Biomedical subjects

Jerry W Shay

Publications and source records attributed to Jerry W Shay.

76 records · Page 5Linked to original sources

PubMed2002

Human telomerase and its regulation.

The telomere is a special functional complex at the end of linear eukaryotic chromosomes, consisting of tandem repeat DNA sequences and associated proteins. It is essential for maintaining the integrity and stability of linear eukaryotic genomes. Telomere length regulation and maintenance contribute to normal human cellular aging and human diseases. The synthesis of telomeres is mainly achieved by the cellular reverse transcriptase telomerase, an RNA-dependent DNA polymerase that adds telomeric DNA to telomeres. Expression of telomerase is usually required for cell immortalization and long-term tumor growth. In humans, telomerase activity is tightly regulated during development and oncogenesis. The modulation of telomerase activity may therefore have important implications in antiaging and anticancer therapy. This review describes the currently known components of the telomerase complex and attempts to provide an update on the molecular mechanisms of human telomerase regulation.

DNA-Binding Proteins↗

PubMedDate not supplied

Lagomorphs (rabbits, pikas and hares) do not use telomere-directed replicative aging in vitro.

Telomere shortening is used for replicative aging in primates and ungulates but not rodents. We examined telomere biology in rabbits to expand the comparative biology of telomere-directed replicative senescence within mammals. The order Lagomorpha consists of two families; Leporidae and Ochotonidae. We examined telomere biology in species representing three leporid genera (European White Rabbit, Black-tailed Jack Rabbit, and Swamp Rabbit) and the monotypic ochotonid genus (North American Pika). Of the leporids one species was a laboratory strain and the others were wild caught. The leporids neither exhibited cellular senescence after sustained periods in culture nor displayed detectable telomerase activity. Continued culture was possible because of their extremely long telomeric arrays. Immunofluorescence showed robust telomere signals at chromosome ends and significant internal chromosomal staining in some instances. Pika was unique in displaying endogenous telomerase activity throughout time in culture. These results show that it is unlikely that lagomorphs use telomere shortening and replicative senescence as a tumor protective mechanism.

Animals↗

PubMedDate not supplied

Small molecule, oligonucleotide-based telomerase template inhibition in combination with cytolytic therapy in an in vitro androgen-independent prostate cancer model.

PURPOSE: Determine the efficacy and timing of small molecule oligonucleotide-based inhibitors to the enzyme telomerase in an in vitro model of androgen-independent, osseous prostate cancer. MATERIALS AND METHODS: Telomerase was inhibited in prostate cancer cell lines C4-2/C4-2B and in controls by using small molecule antisense oligonucleotide-based inhibitors alone or in various combinations of small-dose Taxotere (sanofi-aventis, Bridgewater, NJ) and/or conditionally replication competent adenovirus (AD-BSP-E1a). After transfection and proliferation, telomerase telomeric repeat amplification protocol and telomere restriction fragment assays were performed, with specific times for evaluating telomere length. Specimens were stained for analysis with hematoxylin and eosin (H&E), terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL), and prostate-specific antigen (PSA). RESULTS: C4-2/C4-2B cell lines had the shortest initial mean telomere length (approximately 2.5 kilobase [kb]) compared to PC-3 (approximately 5.5 kb). Dose-dependent inhibition of telomerase activity was seen using match oligonucleotide-based inhibitors to telomerase (50% inhibitory concentration 3-5 nm), whereas mismatch compound showed no telomerase inhibition. Significant growth delay and apoptosis in cell lines occurred after > 50 days of treatment. Cells treated with combination "triple therapy" (i.e., telomerase inhibitors, adenovirus, and Taxotere) had the highest amount of apoptosis. Compared to controls, all combination treatment groups had statistically significant reductions in prostate-specific antigen in the conditioned media. CONCLUSIONS: Combining cytotoxic regimens with small molecule inhibitors to telomerase with oligonucleotide-based agents could be beneficial in controlling osseous hormone refractory prostate cancer, as evidenced by these in vitro, preclinical investigations. Telomerase inhibition needs to move into in vivo models and human studies.

Androgens↗

PubMedDate not supplied

Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient.

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Adenomatous Polyposis Coli↗