Time, telomeres and tumours: is cellular senescence more than an anticancer mechanism?

Normal diploid cells, by definition, have a limited life span: they senesce after a set number of divisions both in vivo and in culture. It has been hypothesized that the molecular mechanism that measures the life span of a cell probably involves the shortening of telomeres that occurs with each round of DNA replication. This loss of telomeres is thought to induce antiproliferative signals that result in the induction of cellular senescence. In this article, Woodring Wright and Jerry Shay present a hypothesis for the mechanisms by which telomere shortening regulates cellular physiology and argue that cellular senescence is not only an anticancer mechanism but is also the cause of many of the degenerative changes of aging.

Characterisation of telomerase immortalised normal human oesophageal squamous cells

BACKGROUND AND AIMS

Oesophageal cell lines derived from malignancies have numerous genetic abnormalities and therefore are of limited value for studying the early events in carcinogenesis. Reported attempts to establish normal human oesophageal cell lines either have failed to achieve immortalisation or have achieved it by disrupting important cell functions. We have used telomerase technology to establish normal human oesophageal cell lines.

METHODS

Endoscopic biopsy specimens of normal oesophageal squamous epithelium were trypsinised, dispersed into single cell suspensions, and cocultivated with ATCC Swiss 3T3 cells. Oesophageal cells were infected with the catalytic subunit of human telomerase (hTERT) using a defective retroviral vector. The integrity of cell cycle checkpoints was tested by measuring p53 response to UV irradiation, and p16 response to infection with H-RasGV12. Expression of a differentiation marker was tested by measuring involucrin response to calcium exposure.

RESULTS

Cultures of uninfected oesophageal cells had weak telomerase activity at baseline but exhibited loss of telomerase activity and progressive telomere shortening before undergoing senescence between population doublings (PD) 40-45. In contrast, hTERT infected cells exhibited sustained telomerase activity and stabilisation of telomere length. These cells have reached PD 100 with no diminution in growth rate, while cell cycle checkpoint integrity and involucrin response to calcium exposure have remained intact.

CONCLUSIONS

By introducing telomerase into normal human oesophageal squamous cells cocultivated with feeder layers, we have established a cell line that retains normal cell cycle checkpoints and normal differentiation markers. This cell line may be useful for studying the early events in oesophageal carcinogenesis.

Correlates of vitamin supplement use in the United States: data from the California Teachers Study cohort

OBJECTIVE

To describe factors associated with vitamin supplement use in a large cohort of adult women.

METHODS

California teachers and administrators (n = 133,479) completed a questionnaire on lifestyle factors and medical history. Specific supplement users regularly used at least one specific vitamin supplement in the past year; multivitamin users regularly used a multivitamin; and multivitamin and specific supplement users took a multivitamin and one or more specific supplements. Associations between supplement use and other variables were quantified using means, cross-tabulations, and age-adjusted prevalence odds ratios.

RESULTS

Multivitamin and specific supplement users tended to be older and Caucasian. Compared to non-users, they were also leaner (odds ratio [OR] for BMI > or = 30 kg/m2 = 0.6 for specific supplement users with or without multivitamins, and OR = 0.7 for multivitamin only users), and were less likely to be current smokers (OR for current smoking = 0.8 for multivitamin plus specific supplement users, OR = 0.9 for specific supplement only users, and OR = 0.7 for multivitamin only users). Specific supplement users (with or without multivitamins) were more likely to use cancer screening tests, eat fruits and vegetables, and exercise than were multivitamin only users or non-users.

CONCLUSIONS

A variety of demographic, dietary, and health-related factors were associated with different categories of supplement use.

Telomerase immortalization of human myometrial cells

Several strategies have been described for the primary culture of human myometrial cells. However, primary cultures of myometrial cells have a limited life span, making continual tissue acquisition and cell isolation necessary. Recent studies have demonstrated that cell culture life span is related to chromosomal telomere length, and cellular senescence results from progressive telomere shortening and the lack of telomerase expression. Transfection of cells with expression vectors containing the human telomerase reverse transcriptase (hTERT) maintains telomere length and effectively gives normal cells an unlimited life span in culture. In addition, hTERT extends the life span of cultured cells far beyond normal senescence without causing neoplastic transformation. In the present study, we developed a cell line from hTERT-infected myometrial cells (hTERT-HM). Cells were isolated from myometrial tissue obtained from women undergoing hysterectomy, and retroviral infection was used to express the catalytic subunit of telomerase in myometrial cells. Cells expressing hTERT have been in continuous culture for >10 mo, whereas the control culture senesced after approximately 2 mo. Telomerase activity was monitored in cells with a polymerase chain reaction-based telomerase activity assay. Telomerase-expressing cells contained mRNA for alpha smooth muscle actin, smoothelin, oxytocin receptor, and estrogen receptor alpha, but the estrogen receptor beta receptor was lost. Immunoblotting analysis identified the expression of calponin, caldesmon, alpha smooth muscle actin, and oxytocin receptor. Although estrogen receptor expression was below the level of detection with immunoblotting, transfection experiments performed with reporter constructs driven by estrogen response elements demonstrated estrogen responsiveness in the hTERT-HM. In addition, treatment of hTERT-HM with oxytocin caused a concentration-dependent increase in intracellular calcium levels, confirming the presence of functional oxytocin receptors. Myometrial cells immortalized with hTERT retained markers of differentiation that are observed in primary cultures of smooth muscle cells. The expression of various smooth muscle/myometrium cell markers suggests that these cells may be an appropriate model system to study certain aspects of human myometrial function.

Thick vs thin loop transurethral resection of the prostate: a double-blind prospective trial of early morbidity

OBJECTIVE

To compare blood loss, irrigation requirements and hospital stay between standard transurethral resection of the prostate (TURP) and resection incorporating vaporization, i.e. transurethral vaporization resection (TUVRP).

PATIENTS AND METHODS

Seventy patients were prospectively randomized in a blinded fashion between TURP with a standard resection loop (thin loop) or resection with a roller cutting electrode (thick loop). The outcome was assessed as the change in haemoglobin at 30 min and 24 h after the resection finished. Secondary outcome measures were irrigation requirements, length of catheterization, hospital stay, changes in serum sodium, and complications. The nursing staff and surgical registrar managing the patients after surgery were unaware of the resection technique used.

RESULTS

Data were available for 65 patients (36 thin loop and 29 thick loop resections). The mean decrease in haemoglobin after TURP was 14.8 g/L at 30 min and 11.8 g/L at 24 h; for TUVRP the corresponding values were 14.6 and 14.2 g/L (P = 0.69). In addition, there was no difference in irrigation requirements, changes in serum sodium, length of catheterization, hospital stay or bleeding complications.

CONCLUSION

The use of a thick loop at higher cutting current settings during TUVRP offers no advantage over standard thin-loop TURP.

Quantitation of telomerase components and hTERT mRNA splicing patterns in immortal human cells

Telomerase is a reverse transcriptase that adds telomeric repeats to chromosomal ends. In most normal human somatic cells, telomerase is repressed and telomeres progressively shorten, leading to limited proliferative life-span. Telomerase reactivation is associated with cellular immortalization and is a frequent event during tumorigenesis. The telomerase ribonucleoprotein complex consists of two essential components, a catalytic protein subunit [human telomerase reverse transcriptase (hTERT)] and a template RNA (hTR). hTR is constitutively expressed, while hTERT is almost universally absent in telomerase-negative cells. Although repression of telomerase is transcriptional in telomerase-negative cells, post-transcriptional and assembly processes are likely to play important roles in regulating telomerase activity in those that are telomerase-positive. The telomerase transcript can also be alternatively spliced into a variety of non-functional forms. To establish the quantitative relationships between telomerase activity and its various components, we determined the numbers of molecules of hTR and hTERT mRNA, and the levels of alternatively spliced hTERT mRNA variants in normal, in vitro immortalized and cancer cell lines. We report here that there is surprisingly little variation in the proportion of alternatively spliced forms of hTERT in different cell lines. The only variation observed occurred when a change in splicing to non-functional forms appeared in response to conditions that repress telomerase activity in IDH4 cells. We also found that most telomerase-positive cell lines only contain a few molecules of potentially functional hTERT mRNA, and there is a correlation between telomerase activity and the levels of both hTR and hTERT +alpha+beta mRNA.

Magnetic resonance imaging of the wrist ligaments

The advent of small arthroscopes has enabled the hand surgeon to visualize the ligaments of the wrist directly with resultant increased accuracy in diagnosing and treating pathology. Orthopaedists are now demanding a preoperative assessment and this, in turn, has necessitated that radiologists have a comprehensive understanding of wrist anatomy. High resolution MR imaging can identify the wrist ligaments reliably and provide information concerning their integrity. Interpretation is not straightforward; there is considerable anatomic variation, and there are perforations, defects and degenerative tears that can be troublesome in diagnosing injury. However, with experience and attention to anatomic detail, the radiologist can provide useful information regarding structural abnormalities. When injured, the ligaments of the wrist behave as other joint ligaments do. Findings following injury include discontinuity of normal striated bands, incomplete disruption, irregularities and alteration in normal signal. Fluid pooling around a ligament and concomitant bone injury are other clues to injury. The identification of such structural abnormalities may help to explain altered biomechanics and improve the management of patients following wrist injury.

Breast cancer stage at diagnosis in relation to duration of medicaid enrollment

BACKGROUND

Stage at diagnosis has been used to compare the quality of cancer screening services by health insurance type, using membership at diagnosis or treatment. This study evaluates breast cancer stage among women on Medi-Cal, California's Medicaid program, in relation to duration of coverage to assess the impact of including women with recently acquired benefits in the Medi-Cal group.

METHODS

Breast cancers diagnosed in 1993 among women ages 30 to 64 were obtained from the statewide, population-based cancer registry and linked to Medi-Cal enrollment files. Women on Medi-Cal when diagnosed were categorized based on months covered during the 12 months preceding diagnosis (12, 1-11, or none), and compared with all other women with breast cancer. Logistic regression models measured the effect of duration of Medi-Cal coverage on the odds of late-stage disease, controlling for demographic, socioeconomic, health access, and tumor characteristics.

RESULTS

Among women with Medi-Cal benefits when diagnosed, 18% were not covered during the year preceding diagnosis, and late-stage disease was common among these women. The odds ratio for late-stage disease among all women on Medi-Cal was 1.67 (95% CI 1.41, 1.97), but was reduced by 42% to 1.39 (95% CI 1.15, 1.67) when women without benefits before diagnosis were excluded from the Medi-Cal group.

CONCLUSIONS

Women with Medi-Cal benefits before diagnosis were more likely to be diagnosed with late-stage disease than other women with breast cancer. However, the practice of assigning health insurance status based on enrollment at diagnosis underestimates the effect of access to breast cancer screening through Medicaid.

Telomere shortening and decline in replicative potential as a function of donor age in human adrenocortical cells

Telomere shortening is the cause of replicative senescence of mammalian cells in culture and may be a cause of cellular aging in vivo. Some tissues clearly show telomere shortening during aging in humans, but the relationship between replication history and telomere length is obscured by complex relationships between stem cells and more differentiated cell types. Previous experiments on the adrenal cortex and human adrenocortical cells in culture indicate that the proliferative biology of this tissue is relatively simple; cell division occurs continuously throughout life, without evidence for a distinct stem cell compartment. In this tissue we investigated the relationship between telomere biology and replicative senescence by measuring replicative capacity and telomere length as a function of donor age. Cells cultured from adrenal tissue from donors of different ages showed a strong age-related decline in total replicative capacity, falling from about 50 population doublings for fetal cells to an almost total lack of division in culture for cells from older donors. Telomere restriction fragment (TRF) length was analyzed in the same sets of cells and decreased from a value of about 12 kb in fetal cells to approximately 7 kb in cells from older donors. The latter value is consistent with that in fibroblasts which have reached replicative senescence. Furthermore, there was a good correlation in individual donor samples between TRF length and replicative capacity in culture. To confirm the relationship between telomere length, telomerase, and replicative capacity, we measured telomere length in cells before and after infection with a retrovirus encoding hTERT, the catalytic component of human telomerase. The adult adrenal cortex does not have telomerase activity; cells after transduction with the hTERT retrovirus had high telomerase activity. Whereas control cells underwent a replication-dependent shortening in telomeres during long-term growth in culture, hTERT-modified cells maintained telomere length and are probably immortalized. Symmetric cell division in human adrenocortical cells, occurring slowly over the life span, is associated with progressive telomere shortening and may result in proliferative defects in vivo in old age, which could partly account for the age-related changes in the structure and function of the human adrenal cortex.

Socioeconomic status and breast cancer incidence in California for different race/ethnic groups

OBJECTIVE

The majority of research on breast cancer risk and socioeconomic status (SES) has been conducted for blacks and whites. This study evaluates the relationship between SES and breast cancer incidence in California for four race/ethnic groups.

METHODS

Principal component analysis was used to create an SES index using 1990 Census data. Untracted cases were randomly allocated to census block groups within their county of residence. A total of 97,227 female breast cancer cases diagnosed in California between 1988 and 1992 were evaluated. Incidence rates and rate ratios (RRs) were estimated and a chi2 test for trend across SES levels was performed.

RESULTS

SES was positively related to breast cancer incidence, and this effect was stronger for Hispanics and Asian/others than for whites and blacks. Adjusting by SES did not eliminate the differences in breast cancer rates among race/ethnic groups. RR differences between the race/ethnic groups were greatest in the lowest SES category and attenuated with increasing SES. An increasing trend over SES was statistically significant for all race/ethnic groups. Including randomly allocated cases affected RR estimates for white women only.

CONCLUSIONS

Our results are consistent with similar findings for the Los Angeles area but differ from previous results for the San Francisco Bay area.

Telomerase can inhibit the recombination-based pathway of telomere maintenance in human cells

Telomere length can be maintained by telomerase or by a recombination-based pathway. Because individual telomeres in cells using the recombination-based pathway of telomere maintenance appear to periodically become extremely short, cells using this pathway to maintain telomeres may be faced with a continuous state of crisis. We expressed telomerase in a human cell line that uses the recombination-based pathway of telomere maintenance to test whether telomerase would prevent telomeres from becoming critically short and examine the effects that this might have on the recombination-based pathway of telomere maintenance. In these cells, telomerase maintains the length of the shortest telomeres. In some cases, the long heterogeneous telomeres are completely lost, and the cells now permanently contain short telomeres after only 40 population doublings. This corresponds to a telomere reduction rate of 500 base pairs/population doubling, a rate that is much faster than expected for normal telomere shortening but is consistent with the rapid telomere deletion events observed in cells using the recombination-based pathway of telomere maintenance (Murnane, J. P., Sabatier, L., Marder, B. A., and Morgan, W. F. (1994) EMBO J. 13, 4953-4962). We also observed reductions in the fraction of cells containing alternative lengthening of telomere-associated promyelocytic leukemia bodies and extrachromosomal telomere repeats; however, no alterations in the rate of sister chromatid exchange were observed. Our results demonstrate that human cells using the recombination-based pathway of telomere maintenance retain factors required for telomerase to maintain telomeres and that once the telomerase-based pathway of telomere length regulation is engaged, recombination-based elongation of telomeres can be functionally inhibited.

The La antigen associates with the human telomerase ribonucleoprotein and influences telomere length in vivo

La is an important component of ribonucleoprotein complexes and telomerase is a ribonucleoprotein that compensates for the shortening of the ends of linear DNA by adding telomeric repeats onto the ends of chromosomes by using an integral RNA as the template. We have identified a direct and specific interaction between La and the RNA component of human telomerase. Antibodies specific to La precipitate the human telomerase ribonucleoprotein complex derived from tumor cells, telomerase immortalized normal cells, and in vitro transformed cells. Overexpression of La in both experimentally immortalized human cells and prostate cancer cells results in gradual telomere shortening. Our results demonstrate that La can associate with telomerase and its expression level can influence telomere homeostasis in vivo.

Telomere position effect in human cells

In yeast, telomere position effect (TPE) results in the reversible silencing of genes near telomeres. Here we demonstrate the presence of TPE in human cells. HeLa clones containing a luciferase reporter adjacent to a newly formed telomere express 10 times less luciferase than do control clones generated by random integration. Luciferase expression is restored by trichostatin A, a histone deacetylase inhibitor. Overexpression of a human telomerase reverse transcriptase complementary DNA results in telomere elongation and an additional 2- to 10-fold decrease in expression in telomeric clones but not control clones. The dependence of TPE on telomere length provides a mechanism for the modification of gene expression throughout the replicative life-span of human cells.

Prospective study of antibody to human papilloma virus type 16 and risk of cervical, endometrial, and ovarian cancers (United States)

OBJECTIVE

Human papilloma virus (HPV) is frequently detectable in cancers of the cervix, vagina, and vulva, but its role in endometrial and ovarian cancers is less certain. This analysis aimed to examine the association of presence of HPV type 16 (HPV-16) antibodies with subsequent risk of cervical, endometrial, and ovarian cancers.

METHODS

In a prospective study enrolling over 15,000 pregnant women, pre-cancer sera from women who developed cervical (n = 83), endometrial (n = 34), and ovarian (n = 35) cancers were compared with sera from 172 control women frequency-matched by age group and race.

RESULTS

HPV-16 seropositivity (OR = 2.0, 95% CI 1.0-3.4) was associated with cervical cancer, with the association more prominent for cancers occurring within 10 years of serum sampling (OR = 2.3, 95% CI 1.0-5.3) than cancers occurring later (OR = 1.6, 95% CI 0.75-3.6). Overall, the associations between HPV-16 seropositivity and endometrial (OR = 1.6, 95% CI 0.64-3.8) and ovarian cancers (OR = 1.1, 95% CI 0.43-2.8) were not significant, although the odds ratios for those cancers occurring within 20 years after serum sampling were similar to that for cervical cancer (OR = 2.2 for both).

CONCLUSIONS

Our results confirm that HPV-16 infection precedes the development of cervical cancer. Predictability of HPV-16 seropositivity for risk of other female cancers warrants further investigation.

The risk of developing breast cancer within the next 5, 10, or 20 years of a woman's life

BACKGROUND

The lifetime risk of developing breast cancer is a frequently misinterpreted statistic. Risk projections over a shorter time period, conditioned on current age, may be less prone to misconceptions and more relevant to populations at different ages. The purpose of this study was to estimate the risk of developing breast cancer within the next 5, 10, or 20 years for women currently aged 30 to 70 years in California's four major race/ethnic groups.

METHODS

Life tables were used to obtain risk estimates based on 1993-1997 breast cancer incidence rates from the California Cancer Registry and statewide mortality rates.

RESULTS

For women currently aged 50, the estimated risk of developing invasive breast cancer within 5 years varied from 0.8% (1 in 133) among Hispanics to 1.3% (1 in 75) among Caucasians. Risk estimates within 10 years were 2.9% (1 in 34) among Caucasians, 2.3% (1 in 43) among African Americans, 2.0% (1 in 51) among Asian/Pacific Islanders, and 1.6% (1 in 63) among Hispanics. Within 20 years, estimated risks increased to 6.6% (1 in 15) among Caucasians, 5.0% (1 in 20) among African Americans, 3.9% (1 in 26) among Asian/Pacific Islanders, and 3.7% (1 in 27) among Hispanics. Risk estimates were 8% to 20% higher when in situ tumors were included in the calculations.

CONCLUSIONS

Based on these estimates, the baseline risk of developing breast cancer in the next 1 or 2 decades of life varies by race/ethnicity and current age, but may be lower than the risk perceived by most women.

Telomerase and cancer

Telomerase, a eukaryotic ribonucleoprotein (RNP) complex, contains both an essential RNA and a protein reverse transcriptase subunit. By reverse transcription, the telomerase RNP maintains telomere length stability in almost all cancer cells. Over the past few years there has been significant progress in identifying the components of the telomerase holoenzyme complex and the proteins that associate with telomeres, in order to elucidate mechanisms of telomere length regulation. This review covers recent advances in the field including the use of telomerase in cancer diagnostics and an overview of anti-telomerase cancer therapeutic approaches.

Telomerase inhibitors

There has been a vast increase in telomerase research over the past several years, with many different pre-clinical approaches being tested for inhibiting the activity of this enzyme as a novel therapeutic modality to treat malignancy. In this review, we will provide some basic background information about telomeres and telomerase and then discuss the pros, cons and challenges of the approaches that are currently under investigation, and what we might expect in the future of this emerging field.

Putative telomere-independent mechanisms of replicative aging reflect inadequate growth conditions

Telomere shortening is the mechanism underlying replicative aging in fibroblasts. A variety of reports now claim that inactivation of the p16(INK4a)/pRB pathway is required in addition to telomere maintenance for the immortalization of cells such as skin keratinocytes and breast epithelial cells. We here show that the premature growth arrest of these cell types can be explained by an inadequate culture environment. Providing mesenchymal/epithelial interactions by cultivating the telomerase-expressing cells on feeder layers avoids the growth arrest associated with increased p16(INK4a). These results do not support a telomere-independent mechanism of replicative aging.

Cellular senescence as a tumor-protection mechanism: the essential role of counting

The term 'cellular senescence' has often been applied indiscriminately to any form of growth arrest of cultured cells that occurs either after some period in culture or following insults such as the overexpression of oncogenes. Recent reports have suggested there may be many mechanisms of cellular senescence. Our increasing understanding of the role of telomere shortening in the replicative aging of cultured fibroblasts now permits a re-examination of what may reasonably be called cellular senescence, and what most likely represents artifacts of the culture environment and/or specific cell-cycle control mechanisms.

Variation in health and risk behavior among youth living with HIV

Lifetime and current health practices and risk behaviors were examined among 350 youth living with HIV (YLH) aged 14-23 years from four AIDS epicenters (72.6% male; 26.2% African American, 36.9% Latino). YLH were relatively healthy (M CD4 cells = 499), had used substantial health care and were satisfied with the care. YLH's sexual and substance-use histories indicated substantial HIV related risk acts: the median number of lifetime partners was 25 with only 8% using condoms consistently; 14.9% had injected drugs, and 61.2% had used hard drugs. Compared with females, males had more lifetime and recent sexual partners and had used more drugs. Youth who were recently sexually active (81.3%) had multiple partners. Most of the sexually active YLH used condoms consistently (81.6%). YLH who were symptomatic or had an AIDS diagnosis were likely to have recently had more seropositive sexual partners than the asymptomatic youth. Youth disclosed their serostatus to about half of their sexual partners (53.9%). YLH with AIDS used fewer hard drugs than those without an AIDS diagnosis. Health and risk behaviors of the YLH varied significantly based on their disease stage, gender, and ethnicity, suggesting the need for tailoring interventions for subgroups of YLH.

Characterization of ataxia telangiectasia fibroblasts with extended life-span through telomerase expression

Ataxia-telangiectasia (A-T) is an autosomal recessive disease characterized by progressive cerebellar degeneration, immunodeficiencies, genomic instability and gonadal atrophy. A-T patients are hypersensitive to ionizing radiation and have an elevated cancer risk. Cells derived from A-T patients require higher levels of serum factors, exhibit cytoskeletal defects and undergo premature senescence in culture. We show here that expression of the catalytic subunit of telomerase (hTERT) in primary A-T patient fibroblasts can rescue the premature senescence phenotype. Ectopic expression of hTERT does not rescue the radiosensitivity or the telomere fusions in A-T fibroblasts. The hTERT+AT cells also retain the characteristic defects in cell-cycle checkpoints, and show increased chromosome damage before and after ionizing radiation. Although A-T patients have an increased susceptibility to cancer, the expression of hTERT in A-T fibroblasts does not stimulate malignant transformation. These immortalized A-T cells provide a more stable cell system to investigate the molecular mechanisms underlying the cellular phenotypes of Ataxia-telangiectasia.