Dissociation among in vitro telomerase activity, telomere maintenance, and cellular immortalization
- Christopher M. Counter*,†,‡,
- William C. Hahn*,†,§,
- Wenyi Wei¶,
- Stephanie Dickinson Caddle*,
- Roderick L. Beijersbergen*,
- Peter M. Lansdorp‖,
- John M. Sedivy¶, and
- Robert A. Weinberg*,**
- *The Whitehead Institute for Biomedical Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142; §Department of Adult Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115; ¶Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912; and ‖Terry Fox Laboratory, British Columbia Cancer Research Centre, 601 West 10th Avenue, Vancouver, British Columbia, V5Z 1L3 Canada
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Contributed by Robert A. Weinberg
Abstract
The immortalization of human cells is a critical step during tumorigenesis. In vitro, normal human somatic cells must overcome two proliferative blockades, senescence and crisis, to become immortal. Transformation with viral oncogenes extends the life span of human cells beyond senescence. Such transformed cells eventually succumb to crisis, a period of widespread cellular death that has been proposed to be the result of telomeric shortening. We now show that ectopic expression of the telomerase catalytic subunit (human telomerase reverse transcriptase or hTERT) and subsequent activation of telomerase can allow postsenescent cells to proliferate beyond crisis, the last known proliferative blockade to cellular immortality. Moreover, we demonstrate that alteration of the carboxyl terminus of human telomerase reverse transcriptase does not affect telomerase enzymatic activity but impedes the ability of this enzyme to maintain telomeres. Telomerase-positive cells expressing this mutant enzyme fail to undergo immortalization, further tightening the connection between telomere maintenance and immortalization.
Footnotes
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↵ † C.M.C. and W.C.H. contributed equally to this work.
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↵ ‡ Present address: Departments of Pharmacology and Cancer Biology, and Radiation Oncology, Box 3813, Duke University Medical Center, Durham, NC 27710.
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↵ ** To whom reprint requests should be addressed at: Whitehead Institute for Biomedical Research, 9 Cambridge Center, Room 367B, Cambridge, MA 02142. e-mail: weinberg{at}wi.mit.edu.
- ABBREVIATIONS:
- hTERT,
- human telomerase reverse transcriptase;
- HEK,
- human embryonic kidney;
- T-Ag,
- simian virus 40 large T antigen;
- HA,
- hemagglutinin;
- pd,
- population doubling;
- TRF,
- terminal restriction fragments
- Copyright © 1998, The National Academy of Sciences
