Telomere shortening associated with chromosome instability is arrested in immortal cells which express telomerase activity

Telomeres: Implications for Cancer Development

Telomeres facilitate the protection of natural ends of chromosomes from constitutive exposure to the DNA damage response (DDR). This is most likely achieved by a lariat structure that hides the linear telomeric DNA through protein-protein and protein-DNA interactions. The telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in unmasked telomeres. Then, the subsequent activation of the DDR will define the fate of cells according to the functionality of cell cycle checkpoints. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptotic pathways, but they can also promote tumour initiation. Studies in telomere dynamics and karyotype analysis underpin telomere crisis as a key event driving genomic instability. Significant attainment of telomerase or alternative lengthening of telomeres (ALT)-pathway to maintain telomere length may be permissive and required for clonal evolution of genomically-unstable cells during progression to malignancy. We summarise current knowledge of the role of telomeres in the maintenance of chromosomal stability and carcinogenesis.

Telomeres and Chromosomal Translocations : There's a Ligase at the End of the Translocation

Chromosomal translocations are now well understood to not only constitute signature molecular markers for certain human cancers but often also to be causative in the genesis of that tumor. Despite the obvious importance of such events, the molecular mechanism of chromosomal translocations in human cells remains poorly understood. Part of the explanation for this dearth of knowledge is due to the complexity of the reaction and the need to archaeologically work backwards from the final product (a translocation) to the original unrearranged chromosomes to infer mechanism. Although not definitive, these studies have indicated that the aberrant usage of endogenous DNA repair pathways likely lies at the heart of the problem. An equally obfuscating aspect of this field, however, has also originated from the unfortunate species-specific differences that appear to exist in the relevant model systems that have been utilized to investigate this process. Specifically, yeast and murine systems (which are often used by basic science investigators) rely on different DNA repair pathways to promote chromosomal translocations than human somatic cells. In this chapter, we will review some of the basic concepts of chromosomal translocations and the DNA repair systems thought to be responsible for their genesis with an emphasis on underscoring the differences between other species and human cells. In addition, we will focus on a specific subset of translocations that involve the very end of a chromosome (a telomere). A better understanding of the relationship between DNA repair pathways and chromosomal translocations is guaranteed to lead to improved therapeutic treatments for cancer.

Allele-Specific DNA Methylation and Its Interplay with Repressive Histone Marks at Promoter-Mutant TERT Genes

A mutation in the promoter of the Telomerase Reverse Transcriptase (TERT) gene is the most frequent noncoding mutation in cancer. The mutation drives unusual monoallelic expression of TERT, allowing immortalization. Here, we find that DNA methylation of the TERT CpG island (CGI) is also allele-specific in multiple cancers. The expressed allele is hypomethylated, which is opposite to cancers without TERT promoter mutations. The continued presence of Polycomb repressive complex 2 (PRC2) on the inactive allele suggests that histone marks of repressed chromatin may be causally linked to high DNA methylation. Consistent with this hypothesis, TERT promoter DNA containing 5-methyl-CpG has much increased affinity for PRC2 in vitro. Thus, CpG methylation and histone marks appear to collaborate to maintain the two TERT alleles in different epigenetic states in TERT promoter mutant cancers. Finally, in several cancers, DNA methylation levels at the TERT CGI correlate with altered patient survival.

Telomere Biology and Thoracic Aortic Aneurysm

Ascending aortic aneurysms are mostly asymptomatic and present a great risk of aortic dissection or perforation. Consequently, ascending aortic aneurysms are a source of lethality with increased age. Biological aging results in progressive attrition of telomeres, which are the repetitive DNA sequences at the end of chromosomes. These telomeres play an important role in protection of genomic DNA from end-to-end fusions. Telomere maintenance and telomere attrition-associated senescence of endothelial and smooth muscle cells have been indicated to be part of the pathogenesis of degenerative vascular diseases. This systematic review provides an overview of telomeres, telomere-associated proteins and telomerase to the formation and progression of aneurysms of the thoracic ascending aorta. A better understanding of telomere regulation in the vascular pathology might provide new therapeutic approaches. Measurements of telomere length and telomerase activity could be potential prognostic biomarkers for increased risk of death in elderly patients suffering from an aortic aneurysm.

Telomeres in cancer

Telomere shortening as a consequence of cell divisions during aging and chronic diseases associates with an increased cancer risk. Experimental data revealed that telomere shortening results in telomere dysfunction, which in turn affects tumorigenesis in two ways. First, telomere dysfunction suppresses tumor progression by the activation of DNA damage checkpoints, which induce cell cycle arrest (senescence) or apoptosis, as well as by inducing metabolic compromise and activation of immune responses directed against senescent cells. Second, telomere dysfunction promotes tumorigenesis by inducing chromosomal instability in tumor initiating cells, by inhibiting proliferative competition of non-transformed cells, and possibly, also by influencing tumor cell plasticity. The tumor promoting effects of telomere dysfunction are context dependent and require the loss of p53-dependent DNA damage checkpoints or other genetic modifiers that attenuate DNA damage responses possibly involving complex interactions of different genes. The activation of telomere stabilizing mechanisms appears as a subsequent step, which is required to enable immortal grotwh of emerging cancer cells. Here, we conceptually discuss our current knowledge and new, unpublished experimental data on telomere dependent influences on tumor initiation and progression.

Detection of circulating tumor cells in cervical cancer using a conditionally replicative adenovirus targeting telomerase-positive cells

Circulating tumor cells (CTC) are newly discovered biomarkers of cancers. Although many systems detect CTC, a gold standard has not yet been established. We analyzed CTC in uterine cervical cancer patients using an advanced version of conditionally replicative adenovirus targeting telomerase-positive cells, which was enabled to infect coxsackievirus-adenovirus receptor-negative cells and to reduce false-positive signals in myeloid cells. Blood samples from cervical cancer patients were hemolyzed and infected with the virus and then labeled with fluorescent anti-CD45 and anti-pan cytokeratin antibodies. GFP (+)/CD45 (-) cells were isolated and subjected to whole-genome amplification followed by polymerase chain reaction analysis of human papillomavirus (HPV) DNA. CTC were detected in 6 of 23 patients with cervical cancers (26.0%). Expression of CTC did not correlate with the stage of cancer or other clinicopathological factors. In 5 of the 6 CTC-positive cases, the same subtype of HPV DNA as that of the corresponding primary lesion was detected, indicating that the CTC originated from HPV-infected cancer cells. These CTC were all negative for cytokeratins. The CTC detected by our system were genetically confirmed. CTC derived from uterine cervical cancers had lost epithelial characteristics, indicating that epithelial marker-dependent systems do not have the capacity to detect these cells in cervical cancer patients.

When forensic odontology met biochemistry: Multidisciplinary approach in forensic human identification

When human remains are found, the priority of the investigation is to ascertain the identity of the deceased. A positive identification is a key factor in providing closure for the family of the deceased; it is also required to issue the death certificate and therefore, to settle legal affairs. Moreover, it is difficult for any forensic investigation involving human remains to be solved without the determination of an identity. Therefore, personal identification is necessary for social, legal and forensic reasons. In the last thirty years forensic odontology has experienced an important transformation, from primarily involving occasional dental identification into a broader role, contributing to the determination of the biological profile. In the same way, "DNA fingerprinting" has evolved not only in terms of improving its technology, but also in its application beyond the "classical": helping with the estimation of sex, age and ancestry. As these two forensic disciplines have developed independently, their pathways have crossed several times through human identification operations, especially the ones that require a multidisciplinary approach. Thus, the aim of this review is to describe the contributions of both forensic odontology and molecular biology/biochemistry to human identification, demonstrating how a multidisciplinary approach can lead to a better and more efficient identification.

Immortalization of Porcine 11β-Hydroxysteroid Dehydrogenase Type 1-Transgenic Liver Cells Using SV40 Large T Antigen

Cortisol is a steroid hormone essential to the maintenance of homeostasis that is released in response to stress and low blood glucose concentration. Cortisol is converted from cortisone by 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1). It has been reported that too much cortisol or overexpression of HSD11B1 induces obesity and the insulin resistance that accompanies metabolic syndrome in rodent adipose tissue. In our previous study, HSD11B1-transgenic (TG) fibroblasts were established, and a porcine model was generated by SCNT using those fibroblasts. Hepatocytes overexpressing HSD11B1 were obtained from livers of this porcine model and cultured in vitro. However, the primary hepatocytes were found to have a short life span or low proliferation rate. To overcome these problems, the SV40 large T antigen was transduced into primary HSD11B1-TG hepatocytes, and those cells were immortalized. Immortalized HSD11B1-TG hepatocytes showed restored morphology, more rapid proliferation rate, and more expression of HSD11B1 than primary hepatocytes. As well, these cells kept the hepatic characteristics such as gluconeogenic response to cortisone and increased expression of hepatic makers. The immortalized HSD11B1-TG hepatocytes may be useful for studying traits and potential therapeutic drugs for treatment of metabolic disorders induced by overexpression of HSD11B1.

Drug Resistance Driven by Cancer Stem Cells and Their Niche

Drug resistance represents one of the greatest challenges in cancer treatment. Cancer stem cells (CSCs), a subset of cells within the tumor with the potential for self-renewal, differentiation and tumorigenicity, are thought to be the major cause of cancer therapy failure due to their considerable chemo- and radioresistance, resulting in tumor recurrence and eventually metastasis. CSCs are situated in a specialized microenvironment termed the niche, mainly composed of fibroblasts and endothelial, mesenchymal and immune cells, which also play pivotal roles in drug resistance. These neighboring cells promote the molecular signaling pathways required for CSC maintenance and survival and also trigger endogenous drug resistance in CSCs. In addition, tumor niche components such as the extracellular matrix also physically shelter CSCs from therapeutic agents. Interestingly, CSCs contribute directly to the niche in a bilateral feedback loop manner. Here, we review the recent advances in the study of CSCs, the niche and especially their collective contribution to resistance, since increasingly studies suggest that this interaction should be considered as a target for therapeutic strategies.

Telomerase in hematologic malignancies

PURPOSE OF REVIEW

The activation of telomere maintenance pathways has long been regarded as a key hallmark of cancer and this has propelled the development of novel inhibitors of telomerase. In this review, we detail the background biology on telomere maintenance in health and disease, then concentrate on the recent preclinical and clinical development behind targeting telomerase in blood cancers.

RECENT FINDINGS

Preclinical and clinical studies have shown that imetelstat, a competitive inhibitor of telomerase, has activity in certain hematologic malignancies, in particular the myeloproliferative neoplasms and acute myeloid leukemia.

SUMMARY

Telomerase inhibition has shown remarkable efficacy in myeloid malignancies, and current and future preclinical and clinical studies are necessary to comprehensively investigate its underlying mechanism of action. Future work should identify the potential genetic susceptibilities to telomerase inhibition therapy, and evaluate rational combinations of telomerase inhibitors with chemotherapy and other novel agents. Robust preclinical evaluation is essential to best translate these new agents successfully into our clinical treatment algorithm for myeloid and other blood cancers.

Telomere biology in aging and cancer: early history and perspectives

The ends of eukaryotic linear chromosomes are protected from undesired enzymatic activities by a nucleoprotein complex called the telomere. Expanding evidence indicates that telomeres have central functions in human aging and tumorigenesis. While it is undoubtedly important to follow current advances in telomere biology, it is also fruitful to be well informed in seminal historical studies for a comprehensive understanding of telomere biology, and for the anticipation of future directions. With this in mind, I here summarize the early history of telomere biology and current advances in the field, mostly focusing on mammalian studies relevant to aging and cancer.

Characterization and Impact of TERT Promoter Region Mutations on Clinical Outcome in Renal Cell Carcinoma

BACKGROUND

Mutations in the promoter region of the TERT gene have been detected in a variety of cancers. These mutations can potentially lead to unlimited cell divisions and result in poor clinical prognosis.

OBJECTIVE

To determine the role and relevance of TERT promoter region mutations in both clear cell (ccRCC) and non-clear cell (nccRCC) renal cell carcinoma using ultra-deep and whole-genome sequencing methods on primary tumor samples.

DESIGN, SETTING, AND PARTICIPANTS

DNA from 281 kidney tumors (147 ccRCC and 134 nccRCC) was sequenced between 2013 and 2015, and clinical outcomes for these patients from a single institution were retrospectively analyzed.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Differences in patient characteristics and mutational status were tested using Fisher's exact test for categorical variables and the Wilcoxon rank sum test for continuous variables. Survival times were estimated using the Kaplan-Meier method and differences were tested using the log-rank test.

RESULTS AND LIMITATIONS

TERT mutations occurred in 12.2% of ccRCC and 10.4% of nccRCC cases. In >80% of the cases, mutations were located at C228T and were found to co-occur only rarely with other relevant RCC driver genes. The median follow-up among survivors overall was 2.5 yr (range 0.1-18.3). TERT promoter mutations were significantly associated with cancer-specific survival in ccRCC (hazard ratio 2.68, 95% confidence interval 1.19-6.01; p=0.013). In nccRCC, TERT mutations were significantly associated with larger tumors and metastatic development. Assessment of further relevant clinical associations was precluded in the nccRCC group by the heterogeneous and small sample size.

CONCLUSIONS

Our data suggests that TERT mutational status reflects a distinct pathogenesis with an aggressive disease course in RCC. Stratifying patients with this unique tumorigenesis that leads to poor clinical outcomes could be a putative target for novel therapeutics.

PATIENT SUMMARY

We show a previously unrecognized frequency of TERT promoter mutations in both clear cell and non-clear cell renal cell carcinoma. TERT promoter mutations were associated with some worse outcomes in patients with clear cell renal cell carcinoma.

Telomere DNA damage signaling regulates cancer stem cell evolution, epithelial mesenchymal transition, and metastasis

Chromosome ends are protected by telomeres that prevent DNA damage response and degradation. When telomeres become critically short, the DNA damage response is activated at chromosome ends which induces cellular senescence or apoptosis. Telomeres are protected by the double stranded DNA binding protein TRF2 and maintained by telomerase or a recombination based mechanism known as alternative lengthening of telomeres (ALT). Telomerase is expressed in the basal layer of the epidermis, and stem cells in epidermis have longer telomeres than proliferating populations. Stem cell expansion has been associated with epithelial-mesenchymal transition (EMT) in cancer. EMT is a critical process in cancer progression in which cells acquire spindle morphology, migrate from the primary tumor, and spread to distant anatomic sites. Our previous study demonstrated that loss of TRF2 expression observed in human squamous cell carcinomas expanded metastatic cancer stem cells during mouse skin carcinogenesis. To determine if telomerase inhibition could block the TRF2-null mediated expansion of metastatic clones, we characterized skin carcinogenesis in a conditional TRF2/Terc double null mutant mouse. Loss of TRF2 and Terc expression resulted in telomere DNA damage, severely depleted CD34 + and Lgr6+ cancer stem cells, and induced terminal differentiation of metastatic cancer cells. However a novel cancer stem cell population evolved in primary tumors exhibiting genomic instability, ALT, and EMT. Surprisingly we discovered that metastatic clones evolved prior to histopathologic onset of primary tumors. These results have important implications for understanding the evolution and treatment of metastatic cancer.

Regulated expression of the lncRNA TERRA and its impact on telomere biology

The telomere protects against genomic instability by minimizing the accelerated end resection of the genetic material, a phenomenon that results in severe chromosome instability that could favor the transformation of a cell by enabling the emergence of tumor-promoting mutations. Some mechanisms that avoid this fate, such as capping and loop formation, have been very well characterized; however, telomeric non-coding transcripts, such as long non-coding RNAs (lncRNAs), should also be considered in this context because they play roles in the organization of telomere dynamics, involving processes such as replication, degradation, extension, and heterochromatin stabilization. Although the mechanism through which the expression of telomeric transcripts regulates telomere dynamics is not yet clear, a non-coding RNA component opens the research options in telomere biology and the impact that it can have on telomere-associated diseases such as cancer.

Implications of telomeres and telomerase in endometrial pathology

BACKGROUND

Eukaryotic chromosomal ends are linear and are protected by nucleoprotein complexes known as telomeres. The complex structural anatomy and the diverse functions of telomeres as well as the unique reverse transcriptase enzyme, telomerase that maintains telomeres are under intensive scientific scrutiny. Both are involved in many human diseases including cancer, but also in ageing and chronic disease such as diabetes. Their intricate involvement in many cellular processes and pathways is being dynamically deciphered in many organs including the endometrium. This review summarizes our current knowledge on the topic of telomeres and telomerase and their potential role in providing plausible explanations for endometrial aberrations related to common gynaecological pathologies.

OBJECTIVE AND RATIONALE

This review outlines the recent major findings in telomere and telomerase functions in the context of endometrial biology. It highlights the contemporary discoveries in hormonal regulation, normal endometrial regeneration, stem cells and common gynaecological diseases such as endometriosis, infertility, recurrent reproductive failure and endometrial cancer (EC).

SEARCH METHODS

The authors carried out systematic PubMed (Medline) and Ovid searches using the key words: telomerase, telomeres, telomere length, human telomerase reverse transcriptase, telomeric RNA component, with endometrium, hormonal regulation, endometrial stem/progenitor cells, endometrial regeneration, endometriosis, recurrent miscarriage, infertility, endometrial hyperplasia, EC and uterine cancer. Publications used in this review date from 1995 until 31st June 2016.

OUTCOMES

The human endometrium is a unique somatic organ, which displays dynamic telomerase activity (TA) related to the menstrual cycle. Telomerase is implicated in almost all endometrial pathologies and appears to be crucial to endometrial stem cells. In particular, it is vital for normal endometrial regeneration, providing a distinct route to formulate possible curative, non-hormonal therapies to treat chronic endometrial conditions. Furthermore, our current understanding of telomere maintenance in EC is incomplete. Data derived from other malignancies on the role of telomerase in carcinogenesis cannot be extrapolated to EC because unlike in other cancers, TA is already present in proliferating healthy endometrial cells.

WIDER IMPLICATIONS

Since telomerase is pivotal to endometrial regeneration, further studies elucidating the role of telomeres, telomerase, their associated proteins and their regulation in normal endometrial regeneration as well as their role in endometrial pathologies are essential. This approach may allow future development of novel treatment strategies that are not only non-hormonal but also potentially curative.

Elucidating high-dimensional cancer hallmark annotation via enriched ontology

MOTIVATION

Cancer hallmark annotation is a promising technique that could discover novel knowledge about cancer from the biomedical literature. The automated annotation of cancer hallmarks could reveal relevant cancer transformation processes in the literature or extract the articles that correspond to the cancer hallmark of interest. It acts as a complementary approach that can retrieve knowledge from massive text information, advancing numerous focused studies in cancer research. Nonetheless, the high-dimensional nature of cancer hallmark annotation imposes a unique challenge.

RESULTS

To address the curse of dimensionality, we compared multiple cancer hallmark annotation methods on 1580 PubMed abstracts. Based on the insights, a novel approach, UDT-RF, which makes use of ontological features is proposed. It expands the feature space via the Medical Subject Headings (MeSH) ontology graph and utilizes novel feature selections for elucidating the high-dimensional cancer hallmark annotation space. To demonstrate its effectiveness, state-of-the-art methods are compared and evaluated by a multitude of performance metrics, revealing the full performance spectrum on the full set of cancer hallmarks. Several case studies are conducted, demonstrating how the proposed approach could reveal novel insights into cancers.

AVAILABILITY

https://github.com/cskyan/chmannot.

Methyltransferase G9a promotes cervical cancer angiogenesis and decreases patient survival

Research suggests that the epigenetic regulator G9a, a H3K9 histone methyltransferase, is involved in cancer invasion and metastasis. Here we show that G9a is linked to cancer angiogenesis and poor patient survival. Invasive cervical cancer has a higher G9a expression than cancer precursors or normal epithelium. Pharmacological inhibition and genetic silencing of G9a suppresses H3K9 methylation, cancer cell proliferation, angiogenesis, and cancer cell invasion/migration, but not apoptosis. Microarray and quantitative reverse transcription polymerase chain reaction analyses reveal that G9a induces a cohort of angiogenic factors that include angiogenin, interleukin-8, and C-X-C motif chemokine ligand 16. Depressing G9a by either pharmacological inhibitor or gene knock down significantly reduces angiogenic factor expression. Moreover, promoting G9a gene expression augments transcription and angiogenic function. A luciferase reporter assay suggests that knockdown of G9a inhibits transcriptional activation of interleukin-8. G9a depletion suppresses xenograft tumor growth in mouse model, which is linked to a decrease in microvessel density and proliferating cell nuclear antigen expression. Clinically, higher G9a expression correlates with poorer survival for cancer patients. For patients’ primary tumors a positive correlation between G9a expression and microvessel density also exists. In addition to increasing tumor cell proliferation, G9a promotes tumor angiogenesis and reduces the patient survival rate. G9a may possess great value for targeted therapies.

Telomeres and telomerase in prostate cancer development and therapy

Aberrations in telomere biology are among the earliest events in prostate cancer tumorigenesis and continue during tumour progression. Substantial telomere shortening occurs in prostate cancer cells and high-grade prostatic intraepithelial neoplasia. Not all mechanisms of telomere shortening are understood, but oxidative stress from local inflammation might accelerate prostatic telomere loss. Critically short telomeres can drive the accumulation of tumour-promoting genomic alterations; however, continued telomere erosion is unsustainable and must be mitigated to ensure cancer cell survival and unlimited replication potential. Prostate cancers predominantly maintain telomeres by activating telomerase, but alternative mechanisms of telomere extension can occur in metastatic disease. Telomerase activity and telomere length assessment might be useful in prostate cancer diagnosis and prognosis. Telomere shortening in normal stromal cells has been associated with prostate cancer, whereas variable telomere lengths in prostate cancer cells and telomere shortening in cancer-associated stromal cells correlated with lethal disease. Single-agent telomerase-targeted treatments for solid cancers were ineffective in clinical trials but have not been investigated in prostate cancer and might be useful in combination with established regimens. Telomere-directed strategies have not been explored as extensively. Telomere deprotection strategies have the advantage of being effective in both telomerase-dependent and telomerase-independent cancers. Disruption of androgen receptor function in prostate cancer cells results in telomere dysfunction, indicating telomeres and telomerase as potential therapeutic targets in prostate cancer.

In Vitro Expansion of Human Hepatocytes is Restricted by Telomere-Dependent Replicative Aging

Currently, different techniques to expand human hepatocytes in vitro are being investigated to generate enough cells for liver-directed cell therapies. However, based on observations in fibroblasts and other cell types, telomere attrition limits the proliferative capacity of normal somatic cells. Therefore, we explored whether telomere-dependent replicative aging restricts the in vitro proliferation of human hepatocytes. Subpopulations of cells isolated from a neonatal liver and characterized as hepatocyte derived by RT-PCR and flow cytometry started to proliferate 5–7 days after plating and were termed proliferating human hepatocytes (PHH). Following retroviral-mediated transduction of the catalytic telomerase subunit, telomerase reverse transcriptase (hTERT), telomerase activity increased from almost undetectable levels to levels as high as in HepG2 and other telomerase-positive cell lines. As expected, untransduced PHH progressively lost telomeric repeats and arrested after 30–35 cell divisions with telomeres of less than 5 kilo bases. In comparison, telomerase-reconstituted PHH maintained elongated telomeres and continued to proliferate as shown by colorimetric assays and cell counts. In this study, telomere stabilization extended the proliferative capacity of in vitro proliferating human neonatal hepatocytes. Therefore, telomere attrition needs to be addressed when developing techniques to expand human hepatocytes.

Maintenance of Mouse, Rat, and Pig Pancreatic Islet Functions by Coculture with Human Islet-Derived Fibroblasts

Development of an efficient preculture system of islets is ideal. Toward that goal, we constructed a human pancreatic islet-derived fibroblast cell line MNNK-1 for a source as a coculture system for freshly isolated islets to maintain islet functions. Human pancreatic islet cells were nucleofected with a plasmid vector pYK-1 expressing simian virus 40 large T antigen gene (SV40T) and hygromycin resistance gene (HygroR). One of the transduced cell lines, MNNK-1, was established and served as a feeder cell in the coculture for freshly isolated mouse, rat, and pig islets. Morphology, viability, and glucose-responding insulin secretion were analyzed in the coculture system. MNNK-1 cells were morphologically spindle shaped and were negative for pancreatic endocrine markers. MNNK-1 cells were positive for α-smooth muscle actin and collagen type I and produced fibroblast growth factor. Coculture of the mouse, rat, and pig islets with MNNK-1 cells maintained their viability and insulin secretion with glucose responsiveness. A human pancreatic islet-derived fibroblast cell line MNNK-1 was established. MNNK-1 cells were a useful means for maintaining morphology and insulin secretion of islets in the coculture system.

Telomere erosion in NF1 tumorigenesis

Neurofibromatosis type 1 (NF1; MIM# 162200) is a familial cancer syndrome that affects 1 in 3,500 individuals worldwide and is inherited in an autosomal dominant fashion. Malignant Peripheral Nerve Sheath Tumors (MPNSTs) represent a significant cause of morbidity and mortality in NF1 and currently there is no treatment or definite prognostic biomarkers for these tumors. Telomere shortening has been documented in numerous tumor types. Short dysfunctional telomeres are capable of fusion and it is considered that the ensuing genomic instability may facilitate clonal evolution and the progression to malignancy. To evaluate the potential role of telomere dysfunction in NF1-associated tumors, we undertook a comparative analysis of telomere length in samples derived from 10 cutaneous and 10 diffused plexiform neurofibromas, and 19 MPNSTs. Telomere length was determined using high-resolution Single Telomere Length Analysis (STELA). The mean Xp/Yp telomere length detected in MPNSTs, at 3.282 kb, was significantly shorter than that observed in both plexiform neurofibromas (5.793 kb; [p = 0.0006]) and cutaneous neurofibromas (6.141 kb; [p = 0.0007]). The telomere length distributions of MPNSTs were within the length-ranges in which telomere fusion is detected and that confer a poor prognosis in other tumor types. These data indicate that telomere length may play a role in driving genomic instability and clonal progression in NF1-associated MPNSTs.

Characterization of an acquired jumping translocation involving 3q13.31-qter in a patient with de novo acute monocytic leukemia

We studied an adult with de novo acute monocytic leukemia and a dismal outcome where her leukemic cells harbored an acquired rare jumping translocation (JT). We used oligo-based array CGH (oaCGH) analysis, fluorescence in situ hybridization (FISH), and 24-color karyotyping to enhance the characterization of the JT. G-banding detected a JT involving the 3q13.3-qter chromosomal segment and the recipient chromosomal regions 17p, 8q, and 15q. Each clone with JT was associated with trisomy 8. oaCGH analysis revealed an additional submicroscopic deletion in 3q13.31 as well as small subtelomeric duplications on several chromosomes. Locus-specific FISH with BAC-based probes from the 3q13.31-q13.32 region showed great heterogeneity. Telomere FISH revealed significantly reduced telomeric content in the aberrant cells with JT compared with cytogenetically normal cells at diagnosis and in normal cells at complete remission. A literature search revealed two previous de novo AML-M5 cases of JT involving the 3q13.3-qter chromosomal segment and concomitant trisomy 8. In addition, a case with an unbalanced der(Y)t(Y;3)(q12;q13.31) and additional trisomy 8 was previously reported in a patient with de novo AML-M5. All of these cases had a dismal outcome. In the present case, and in the der(Y)t(Y;3) case, a concurrent submicroscopic deletion at 3q13.31 was observed affecting the TUSC7 gene. Duplication of 3q13.31-qter might be a non-random chromosomal abnormality with concomitant submicroscopic deletion at 3q13.31 occurring in rare cases of acute monocytic leukemia, being associated with adverse prognosis. The impact of shortened telomeres in forming the JT is reviewed.

Immortalization of chicken preadipocytes by retroviral transduction of chicken TERT and TR

The chicken is an important agricultural animal and model for developmental biology, immunology and virology. Excess fat accumulation continues to be a serious problem for the chicken industry. However, chicken adipogenesis and obesity have not been well investigated, because no chicken preadipocyte cell lines have been generated thus far. Here, we successfully generated two immortalized chicken preadipocyte cell lines through transduction of either chicken telomerase reverse transcriptase (chTERT) alone or in combination with chicken telomerase RNA (chTR). Both of these cell lines have survived >100 population doublings in vitro, display high telomerase activity and have no sign of replicative senescence. Similar to primary chicken preadipocytes, these two cell lines display a fibroblast-like morphology, retain the capacity to differentiate into adipocytes, and do not display any signs of malignant transformation. Isoenzyme analysis and PCR-based analysis confirmed that these two cell lines are of chicken origin and are free from inter-species contamination. To our knowledge, this is the first report demonstrating the generation of immortal chicken cells by introduction of chTERT and chTR. Our established chicken preadipocyte cell lines show great promise as an in vitro model for the investigation of chicken adipogenesis, lipid metabolism, and obesity and its related diseases, and our results also provide clues for immortalizing other avian cell types.

Control of Cellular Aging, Tissue Function, and Cancer by p53 Downstream of Telomeres

Telomeres, the nucleoprotein complex at the ends of eukaryotic chromosomes, perform an essential cellular role in part by preventing the chromosomal end from initiating a DNA-damage response. This function of telomeres can be compromised as telomeres erode either as a consequence of cell division in culture or as a normal part of cellular ageing in proliferative tissues. Telomere dysfunction in this context leads to DNA-damage signaling and activation of the tumor-suppressor protein p53, which then can prompt either cellular senescence or apoptosis. By culling cells with dysfunctional telomeres, p53 plays a critical role in protecting tissues against the effects of critically short telomeres. However, as telomere dysfunction worsens, p53 likely exacerbates short telomere-driven tissue failure diseases, including pulmonary fibrosis, aplastic anemia, and liver cirrhosis. In cells lacking p53, unchecked telomere shortening drives chromosomal end-to-end fusions and cycles of chromosome fusion-bridge-breakage. Incipient cancer cells confronting these telomere barriers must disable p53 signaling to avoid senescence and eventually up-regulate telomerase to achieve cellular immortality. The recent findings of highly recurrent activating mutations in the promoter for the telomerase reverse transcriptase (TERT) gene in diverse human cancers, together with the widespread mutations in p53 in cancer, provide support for the idea that circumvention of a telomere-p53 checkpoint is essential for malignant progression in human cancer.

The protein subunit of telomerase displays patterns of dynamic evolution and conservation across different metazoan taxa

BACKGROUND

Most animals employ telomerase, which consists of a catalytic subunit known as the telomerase reverse transcriptase (TERT) and an RNA template, to maintain telomere ends. Given the importance of TERT and telomere biology in core metazoan life history traits, like ageing and the control of somatic cell proliferation, we hypothesised that TERT would have patterns of sequence and regulatory evolution reflecting the diverse life histories across the Animal Kingdom.

RESULTS

We performed a complete investigation of the evolutionary history of TERT across animals. We show that although TERT is almost ubiquitous across Metazoa, it has undergone substantial sequence evolution within canonical motifs. Beyond the known canonical motifs, we also identify and compare regions that are highly variable between lineages, but show conservation within phyla. Recent data have highlighted the importance of alternative splice forms of TERT in non-canonical functions and although animals may share some conserved introns, we find that the selection of exons for alternative splicing appears to be highly variable, and regulation by alternative splicing appears to be a very dynamic feature of TERT evolution. We show that even within a closely related group of triclad flatworms, where alternative splicing of TERT was previously correlated with reproductive strategy, we observe highly diverse splicing patterns.

CONCLUSIONS

Our work establishes that the evolutionary history and structural evolution of TERT involves previously unappreciated levels of change and the emergence of lineage specific motifs. The sequence conservation we describe within phyla suggests that these new motifs likely serve essential biological functions of TERT, which along with changes in splicing, underpin diverse functions of TERT important for animal life histories.

Establishment of a novel human lymphoblastic cell strain with the long arm of chromosome 11 aberration without MLL rearrangement

At present, all cell strains derived from acute lymphoblastic leukemia (ALL) patients with the long arm of chromosome 11 aberration are accompanied with mixed lineage leukemia (MLL) gene rearrangement. In this study, we established a permanent ALL cell strain CHH-1 with the long arm of chromosome 11 aberration and without MLL rearrangement, hoping that it could be used for the research of ALL with such genetic abnormality. CHH-1 cell strain was certified through morphology, immunophenotype, genetics and immunoglobulin (Ig) gene rearrangement analysis. Cell characteristics including tumorigenic ability, semisolid colony forming ability, telomerase activity, autocrine and invasion were further detected. Cells were with an add(11)(q23) structural abnormality without MLL rearrangement, and were consistent with the genetic abnormality of the patient. In addition, these cells had features of tumor-forming ability, high colony forming capacity, unique cytokine autocrine mode, high telomerase activity, and high invasion ability. CHH-1 may prove to be a useful cell model for the research of human leukemia with genetic aberration in chromosome 11, and help explore the role of such genetic abnormality in the pathogenesis, progression and prognosis of ALL, and in developing new target drugs.

Sensing telomerase: From in vitro detection to in vivo imaging

Telomerase is a ribonucleoprotein reverse transcriptase that is responsible for maintaining the telomere length in cells. Telomerase overexpresses in almost all malignant tumor cells, and it has become a promising biomarker and a potential therapy target for cancers. Consequently, accurate and efficient quantification of the telomerase is highly essential to medical diagnostics and therapeutics. Recently, a series of novel telomerase detection methods with excellent performance have been developed, but a overview of in vivo telomerase detection methods is lacking. In this Minireview, we summarize the emerging strategies for telomerase assays in the last five years, including both in vitro assays and in vivo imaging methods, and discuss their future directions as well.

Extensive telomere erosion is consistent with localised clonal expansions in Barrett's metaplasia

Barrett's oesophagus is a premalignant metaplastic condition that predisposes patients to the development of oesophageal adenocarcinoma. However, only a minor fraction of Barrett's oesophagus patients progress to adenocarcinoma and it is thus essential to determine bio-molecular markers that can predict the progression of this condition. Telomere dysfunction is considered to drive clonal evolution in several tumour types and telomere length analysis provides clinically relevant prognostic and predictive information. The aim of this work was to use high-resolution telomere analysis to examine telomere dynamics in Barrett's oesophagus. Telomere length analysis of XpYp, 17p, 11q and 9p, chromosome arms that contain key cancer related genes that are known to be subjected to copy number changes in Barrett's metaplasia, revealed similar profiles at each chromosome end, indicating that no one specific telomere is likely to suffer preferential telomere erosion. Analysis of patient matched tissues (233 samples from 32 patients) sampled from normal squamous oesophagus, Z-line, and 2 cm intervals within Barrett's metaplasia, plus oesophago-gastric junction, gastric body and antrum, revealed extensive telomere erosion in Barrett's metaplasia to within the length ranges at which telomere fusion is detected in other tumour types. Telomere erosion was not uniform, with distinct zones displaying more extensive erosion and more homogenous telomere length profiles. These data are consistent with an extensive proliferative history of cells within Barrett's metaplasia and are indicative of localised clonal growth. The extent of telomere erosion highlights the potential of telomere dysfunction to drive genome instability and clonal evolution in Barrett's metaplasia.

Targeting telomerase and telomeres to enhance ionizing radiation effects in in vitro and in vivo cancer models

One of the hallmarks of cancer consists in the ability of tumor cells to divide indefinitely, and to maintain stable telomere lengths throughout the activation of specific telomere maintenance mechanisms (TMM). Therefore in the last fifteen years, researchers proposed to target telomerase or telomeric structure in order to block limitless replicative potential of cancer cells providing a fascinating strategy for a broad-spectrum cancer therapy. In the present review, we report in vitro and in vivo evidence regarding the use of chemical agents targeting both telomerase or telomere structure and showing promising antitumor effects when used in combination with ionizing radiation (IR). RNA interference, antisense oligonucleotides (e.g., GRN163L), non-nucleoside inhibitors (e.g., BIBR1532) and nucleoside analogs (e.g., AZT) represent some of the most potent strategies to inhibit telomerase activity used in combination with IR. Furthermore, radiosensitizing effects were demonstrated also for agents acting directly on the telomeric structure such as G4-ligands (e.g., RHPS4 and Telomestatin) or telomeric-oligos (T-oligos). To date, some of these compounds are under clinical evaluation (e.g., GRN163L and KML001). Advantages of Telomere/Telomerase Targeting Compounds (T/TTCs) coupled with radiotherapy may be relevant in the treatment of radioresistant tumors and in the development of new optimized treatment plans with reduced dose adsorbed by patients and consequent attenuation of short- end long-term side effects. Pros and cons of possible future applications in cancer therapy based on the combination of T/TCCs and radiation treatment are discussed.

Cytogenetic features of human trophoblast cell lines SWAN-71 and 3A-subE

Immortalization of primary cells with telomerase is thought to maintain normal phenotypic properties and avoid chromosomal abnormalities and other cancer-associated changes that occur following simian virus 40 tumor antigen (SV40 Tag) induced immortalization. However, we report that the human telomerase reverse transcriptase (hTERT)-immortalized SWAN-71 trophoblast cell line has a near pentaploid 103∼119,XXXX[cp20] karyotype. Additionally, DNA typing analysis indicated that SWAN-71 cells have acquired microsatellite instability. In comparison, the post-crisis SV40-transformed trophoblast cell line 3A-subE was hypertriploid 69∼81,XX[cp20]. Both cell lines contained multiple specific clonal rearrangements. These findings emphasize the need to monitor for genetic instability in hTERT-immortalized cells.

The Regulation of Cellular Functions by the p53 Protein: Cellular Senescence

Transformed cells have properties that allow them to survive and proliferate inappropriately. These characteristics often arise as a result of mutations caused by DNA damage. p53 suppresses transformation by removing the proliferative or survival capacity of cells with DNA damage or inappropriate cell-cycle progression. Cellular senescence, marked by morphological and gene expression changes, is a critical component of p53-mediated tumor suppression. In response to stress, p53 can facilitate an arrest and senescence program in cells exposed to stresses such as DNA damage and oncogene activation, preventing transformation. Senescent cells are evident in precancerous adenoma-type lesions, whereas proliferating, malignant tumors have bypassed senescence, either by p53 mutation or inactivation of the p53 pathway by other means. Tumors that have retained wild-type p53 often show a p53-mediated senescence response to chemotherapy. This response is actually detrimental in some tumor types, as senescent cells can drive relapse by persisting and producing cytokines and chemokines through an acquired secretory phenotype.

Relative Telomere Repeat Mass in Buccal and Leukocyte-Derived DNA

Telomere length has garnered interest due to the potential role it may play as a biomarker for the cellular aging process. Telomere measurements obtained from blood-derived DNA are often used in epidemiological studies. However, the invasive nature of blood draws severely limits sample collection, particularly with children. Buccal cells are commonly sampled for DNA isolation and thus may present a non-invasive alternative for telomere measurement. Buccal and leukocyte derived DNA obtained from samples collected at the same time period were analyzed for telomere repeat mass (TRM). TRM was measured in buccal-derived DNA samples from individuals for whom previous TRM data from blood samples existed. TRM measurement was performed by qPCR and was normalized to the single copy 36B4 gene relative to a reference DNA sample (K562). Correlations between TRM from blood and buccal DNA were obtained and also between the same blood DNA samples measured in separate laboratories. Using the classical twin design, TRM heritability was estimated (N = 1892, MZ = 1044, DZ = 775). Buccal samples measured for TRM showed a significant correlation with the blood-1 (R = 0.39, p < 0.01) and blood-2 (R = 0.36, p < 0.01) samples. Sex and age effects were observed within the buccal samples as is the norm within blood-derived DNA. The buccal, blood-1, and blood-2 measurements generated heritability estimates of 23.3%, 47.6% and 22.2%, respectively. Buccal derived DNA provides a valid source for the determination of TRM, paving the way for non-invasive projects, such as longitudinal studies in children.

TERT promoter mutations and long telomere length predict poor survival and radiotherapy resistance in gliomas

Increasing evidences have implicated somatic gain-of-function mutations at the telomerase reverse transcriptase (TERT) promoter as one of the major mechanisms that promote transcriptional activation of TERT and subsequently maintain telomere length in human cancers including glioma. To investigate the prognostic value of these mutations and telomere length, individually and their coexistence, in gliomas, we analyzed two somatic mutations C228T and C250T in the TERT promoter, relative telomere length (RTL), IDH1 mutation and MGMT methylation in 389 glioma patients, and explored their associations with patient characteristics and clinical outcomes. Our data showed that C228T and C250T mutations were found in 17.0% (66 of 389) and 11.8% (46 of 389) of gliomas, respectively, and these two mutations were mutually exclusive in this cancer. Moreover, they were significantly associated with WHO grade. We also found that the RTL was significant longer in gliomas than in meningiomas and normal brain tissues (Median, 0.89 vs. 0.44 and 0.50; P < 0.001), and demonstrated that the RTL was strongly correlated with tumor recurrence. Importantly, TERT promoter mutations or long RTL caused a significantly poorer survival than TERT wild-type or short RTL. Coexisting TERT promoter mutations and long RTL were more commonly associated with poor patient survival than they were individually. Notably, the patients with TERT promoter mutations particularly C228T or long RTL were resistant to radiotherapy. Collectively, TERT promoter mutations and long RTL are not only prognostic factors for poor clinical outcomes, but also the predictors of radiotherapy resistance in gliomas.

Premature senescence of endothelial cells upon chronic exposure to TNFα can be prevented by N-acetyl cysteine and plumericin

Cellular senescence is characterized by a permanent cell-cycle arrest and a pro-inflammatory secretory phenotype, and can be induced by a variety of stimuli, including ionizing radiation, oxidative stress, and inflammation. In endothelial cells, this phenomenon might contribute to vascular disease. Plasma levels of the inflammatory cytokine tumor necrosis factor alpha (TNFα) are increased in age-related and chronic conditions such as atherosclerosis, rheumatoid arthritis, psoriasis, and Crohn's disease. Although TNFα is a known activator of the central inflammatory mediator NF-κB, and can induce the intracellular generation of reactive oxygen species (ROS), the question whether TNFα can induce senescence has not been answered conclusively. Here, we investigated the effect of prolonged TNFα exposure on the fate of endothelial cells and found that such treatment induced premature senescence. Induction of endothelial senescence was prevented by the anti-oxidant N-acetyl cysteine, as well as by plumericin and PHA-408, inhibitors of the NF-κB pathway. Our results indicated that prolonged TNFα exposure could have detrimental consequences to endothelial cells by causing senescence and, therefore, chronically increased TNFα levels might possibly contribute to the pathology of chronic inflammatory diseases by driving premature endothelial senescence.

Discovery of new dual binding TNKS inhibitors of Wnt signaling inhibition by pharmacophore modeling, molecular docking and bioassay

Discovery of novel dual site TNKS inhibitors by pharmacophore modeling, molecular docking and bioassay.

Implementation of Nanoparticles in Cancer Therapy

Cancer is a wide group of diseases and generally characterized by uncontrolled proliferation of cells whose metabolic activities are disrupted. Conventionally, chemotherapy, radiotherapy, and surgery are used in the treatment of cancer. However, in theory, even a single cancer cell may trigger recurrence. Therefore, these treatments cannot provide high survival rate for deadly types. Identification of alternative methods in treatment of cancers is inevitable because of adverse effects of conventional methods. In the last few decades, nanotechnology developed by scientists working in different disciplines—physics, chemistry, and biology—offers great opportunities. It is providing elimination of both circulating tumor cells and solid cancer cells by targeting cancer cells. In this chapter, inadequate parts of conventional treatment methods, nanoparticle types used in new treatment methods of cancer, and targeting methods of nanoparticles are summarized; furthermore, recommendations of future are provided.

Autophagy induction reduces telomerase activity in HeLa cells

Autophagy is a cellular homeostatic process whereby damaged proteins and organelles are encapsulated into double membrane vesicles, called autophagosomes, for lysosomal digestion. Beclin1 plays a key role in the initial steps of autophagosome formation. In this study, we evaluated the effect of Beclin 1 overexpression in induction of autophagy and the relationship between autophagy induction and telomerase activity in HeLa cells. We found that overexpression of Beclin 1 in HeLa cells leads to autophagosome formation as shown by intracellular autophagosomal marker LC3-II staining. Expression of Beclin1 reduced telomerase activity for about 100 fold compared with the control while it did not affect TERT expression level. The results of cell cycle analysis indicated that the cell cycle and proliferation progressed normally up to 48h post-transfection. Understanding the role of autophagy induction and telomerase in the pathophysiology of aging and human cancer reveal new strategies that hold much promise for intervention and therapeutic uses.

Means to the ends: The role of telomeres and telomere processing machinery in metastasis

Despite significant clinical advancements, cancer remains a leading cause of mortality throughout the world due largely to the process of metastasis and the dissemination of cancer cells from their primary tumor of origin to distant secondary sites. The clinical burden imposed by metastasis is further compounded by a paucity of information regarding the factors that mediate metastatic progression. Linear chromosomes are capped by structures known as telomeres, which dictate cellular lifespan in humans by shortening progressively during successive cell divisions. Although telomere shortening occurs in nearly all somatic cells, telomeres may be elongated via two seemingly disjoint pathways: (i) telomerase-mediated extension, and (ii) homologous recombination-based alternative lengthening of telomeres (ALT). Both telomerase and ALT are activated in various human cancers, with more recent evidence implicating both pathways as potential mediators of metastasis. Here we review the known roles of telomere homeostasis in metastasis and posit a mechanism whereby metastatic activity is determined by a dynamic fluctuation between ALT and telomerase, as opposed to the mere activation of a generic telomere elongation program. Additionally, the pleiotropic nature of the telomere processing machinery makes it an attractive therapeutic target for metastasis, and as such, we also explore the therapeutic implications of our proposed mechanism.

TNF-α-induced IL-6 and MMP-9 expression in immortalized ameloblastoma cell line established by hTERT

OBJECTIVE

Ameloblastoma (AM) shows locally invasive behaviour. However, biological investigations regarding regulation of gene expression associated with AM pathological features are difficult to perform, because AM cells can be passaged for a few generations due to senescence. We report a newly established immortalized AM cell line, AMB cells, by transfection with human telomerase reverse transcriptase (hTERT). Furthermore, we examined whether TNF-α modulates bone resorption-related genes, IL-6 and MMP-9 in cooperation with TGF-β or IFN-γ.

MATERIALS AND METHODS

Following transfection of an hTERT expression vector into AM cells using a non-viral method, the effects of cytokines on the expressions of IL-6 and MMP-9 mRNA were examined using real-time PCR. TNF-α-induced NF-κB activity was examined by western blotting and transcription factor assays.

RESULTS

AMB cells continued to grow for more than 100 population doublings. Stimulation with TNF-α increased IL-6 and MMP-9 mRNA expressions, as well as NF-κB activation. Furthermore, TGF-β and IFN-γ dramatically increased TNF-α-mediated expressions of MMP-9 and IL-6 mRNA, respectively, while those responses were suppressed by NF-κB inhibitor.

CONCLUSION

We established an immortalized AM cell line by hTERT transfection. TNF-α-mediated regulation of MMP-9 and IL-6 via NF-κB may play an important role in the pathological behaviour of AMs, such as bone resorption.

Alternative lengthening of human telomeres is a conservative DNA replication process with features of break-induced replication

Human malignancies overcome replicative senescence either by activating the reverse-transcriptase telomerase or by utilizing a homologous recombination-based mechanism, referred to as alternative lengthening of telomeres (ALT). In budding yeast, ALT exhibits features of break-induced replication (BIR), a repair pathway for one-ended DNA double-strand breaks (DSBs) that requires the non-essential subunit Pol32 of DNA polymerase delta and leads to conservative DNA replication. Here, we examined whether ALT in human cancers also exhibits features of BIR A telomeric fluorescence in situ hybridization protocol involving three consecutive staining steps revealed the presence of conservatively replicated telomeric DNA in telomerase-negative cancer cells. Furthermore, depletion of PolD3 or PolD4, two subunits of human DNA polymerase delta that are essential for BIR, reduced the frequency of conservatively replicated telomeric DNA ends and led to shorter telomeres and chromosome end-to-end fusions. Taken together, these results suggest that BIR is associated with conservative DNA replication in human cells and mediates ALT in cancer.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Assessment of Telomere Length in Archived Formalin-Fixed, Paraffinized Human Tissue Is Confounded by Chronological Age and Storage Duration

Telomeres shorten with physiological aging but undergo substantial restoration during cancer immortalization. Increasingly, cancer studies utilize the archive of formalin-fixed, paraffin-embedded (FFPE) tissues in diagnostic pathology departments. Conceptually, such studies would be confounded by physiological telomere attrition and loss of DNA integrity from prolonged tissue storage. Our study aimed to investigate these two confounding factors. 145 FFPE tissues of surgically-resected, non-diseased appendixes were retrieved from our pathology archive, from years 2008 to 2014. Cases from 2013 to 2014 were categorized by patient chronological age (0–20 years, 21–40 years, 41–60 years, > 60 years). Telomere lengths of age categories were depicted by telomere/chromosome 2 centromere intensity ratio (TCR) revealed by quantitative fluorescence in situ hybridization. Material from individuals aged 0–20 years from years 2013/2014, 2011/2012, 2009/2010, and 2008 were compared for storage effect. Telomere integrity was assessed by telomere fluorescence intensity (TFI). Epithelial TCRs (mean ± SD) for the respective age groups were 4.84 ± 2.08, 3.64 ± 1.21, 2.03 ± 0.37, and 1.93 ± 0.45, whereas corresponding stromal TCRs were 5.16 ± 2.55, 3.84 ± 1.36, 2.49 ± 1.20, and 2.93 ± 1.24. A trend of inverse correlation with age in both epithelial and stromal tissues is supported by r = -0.69, p < 0.001 and r = -0.42, p < 0.001 respectively. Epithelial TFIs (mean ± SD) of years 2013/2014, 2011/2012, 2009/2010 and 2008 were 852.60 ± 432.46, 353.04 ± 127.12, 209.24 ± 55.57 and 429.22 ± 188.75 respectively. Generally, TFIs reduced with storage duration (r = -0.42, p < 0.001). Our findings agree that age-related telomere attrition occurs in normal somatic tissues, and suggest that an age-based reference can be established for telomere studies on FFPE tissues. We also showed that FFPE tissues archived beyond 2 years are suboptimal for telomere analysis.

Understanding specific functions of PARP-2: new lessons for cancer therapy

Poly(ADP-ribosyl)ation (PARylation) is a widespread and highly conserved post-translational modification catalysed by a large family of enzymes called poly(ADP-ribose) polymerases (PARPs). PARylation plays an essential role in various cardinal processes of cellular physiology and recent approvals and breakthrough therapy designations for PARP inhibitors in cancer therapy have sparked great interest in pharmacological targeting of PARP proteins. Although, many PARP inhibitors have been developed, existing compounds display promiscuous inhibition across the PARP superfamily which could lead to unwanted off-target effects. Thus the prospect of isoform-selective inhibition is being increasingly explored and research is now focusing on understanding specific roles of PARP family members. PARP-2, alongside PARP-1 and PARP-3 are the only known DNA damage-dependent PARPs and play critical roles in the DNA damage response, DNA metabolism and chromatin architecture. However, growing evidence shows that PARP-2 plays specific and diverse regulatory roles in cellular physiology, ranging from genomic stability and epigenetics to proliferative signalling and inflammation. The emerging network of PARP-2 target proteins has uncovered wide-ranging functions of the molecule in many cellular processes commonly dysregulated in carcinogenesis. Here, we review novel PARP-2-specific functions in the hallmarks of cancer and consider the implications for the development of isoform-selective inhibitors in chemotherapy. By considering the roles of PARP-2 through the lens of tumorigenesis, we propose PARP-2-selective inhibition as a potentially multipronged attack on cancer physiology.

Selective recognition and stabilization of new ligands targeting the potassium form of the human telomeric G-quadruplex DNA

The development of a ligand that is capable of distinguishing among the wide variety of G-quadruplex structures and targeting telomeres to treat cancer is particularly challenging. In this study, the ability of two anthraquinone telomerase inhibitors (NSC749235 and NSC764638) to target telomeric G-quadruplex DNA was probed. We found that these ligands specifically target the potassium form of telomeric G-quadruplex DNA over the DNA counterpart. The characteristic interaction with the telomeric G-quadruplex DNA and the anticancer activities of these ligands were also explored. The results of this present work emphasize our understanding of the binding selectivity of anthraquinone derivatives to G-quadruplex DNA and assists in future drug development for G-quadruplex-specific ligands.