Upstream stimulatory factor (USF) as a transcriptional suppressor of human telomerase reverse transcriptase (hTERT) in oral cancer cells

PUS1 facilitates cell migration in clear cell renal cell carcinoma through the promotion of mRNA pseudouridylation and the stabilization of the SMOX gene

Clear cell renal cell carcinoma (ccRCC) is a highly aggressive malignancy characterized by its propensity for metastasis. Pseudouridine synthase 1 (PUS1), an enzyme involved in RNA modification, has been implicated in cancer progression, but its role in ccRCC remains unclear. This study investigates PUS1's role in ccRCC and evaluates its potential as a prognostic biomarker and therapeutic target. We assessed PUS1 expression in 541 ccRCC samples from The Cancer Genome Atlas (TCGA) and utilized Receiver Operating Characteristic (ROC) analyses to determine its prognostic value. High PUS1 levels were associated with reduced overall and disease-specific survival in ccRCC patients. Functional assays demonstrated that PUS1 promotes cell migration by stabilizing SMOX mRNA via pseudouridylation. The transcription factor USF1 regulates PUS1 expression by binding to its promoter region, enhancing its transcriptional activity. PUS1 silencing in ccRCC cell lines significantly reduced cell migration, while its overexpression had the opposite effect. These findings implicate the USF1-PUS1-SMOX signaling axis in regulating the migratory abilities of ccRCC cells. In conclusion, PUS1 plays a pivotal role in ccRCC progression and serves as an independent prognostic biomarker. Targeting PUS1 may offer promising therapeutic strategies for ccRCC patients. Further research is needed to explore its function in other cancers and to clarify its underlying molecular mechanisms.

Upstream stimulating factor 1 (USF1) -202 G/A polymorphism and serum levels of USF1 and USF2 are associated with gastric cancer risk: a case control study

PURPOSE

Gastric cancer is an inflammation-driven disease often associated with a bad prognosis. Upstream stimulatory factors USF1 and USF2 are pleiotropic transcription factors, with tumor suppressor function. Low expression of USF1 is associated with low survival in gastric cancer patients. USF1 genetic polymorphism -202G > A has been associated with cancer susceptibility. Our aim was to investigate USF1 gene polymorphism and serum level with the risk of gastric cancer.

METHODS

USF1-202 G/A polymorphism was analyzed by sanger sequencing, with the measure of USF1/USF2 serum levels by ELISA in H. pylori-positive patients with chronic gastritis, gastric precancerous lesions, gastric cancer and in healthy controls.

RESULTS

Our results show that the presence of the USF1-202 A allele increased the risk of gastric cancer compared to G (OR = 2; 95% CI 1.07-3.9; P = 0.02). Genotypically and under the dominant mutation model, the combined USF1- GA/AA -202 genotypes corresponded to higher risk of gastric cancer (OR = 3.5; 95% CI 1.4-8.2; p-value = 0.005) than the GG genotype. Moreover, the G/A transition at USF1-202 was associated with lower USF1 serum level, and mostly observed in gastric cancer patients where the average serological level of USF1 were 2.3 and twofold lower for the AA and GA genotypes, respectively, compared to GG.

CONCLUSION

USF1-202 G/A polymorphism constitutes a gastric cancer genetic risk factor. Together with USF1/USF2 serum level, they can be proposed as promising biomarkers for gastric cancer detection/prevention.

USF1 modulates transcription and cellular functions by regulating multiple transcription factors in Huh7 cells

Liver cancer, including hepatocellular carcinoma (HCC), is a malignant tumor that has high rates of metastasis and mortality worldwide. Upstream transcription factor 1 (USF1) is a canonical transcription factor (TF) and is associated with the pathogenesis of several cancers, but its biological functions and molecular targets in HCC remain unclear. Huh7 cells that overexpress USF1 were used with whole transcriptome profiling through RNA sequencing and chromatin immunoprecipitation (ChIP) sequencing methods to investigate the downstream targets of USF1. Reverse transcription-quantitative PCR was then used to validate the downstream targets. The results showed that USF1 significantly regulates 350 differentially expressed genes (DEGs). The upregulated DEGs were primarily protein-coding genes enriched in immune and inflammation response pathways, while the downregulated DEGs were mainly coding long non-coding (lnc)RNAs, indicating the regulatory function of USF1. It was also demonstrated that USF1 directly binds to the promoter region of 2,492 genes, which may be involved in the viral progression and cell proliferation pathways. By integrating these two datasets, 16 overlapped genes were detected, including downregulated lncRNA-NEAT1 and upregulated TF-ETV5. The downregulated lncRNA-NEAT1 showed reverse expression pattern and prognosis result compared with that of USF1 in patients with liver cancer, while upregulated TF-ETV5 showed consistent results with USF1. Promoter region motif analysis indicated that ETV5 has more binding motifs and genes than USF1 itself for USF1-regulated DEGs, indicating that USF1 may indirectly modulate gene expression by regulating ETV5 expression in Huh7 cells. The study also validated the direct interaction between USF1 and the promoter of ETV5 using ChIP-qPCR. In summary, the results demonstrated that USF1 binds to the promoter region of thousands of genes and affects a large part of DEGs indirectly. Downstream genes, including lncRNA-NEAT1 and TF-ETV5, may also have potential functions in the regulated network by USF1 and have potential functions in the progression of HCC. The present findings suggested that USF1 and its downstream targets could be potential targets for HCC therapy in the future.

Systematic analysis reveals distinct roles of USF family proteins in various cancer types

BACKGROUND

Upstream stimulatory factors (USFs) are members of the basic helix-loop-helix leucine zipper transcription factor family, including USF1, USF2, and USF3. The first two members have been well studied compared to the third member, USF3, which has received scarce attention in cancer research to date. Despite a recently reported association of its alteration with thyroid carcinoma, its expression has not been previously analyzed.

METHODS

We comprehensively analyzed differential levels of USFs expression, genomic alteration, DNA methylation, and their prognostic value across different cancer types and the possible correlation with tumor-infiltrating immune cells and drug response by using different bioinformatics tools.

RESULTS

Our findings established that USFs play an important role in cancers related to the urinary system and justify the necessity for further investigation. We implemented and offer a useful ShinyApp to facilitate researchers' efforts to inquire about any other gene of interest and to perform the analysis of drug response in a user-friendly fashion at http://zzdlab.com:3838/Drugdiscovery/.

USF1-mediated ALKBH5 stabilizes FLII mRNA in an m6A-YTHDF2-dependent manner to repress glycolytic activity in prostate adenocarcinoma

Upstream-stimulating factor 1 (USF1) is a ubiquitously expressed transcription factor implicated in multiple cellular processes, including metabolism and proliferation. This study focused on the function of USF1 in glycolysis and the malignant development of prostate adenocarcinoma (PRAD). Bioinformatics predictions suggested that USF1 is poorly expressed in PRAD. The clinical PRAD samples revealed a low level of USF1, which was correlated with an unfavorable prognosis. Artificial upregulation of USF1 significantly repressed glycolytic activity in PRAD cells and reduced cell growth and metastasis in vitro and in vivo. Potential downstream genes of USF1 were probed by integrated bioinformatics analyses. The chromatin immunoprecipitation and luciferase assays indicated that USF1 bound to the α-ketoglutarate-dependent dioxygenase alkB homolog 5 (ALKBH5) promoter for transcription activation. Flightless I (FLII) was identified as the gene showing the highest degree of correlation with ALKBH5. As an m6A demethylase, ALKBH5 enhanced FLII mRNA stability by inducing m6A demethylation in an m6A-YTH N6-methyladenosine RNA-binding protein F2 (YTHDF2)-dependent manner. Either silencing of ALKBH5 or FLII blocked the role of USF1 in PARD cells and restored glycolysis, cell proliferation, and invasion. This study demonstrates that USF1 activates ALKBH5 to stabilize FLII mRNA in an m6A-YTHDF2-dependent manner, thereby repressing glycolysis processes and the progression of PRAD.

The Relevance of Telomerase and Telomere-Associated Proteins in B-Acute Lymphoblastic Leukemia

Telomeres and telomerase are closely linked to uncontrolled cellular proliferation, immortalization and carcinogenesis. Telomerase has been largely studied in the context of cancer, including leukemias. Deregulation of human telomerase gene hTERT is a well-established step in leukemia development. B-acute lymphoblastic leukemia (B-ALL) recovery rates exceed 90% in children; however, the relapse rate is around 20% among treated patients, and 10% of these are still incurable. This review highlights the biological and clinical relevance of telomerase for B-ALL and the implications of its canonical and non-canonical action on signaling pathways in the context of disease and treatment. The physiological role of telomerase in lymphocytes makes the study of its biomarker potential a great challenge. Nevertheless, many works have demonstrated that high telomerase activity or hTERT expression, as well as short telomeres, correlate with poor prognosis in B-ALL. Telomerase and related proteins have been proven to be promising pharmacological targets. Likewise, combined therapy with telomerase inhibitors may turn out to be an alternative strategy for B-ALL.

USF1-CHCHD4 axis promotes lung adenocarcinoma progression partially via activating the MYC pathway

BACKGROUND

This study aimed to identify genes related to lung adenocarcinoma (LUAD) and investigate the effects and molecular mechanisms of coiled-coil-helix-coiled-coil-helix domain containing 4 (CHCHD4) in the progression of LUAD.

METHODS

The GEPIA database was used to evaluate the differential expression of CHCHD4 and the survival data of LUAD patients compared to controls. TCGA-LUAD database, JASPAR website, and GSEA were used to analyse the relationship between CHCHD4 and the upstream stimulating factor 1 (USF1) or MYC pathways. The proliferation, apoptosis, migration, and invasion of LUAD cells were evaluated using cell counting kit-8, 5-ethynyl-2'-deoxyuridine, colony formation, flow cytometry, wound healing, and transwell assays. qRT-PCR, western blotting, and immunohistochemistry were used to detect the mRNA and protein expression, respectively. Furthermore, xenograft tumours from nude mice were used to verify the effect of CHCHD4 on LUAD in vivo.

RESULTS

CHCHD4 overexpression was found in LUAD tumor tissues and cells, and high CHCHD4 was associated with a poor prognosis. Interestingly, CHCHD4 knockdown suppressed the malignant phenotype of the LUAD cells. Moreover, we found that USF1 upregulated CHCHD4 and promoted LUAD progression. CHCHD4 knockdown also inhibited the progression of LUAD. In addition, CHCHD4 knockdown suppressed xenograft tumour growth.

CONCLUSION

USF1-CHCHD4 axis can promote LUAD progress, which may be through activating MYC pathway.

Multifaceted and Intricate Oncogenic Mechanisms of NDRG1 in Head and Neck Cancer Depend on Its C-Terminal 3R-Motif

N-Myc downstream-regulated 1 (NDRG1) has inconsistent oncogenic functions in various cancers. We surveyed and characterized the role of NDRG1 in head and neck cancer (HNC). Cellular methods included spheroid cell formation, clonogenic survival, cell viability, and Matrigel invasion assays. Molecular techniques included transcriptomic profiling, RT-qPCR, immunoblotting, in vitro phosphorylation, immunofluorescent staining, and confocal microscopy. Prognostic significance was assessed by Kaplan–Meier analysis. NDRG1 participated in diverse oncogenic functions in HNC cells, mainly stress response and cell motility. Notably, NDRG1 contributed to spheroid cell growth, radio-chemoresistance, and upregulation of stemness-related markers (CD44 and Twist1). NDRG1 facilitated cell migration and invasion, and was associated with modulation of the extracellular matrix molecules (fibronectin, vimentin). Characterizing the 3R-motif in NDRG1 revealed its mechanism in the differential regulation of the phenotypes. The 3R-motif displayed minimal effect on cancer stemness but was crucial for cell motility. Phosphorylating the motif by GSK3b at serine residues led to its nuclear translocation to promote motility. Clinical analyses supported the oncogenic function of NDRG1, which was overexpressed in HNC and associated with poor prognosis. The data elucidate the multifaceted and intricate mechanisms of NDRG1 in HNC. NDRG1 may be a prognostic indicator or therapeutic target for refractory HNC.

Mechanism of Human Telomerase Reverse Transcriptase (hTERT) Regulation and Clinical Impacts in Leukemia

The proliferative capacity and continuous survival of cells are highly dependent on telomerase expression and the maintenance of telomere length. For this reason, elevated expression of telomerase has been identified in virtually all cancers, including leukemias; however, it should be noted that expression of telomerase is sometimes observed later in malignant development. This time point of activation is highly dependent on the type of leukemia and its causative factors. Many recent studies in this field have contributed to the elucidation of the mechanisms by which the various forms of leukemias increase telomerase activity. These include the dysregulation of telomerase reverse transcriptase (TERT) at various levels which include transcriptional, post-transcriptional, and post-translational stages. The pathways and biological molecules involved in these processes are also being deciphered with the advent of enabling technologies such as next-generation sequencing (NGS), ribonucleic acid sequencing (RNA-Seq), liquid chromatography-mass spectrometry (LCMS/MS), and many others. It has also been established that TERT possess diagnostic value as most adult cells do not express high levels of telomerase. Indeed, studies have shown that prognosis is not favorable in patients who have leukemias expressing high levels of telomerase. Recent research has indicated that targeting of this gene is able to control the survival of malignant cells and therefore offers a potential treatment for TERT-dependent leukemias. Here we review the mechanisms of hTERT regulation and deliberate their association in malignant states of leukemic cells. Further, we also cover the clinical implications of this gene including its use in diagnostic, prognostic, and therapeutic discoveries.

The transcription factor USF1 promotes glioma cell invasion and migration by activating lncRNA HAS2-AS1

Objective: The role of lncRNAs in tumor has been widely concerned. The present study took HAS2-AS1 (the antisense RNA 1 of HAS2) as a starting point to explore its expression in glioma and its role in the process of migration and invasion, providing a strong theoretical basis for mining potential therapeutic targets of glioma.

Methods: Clinical data of glioma were obtained from The Cancer Genome Atlas (TCGA) database and differentially expressed lncRNAs were analyzed by edgeR. The hTFtarget database was used to predict the upstream transcription factors of HAS2-AS1 and the JASPAR website was used to predict the binding sites of human upstream transcription factor 1 (USF1) and HAS2-AS1. qRT-PCR was used to detect the expressions of HAS2-AS1 and USF1 in glioma tissues and cell lines. The effects of silencing HAS2-AS1 on the migration and invasion of cancer cells were verified by wound healing and Transwell invasion assays. The chromatin immunoprecipitation (ChIP) and dual luciferase reporter assays were applied to demonstrate the binding of USF1 and HAS2-AS1 promoter region. Western blot was used to detect the expressions of epithelial–mesenchymal transition (EMT)-related proteins.

Results: HAS2-AS1 was highly expressed in glioma tissues and cells, and was significantly associated with poor prognosis. Silencing HAS2-AS1 expression inhibited glioma cell migration, invasion and EMT. USF1 was highly expressed in glioma and positively correlated with HAS2-AS1. The transcription of HAS2-AS1 was activated by USF1 via binding to HAS2-AS1 promoter region, consequently potentiating the invasion and migration abilities of glioma cells.

Conclusion: These results suggested that the transcription factor USF1 induced up-regulation of lncRNA HAS2-AS1 and promoted glioma cell invasion and migration.

S100A8 promotes epithelial-mesenchymal transition and metastasis under TGF-β/USF2 axis in colorectal cancer

Background

The transforming growth factor‐β (TGF‐β) pathway plays a pivotal role in inducing epithelial‐mesenchymal transition (EMT), which is a key step in cancer invasion and metastasis. However, the regulatory mechanism of TGF‐β in inducing EMT in colorectal cancer (CRC) has not been fully elucidated. In previous studies, it was found that S100A8 may regulate EMT. This study aimed to clarify the role of S100A8 in TGF‐β‐induced EMT and explore the underlying mechanism in CRC.

Methods

S100A8 and upstream transcription factor 2 (USF2) expression was detected by immunohistochemistry in 412 CRC tissues. Kaplan‐Meier survival analysis was performed. In vitro, Western blot, and migration and invasion assays were performed to investigate the effects of S100A8 and USF2 on TGF‐β‐induced EMT. Mouse metastasis models were used to determine in vivo metastasis ability. Luciferase reporter and chromatin immunoprecipitation assay were used to explore the role of USF2 on S100A8 transcription.

Results

During TGF‐β‐induced EMT in CRC cells, S100A8 and the transcription factor USF2 were upregulated. S100A8 promoted cell migration and invasion and EMT. USF2 transcriptionally regulated S100A8 expression by directly binding to its promoter region. Furthermore, TGF‐β enhanced the USF2/S100A8 signaling axis of CRC cells whereas extracellular S100A8 inhibited the USF2/S100A8 axis of CRC cells. S100A8 expression in tumor cells was associated with poor overall survival in CRC. USF2 expression was positively related to S100A8 expression in tumor cells but negatively related to S100A8‐positive stromal cells.

Conclusions

TGF‐β was found to promote EMT and metastasis through the USF2/S100A8 axis in CRC while extracellular S100A8 suppressed the USF2/S100A8 axis. USF2 was identified as an important switch on the intracellular and extracellular S100A8 feedback loop.

USF1 defect drives p53 degradation during Helicobacter pylori infection and accelerates gastric carcinogenesis

OBJECTIVE

Helicobacter pylori (Hp) is a major risk factor for gastric cancer (GC). Hp promotes DNA damage and proteasomal degradation of p53, the guardian of genome stability. Hp reduces the expression of the transcription factor USF1 shown to stabilise p53 in response to genotoxic stress. We investigated whether Hp-mediated USF1 deregulation impacts p53-response and consequently genetic instability. We also explored in vivo the role of USF1 in gastric carcinogenesis.

DESIGN

Human gastric epithelial cell lines were infected with Hp7.13, exposed or not to a DNA-damaging agent camptothecin (CPT), to mimic a genetic instability context. We quantified the expression of USF1, p53 and their target genes, we determined their subcellular localisation by immunofluorescence and examined USF1/p53 interaction. Usf1^-/- and INS-GAS mice were used to strengthen the findings in vivo and patient data examined for clinical relevance.

RESULTS

In vivo we revealed the dominant role of USF1 in protecting gastric cells against Hp-induced carcinogenesis and its impact on p53 levels. In vitro, Hp delocalises USF1 into foci close to cell membranes. Hp prevents USF1/p53 nuclear built up and relocates these complexes in the cytoplasm, thereby impairing their transcriptional function. Hp also inhibits CPT-induced USF1/p53 nuclear complexes, exacerbating CPT-dependent DNA damaging effects.

CONCLUSION

Our data reveal that the depletion of USF1 and its de-localisation in the vicinity of cell membranes are essential events associated to the genotoxic activity of Hp infection, thus promoting gastric carcinogenesis. These findings are also of clinical relevance, supporting USF1 expression as a potential marker of GC susceptibility.

LncRNA LOXL1-AS1 facilitates the tumorigenesis and stemness of gastric carcinoma via regulation of miR-708-5p/USF1 pathway

Objectives

As one of the most life‐threatening malignancies, gastric cancer is the third contributor of cancer mortalities globally. Increasing studies have proven the regulatory roles of lncRNAs in the development of diverse malignant tumours. But little is known about its function and molecular mechanism in gastric carcinoma.

Materials and methods

RT‐qPCR was performed to measure the expression pattern of LOXL1‐AS1 in gastric cancer. To ascertain its definite role, CCK‐8, EdU, Western blot, transwell and sphere formation assays were adopted. RNA pull‐down, RIP, ChIP and luciferase reporter assays were carried out to investigate the molecular mechanism of LOXL1‐AS1 in gastric carcinoma.

Results

LOXL1‐AS1 was highly expressed in tissues and cells of gastric cancer. The upregulation of LOXL1‐AS1 predicted poor prognosis in gastric carcinoma. Our findings demonstrated that LOXL1‐AS1 accelerated the deterioration of gastric cancer by inducing cell proliferation, migration, EMT and stemness. Moreover, the expression of USF1 in gastric cancer was higher than in normal control and LOXL1‐AS1 negatively modulated USF1. Functionally, LOXL1‐AS1 acted as a ceRNA to upregulate USF1 via sponging miR‐708‐5p. Besides, we confirmed USF1 promoted the transcription of stemness marker SOX2. Rescue experiments testified the stimulative role of LOXL1‐AS1/miR‐708‐5p/USF1 pathway in gastric cancer progression. It was also validated that LOXL1‐AS1 facilitated cell growth of gastric carcinoma in vivo.

Conclusions

Our study unravelled that LOXL1‐AS1/miR‐708‐5p/USF1 pathway contributed to the development of gastric cancer.

Cyclin-Dependent Kinase 5 (CDK5)-Mediated Phosphorylation of Upstream Stimulatory Factor 2 (USF2) Contributes to Carcinogenesis

The transcription factor USF2 is supposed to have an important role in tumor development. However, the regulatory mechanisms contributing to the function of USF2 are largely unknown. Cyclin-dependent kinase 5 (CDK5) seems to be of importance since high levels of CDK5 were found in different cancers associated with high USF2 expression. Here, we identified USF2 as a phosphorylation target of CDK5. USF2 is phosphorylated by CDK5 at two serine residues, serine 155 and serine 222. Further, phosphorylation of USF2 at these residues was shown to stabilize the protein and to regulate cellular growth and migration. Altogether, these results delineate the importance of the CDK5-USF2 interplay in cancer cells.

Knockdown of USF1 Inhibits the Vasculogenic Mimicry of Glioma Cells via Stimulating SNHG16/miR-212-3p and linc00667/miR-429 Axis

The anti-angiogenic treatment of malignant glioma cells is an effective method to treat high-grade gliomas. However, due to the presence of vasculogenic mimicry (VM), the anti-angiogenic treatment of gliomas is not significantly effective in improving overall patient median survival. Therefore, this study investigated the mechanism of mimic formation of angiogenesis in gliomas. The results of this experiment indicate that the expression of upstream transcription factor 1 (USF1) is upregulated in glioma tissues and cells. USF1 knockdown inhibits the proliferation, migration, invasion, VM, and expression of VM-associated proteins in glioma cells by stimulating SNHG16 and linc00667. These two long non-coding RNAs (lncRNAs) regulate ALHD1A1 through the competing endogenous RNA (ceRNA) mechanism influencing the VM of glioma. This study is the first to demonstrate that the USF1/SNHG16/miR-212-3p/ALDH1A1 (aldehyde dehydrogenase-1) and USF1/linc00667/miR-429/ALDH1A1 axis regulates the VM of glioma cells, and these findings might provide a novel strategy for glioma treatment.

Suppression of metastasis through inhibition of chitinase 3-like 1 expression by miR-125a-3p-mediated up-regulation of USF1

Rationale: Chitinase 3-like 1 (Chi3L1) protein is up-regulated in various diseases including solid cancers. According to Genome-Wide Association Study (GWAS)/Online Mendelian Inheritance in Man (OMIM)/Differentially Expressed Gene (DEG) analyses, Chi3L1 is associated with 38 cancers, and more highly associated with cancer compared to other oncogenes such as EGFR, TNFα, etc. However, the mechanisms and pathways by which Chi3L1 is associated with cancer are not clear. In current study, we investigated the role of Chi3L1 in lung metastasis. Methods: We performed the differentially expressed gene analysis to explore the genes which are associated with Chi3L1 using the web-based platform from Biomart. We investigated the metastases in lung tissues of C57BL/6 mice injected with B16F10 melanoma following treatment with Ad-shChi3L1. We also investigated the expression of USF1 and Chi3L1 in Chi3L1 KD mice lung tissues by Western blotting and IHC. We also analyzed lung cancer cells metastases induced by Chi3L1 using migration and cell proliferation assay in human lung cancer cell lines. The involvement of miR-125a-3p in Chi3L1 regulation was determined by miRNA qPCR and luciferase reporter assay. Results: We showed that melanoma metastasis in lung tissues was significantly reduced in Chi3L1 knock-down mice, accompanied by down-regulation of MMP-9, MMP-13, VEGF, and PCNA in Chi3L1 knock-down mice lung tissue, as well as in human lung cancer cell lines. We also found that USF1 was conversely expressed against Chi3L1. USF1 was increased by knock-down of Chi3L1 in mice lung tissues, as well as in human lung cancer cell lines. In addition, knock-down of USF1 increased Chi3L1 levels in addition to augmenting metastasis cell migration and proliferation in mice model, as well as in human cancer cell lines. Moreover, in human lung tumor tissues, the expression of Chi3L1 was increased but USF1 was decreased in a stage-dependent manner. Finally, Chi3L1 expression was strongly regulated by the indirect translational suppressing activity of USF1 through induction of miR-125a-3p, a target of Chi3L1. Conclusion: Metastases in mice lung tissues and human lung cancer cell lines were decreased by KD of Chi3L1. USF1 bound to the Chi3L1 promoter, however, Chi3L1 expression was decreased by USF1, despite USF1 enhancing the transcriptional activity of Chi3L1. We found that USF1 induced miR-125a-3p levels which suppressed Chi3L1 expression. Ultimately, our results suggest that lung metastasis is suppressed by knock-down of Chi3L1 through miR-125a-3p-mediated up-regulation of USF1.

Regulation of Telomere Homeostasis during Epstein-Barr virus Infection and Immortalization

The acquisition of unlimited proliferative potential is dependent on the activation of mechanisms for telomere maintenance, which counteracts telomere shortening and the consequent triggering of the DNA damage response, cell cycle arrest, and apoptosis. The capacity of Epstein Barr virus (EBV) to infect B-lymphocytes in vitro and transform the infected cells into autonomously proliferating immortal cell lines underlies the association of this human gamma-herpesvirus with a broad variety of lymphoid and epithelial cell malignancies. Current evidence suggests that both telomerase-dependent and -independent pathways of telomere elongation are activated in the infected cells during the early and late phases of virus-induced immortalization. Here we review the interaction of EBV with different components of the telomere maintenance machinery and the mechanisms by which the virus regulates telomere homeostasis in proliferating cells. We also discuss how these viral strategies may contribute to malignant transformation.

Telomerase Induction in HPV Infection and Oncogenesis

Telomerase extends the repetitive DNA at the ends of linear chromosomes, and it is normally active in stem cells. When expressed in somatic diploid cells, it can lead to cellular immortalization. Human papillomaviruses (HPVs) are associated with and high-risk for cancer activate telomerase through the catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT). The expression of hTERT is affected by both high-risk HPVs, E6 and E7. Seminal studies over the last two decades have identified the transcriptional, epigenetic, and post-transcriptional roles high-risk E6 and E7 have in telomerase induction. This review will summarize these findings during infection and highlight the importance of telomerase activation as an oncogenic pathway in HPV-associated cancer development and progression.

Transcription Regulation of the Human Telomerase Reverse Transcriptase (hTERT) Gene

Embryonic stem cells and induced pluripotent stem cells have the ability to maintain their telomere length via expression of an enzymatic complex called telomerase. Similarly, more than 85%–90% of cancer cells are found to upregulate the expression of telomerase, conferring them with the potential to proliferate indefinitely. Telomerase Reverse Transcriptase (TERT), the catalytic subunit of telomerase holoenzyme, is the rate-limiting factor in reconstituting telomerase activity in vivo. To date, the expression and function of the human Telomerase Reverse Transcriptase (hTERT) gene are known to be regulated at various molecular levels (including genetic, mRNA, protein and subcellular localization) by a number of diverse factors. Among these means of regulation, transcription modulation is the most important, as evident in its tight regulation in cancer cell survival as well as pluripotent stem cell maintenance and differentiation. Here, we discuss how hTERT gene transcription is regulated, mainly focusing on the contribution of trans-acting factors such as transcription factors and epigenetic modifiers, as well as genetic alterations in hTERT proximal promoter.

Association between single nucleotide polymorphisms of upstream transcription factor 1 (USF1) and susceptibility to papillary thyroid cancer

BACKGROUND

Thyroid cancer, predominantly by papillary thyroid cancer (PTC), is a malignant tumour of endocrine system with increasing incidence rate worldwide. Upstream transcription factor 1 (USF1) regulates a variety of biological processes by transactivation of functional genes. In this study, we investigated the association between USF1 polymorphisms and PTC risk.

MATERIAL & METHODS

A total of 334 patients with PTC, 186 patients with benign nodules (BN) and 668 healthy controls were enrolled in our study. Tag-SNPs were identified in Chinese Han in Beijing (CHB) from International HapMap Project Databases. Genomic DNAs were extracted by TaqMan Blood DNA kits. SNPs of USF1 were genotyped by TaqMan SNPs genotyping assay. Odds ratios (OR) and corresponding 95% confidence interval (CI) were used to assess the association between USF1 genetic variants and PTC risk. The statistical analyses were carried out with spss 13.0 software.

RESULTS

Five tag-SNPs were retrieved to capture all the genetic variants of USF1. Among the five tag-SNPs, genetic variants in rs2516838, rs3737787 and rs2516839 have significant association with PTC risk. The rs2516838 polymorphisms dominant model (CG+GG vs CC: OR = 0·71; 95% CI: 0·52-0·97; P = 0·033) and allelic model (C vs G: OR = 0·031; 95% CI: 0·56-0·97; P = 0·031) indicated it may act as a protective factor against PTC. On the contrary, the results of rs3737787 polymorphisms: dominant model (CT+TT vs CC: OR = 1·55; 95%CI: 1·09-2·02; P = 0·001) and allelic model (C vs T: OR = 1·35; 95%CI: 1·10-1·64; P = 0·003), as well as the results of rs2516839 polymorphisms: dominant model (GA+AA vs GG: OR = 1·77; 95%CI: 1·31-2·38; P < 0·001) and allelic model (G vs A: OR = 1·36; 95%CI: 1·13-1·63; P = 0·014), revealed that they may act as risk factors for PTC.

CONCLUSION

In this study, we found the SNPs of rs2516838 (mutant G alleles vs wild C alleles), rs3737787 (mutant T alleles vs wild C alleles) and rs2516839 (mutant A alleles vs wild G alleles) were significantly associated with PTC risk. Further large-scale studies with different ethnicities are still needed to validate our findings and explore the underlying mechanism of USF1 in PTC development.

Protein kinases as switches for the function of upstream stimulatory factors: implications for tissue injury and cancer

The upstream stimulatory factors (USFs) are regulators of important cellular processes. Both USF1 and USF2 are supposed to have major roles in metabolism, tissue protection and tumor development. However, the knowledge about the mechanisms that control the function of USFs, in particular in tissue protection and cancer, is limited. Phosphorylation is a versatile tool to regulate protein functions. Thereby, phosphorylation can positively or negatively affect different aspects of transcription factor function including protein stability, protein-protein interaction, cellular localization, or DNA binding. The present review aims to summarize the current knowledge about the regulation of USFs by direct phosphorylation and the consequences for USF functions in tissue protection and cancer.

GSK3β-dependent phosphorylation alters DNA binding, transactivity and half-life of the transcription factor USF2

The upstream stimulatory factor 2 (USF2) is a regulator of important cellular processes and is supposed to have also a role during tumor development. However, the knowledge about the mechanisms that control the function of USF2 is limited. The data of the current study show that USF2 function is regulated by phosphorylation and identified GSK3β as an USF2-phosphorylating kinase. The phosphorylation sites within USF2 could be mapped to serine 155 and threonine 230. In silico analyses of the 3-dimensional structure revealed that phosphorylation of USF2 by GSK3β converts it to a more open conformation which may influence transactivity, DNA binding and target gene expression. Indeed, experiments with GSK-3β-deficient cells revealed that USF2 transactivity, DNA binding and target gene expression were reduced upon lack of GSK3β. Further, experiments with USF2 variants mimicking GSK3β phosphorylated USF2 in GSK3β-deficient cells showed that phosphorylation of USF2 by GSK3β did not affect cell proliferation but increased cell migration. Together, this study reports a new mechanism by which USF2 may contribute to cancerogenesis.

Identifying differentially expressed genes and small molecule drugs for prostate cancer by a bioinformatics strategy

PURPOSE

Prostate cancer caused by the abnormal disorderly growth of prostatic acinar cells is the most prevalent cancer of men in western countries. We aimed to screen out differentially expressed genes (DEGs) and explore small molecule drugs for prostate cancer.

MATERIALS AND METHODS

The GSE3824 gene expression profile of prostate cancer was downloaded from Gene Expression Omnibus database which including 21 normal samples and 18 prostate cancer cells. The DEGs were identified by Limma package in R language and gene ontology and pathway enrichment analyses were performed. In addition, potential regulatory microRNAs and the target sites of the transcription factors were screened out based on the molecular signature database. In addition, the DEGs were mapped to the connectivity map database to identify potential small molecule drugs.

RESULTS

A total of 6,588 genes were filtered as DEGs between normal and prostate cancer samples. Examples such as ITGB6, ITGB3, ITGAV and ITGA2 may induce prostate cancer through actions on the focal adhesion pathway. Furthermore, the transcription factor, SP1, and its target genes ARHGAP26 and USF1 were identified. The most significant microRNA, MIR-506, was screened and found to regulate genes including ITGB1 and ITGB3. Additionally, small molecules MS-275, 8-azaguanine and pyrvinium were discovered to have the potential to repair the disordered metabolic pathways, abd furthermore to remedy prostate cancer.

CONCLUSIONS

The results of our analysis bear on the mechanism of prostate cancer and allow screening for small molecular drugs for this cancer. The findings have the potential for future use in the clinic for treatment of prostate cancer.

p53 requires the stress sensor USF1 to direct appropriate cell fate decision

Genomic instability is a major hallmark of cancer. To maintain genomic integrity, cells are equipped with dedicated sensors to monitor DNA repair or to force damaged cells into death programs. The tumor suppressor p53 is central in this process. Here, we report that the ubiquitous transcription factor Upstream Stimulatory factor 1 (USF1) coordinates p53 function in making proper cell fate decisions. USF1 stabilizes the p53 protein and promotes a transient cell cycle arrest, in the presence of DNA damage. Thus, cell proliferation is maintained inappropriately in Usf1 KO mice and in USF1-deficient melanoma cells challenged by genotoxic stress. We further demonstrate that the loss of USF1 compromises p53 stability by enhancing p53-MDM2 complex formation and MDM2-mediated degradation of p53. In USF1-deficient cells, the level of p53 can be restored by the re-expression of full-length USF1 protein similarly to what is observed using Nutlin-3, a specific inhibitor that prevents p53-MDM2 interaction. Consistent with a new function for USF1, a USF1 truncated protein lacking its DNA-binding and transactivation domains can also restore the induction and activity of p53. These findings establish that p53 function requires the ubiquitous stress sensor USF1 for appropriate cell fate decisions in response to DNA-damage. They underscore the new role of USF1 and give new clues of how p53 loss of function can occur in any cell type. Finally, these findings are of clinical relevance because they provide new therapeutic prospects in stabilizing and reactivating the p53 pathway.

Cancer is a complex disease that is characterized by the sequential accumulation of genetic mutations. Exposure to environmental agents, such as solar ultraviolet, induces such alterations and thus contributes to the development of genomic instability. The tumor suppressor p53 has a central role in orchestrating cellular responses to genotoxic stress. In response to DNA-damage, p53 is stabilized and activated to direct cell fate decisions. Cells in which p53 stabilization is compromised become more vulnerable to mutagenic agents and hence the mutation rate increases, which promotes tumor development. Stabilization of p53 is thus a critical step towards cancer prevention. Using a genetic approach, we demonstrate that the ubiquitous transcription factor Upstream Stimulatory factor 1 (USF1) is required for immediate p53 stabilization and appropriate cell fate decisions following genotoxic stress. Furthermore, we show that this involves a novel function of USF1 that underscores its critical role as a stress sensor. The loss of USF1 expression should thus be considered as a potential initiator of tumorigenesis in the context of environmental insults.

Chromatin redistribution of the DEK oncoprotein represses hTERT transcription in leukemias

Although numerous factors have been found to modulate hTERT transcription, the mechanism of its repression in certain leukemias remains unknown. We show here that DEK represses hTERT transcription through its enrichment on the hTERT promoter in cells from chronic and acute myeloid leukemias, chronic lymphocytic leukemia, but not acute lymphocytic leukemias where hTERT is overexpressed. We isolated DEK from the hTERT promoter incubated with nuclear extracts derived from fresh acute myelogenous leukemia (AML) cells and from cells expressing Tax, an hTERT repressor encoded by the human T cell leukemia virus type 1. In addition to the recruitment of DEK, the displacement of two potent known hTERT transactivators from the hTERT promoter characterized both AML cells and Tax-expressing cells. Reporter and chromatin immunoprecipitation assays permitted to map the region that supports the repressive effect of DEK on hTERT transcription, which was proportionate to the level of DEK-promoter association but not with the level of DEK expression. Besides hTERT repression, this context of chromatin redistribution of DEK was found to govern about 40% of overall transcriptional modifications, including those of cancer-prone genes. In conclusion, DEK emerges as an hTERT repressor shared by various leukemia subtypes and seems involved in the deregulation of numerous genes associated with leukemogenesis.

Genomic organization of the cytosolic manganese superoxide dismutase gene from the Pacific white shrimp, Litopenaeus vannamei, and its response to thermal stress

Cytosolic manganese superoxide dismutase (cMnSOD) is an important antioxidant enzyme which catalyzes the conversion of superoxides to oxygen and hydrogen peroxide in several organisms. In the Pacific white shrimp, Litopenaeus vannamei, three cMnSOD genes (LvcMnSOD1-3) have previously been characterized. Here, the genomic structure of LvcMnSOD2 and its mRNA expression in response to thermal stress was examined. Analysis of the nucleotide sequence demonstrated that LvcMnSOD2 is comprised of 2392 bp spanning from the ATG translation start site to the stop codon and contains six exons interrupted by five introns. The 5' region upstream of the LvcMnSOD2 gene contains several putative regulatory elements but lacks the accepted TATA sequence. The putative transcription factor binding elements that may be involved in LvcMnSOD2 mRNA expression level include activator protein-1 (AP-1), cAMP response element binding protein (CREB), upstream stimulatory factor (USF), CAAT-enhancer binding protein (C/EBP), nuclear factor-κB (NF-κB) and heat shock regulatory element (HSE). In addition, we compared the 5' upstream sequences of the LvcMnSOD2 gene between two shrimp strains that are resistant or susceptible to Taura syndrome virus (TSV), respectively, which revealed the absence of the USF and C/EBP elements at positions -2125 and -1986, respectively, in the TSV-susceptible shrimp line. Moreover, genomic variations between the two shrimp strains were detected in some of the putative C/EBP, USF, HSE and NF-κB transcription factor binding elements. That these genomic variations might be involved in the TSV resistance as well as in stress responses remains to be evaluated. The presence of 15 putative HSEs suggests that the expression of LvcMnSOD2 is regulated under thermal stress. Here, we found that in response to a 1 or 3 h thermal stress (35 °C), the mRNA expression levels of LvcMnSOD2 were significantly increased and then gradually decreased in the recovering phase at room temperature (25 °C) to control levels by 3 h after the heat shock. Thus, the antioxidant system may be induced to protect cells from the oxidative damage caused by thermal stress. The genomic organization of LvcMnSOD2 likely provides a clue to the mechanisms that might regulate the antioxidant defense pathway in shrimps and so potentially in marine invertebrates.

Upstream stimulatory factor 2 and hypoxia-inducible factor 2α (HIF2α) cooperatively activate HIF2 target genes during hypoxia

While the functions of hypoxia-inducible factor 1α (HIF1α)/aryl hydrocarbon receptor nuclear translocator (ARNT) and HIF2α/ARNT (HIF2) proteins in activating hypoxia-inducible genes are well established, the role of other transcription factors in the hypoxic transcriptional response is less clear. We report here for the first time that the basic helix-loop-helix-leucine-zip transcription factor upstream stimulatory factor 2 (USF2) is required for the hypoxic transcriptional response, specifically, for hypoxic activation of HIF2 target genes. We show that inhibiting USF2 activity greatly reduces hypoxic induction of HIF2 target genes in cell lines that have USF2 activity, while inducing USF2 activity in cells lacking USF2 activity restores hypoxic induction of HIF2 target genes. Mechanistically, USF2 activates HIF2 target genes by binding to HIF2 target gene promoters, interacting with HIF2α protein, and recruiting coactivators CBP and p300 to form enhanceosome complexes that contain HIF2α, USF2, CBP, p300, and RNA polymerase II on HIF2 target gene promoters. Functionally, the effect of USF2 knockdown on proliferation, motility, and clonogenic survival of HIF2-dependent tumor cells in vitro is phenocopied by HIF2α knockdown, indicating that USF2 works with HIF2 to activate HIF2 target genes and to drive HIF2-depedent tumorigenesis.

Interaction of HIF and USF signaling pathways in human genes flanked by hypoxia-response elements and E-box palindromes

Rampant activity of the hypoxia-inducible factor (HIF)-1 in cancer is frequently associated with the malignant progression into a harder-to-treat, increasingly aggressive phenotype. Clearly, anti-HIF strategies in cancer cells are of considerable clinical interest. One way to fine-tune, or inhibit, HIF's transcriptional outflow independently of hydroxylase activities could be through competing transcription factors. A CACGTG-binding activity in human hepatoma cells was previously found to restrict HIF's access to hypoxia response cis-elements (HRE) in a Daphnia globin gene promoter construct (phb2). The CACGTG factor, and its impact on hypoxia-responsive human genes, was analyzed in this study by genome-wide computational scans as well as gene-specific quantitative PCR, reporter and DNA-binding assays in hepatoma (Hep3B), cervical carcinoma (HeLa), and breast carcinoma (MCF7) cells. Among six basic helix-loop-helix transcription factors known to target CACGTG palindromes, we identified upstream stimulatory factor (USF)-1/2 as predominant phb2 CACGTG constituents in Hep3B, HeLa, and MCF7 cells. Human genes with adjacent or overlapping HRE and CACGTG motifs included with lactate dehydrogenase A (LDHA) and Bcl-2/E1B 19 kDa interacting protein 3 (BNIP3) hypoxia-induced HIF-1 targets. Parallel recruitment of HIF-1α and USF1/2a to the respective promoter chromatin was verified for all cell lines investigated. Mutual complementing (LDHA) or moderating (BNIP3) cross-talk was seen upon overexpression or silencing of HIF-1α and USF1/2a. Distinct (LDHA) or overlapping (BNIP3) promoter-binding sites for HIF-1 and USFs were subsequently characterized. We propose that, depending on abundance or activity of its protein constituents, O(2)-independent USF signaling can function to fine-tune or interfere with HIF-mediated transcription in cancer cells.

Human telomerase expression regulation

Since telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells, it has become a very promising target for anti-cancer therapy. A correlation between short telomere length and increased mortality was revealed in many studies. The telomerase expression/activity appears to be one of the most crucial factors to study to improve cancer therapy and prevention. However, this multisubunit enzymatic complex can be regulated at various levels. Thus, several strategies have been proposed to control telomerase in cancer cells such as anti-sense technology against TR and TERT, ribozymes against TERT, anti-estrogens, progesterone, vitamin D, retinoic acid, quadruplex stabilizers, telomere and telomerase targeting agents, modulation of interaction with other proteins involved in the regulation of telomerase and telomeres, etc. However, the transcription control of key telomerase subunits seems to play the crucial role in whole complexes activity and cancer cells immortality. Thus, the research of telomerase regulation can bring significant insight into the knowledge concerning stem cells metabolism but also ageing. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms at the transcription level in human that might become attractive anti-cancer therapy targets.

Molecular chaperones as a common set of proteins that regulate the invasion phenotype of head and neck cancer

PURPOSE

The goal of this study was to establish a common set of molecules that regulate cell invasion in head and neck cancer (HNC).

EXPERIMENTAL DESIGN

Five invasive sublines derived from HNC cell lines were established using the Matrigel selection method. Proteomic technology, MetaCore algorithm, and reverse transcriptase-PCR methods were used to search for molecules that contribute to the invasion phenotype. Cellular functional analyses and clinical association studies were applied to examine the significance of the molecules.

RESULTS

Fifty-two proteins were identified in more than two of the four independent proteomic experiments, including 10 (19%) molecular chaperones. Seven chaperones were confirmed to be differentially expressed in five sublines, Hsp90α, Hsp90β, Hsp90-B1/Gp96, Hsp70-A5/Grp78, and HYOU1, that upregulate, whereas Hsp60 and glucosidase-α neutral AB (GANAB) downregulate. Four molecules were further investigated. In all cell lines, knockdown of Hsp60 or GANAB and silencing of Gp96 or Grp78 considerably enhanced or reduced cell migration and invasion, respectively. Clinical association studies consistently revealed that low levels of Hsp60 or GANAB and high levels of Gp96 or Grp78 are significantly associated with advanced cancer (P < 0.001 to P = 0.047, respectively, for the four molecules) and poor survival (P < 0.001 to P = 0.025, respectively, for the four molecules).

CONCLUSION

Our study defined molecular chaperones as a common set of proteins that regulate the invasion phenotype of HNC. Loss of the tumor suppression function of Hsp60 or GANAB and acquisition of the oncogenic function of Gp96 or Grp78 contribute to aggressive cancers. These molecules may serve as prognostic markers and targets for cancer drug development.

Purification and identification of a transcription factor, USF-2, binding to E-box element in the promoter of human telomerase reverse transcriptase (hTERT)

Controversy remains about the identity of the transcription factor(s) (TFs), which bind to the two E-box elements (CACGTG, proximal and distal) of the human telomerase (hTERT) gene promoter, the essential elements in the regulation of telomerase. Here, systematic oligonucleotide trapping supplemented with 2-DE and proteomic methods was used to identify E-box binding TFs. Although insufficient purity was obtained from the proximal E-box element trapping, further fractionation provided by 2-DE and specific identification from Southwestern blotting analysis allow us to clearly identify an E-box binding TF. The protein spot was cut from 2-DE and in-gel digested with trypsin for LC-nanospray ESI-MS/MS analysis. This identified upstream stimulatory factor 2 (USF2). Western blotting analysis with specific antibodies clearly shows USF2 present in the purified fraction and USF2 antibody supershifts the specific DNA-binding complex on non-denaturing gels. Furthermore, a novel method was developed in which the specific DNA-TF complex was separated on a non-denaturing gel, the band was cut and applied to SDS-PAGE for a second dimension. Western blots of this second gel also confirmed the presence of USF2.

H. pylori-induced promoter hypermethylation downregulates USF1 and USF2 transcription factor gene expression

Helicobacter pylori infection is associated with the development of gastric adenocarcinoma. Upstream stimulatory factors USF1 and USF2 regulate the transcription of genes related to immune response, cell cycle and cell proliferation. A decrease in their expression is observed in human gastric epithelial cells infected with H. pylori, associated to a lower binding to their DNA E-box recognition site as shown by electrophoretic mobility shift assay. DNA methylation leads to gene silencing. The treatment of cells with 5'-azacytidine, an inhibitor of DNA methylation, restored the USF1 and USF2 gene expression in the presence of infection. Using promoter PCR methylation assay, a DNA hypermethylation was shown in the promoter region of USF1 and USF2 genes, in infected cells. The inhibition of USF1 and USF2 expression by H. pylori and the DNA hypermethylation in their gene promoter region was confirmed in gastric tissues isolated from 12 to 18 months infected mice. Our study demonstrated the involvement of USF1 and USF2 as molecular targets of H. pylori and the key role of DNA methylation in their regulation. These mechanisms occurred in the context of metaplastic lesions, suggesting that alteration of USF1 and USF2 levels could participate in the promotion of neoplastic process during H. pylori infection.

NFX1-123 increases hTERT expression and telomerase activity posttranscriptionally in human papillomavirus type 16 E6 keratinocytes

High-risk human papillomavirus (HPV) E6 protein induces telomerase activity through transcriptional activation of hTERT, the catalytic subunit of telomerase. HPV type 16 (HPV16) E6 interacts with two splice variants of NFX1 to increase hTERT expression. NFX1-91 is a transcriptional repressor of hTERT that is polyubiquitinated and targeted for degradation by HPV16 E6 in concert with E6-associated protein. We previously showed that NFX1-123 augments hTERT expression through binding to cytoplasmic poly(A) binding proteins (PABPCs). In this study, we determined that unlike NFX1-91, NFX1-123 is a cytoplasmic protein that colocalized with PABPCs but does not shuttle with PABPCs between the nucleus and cytoplasm. NFX1-123 requires both its PAM2 motif, with which it binds PABPCs, and its R3H domain, which has putative nucleic acid binding capabilities, to increase hTERT mRNA levels and telomerase activity in keratinocytes expressing HPV16 E6. In keratinocytes expressing HPV16 E6 and overexpressing NFX1-123, there was increased protein expression from in vitro-transcribed RNA fused with the 5' untranslated region (5' UTR) of hTERT. This posttranscriptional increase in expression required the PAM2 motif and R3H domain of NFX1-123 as well as the coexpression of HPV16 E6. NFX1-123 bound endogenous hTERT mRNA and increased its stability in HPV16 E6-expressing human foreskin keratinocytes, and NFX1-123 increased the stability of in vitro-transcribed RNA fused with the 5' UTR of hTERT. Together, these studies describe the first evidence of posttranscriptional regulation of hTERT, through the direct interaction of the cytoplasmic protein NFX1-123 with hTERT mRNA, in HPV16 E6-expressing keratinocytes.

Telomerase regulation in hematological cancers: a matter of stemness?

Human telomerase is a nuclear ribonucleoprotein enzyme complex that catalyzes the synthesis and extension of telomeric DNA. This enzyme is highly expressed and active in most malignant tumors while it is usually not or transiently detectable in normal somatic cells, suggesting that it plays an important role in cellular immortalization and tumorigenesis. As most leukemic cells are generally telomerase-positive and have often shortened telomeres, our understanding of how telomerase is deregulated in these diseases could help to define novel therapies targeting the telomere/telomerase complex. Nonetheless, considering that normal hematopoietic stem cells and some of their progeny do express a functional telomerase, it is tempting to consider such an activity in leukemias as a sustained stemness feature and important to understand how telomere length and telomerase activity are regulated in the various forms of leukemias.

Telomere instability and cancer

Telomeres are required to preserve genome integrity, chromosome stability, nuclear architecture and chromosome pairing during meiosis. Given that telomerase activity is limiting or absent in most somatic tissues, shortening of telomeres during development and aging is the rule. In vitro, telomere length operates as a mechanism to prevent uncontrolled cell growth and therefore defines the proliferation potential of a cell. In vitro, in somatic cells that have lost proliferation control, shortening of telomeres becomes the main source of genome instability leading to genetic or epigenetic changes that may allow cells to become immortal and to acquire tumor phenotypes. In vivo, mice models have indisputably shown both the protective and the promoting role of very short telomeres in cancer development. In humans, although telomere shortening and other types of telomere dysfunction probably contribute to the genome instability often detected in tumors, the specific contributions of such instability to the development of cancer remain largely undetermined.

Vitamin E suppresses telomerase activity in ovarian cancer cells

BACKGROUND

Dietary factors influence tumor formation and progression. Vitamin E is a dietary anti-oxidant capable of eliminating free radical damage, inducing apoptosis and decreasing oncogene expression. Therefore, Vitamin E may be a strong candidate for cancer prevention and/or chemotherapeutic intervention. Since telomerase, a ribonucleoprotein uniquely expressed in over 95% of cancers, plays an important role in cellular immortalization, cell growth and tumor progression, the present study investigated the effects of Vitamin E on telomerase activity in human ovarian cancer.

METHODS

Normal and malignant ovarian surface epithelial (OSE) cells were cultured with and without D-alpha tocopheryl acetate (Vitamin E). MTS and Western immunoblot assays were used to examine the effect of Vitamin E on cell growth, survival and cytotoxicity. PCR-ELISA, RT-PCR and luciferase reporter assays were performed to determine the effect of Vitamin E on telomerase activity.

RESULTS

Vitamin E suppressed endogenous telomerase activity in ovarian cancer cells, but had no similar effects in telomerase-negative normal OSE cells. Vitamin E also reduced hTERT-mRNA transcript levels and reduced hTERT promoter activity maximally targeting the -976 to -578bp promoter regions. In addition, Vitamin E improved cisplatin-mediated cytotoxicity as evidenced by reduced cancer cell growth and increased cleaved caspase 3 activity. In contrast, Vitamin E protected telomerase-negative OSE cells from cisplatin-mediated cytotoxicity as evidenced by decreased cleaved caspase 3 activity.

CONCLUSION

Our data suggest that, by suppressing telomerase activity, Vitamin E may be an important protective agent against ovarian cancer cell growth as well as a potentially effective therapeutic adjuvant.