Telomerase activity

ITowever, most normal somatic cells lack telomerase. Consequently, upon every cycle of cell division when the cell replicates its DNA, about 50-nucleotide portions are lost from the end of each telomere. Thus, over time, the telomeres of somatic cells in animals become shorter and shorter, eventually leading to chromosome instability and cell death. This phenomenon has led some scientists to espouse a telomere theory of aging that implicates telomere shortening as the principal factor in cell, tissue, and even organism aging. Interestingly, cancer cells appear immortal because they continue to reproduce indefinitely. A survey of 20 different tumor types by Geron Corporation of Menlo Park, California, revealed that all contained telomerase activity. 

Telomerase Ribonucleoprotein Suppression of telomerase activity inhibition of cell proliferation change in morphology induction of apoptosis... 

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Brandt S, ffeller H, Schuster KD, Grote J (2004) Tamoxifen induces suppression of cell viability and apoptosis in the human hepatoblastoma cell line ElepG2 via down-regulation of telomerase activity. Liver Int 24(l) 46-54... 

The dicytodendrins A-E (Fig. 9) are one of the most recent 3,4-diarylpyrrole natural products to be reported [64], Their isolation by Fusetani and coworkers from a Japanese marine sponge was reported in 2003. These substances (144-148) have been shown to inhibit telomerase at a concentration of 50 pg/mL thereby making such compounds potentially useful as antitumor agents given that telomerase activity is found in 90% of cancer cells but... 

Kiyono, T., S. A. Foster, J. I. Koop, J. K. McDougall, D. A. Galloway, and A. J. Klingelhutz. 1998. Both Rb/pl6INK4a inactivation and telomerase activity are required to immortalize human epithelial cells [see comments]. Nature 396(6706) 84-8. 

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Halvorsen, T. L., G. Leibowitz, and F. Levine. 1999. Telomerase activity is sufficient to allow transformed cells to escape from crisis. Mol Cell Biol 19(3) 1864— 70. 

Tian, X.X., Pang, J.C., To, S.S., Ng, H.K., 1999, Restoration of wild type PTEN expression leads to apaotosis, induces differentiation, and reduces telomerase activity in human glyoma ceUs. 7. Neuropathol. Exp. Neurol. 58 472-479. 

Ge Z, Liu C, Bjorkholm M, Gruber A, Xu D (2006) Mitogen-activated protein kinase cascade-mediated histone H3 phosphorylation is critical for telomerase reverse transcriptase expression/telomerase activation induced by proliferation. Mol Cell Biol 26(l) 230-237 Giet R, Glover DM (2001) Drosophila aurora B kinase is required for histone H3 phosphorylation and condensin recruitment during chromosome condensation and to organize the central spindle during cytokinesis. J Cell Biol 152(4) 669-682... 

Telomerase is an enzyme in eukaryotes used to maintain the telomeres. It contains a short RNA template complementary to the DNA telomere sequence, as well as telomerase reverse transcriptase activity (hTRT). Telomerase is thus able to replace telomere sequences that would otherwise be lost during replication. Normally telomerase activity is present only in embryonic cells, germ (reproductive) cells, and stem cells, but not in somatic cells. 

Greider CW. Telomerase activation. One step on the road to cancer Trends Genet. 1999 15 109-112. 

Hartmann U, Balabanov S, Ziegler P et al. Telomere length and telomerase activity in the BCR ABL transformed miuine Pro B cell line BaF3 is unaffected by treatment with imatinib. Exp.Hematol. 2005 33 542 549. 

Engelhardt M, Mackenzie K, Drullinsky P, Silver RT, Moore MA. Telomerase activity and telomere length in acute and chronic leukemia, pre and post ex vivo cultiue. Cancer Res. 2000 60 610-617. 

Rasoul NA, Elhalawani N, Nafae MH, Elkaffash DM, Moiuad Zl. Telomerase activity in Philadelphia positive chronic myeloid leukaemia. Eg3rpt.J.lnununol. 2004 11 1 8. 

The dictyodendrin class of carbazole alkaloids (see Schemes 2.70 and 2.71) completely inhibit telomerase activity (at a concentration of 50 pg/mL). It is known that 90% of human tumors show telomerase activity, which is absent in normal cells. Telemorase is a ribonucleoprotein enzyme that adds repeating known telomers to the DNA sequence (251). 

Most human cells have very low telomerase activity, but cancer cells have high telomerase activity, which allows them to avoid senescence and become "immortal."... 

The control of telomerase must be important. The enzyme is active in early embryonic cells and some stem cells. However, most normal cells have little or no telomerase activity and lose telomere length throughout their lifespan with eventual growth arrest.448/454/457 On the other hand, excessive telomerase activity may induce cancer.451/458/459 Certain mutations in the telomerase guide RNA can cause greatly increased telomerase activity.459 The control of telomerase is still poorly understood but involves specific telomere-binding proteins 448,454,460-460b... 

Fuggetta MP, Lanzilli G, Tricarico M, Cottarelli A, Falchetti R, Ravagnan G, Bonmassar E. 2006. Effect of resveratrol on proliferation and telomerase activity of human colon cancer cells in vitro. J Exp Clin Cancer Res 25 189-193. 

Chakraborty S, Ghosh U, Bhattacharyya NP, Bhattacharya RK, Roy M. 2006. Inhibition of telomerase activity and induction of apoptosis by curcumin in K-562 cells. Mutat Res 596 81-90. 

Ramachandran C, Fonseca HB, Jhabvala P, Escalon EA, Melnick SJ. 2002. Curcumin inhibits telomerase activity through human telomerase reverse transcritpase in MCF-7 breast cancer cell line. Cancer Lett 184 1-6. 

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