Cellular senescence and cancer

Purinergic signaling promotes premature senescence

Extracellular ATP activates P2 purinergic receptors. Whether purinergic signaling is functionally coupled to cellular senescence is largely unknown. We find that oxidative stress induced release of ATP and caused senescence in human lung fibroblasts. Inhibition of P2 receptors limited oxidative stress-induced senescence, while stimulation with exogenous ATP promoted premature senescence. Pharmacological inhibition of P2Y11 receptor (P2Y11R) inhibited premature senescence induced by either oxidative stress or ATP, while stimulation with a P2Y11R agonist was sufficient to induce cellular senescence. Our data show that both extracellular ATP and a P2Y11R agonist induced calcium (Ca++) release from the endoplasmic reticulum (ER) and that either inhibition of phospholipase C or intracellular Ca++ chelation impaired ATP-induced senescence. We also find that Ca++ that was released from the ER, following ATP-mediated activation of phospholipase C, entered mitochondria in a manner dependent on P2Y11R activation. Once in mitochondria, excessive Ca++ promoted the production of reactive oxygen species in a P2Y11R-dependent fashion, which drove development of premature senescence of lung fibroblasts. Finally, we show that conditioned medium derived from senescent lung fibroblasts, which were induced to senesce through the activation of ATP/P2Y11R-mediated signaling, promoted the proliferation of triple-negative breast cancer cells and their tumorigenic potential by secreting amphiregulin. Our study identifies the existence of a novel purinergic signaling pathway that links extracellular ATP to the development of a protumorigenic premature senescent phenotype in lung fibroblasts that is dependent on P2Y11R activation and ER-to-mitochondria calcium signaling.

Lectins as a promising therapeutic agent for breast cancer: A review

Efficient treatment of cancer has been a subject of research by scientists for many years. Current treatments for cancer, such as radiotherapy, chemotherapy and surgery have been used in traditional combination therapy, but they have major setbacks like non-specificity, non-responsiveness in certain cancer types towards treatment, tumor recurrence, etc. Epidemiological data has shown that breast cancer accounts for 14% of cancer cases occurring in Indian women. In recent years, scientists have started to focus on the use of natural compounds like lectins obtained from various sources to counter the side effects of traditional therapy. Lectins like Sambucus nigra Agglutinin, Maackia amurensis lectin, Okra lectins, Haliclona caerulea lectin, Sclerotium rolfsii lectin, etc., have been discovered to have both diagnostic and therapeutic potential for breast cancer patients. Lectins have been found to have inhibitory effects on various cancer cell activities such as neo-angiogenesis, causing cell cycle arrest at the G1 phase, and inducing apoptosis. The major idea behind the use of lectins in cancer diagnostics and therapeutics is their capability to bind to glycosylated proteins that are expressed on the cell surface. This review focuses on an exploration of the roles of post-translational modification in cancer cells, especially glycosylation, and the potential of lectins in cancer diagnosis and therapeutics.

Impaired Cdc20 signaling promotes senescence in normal cells and apoptosis in non-small cell lung cancer cells

Cellular senescence is a form of irreversible growth arrest that cancer cells evade. The cell division cycle protein 20 homolog (Cdc20) is a positive regulator of cell division, but how its dysregulation may relate to senescence is unclear. Here, we find that Cdc20 mRNA and protein expression are downregulated in stress-induced premature senescent lung fibroblasts in a p53-dependent manner. Either Cdc20 downregulation or inhibition of anaphase-promoting complex/cyclosome (APC/C) is sufficient to induce premature senescence in lung fibroblasts, while APC/C activation inhibits stress-induced premature senescence. Mechanistically, we show both Cdc20 downregulation and APC/C inhibition induce premature senescence through glycogen synthase kinase (GSK)-3β-mediated phosphorylation and downregulation of securin expression. Interestingly, we determined Cdc20 expression is upregulated in human lung adenocarcinoma. We find that downregulation of Cdc20 in non-small cell lung cancer (NSCLC) cells is sufficient to inhibit cell proliferation and growth in soft agar and to promote apoptosis, but not senescence, in a manner dependent on downregulation of securin following GSK-3β-mediated securin phosphorylation. Similarly, we demonstrate securin expression is downregulated and cell viability is inhibited in NSCLC cells following inhibition of APC/C. Furthermore, we show chemotherapeutic drugs downregulate both Cdc20 and securin protein expression in NSCLC cells. Either Cdc20 downregulation by siRNA or APC/C inhibition sensitize, while securin overexpression inhibits, chemotherapeutic drug-induced NSCLC cell death. Together, our findings provide evidence that Cdc20/APC/C/securin-dependent signaling is a key regulator of cell survival, and its disruption promotes premature senescence in normal lung cells and induces apoptosis in lung cancer cells that have bypassed the senescence barrier.

Dual Inhibition of H3K9me2 and H3K27me3 Promotes Tumor Cell Senescence without Triggering the Secretion of SASP

Chemotherapy remains the most common cancer treatment. Although chemotherapeutic drugs induce tumor cell senescence, they are often associated with post-therapy tumor recurrence by inducing the senescence-associated secretory phenotype (SASP). Therefore, it is important to identify effective strategies to induce tumor cell senescence without triggering SASP. In this study, we used the small molecule inhibitors, UNC0642 (G9a inhibitor) and UNC1999 (EZH2 inhibitor) alone or in combination, to inhibit H3K9 and H3K27 methylation in different cancer cells. Dual inhibition of H3K9me2 and H3K27me3 in highly metastatic tumor cells had a stronger pro-senescence effect than either inhibitor alone and did not trigger SASP in tumor cells. Dual inhibition of H3K9me2 and H3K27me3 suppressed the formation of cytosolic chromatin fragments, which inhibited the cGAS-STING-SASP pathway. Collectively, these data suggested that dual inhibition of H3K9 and H3K27 methylation induced senescence of highly metastatic tumor cells without triggering SASP by inhibiting the cGAS-STING-SASP pathway, providing a new mechanism for the epigenetics-based therapy targeting H3K9 and H3K27 methylation.

TP53 Expression and Mutational Analysis in Hematological Malignancy in Jeddah, Saudi Arabia

Background: Tumor protein 53 (TP53) is a tumor-suppressor gene and plays an essential role in apoptosis, cell cycle arrest, genomic stability, and DNA repair. Although it is the most often mutated gene in human cancer, it has respectively low frequency in hematological malignancy but is significantly linked with complex karyotype, poor prognosis, and chemotherapeutic response. Nevertheless, the prevalence and prognostic role of TP53 mutations in hematological malignancy in Saudi patients are not well reported. We, therefore, aim to assess the frequency of TP53 mutations in hematological malignancies in Saudi Arabia. Method: 20 different hematological malignancy samples were tested using fluorescence in situ hybridization (FISH) technique for TP53 deletion detection and next-generation sequencing (NGS) targeted panel was applied on 10 samples for mutations identification specifically TP53 mutation. Results: TP53 deletion was detected in 6 of 20 samples by FISH. Most of the 6 patients with TP53 deletion had acute lymphoblastic leukemia (ALL), and majority of them were child. NGS result revealed one heterozygous missense mutation in exon 5 of the TP53 gene (c. G9963A, p.H175R). Conclusion: To the best of our knowledge, the TP53 mutation is novel variant, and the first time we are reporting their association with myelodysplastic syndromic individual with complex karyotype. This study recommends further analysis of genomic mutations on bigger cohorts, utilizing high throughput technologies.

Caveolin-1, a master regulator of cellular senescence

Cellular senescence is a feature of most somatic cells. It is characterized by an irreversible cell cycle arrest and by the ability to secrete a plethora of mediators of inflammation and growth factors, which can alter the senescent cell's microenvironment. Senescent cells accumulate in tissues over time and contribute to both aging and the development of age-associated diseases. Senescent cells have antagonistic pleiotropic roles in cancer. Given the inability of senescent cells to proliferate, cellular senescence is a powerful tumor suppressor mechanism in young individuals. However, accumulation of senescent stromal cells during aging can fuel cancer cell growth in virtue of their capacity to release factors that stimulate cell proliferation. Caveolin-1 is a structural protein component of caveolae, invaginations of the plasma membrane involved in a variety of cellular processes, including signal transduction. Mounting evidence over the last 10-15 years has demonstrated a central role of caveolin-1 in the development of a senescent phenotype and the regulation of both the anti-tumorigenic and pro-tumorigenic properties of cellular senescence. In this review, we discuss the cellular mechanisms and functions of caveolin-1 in the context of cellular senescence and their relevance to the biology of cancer.

A pilot study for early detection of oral premalignant diseases using oral cytology and Raman micro-spectroscopy: Assessment of confounding factors

This study demonstrates the efficacy of Raman micro-spectroscopy of oral cytological samples for differentiating dysplastic, potentially malignant lesions from those of normal, healthy donors. Cells were collected using brush biopsy from healthy donors (n = 20) and patients attending a Dysplasia Clinic (n = 20). Donors were sampled at four different sites (buccal mucosa, tongue, alveolus, gingiva), to ensure matched normal sites for all lesions, while patient samples were taken from clinically evident, histologically verified dysplastic lesions. Spectra were acquired from the nucleus and cytoplasm of individual cells of all samples and subjected to partial least squares-discriminant analysis. Discriminative sensitivities of 94% and 86% and specificity of 85% were achieved for the cytoplasm and nucleus, respectively, largely based on lipidic contributions of dysplastic cells. Alveolar/gingival samples were differentiated from tongue/buccal samples, indicating that anatomical site is potentially a confounding factor, while age, gender, smoking and alcohol consumption were confirmed not to be.

Loss of BRG1 induces CRC cell senescence by regulating p53/p21 pathway

Brahma-related gene-1 (BRG1) is the specific ATPase of switch/sucrose nonfermentable chromatin-remodeling complex that is aberrantly expressed or mutated in various cancers. However, the exact role of BRG1 in oncogenesis remains unknown. In this study, we demonstrate that the knockdown (KD) of BRG1 promotes cellular senescence by influencing the SIRT1/p53/p21 signal axis in colorectal cancer (CRC). In particular, we reveal that the expression level of BRG1 is inversely correlated with p21, one of the classic senescence regulators, and is decreased in senescent CRC cells. KD of BRG1 promoting senescence is indicated by the increase of senescence-associated β-galactosidase (SA-β-gal) activity, inhibition of cell proliferation, induction of cell cycle arrest, and formation of senescence-associated heterochromatin foci. BRG1 binds to SIRT1 and interferes with SIRT1-mediated deacetylation of p53 at K382. Rescue experiments by co-silencing p53 or treatment with EX527, a SIRT1-specific inhibitor, abrogated the cellular senescence induced by KD of BRG1. BRG1 KD cells resulted in smaller tumor formation than that in control cells in vivo. Collectively, our study shows that BRG1 has an important role in cellular senescence and tumor growth. The BRG1/SIRT1/p53 signal axis is a novel mechanism of cell senescence in CRC and is a new potential target for cancer therapy.

The impact of TP53 mutations and TP53 deletions on survival varies between AML, ALL, MDS and CLL: an analysis of 3307 cases

Alterations in TP53 have been described in many cancer types including hematological neoplasms. We aimed at comparing TP53 mutations (mut) and deletions (del) in a large cohort of patients with hematological malignancies (n=3307), including AML (n=858), MDS (n=943), ALL (n=358), CLL (n=1148). Overall, alterations in TP53 were detected in 332/3307 cases (10%). The highest frequency was observed in ALL (total: 19%; mut+del: 6%; mut only: 8%; del only: 5%) and AML (total: 13%; mut+del: 5%; mut only: 7%; del only: 1%), whereas TP53 alterations occurred less frequently in CLL (total: 8%) and MDS (total: 7%). TP53 mutations were significantly more frequent in patients ⩾60 vs <60 years in AML (9% vs 2%, P<0.001) and ALL (12% vs 6%, P<0.001). TP53mut+del had a significant negative impact on overall survival in all entities, whereas differences were observed regarding TP53mut only or TP53del only: TP53mut only impacted survival in AML (36 vs 9 months, P<0.001) and MDS (65 vs 19 months, P<0.001), TP53del only in CLL (not reached vs 64 months, P=0.008) and MDS (65 vs 24 months, P=0.011). As substantial differences between the entities are observed regarding correlation to age and survival, we suggest evaluation of both TP53 deletion and mutation status.

A quantitative model of cellular senescence influence on cancer and longevity

Contrary to the paradigm that cancer incidence increases indefinitely with age, significant data now suggest cancer incidence may markedly reduce beyond age 80 years for humans and beyond 800 days for mice, and is not inevitable. We show that increasing cellular senescence with age is a possible cause of this reduction, since senescent cells are removed from the pool of cells that retain proliferative ability necessary for cancer. We further show that animal interventions appearing to alter senescence, p53 mutation and melatonin dosing, support the prediction that increasing senescence rate reduces cancer while reducing lifespan, and vice versa. Studies of environmental agents associated with increased cancer might be re-examined to find if there is an association with longevity increases, which may markedly alter our view of such agents. We also show that if an agent functions by slowing both senescence and carcinogenesis, longevity is increased while reducing cancer. Dietary restriction is the only known intervention that accomplishes this, but there may be others.

Oxidative stress-induced inhibition of Sirt1 by caveolin-1 promotes p53-dependent premature senescence and stimulates the secretion of interleukin 6 (IL-6)

Oxidative stress can induce premature cellular senescence. Senescent cells secrete various growth factors and cytokines, such as IL-6, that can signal to the tumor microenvironment and promote cancer cell growth. Sirtuin 1 (Sirt1) is a class III histone deacetylase that regulates a variety of physiological processes, including senescence. We found that caveolin-1, a structural protein component of caveolar membranes, is a direct binding partner of Sirt1, as shown by the binding of the scaffolding domain of caveolin-1 (amino acids 82-101) to the caveolin-binding domain of Sirt1 (amino acids 310-317). Our data show that oxidative stress promotes the sequestration of Sirt1 into caveolar membranes and the interaction of Sirt1 with caveolin-1, which lead to inhibition of Sirt1 activity. Reactive oxygen species stimulation promotes acetylation of p53 and premature senescence in wild-type but not caveolin-1 null mouse embryonic fibroblasts (MEFs). Either down-regulation of Sirt1 expression or re-expression of caveolin-1 in caveolin-1 null MEFs restores reactive oxygen species-induced acetylation of p53 and premature senescence. In addition, overexpression of caveolin-1 induces stress induced premature senescence in p53 wild-type but not p53 knockout MEFs. Phosphorylation of caveolin-1 on tyrosine 14 promotes the sequestration of Sirt1 into caveolar membranes and activates p53/senescence signaling. We also identified IL-6 as a caveolin-1-specific cytokine that is secreted by senescent fibroblasts following the caveolin-1-mediated inhibition of Sirt1. The caveolin-1-mediated secretion of IL-6 by senescent fibroblasts stimulates the growth of cancer cells. Therefore, by inhibiting Sirt1, caveolin-1 links free radicals to the activation of the p53/senescence pathway and the protumorigenic properties of IL-6.

TP53 mutations occur in 15.7% of ALL and are associated with MYC-rearrangement, low hypodiploidy, and a poor prognosis

TP53 is the most extensively studied gene in cancer. However, data on frequency and the prognostic impact of TP53 mutations in acute lymphoblastic leukemia (ALL) remain scarce. Thus, we aimed at identifying the mutation frequency of TP53, its association with cytogenetic subgroups, and its impact on survival in a large cohort of 625 patients with ALL. Our data revealed an overall mutation incidence of 15.7%, which increases with age. Correlation with cytogenetic subgroups showed that mutations were most frequent in ALL with low hypodiploidy or MYC-rearrangements. Furthermore, for a large number of patients, both TP53 alleles were altered, either by 2 TP53 mutations (12%) or by a TP53 mutation and a TP53 deletion in the second allele (39%). A high TP53 mutation load was correlated to low hypodiploidy, high hyperdiploidy, and a complex karyotype. Moreover, a higher mutation load was found in B-lineage ALL compared with T-lineage ALL. Similar to other cancers, the median overall survival was significantly shorter in patients with TP53 mutation compared with patients with wild-type TP53. This effect was especially pronounced when both TP53 alleles were affected, either by 2 TP53 mutations or by both a mutation and an accompanying TP53 deletion.

Molecular basis of cancer-therapy-induced cardiotoxicity: introducing microRNA biomarkers for early assessment of subclinical myocardial injury

Development of reliable biomarkers for early clinical assessment of drug-induced cardiotoxicity could allow the detection of subclinical cardiac injury risk in vulnerable patients before irreversible damage occurs. Currently, it is difficult to predict who will develop drug-induced cardiotoxicity owing to lack of sensitivity and/or specificity of currently used diagnostics. miRNAs are mRNA regulators and they are currently being extensively profiled for use as biomarkers due to their specific tissue and disease expression signature profiles. Identification of cardiotoxicity-specific miRNA biomarkers could provide clinicians with a valuable tool to allow prognosis of patients at risk of cardiovascular injury, alteration of a treatment regime or the introduction of an adjunct therapy in order to increase the long-term survival rate of patients treated with cardiotoxic drugs.

Inhibition of nuclear factor-erythroid 2-related factor (Nrf2) by caveolin-1 promotes stress-induced premature senescence

Reactive oxygen species can induce premature senescence. Caveolin-1 promotes oxidative stress–induced activation of the p53/p21Waf1/Cip1 pathway and development of premature senescence by acting as an endogenous inhibitor of the transcription factor Nrf2.

Reactive oxygen species (ROS) can induce premature cellular senescence, which is believed to contribute to aging and age-related diseases. The nuclear erythroid 2 p45–related factor-2 (Nrf2) is a transcription factor that mediates cytoprotective responses against stress. We demonstrate that caveolin-1 is a direct binding partner of Nrf2, as shown by the binding of the scaffolding domain of caveolin-1 (amino acids 82–101) to the caveolin-binding domain of Nrf2 (amino acids 281–289). Biochemical studies show that Nrf2 is concentrated into caveolar membranes in human and mouse fibroblasts, where it colocalizes with caveolin-1, under resting conditions. After oxidative stress, caveolin-1 limits the movement of Nrf2 from caveolar membranes to the nucleus. In contrast, Nrf2 is constitutively localized to the nucleus before and after oxidative stress in caveolin-1–null mouse embryonic fibroblasts (MEFs), which do not express caveolin-1. Functional studies demonstrate that caveolin-1 acts as an endogenous inhibitor of Nrf2, as shown by the enhanced up-regulation of NQO1, an Nrf2 target gene, in caveolin-1–null MEFs and the activation or inhibition of a luciferase construct carrying an antioxidant responsive element (ARE) after down-regulation of caveolin-1 by small interfering RNA or overexpression of caveolin-1, respectively. Expression of a mutant form of Nrf2 that cannot bind to caveolin-1 (Φ→A-Nrf2) hyperactivates ARE and inhibits oxidative stress–induced activation of the p53/p21^Waf1/Cip1 pathway and induction of premature senescence in fibroblasts. Finally, we show that overexpression of caveolin-1 in colon cancer cells inhibits oxidant-induced activation of Nrf2-dependent signaling, promotes premature senescence, and inhibits their transformed phenotype. Thus, by inhibiting Nrf2-mediated signaling, caveolin-1 links free radicals to the activation of the p53/senescence pathway.

Expression of human telomerase reverse transcriptase in vulvar intraepithelial neoplasia and squamous cell carcinoma: an immunohistochemical study with survivin and p53

CONTEXT

Human telomerase reverse transcriptase (hTERT), an enzyme that enables cells to overcome replicative senescence and to divide indefinitely, is overexpressed in many cancers and their precursor lesions.

OBJECTIVE

To test whether hTERT expression is related to neoplastic progression and resistance to apoptosis in vulvar epithelia.

DESIGN

Immunoexpression of hTERT was evaluated in 101 formalin-fixed, paraffin-embedded archival vulvar epithelia consisting of normal squamous vulvar epithelia (n  =  25), lichen sclerosus (n  =  10), high-grade classic vulvar intraepithelial neoplasia (n  =  16), differentiated vulvar intraepithelial neoplasia (n  =  18), and vulvar invasive keratinizing squamous cell carcinoma (n  =  32) and related to survivin and p53 expression. Immunostaining for all factors was scored for moderate and strong intensities with regard to quantity to determine upregulation and overexpression (score 0, 0% immunoreactive cells; score 1+, <5% immunoreactive cells; score 2+, 5% to 50% immunoreactive cells; score 3+, >50% immunoreactive cells). Score 3+ was considered as overexpression.

RESULTS

Nuclear hTERT immunoexpression was closely related to survivin reactivity, increased from normal vulvar squamous epithelia to lichen sclerosus and to high-grade classic vulvar intraepithelial neoplasia, differentiated vulvar intraepithelial neoplasia, and invasive keratinizing squamous cell carcinoma (P < .001), and followed the morphologic distribution of atypical squamous epithelial cells. Overexpression of hTERT was comparable to that seen for p53 in invasive keratinizing squamous cell carcinoma (P  =  .62); significant differences were calculated for differentiated vulvar intraepithelial neoplasia (P  =  .003) and high-grade classic vulvar intraepithelial neoplasia (P  =  .001).

CONCLUSION

Human telomerase reverse transcriptase is upregulated in vulvar intraepithelial neoplasia and invasive keratinizing squamous cell carcinoma compared with nonneoplastic squamous epithelia of the vulva as an apparently early and preinvasive event in the neoplastic transformation, with development of cellular longevity and resistance to apoptosis by survivin activation as associated features, independent of the etiology of vulvar intraepithelial neoplasia.

Senescence regulation by the p53 protein family

p53, a guardian of the genome, exerts its tumor suppression activity by regulating a large number of downstream targets involved in cell cycle arrest, DNA repair, apoptosis, and cellular senescence. Although p53-mediated apoptosis is able to kill cancer cells, a role for cellular senescence in p53-dependent tumor suppression is becoming clear. Mouse studies showed that activation of p53-induced premature senescence promotes tumor regression in vivo. However, p53-mediated cellular senescence also leads to aging-related phenotypes, such as tissue atrophy, stem cell depletion, and impaired wound healing. In addition, several p53 isoforms and two p53 homologs, p63 and p73, have been shown to play a role in cellular senescence and/or aging. Importantly, p53, p63, and p73 are necessary for the maintenance of adult stem cells. Therefore, understanding the dual role the p53 protein family in cancer and aging is critical to solve cancer and longevity in the future. In this chapter, we provide an overview on how p53, p63, p73, and their isoforms regulate cellular senescence and aging.

Autophagy, apoptosis, mitoptosis and necrosis: interdependence between those pathways and effects on cancer

Cell death is a fundamental ingredient of life. Thus, not surprisingly more than one form of cell death exists. Several excellent reviews on various forms of cell death have already been published but manuscripts describing interconnection and interdependence between such processes are uncommon. Here, what follows is a brief introduction on all three classical forms of cell death, followed by a more detailed insight into the role of p53, the master regulator of apoptosis, and other forms of cell death. While discussing p53 and also the role of caspases in cell death forms, we offer insight into the interplay between autophagy and apoptosis, or necrosis, where autophagy may initially serve pro-survival functions. The review moves further to present some details about less researched forms of programmed cell death, namely necroptosis, necrosis and mitoptosis. These "mixed" forms of cell death allow us to highlight the interconnected nature of cell death forms, particularly apoptosis and necrosis. The interdependence between apoptosis, autophagy and necrosis, and their significance for cancer development and treatment are also analyzed in further parts of the review. In the concluding parts, the afore-mentioned issues will be put in perspective for the development of novel anti-cancer therapies.

Caveolin-1, cellular senescence and age-related diseases

According to the "free radical theory" of aging, normal aging occurs as the result of tissue damages inflicted by reactive oxygen species (ROS) when ROS production exceeds the antioxidant capacity of the cell. ROS induce cellular dysfunctions such as stress-induced premature senescence (SIPS), which is believed to contribute to normal organismal aging and play a role in age-related diseases. Consistent with this hypothesis, increased oxidative damage of DNA, proteins, and lipids have been reported in aged animals and senescent cells accumulate in vivo with advancing age. Caveolin-1 acts as a scaffolding protein that concentrates and functionally regulates signaling molecules. Recently, great progress has been made toward understanding of the role of caveolin-1 in stress-induced premature senescence. Data show that caveolin-mediated signaling may contribute to explain, at the molecular level, how oxidative stress promotes the deleterious effects of cellular senescence such as aging and age-related diseases. In this review, we discuss the cellular mechanisms and functions of caveolin-1 in the context of SIPS and their relevance to the biology of aging.

Tubal metaplasia of the endometrium with cytologic atypia: analysis of p53, Ki-67, TERT, and long-term follow-up

Tubal metaplasia of the endometrium may occasionally display cytologic atypia (atypical tubal metaplasia) resembling serous carcinoma or endometrial intraepithelial carcinoma. Although atypical tubal metaplasia is presumed to be reactive or degenerative in etiology, its clinical significance is unknown. In this study, we investigated atypical tubal metaplasia in regard to its immunoexpression of p53, Ki-67, and human telomerase reverse transcriptase (TERT), and its long-term clinical outcome. A total of 63 cases of atypical tubal metaplasia and 200 cases of endometrial samples with typical tubal metaplasia were followed for a mean of 64 and 61 months, respectively. Of the 63 atypical tubal metaplasia cases, formalin-fixed, paraffin-embedded tissue sections from 16 cases were immunostained with antibodies to p53, Ki-67, and TERT. Sections from 13 cases of uterine serous carcinoma were also stained for TERT as control. After long-term follow-up, 5% of patients in the atypical tubal metaplasia group developed hyperplasia without atypia compared with 4% of patients in the control group (P=0.44), whereas 3% in the atypical tubal metaplasia group developed atypical hyperplasia or carcinoma compared with 2% in the control group (P=0.44). p53 immunoreactivity was either focal and weak or negative in all cases of both atypical and typical tubal metaplasia (P>0.05). Ki-67 immunoreactivity was present in 0-5% of cells in 94% of both atypical and typical tubal metaplasia (P>0.05). TERT immunoexpression was absent in all 16 cases of atypical tubal metaplasia, but present in all 13 cases of uterine serous carcinoma (P<0.0001). Our study indicates that atypical tubal metaplasia displays an immunostaining pattern similar to otherwise typical tubal metaplasia of the endometrium, and distinct from uterine serous neoplasms. The presence of atypical tubal metaplasia in endometrial samplings does not increase the risk of developing endometrial hyperplasia or malignancy.

Pirin inhibits cellular senescence in melanocytic cells

Cellular senescence has been widely recognized as a tumor suppressing mechanism that acts as a barrier to cancer development after oncogenic stimuli. A prominent in vivo model of the senescence barrier is represented by nevi, which are composed of melanocytes that, after an initial phase of proliferation induced by activated oncogenes (most commonly BRAF), are blocked in a state of cellular senescence. Transformation to melanoma occurs when genes involved in controlling senescence are mutated or silenced and cells reacquire the capacity to proliferate. Pirin (PIR) is a highly conserved nuclear protein that likely functions as a transcriptional regulator whose expression levels are altered in different types of tumors. We analyzed the expression pattern of PIR in adult human tissues and found that it is expressed in melanocytes and has a complex pattern of regulation in nevi and melanoma: it is rarely detected in mature nevi, but is expressed at high levels in a subset of melanomas. Loss of function and overexpression experiments in normal and transformed melanocytic cells revealed that PIR is involved in the negative control of cellular senescence and that its expression is necessary to overcome the senescence barrier. Our results suggest that PIR may have a relevant role in melanoma progression.

Quantitative cytomorphometric analysis of exfoliated normal gingival cells

Background:

The use of oral exfoliative cytology as a diagnostic aid accentuates the need for establishing an accurate baseline, thereby enabling the comparison of abnormal oral tissue with established baseline.

Aims and Objective:

To detect any changes in the nuclear area (NA), cytoplasmic area (CA), and nuclear:cytoplasmic ratio (N:C ratio) values for clinically normal gingival smears in relation to age and sex of apparently healthy subjects.

Materials and Methods:

Gingival smears were collected from 80 (40 male, 40 female) apparently healthy subjects belonging to the age group of 0–20, 21–40, 41–60, and more than 60 years. Smear slides were fixed by using spray fixative. The smears were stained using Papanicolaou procedure. The cytoplasmic and NAs were measured using image analysis software. Statistical analysis of the data was done using one-way ANOVA with Tukey–HSD procedure and Student's t test.

Results:

The result showed that there was a significant difference (P<0.001) in NA, CA, and N:C in males of different age groups. There was a significant difference (P<0.001) in NA, CA, and N:C in females of different age groups. The difference in N:C between males and females was significant (P<0.001) in all the groups. The difference in NA, CA, and N:C with age irrespective of gender was significant (P<0.05). There was a significant difference (P<0.05) between males and females with respect to NA, CA, and N:C irrespective of age.

Conclusion:

Age-and sex-related alterations were observed in gingival smears, which could be a baseline for these variables to compare identical measurements, made on pathologic smears of oral premalignant and malignant lesions.

Polymerase I and transcript release factor (PTRF)/cavin-1 is a novel regulator of stress-induced premature senescence

According to the "free radical theory" of aging, premature senescence induced by oxidative stress contributes to organismal aging. Polymerase I and transcript release factor (PTRF)/cavin-1 is a structural protein component of caveolae, invaginations of the plasma membrane involved in signal transduction. We show that oxidative stress up-regulates PTRF/cavin-1 protein expression and promotes the interaction between PTRF/cavin-1 and caveolin-1, another structural protein component of caveolae. Consistent with these data, the number of caveolae is dramatically increased in cells subjected to oxidative stress. We demonstrate that down-regulation of PTRF/cavin-1 by shRNA significantly inhibits oxidative stress-induced premature senescence. Mechanistically, we found that PTRF/cavin-1 expression is necessary for the oxidant-induced sequestration of Mdm2, a negative regulator of p53, into caveolar membranes, away from p53, and activation of the p53/p21(Waf1/Cip1) pathway. Expression of a mutant form of PTRF/cavin-1, which fails to localize to caveolar membranes after oxidative stress, inhibits oxidative stress-induced activation of p53 and induction of premature senescence. Thus, PTRF/cavin-1 is a novel regulator of oxidative stress-induced premature senescence by acting as a link between free radicals and activation of the p53/p21(Waf1/Cip1) pathway.

Malignancy without immortality? Cellular immortalization as a possible late event in melanoma progression

Cell senescence is a permanent growth arrest following extended proliferation. Cultured cancer cells including metastatic melanoma cells often appear immortal (proliferate indefinitely), while uncultured benign nevi (moles) show senescence markers. Here, with new explantation methods, we investigated which classes of primary pigmented lesions are typically immortal. Nevi yielded a few proliferating cells, consistent with most nevus cells being senescent. No nevus culture (0/28) appeared immortal. Some thin and thick melanoma cultures proved immortal under these conditions, but surprisingly few (4/37). All arrested cultures displayed three senescence markers in some cells: β-galactosidase, nuclear p16, and heterochromatic foci/aggregates. However, melanoma cultures also showed features of telomeric crisis (arrest because of ultrashort telomeres). Moreover, crisis markers including anaphase bridges were frequent in uncultured vertical growth-phase (VGP) melanomas. Conversely, all immortal melanoma cultures expressed telomerase reverse transcriptase and telomerase, showing aneuploidy. The findings suggest that primary melanomas are typically precrisis, with immortalization/telomere maintenance as a late event.

The central nervous system-restricted transcription factor Olig2 opposes p53 responses to genotoxic damage in neural progenitors and malignant glioma

High-grade gliomas are notoriously insensitive to radiation and genotoxic drugs. Paradoxically, the p53 gene is structurally intact in the majority of these tumors. Resistance to genotoxic modalities in p53-positive gliomas is generally attributed to attenuation of p53 functions by mutations of other components within the p53 signaling axis, such as p14(Arf), MDM2, and ATM, but this explanation is not entirely satisfactory. We show here that the central nervous system (CNS)-restricted transcription factor Olig2 affects a key posttranslational modification of p53 in both normal and malignant neural progenitors and thereby antagonizes the interaction of p53 with promoter elements of multiple target genes. In the absence of Olig2 function, even attenuated levels of p53 are adequate for biological responses to genotoxic damage.

Mapping of oxidative stress response elements of the caveolin-1 promoter

According to the "free radical theory" of aging, normal aging occurs as the result of tissue damages inflicted by reactive oxygen species (ROS). ROS are known to induce cellular senescence, and senescent cells are believed to contribute to organismal aging. The molecular mechanisms that mediate the cellular response to oxidants remain to be fully identified. We have shown that oxidative stress induces cellular senescence through activation of the caveolin-1 promoter and upregulation of caveolin-1 protein expression. Here, we describe how reactive oxygen species activate the caveolin-1 promoter and how the signaling may be assayed. These approaches provide insight into the functional role of caveolin-1 and potentially allow the identification of novel ROS-regulated genes that are part of the signaling machinery regulating cellular senescence/aging.

Telomere biology in healthy aging and disease

Aging is a biological process that affects most cells, organisms and species. Telomeres have been postulated as a universal biological clock that shortens in parallel with aging in cells. Telomeres are located at the end of the chromosomes and consist of an evolutionary conserved repetitive nucleotide sequence ranging in length from a few hundred base pairs in yeast till several kilo base pairs in vertebrates. Telomeres associate with shelterin proteins and form a complex protecting the chromosomal deoxyribonucleic acid (DNA) from recognition by the DNA damage-repair system. Due to the “end-replication problem” telomeres shorten with each mitotic cycle resulting in cumulative telomere attrition during aging. When telomeres reach a critical length the cell will not further undergo cell divisions and become senescent or otherwise dysfunctional. Telomere shortening has not only been linked to aging but also to several age associated diseases, including tumorigenesis, coronary artery disease, and heart failure. In the current review, we will discuss the role of telomere biology in relation to aging and aging associated diseases.

Caveolin-1, cellular senescence and pulmonary emphysema

Caveolae are vesicular invaginations of the plasma membrane. Caveolin-1 is the structural protein component of caveolae. Caveolin-1 participates in signal transduction processes by acting as a scaffolding protein that concentrates, organizes and functional regulates signaling molecules within caveolar membranes. Cigarette smoke, a source of oxidants, is an environmental hazard that causes pulmonary emphysema. Recently, we reported that the development of cigarette smoking-induced pulmonary emphysema was inhibited in caveolin-1 null mice, which do not express caveolin-1. We demonstrated that lack of caveolin-1 expression in lung fibroblasts dramatically inhibited premature senescence induced by oxidants contained in cigarette smoke. Mechanistically, we uncovered that premature senescence of lung fibroblasts induced by oxidative stress occurred through activation of an ataxia telangiectasia-mutated (ATM)/p53-depedent pathway following sequestration of the catalytic subunit of protein phosphatase 2A (PP2A-C), an inhibitor of ATM, by caveolin-1 into caveolar membranes. We propose caveolin-1 as a key player of a novel signaling pathway that links cigarette smoke to premature senescence of lung fibroblasts and development of pulmonary emphysema.

Caveolin-1 regulates the antagonistic pleiotropic properties of cellular senescence through a novel Mdm2/p53-mediated pathway

We show that caveolin-1 is a novel binding protein for Mdm2. After oxidative stress, caveolin-1 sequesters Mdm2 away from p53, leading to stabilization of p53 and up-regulation of p21(Waf1/Cip1) in human fibroblasts. Expression of a peptide corresponding to the Mdm2 binding domain of caveolin-1 is sufficient to up-regulate p53 and p21(Waf1/Cip1) protein expression and induce premature senescence. Oxidative stress-induced activation of the p53/p21(Waf1/Cip1) pathway and induction of premature senescence are compromised in caveolin-1 null mouse embryonic fibroblasts (MEF). We also show that reintroduction of caveolin-1 in oncogenic Ras (Ras(G12V))-transformed fibroblasts, which express residual levels of caveolin-1, is sufficient to promote cellular senescence. Moreover, caveolin-1 expression in MEFs is required for senescent fibroblast-induced stimulation of cell growth and tumorigenesis of both Ras(G12V)-transformed fibroblasts and MDA-MB-231 breast cancer epithelial cells both in vitro and in vivo. Thus, our results propose caveolin-1 as a key mediator of the antagonistic pleiotropic properties of cellular senescence.

Melanomagenesis: overcoming the barrier of melanocyte senescence

Although melanoma ultimately progresses to a highly aggressive and metastatic disease that is typically resistant to currently available therapy, it often begins as a benign nevus consisting of a clonal population of hyperplastic melanocytes that cannot progress because they are locked in a state of cellular senescence. Once senescence is overcome, the nevus can exhibit dysplastic features and readily progress to more lethal stages. Recent advances have convincingly demonstrated that senescence represents a true barrier to the progression of many types of cancer, including melanoma. Thus, understanding the mechanism(s) by which melanoma evades senescence has become a priority in the melanoma research community. Senescence in most cells is regulated through some combination of activities within the RB and p53 pathways. However, differences discovered among various tumor types, some subtle and others quite profound, have revealed that senescence frequently operates in a context-dependent manner. Here we review what is known about melanocyte senescence, and how such knowledge may provide a much-needed edge in our struggles to contain or perhaps vanquish this often-fatal malignancy.

Protein-protein interactions as targets for small-molecule therapeutics in cancer

Small-molecule inhibition of the direct protein-protein interactions that mediate many important biological processes is an emerging and challenging area in drug design. Conventional drug design has mainly focused on the inhibition of a single protein, usually an enzyme or receptor, since these proteins often contain a clearly defined ligand-binding site with which a small-molecule drug can be designed to interact. Designing a small molecule to bind to a protein-protein interface and subsequently inhibit the interaction poses several challenges, including the initial identification of suitable protein-protein interactions, the surface area of the interface (it is often large), and the location of 'hot spots' (small regions suitable for drug binding). This article reviews the general approach to designing inhibitors of protein-protein interactions, and then focuses on recent advances in the use of small molecules targeted against a variety of protein-protein interactions that have therapeutic potential for cancer.

New highly hydrosoluble and not self-aggregated perylene derivatives with three and four polar side-chains as G-quadruplex telomere targeting agents and telomerase inhibitors

Four new perylene derivatives with three and four basic side-chains are reported here as G-quadruplex interactive compounds. The new perylene derivatives are readily soluble in water and not self-aggregated, in contrast to what happens with the previously reported two side-chain perylene derivatives. All four compounds are able to induce the G-quadruplex and to inhibit 50% of telomerase activity at about 5 microM concentration, showing a similar efficiency with respect to each other. Molecular modelling studies are presented to try to explain these findings.

Oxidative stress induces premature senescence by stimulating caveolin-1 gene transcription through p38 mitogen-activated protein kinase/Sp1-mediated activation of two GC-rich promoter elements

Cellular senescence is believed to represent a natural tumor suppressor mechanism. We have previously shown that up-regulation of caveolin-1 was required for oxidative stress-induced premature senescence in fibroblasts. However, the molecular mechanisms underlying caveolin-1 up-regulation in senescent cells remain unknown. Here, we show that subcytotoxic oxidative stress generated by hydrogen peroxide application promotes premature senescence and stimulates the activity of a (-1,296) caveolin-1 promoter reporter gene construct in fibroblasts. Functional deletion analysis mapped the oxidative stress response elements of the mouse caveolin-1 promoter to the sequences -244/-222 and -124/-101. The hydrogen peroxide-mediated activation of both Cav-1 (-244/-222) and Cav-1 (-124/-101) was prevented by the antioxidant quercetin. Combination of electrophoretic mobility shift studies, chromatin immunoprecipitation analysis, Sp1 overexpression experiments, as well as promoter mutagenesis identifies enhanced Sp1 binding to two GC-boxes at -238/-231 and -118/-106 as the core mechanism of oxidative stress-triggered caveolin-1 transactivation. In addition, signaling studies show p38 mitogen-activated protein kinase (MAPK) as the upstream regulator of Sp1-mediated activation of the caveolin-1 promoter following oxidative stress. Inhibition of p38 MAPK prevents the oxidant-induced Sp1-mediated up-regulation of caveolin-1 protein expression and development of premature senescence. Finally, we show that oxidative stress induces p38-mediated up-regulation of caveolin-1 and premature senescence in normal human mammary epithelial cells but not in MCF-7 breast cancer cells, which do not express caveolin-1 and undergo apoptosis. This study delineates for the first time the molecular mechanisms that modulate caveolin-1 gene transcription upon oxidative stress and brings new insights into the redox control of cellular senescence in both normal and cancer cells.

An accelerated senescence response to radiation in wild-type p53 glioblastoma multiforme cells

OBJECT

Radiotherapy is one of the few treatment options available for glioblastoma multiforme (GBM); however, the basis for its overall ineffectiveness in GBM is not fully understood. The present study was designed to explore the nature of the response to ionizing radiation in GBM cells to gain insight into the basis for the general failure of radiotherapy in the treatment of this disease.

METHODS

The response to fractionated radiotherapy was examined in GBM cell lines with differing p53 status. A viable cell number was determined during an 8-day period; accelerated senescence was based on beta-galactosidase staining and cell morphology; apoptosis was evaluated by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay and fluorescence-activated cell-sorter analysis, whereas the expression of cell-cycle regulatory proteins was monitored by Western blot analysis. Based on clonogenic survival, the wild-type p53 U87 cells and mutant p53 T98 cells demonstrated essentially identical sensitivity to fractionated radiotherapy; however, neither cell line underwent apoptosis, and the primary response to irradiation was growth arrest. The wild-type p53 GBM cells showed clear evidence of accelerated senescence in response to irradiation. In contrast, senescence was not evident in mutant p53 GBM cells or GBM cells in which p53 function was abrogated by the viral E6 protein. The T98 (mutant p53) cells demonstrated a relatively robust proliferative recovery whereas both the rate and extent of recovery were attenuated in the wild-type p53 U87 cells.

CONCLUSIONS

Both accelerated senescence and conventional growth arrest are likely to represent alternative responses to apoptosis in irradiated GBM cells.

The evolving portrait of cancer metastasis

The phenomenon of cancer metastasis remains poorly understood. We discuss here various conceptual frameworks that attempt to rationalize the mechanisms by which tumors acquire metastatic ability. Portrayal of cancer as a somatic Darwinian process occurring within a tissue fails to fully explain the phenomenon of metastatic competence. The biology of pre-neoplastic cells also complicates this picture, since the phenotypes of normal cellular precursors are clearly relevant to metastatic behavior following transformation. Recent experimental results help to shed light on these and other considerations regarding the molecular mechanisms of malignant progression.

Cellular senescence in naevi and immortalisation in melanoma: a role for p16?

Cellular senescence, the irreversible proliferative arrest seen in somatic cells after a limited number of divisions, is considered a crucial barrier to cancer, but direct evidence for this in vivo was lacking until recently. The best-known form of human cell senescence is attributed to telomere shortening and a DNA-damage response through p53 and p21. There is also a more rapid form of senescence, dependent on the p16-retinoblastoma pathway. p16 (CDKN2A) is a known melanoma susceptibility gene. Here, we use retrovirally mediated gene transfer to confirm that the normal form of senescence in cultured human melanocytes involves p16, since disruption of the p16/retinoblastoma pathway is required as well as telomerase activation for immortalisation. Expression (immunostaining) patterns of senescence mediators and markers in melanocytic lesions provide strong evidence that cell senescence occurs in benign melanocytic naevi (moles) in vivo and does not involve p53 or p21 upregulation, although p16 is widely expressed. In comparison, dysplastic naevi and early (radial growth-phase, RGP) melanomas show less p16 and some p53 and p21 immunostaining. All RGP melanomas expressed p21, suggesting areas of p53-mediated senescence, while most areas of advanced (vertical growth-phase) melanomas lacked both p16 and p21, implying escape from both forms of senescence (immortalisation). Moreover, nuclear p16 but not p21 expression can be induced in human melanocytes by oncogenic BRAF, as found in around 80% of naevi. We conclude that cell senescence can form a barrier to melanoma development. This also provides a potential explanation of why p16 is a melanoma suppressor gene.

Polynucleotide phosphorylase: an evolutionary conserved gene with an expanding repertoire of functions

RNA metabolism plays a seminal role in regulating diverse physiological processes. Polynucleotide phosphorylase (PNPase) is an evolutionary conserved 3',5' exoribonuclease, which plays a central role in RNA processing in bacteria and plants. Human polynucleotide phosphorylase (hPNPase old-35) was cloned using an inventive strategy designed to identify genes regulating the fundamental physiological processes of differentiation and senescence. Although hPNPase old-35 structurally and biochemically resembles PNPase of other species, targeted overexpression and inhibition studies reveal that hPNPase old-35 has evolved to serve more specialized functions in humans. The present review provides a global perspective on the structure and function of PNPase and then focuses on hPNPase old-35 in the contexts of differentiation and senescence.

In vivo inhibition of lung cancer by GRN163L: a novel human telomerase inhibitor

Differential regulation of telomerase activity in normal and tumor cells provides a rationale for the design of new classes of telomerase inhibitors. The telomerase enzyme complex presents multiple potential sites for the development of inhibitors. GRN163L, a telomerase enzyme antagonist, is a lipid-modified 13-mer oligonucleotide N3' --> P5'-thio-phosphoramidate, complementary to the template region of telomerase RNA (hTR). We evaluated both the in vitro and in vivo effects of GRN163L using A549-luciferase (A549-Luc) human lung cancer cells expressing a luciferase reporter. GRN163L (1 micromol/L) effectively inhibits telomerase activity of A549-Luc cells, resulting in progressive telomere shortening. GRN163L treatment also reduces colony formation in soft agar assays. Surprisingly, after only 1 week of treatment with GRN163L, A549-Luc cells were unable to form robust colonies in the clonal efficiency assay, whereas the mismatch control compound had no effect. Finally, we show that in vivo treatment with GRN163L is effective in preventing lung metastases in xenograft animal models. These in vitro and in vivo data support the development of GRN163L as a therapeutic for the treatment of cancer.

Molecular analysis of primary and recurrent giant cell tumors of bone

The status of microsatellite markers located on chromosomes 1p36, 3p25, 5q23, 9p22, 10q23, 10q24, 17p13, and 19q12 was used to determine loss of heterozygosity (LOH) in primary giant cell tumors (GCT) of bone in 12 patients. The cases included primary, locally recurrent, and metastatic GCT; three tumors were classified as malignant GCT, based on their morphological features. Microdissection was performed on 24 paraffin-embedded tissue samples. An average of three separate topographic sites were microdissected from each tumor. Case selection in each instance was based on the availability of paired samples of tumor in primary GCTs and their corresponding recurrences, and the presence of normal tissue. The number of cases studied is too small for statistical studies, and thus the analysis is descriptive. All cases were informative for >80% of the markers used. Both primary GCTs and local recurrences and lung metastases displayed LOH of three or more markers, and intratumoral heterogeneity was frequent. Fractional allelic losses (FAL) were not different in recurrent and nonrecurrent GCT. FAL was greatest (>30%) in the metastatic group of GCT. Allelic losses of 1p, 9q, and 19q regions were frequent in all groups. LOH of 17p (in proximity to the p53 locus) and 9p occurred exclusively in the pulmonary metastases from GCT. LOH of 9q and 19q was present in primary as well as recurrent GCTs and in one malignant GCT. Involvement of 1p (including MYCL) and 9q regions has not been previously reported in GCT of bone. The pattern of LOH evident in the 17 markers used in the present study suggests that GCT with malignant features may follow an evolutionary pathway similar to the usual primary GCT of bone.

Immunohistochemical Detection of Human Telomerase Reverse Transcriptase (hTERT), Topoisomerase II?? Expression, and Apoptosis in Endometrial Adenocarcinoma and Atypical Hyperplasia

This study evaluated the immunohistochemical expression of human telomerase reverse transcriptase (hTERT) in endometrial carcinoma and atypical endometrial hyperplasia, and related it to the expression of topoisomerase (TP)IIalpha (a proliferation associated enzyme); apoptosis as determined by the frequency of apoptotic bodies (ABI); mitotic counts; and other clinicopathologic variables. Immunoreactivity for hTERT and TPIIalpha as well as ABI were assessed in 57 endometrial samples (12 atypical hyperplasias, 33 endometrioid carcinomas, 12 serous/clear cell carcinomas). hTERT immunoreactivity, TPIIalpha labeling indices (LI), ABI, and ratios of the indices (ABI/TPIIalpha LI) increased from atypical hyperplasias to endometrioid carcinomas to serous/clear cell carcinomas (p < 0.0001 for each variable). hTERT expression increased with ABI (p < 0.0001), TPIIalpha LI (p = 0.0019), ABI/TPIIalpha ratios (p < 0.0001), and grade (p = 0.0005), but not with FIGO stage (p = 0.2775). TPIIalpha LI, ABI, and ratios were related to high grade (p = 0.0001 for each variable), but not with FIGO stage (p = 0.7362, p = 0.7554, and p = 0.7405, respectively). TPIIalpha LI and ABI were significantly correlated in atypical hyperplasias (p = 0.0004), endometrioid carcinomas (p < 0.0001), and serous/clear cell carcinomas (p = 0.024). Immunostaining levels for hTERT were similar in atypical hyperplasias and grade 1 endometrioid carcinomas (p = 0.1956). These results suggest that hTERT expression is closely related to proliferation, apoptosis, and high grade in endometrial carcinomas, reflecting cell cycle deregulation in endometrial carcinogenesis.

Tbx2 Is Overexpressed and Plays an Important Role in Maintaining Proliferation and Suppression of Senescence in Melanomas

The INK4a and ARF genes found at the CDKN2A locus are key effectors of cellular senescence that is believed to act as a powerful anticancer mechanism. Accordingly, mutations in these genes are present in a wide variety of spontaneous human cancers and CDKN2A germ line mutations are found in familial melanoma. The TBX2 gene encoding a key developmental transcription factor is amplified in pancreatic cancer cell lines and preferentially amplified and overexpressed in BRCA1 and BRCA2 mutated breast tumors. Overexpression of Tbx2 and the related factor Tbx3, which is also overexpressed in breast cancer and melanomas, can suppress senescence in defined experimental systems through repression of ARF expression. However, it is not known how Tbx2 mediates its repressive effect nor whether endogenous Tbx2 or Tbx3 perform a similar antisenescence function in transformed cells. This is a particularly important question because the loss of CDKN2A in many human cancers would, in principle, bypass the requirement for Tbx2/3-mediated repression of ARF in suppressing senescence. We show here that Tbx2 is overexpressed in melanoma cell lines and that Tbx2 targets histone deacetylase 1 to the p21Cip1 (CDKN1A) initiator. Strikingly, expression of an inducible dominant-negative Tbx2 (dnTbx2) leads to displacement of histone deacetylase 1, up-regulation of p21(Cip1) expression, and the induction of replicative senescence in CDKN2A-null B16 melanoma cells. In human melanoma cells, expression of dnTbx2 leads to severely reduced growth and induction of senescence-associated heterochromatin foci. The results suggest that the activity of endogenous Tbx2 is critically required to maintain proliferation and suppress senescence in melanomas.

Influence of ischaemia/reperfusion and LFA-1 inhibition on telomere lengths and CDKI genes in ex vivo haemoperfusion of primate kidneys

The telomere (T) length, p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor (CDKI) genes are the markers of cell senescence and DNA damage. The aim of the study was to determine the influence of renal ischaemia/reperfusion (I/R) and anti-lymphocyte function-associated antigen-1 (LFA-1) monoclonal antibody (mAb) treatment on the value of the above-mentioned markers. Significantly higher levels of p21 and p27 were expressed by the glomeruli (P=0.001 and P=0.0001), tubules (P=0.0065 and P=0.0006), and interstitial cells (P=0.0017 and P=0.0022, respectively) of the xenoperfused kidneys. The mean T length of non-perfused renal specimens (5.56+/-0.60 kbp) was longer than that of the xenoperfused kidneys (5.46+/-0.36 kbp) [P= non-significant (NS)]. Addition of anti-LFA-1 mAb did not significantly influence the gene expression profile in the xenoperfused kidneys. The mean T length was longer in the kidneys with anti-LFA-1 mAb than in those without the medication (5.7+/-0.11 vs 5.13+/-0.31 kbp) (P=0.0661). Kidney I/R is associated with telomere shortening and an over-expression of p21 and p27 CDKIs, which indicates substantial DNA damage and/or accelerated tissue senescence. Although anti-LFA-1 mAb had some protective effect on the telomeres, it did not influence the gene expression profile in this study.

Ninjurin1 increases p21 expression and induces cellular senescence in human hepatoma cells

BACKGROUND/AIMS

Ninjurin1 is a novel adhesion molecule that has a role in promoting nerve regeneration. Although ninjurin1 is ubiquitously expressed in various human tissues, including the liver, the biologic functions of ninjurin1 in tissues other than the nervous system remain unknown. The aim of this study was to investigate the function of ninjurin1 in hepatocytes.

METHODS

The effect of ninjurin1 overexpression was examined in Huh-7 hepatoma cells. Ninjurin1 expression was examined by Western blot in human hepatocellular carcinoma tissues as well as their adjacent liver tissues.

RESULTS

Ninjurin1-overexpressing clones exhibited strong growth inhibition due to G1 cell cycle arrest, which is associated with a posttranscriptional increase in p21WAF1/Cip1, a decrease of cyclin-dependent kinase 2 activity and the hypophosphorylation of Rb. The ninjurin1-overexpressing clones had increased senescence-associated beta-galactosidase activity and autofluorescent pigment, characteristic features of cellular senescence. The levels of ninjurin1 expression were higher in hepatocellular carcinoma tissues than those in adjacent liver tissues.

CONCLUSIONS

The present study provides the first evidence that ninjurin1 is able to induce the senescence program. Ninjurin1 may be involved in the regulation of cellular senescence in the liver during carcinogenesis.

Highly penetrant hereditary cancer syndromes

The past two decades have brought many important advances in our understanding of the hereditary susceptibility to cancer. Approximately 5-10% of all cancers are inherited, the majority in an autosomal dominant manner with incomplete penetrance. While this is a small fraction of the overall cancer burden worldwide, the molecular genetic discoveries that have resulted from the study of families with heritable cancer have not only changed the way these families are counselled and managed, but have shed light on molecular regulatory pathways important in sporadic tumour development as well. In this review, we consider 10 of the more highly penetrant cancer syndromes, with emphasis on those predisposing to breast, colon, and/or endocrine neoplasia. We discuss the prevalence, penetrance, and tumour spectrum associated with these syndromes, as well as their underlying genetic defects.

Telomerase expression and proliferative activity suggest a stem cell role for thyroid solid cell nests

Solid cell nests of the human thyroid gland are composed of main cells and C cells. In order to investigate the putative stem cell nature of the role for solid cell nests, we evaluated the histological features, and the immunohistochemical expression of p63, bcl-2, telomerase catalytic subunit, and two proliferative markers (Ki-67 and minichromosome maintenance protein 2), in a series of 24 cases of solid cell nests. Proliferative indices were determined in (a) solid cell nests, (b) thyroid follicular cells in the vicinity of solid cell nests within a low-power field, and (c) distant thyroid tissue, at a distance of at least three low-power fields from solid cell nests. In 15 cases of solid cell nests (62.5%), mixed follicles were observed; papillary formations were observed in four cases (16.6%), and ciliated cells were observed in the lining of microcysts associated with two cases (8.3%). Salivary gland-type tissue, cartilage islands, adipose and fibrous tissues, and small nerves were also associated with some cases of solid cell nests. We observed that the main cells of the solid cell nests express consistently telomerase, although at lower levels than p63, and show strong cytoplasmic immunoreactivity for bcl-2, which is associated with an increased differentiation potential. We also observed that despite their relative low proliferative index, main cells of the solid cell nests display higher proliferation than follicular cells in the vicinity and follicular cells in more distant thyroid tissue. We conclude that main cells of the solid cell nests apparently harbor the minimal properties of a stem cell phenotype (capacity for both self-renewal, conferred by telomerase activity, and differentiation to one or more than one type of specialized cells, given by the high expression of p63 and bcl-2) and may thus represent a pool of stem cells of the adult thyroid.

Drop of connexins: a possible link between aging and cancer?

The incidence of cancer increases with age but we do not know why. As a working hypothesis we propose here that cells somehow initiated in vivo in the course of life and finally engaged in the aging program, which involves a drop of connexins with loss of cell-to-cell communication (equivalent to the promotion phase in the multistep process of carcinogenesis), may recover their growth potential, thus allowing cancer to progress. This is supported by evidence that: (i) connexin 43 (Cx43) acts as a tumor suppressor; (ii) cx43 and gap junction intercellular communication drop in precancerous lesions and in tumors of various origins, as well as in aging cells; (iii) telomerase is activated in cancerous somatic cells.

TP53 is frequently altered by methylation, mutation, and/or deletion in acute lymphoblastic leukaemia

Different mechanisms, such as chromosomal rearrangements, deletions, mutations, and methylation/demethylation of the promoter regions of genes, have been shown to be involved in acute lymphoblastic leukaemia (ALL). These genetic and epigenetic alterations lead to the activation of protooncogenes or to inactivation of tumour suppressor genes promoting cell proliferation. One of the most frequently inactivated tumour suppressor genes is TP53, which is altered in 50% of human tumours. In this study, we have analysed: (1) the complete coding region, all intron-exon junctions and noncoding regions of exons 1-11 of TP53 by lexon-DGGE; (2) the methylation status of the 5' region of TP53 and (3) the deletion of one or both alleles of the gene by fluorescence in situ hybridisation (FISH) in 57 ALL patients. Using these techniques, we have found promoter methylation in 32% of the cases, missense mutations in 8.8%, and deletion of one allele in 7.5% of the samples, with TP53 being altered in 40% of the ALL samples studied in this series.

Telomerase activity is sufficient to bypass replicative senescence in human limbal and conjunctival but not corneal keratinocytes

The human ocular surface is covered by the conjunctival, corneal and limbal stratified epithelia. While conjunctival stem cells are distributed in bulbar and forniceal conjunctiva, corneal stem cells are segregated in the basal layer of the limbus, which is the transitional zone between the cornea and the bulbar conjunctiva. Keratinocyte stem and transient amplifying (TA) cells when isolated in culture give rise to holoclones and paraclones, respectively. Keratinocyte replicative senescence ensues when all holoclones have generated paraclones which express high levels of p16(INK4a). In the present study, we show that enforced telomerase activity induces the bypass of replicative senescence in limbal and conjunctival keratinocytes, without the inactivation of the p16(INK4a)/Rb pathway or the abrogation of p53 expression. hTERT-transduced limbal and conjunctival keratinocytes are capable to respond to both growth inhibitory and differentiation stimuli, since they undergo growth arrest in response to phorbol esters, and activate p53 upon DNA damage. Following a sustained PKC stimulation, occasional clones of p16(INK4a)-negative cells emerge and resume ability to proliferate. Telomerase activity, however, is unable to induce the bypass of senescence in corneal TA keratinocytes cultured under the same conditions. These data support the notion that telomere-dependent replicative senescence is a general property of all human somatic cells, including keratinocytes, and suggest that telomerase activity is sufficient to extend the lifespan only of keratinocytes endowed with high proliferative potentials (which include stem cells), but not of TA keratinocytes.

Central role of the proteasome in senescence and survival of human fibroblasts: induction of a senescence-like phenotype upon its inhibition and resistance to stress upon its activation

Normal human fibroblasts undergo a limited number of divisions in culture and progressively they reach a state of irreversible growth arrest, a process termed as replicative senescence. The proteasome is the major cellular proteolytic machinery, the function of which is impaired during replicative senescence. However, the exact causes of its malfunction in these conditions are unknown. Using WI38 fibroblasts as a model for cellular senescence we have observed reduced levels of proteasomal peptidase activities coupled with increased levels of both oxidized and ubiquitinated proteins in senescent cells. We have found the catalytic subunits of the 20 S complex and subunits of the 19 S regulatory complex to be down-regulated in senescent cells. This is accompanied by a decrease in the level of both 20 S and 26 S complexes. Partial inhibition of proteasomes in young cells caused by treatment with specific inhibitors induced a senescence-like phenotype, thus demonstrating the fundamental importance of the proteasome for retaining cellular maintenance and homeostasis. Stable overexpression of beta1 and beta5 subunits in WI38 established cell lines was shown to induce elevated expression levels of beta1 subunit in beta5 transfectants and vice versa. Transfectants possess increased proteasome activities and most importantly, increased capacity to cope better with various stresses. In summary these data demonstrate the central role of the proteasome during cellular senescence and survival as well as provide insights toward a better understanding of proteasome regulation.