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Absence of cancer–associated changes in human fibroblasts immortalized with telomerase

Abstract

The ectopic expression of telomerase1,2 in normal human cells results in an extended lifespan3,4, indicating that telomere shortening regulates the timing of cellular senescence. As telomerase expression is a hallmark of cancer, we investigated the long–term effects of forced expression of human telomerase catalytic component (hTERT) in normal human fibroblasts. In vitro growth requirements, cell–cycle checkpoints and karyotypic stability in telomerase–expressing cells are similar to those of untransfected controls. In addition, co–expression of telomerase, the viral oncoproteins HPV16 E6/E7 (which inactivate p53 and pRB) and oncogenic HRAS does not result in growth in soft agar. Thus, although ectopic expression of telomerase in human fibroblasts is sufficient for immortalization, it does not result in changes typically associated with malignant transformation.

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Figure 1: Growth rates and relative telomerase activity in fibroblasts transfected with TERT.
Figure 2: The retinoblastoma protein phosphorylation status in normal and telomerase–expressing fibroblasts.
Figure 3: Effects of UV irradiation on the expression of p53 and p21Cip1/Waf1 protein in TERT–expressing fibroblast clones, B52 and G6, measured by western–blot analysis.
Figure 4: Oncogenic HRAS induces a senescence–like phenotype in telomerase–expressing fibroblasts.
Figure 5: Lack of anchorage–independent growth of telomerase–expressing fibroblasts expressing HPV16 E6/E7 and oncogenic HRAS.

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Acknowledgements

We acknowledge J. Rohde, M. Liao, D. Cohen, J. Doolittle, S. Donovan and S. Patel for excellent technical assistance. This work was supported in part by the National Institutes of Aging (AG07992), the National Cancer Institute (CA71443) and Geron Corporation. C.P.M. is supported by The Robert Wood Johnson Foundation Minority Medical Faculty Development Program. J.W.S. is an Ellison Medical Foundation Senior Scholar. S.E.H. was supported by a postdoctoral fellowship from the National Institute of Aging.

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Correspondence to Jerry W. Shay.

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Morales, C., Holt, S., Ouellette, M. et al. Absence of cancer–associated changes in human fibroblasts immortalized with telomerase. Nat Genet 21, 115–118 (1999). https://doi.org/10.1038/5063

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