¹INSERM U362, PR-1, Institut Gustave Roussy, 39/53 rue Camille Desmoulins, 94805 Villejuif, France

²Service d'Hématologie et de Cytogénétique, Hôpital de Bicêtre, 78 rue du Général Leclerc, 94270 Le Kremblin Bicêtre, France

³Department of Clinical Biology, Service d'Hématologie Biologique, Institut Gustave Roussy, 39/53 rue Camille Desmoulins, 94805 Villejuif, France

Correspondence to: A Bennaceur-Griscelli, E-mail: abenna@igr.fr

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.

Oncogene (2002) 21, 8262-8271. doi:10.1038/sj.onc.1206054

telomere; telomerase; leukemia; retrovirus; cell death; therapy