Telomere length variation and maintenance in hepatocarcinogenesis

Hepatitis B Viral Protein HBx and the Molecular Mechanisms Modulating the Hallmarks of Hepatocellular Carcinoma: A Comprehensive Review

With 296 million cases estimated worldwide, chronic hepatitis B virus (HBV) infection is the most common risk factor for hepatocellular carcinoma (HCC). HBV-encoded oncogene X protein (HBx), a key multifunctional regulatory protein, drives viral replication and interferes with several cellular signalling pathways that drive virus-associated hepatocarcinogenesis. This review article provides a comprehensive overview of the role of HBx in modulating the various hallmarks of HCC by supporting tumour initiation, progression, invasion and metastasis. Understanding HBx-mediated dimensions of complexity in driving liver malignancies could provide the key to unlocking novel and repurposed combinatorial therapies to combat HCC.

Non-canonical roles of canonical telomere binding proteins in cancers

Reactivation of telomerase is a major hallmark observed in 90% of all cancers. Yet paradoxically, enhanced telomerase activity does not correlate with telomere length and cancers often possess short telomeres; suggestive of supplementary non-canonical roles that telomerase might play in the development of cancer. Moreover, studies have shown that aberrant expression of shelterin proteins coupled with their release from shortening telomeres can further promote cancer by mechanisms independent of their telomeric role. While targeting telomerase activity appears to be an attractive therapeutic option, this approach has failed in clinical trials due to undesirable cytotoxic effects on stem cells. To circumvent this concern, an alternative strategy could be to target the molecules involved in the non-canonical functions of telomeric proteins. In this review, we will focus on emerging evidence that has demonstrated the non-canonical roles of telomeric proteins and their impact on tumorigenesis. Furthermore, we aim to address current knowledge gaps in telomeric protein functions and propose future research approaches that can be undertaken to achieve this.

Telomere length variation in tumor cells and cancer-associated fibroblasts: potential biomarker for hepatocellular carcinoma

The role of telomere dysfunction and aberrant telomerase activities in hepatocellular carcinoma (HCC) has been overlooked for many years. This study aimed to delineate the variation and prognostic value of telomere length in HCC. Telomere‐specific fluorescence in situ hybridization (FISH) and qPCR were used to evaluate telomere length in HCC cell lines, tumor tissues, and isolated non‐tumor cells within the tumor. Significant telomere attrition was found in tumor cells and cancer‐associated fibroblasts (CAFs) compared to their normal counterparts, but not in intratumor leukocytes or bile duct epithelial cells. Clinical relevance and prognostic value of telomere length were investigated on tissue microarrays of 257 surgically treated HCC patients. Reduced intensity of telomere signals in tumor cells or CAFs correlated with larger tumor size and the presence of vascular invasion (p < 0.05). Shortened telomeres in tumor cells or CAFs associated with reduced survival and increased recurrence, and were identified as independent prognosticators for HCC patients (p < 0.05). These findings were validated in an independent HCC cohort of 371 HCC patients from The Cancer Genome Atlas (TCGA) database, confirming telomere attrition and its prognostic value in HCC. We also showed that telomerase reverse transcriptase promoter (TERTp) mutation correlated with telomere shortening in HCC. Telomere variation in tumor cells and non‐tumor cells within the tumor microenvironment of HCC was a valuable prognostic biomarker for this fatal malignancy. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Paired assessment of liver telomere lengths in hepatocellular cancer is a reliable predictor of disease persistence

In the present study, we used a small series of highly defined patients, where we had matched timed peripheral blood samples (PBS), as well as paired liver biopsies obtained during collection of blood samples from patients with diagnosed hepatocellular carcinoma (HCC) and compared the correlation between the changes of telomere lengths in these defined samples. Patients included had either HCC alone or in conjunction with either pre-existing hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. PCR-based assay incorporating primers to the telomeric hexamer repeats to polymerize and detect telomeric DNA was used. The average telomere length for each independent assessment was measured by seeing the differences in the intensity of the sample’s telomere signal (T) to the signal from a single-copy gene (S-, β-globin) to estimate the standard ratio. Our results provide the first convincing evidence that PBS may be utilized to assay telomere shortening as a predictor for disease persistence in HCC resulting after HBV or HCV infection, but not in non-infectious cause-stimulated HCC. These findings provide incipient opportunity to develop telomere length assessment as a biomarker tool for prediction of HCC in patients with HBV or HCV infection, as well as to gauge responses to chemotherapy and other treatment modalities.

Clinicopathological characteristics of TERT promoter mutation and telomere length in hepatocellular carcinoma

Promoter mutations in telomerase reverse transcriptase (TERT) and telomere length have been studied in various tumors. In the present study, the frequency and clinical characteristics of TERT promoter mutation and telomere length were studied in hepatocellular carcinoma (HCC). TERT promoter mutation and telomere length were analyzed in 162 tumor samples of the patients with HCC by sequencing and real-time PCR, respectively. The TERT promoter mutation rate was 28.8% (46/160) in HCC and was associated with males (P = 0.027). The telomere length was not significantly different in the presence of a TERT promoter mutation but was shorter in high-grade tumor stages (P = 0.048). Survival analyses showed that poor overall survival was associated with longer telomere length (P = 0.013). However, the TERT promoter mutation did not have a prognostic value for HCC. Multivariate survival analyses demonstrated that the telomere length was an independent prognostic marker for poor overall survival (hazard ratio = 1.75, 95% confidence interval: 1.046-2.913, P = 0.033). These data demonstrated that TERT promoter mutation is a frequent event in HCC; however, telomere length, but not the presence of a TERT promoter mutation, might have potential value as a prognostic indicator of HCC.

Telomere Length and Survival of Patients with Hepatocellular Carcinoma in the United States

BACKGROUND

Telomere shortening is an important molecular event in hepatocellular carcinoma (HCC) initiation; however, its role in HCC progression and prognosis is less clear. Our study aimed to examine the association of telomere length with survival of patients with HCC.

METHODS

We measured telomere length in tumor and adjacent non-tumor tissues from 126 persons with HCC in the United States (U.S.) who were followed for mortality outcomes. Relative telomere length (RTL) was measured by a monochrome multiplex quantitative polymerase chain reaction assay. Multivariable Cox proportional hazards modeling was used to calculate hazard ratios (HRs) and 95% CIs for the association between telomere length and all-cause mortality. We also examined associations between telomere length and patient characteristics using multiple linear regression.

RESULTS

During a mean follow-up of 6.0 years, 79 deaths occurred among 114 individuals for whom survival data were available. The ratio of RTL in tumor relative to non-tumor tissue was greater for individuals with regional or distant stage tumors (0.97) than localized stage tumors (0.77), and for individuals with grade III or IV tumors (0.95) than grade II (0.88) or grade I (0.67) tumors. An RTL ratio ≥1 was not associated with survival (HR 0.92, 95% CI 0.55, 1.55) compared to a ratio <1, after adjusting for age at diagnosis, sex, tumor stage and tumor size. Similarly, RTL in the tumor and non-tumor tissue, respectively, were not associated with survival.

CONCLUSIONS

This U.S. based study found that telomeres may be longer in more aggressive HCCs. There was no evidence, however, that telomere length was associated with survival of patients with HCC. Future investigations are warranted to clarify the role of telomere length in HCC prognosis.

Hepatitis B virus, HBx mutants and their role in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of death induced by cancer in the modern world and majority of the cases are related to chronic hepatitis B virus (HBV) infection. HBV-encoded X protein (HBx) is known to play a pivotal role in the pathogenesis of viral induced HCC. HBx is a multifunctional protein of 17 kDa which modulates several cellular processes by direct or indirect interaction with a repertoire of host factors resulting in HCC. HBX might interfere with several cellular processes such as oxidative stress, DNA repair, signal transduction, transcription, protein degradation, cell cycle progression and apoptosis. A number of reports have indicated that HBx is one of the most common viral ORFs that is often integrated into the host genome and its sequence variants play a crucial role in HCC. By mutational or deletion analysis it was shown that carboxy terminal of HBx has a likely role in protein-protein interactions, transcriptional transactivation, DNA repair, cell, signaling and pathogenesis of HCC. The accumulated evidence thus far suggests that it is difficult to understand the mechanistic nature of HBx associated HCC, and HBx mediated transcriptional transactivation and signaling pathways may be a major determinant. This article addresses the role of HBx in the development of HCC with particular emphasis on HBx mutants and their putative targets.

Prognostic impact of telomere maintenance gene polymorphisms on hepatocellular carcinoma patients with chronic hepatitis B

Our goal was to determine whether single-nucleotide polymorphisms (SNPs) of telomere maintenance genes influence the development and clinical outcomes of patients with hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC). We evaluated 20 SNPs of five telomere maintenance genes in 702 patients with HCC and 351 hepatitis B virus surface antigen-positive controls without HCC. Significant SNPs were then validated in an independent cohort of 857 HCC patients and 429 controls. We assessed the association of each SNP with the development of HCC and overall survival through a multivariate Cox proportional analysis. A significantly increased risk of HCC development was identified for the telomerase-associated protein 1 (TEP1) rs1713449 SNP in both the discovery and replication phases (combined odds ratio = 1.42, P = 9.378 × 10(-5) ). In addition, the TEP1 rs1713449, TEP1 rs872072, protection of telomeres 1 homolog rs7784168, telomerase reverse transcriptase rs13167280, and telomeric repeat binding factor 1 rs2306494 SNPs had a significant effect on the overall survival, and a similar survival effect was validated in the replication cohort. Moreover, there was a significant dose-dependent association between the number of putatively high-risk genotypes of the five aforementioned SNPs and overall survival. The median survival time was significantly prolonged for patients with HCC with two or fewer putatively high-risk genotypes versus those with three or more high-risk genotypes (85 versus 44 months, log-rank P = 4.483 × 10(-5) ), and this was demonstrated in the replication cohort (52 versus 37 months, log-rank P = 0.026).

CONCLUSION

These observations suggest that the SNPs of telomere maintenance genes play a potential role in the development of HCC and the survival of HCC patients with chronic HBV infections.

Tumor viruses and replicative immortality--avoiding the telomere hurdle

Tumor viruses promote cell proliferation in order to gain access to an environment suitable for persistence and replication. The expression of viral products that promote growth transformation is often accompanied by the induction of multiple signs of telomere dysfunction, including telomere shortening, damage of telomeric DNA and chromosome instability. Long-term survival and progression to full malignancy require the bypassing of senescence programs that are triggered by the damaged telomeres. Here we review different strategies by which tumor viruses interfere with telomere homeostasis during cell transformation. This frequently involves the activation of telomerase, which assures both the integrity and functionality of telomeres. In addition, recent evidence suggests that oncogenic viruses may activate a recombination-based mechanism for telomere elongation known as Alternative Lengthening of Telomeres (ALT). This error-prone strategy promotes genomic instability and could play an important role in viral oncogenesis.

Direct effects of hepatitis B virus-encoded proteins and chronic infection in liver cancer development

Hepatocellular carcinoma (HCC) ranks as the third leading cause of cancer-related death worldwide with currently limited treatment options. Chronic hepatitis B virus (HBV) infection accounts for HCC development in more than 50% of cases. The lifetime risk of HBV carriers to develop cirrhosis, liver failure or HCC is estimated to be as high as 15-40%. Although several pathways and triggers contributing to HCC development have been described, many features of hepatocellular carcinogenesis and the attributed direct role of viral factors remain elusive. Host genetic factors, the geographic area and epidemiologic factors, as well as the direct risk related to chronic HBV and hepatitis C virus (HCV) infections, account for geographical and gender differences of HCC prevalence. There is growing evidence that hepatocarcinogenesis is a multistep process. Human HCC is typically preceded by chronic inflammation and apoptotic and nonapoptotic cell death with compensatory liver proliferation. However, we still lack a thorough understanding of the common underlying molecular mechanisms. High levels of HBV replication and chronicity of inflammation are known to independently increase the risk for HCC. A direct carcinogenic role of viral factors is very likely to contribute to liver cancer since HCC is known to also occur in noncirrhotic livers of individuals with an inactive chronic or even with occult HBV infection with no significant histological signs of inflammation or cytopathic effects. Furthermore, synergistic or independent viral risk factors for primary liver cancer development have been described, such as HBV genotype, integration of viral DNA into the host genome and direct effects of viral proteins. A broader understanding of these viral factors in hepatocarcinogenesis might give rise to new diagnostic and therapeutic means in the future. We review the current state of research in liver cancer development and focus on the role of direct viral factors in HBV infection.

Telomere length modulation in human astroglial brain tumors

Background

Telomeres alteration during carcinogenesis and tumor progression has been described in several cancer types. Telomeres length is stabilized by telomerase (h-TERT) and controlled by several proteins that protect telomere integrity, such as the Telomere Repeat-binding Factor (TRF) 1 and 2 and the tankyrase-poli-ADP-ribose polymerase (TANKs-PARP) complex.

Objective

To investigate telomere dysfunction in astroglial brain tumors we analyzed telomeres length, telomerase activity and the expression of a panel of genes controlling the length and structure of telomeres in tissue samples obtained in vivo from astroglial brain tumors with different grade of malignancy.

Materials and Methods

Eight Low Grade Astrocytomas (LGA), 11 Anaplastic Astrocytomas (AA) and 11 Glioblastoma Multiforme (GBM) samples were analyzed. Three samples of normal brain tissue (NBT) were used as controls. Telomeres length was assessed through Southern Blotting. Telomerase activity was evaluated by a telomere repeat amplification protocol (TRAP) assay. The expression levels of TRF1, TRF2, h-TERT and TANKs-PARP complex were determined through Immunoblotting and RT-PCR.

Results

LGA were featured by an up-regulation of TRF1 and 2 and by shorter telomeres. Conversely, AA and GBM were featured by a down-regulation of TRF1 and 2 and an up-regulation of both telomerase and TANKs-PARP complex.

Conclusions

In human astroglial brain tumours, up-regulation of TRF1 and TRF2 occurs in the early stages of carcinogenesis determining telomeres shortening and genomic instability. In a later stage, up-regulation of PARP-TANKs and telomerase activation may occur together with an ADP-ribosylation of TRF1, causing a reduced ability to bind telomeric DNA, telomeres elongation and tumor malignant progression.

Hepatocellular telomere length in biliary atresia measured by Q-FISH

BACKGROUND

Liver transplantation for biliary atresia is indicated whenever a Kasai portoenterostomy is considered unfeasible. However, the timing of liver transplantation in biliary atresia has not been precisely defined. Excessive shortening of hepatocellular telomeres may occur in patients with biliary atresia, and therefore, telomere length could be a predictor of hepatocellular reserve capacity.

METHODS

Hepatic tissues were obtained from 20 patients with biliary atresia who underwent LT and 10 age-matched autopsied individuals (mean age, 1.7 and 1.2 years, respectively). Telomere lengths were measured by Southern blotting and quantitative fluorescence in situ hybridization using the normalized telomere-centromere ratio. The correlation between the normalized telomere-centromere ratio for the hepatocytes in biliary atresia and the pediatric end-stage liver disease score was analyzed.

RESULTS

The median terminal restriction fragment length of the hepatic tissues in biliary atresia was not significantly different from that of the control (p = 0.425), whereas the median normalized telomere-centromere ratio of hepatocytes in biliary atresia was significantly smaller than that of the control (p < 0.001). Regression analysis demonstrated a negative correlation of the normalized telomere-centromere ratio with the pediatric end-stage liver disease score in biliary atresia (p < 0.001).

CONCLUSIONS

Telomere length analysis using quantitative fluorescence in situ hybridization could be an objective indicator of hepatocellular reserve capacity in patients with biliary atresia, and excessive telomere shortening supports the early implementation of liver transplantation.

Leukocyte telomere length predicts overall survival in hepatocellular carcinoma treated with transarterial chemoembolization

Previous studies have reported that telomere length in peripheral blood leukocytes can predict the clinical outcome of several cancers. However, whether leukocyte telomere length is associated with the prognosis of hepatocellular carcinoma (HCC) remains to be determined. In this study, relative telomere length (RTL) in peripheral blood leukocytes was measured using a real-time PCR-based method for 269 HCC patients treated with transarterial chemoembolization (TACE) from two independent hospitals. The association between RTL and the overall survival (OS) of HCC was analyzed. The immunological function of the HCC patients with different leukocyte RTLs was evaluated. Multivariate analyses indicated that long leukocyte RTL was significantly associated with poor OS of HCC patients, with a hazard ratio of 2.04 (95% confidence interval, 1.46-2.86; P < 0.001). Kaplan-Meier analyses showed a significant difference of median survival time between patients with long and short RTL (log rank P < 0.001). Fluorescence-activated cell sorting analyses showed that the long RTL group had a significantly increased percentage of CD4(+)CD25(+)FOXP3(+) Treg in CD4(+) T cells compared with short RTL group (P = 0.002). In conclusion, our results suggest that leukocyte RTL may serve as an independent prognostic marker for HCC patients treated with TACE.

The role of oncogenic viruses in the pathogenesis of hepatocellular carcinoma

HBV and HCV have major roles in hepatocarcinogenesis. More than 500 million people are infected with hepatitis viruses and, therefore, HCC is highly prevalent, especially in those countries endemic for HBV and HCV. Viral and host factors contribute to the development of HCC. The main viral factors include the circulating load of HBV DNA or HCV RNA and specific genotypes. Various mechanisms are involved in the host-viral interactions that lead to HCC development, among which are genetic instability, self-sufficiency in growth signals, insensitivity to antigrowth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, and tissue invasiveness. Prevention of HBV by vaccination, as well as antiviral therapy against HBV and for HCV seem able to inhibit the development of HCC.

Hepatitis B virus x protein in the pathogenesis of hepatitis B virus-induced hepatocellular carcinoma

Currently available evidence supports a role for the hepatitis B virus (HBV) x gene and protein in the pathogenesis of HBV-induced hepatocellular carcinoma (HCC). HBx gene is often included, and remains functionally active, in the HBV DNA that is frequently integrated into cellular DNA during hepatocellular carcinogenesis. HBx protein promotes cell cycle progression, inactivates negative growth regulators, and binds to and inhibits the expression of p53 tumour suppressor gene and other tumour suppressor genes and senescence-related factors. However, the molecular mechanisms responsible for HBx protein-induced HCC remain uncertain. Only some of the more fully documented or more recently recognised mechanisms are reviewed. During recent years evidence has accumulated that HBx protein modulates transcription of methyl transferases, causing regional hypermethylation of DNA that results in silencing of tumour suppressor genes, or global hypomethylation that results in chromosomal instability, thereby playing a role in hepatocarcinogenesis. HBx protein has both anti-apoptotic and pro-apoptotic actions, apparently contradictory effects that have yet to be explained. Particularly important among the anti-apoptotic properties is inhibition of p53. Recent experimental observations suggest that HBx protein may increase the expression of TERT and telomerase activity, prolonging the life-span of hepatocytes and contributing to malignant transformation. The protein also interferes with nucleotide excision repair through both p53-dependent and p53- independent mechanisms. Carboxy-terminal truncated HBx protein loses its inhibitory effects on cell proliferation and pro-apoptotic properties, and it may enhance the protein's ability to transform oncogenes. Dysregulation of IGF-II enhances proliferation and anti-apoptotic effects of oncogenes, resulting in uncontrolled cell growth.

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.

Dynamics of telomere erosion and its association with genome instability in myelodysplastic syndromes (MDS) and acute myelogenous leukemia arising from MDS: a marker of disease prognosis?

Telomere length was evaluated by terminal repeat fragment method (TRF) in 50 patients with myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML) arising from MDS and in 21 patients with untreated primary AML to ascertain, whether telomere erosion was associated with progression of MDS towards overt leukemia. Heterogeneity of TRF among MDS FAB subgroups (P=0.004) originated from its shortening in increased number of patients during progression of the disease. Chromosomal aberrations were present in 32% MDS patients with more eroded telomeres (P=0.022), nevertheless a difference between mean TRF in the subgroups with normal and abnormal karyotype diminished during progression of MDS. A negative correlation between individual TRF and IPSS value (P=0.039) showed that telomere dynamics might serve as a useful prognostic factor for assessment of an individual MDS patient's risk and for decision of an optimal treatment strategy.

Increased expression of telomere length regulating factors TRF1, TRF2 and TIN2 in patients with adult T-cell leukemia

Here, we report that freshly isolated unstimulated adult T-cell leukemia (ATL) cells present high telomerase activity compared to asymptomatic carriers or normal donors. In spite of this high telomerase activity, ATL cells retained shorter telomeres compared to those of uninfected cells isolated from the same patients. Because the safeguarding of telomere length is critical to the unlimited proliferation of tumor cells, we investigated the underlying mechanism for short telomere maintenance in ATL cells. Transcriptional and posttranscriptional expression of telomere-binding proteins TRF1, TRF2, TIN2 and POT1, known to regulate telomere homeostasis and protection, were evaluated. We found that TRF1 and TRF2 are overexpressed in in vivo patient's samples from ATL but not asymptomatic carriers, while levels of POT1 expression did not specifically increase in ATL. To gain insights into the regulation of TRF genes in HTLV-I infected cells, we investigated the expression of TIN2, a regulator of these genes, and found an increase in TIN2 expression in ATL patients. Together our results underscore the importance of telomerase and telomere length regulating factors as novel markers for ATL disease progression and as potential therapeutic targets for the treatment of HTLV-I-associated malignancies.

Dynamic alteration of telomerase expression and its diagnostic significance in liver or peripheral blood for hepatocellular carcinoma

AIM: To investigate the dynamic alteration of telomerase expression during development of hepatocellular carcinoma (HCC) and its diagnostic implications in liver tissues or peripheral blood mononuclear cells for HCC.

METHODS: Dynamic expressions of liver telomerase during malignant transformation of hepatocytes were observed in Sprague-Dawly (SD) rats fed with 0.05% of 2-fluoenyacetamide (2-FAA). Total RNA and telomerase were extracted from rat or human liver tissues. The telomerase activities in livers and in circulating blood were detected by a telomeric repeat amplification protocol-enzyme-linked immunosorbent assay (TRAP-ELISA), and its diagnostic value was investigated in patients with benign or malignant liver diseases.

RESULTS: The hepatoma model displayed the dynamic expression of hepatic telomerase during HCC development. The telomerase activities were consistent with liver total RNA levels (r = 0.83, P < 0.01) at the stages of degeneration, precancerosis, and cancerization of hepatocytes. In HCC patients, the telomerase levels in HCC tissues were significantly higher than in their adjacent non-cancerous tissues, but liver total RNA levels were lower in the former than in the latter. Although the circulating telomerase of HCC patients was abnormally expressed among patients with chronic liver diseases, the telomerase activity was a non-specific marker for HCC diagnosis, because the incidence was 15.7% in normal control, 25% in chronic hepatitis, 45.9% in liver cirrhosis, and 85.2% in HCC, respectively when absorbance value of telomerase activity was more than 0.2. If the value was over 0.6, the incidence was 60% in HCC group and 0% in any of the others (P < 0.01) except in two cases with liver cirrhosis. However, the combination of circulating telomerase with serum alpha-fetoprotein level could increase the positive rate and the accuracy (92.6%, 125 of 135) of HCC diagnosis.

CONCLUSION: The overexpression of telomerase is associated with HCC development, and its abnormality in liver tissues or in peripheral blood could be a useful marker for diagnosis and prognosis of HCC.

Telomere shortening correlates with increasing aneuploidy of chromosome 8 in human hepatocellular carcinoma

Chromosomal instability (CIN) leads to an increase in aneuploidy and chromosomal aberrations in human hepatocellular carcinoma (HCC). Telomere shortening appears as one mechanism fostering the development of CIN. Whether telomere shortening correlates to specific genetic changes that characterize a certain type of cancer has yet to be established. In our recent study, we combined on a cellular level the analysis of hepatocellular telomere fluorescent intensity (TFI) and copy number of chromosome 8-one of the hallmark chromosomal alterations in hepatocellular carcinoma (HCC). We investigated 15 cytological fine-needle biopsies of aneuploid HCC and 5 touch prints of cadaver livers without cancer. Hepatocyte-specific TFI and the measurement of centromere-specific probe for chromosome 8 were both performed by quantitative fluorescence in situ hybridization (qFISH) or FISH. Combined analysis of both methods (coFISH) allowed measurement of telomere length and chromosome 8 copy number on a single cell level. We observed that telomere shortening correlates significantly with increasing copy number of chromosome 8 in HCC on the cellular level. Above the level of 5 copies of chromosome 8 per nucleus, no further shortening of telomeres was found, indicating that telomeres had reached a critically short length at this stage of aneuploidy. In conclusion, our study gives direct evidence that telomere shortening is linked to a specific genetic alteration characteristic for human HCC.

Expression of Telomeric Repeat Binding Factor-1 in Astroglial Brain Tumors

OBJECTIVE

In human somatic cells, telomeres shorten with successive cell divisions, resulting in progressive genomic instability, altered gene expression, and cell death. Recently, telomere-specific deoxyribonucleic acid-binding proteins, such as telomeric repeat binding factor-1 (TRF1), have been proposed as candidates for the role of molecules regulating telomerase activity, and they have been suggested to play key roles in the maintenance of telomere function. The present study was designed to assess TRF1 expression in human astroglial brain tumors and to speculate on the clinical implications of its expression.

METHODS

Twenty flash-frozen surgical specimens obtained from adult patients who underwent craniotomy for microsurgical tumor resection, histologically verified as World Health Organization Grade II to IV astrocytomas, were used. Expression of TRF1 in astrocytomas of different grades was studied by means of both immunohistochemical and Western blotting analysis. The correlation between the extent of TRF1 expression and histological grading, performance status, and length of survival of patients underwent statistical analyses.

RESULTS

TRF1 was expressed in all tumor samples. The level of its expression was variable, decreasing from low-grade through high-grade astrocytomas (P = 0.0032). TRF1 expression correlated with the patient's length of survival (P < 0.001) and performance status (P < 0.001) and proved to be an independent indicator of length of survival.

CONCLUSION

Our findings suggest that the loss of TRF1 expression capability, as a result of down-regulation of TRF1 expression in malignant gliomas cells, may play a role in the malignant progression of astroglial brain tumors.

Telomeres and telomerase: a dual role in hepatocarcinogenesis

Telomere shortening limits the proliferative capacity of primary human cells and restrains the regenerative capacity of organ systems during chronic diseases and aging. Telomere shortening apparently has a dual role in tumor development and progression. On the one hand, it induces chromosomal instability and the initiation of cancer; on the other hand, tumor progression requires stabilization of telomeres. The predominant mechanism of telomere stabilization in tumor cells is the activation of the telomere-synthesizing enzyme telomerase. The potential use of telomerase activators for the treatment of regenerative disorders will ultimately depend on their effects on tumorigenesis. This review focuses on the role of telomere shortening and telomerase in carcinogenesis with a special focus on hepatocellular carcinoma.

Relationship between microvessel density and telomerase activity in hepatocellular carcinoma

AIM: To study the relationship between microvessel density (MVD), telomerase activity and biological characteristics in hepatocellular carcinoma (HCC).

METHODS: S-P immunohistochemical method and telomeric repeat amplification protocol (TRAP) were respectively used to analyze the MVD and telomerase activity in 58 HCC and adjacent normal tissues.

RESULTS: The MVD in HCC with metastasis, lower differentiation or without intact capsule was significantly higher than that in HCC with intact capsule, higher differentiation, or without metastasis. While MVD had no relationship with tumor size, hepatic virus infection and other clinical factors. Telomerase activity was related to differentiation degree, but not to tumor size or histological grade. MVD in HCC with telomerase activity was higher than that in HCC without telomerase activity.

CONCLUSION: MVD and telomerase activity may serve as diagnostic criteria of HCC in earlier stage. Meanwhile, there may be a cooperative effect between MVD and telomerase on the growth and metastasis of HCC.

Hepatocellular telomere shortening correlates with chromosomal instability and the development of human hepatoma

The telomere hypothesis of cancer initiation indicates that telomere shortening initiates cancer by induction of chromosomal instability. To test whether this hypothesis applies to human hepatocellular carcinoma (HCC), we analyzed the telomere length of hepatocytes in cytological smears of fine-needle biopsies of liver tumors from patients with cirrhosis (n = 39). The tumors consisted of 24 HCC and 15 regenerative nodules as diagnosed by combined histological and cytological diagnostics. In addition, we analyzed the telomere length of hepatocytes in HCC and surrounding noncancerous liver tissue within individual patients in another cohort of 10 patients with cirrhosis. Telomere length analysis of hepatocytes was correlated with tumor pathology and ploidy grade of the tumors, which was analyzed by cytophotometry. Telomeres were significantly shortened in hepatocytes of HCC compared to hepatocytes in regenerative nodules or surrounding noncancerous liver tissue. Hepatocyte telomere shortening in HCC was independent of the patient's age. There was no overlap in mean telomere lengths of individual samples when comparing HCC with regenerative nodules or noncancerous surrounding liver. Within the HCC group, telomeres were significantly shorter in hepatocytes of aneuploid tumors compared to diploid tumors. In conclusion, our data suggest that the telomere hypothesis of cancer initiation applies to human HCC and that cell type-specific telomere length analysis might indicate the risk of HCC development.