In vitro aging of rat lung cells. Downregulation of telomerase activity and continuous decrease of telomere length are not incompatible with malignant transformation.
Most normal mammalian somatic cells cultivated in vitro enter replicative senescence after a finite number of divisions, as a consequence of the progressive shortening of telomeres during proliferation that reflects one aspect of organism/cellular aging. The situation appears more complex in rodent cells due to physiological telomerase expression in most somatic normal tissues, great telomere length, and the difficulties of finding suitable in vitro culture conditions. To study in vitro aging of rat lung epithelial cells, we have developed primary culture conditions adapted to rat fresh lung explants and have studied for 1 year (50 passages) the changes in cellular proliferation and mortality, genetic instability, telomerase activity, telomere length, and tumorigenic potential. We have observed an absence of senescence and/or crisis, a transient genetic instability, the persistence of a differentiated Clara cell phenotype, a steady decrease in telomerase activity followed by a low residual activity together with a continuous decrease in telomere length, a constant rate of proliferation, and the acquisition of tumorigenic potential. The bypass of the growth arrest and the acquisition of long-term growth properties could be explained by the loss of p16(INK4a) expression, the ARF/p53 pathway not being altered. In conclusion, these results clearly indicate that, in rat lung epithelial cells, in vitro transformation and acquisition of tumorigenic properties can occur even if the telomere length is still decreasing and telomerase activity remains downregulated.
Laboratoire de Cancérologie Expérimentale, Département de Radiobiologie et Radiopathologie, Commissariat à l'Energie Atomique, 60-68 Avenue du Général Leclerc, BP6, 92265 Fontenay-aux-Roses cedex, France.
Fabrice
F
Petitot
Jérôme
J
Lebeau
Laurent
L
Dano
Bruno
B
Lectard
Sandrine
S
Altmeyer
Céline
C
Levalois
Sylvie
S
Chevillard
D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D016922:Cellular Senescence; D046508:Culture Techniques; D004247:DNA / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology; D016147:Genes, Tumor Suppressor; D008168:Lung / Q000166:cytology* / Q000502:physiology; D008297:Male; D051379:Mice; D008819:Mice, Nude; D051381:Rats; D017207:Rats, Sprague-Dawley; D020545:Respiratory Mucosa / Q000166:cytology* / Q000502:physiology; D019098:Telomerase / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*
D004247:DNA; D019098:Telomerase