title: Telomerase reverse transcriptase expression protects transformed human cells against DNA-damaging agents, and increases tolerance to chromosomal instability.
abstract: Reactivation of telomerase reverse transcriptase (TERT) expression is found in more than 85% of human cancers. The remaining cancers rely on the alternative lengthening of telomeres (ALT), a recombination-based mechanism for telomere-length maintenance. Prevalence of TERT reactivation over the ALT mechanism was linked to secondary TERT function unrelated to telomere length maintenance. To characterize this non-canonical function, we created a panel of ALT cells with recombinant expression of TERT and TERT variants: TERT-positive ALT cells showed higher tolerance to genotoxic insults compared with their TERT-negative counterparts. We identified telomere synthesis-defective TERT variants that bestowed similar genotoxic stress tolerance, indicating that telomere synthesis activity is dispensable for this survival phenotype. TERT expression improved the kinetics of double-strand chromosome break repair and reduced DNA damage-related nuclear division abnormalities, a phenotype associated with ALT tumors. Despite this reduction in cytological abnormalities, surviving TERT-positive ALT cells were found to have gross chromosomal instabilities. We sorted TERT-positive cells with cytogenetic changes and followed their growth. We found that the chromosome-number changes persisted, and TERT-positive ALT cells surviving genotoxic events propagated through subsequent generations with new chromosome numbers. Our data confirm that telomerase expression protects against double-strand DNA (dsDNA)-damaging events, and show that this protective function is uncoupled from its role in telomere synthesis. TERT expression promotes oncogene-transformed cell growth by reducing the inhibitory effects of cell-intrinsic (telomere attrition) and cell-extrinsic (chemical- or metabolism-induced genotoxic stress) challenges. These data provide the impetus to develop new therapeutic interventions for telomerase-positive cancers through simultaneous targeting of multiple telomerase activities.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: H B
authors.initials: HB
authors.lastname: Fleisig
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: K R
authors.initials: KR
authors.lastname: Hukezalie
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: C A H
authors.initials: CA
authors.lastname: Thompson
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: T T T
authors.initials: TT
authors.lastname: Au-Yeung
authors.affiliation: Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: A T
authors.initials: AT
authors.lastname: Ludlow
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: C R
authors.initials: CR
authors.lastname: Zhao
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: J M Y
authors.initials: JM
authors.lastname: Wong
mesh_terms: D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D002461:Cell Line, Transformed / Q000187:drug effects; D043171:Chromosomal Instability; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D000077146:Irinotecan; D008938:Mitosis; D009154:Mutation; D009944:Organoplatinum Compounds / Q000494:pharmacology; D000077150:Oxaliplatin; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere
chemical_list: D009944:Organoplatinum Compounds; D011994:Recombinant Proteins; D000077150:Oxaliplatin; D005047:Etoposide; D000077146:Irinotecan; C509186:TERT protein, human; D019098:Telomerase; D002166:Camptothecin