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Biomedical subjects

W E Wright

Publications and source records attributed to W E Wright.

At least 37 records · Page 2Linked to original sources
PubMed2001

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.

Adult↗
PubMed2001

Telomeres and telomerase: implications for cancer and aging.

Maintenance of telomere stability is required for cells to escape from replicative senescence and proliferate indefinitely. Telomere length is maintained by a balance between processes that lengthen telomeres (telomerase) and processes that shorten telomeres (the end-replication problem). Telomerase is a cellular ribonucleoprotein reverse transcriptase which stabilizes telomere length by adding hexameric (TTAGGG) repeats to the telomeric ends of the chromosomes, thus compensating for the continued erosion of telomeres. Introduction of the telomerase catalytic protein component into normal telomerase-negative human cells results in restoration of telomerase activity and extension of cellular life span. Human cells with introduced telomerase maintain a normal chromosome complement and continue to grow in a normal manner. Telomerase-induced manipulations of telomere length may thus be important not only for cell and tissue engineering but also for dissecting the molecular mechanisms underlying inherited genetic diseases, as well as defining the genetic pathways leading to cancer. Because almost all human tumors express telomerase activity, inhibition of telomerase may result in gradual erosion of telomeres and eventual cessation of cell proliferation or induction of apoptosis. Thus telomerase may also be a promising target for cancer therapy.

Animals↗
PubMed2001

Ageing and cancer: the telomere and telomerase connection.

Telomeres are repetitive DNA sequences at the ends of linear chromosomes. Telomerase, a cellular reverse transcriptase, helps stabilize telomere length in human stem, reproductive and cancer cells by adding TTAGGG repeats onto the telomeres. Each time a telomerase-negative cell divides some telomeric sequences are lost. When telomeres are short, cells enter an irreversible growth arrest state called replicative senescence. In most instances cells become senescent before they can become cancerous, thus the growth arrest induced by short telomeres may be a potent anti-cancer mechanism. Since most cancers express telomerase, maintenance of telomere stability is likely to be required for the long-term viability of tumours. Inhibition of telomerase results in gradual erosion of telomeres followed by cessation of proliferation or apoptosis, and thus may be a promising target for cancer therapy. Introduction of the telomerase catalytic protein component into telomerase-silent cells is sufficient to restore telomerase activity and extend cellular life span. However, cells with introduced telomerase are not cancer cells since they have not accumulated the other changes needed to become cancerous. This indicates that telomerase-induced telomere length manipulations may have utility for tissue engineering and for dissecting the molecular mechanisms underlying genetic diseases including cancer.

Aging↗
PubMed2000

Transient expression of human telomerase extends the life span of normal human fibroblasts.

We utilized the Cre/lox recombination system to transiently express the catalytic subunit of telomerase (hTERT) in normal diploid foreskin fibroblasts (BJ cells). A retroviral construct containing an hTERT cDNA, flanked by loxP-sites was introduced into near senescent BJ cells (population doubling 85). At population doubling (PD) 92, which exceeds the typical life span of these cells, we excised the gene via Cre-mediated recombination. All clones lost telomerase activity and showed telomere shortening over an additional 50 PDs. Interestingly, the average telomere length in these cells became shorter than in untreated BJ cells at senescence. This may be due to hTERT preferentially elongating the shortest telomeres, leading to greater length uniformity. In summary, transient telomerase expression and only a very small average telomere elongation by hTERT resulted in a 50% increase in life span of human fibroblasts. This suggests a potentially safe use of hTERT in tissue engineering.

Catalytic Domain↗
PubMed2000

Telomere shortening is proportional to the size of the G-rich telomeric 3'-overhang.

Most normal diploid human cells do not express telomerase activity and are unable to maintain telomere length with ongoing cell divisions. We show that the length of the single-stranded G-rich telomeric 3'-overhang is proportional to the rate of shortening in four human cell types that exhibit different rates of telomere shortening in culture. These results provide direct evidence that the size of the G-rich overhang is not fixed but subject to regulation. The potential ability to manipulate this rate has profound implications both for slowing the rate of replicative aging in normal cells and for accelerating the rate of telomere loss in cancer cells in combination with anti-telomerase therapies.

Breast↗
PubMed2000

Transplantation of normal and DMD myoblasts expressing the telomerase gene in SCID mice.

The limited proliferative capacity of dystrophic human myoblasts severely limits their ability to be genetically modified and used for myoblast transplantation. The forced expression of the catalytic subunit of telomerase can prevent telomere erosion and can immortalize different cell types. We thus tested the ability of telomerase to immortalize myoblasts and analyzed the effect of telomerase expression on the success of myoblast transplantation. Telomerase expression did not significantly extend the human myoblast life span. The telomerase expressing myoblasts were nonetheless competent to participate in myofiber formation after infection with the retroviral vector. Although the new fibers obtained are less numerous than after the transplantation of normal myoblasts, these results demonstrate that the forced expression of telomerase does not block the ability of normal or dystrophic myoblasts to differentiate in vivo. It will be now necessary to determine the factors that prevent telomerase from extending the life span of human myoblasts before the potential of this intervention can be fully examined.

Animals↗
PubMed2000

Subsenescent telomere lengths in fibroblasts immortalized by limiting amounts of telomerase.

Human fibroblasts expressing the catalytic component of human telomerase (hTERT) have been followed for 250-400 population doublings. As expected, telomerase activity declined in long term culture of stable transfectants. Surprisingly, however, clones with average telomere lengths several kilobases shorter than those of senescent parental cells continued to proliferate. Although the longest telomeres shortened, the size of the shortest telomeres was maintained. Cells with subsenescent telomere lengths proliferated for an additional 20 doublings after inhibiting telomerase activity with a dominant-negative hTERT mutant. These results indicate that, under conditions of limiting telomerase activity, cis-acting signals may recruit telomerase to act on the shortest telomeres, argue against the hypothesis that the mortality stage 1 mechanism of cellular senescence is regulated by telomere positional effects (in which subtelomeric loci silenced by long telomeres are expressed when telomeres become short), and suggest that catalytically active telomerase is not required to provide a protein-capping role at the end of very short telomeres.

Cell Line, Transformed↗
PubMed2000

The establishment of telomerase-immortalized cell lines representing human chromosome instability syndromes.

The limited life span of normal human cells represents a substantial obstacle for biochemical analysis, genetic manipulation and genetic screens. To overcome this technical barrier, immortal human cell lines are often derived from tumors or produced by transformation with viral oncogenes such as SV40 large T antigen. Cell lines produced by these approaches are invariably transformed, genomically unstable and display cellular properties that differ from their normal counterpart. It was recently shown that the ectopic expression of hTERT, encoding the catalytic subunit of human telomerase, can extend the life span of normal human cells without causing cellular transformation and genomic instability. In the present study, we have used hTERT to extend the life span of normal human skin fibroblasts derived from patients afflicted with syndromes of genomic instability and/or premature aging. Our results show that hTERT efficiently extends the life span without altering the characteristic phenotypic properties of the cells. Thus, the ectopic expression of telomerase represents a major improvement over the use of viral oncogenes for the establishment of human cell lines.

Abnormalities, Multiple↗
PubMed2000

Telomere dynamics in cells with introduced telomerase: a rapid assay for telomerase activity on telomeres.

Most immortal cell lines derived from human cancers or transformed in vitro maintain telomeres by endogenous expression of telomerase. In the present work, immortal cells that already express endogenous telomerase activity were induced to overexpress an exogenous telomerase (hTERT) and were analyzed for changes in telomere length. Introduction of hTERT into telomerase-positive immortal cell lines results in elevated telomerase activity as measured by the TRAP assay, leading to elongated telomeres in the cell lines tested. We explore possibilities for regulatory differences among the cell lines, including the level of overexpression of the catalytic subunit hTERT and the endogenous levels of telomere binding proteins. Reducing levels of hTERT expression with a construct containing an inefficient translation initiation sequence provided sufficient telomerase expression for maximal rates of telomere elongation. Overexpression of the hTERT alters the telomere length normally maintained in these cells and provides a very useful assay for the rapid analysis of telomerase activity on its native substrate, telomeres.

Blotting, Western↗
PubMed2000

Hayflick, his limit, and cellular ageing.

Almost 40 years ago, Leonard Hayflick discovered that cultured normal human cells have limited capacity to divide, after which they become senescent -- a phenomenon now known as the 'Hayflick limit'. Hayflick's findings were strongly challenged at the time, and continue to be questioned in a few circles, but his achievements have enabled others to make considerable progress towards understanding and manipulating the molecular mechanisms of ageing.

Aging↗
PubMed2000

Heterogeneous nuclear ribonucleoproteins C1 and C2 associate with the RNA component of human telomerase.

Here we demonstrate that heterogeneous nuclear ribonucleoproteins (hnRNPs) C1 and C2 can associate directly with the integral RNA component of mammalian telomerase. The binding site for hnRNPs C1 and C2 maps to a 6-base uridylate tract located directly 5' to the template region in the human telomerase RNA (TR) and a 4-base uridylate tract directly 3' to the template in the mouse TR. Telomerase activity is precipitated with antibodies specific to hnRNPs C1 and C2 from cells expressing wild-type human TR but not a variant of the human TR lacking the hnRNPs C1 and C2 binding site, indicating that hnRNPs C1 and C2 require the 6-base uridylate tract within the human TR to associate with the telomerase holoenzyme. In addition, we demonstrate that binding of hnRNPs C1 and C2 to telomerase correlates with the ability of telomerase to access the telomere. Although correlative, these data do suggest that the binding of hnRNPs C1 and C2 to telomerase may be important for the ability of telomerase to function on telomeres. The C proteins of the hnRNP particle are also capable of colocalizing with telomere binding proteins, suggesting that the C proteins may associate with telomeres in vivo. Therefore, human telomerase is capable of associating with core members of the hnRNP family of RNA binding proteins through a direct and sequence-specific interaction with the human TR. This is also the first account describing the precise mapping of a sequence in the human TR that is required to associate with an auxiliary component of the human telomerase holoenzyme.

Base Sequence↗
PubMed2000

Increasing trends in the use of breast-conserving surgery in California.

OBJECTIVES: The purpose of this study was to determine temporal trends in breast-conserving surgery in California from 1988 through 1995. METHODS: Logistic regression was used to analyze data on 104,466 cases of early-stage breast cancer reported to the California Cancer Registry. RESULTS: A monotonically increasing trend in breast-conserving surgery was detected after adjustment for age, race/ethnicity, stage at diagnosis, and neighborhood education level. Breast-conserving surgery increased at similar rates among all racial/ethnic groups. Older age, Asian or Hispanic race/ethnicity, late-stage diagnosis, and residence in an undereducated neighborhood were factors associated with lower use of breast-conserving surgery. CONCLUSIONS: Although disparities are evident, use of breast-conserving surgery increased steadily in all groups examined in this study.

Adult↗
PubMed1999

Inhibition of human telomerase in immortal human cells leads to progressive telomere shortening and cell death.

The correlation between telomerase activity and human tumors has led to the hypothesis that tumor growth requires reactivation of telomerase and that telomerase inhibitors represent a class of chemotherapeutic agents. Herein, we examine the effects of inhibition of telomerase inside human cells. Peptide nucleic acid and 2'-O-MeRNA oligomers inhibit telomerase, leading to progressive telomere shortening and causing immortal human breast epithelial cells to undergo apoptosis with increasing frequency until no cells remain. Telomere shortening is reversible: if inhibitor addition is terminated, telomeres regain their initial lengths. Our results validate telomerase as a target for the discovery of anticancer drugs and supply general insights into the properties that successful agents will require regardless of chemical type. Chemically similar oligonucleotides are in clinical trials and have well characterized pharmacokinetics, making the inhibitors we describe practical lead compounds for testing for an antitelomerase chemotherapeutic strategy.

Antineoplastic Agents↗
PubMed1999

Normal human telomeres are not late replicating.

Telomeres in yeast are late replicating. Genes placed next to telomeres in yeast can be repressed (telomere positional effects), leading to the hypothesis that telomeres may be heterochromatic and may control the expression of subtelomeric genes. In addition, yeast telomeres are processed to have a transient long overhang at the end of S phase. The applicability of the yeast data to human biology was examined by determining the timing of telomere replication and processing in normal human diploid fibroblasts. Telomeres were purified from synchronized cells that had been labeled with 5-bromodeoxyuridine (BrdU) at hourly intervals, and the fraction of labeled telomeres was analyzed by retrieval with anti-BrdU antibodies. We determined that normal human telomeres replicate throughout S phase rather than being very late replicating. Furthermore, the overall timing of replication was unaffected by telomere length in young versus old cells or cells whose telomeres had been elongated following transfection with the catalytic subunit of telomerase. Finally, the asymmetry in the length of the G-rich overhang in daughter telomeres produced by leading versus lagging strand synthesis was shown to be established within 1 h of telomere replication, indicating there is no significant delay between synthesis and the processing events that contribute to the establishment of asymmetric overhangs. Therefore, the timings of replication and processing of human telomeres are very different from those of yeast.

Base Composition↗