hTERT phosphorylation by PKC is essential for telomerase holoprotein integrity and enzyme activity in head neck cancer cells

The regulations of telomerase reverse transcriptase (TERT) in cancer

Abnormal activation of telomerase occurs in most cancer types, which facilitates escaping from cell senescence. As the key component of telomerase, telomerase reverse transcriptase (TERT) is regulated by various regulation pathways. TERT gene changing in its promoter and phosphorylation respectively leads to TERT ectopic expression at the transcription and protein levels. The co-interacting factors play an important role in the regulation of TERT in different cancer types. In this review, we focus on the regulators of TERT and these downstream functions in cancer regulation. Determining the specific regulatory mechanism will help to facilitate the development of a cancer treatment strategy that targets telomerase and cancer cell senescence. As the most important catalytic subunit component of telomerase, TERT is rapidly regulated by transcriptional factors and PTM-related activation. These changes directly influence TERT-related telomere maintenance by regulating telomerase activity in telomerase-positive cancer cells, telomerase assembly with telomere-binding proteins, and recruiting telomerase to the telomere. Besides, there are also non-canonical functions that are influenced by TERT, including the basic biological functions of cancer cells, such as proliferation, apoptosis, cell cycle regulation, initiating cell formation, EMT, and cell invasion. Other downstream effects are the results of the influence of transcriptional factors by TERT. Currently, some small molecular inhibitors of TERT and TERT vaccine are under research as a clinical therapeutic target. Purposeful work is in progress.

Hypermethylation of PRKCZ Regulated by E6 Inhibits Invasion and EMT via Cdc42 in HPV-Related Head and Neck Squamous Cell Carcinoma

Purpose: To study the role of target genes with aberrant DNA methylation in HPV+ HNSCC. Methods: A HumanMethylation450 BeadChip array (Illumina) was used to identify differentially methylated genes. CCK-8, flow cytometry, wound healing, and cell invasion assays were conducted to analyze the biological roles of PRKCZ. Western blot, qRT-PCR, immunohistochemistry, and animal studies were performed to explore the mechanisms underlying the functions of PRKCZ. Results: We selected PRKCZ, which is associated with HPV infection, as our target gene. PRKCZ was hypermethylated in HPV+ HNSCC patients, and PRKCZ methylation status was negatively related to the pathological grading of HNSCC patients. Silencing PRKCZ inhibited the malignant capacity of HPV+ HNSCC cells. Mechanistically, HPV might promote DNMT1 expression via E6 to increase PRKCZ methylation. Cdc42 was required for the PRKCZ-mediated mechanism of action, contributing to the occurrence of epithelial-mesenchymal transition (EMT) in HPV+ HNSCC cells. In addition, blocking PRKCZ delayed tumor growth in HPV16-E6/E7 transgenic mice. Cdc42 expression was decreased, whereas E-cadherin levels increased. Conclusion: We suggest that PRKCZ hypermethylation induces EMT via Cdc42 to act as a potent tumor promoter in HPV+ HNSCC.

Establishment of an Efficient Immortalization Strategy Using HMEJ-Based bTERT Insertion for Bovine Cells

Immortalized cell lines have been used in a wide range of applications in research on immune disorders and cellular metabolic regulation due to the stability and uniformity of their cellular characteristics. At present, the investigation into molecular functions and signaling pathways within bovine cells remains largely limited by the lack of immortalized model cells. Current methods for immortalizing bovine cells are mainly restricted to the ectopic expression of human telomerase reverse transcriptase (hTERT) through transient transfection or virus-mediated delivery, which have defects in efficiency and reliability. In this study, we identified bovine TERT (bTERT) as a novel potent biofactor for immortalizing bovine cells with great advantages over hTERT, and established an efficient and easily manipulated strategy for the immortalization of bovine primary cells. Through the homology-mediated end-joining-based insertion of bTERT at the ROSA26 locus, we successfully generated immortalized bovine fetal fibroblast cell lines with stable characteristics. The observed limitation of this strategy in immortalizing bovine bone marrow-derived macrophages was attributed to the post-translational modification of bTERT, causing inhibited nuclear localization and depressed activity of bTERT in this terminally differentiated cell. In summary, we constructed an innovative method to achieve the high-quality immortalization of bovine primary cells, thereby expanding the prospects for the future application of immortalized bovine model cell lines.

Dual effect of Sapogenins extracted from Spirulina platensis on telomerase activity in two different cell lines

Spirulina platensis is a photosynthetic filamentous, edible cyanobacterium that is known as a superfood. In this study, sapogenins were extracted from the spirulina and the effects of these compounds on telomerase activity were evaluated in MCF7 and HDF cell lines using Telomeric Repeat Amplification Protocol and ELIZA assay. The highest increase in telomerase activity was observed at 0.004 mg/ml of sapogenin by 26% ±20.5 in MCF7 cells, while in HDF cells in the same concentration telomerase activity decreased down to 47%±0.48 and the highest inhibition of telomerase activity was observed at 0.070 mg/ml of sapogenins from Spirulina by 68%±0.43. In conclusion, a compound could play a role as a telomerase activator in one cell line while it could play another role as a telomerase inhibitor in another cell line so introducing compounds as a telomerase inhibitor (anticancer) or as a telomerase activator (anti-aging) should be done with discreet.

SUMO E3 ligase CBX4 regulates hTERT-mediated transcription of CDH1 and promotes breast cancer cell migration and invasion

hTERT, the catalytic component of the human telomerase enzyme, is regulated by post-translational modifications, like phosphorylation and ubiquitination by multiple proteins which remarkably affects the overall activity of the enzyme. Here we report that hTERT gets SUMOylated by SUMO1 and polycomb protein CBX4 acts as the SUMO E3 ligase of hTERT. hTERT SUMOylation positively regulates its telomerase activity which can be inhibited by SENP3-mediated deSUMOylation. Interestingly, we have established a new role of hTERT SUMOylation in the repression of E-cadherin gene expression and consequent triggering on the epithelial-mesenchymal-transition (EMT) program in breast cancer cells. We also observed that catalytically active CBX4, leads to retention of hTERT/ZEB1 complex onto E-cadherin promoter leading to its repression through hTERT-SUMOylation. Further through wound healing and invasion assays in breast cancer cells, we showed the tumor promoting ability of hTERT was significantly compromised upon overexpression of SUMO-defective mutant of hTERT. Thus our findings establish a new post-translational modification of hTERT which on one hand is involved in telomerase activity maintenance and on the other hand plays a crucial role in the regulation of gene expression thereby promoting migration and invasion of breast cancer cells.

Telomere-related Markers for Cancer

Telomeres are structurally nucleoprotein complexes at termini of linear chromosomes and essential to chromosome stability/integrity. In normal human cells, telomere length erodes progressively with each round of cell divisions, which serves as an important barrier to uncontrolled proliferation and malignant transformation. In sharp contrast, telomere maintenance is a key feature of human malignant cells and required for their infinite proliferation and maintenance of other cancer hallmarks as well. Thus, a telomere-based anti-cancer strategy has long been suggested. However, clinically efficient and specific drugs targeting cancer telomere-maintenance have still been in their infancy thus far. To achieve this goal, it is highly necessary to elucidate how exactly cancer cells maintain functional telomeres. In the last two decades, numerous studies have provided profound mechanistic insights, and the identified mechanisms include the aberrant activation of telomerase or the alternative lengthening of telomere pathway responsible for telomere elongation, dysregulation and mutation of telomere-associated factors, and other telomere homeostasis-related signaling nodes. In the present review, these various strategies employed by malignant cells to regulate their telomere length, structure and function have been summarized, and potential implications of these findings in the rational development of telomere-based cancer therapy and other clinical applications for precision oncology have been discussed.

Long non-coding RNA LINC01963 inhibits progression of pancreatic carcinoma by targeting miR-641/TMEFF2

PURPOSE

The aim of this study was to research the molecular mechanism of lncRNA LINC01963 in pancreatic carcinoma progression.

METHODS

Total 67 pancreatic cancer patients diagnosed and undergoing pancreatic cancer surgery in our hospital from April 2018 to April 2019 were included in this study. Pancreatic cancer cell lines including PANC-1, CFPAC-1, BxPC-3, SW1990 and AsPC1 were used. Based on bioinformatics information, pIRES2-LINC01963 plasmid, siLINC01963, miRNA mimics, miRNA inhibitor or siTMEFF2 were transfected. qRT-PCR and western blot were used to detect the expression of LINC01963, miR-641 and TMEFF2. CCK8 and Colony formation assay were processed for proliferation. Flow Cytometry Assay was processed to detect cell cycle and apoptosis. Transwell experiment was undertaken for invasion and migration. Luciferase assay and RNA Immunoprecipitation assay were used to verify the binding site among LINC01963, miR-641 and TMEFF2. Tumorigenic experiment was processed to confirm the above mechanisms in vivo.

RESULTS

lncRNA LINC01963 was confirmed to be lower expressed in pancreatic carcinoma tissues and cell lines. By up-regulating the expression of lncRNA LINC01963 in pancreatic carcinoma cell lines, colony number, cell cycle, proliferation and invasion were inhibited, while apoptosis was improved. More importantly, shLINC01963 could improve development of tumor in vivo. Besides, lncRNA LINC01963 negatively regulated the expression of miR-641, while miR-641 negatively targeted TMEFF2. Both miR-641 mimic and siTMEFF2 could reverse the effects of lncRNA LINC01963 overexpression in vitro.

CONCLUSIONS

Long non-coding RNA LINC01963 inhibits progression of pancreatic carcinoma by targeting miR-641/TMEFF2.

Targeting telomerase for its advent in cancer therapeutics

Telomerase has emerged as an important primary target in anticancer therapy. It is a distinctive reverse transcriptase enzyme, which extends the length of telomere at the 3' chromosomal end, and uses telomerase reverse transcriptase (TERT) and telomerase RNA template-containing domains. Telomerase has a vital role and is a contributing factor in human health, mainly affecting cell aging and cell proliferation. Due to its unique feature, it ensures unrestricted cell proliferation in malignancy and plays a major role in cancer disease. The development of telomerase inhibitors with increased specificity and better pharmacokinetics is being considered to design and develop newer potent anticancer agents. Use of natural and synthetic compounds for the inhibition of telomerase activity can lead to an opening of new vistas in cancer treatment. This review details about the telomerase biochemistry, use of natural and synthetic compounds; vaccines and oncolytic virus in therapy that suppress the telomerase activity. We have discussed structure-activity relationships of various natural and synthetic telomerase inhibitors to help medicinal chemists and chemical biology researchers with a ready reference and updated status of their clinical trials. Suppression of human TERT (hTERT) activity through inhibition of hTERT promoter is an important approach for telomerase inhibition.

HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells

High-mobility group box (HMGB)1 and HMGB2 proteins are the subject of intensive research because of their involvement in DNA replication, repair, transcription, differentiation, proliferation, cell signaling, inflammation, and tumor migration. Using inducible, stably transfected human embryonic stem cells (hESCs) capable of the short hairpin RNA-mediated knockdown (KD) of HMGB1 and HMGB2, we provide evidence that deregulation of HMGB1 or HMGB2 expression in hESCs and their differentiated derivatives (neuroectodermal cells) results in distinct modulation of telomere homeostasis. Whereas HMGB1 enhances telomerase activity, HMGB2 acts as a negative regulator of telomerase activity in the cell. Stimulation of telomerase activity in the HMGB2-deficient cells may be related to activation of the PI3K/protein kinase B/ glycogen synthase kinase-3β/β-catenin signaling pathways by HMGB1, augmented TERT/telomerase RNA subunit transcription, and possibly also because of changes in telomeric repeat-containing RNA (TERRA) and TERRA-polyA⁺ transcription. The impact of HMGB1/2 KD on telomerase transcriptional regulation observed in neuroectodermal cells is partially masked in hESCs by their pluripotent state. Our findings on differential roles of HMGB1 and HMGB2 proteins in regulation of telomerase activity may suggest another possible outcome of HMGB1 targeting in cells, which is currently a promising approach aiming at increasing the anticancer activity of cytotoxic agents.-Kučírek, M., Bagherpoor, A. J., Jaroš, J., Hampl, A., Štros, M. HMGB2 is a negative regulator of telomerase activity in human embryonic stem and progenitor cells.

Diverse regulatory manners of human telomerase reverse transcriptase

Human telomerase reverse transcriptase (hTERT) is the core subunit of human telomerase and plays important roles in human cancers. Aberrant expression of hTERT is closely associated with tumorigenesis, cancer cell stemness maintaining, cell proliferation, apoptosis inhibition, senescence evasion and metastasis. The molecular basis of hTERT regulation is highly complicated and consists of various layers. A deep and full-scale comprehension of the regulatory mechanisms of hTERT is pivotal in understanding the pathogenesis and searching for therapeutic approaches. In this review, we summarize the recent advances regarding the diverse regulatory mechanisms of hTERT, including the transcriptional (promoter mutation, promoter region methylation and histone acetylation), post-transcriptional (mRNA alternative splicing and non-coding RNAs) and post-translational levels (phosphorylation and ubiquitination), which may provide novel perspectives for further translational diagnosis or therapeutic strategies targeting hTERT.

Telomere length regulation through epidermal growth factor receptor signaling in cancer

Length of the telomere (TL), a structure at the tip of chromosome that protects and ensures stability, is determined by multi-protein complexes such as telosome/shelterin and telomerase. Earlier studies from our laboratory show that longer TL has potential to be positive predictive biomarker of clinical outcome to anti-epidermal growth factor receptor (EGFR) monoclonal antibody therapy in patients with KRAS WT metastatic colorectal cancer. Although there is extensive literature suggesting the role of shelterin and telomerase, not much literature exists that describes the role of EGFR and KRAS pathway in regulating TL. This detailed review focuses on an insight into various components, including proteins, enzymes and transcription factors, interlinking between EGFR pathways and telomerase that regulate TL.

Telomeres and telomerase in head and neck squamous cell carcinoma: from pathogenesis to clinical implications

Strongly associated with tobacco use, heavy alcohol consumption, and with high-risk human papillomavirus (HPV) infection, head and neck squamous cell carcinoma (HNSCC) is a frequently lethal, heterogeneous disease whose pathogenesis is a multistep and multifactorial process involving genetic and epigenetic events. The majority of HNSCC patients present with locoregional advanced stage disease and are treated with combined modality strategies that can markedly impair quality of life and elicit unpredictable results. A large fraction of those who undergo locoregional treatment and achieve a complete response later develop locoregional recurrences or second field tumors. Biomarkers that are thus able to stratify risk and enable clinicians to tailor treatment plans and to personalize post-therapeutic surveillance strategies are highly desirable. To date, only HPV status is considered a reliable independent predictor of treatment response and survival in patients with HNSCC arising from the oropharyngeal site. Recent studies suggest that telomere attrition, which may be an early event in human carcinogenesis, and telomerase activation, which is detected in up to 90 % of malignancies, could be potential markers of cancer risk and disease outcome. This review examines the current state of knowledge on and discusses the implications linked to telomere dysfunction and telomerase activation in the development and clinical outcome of HNSCC.

Variations in telomere maintenance and the role of telomerase inhibition in gastrointestinal cancer

Immortalization is an important step toward the malignant transformation of human cells and is critically dependent upon telomere maintenance. There are two known mechanisms to maintain human telomeres. The process of telomere maintenance is either mediated through activation of the enzyme telomerase or through an alternative mechanism of telomere lengthening called ALT. While 85% of all human tumors show reactivation of telomerase, the remaining 15% are able to maintain telomeres via ALT. The therapeutic potential of telomerase inhibitors is currently investigated in a variety of human cancers. Gastrointestinal tumors are highly dependent on telomerase as a mechanism of telomere maintenance, rendering telomeres as well as telomerase potential targets for cancer therapy. This article focuses on the molecular mechanisms of telomere biology and telomerase activation in gastrointestinal cancers and reviews strategies of telomerase inhibition and their potential therapeutic use in these tumor entities.

DNA methylation profiles and biomarkers of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) constitutes >90% of oral cancers and is the sixth most common malignancy among males worldwide and the fourth leading cause of death due to cancer among males in Taiwan. However, most patients do not receive a diagnosis of OSCC until the late stages, which have a lower survival rate. The use of molecular marker analysis to identify early-stage OSCC would permit optimal timing for treatments and consequently prolong survival. The aim of this study was to identify biomarkers of OSCC using the Illumina GoldenGate Methylation Cancer Panel, which comprised a total of 1,505 CpG sites covering 807 genes. Samples of buccal mucosa resected from 40 OSCC patients and normal tissue samples obtained from 15 patients (normal mucosa from OSCC patients or from patients undergoing surgery unrelated to OSCC) were analyzed. Fms-related tyrosine kinase 4 (FLT4) methylation exhibited a perfect specificity for detecting OSCC, with an area under the receiver operating characteristic curve of 0.91 for both all-stage and early-stage OSCC. Methylation of 7 genes (ASCL1, FGF3, FLT4, GAS7, KDR, TERT, and TFPI2) constitutes the top-20 panels for detecting OSCC. The top-20 panels for detecting early-stage OSCC contain 8 genes: ADCYAP1, EPHA7, FLT4, GSTM2, KDR, MT1A, NPY, and TFPI2. FLT4 RNA expression and methylation level were validated using RT-PCR and a pyrosequencing methylation assay. The median level of FLT4 expression was 2.14-fold for normal relative to OSCC tissue samples (P < 0.0001). Among the 8 pyrosequenced FLT4 CpG sites, methylation level was much higher in the OSCC samples. In conclusion, methylation statuses of selected genes, and especially FLT4, KDR, and TFPI2, might be of great potential as biomarkers for early detection of buccal OSCC.

Polo-like Kinase 1 (Plk1) Up-regulates Telomerase Activity by Affecting Human Telomerase Reverse Transcriptase (hTERT) Stability

Maintenance of telomere is regulated by active telomerase complex, including telomerase holoenzyme and its associated proteins. The activity of telomerase is precisely controlled in cells, and its dysregulation is one of the hallmarks of cancer. The telomerase catalytic subunit human telomerase reverse transcriptase (hTERT) plays a central role for telomerase activity. In this study, we indentified that Polo-like kinase 1 (Plk1) is a novel telomerase-associated protein. Plk1 can interact with hTERT independently of its kinase activity. More importantly, we found that Plk1 is associated with active telomerase complex. In addition, we demonstrated that knockdown of Plk1 caused the reduction of telomerase activity, whereas overexpression of Plk1 increased telomerase activity. Further analysis showed that overexpression of Plk1 led to a significant increase of hTERT protein by prolonging its half-life but did not affect the level of hTERT mRNA. Furthermore, we found that Plk1 enhanced the chromatin loading of hTERT and inhibited its ubiquitination. This implied that Plk1 affected hTERT stability by inhibiting its ubiquitin-mediated degradation. Collectively, these observations suggested that Plk1 is a positive modulator of telomerase by enhancing the stability of hTERT.

Multiple Pathways Control the Reactivation of Telomerase in HTLV-I-Associated Leukemia

While telomerase (hTERT) activity is absent from normal somatic cells, reactivation of hTERT expression is a hallmark of cancer cells. Telomerase activity is required for avoiding replicative senescence and supports immortalization of cellular proliferation. Only a minority of cancer cells rely on a telomerase-independent process known as alternative lengthening of telomeres, ALT, to sustain cancer cell proliferation. Multiple genetic, epigenetic, and viral mechanisms have been found to de-regulate telomerase gene expression, thereby increasing the risk of cellular transformation. Here, we review the different strategies used by the Human T-cell leukemia virus type 1, HTLV-I, to activate hTERT expression and stimulate its enzymatic activity in virally infected CD4 T cells. The implications of hTERT reactivation in HTLV-I pathogenesis and disease treatment are discussed.

Telomerase inhibition decreases alpha-fetoprotein expression and secretion by hepatocellular carcinoma cell lines: in vitro and in vivo study

Alpha-fetoprotein (AFP) is a diagnostic marker for hepatocellular carcinoma (HCC). A direct relationship between poor prognosis and the concentration of serum AFP has been observed. Telomerase, an enzyme that stabilizes the telomere length, is expressed by 90% of HCC. The aim of this study was to investigate the effect of telomerase inhibition on AFP secretion and the involvement of the PI3K/Akt/mTOR signaling pathway. Proliferation and viability tests were performed using tetrazolium salt. Apoptosis was determined through the Annexin V assay using flow cytometry. The concentrations of AFP were measured using ELISA kits. The AFP mRNA expression was evaluated using RT-PCR, and cell migration was evaluated using a Boyden chamber assay. The in vivo effect of costunolide on AFP production was tested in NSG mice. Telomerase inhibition by costunolide and BIBR 1532 at 5 and 10 μM decreased AFP mRNA expression and protein secretion by HepG2/C3A cells. The same pattern was obtained with cells treated with hTERT siRNA. This treatment exhibited no apoptotic effect. The AFP mRNA expression and protein secretion by PLC/PRF/5 was decreased after treatment with BIBR1532 at 10 μM. In contrast, no effect was obtained for PLC/PRF/5 cells treated with costunolide at 5 or 10 μM. Inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP concentration. In contrast, the MAPK/ERK pathway appeared to not be involved in HepG2/C3A cells, whereas ERK inhibition decreased the AFP concentration in PLC/PRF/5 cells. Modulation of the AFP concentration was also obtained after the inhibition or activation of PKC. Costunolide (30 mg/kg) significantly decreased the AFP serum concentration of NSG mice bearing HepG2/C3A cells. Both the inhibition of telomerase and the inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP production of HepG2/C3A and PLC/PRF/5 cells, suggesting a relationship between telomerase and AFP expression through the PI3K/Akt/mTOR pathway.

Inhibition of protein kinase C enhances angiogenesis induced by platelet-derived growth factor C in hyperglycemic endothelial cells

Background

Diabetes is a risk factor for the development of cardiovascular diseases with impaired angiogenesis. We have previously shown that platelet-derived growth factor C (PDGF-C) and its receptor, PDGF receptor α (PDGFR-α) were downregulated in ischemic limbs of diabetic mice, although the underlying mechanisms remained elusive. Protein kinase C (PKC) is a family of serine/threonine kinases and is known to be involved in angiogenesis. The purpose of this study is to elucidate the mechanisms of how PDGF-C/PDGFR-α axis is impaired in diabetes.

Methods

Human umbilical vein endothelial cells (HUVECs) and human cardiac microvascular endothelial cells (HMVECs) cultured in normoglycemic or hyperglycemic conditions were examined. We also examined the effects of PKC inhibition on the PDGF-C/PDGFR-α axis in endothelial cells exposed to hyperglycemia.

Results

Hyperglycemia inhibited proliferation and decreased viability of both HUVECs and HMVECs. Hyperglycemic endothelial cells exhibited decreased PDGFR-α expression both at messenger RNA (mRNA) and protein levels, while there was no significant change in expression of PDGF-C. We also found that expression of PKC-α, one of the PKC isoforms, was increased in hyperglycemic endothelial cells and that inhibition of PKC upregulated PDGFR-α expression in these cells. Phosphorylation of extracellular signal-regulated kinase (ERK) and Akt induced by PDGF-C was significantly attenuated in hyperglycemic endothelial cells, whereas inhibition of PKC effectively reversed these inhibitory effects. Moreover, inhibition of PKC also promoted angiogenesis induced by PDGF-C in hyperglycemic endothelial cells, which was not observed in vascular endothelial growth factor-A (VEGF-A)-induced angiogenesis.

Conclusions

These findings suggest that downregulation of the PDGF-C/PDGFR-α axis is involved in impaired angiogenesis of hyperglycemia through upregulation of PKC. Targeting PKC to restore PDGF-C signaling might be a novel therapeutic strategy for the treatment of vascular complications in diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-015-0180-9) contains supplementary material, which is available to authorized users.

The effect of Bortezomib and Rapamycin on Telomerase Activity in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a hematological malignancy with unfavorable prognosis. Novel therapeutic approaches for treating the disease are aimed at the mechanisms regulating growth signals, cellular proliferation, and survival pathways of the malignant clones. Bortezomib (Brt), a proteasome inhibitor with pleiotropic activities was shown to be active in MCL and is currently implemented in therapeutic combinations for this disease. Telomerase activity is essential for survival of malignant cells and as such is considered a valid therapeutic target. This study evaluated the effects of bortezomib on telomerase activity and its regulation in MCL cells in vitro and ex vivo.

Our study shows that bortezomib exerts a cytotoxic effect in a dose dependent manner in two MCL cell lines, with differential sensitivity. While the IC₅₀ for HBL-2 cells ranged between 2.5 ng/ml to 1.5 ng/ml during 24-72 h respectively, the IC₅₀ for the NCEB cells was twice. Bortezomib differentially inhibited telomerase activity (TA): in HBL-2 cells there was a decline of 20%-55% during 24-72 h respectively. However in NCEB cells the decline was much smaller, and did not exceed 25%. Inhibition of telomerase activity is shown to be operated by two separate mechanisms: reduction of the hTERT mRNA expression (controlled by the binding of transcription factors) and reduction in phosphorylation of the catalytic subunit of hTERT by its kinases, AKT and PKCα.

A decrease in telomerase activity was demonstrated also in mononuclear cells, isolated from three MCL patients following incubation of the cells in the presence of bortezomib for 24-72 h. In one patient the decrease in TA ranged between 17%-37% respectively, in the second patient between 63%-76% and in the third patient between 70-100% for 24-72 h respectively.

The current study indicates that a combination of bortezomib and rapamycin, (an m-Tor pathway inhibitor used in MCL treatment) induced synergistic inhibition of telomerase activity. In HBL-2 cells, the combined treatment of bortezomib and rapamycin decreased TA by 80% compared to the expected value (40%) and for NCEB cells a similar trend was observed. In contrast, there was neither additive nor synergistic effect of this combination on cell proliferation.

In the light of the crucial role of telomerase in cancer cells, it was important to characterize the possible relations between telomerase and bortezomib and to distinguish the biochemical mechanisms of its regulation and its interactions with other signal transduction inhibitors such as rapamycin. The results of this work encourage the in vivo examination of the therapeutic potential of the combination of bortezomib and rapamycin in Mantle Cell Lymphoma patients.

Protein kinase C delta (PKCδ) splice variant modulates senescence via hTERT in adipose-derived stem cells

BACKGROUND

Adipose-derived stem cells (ADSC) were isolated and characterized from lean and obese subjects. We previously reported that distinct differences were observed in differentiating lean and obese preadipocytes. Protein kinase C delta (PKCδ) is alternatively spliced and has important roles in apoptosis. PKCδI promotes apoptosis and PKCδVIII promotes survival. Our previous data indicated an increase in the survival kinase, PKCδVIII in ADSC derived from an obese donor. We also determined that obese adipocytes were resistant to apoptosis. Here, we determine the relationship between a survival kinase PKCδVIII and hTERT expression in adipose derived stem cells from a lean and obese subject.

METHODS

We evaluated the telomerase activity and human telomerase reverse transcriptase (hTERT) expression in lean and obese ADSC. The lean and obese ADSC were purchased as cryopreserved cells from ZenBio™ (Research Triangle Park, NC, USA). Analyses were performed using PRISM™ software and analyzed using two-tailed Student's t-test.

RESULTS

We observed an increase in telomerase in differentiating obese ADSC using western blot analysis. We determined the levels of hTERT splice variants. hTERT α+/β+ splice variant was increased after transfected of PKCδVIII. We next determined whether PKCδVIII over-expression affected the levels of telomerase. The results indicate an increase in telomerase with PKCδVIII over-expression.

CONCLUSIONS

Over-expression of PKCδVIII in lean ADSC substantially increased expression of hTERT and telomerase. The decreased senescence seen in obese ADSC may in part be attributed to PKCδVIII. Obese ADSC undergo lower senescence and may have increased growth potential. These results propose a larger epigenetic modification in obese ADSC compared to lean ADSC.

Exploring the effects of isothiocyanates on chemotherapeutic drugs

INTRODUCTION

Chemoprevention has emerged as a promising strategy to reduce the risk and to control cancer. In this context, isothiocyanates (ITCs), found in abundance in the form of glucosinolates in cruciferous vegetables, have gained increasing consideration for their chemopreventive activity. ITCs exert their effects mainly by inducing carcinogen metabolism or by inhibiting tumor cell proliferation.

AREAS COVERED

In recent years, novel combination treatments, by coupling chemopreventive agents and typical chemotherapeutics, have been exploited to increase the antitumor activities. The aim of this article is to examine the foremost studies carried out, so far, on the effects of dietary and synthetic ITCs on different signaling pathways involved in the pharmacokinetics and pharmacodynamics of chemotherapeutic agents, in order to enhance their effectiveness.

EXPERT OPINION

Undoubtedly, the beneficial anticarcinogenic potential of ITCs, both singly and in combination, has emerged in in vitro and in vivo studies. However, only a few clinical trials have been carried out so far with ITCs, which try to better define both the pharmacokinetic and pharmacodynamic impacts in humans. More toxicological evaluations after long-term administration of ITCs in different species are required for the clinical development of ITCs as anticarcinogenic agents.

The role of the JAK-STAT pathway and related signal cascades in telomerase activation during the development of hematologic malignancies

Telomerase, comprising a reverse transcriptase protein (TERT) and an RNA template, plays a critical role during senescence and carcinogenesis; however, the mechanisms by which telomerase is regulated remain to be elucidated. Several signaling pathways are involved in the activation of TERT at multistep levels. The JAK-STAT pathway is indispensable for mediating signals through growth factor and cytokine receptors during the development of hematopoietic cells, and its activity is frequently upregulated in hematological malignancies. Here, we review the role of the JAK-STAT pathway and related signaling cascades in the regulation of telomerase in hematological malignancies.

DSG3 facilitates cancer cell growth and invasion through the DSG3-plakoglobin-TCF/LEF-Myc/cyclin D1/MMP signaling pathway

Desmoglein 3 (DSG3) is a component of the desmosome, which confers strong cell-cell adhesion. Previously, an oncogenic function of DSG3 has been found in head neck cancer (HNC). Here, we investigated how this molecule contributes to the malignant phenotype. Because DSG3 is associated with plakoglobin, we examined whether these phenotypic alterations were mediated through the plakoglobin molecule. Immunoprecipitation and immunofluorescence staining revealed that DSG3 silencing disrupted its interaction with plakoglobin and induced plakoglobin translocation from the cytoplasm to the nucleus. Knockdown of DSG3 significantly increased the interaction of plakoglobin with the transcriptional factor TCF and suppressed the TCF/LEF transcriptional activity. These effects further conferred to reduced expression of the TCF/LEF downstream target genes, including c-myc, cyclin D1, and MMP-7. Functional analyses showed that DSG3 silencing reduced cell growth and arrested cells at G0/G1 phase. Besides, cell migration and invasion abilities were also decreased. These cellular results were confirmed using tumor xenografts in mice, as DSG3 silencing led to the suppressed tumor growth, plakoglobin translocation and reduced expression of TCF/LEF target genes in tumors. Therefore, our study shows that the desmosomal protein DSG3 additionally functions to regulate malignant phenotypes via nuclear signaling. In conclusion, we found that DSG3 functions as an oncogene and facilitates cancer growth and invasion in HNC cells through the DSG3-plakoglobin-TCF/LEF pathway.

Histone deacetylase inhibitor AR42 regulates telomerase activity in human glioma cells via an Akt-dependent mechanism

Epigenetic regulation via abnormal activation of histone deacetylases (HDACs) is a mechanism that leads to cancer initiation and promotion. Activation of HDACs results in transcriptional upregulation of human telomerase reverse transcriptase (hTERT) and increases telomerase activity during cellular immortalization and tumorigenesis. However, the effects of HDAC inhibitors on the transcription of hTERT vary in different cancer cells. Here, we studied the effects of a novel HDAC inhibitor, AR42, on telomerase activity in a PTEN-null U87MG glioma cell line. AR42 increased hTERT mRNA in U87MG glioma cells, but suppressed total telomerase activity in a dose-dependent manner. Further analyses suggested that AR42 decreases the phosphorylation of hTERT via an Akt-dependent mechanism. Suppression of Akt phosphorylation and telomerase activity was also observed with PI3K inhibitor LY294002 further supporting the hypothesis that Akt signaling is involved in suppression of AR42-induced inhibition of telomerase activity. Finally, ectopic expression of a constitutive active form of Akt restored telomerase activity in AR42-treated cells. Taken together, our results demonstrate that the novel HDAC inhibitor AR42 can suppress telomerase activity by inhibiting Akt-mediated hTERT phosphorylation, indicating that the PI3K/Akt pathway plays an important role in the regulation of telomerase activity in response to this HDAC inhibitor.

Super-telomeres in transformed human fibroblasts

Telomere length maintenance is critical for organisms' long-term survival and cancer cell proliferation. Telomeres are kept within species-specific length ranges by the interplay between telomerase activity and telomeric chromatin organization. In this paper, we exploited telomerase immortalized human fibroblasts (cen3tel) that gradually underwent neoplastic transformation during culture propagation to study telomere composition and length regulation during the transformation process. Just after telomerase catalytic subunit (hTERT) expression, cen3tel telomeres shortened despite the presence of telomerase activity. At a later stage and concomitantly with transformation, cells started elongating telomeres, which reached a mean length greater than 100kb in about 900 population doublings. Super-telomeres were stable and compatible with cell growth and tumorigenesis. Telomere extension was associated with increasing levels of telomerase activity that were linked to the deregulation of endogenous telomerase RNA (hTERC) and exogenous telomerase reverse transcriptase (hTERT) expression. Notably, the increase in hTERC levels paralleled the increase in telomerase activity, suggesting that this subunit plays a role in regulating enzyme activity. Telomeres ranging in length between 10 and more than 100kb were maintained in an extendible state although TRF1 and TRF2 binding increased with telomere length. Super-telomeres neither influenced subtelomeric region global methylation nor the expression of the subtelomeric gene FRG1, attesting the lack of a clear-cut relationship between telomere length, subtelomeric DNA methylation and expression in human cells. The cellular levels of the telomeric proteins hTERT, TRF1, TRF2 and Hsp90 rose with transformation and were independent of telomere length, pointing to a role of these proteins in tumorigenesis.

Increased mitotic rate coincident with transient telomere lengthening resulting from pim-1 overexpression in cardiac progenitor cells

Cardiac regeneration following myocardial infarction rests with the potential of c-kit+ cardiac progenitor cells (CPCs) to repopulate damaged myocardium. The ability of CPCs to reconstitute the heart is restricted by patient age and disease progression. Increasing CPC proliferation, telomere length, and survival will improve the ability of autologous CPCs to be successful in myocardial regeneration. Prior studies have demonstrated enhancement of myocardial regeneration by engineering CPCs to express Pim-1 kinase, but cellular and molecular mechanisms for Pim-1-mediated effects on CPCs remain obscure. We find CPCs rapidly expand following overexpression of cardioprotective kinase Pim-1 (CPCeP), however, increases in mitotic rate are short-lived as late passage CPCePs proliferate similar to control CPCs. Telomere elongation consistent with a young phenotype is observed following Pim-1 modification of CPCeP; in addition, telomere elongation coincides with increased telomerase expression and activity. Interestingly, telomere length and telomerase activity normalize after several rounds of passaging, consistent with the ability of Pim-1 to transiently increase mitosis without resultant oncogenic transformation. Accelerating mitosis in CPCeP without immortalization represents a novel strategy to expand the CPC population in order to improve their therapeutic efficacy. Stem Cells2012;30:2512–2522

Computationally designed peptide inhibitors of the ubiquitin E3 ligase SCF(Fbx4)

A structure-based computational approach was used to rationally design peptide inhibitors that can target an E3 ligase (SCF(Fbx4) )-substrate (TRF1) interface and subsequent ubiquitylation. Characterization of the inhibitors demonstrates that our sequence-optimization protocol results in an increase in peptide-TRF1 affinity without compromising peptide-protein specificity.

Network analysis of the focal adhesion to invadopodia transition identifies a PI3K-PKCα invasive signaling axis

In cancer, deregulated signaling can produce an invasive cellular phenotype. We modeled the invasive transition as a theoretical switch between two cytoskeletal structures: focal adhesions and extracellular matrix-degrading invadopodia. We constructed molecular interaction networks of each structure and identified upstream regulatory hubs through computational analyses. We compared these regulatory hubs to the status of signaling components from head and neck carcinomas, which led us to analyze phosphatidylinositol 3-kinase (PI3K) and protein kinase C α (PKCα). Consistent with previous studies, PI3K activity promoted both the formation and the activity of invadopodia. We found that PI3K induction of invadopodia was increased by overexpression of SH2 (Src homology 2) domain-containing inositol 5'-phosphatase 2 (SHIP2), which converts the phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] that is produced by PI3K activity to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], which is believed to promote invadopodia formation. Knockdown of PKCα had divergent effects on invadopodia formation, depending on the status of PI3K. Loss of PKCα inhibited invadopodia formation in cells with wild-type PI3K pathway status. Conversely, in cells with constitutively active PI3K (through activating PI3K mutants or lacking the endogenous opposing enzyme PTEN), PKCα knockdown increased invadopodia formation. Mechanistic studies revealed a negative feedback loop from PKCα that dampened PI3K activity and invasive behavior in cells with genetic hyperactivation of the PI3K pathway. These studies demonstrated the potential of network modeling as a discovery tool and identified PI3K and PKCα as interacting regulators of invasive behavior.

The isoprenoid perillyl alcohol inhibits telomerase activity in prostate cancer cells

Isoprenoids are recognized for their ability to suppress carcinogenic processes in vivo and in vitro. We previously established that the isoprenoid, perillyl alcohol, acted mechanistically on translation of specific proteins through modulation of mechanistic target of rapamycin (mTOR) signaling. Telomerase-the enzyme responsible for immortalizing cells through the addition of telomeric repeats-is de-repressed early in an aspiring cancer cell. Here the effects of biologically-relevant concentrations and short incubations (1-16 h) of perillyl alcohol or the mTOR inhibitor, rapamycin, on telomerase activity were examined in prostate cancer cell lines. A rapid suppression of telomerase activity was observed (from ∼65% to >95%) determined by real-time quantitative telomerase repeat amplification protocol and confirmed by polyacrylamide gel-analysis. Using real-time reverse transcriptase-PCR, we demonstrated that human telomerase reverse transcriptase (hTERT) mRNA levels were unaltered. Western blot analysis revealed that hTERT protein levels decreased in response to perillyl alcohol or rapamycin. This decrease was partially blocked by pretreatment with a proteasome inhibitor MG-132, indicating that proteasomal degradation contributed to the loss of hTERT protein. No change in hTERT phosphorylation at Ser824 was observed, indicating the absence of cellular hTERT protein redistribution. These findings provide evidence for a unique link between nutrient- and macrolide-mediated regulation of mTOR and hTERT, a key enzyme that regulates DNA structure and stability.

Apigenin decreases cell viability and telomerase activity in human leukemia cell lines

Recent studies have shown that apigenin (4',5,7-trihydroxyflavone inhibits human malignant cancer cell growth through cell cycle arrest and apoptosis. However, the underlying relationship between apoptosis and telomerase activity in response to apigenin exposure is not well understood. In this study, we found that apigenin significantly induces direct cytotoxicity in human leukemia cells (U937, THP-1 and HL60) through activation of the caspase pathway. As we presumed, treatment with apigenin was found to increase the level of intracellular reactive oxygen species (ROS), whereas pretreatment with antioxidants, N-acetyl-cysteine (NAC) or glutathione (GSH), completely attenuated ROS generation. Surprisingly, these antioxidants did not promote recuperation from apigenin-induced cell death. We further showed that apigenin downregulates telomerase activity in caspase-dependent apoptosis and observed that apigenin dosing results in downregulation of telomerase activity by suppression of c-Myc-mediated telomerase reverse transcriptase (hTERT) expression. In addition, treatment of apigenin-dosed cells with the two antioxidants did not restore telomerase activity. Taken together, this data suggests that ROS is not essential for suppression of apigenin-mediated apoptosis associated with the activation of caspases and regulation of telomerase activity via suppression of hTERT. We conclude that apigenin has a direct cytotoxic effect and the loss of telomerase activity in leukemia cells.

Molecular regulation of telomerase activity in aging

The process of aging is mitigated by the maintenance and repair of chromosome ends (telomeres), resulting in extended lifespan. This review examines the molecular mechanisms underlying the actions and regulation of the enzyme telomerase reverse transcriptase (TERT), which functions as the primary mechanism of telomere maintenance and regulates cellular life expectancy. Underpinning increased cell proliferation, telomerase is also a key factor in facilitating cancer cell immortalization. The review focuses on aspects of hormonal regulations of telomerase, and the intracellular pathways that converge to regulate telomerase activity with an emphasis on molecular interactions at protein and gene levels. In addition, the basic structure and function of two key telomerase enzyme components-the catalytic subunit TERT and the template RNA (TERC) are discussed briefly.

High-throughput RNAi screening reveals novel regulators of telomerase

Telomerase is considered an attractive anticancer target on the basis of its common and specific activation in most human cancers. While direct telomerase inhibition is being explored as a therapeutic strategy, alternative strategies to target regulators of telomerase that could disrupt telomere maintenance and cancer cell proliferation are not yet available. Here, we report the findings of a high-throughput functional RNA interference screen to globally profile the contribution of kinases to telomerase activity (TA). This analysis identified a number of novel telomerase modulators, including ERK8 kinase, whose inhibition reduces TA and elicited characteristics of telomere dysfunction. Given that kinases represent attractive drug targets, we addressed the therapeutic implications of our findings, such as demonstrating how limiting TA via kinase blockade could sensitize cells to inhibition of the telomere-associated protein tankyrase. Taken together, our findings suggest novel combinatorial approaches to targeting telomere maintenance as a strategy for cancer therapy.

Human telomerase reverse transcriptase regulates cyclin D1 and G1/S phase transition in laryngeal squamous carcinoma

CONCLUSION

Down-regulating human telomerase reverse transcriptase (hTERT) expression will significantly suppress the cell viability of laryngeal squamous cell carcinoma Hep-2, which was mainly due to the inhibition of cyclin D1 and thus G1/S phase transition.

OBJECTIVE

Small-interfering RNA (siRNA) targeting hTERT can arrest the cell cycle of cancer cells, as well as inhibit telomerase activity and cell viability. However, the precise mechanisms still remain unclear. Here, we investigate the regulatory role of hTERT in cyclin D1 in laryngeal squamous carcinoma.

METHODS

Short hairpin RNAs (shRNAs) specifically targeting hTERT were constructed and expressed in Hep-2 cells. Cell proliferation was measured by CCK-8 assay. Expression of hTERT, cyclin D1, cyclin E, c-myc, and GAPDH was detected by RT-PCR and Western blot; cyclin D1 and hTERT proteins in laryngeal squamous carcinoma tissue microarray were analyzed by quantum dots immunofluorescence.

RESULTS

hTERT silence by shRNAs decreased the proliferation of Hep-2 cells by 76.8% at day 4 (96 h). Furthermore, transfection with hTERT shRNA for 48 h also significantly reduced expression of hTERT, cyclin D1, and c-Myc, but not cyclin E. Quantum dots immunofluorescence analysis of 36 laryngeal squamous carcinoma tissue samples found that hTERT expression was highly correlated with cyclin D1 expression.

EGFR overexpression induces activation of telomerase via PI3K/AKT-mediated phosphorylation and transcriptional regulation through Hif1-alpha in a cellular model of oral-esophageal carcinogenesis

Telomerase plays an important role during immortalization and malignant transformation as crucial steps in the development of human cancer. In a cellular model of oral-esophageal carcinogenesis, recapitulating the human disease, immortalization occurred independent of the activation of telomerase but through the recombination-based alternative lengthening of telomeres (ALT). In this stepwise model, additional overexpression of EGFR led to in vitro transformation and activation of telomerase with homogeneous telomere elongation in already immortalized oral squamous epithelial cells (OKF6-D1_dnp53). More interestingly, EGFR overexpression activated the PI3K/AKT pathway. This strongly suggested a role for telomerase in tumor progression in addition to just elongating telomeres and inferring an immortalized state. Therefore, we sought to identify the regulatory mechanisms involved in this activation of telomerase and in vitro transformation induced by EGFR. In the present study we demonstrate that telomerase expression and activity are induced through both direct phosphorylation of hTERT by phospho-AKT as well as PI3K-dependent transcriptional regulation involving Hif1-alpha as a key transcription factor. Furthermore, EGFR overexpression enhanced cell cycle progression and proliferation via phosphorylation and translocation of p21. Whereas immortalization was induced by ALT, in vitro transformation was associated with telomerase activation, supporting an additional role for telomerase in tumor progression besides elongating telomeres.

Human telomerase activity regulation

Telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells. Thus, it has become a very promising target for anticancer therapy. The cell proliferative potential can be limited by replication end problem, due to telomeres shortening, which is overcome in cancer cells by telomerase activity or by alternative telomeres lengthening (ALT) mechanism. However, this multisubunit enzymatic complex can be regulated at various levels, including expression control but also other factors contributing to the enzyme phosphorylation status, assembling or complex subunits transport. Thus, we show that the telomerase expression targeting cannot be the only possibility to shorten telomeres and induce cell apoptosis. It is important especially since the transcription expression is not always correlated with the enzyme activity which might result in transcription modulation failure or a possibility for the gene therapy to be overcome. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms that take place after telomerase subunits coding genes transcription. Thus we show the possible mechanisms of telomerase activity regulation which might become attractive anticancer therapy targets.

Mixed pH-sensitive polymeric micelles for combination drug delivery

PURPOSE

To prepare mixed polymeric micelles that can carry two different drugs, doxorubicin (DOX) and 17-hydroxyethylamino-17-demethoxygeldanamycin (GDM-OH), for combination cancer chemotherapy.

METHODS

The pH-sensitive micelles were prepared from poly(ethylene glycol)-poly(aspartate hydrazide) block copolymers to which either DOX or GDM-OH is conjugated through acid-labile hydrazone bond (individual micelles). Mixed micelles were formed not only by simply mixing two different individual micelles in aqueous solutions (aqueous mixed micelles) but also by evaporating organic solvents from the organic/aqueous mixed solvents in which two block copolymers possessing different drugs were dissolved homogeneously (organic mixed micelles). Particle size measurements, pH-dependent drug release tests, cytotoxicity assays and western blot analysis were subsequently conducted.

RESULTS

Individual and aqueous/organic mixed micelles showed clinically relevant particle size (<100 nm) and pH-dependent drug release patterns. Mixed polymer micelles suppress cancer cell growth effectively in a drug concentration, mixing method and schedule-dependent way.

CONCLUSION

Combination chemotherapy using polymeric micelles seems to minimize a schedule-dependent change in combination drug efficacy in comparison to drug combination using DMSO formulations.

Proteomics of the radioresistant phenotype in head-and-neck cancer: Gp96 as a novel prediction marker and sensitizing target for radiotherapy

PURPOSE

Radiotherapy is an integral part of the treatment modality for head-neck cancer (HNC), but in some cases the disease is radioresistant. We designed this study to identify molecules that may be involved in this resistance.

METHODS AND MATERIALS

Two radioresistant sublines were established by fractionated irradiation of the HNC cell lines, to determine differentially proteins between parental and radioresistant cells. Proteomic analysis and reverse-transcription polymerase chain reaction were used to identify and confirm the differential proteins. The siRNA knockdown experiments were applied to examine cellular functions of a radioresistant gene, with investigation of the alterations in colonogenic survival, cell cycle status, and reactive oxygen species levels. Xenografted mouse tumors were studied to validate the results.

RESULTS

IN all, 64 proteins were identified as being potentially associated with radioresistance, which are involved in several cellular pathways, including regulation of stimulus response, cell apoptosis, and glycolysis. Six genes were confirmed to be differentially expressed in both radioresistant sublines, with Gp96, Grp78, HSP60, Rab40B, and GDF-15 upregulated, and annexin V downregulated. Gp96 was further investigated for its functions in response to radiation. Gp96-siRNA transfectants displayed a radiation-induced growth delay, reduction in colonogenic survival, increased cellular reactive oxygen species levels, and increased proportion of the cells in the G2/M phase. Xenograft mice administered Gp96-siRNA showed significantly enhanced growth suppression in comparison with radiation treatment alone (p = 0.009).

CONCLUSIONS

We identified 64 proteins and verified 6 genes that are potentially involved in the radioresistant phenotype. We further demonstrated that Gp96 knockdown enhances radiosensitivity both in cells and in vivo, which may lead to a better prognosis of HNC treatment.

The intrabody targeting of hTERT attenuates the immortality of cancer cells

hTERT (human telomerase reverse transcriptase) plays a key role in the process of cell immortalization. Overexpression of hTERT has been implicated in 85% of malignant tumors and offers a specific target for cancer therapy. In this paper, we describe an effective approach using a single-chain variable fragment (scFv) intrabody derived from monoclonal hybridoma directed against hTERT to attenuate the immortalization of human uterine cervix and hepatoma cells. The scFv we constructed had a high affinity to hTERT, and specifically neutralized over 70% of telomere synthesis activity, thereby inhibiting the viability and proliferation of the cancer cells. Our results indicate that this anti-hTERT intrabody is a promising tool to target hTERT and intervene in the immortalization process of cancer cells.

Glucose-regulated protein 78 regulates multiple malignant phenotypes in head and neck cancer and may serve as a molecular target of therapeutic intervention

Glucose-regulated protein 78 (Grp78) is an endoplasmic reticulum chaperone protein and is overexpressed in various cancers. However, it is unclear how significance of this molecule play an active role contributing to the oncogenic effect of head and neck cancer (HNC). To investigate the potential function of Grp78, six HNC cell lines were used. We found that Grp78 is highly expressed in all six cell lines and many of the proteins were localized in the periphery regions, implying other function of this molecule aside from endoplasmic reticulum stress response. Knockdown of Grp78 by small interfering RNA significantly reduced cell growth and colony formation to 53% to 12% compared with that of controls in all six HNC cell lines. Using in vitro wound healing and Matrigel invasion assays, we found that cell migration and invasive ability were also inhibited to 23% to 2% in all these cell lines tested. In vivo xenograft studies showed that administration of Grp78-small interfering RNA plasmid into HNC xenografts significantly inhibited both tumor growth in situ (>60% inhibition at day 34) and liver metastasis (>90% inhibition at day 20). Our study showed that Grp78 actively regulates multiple malignant phenotypes, including cell growth, migration, and invasion. Because knockdown Grp78 expression succeeds in the reduction of tumor growth and metastatic potential, this molecule may serve as a molecular target of therapeutic intervention for HNC.

Central role of PI3K in transcriptional activation of hTERT in HTLV-I-infected cells

The persistence of human T-cell leukemia/lymphoma virus-I (HTLV-I)-infected cells is dependent upon clonal expansion and up-regulation of telomerase (hTERT). We have previously found that in interleukin (IL)-2-independent transformed HTLV-I cells, Tax strongly activates the hTERT promoter through nuclear factor-kappaB (NF-kappaB)-mediated Sp1 and c-Myc activation. In IL-2-dependent cells and adult T-cell leukemia/lymphoma (ATLL) patient samples, however, Tax expression is very low to undetectable, yet these cells retain strong telomerase activity. This suggests the existence of compensatory mechanisms in IL-2-dependent cells and ATLL patients. In this study, we demonstrate that telomerase activity is significantly decreased upon IL-2 withdrawal in immortalized HTLV-I cell lines. Inhibition of PI3K or AKT signaling pathways reduced telomerase activity in HTLV-I cells. We found that IL-2/IL-2R signaling was associated with a PI3K-dependent/AKT-independent transcriptional up-regulation of the endogenous hTERT promoter. We found that activation of the PI3K pathway mediated cytoplasmic retention of the Wilms tumor (WTI) protein, which strongly suppressed the hTERT promoter. The importance of this regulatory pathway for telomerase expression is underscored by findings that the PI3K pathway is commonly found activated in cancer cells.

Regulation of telomerase and telomeres: human tumor viruses take control

Human tumor viruses are responsible for one-fifth of all cancers worldwide. These viruses have evolved multiple strategies to evade immune defenses and to persist in the host by establishing a latent infection. Proliferation is necessary for pretumor cells to accumulate genetic alterations and to acquire a transformed phenotype. However, each cell division is associated with a progressive shortening of the telomeres, which can suppress tumor development by initiating senescence and irreversible cell cycle arrest. Therefore, the ability of virus-infected cells to circumvent the senescence program is essential for the long-term survival and proliferation of infected cells and the likelihood of transformation. We review the multiple strategies used by human DNA and RNA tumor viruses to subvert telomerase functions during cellular transformation and carcinogenesis. Epstein-Barr virus, Kaposi sarcoma-associated herpesvirus, human papillomavirus, hepatitis B virus, hepatitis C virus, and human T-cell leukemia virus-1 each can increase transcription of the telomerase reverse transcriptase. Several viruses appear to mediate cis-activation or enhance epigenetic activation of telomerase transcription. Epstein-Barr virus and human papillomavirus have each developed posttranscriptional mechanisms to regulate the telomerase protein. Finally, some tumor virus proteins can also negatively regulate telomerase transcription or activity. It is likely that, as future studies further expose the strategies used by viruses to deregulate telomerase activity and control of telomere length, novel mechanisms will emerge and underscore the importance of increased telomerase activity in sustaining virus-infected cells and its potential in therapeutic targeting.

Latent membrane protein 1 encoded by Epstein-Barr virus induces telomerase activity via p16INK4A/Rb/E2F1 and JNK signaling pathways

Elevated telomerase activity is observed in about 90% of human cancers. This activity correlates strictly with human telomerase reverse transcriptase (hTERT). Previously, it was shown that the Epstein-Barr virus-encoded latent membrane protein 1 (LMP1) induced telomerase activity in nasopharyngeal carcinoma cells. In this study, it was indicated that LMP1 inhibited p16(INK4A) expression, promoted phosphorylation of p105 Rb and upregulated E2F1 expression as well as transactivation, and overexpression of E2F1 alone was sufficient to upregulate telomerase activity. The JNK kinase cascade could also promote telomerase activity modulated by LMP1, that inhibition of JNK by JIP and TAM 67 dominant negative mutant abrogated telomerase activity. The data show that p16(INK4A)/Rb/E2F1 and JNK signaling pathways are involved in the regulation of telomerase activity via LMP1. The present study provides new perspectives on carcinogenesis of nasopharyngeal carcinoma that may be exploited for novel therapeutic strategies.

Differentially expressed genes in radioresistant nasopharyngeal cancer cells: gp96 and GDF15

Radiotherapy is the major treatment modality for nasopharyngeal cancer (NPC), but in some cases, the disease is radioresistant. We designed this study to identify genes that may be involved in this resistance. We first established two radioresistant subclone cell lines derived from NPC parental cell lines (NPC-076 and NPC-BM1) by treating the cells with four rounds of sublethal ionizing radiation. cDNA microarray analysis was then done, comparing the two resistant cell lines with their corresponding parental cell lines. Seven genes were found to be up-regulated in radioresistant subclones, including gp96 and GDF15, which had shown highest overexpressions. We constructed small interfering RNA plasmids (gp96si and GDF15si) and transfected them into NPC cells to knock down these genes and examine whether this changed their response to radiation. Both gp96si and GDF15si transfectants had radiation-induced growth delay and reduction in colonogenic survival compared with control cells. Knockdown of either gp96 or GDF15 increased the proportion of the cells in G(2)-M phase, the most radiosensitive phase of the cell cycle. We have therefore identified at least two genes, gp96 and GDF15, involved in radioresistance of NPC cell lines and showed that knockdown of the genes enhances radiosensitivity.

Targeting telomeres and telomerase

Telomeres and telomerase represent, at least in theory, an extremely attractive target for cancer therapy. The objective of this review is to present the latest view on the mechanism(s) of action of telomerase inhibitors, with an emphasis on a specific class of telomere ligands called G-quadruplex ligands, and to discuss their potential use in oncology.

DSG3 is overexpressed in head neck cancer and is a potential molecular target for inhibition of oncogenesis

To identify genes that could potentially serve as molecular therapeutic markers for human head and neck cancer (HNC), we employed differential display analysis to compare the gene expression profiles between HNC and histopathologically normal epithelial tissues. Using reverse transcription-polymerase chain reaction and Western blot analysis, desmoglein 3 (DSG3) was identified as being differentially expressed at both the RNA and protein levels. Of 56 patients assayed, 34 (61%) had overexpression of DSG3, which correlated statistically with T stage (P=0.009), N stage (P=0.047), overall stage (P=0.011), tumor depth (P=0.009) and extracapsular spread in lymph nodes (P=0.044), suggesting that DSG3 participates in carcinogenesis of HNC. Consistent with the clinical findings, inhibition of DSG3 by RNA interference (RNAi) significantly reduced cell growth and colony formation to 57-21% in three HNC cell lines. Use of an in vitro wound healing and Matrigel invasion assays, we found that cell migration and invasive ability were also inhibited to 30-48% in three cell lines tested. An in vivo xenograft study showed that administration of DSG3-RNAi plasmid significantly inhibited tumor growth for 2 months in BALB/C nude mice. In conclusion, DSG3 is identified overexpressed in HNC, with the degree of overexpression associated with clinicopathologic features of the tumor. Inhibition of DSG3 significantly suppresses carcinogenic potential in cellular and in vivo animal studies. These findings suggest that DSG3 is a potential molecular target in the development of adjuvant therapy for HNC.

Inhibitory effects of antisense phosphorothioate oligodeoxynucleotides on pancreatic cancer cell Bxpc-3 telomerase activity and cell growth in vitro

AIM: To investigate the effect of telomerase hTERT gene antisense oligonucleotide (hTERT-ASO) on proliferation and telomerase activity of pancreatic cancer cell line Bxpc-3.

METHODS: MTT assay was used to detect the effect of different doses of hTERT-ASO on proliferation of Bxpc-3 cell for different times. To study the anti-tumor activity, the cells were divided into there groups: Control group (pancreatic cancer cell Bxpc-3); antisense oligonucleotide (hTERT-ASO) group; and nosense oligonucleotide group decorated with phosphorothioate. Telomerase activity was detected using TRAP-PCR-ELISA. Cell DNA distribution was examined using flow cytometry assay. Cell apoptosis was observed by transmission electron microscope in each group.

RESULTS: After treatment with 6 mmol/L hTERT-ASO, cell proliferation was inhibited in dose- and time-dependent manner. The telomerase activity decreased after treatment with hTERT-ASO for 72 h. Flow cytometry showed the cell number of G₀/G₁ phase increased from 2.7% to 14.7%, the cell number of S phase decreased from 72.7% to 51.0%, and a sub-G1 stage cell apoptosis peak appeared in front of G1 stage.

CONCLUSION: Telomerase antisense oligodeoxy-nucleotide can inhibit the proliferation of pancreatic cancer cell line Bxpc-3 and decrease the telomerase activity and increase cell apoptosis rate in vitro.