title: Telomere dysfunction and telomerase reactivation in human leukemia cell lines after telomerase inhibition by the expression of a dominant-negative hTERT mutant.
abstract: As activation of telomerase represents a key step in the malignant transformation process, experimental models to develop anti-telomerase drugs provide a rational basis for anticancer strategies. We analysed the short and long-term efficacy of a stably expressed dominant-negative mutant (DN) of the telomerase catalytic unit (hTERT) in UT-7 and U937 human leukemia cell lines by using an IRES-e-GFP retrovirus. As expected, telomerase inactivation resulted in drastic telomere shortening, cytogenetic instability and cell growth inhibition in all e-GFP positive DN clones after 15-35 days of culture. However, despite this initial response, 50% of e-GFP positive DN clones with short telomeres escaped from crisis after 35 days of culture and recovered a proliferation rate similar to the control cells. This rescue was associated with a telomerase reactivation inducing telomere lengthening. We identified two pathways, one involving the loss of the DN transgene expression and the other the transcriptional up-regulation of endogenous hTERT with persistence of the DN transgene expression. Although this second mechanism appears to be a very rare event (one clone), these findings suggest that genomic instability induced by short telomeres after telomerase inhibition might enhance the probability of activation or selection of telomere maintenance mechanisms dependent on hTERT transcription.
authors.affiliation: INSERM U362, PR-1, Institut Gustave Roussy, 39/53 rue Camille Desmoulins, 94805 Villejuif, France.
authors.forename: François
authors.initials: F
authors.lastname: Delhommeau
authors.forename: Antoine
authors.initials: A
authors.lastname: Thierry
authors.forename: Danièle
authors.initials: D
authors.lastname: Feneux
authors.forename: Evelyne
authors.initials: E
authors.lastname: Lauret
authors.forename: Edwige
authors.initials: E
authors.lastname: Leclercq
authors.forename: Marie Hélène
authors.initials: MH
authors.lastname: Courtier
authors.forename: Françoise
authors.initials: F
authors.lastname: Sainteny
authors.forename: William
authors.initials: W
authors.lastname: Vainchenker
authors.forename: Annelise
authors.initials: A
authors.lastname: Bennaceur-Griscelli
mesh_terms: D002455:Cell Division / Q000235:genetics; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D006801:Humans; D007938:Leukemia / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D009154:Mutation; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism*; D016615:Telomere; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D019098:Telomerase