title: Telomerase levels control the lifespan of human T lymphocytes.
abstract: The loss of telomeric DNA with each cell division contributes to the limited replicative lifespan of human T lymphocytes. Although telomerase is transiently expressed in T lymphocytes upon activation, it is insufficient to confer immortality. We have previously shown that immortalization of human CD8+ T lymphocytes can be achieved by ectopic expression of the human telomerase reverse transcriptase (hTERT) gene, which encodes for the catalytic component of the telomerase complex. To study the role of endogenous hTERT in the lifespan of human T cells, we blocked endogenous hTERT expression by ectopic expression of dominant-negative (DN) hTERT. Cells expressing DN-hTERT had a decreased lifespan and showed cytogenetic abnormalities, including chromosome ends without detectable telomeric DNA as well as chromosome fusions. These results indicate that while endogenous hTERT cannot prevent overall telomere shortening, it has a major influence on the longevity of human T cells. Furthermore, we show that up-regulation of hTERT in T cells upon activation decreases over time in culture. Long-term-cultured T cells also show a decreased expression of c-myc upon activation, resulting in less c-myc-induced transcription of hTERT. Moreover, memory T cells, which have expanded in vivo upon antigen encounter, expressed a lower level of hTERT upon activation than naive cells from the same donor. The observed inverse correlation between telomerase levels and replicative history suggests that telomerase levels in T cells are limiting and increasingly insufficient to sustain their proliferation.
authors.affiliation: Terry Fox Laboratory, British Columbia Cancer Agency and University of British Columbia, Vancouver, Canada.
authors.forename: Alexander
authors.initials: A
authors.lastname: Roth
authors.forename: Hans
authors.initials: H
authors.lastname: Yssel
authors.forename: Jerome
authors.initials: J
authors.lastname: Pene
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Chavez
authors.forename: Mike
authors.initials: M
authors.lastname: Schertzer
authors.forename: Peter M
authors.initials: PM
authors.lastname: Lansdorp
authors.forename: Hergen
authors.initials: H
authors.lastname: Spits
authors.forename: Rosalie M
authors.initials: RM
authors.lastname: Luiten
mesh_terms: D018929:Cell Culture Techniques; D016922:Cellular Senescence; D002869:Chromosome Aberrations; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation; D006801:Humans; D007156:Immunologic Memory; D008213:Lymphocyte Activation / Q000502:physiology; D020598:Proto-Oncogene Proteins c-myb / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000166:cytology*; D019098:Telomerase / Q000096:biosynthesis / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D020598:Proto-Oncogene Proteins c-myb; D019098:Telomerase