Gene expression for suppressors of telomerase activity (telomeric-repeat binding factors) in breast cancer

Telomere shortening and expression of TRF1 and TRF2 in uterine leiomyoma

Uterine leiomyoma is a benign smooth muscle tumor of the uterus that can exhibit histopathological traits that mimic malignancy. Telomere shortening is an early event in tumorigenesis and telomerase activation facilitates tumor progression later in the course of carcinogenesis. Telomeric repeat‑binding factor (TRF)1 and TRF2 protect telomeres, and their gene expression levels are dysregulated in various cancer types. However, the roles of telomeres and telomere protection proteins in uterine leiomyoma remain largely unknown. In this study, telomere length and the mRNA levels of various telomere‑related genes in normal tissues and leiomyoma were determined, and their relationships were evaluated. Uterine leiomyoma and normal myometrium were surgically obtained from 18 and 13 patients, respectively. Telomere length and gene expression were determined by Southern blot analysis and reverse transcription‑quantitative PCR, respectively. In matched samples, telomeres were consistently shorter in leiomyoma tissue than in adjacent normal tissue. TRF1, TRF2, PIN2‑interacting telomerase inhibitor 1 (PINX1), and telomerase RNA component were expressed at comparable levels in both leiomyoma and normal tissues. None of these genes were associated with telomere length in leiomyoma. All tested tissues were negative for telomerase reverse transcriptase, which encodes the catalytic component of telomerase, indicating that cells in uterine leiomyoma were not immortalized. In summary, telomere erosion, which reflects active proliferation during tumor evolution, was evident in uterine leiomyoma. Steady‑state expression of TRF1, TRF2 and PINX1 may be important for maintenance of telomere integrity in leiomyoma, where telomere length is shortened.

Role of Telomeres and Telomeric Proteins in Human Malignancies and Their Therapeutic Potential

Telomeres are the ends of linear chromosomes comprised of repetitive nucleotide sequences in humans. Telomeres preserve chromosomal stability and genomic integrity. Telomere length shortens with every cell division in somatic cells, eventually resulting in replicative senescence once telomere length becomes critically short. Telomere shortening can be overcome by telomerase enzyme activity that is undetectable in somatic cells, while being active in germline cells, stem cells, and immune cells. Telomeres are bound by a shelterin complex that regulates telomere lengthening as well as protects them from being identified as DNA damage sites. Telomeres are transcribed by RNA polymerase II, and generate a long noncoding RNA called telomeric repeat-containing RNA (TERRA), which plays a key role in regulating subtelomeric gene expression. Replicative immortality and genome instability are hallmarks of cancer and to attain them cancer cells exploit telomere maintenance and telomere protection mechanisms. Thus, understanding the role of telomeres and their associated proteins in cancer initiation, progression and treatment is very important. The present review highlights the critical role of various telomeric components with recently established functions in cancer. Further, current strategies to target various telomeric components including human telomerase reverse transcriptase (hTERT) as a therapeutic approach in human malignancies are discussed.

Oncoviruses Can Drive Cancer by Rewiring Signaling Pathways Through Interface Mimicry

Oncoviruses rewire host pathways to subvert host immunity and promote their survival and proliferation. However, exactly how is challenging to understand. Here, by employing the first and to date only interface-based host-microbe interaction (HMI) prediction method, we explore a pivotal strategy oncoviruses use to drive cancer: mimicking binding surfaces-interfaces-of human proteins. We show that oncoviruses can target key human network proteins and transform cells by acquisition of cancer hallmarks. Experimental large-scale mapping of HMIs is difficult and individual HMIs do not permit in-depth grasp of tumorigenic virulence mechanisms. Our computational approach is tractable and 3D structural HMI models can help elucidate pathogenesis mechanisms and facilitate drug design. We observe that many host proteins are unique targets for certain oncoviruses, whereas others are common to several, suggesting similar infectious strategies. A rough estimation of our false discovery rate based on the tissue expression of oncovirus-targeted human proteins is 25%.

Emerging roles of telomeric chromatin alterations in cancer

Telomeres, the nucleoprotein structures that cap the ends of eukaryotic chromosomes, play important and multiple roles in tumorigenesis. Functional telomeres need the establishment of a protective chromatin structure based on the interplay between the specific complex named shelterin and a tight nucleosomal organization. Telomere shortening in duplicating somatic cells leads eventually to the destabilization of the telomere capping structure and to the activation of a DNA damage response (DDR) signaling. The final outcome of this process is cell replicative senescence, which constitute a protective barrier against unlimited proliferation. Cells that can bypass senescence checkpoint continue to divide until a second replicative checkpoint, crisis, characterized by chromosome fusions and rearrangements leading to massive cell death by apoptosis. During crisis telomere dysfunctions can either inhibit cell replication or favor tumorigenesis by the accumulation of chromosomal rearrangements and neoplastic mutations. The acquirement of a telomere maintenance mechanism allows fixing the aberrant phenotype, and gives the neoplastic cell unlimited replicative potential, one of the main hallmarks of cancer.Despite the crucial role that telomeres play in cancer development, little is known about the epigenetic alterations of telomeric chromatin that affect telomere protection and are associated with tumorigenesis. Here we discuss the current knowledge on the role of telomeric chromatin in neoplastic transformation, with a particular focus on H3.3 mutations in alternative lengthening of telomeres (ALT) cancers and sirtuin deacetylases dysfunctions.

Molecular and cellular basis of mammary gland fibrosis and cancer risk

Mammary gland luminal cells are maintained by the proliferation of ER- luminal progenitor (LP) cells. Human breast LP cells exhibit telomere DNA damage, which is associated with mammographic density and increased cancer risk. Telomeric repeat factor 2 (TRF2) protects telomeres from DNA damage response. TRF2 expression is reduced in human breast cancers. We deleted TRF2 expression in mammary gland epithelium. Mammary glands lacking TRF2 expression exhibited increased telomere DNA damage response, histopathological and functional degeneration, and prominent ductal fibrosis. TRF2-deficient mammary tumors exhibited rapid onset and increased proliferation. Tumor derived LP cells failed to form tumors after transplantation. The MSC population was highly tumorigenic and maintained telomeres via the ALT mechanism. Telomere DNA damage response in mammary tumors resulted in p53 dependent ER+ cellular differentiation and sensitivity to anti-estrogen therapy. Our results provide a new in vivo model of mammographic density, stem cell differentiation, cancer risk, and therapeutic sensitivity.

Effects of TIN2 on telomeres and chromosomes in the human gastric epithelial cell line GES-1

TERF1-interacting nuclear factor 2 (TIN2) is a key member of the protein complexes that protect telomeres. TIN2 contributes an important role in biological processes. In a previous study by the present authors, an association was reported between high TIN2 protein expression and gastric cancer. Therefore, it was hypothesized that abnormal TIN2 expression may cause the development of malignancies, including, gastric carcinomas. To investigate this hypothesis, the present study employed peptide nucleic acid fluorescence in situ hybridization technology to analyze the human gastric epithelial GES-1 cells with high TIN2 expression or inhibited TIN2 expression. The results indicated that GES-1 cell lines with high TIN2 expression exhibited greater telomere dysfunction-induced damage compared with GES-1 cell lines with inhibited TIN2 expression. Chromosome analysis indicated that GES-1 cells with high TIN2 expression exhibited 2.48±1.30 aberrant chromosomal changes per 100 cells, that may contribute to telomere DNA damage. Therefore, aberrant chromosomal alterations may provide a novel perspective for the pathogenesis of gastric cancer.

Telomere-driven diseases and telomere-targeting therapies

Martínez and Blasco review the molecular mechanisms underlying diseases associated with telomere dysfunction, including telomeropathies, age-related disorders, and cancer. Current and future therapeutic strategies to treat and prevent these diseases, including preclinical development of telomere-targeted therapies using mouse models, are discussed.

Telomeres, the protective ends of linear chromosomes, shorten throughout an individual’s lifetime. Telomere shortening is proposed to be a primary molecular cause of aging. Short telomeres block the proliferative capacity of stem cells, affecting their potential to regenerate tissues, and trigger the development of age-associated diseases. Mutations in telomere maintenance genes are associated with pathologies referred to as telomere syndromes, including Hoyeraal-Hreidarsson syndrome, dyskeratosis congenita, pulmonary fibrosis, aplastic anemia, and liver fibrosis. Telomere shortening induces chromosomal instability that, in the absence of functional tumor suppressor genes, can contribute to tumorigenesis. In addition, mutations in telomere length maintenance genes and in shelterin components, the protein complex that protects telomeres, have been found to be associated with different types of cancer. These observations have encouraged the development of therapeutic strategies to treat and prevent telomere-associated diseases, namely aging-related diseases, including cancer. Here we review the molecular mechanisms underlying telomere-driven diseases and highlight recent advances in the preclinical development of telomere-targeted therapies using mouse models.

ERCC1 and telomere status in breast tumours treated with neoadjuvant chemotherapy and their association with patient prognosis

Dysfunctional telomeres and DNA damage repair (DDR) play important roles in cancer progression. Studies have reported correlations between these factors and tumour aggressiveness and clinical outcome in breast cancer. We studied the characteristics of telomeres and expression of ERCC1, a protein involved in a number of DNA repair pathways and in telomere homeostasis, to assess their prognostic value, alone or in combination, in 90 residual breast tumours after treatment with neoadjuvant chemotherapy (NCT). ERCC1 status was investigated at different molecular levels (protein and gene expression and gene copy‐number variations) by immunohistochemistry, qRT‐PCR and quantitative multiplex fluorescent‐PCR (QMF‐PCR). A comprehensive analysis of telomere characteristics was performed using qPCR for telomere length and qRT‐PCR for telomerase (hTERT), tankyrase 1 (TNKS) and shelterin complex (TRF1, TRF2, POT1, TPP1, RAP1 and TIN2) gene expression. Short telomeres, high hTERT and TNKS expression and low ERCC1 protein expression were independently associated with worse survival outcome. Interestingly, ERCC1 gains and losses correlated with worse disease‐free (p = 0.026) and overall (p = 0.043) survival as compared to survival of patients with normal gene copy‐numbers. Unsupervised hierarchical clustering of all ERCC1 and telomere parameters identified four subgroups with distinct prognosis. In particular, a cluster combining low ERCC1, ERCC1 gene alterations, dysfunctional telomeres and high hTERT and a cluster with high TNKS and shelterin expression correlated with poor disease‐free (HR= 5.41, p= 0.0044) and overall survival (HR= 6.01, p= 0.0023) irrespective of tumour stage and grade. This comprehensive study demonstrates that telomere dysfunction and DDR can contribute synergistically to tumour progression and chemoresistance. These parameters are predictors of clinical outcome in breast cancer patients treated with NCT and could be useful clinically as prognostic biomarkers to tailor adjuvant chemotherapy post‐NCT.

Low-level infrared laser modulates muscle repair and chromosome stabilization genes in myoblasts

Infrared laser therapy is used for skeletal muscle repair based on its biostimulative effect on satellite cells. However, shortening of telomere length limits regenerative potential in satellite cells, which occurs after each cell division cycle. Also, laser therapy could be more effective on non-physiologic tissues. This study evaluated low-level infrared laser exposure effects on mRNA expression from muscle injury repair and telomere stabilization genes in myoblasts in normal and stressful conditions. Laser fluences were those used in clinical protocols. C2C12 myoblast cultures were exposed to low-level infrared laser (10, 35, and 70 J/cm(2)) in standard or normal (10 %) and reduced (2 %) fetal bovine serum concentrations; total RNA was extracted for mRNA expression evaluation from muscle injury repair (MyoD and Pax7) and chromosome stabilization (TRF1 and TRF2) genes by real time quantitative polymerization chain reaction. Data show that low-level infrared laser increases the expression of MyoD and Pax7 in 10 J/cm(2) fluence, TRF1 expression in all fluences, and TRF2 expression in 70 J/cm(2) fluence in both 10 and 2 % fetal bovine serum. Low-level infrared laser increases mRNA expression from genes related to muscle repair and telomere stabilization in myoblasts in standard or normal and stressful conditions.

Differential senescence capacities in meibomian gland carcinoma and basal cell carcinoma

Meibomian gland carcinoma (MGC) and basal cell carcinoma (BCC) are common eyelid carcinomas that exhibit highly dissimilar degrees of proliferation and prognoses. We address here the question of the differential mechanisms between these two eyelid cancers that explain their different outcome. A total of 102 confirmed MGC and 175 diagnosed BCC cases were analyzed. Twenty confirmed MGC and twenty diagnosed BCC cases were collected to determine the telomere length, the presence of senescent cells, and the expression levels of the telomere capping shelterin complex, P53, and the E3 ubiquitin ligase Siah1. Decreased protein levels of the shelterin subunits, shortened telomere length, over-expressed Ki-67, and Bcl2 as well as mutations in P53 were detected both in MGC and BCC. It suggests that the decreased protein levels of the shelterin complex and the shortened telomere length contribute to the tumorigenesis of MGC and BCC. However, several parameters distinguish MGC from BCC samples: (i) the mRNA level of the shelterin subunits decreased in MGC but it increased in BCC; (ii) P53 was more highly mutated in MGC; (iii) Siah1 mRNA was over-expressed in BCC; (iv) BCC samples contain a higher level of senescent cells; (v) Ki-67 and Bcl2 expression were lower in BCC. These results support a model where a preserved P53 checkpoint in BCC leads to cellular senescence and reduced tumor proliferation as compared to MGC.

Over-expression of telomere binding factors (TRF1 & TRF2) in renal cell carcinoma and their inhibition by using SiRNA induce apoptosis, reduce cell proliferation and migration invitro

Telomere binding factors viz. TRF1 and TRF2 are a part of sheltrin complex that are present exclusively at the ends of chromosomes. These factors play an important role in maintaining chromosomal integrity at the ends. However, their status and role are not clear in renal cell carcinoma (RCC). Therefore, the present study was conducted to evaluate TRF1 and TRF2 expressions in RCC tissues. Further, the role of these factors involved in tumorigenesis was elucidated by gene silencing using siRNA in RCC cell line (A498). The present study documented a significant over-expression of TRF1 (P = 0.005) and TRF2 (P = 0.0048) mRNAs by real time PCR in RCC tissues as compared with adjacent normal kidney tissues. Immunohistochemistry studies also revealed higher expression of TRF1 and TRF2 proteins in RCC. Moreover, TRF1 or TRF2 gene silencing using siRNA showed marked reduction in proliferation of RCC cells (P = 0.000). Further, significantly induced cell cycle arrest (P = 0.000) and apoptosis of RCC cells (P = 0.000) was documented upon TRF1 or TRF2 gene silencing. Henceforth, the results deduce that TRF1 or TRF2 inhibitions play an important role in the induction of apoptosis in A498 cells, which may serve as a potential therapeutic target in RCC.

Reduced expression of TRF1 is associated with tumor progression and poor prognosis in oral squamous cell carcinoma

The functions of telomeric repeat-binding factor 1 (TRF1) and 2 (TRF2) in oral carcinogenesis are largely unexplored. This study examined the relationship between the expression of TRF1 and TRF2 and clinicopathological variables and survival in oral cavity squamous cell carcinoma (OCSCC). Western blotting and immunohistochemistry were used to evaluate the protein expression of TRF1 and TRF2 in paired OCSCC patient specimens. Expression of TRF1 and TRF2 was assessed by immunohistochemistry in 256 OCSCC patients who underwent tumor resection without previous radiotherapy. The results were analyzed using Fisher's exact test. Protein expression of TRF1 and TRF2 was significantly lower in the OCSCC than in the adjacent non-tumor tissue. Reduced TRF1 and TRF2 levels in 256 patients, as revealed by immunohistochemistry, were significantly associated with aggressive clinicopathological features, such as advanced tumor stage (p<0.001) and advanced tumor node metastasis stage (p<0.001). According to Kaplan-Meier analysis, reduced TRF1 expression was significantly correlated with an unfavorable cumulative 5-year overall survival rate (p<0.001). In conclusion, decreased expression of TRF1 was significantly associated with tumor progression and poor prognosis in OCSCC patients.

Telomere length, telomeric proteins and genomic instability during the multistep carcinogenic process

Telomeres form specialized structures at the ends of eukaryotic chromosomes, preventing them from being wrongly recognized as DNA damage. The human telomere DNA sequence is a tandem repetition of the sequence TTAGGG. In normal cells, the DNA replication machinery is unable to completely duplicate the telomeric DNA; thus, telomeres are shortened after every cell division. Having reached a critical length, telomeres may be recognized as double strand break DNA lesions, and cells eventually enter senescence. Carcinogenesis is a multistep process involving multiple mutations and chromosomal aberrations. One of the most prevalent aberrations in pre-cancerous lesions is telomere shortening and telomerase activation. We discuss the role and homeostasis of telomeres in normal cells and their implication in the early steps of carcinogenesis. We also discuss various techniques used, and their limitations, in the study of telomeres and genome instability and their role in carcinogenesis and related genomic modifications.

The expression of gene transcripts of telomere-associated genes in human breast cancer: correlation with clinico-pathological parameters and clinical outcome

BACKGROUND

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres in human germ cells, embryogenesis and in cancer, maintaining chromosomal length, stability and cellular immortality. The hTERT gene is the rate-limiting determinant of telomerase reactivation during immortalization and malignant transformation. Telomeric DNA-binding proteins have been attracting increasing interest due to their essential role in the regulation of telomeric DNA length and in protecting against chromosomal end-to-end fusion. These proteins include hTR, TRF1, TRF2, TANK1, TANK2, POT1, TIN2, EST1, and TEP. This study represents the first comprehensive investigation of the mRNA expression of key telomere-related genes in human breast cancer.

METHODS

One hundred and twenty seven tumour tissues and 33 normal tissues were analyzed. Levels of transcription of hTERT, hTR, TRF1, TRF2, TANK1, TANK2, POT1, TIN2, EST1, and TEP1 were determined using real-time quantitative PCR. The mRNA expression of these genes was normalized against CK19 and was then analyzed against the pathological parameters and clinical outcome over a 10 year follow up period.

RESULTS

The mRNA expressions of hTERT, hTR, TANK1, EST1, and TEP1 were higher in tumour samples compared with normal breast tissue. This reached statistical significance for EST1 when comparing good prognosis tumours with normal breast tissue (means=11013 vs 1160, P=0.05). Both hTERT and TEP1 levels significantly predicted overall survival (P=0.012 and 0.005 respectively) and disease-free survival (P=0.0011 and 0.01 respectively). The mRNA levels of TANK2 and POT1 were lower in malignant tissues compared with non-malignant breast tissues and this difference reached statistical significance when comparing the levels in normal tissues with those in advanced tumours (P=0.0008 and P=0.038 respectively). Their levels fell further with increasing tumour's stage and were higher in tumours from patients who remained disease free compared with those who developed local recurrence or distant metastasis or died from breast cancer.TRF2 showed a trend similar to that of TANK2 and POT1. Furthermore, there was a highly significant correlation between TANK1 expression and that of hTERT, hTR, TRF1, TRF2 and EST1, (r=0.533, 0.586, 0.608, 0.644 and 0.551 respectively, P<0.001).

CONCLUSIONS

Genes encoding telomere-associated proteins display different patterns of mRNA expression in human breast cancer, and in normal breast tissue, suggesting different and sometimes opposing roles in mammary carcinogenesis. hTERT, hTR, TANK1, EST1 and TEP1 seem to be up-regulated, with hTERT and TEP1 correlating with clinical outcome. Conversely, TANK2 and POT1 transcription levels demonstrate a compelling trend to be lower in malignant tissues and lower still in those patients who develop recurrent disease suggesting that TANK2 and POT1 may act as tumour suppressor genes possibly by negatively regulating telomerase activity.

Specific overexpression of OLFM4(GW112/HGC-1) mRNA in colon, breast and lung cancer tissues detected using quantitative analysis

Overexpression of the olfactomedin 4 (OLFM4(GW112,/hGC-1)) gene was recently reported to inhibit various apoptotic pathways and promote proliferation of cancer cells, suggesting that OLFM4 might serve as a diagnostic marker for human cancers. Therefore, we examined cancer-specific OLFM4 overexpression. OLFM4 mRNA was highly expressed in cancerous tissues obtained from the colon, breast and lung. Positivity for OLFM4 mRNA, defined as the mean + 2 SD in non-cancerous colon and breast tissues, was observed in 68 and 50% of the studied colon and breast cancer tissues. OLFM4 mRNA expression was not detected in non-cancerous lung tissues but was evident in 62% of the lung cancer tissues. On comparing paired samples, the expression of OLFM4 mRNA was observed to be elevated in 90, 69 and 85% of colon, breast and lung cancer tissues, respectively. OLFM4 mRNA expression was observed even in the early stages of each cancer type. The expression of OLFM4 mRNA did not correlate with that of the antiapoptotic molecule survivin, indicating that it can be used independently in cancer diagnosis. Combining OLFM4 and survivin resulted in higher positivity. Thus, OLFM4 mRNA might be a useful tool to support the diagnosis of cancer, irrespective of the clinical stages.

Identification of differentially expressed genes in mouse hepatocarcinoma ascites cell line with low potential of lymphogenous metastasis

AIM: To identify genes differentially expressed in mouse hepatocarcinoma ascites cell line with low potential of lymphogenous metastasis.

METHODS: A subtracted cDNA library of mouse hepatocarcinoma cell line with low potential of lympho-genous metastasis Hca-P and its synogenetic cell line Hca-F with high metastatic potential was constructed by suppression subtracted hybridization (SSH) method. The screened clones of the subtracted library were sequenced and GenBank homology search was performed.

RESULTS: Fifteen differentially expressed cDNA fragments of Hca-P were obtained which revealed 8 known genes, 4 expressed sequence tags (ESTs) and 3 cDNAs showed no homology.

CONCLUSION: Tumor metastasis is an incident involving multiple genes. SSH is a useful technique to detect differentially expressed genes and an effective method to clone novel genes.

Expression of telomere-associated genes as prognostic markers for overall survival in patients with non-small cell lung cancer

PURPOSE

Human telomeres, which are composed of long, repetitive sequences of TTAGGG and a variety of proteins, function as a protective structure capping the ends of chromosomes. Telomere dysfunction plays important roles in cancer initiation and progression. TRF1, TRF2, POT1, and RAP1 are four major telomere proteins that regulate telomere stability and telomere length. We hypothesized that the expression of these genes would have significant predictive value for cancer development and prognosis.

EXPERIMENTAL DESIGN

We compared the mRNA expression level of TRF1, TRF2, POT1, and RAP1 between tumor and adjacent normal tissues from 148 patients with non-small cell lung cancer using real-time quantitative PCR. We then estimated the prognostic value of the mRNA expression of these genes in tumors.

RESULTS

The expression level of TRF1 was significantly lower in tumor tissues than in adjacent normal tissues (P < 0.0001); no significant difference was found for TRF2, POT1, and RAP1. The expression of RAP1 gene in tumors was highly predictive of overall survival. In the Cox proportional hazards model, patients with higher RAP1 expression were associated with a significantly better survival [hazard ratio (HR), 0.47; 95% confidence interval (95% CI), 0.24-0.91]. This improved survival was more prominent in men (HR, 0.45; 95% CI, 0.22-0.996) and in ever smokers (HR, 0.50; 95% CI, 0.24-1.02). Kaplan-Meier survival curves showed that patients with higher RAP1 expression had significantly longer median survival than patients with lower expression (median = 51.21 versus 15.34 months, P < 0.0009). The expressions of TRF2 in tumor tissues were significantly correlated with tumor grades (P = 0.0114).

CONCLUSIONS

RAP1 expression may be a useful biomarker of tumor progression and survival.

Expression of telomeric repeat binding factor 1 in non-small cell lung cancer

BACKGROUND AND OBJECTIVES

Telomeric repeat binding factor 1 (TRF1) is crucial for forming and maintaining the protective telomeric structure. However, the relationship between TRF1 and non-small cell lung cancer(NSCLC) is not well understood. With this background, we investigated the expressions of the mRNA encoded by the TRF1 gene in cancer tissue and the paired non-cancerous tissue. We also examined whether TRF1 expression is correlated with histopathological features.

METHODS

From October 2004 to August 2005, 40 patients with NSCLCs had undergone curative operations, including 29 males and 11 females. There were 20 cases of squamous cell carcinoma and 20 cases of adenocarcinoma. We measured the expression of TRF1 mRNA using RT-PCR on 40 surgically resected specimens and the paired non-cancerous tissues.

RESULTS

TRF1 mRNA was significantly downregulated in cancer tissue compared with the paired non-cancerous tissue. Additionally, the expression of TRF1 mRNA was significantly associated with the grade of tumor differentiation. No significant difference of TRF1 mRNA level was found between sexes, or among different T-status, clinical stages, pathological subtypes, and lymph node metastasis.

CONCLUSIONS

Downregulation of TRF1 mRNA expression appeared in lung cancer tissue. TRF1 may play a significant role in cell differentiation in NSCLC.

Up-regulation of telomere-binding proteins, TRF1, TRF2, and TIN2 is related to telomere shortening during human multistep hepatocarcinogenesis

The telomeric repeat-binding factor 1 (TRF1), TRF2, and the TRF1-interacting nuclear protein 2 (TIN2) are involved in telomere maintenance. We describe the regulation of expression of these genes along with their relationship to telomere length in hepatocarcinogenesis. The transcriptional expression of these genes, TRF1 protein, and telomere length was examined in 9 normal livers, 14 chronic hepatitis, 24 liver cirrhosis, 5 large regenerative nodules, 14 low-grade dysplastic nodules (DNs), 7 high-grade DNs, 10 DNs with hepatocellular carcinoma (HCC) foci, and 31 HCCs. The expression of TRF1, TRF2, TIN2 mRNA, and TRF1 protein was gradually increased according to the progression of hepatocarcinogenesis with a marked increase in high-grade DNs and DNs with HCC foci and a further increase in HCCs. There was a gradual shortening of telomere during hepatocarcinogenesis with a significant reduction in length in DNs. Most nodular lesions (52 of 67) had shorter telomeres than their adjacent chronic hepatitis or liver cirrhosis, and the telomere lengths were inversely correlated with the mRNA level of these genes (P </= 0.001). This was more evident in DNs and DNs with HCC foci. In conclusion, TRF1, TRF2, and TIN2 might be involved in multistep hepatocarcinogenesis by playing crucial roles in telomere shortening.

Télomère et cancer : quoi de plus à la fin ?

Telomeres are nucleoprotein complexes that cap the end of eukaryotic chromosomes. They are essential for the functions and the stability of the genomes. There is now compelling evidences that telomerase, the enzyme that adds telomeric DNA repeats to chromosome end, is an important player in oncogenesis. The absence of telomerase in somatic tissues is thought to promote genome instability at initial stages of oncogenesis, favoring the emergence of cancer-associated chromosomal abnormalities \; restablishment of telomerase activity is expected afterwards if long term cell cycling is to occur. In addition to telomerase, various factors control the structure and function of telomeres, suggesting that additional telomeric components play important roles during oncogenesis.

The telomerase cycle: normal and pathological aspects

Telomeres are nucleoprotein complexes that cap the end of eukaryotic chromosomes and are essential for their function and stability. Telomerase, a reverse transcriptase that extends the single-stranded G-rich 3' protruding ends of chromosomes, stabilizes telomere length in germ line cells and regenerative tissues as well as in tumor cells. In the absence of telomerase telomeres shorten with cell division, a process able to trigger cell growth arrest. When telomerase is present in the cell, its activity is tightly regulated at its site of action by factors specifically bound to the telomeric DNA. Recent data indicate that telomeres reorganize during the cell cycle. This review summarizes our current knowledge on how telomeres are dynamically organized and remodeled during cell cycle and stress response, pointing out the conservation and the difference between yeast and human. We then focus on the cellular consequences of telomere modifications in normal and cancer cells. This leads to a discussion of the different roles, seemingly contradictory, of telomeres and telomerase during the initiation and the progression of a cancer.

Telomerase in breast cancer: a critical evaluation

Human chromosomes have highly specialized structures at their ends termed telomeres, repetitive, non-coding DNA sequences (5'-TTAGGG-3'), ranging in size from 5 to 20 kb in human cells. These highly specialized structures prevent chromosome ends from being recognized as double-strand DNA breaks, and they also provide protection from destabilizing agents. The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences lost during replication by using an intrinsic RNA component as a template for polymerization. Telomerase has two core functional components required for its activity: the catalytic subunit of human telomerase reverse transcriptase (hTERT) and a telomerase RNA template (hTR). Telomerase is activated in the majority of immortal cell lines in culture and in most malignant tumors. This review outlines our current understanding of telomerase in breast cancer development and critically evaluates potential utilities in diagnosis, prognosis, and therapy.

Cell cycle-dependent 3D distribution of telomeres and telomere repeat-binding factor 2 (TRF2) in HaCaT and HaCaT-myc cells

Telomeres are specialized structures at the ends of the chromosomes that, with the help of proteins--such as the telomere repeat-binding factor TRF2 -, form protective caps which are essential for chromosomal integrity. Investigating the structure and three-dimensional (3D) distribution of the telomeres and TRF2 in the nucleus, we now show that the telomeres of the immortal HaCaT keratinocytes are distributed in distinct non-overlapping territories within the inner third of the nuclear space in interphase cells, while they extend more widely during mitosis. TRF2 is present at the telomeres at all cell cycle phases. During mitosis additional TRF2 protein concentrates all around the chromosomes. This change in staining pattern correlates with a significant increase in TRF2 protein at the S/G2 transition as seen in Western blots of synchronized cells and is paralleled by a cell cycle-dependent regulation of TRF2 mRNA, arguing for a specific role of TRF2 during mitosis. The distinct territorial localization of telomeres is abrogated in a HaCaT variant that constitutively expresses c-Myc--a protein known to contribute to genomic instability. These cells are characterized by overlapping telomere territories, telomeric aggregates (TAs), that are accompanied by an overall irregular telomere distribution and a reduced level in TRF2 protein. These TAs which are readily detectable in interphase nuclei, are similarly present in mitotic cells, including cells in telophase. Thus, we propose that TAs, which subsequently also cluster their respective chromosomes, contribute to genomic instability by forcing an abnormal chromosome segregation during mitosis.

Novel perspective: focusing on the X chromosome in reproductive cancers

In an XX female, one of the two X chromosomes has been inactivated during early embryonic life to achieve a compensation of X-linked gene products between males and females, leaving only one allele of X-linked genes functional. There are some X-linked genes escaping the X-inactivation, i.e., being expressed from both alleles. Escape from X-inactivation varies at different levels; some genes have both alleles active in some women but only one allele active in others, whereas some other genes have both alleles active in neoplastic tissue but only one allele active normally. The X-inactivation may be considered functionally equivalent to a loss of heterozygosity (LOH) for some genes, whereas escape from X-inactivation may be equivalent to functional gene amplification for others. The physiological LOH may make X-linked tumor suppressor genes lose their function more easily, compared with autosomal tumor suppressor genes, thus predisposing women to cancer formation more easily. Moreover, the human X chromosome contains many genes related to cancer or to sex and reproduction. All these properties of the X chromosome suggest that it may play more important roles than any autosomal chromosome in the development and progression of reproductive and urologic cancers.

Telomerase-dependent oncolytic adenovirus for cancer treatment

Conditionally replicative adenovirus (CRAD) is an attractive anticancer agent as it can selectively replicate in tumor cells. Expression of telomerase reverse transcriptase (TERT) is a unique tumor cell characteristic, being absent in normal postmitotic cells. Thus, we constructed a TERT promoter regulated CRAD for tumor-specific oncolysis by replacing the endogenous adenovirus E1A promoter with that of human TERT (Adv-TERTp-E1A). We showed that its replication was severely attenuated in TERT-negative cells, but that it replicated almost as efficiently as wild-type adenovirus in TERT-positive cells. Accordingly, Adv-TERTp-E1A conferred cytopathicity to TERT-positive, but not TERT-negative, cells. In vivo replication of Adv-TERTp-E1A after local administration into a xenograft model of human hepatocellular carcinoma in nude mice was demonstrated by an increase in adenovirus titers in tumor extracts by several orders of magnitude between 6 h and 3 days postvector injection. Furthermore, significant inhibition of tumor growth with substantial necrotic tumor areas staining positively for adenovirus was observed with Adv-TERTp-E1A, but not with a control replication-deficient adenovirus. There was also the absence of hepatotoxicity in tumor-bearing animals after intratumoral delivery of the CRAD. The results indicate that the TERT promoter-driven CRAD is capable of tumor-selective replication and oncolysis in vitro and in vivo, and can be utilized as an adjuvant treatment agent for cancer.