Upregulation of telomerase function during tissue regeneration.

Telomerase plays a primary role in the maintenance of telomeres in immortal, germ, and tumor cells in humans but is lacking in most somatic cells and tissues. However, many species, including fish and inbred mice, express telomerase in most cells and tissues. Little is known about the expression of telomerase in aquatic species, although the importance of telomerase for longevity has been suggested. We compared telomerase activity and telomere lengths among a broad range of tissues from aquatic species and found telomerase at significant levels in both long- and short-lived aquatic species, suggesting constitutive telomerase expression has an alternative function. Telomere lengths in these aquatic species were comparable to those observed in normal human tissues and cell strains. Given that a host of aquatic species with short life spans have telomerase and a tremendous capacity to regenerate, we tested the hypothesis that telomerase upregulation is important for tissue regeneration. During regeneration, telomerase activity was upregulated and telomere lengths are maintained with the shortest telomeres being elongated, indicating the importance for maintaining telomere length and integrity during tissue regeneration. Thus, the expression of telomerase in aquatic animals is likely not related to longevity but to their ability to regenerate injured tissue.

Cofactor of BRCA1: a novel transcription factor regulator in upper gastrointestinal adenocarcinomas.

Cofactor of BRCA1 (COBRA1) is a newly characterized member of the negative elongation factor (NELF) complex. In this work, we show that COBRA1 is overexpressed in the majority of primary upper gastrointestinal adenocarcinomas (UGC), and its overexpression correlates with down-regulation of TFF1. We have detected overexpression of COBRA1 mRNA using quantitative real-time reverse transcription-PCR in 28 (79%) primary UGCs. Immunohistochemical analysis of UGC tissue arrays that contained 70 tumor samples showed moderate-strong staining for COBRA1 in 60 (84%) tumors. Interestingly, the tumor samples showed absent-weak staining for TFF1 in 45 (65%) of the tumors. Simultaneous loss of TFF1 expression and overexpression of COBRA1 was observed in 42 of 70 (60%) tumors. Using small interfering RNA technology with gastric cancer cells, we have shown that COBRA1 inhibition leads to increased TFF1 promoter activity and gene expression. Promoter analysis of TFF1 indicated that regulation of TFF1 by COBRA1 is estrogen independent in contrast to breast cancer. Moreover, COBRA1 regulation of TFF1 in gastric cancer cells was independent of NELF-E. Using several truncated mutants and site mutants of the TFF1 promoter, we have shown that COBRA1 can negatively regulate the activator protein-1 (AP-1) complex at the TFF1 promoter and thus down-regulate TFF1 expression in gastric cancer cell lines. Electrophoretic mobility shift assay showed that COBRA1 attenuates AP-1 binding to DNA. Our results suggest COBRA1 as a novel oncogene in UGCs that regulate AP-1 binding and the expression of TFF1 in upper gastric epithelia.

Hypermethylation and loss of expression of glutathione peroxidase-3 in Barrett's tumorigenesis.

Chronic gastroesophageal reflux disease is a known risk factor for Barrett's esophagus (BE), which induces oxidative mucosal damage. Glutathione peroxidase-3 (GPx3) is a secretory protein with potent extracellular antioxidant activity. In this study, we have investigated the mRNA and protein expression of GPx3, and explored promoter hypermethylation as an epigenetic mechanism for GPx3 gene inactivation during Barrett's carcinogenesis. Quantitative real-time reverse transcription polymerase chain reaction on 42 Barrett's adenocarcinomas (BAs) revealed consistently reduced levels of GPx3 mRNA in 91% of tumor samples. GPx3 promoter hypermethylation was detected in 62% of Barrett's metaplasia, 82% of dysplasia, and 88% of BA samples. Hypermethylation of both alleles of GPx3 was most frequently seen in BAs (P = .001). Immunohistochemical staining of GPx3 in matching tissue sections (normal, BE, Barrett's dysplasia, and BA) revealed strong immunostaining for GPx3 in normal esophageal and gastric tissues. However, weak to absent GPx3 staining was observed in Barrett's dysplasia and adenocarcinoma samples where the promoter was hypermethylated. The degree of loss of immunohistochemistry correlated with the hypermethylation pattern (monoallelic versus biallelic). The observed high frequency of promoter hypermethylation and progressive loss of GPx3 expression in BA and its associated lesions, together with its known function as a potent antioxidant, suggest that epigenetic inactivation and regulation of glutathione pathway may be critical in the development and progression of BE.

Vertebrate marine species as model systems for studying telomeres and telomerase.

Due to the limitations of in vitro human tissue culture systems, it has long been recognized that in vivo model organisms are critically necessary for studying important biological processes related to human disease. Telomere shortening and dysfunction have been shown as a contributing factor in aging using tissue culture systems and after 6 generations in inbred strains of mice. Currently, there are no models and little or no data defining the role of telomeres and telomerase in toxicological response, metal-induced carcinogenesis, or aging in marine animals. One of our primary objectives has been to determine if fish have similar utility to mouse models of aging and cancer, at least related to telomere biogenesis and telomerase function. We have found that the vast majority of tissues from marine species have functional telomerase activity, and that several of these vertebrates, although telomerase-expressing, have telomere lengths that resemble those found in human cells and tissues. Thus, because aquatic species have "normal" telomere sizes, marine animals may be more biologically relevant and cost-effective models for studying stem cells, aging, and cancer than inbred strains of rodents.

Adriamycin-induced senescence in breast tumor cells involves functional p53 and telomere dysfunction.

Direct experimental evidence implicates telomere erosion as a primary cause of cellular senescence. Using a well characterized model system for breast cancer, we define here the molecular and cellular consequences of adriamycin treatment in breast tumor cells. Cells acutely exposed to adriamycin exhibited an increase in p53 activity, a decline in telomerase activity, and a dramatic increase in beta-galactosidase, a marker of senescence. Inactivation of wild-type p53 resulted in a transition of the cellular response to adriamycin treatment from replicative senescence to delayed apoptosis, demonstrating that p53 plays an integral role in the fate of breast tumor cells treated with DNA-damaging agents. Stable introduction of hTERT, the catalytic protein component of telomerase, into MCF-7 cells caused an increase in telomerase activity and telomere length. Treatment of MCF-7-hTERT cells with adriamycin produced an identical senescence response as controls without signs of telomere shortening, indicating that the senescence after treatment is telomere length-independent. However, we found that exposure to adriamycin resulted in an overrepresentation of cytogenetic changes involving telomeres, showing an altered telomere state induced by adriamycin is probably a causal factor leading to the senescence phenotype. To our knowledge, these data are the first to demonstrate that the mechanism of adriamycin-induced senescence is dependent on both functional p53 and telomere dysfunction rather than overall shortening.