title: Super-telomeres in transformed human fibroblasts.
abstract: Telomere length maintenance is critical for organisms' long-term survival and cancer cell proliferation. Telomeres are kept within species-specific length ranges by the interplay between telomerase activity and telomeric chromatin organization. In this paper, we exploited telomerase immortalized human fibroblasts (cen3tel) that gradually underwent neoplastic transformation during culture propagation to study telomere composition and length regulation during the transformation process. Just after telomerase catalytic subunit (hTERT) expression, cen3tel telomeres shortened despite the presence of telomerase activity. At a later stage and concomitantly with transformation, cells started elongating telomeres, which reached a mean length greater than 100kb in about 900 population doublings. Super-telomeres were stable and compatible with cell growth and tumorigenesis. Telomere extension was associated with increasing levels of telomerase activity that were linked to the deregulation of endogenous telomerase RNA (hTERC) and exogenous telomerase reverse transcriptase (hTERT) expression. Notably, the increase in hTERC levels paralleled the increase in telomerase activity, suggesting that this subunit plays a role in regulating enzyme activity. Telomeres ranging in length between 10 and more than 100kb were maintained in an extendible state although TRF1 and TRF2 binding increased with telomere length. Super-telomeres neither influenced subtelomeric region global methylation nor the expression of the subtelomeric gene FRG1, attesting the lack of a clear-cut relationship between telomere length, subtelomeric DNA methylation and expression in human cells. The cellular levels of the telomeric proteins hTERT, TRF1, TRF2 and Hsp90 rose with transformation and were independent of telomere length, pointing to a role of these proteins in tumorigenesis.
authors.affiliation: Istituto di Genetica Molecolare, Pavia, Italy. chiodi@igm.cnr.it
authors.forename: Ilaria
authors.initials: I
authors.lastname: Chiodi
authors.forename: Cristina
authors.initials: C
authors.lastname: Belgiovine
authors.forename: Samantha
authors.initials: S
authors.lastname: Zongaro
authors.forename: Roberta
authors.initials: R
authors.lastname: Ricotti
authors.forename: Beatrice
authors.initials: B
authors.lastname: Horard
authors.forename: Andrea
authors.initials: A
authors.lastname: Lossani
authors.forename: Federico
authors.initials: F
authors.lastname: Focher
authors.forename: Eric
authors.initials: E
authors.lastname: Gilson
authors.forename: Elena
authors.initials: E
authors.lastname: Giulotto
authors.forename: Chiara
authors.initials: C
authors.lastname: Mondello
mesh_terms: D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D008840:Microfilament Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000235:genetics; D016601:RNA-Binding Proteins; D019098:Telomerase / Q000235:genetics; D016615:Telomere / Q000235:genetics* / Q000378:metabolism*; D059505:Telomere Homeostasis / Q000235:genetics*; D035321:Telomeric Repeat Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D035341:Telomeric Repeat Binding Protein 2 / Q000235:genetics / Q000378:metabolism
chemical_list: C101270:FRG1 protein, human; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; C504753:TERF2 protein, human; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; C422952:telomerase RNA; D012313:RNA; D019098:Telomerase