack contact-inhibited growth control. Activation of JNK was not apparent in these cells, though p38 was found to be active in proliferating cells, but attenuated in contact-inhibited cultures. Such fluctuations in p38 activity were not seen in cultures of fibrosarcoma cells of increasing density. This alteration in p38 activity was also reflected by attenuated activation of the downstream transcription factor ATF-2 upon contact inhibition. Overexpression of MKP-1 in fibrosarcoma cells and fibroblasts reduced proliferation, while expression of a phosphatase-resistant p38 protein (p38(N316)) enhanced proliferation of normal fibroblasts. Taken together, these results suggest the involvement of negative regulation of p38 in contact-inhibited growth control.

Polyamines regulate the stability of activating transcription factor-2 mRNA through RNA-binding protein HuR in intestinal epithelial cells

Maintenance of intestinal mucosal epithelial integrity requires polyamines that modulate the expression of various genes involved in cell proliferation and apoptosis. Recently, polyamines were shown to regulate the subcellular localization of the RNA-binding protein HuR, which stabilizes its target transcripts such as nucleophosmin and p53 mRNAs. The activating transcription factor-2 (ATF-2) mRNA encodes a member of the ATF/CRE-binding protein family of transcription factors and was computationally predicted to be a target of HuR. Here, we show that polyamines negatively regulate ATF-2 expression posttranscriptionally and that polyamine depletion stabilizes ATF-2 mRNA by enhancing the interaction of the 3'-untranslated region (UTR) of ATF-2 with cytoplasmic HuR. Decreasing cellular polyamines by inhibiting ornithine decarboxylase (ODC) with alpha-difluoromethylornithine increased the levels of ATF-2 mRNA and protein, whereas increasing polyamines by ectopic ODC overexpression repressed ATF-2 expression. Polyamine depletion did not alter transcription via the ATF-2 gene promoter but increased the stability of ATF-2 mRNA. Increased cytoplasmic HuR in polyamine-deficient cells formed ribonucleoprotein complexes with the endogenous ATF-2 mRNA and specifically bound to 3'-UTR of ATF-2 mRNA on multiple nonoverlapping 3'-UTR segments. Adenovirus-mediated HuR overexpression elevated ATF-2 mRNA and protein levels, whereas HuR silencing rendered the ATF-2 mRNA unstable and prevented increases in ATF-2 mRNA and protein. Furthermore, inhibition of ATF-2 expression prevented the increased resistance of polyamine-deficient cells to apoptosis induced by treatment with tumor necrosis factor-alpha and cycloheximide. These results indicate that polyamines modulate the stability of ATF-2 mRNA by altering cytoplasmic HuR levels and that polyamine-modulated ATF-2 expression plays a critical role in regulating epithelial apoptosis.

The activator protein-1 transcription factor in respiratory epithelium carcinogenesis

Respiratory epithelium cancers are the leading cause of cancer-related death worldwide. The multistep natural history of carcinogenesis can be considered as a gradual accumulation of genetic and epigenetic aberrations, resulting in the deregulation of cellular homeostasis. Growing evidence suggests that cross-talk between membrane and nuclear receptor signaling pathways along with the activator protein-1 (AP-1) cascade and its cofactor network represent a pivotal molecular circuitry participating directly or indirectly in respiratory epithelium carcinogenesis. The crucial role of AP-1 transcription factor renders it an appealing target of future nuclear-directed anticancer therapeutic and chemoprevention approaches. In the present review, we will summarize the current knowledge regarding the implication of AP-1 proteins in respiratory epithelium carcinogenesis, highlight the ongoing research, and consider the future perspectives of their potential therapeutic interest.

p38MAPK regulation of transcription factor targets in muscle and heart of the hibernating bat,Myotis lucifugus

Mammalian hibernation combines a profound net metabolic rate suppression with the selective up-regulation of key genes whose protein products address specific metabolic needs of the hibernator. The signal transduction pathways and transcription factors involved in regulating hibernation-responsive gene expression are of great interest. The present study suggests an important role for the p38 mitogen-activated protein kinase (p38 MAPK) and selected downstream transcription factors under its control (CREB, ATF-2, Elk-1) in the metabolic response by skeletal muscle during hibernation of little brown bats, Myotis lucifugus. Western blotting was used to quantify both total protein and levels of the phosphorylated, active forms of p38 MAPK, CREB, ATF-2 and Elk-1 in both skeletal muscle and heart of euthermic and hibernating bats. The p38 MAPK pathway was not apparently activated in heart during torpor but skeletal muscle showed strong increases (2.2-11-fold) in the amounts of phosphorylated p38 T180/Y182, CREB S133, ATF-2T69/71 and Elk-1(S383) in the torpid versus aroused state. By contrast both total and phosphorylated levels of Elk-1 in heart were reduced during hibernation to just 30% of the euthermic values. These data implicate p38 MAPK and its transcription factor targets, CREB, ATF-2 and Elk-1 in skeletal muscle maintenance during hibernation.

The bZip proteins CES-2 and ATF-2 alter the timing of transcription for a cell-specific target gene in C. elegans

The Caenorhabditis elegans basic leucine zipper (bZip) protein CES-2 regulates the transcription of different genes in different cells. Here, we show that CES-2 mediates its effects in one cell (the excretory duct cell) together with another bZip protein, ATF-2. Both proteins influence transactivation of a target gene, lin-48. Although lin-48 is required for both anatomical and physiological features of the excretory duct cell, ces-2 and atf-2 mutants only exhibit anatomical defects. We show that CES-2 and ATF-2 modify the temporal transcription of lin-48, acting to initiate embryonic expression required for normal excretory system development and anatomy. In contrast, CES-2 and ATF-2 do not influence post-embryonic lin-48 expression. We provide evidence that CES-2 and ATF-2 can interact with each other, and that they cooperate to form a complex on lin-48 regulatory sequences. Thus, the two bZip proteins function together as one of several inputs that influence the spatial and temporal regulation of lin-48.

Characterization and expression pattern of two zebrafishatf7 genes

Members of the ATF/CREB (activating transcription factor/cAMP-responsive element binding protein) transcription factor family play diverse roles in controlling cell proliferation, apoptosis, and oncogenesis, as well as in embryonic development of vertebrates. We identified two zebrafish orthologs of human ATF7 gene: atf7a and atf7b. Whole-mount in situ hybridization shows that zebrafish atf7a is first expressed in the notochord precursors at 80% epiboly stage and then in the developing notochord during segmentation. The expression of atf7a is positively regulated by ntl, flh, and spr2, which are involved in development of the notochord. In contrast, atf7b is maternally expressed and during embryogenesis its mRNA is ubiquitously distributed, showing an expression pattern similar to that of mammalian Atf7.