title: Alternative mechanisms of telomere lengthening: permissive mutations, DNA repair proteins and tumorigenic progression.
abstract: Telomeres protect chromosome termini to maintain genomic stability and regulate cellular lifespan. Maintenance of telomere length is required for neoplastic cells after the acquisition of mutations that deregulate cell cycle control and increase cellular proliferation, and can occur through expression of the enzyme telomerase or in a telomerase-independent manner termed alternative lengthening of telomeres (ALT). The precise mechanisms that govern the activation of ALT or telomerase in tumor cells are unknown, although cellular origin may favor one or the other mechanisms. ALT pathways are incompletely understood to date; however, recent publications have increasingly broadened our understanding of how ALT is activated, how it proceeds, and how it influences tumor growth. Specific mutational events influence ALT activation, as mutations in genes that suppress recombination and/or alterations in the regulation of telomerase expression are associated with ALT. Once engaged, ALT uses DNA repair proteins to maintain telomeres in the absence of telomerase; experiments that manipulate the expression of specific proteins in cells using ALT are illuminating some of its mechanisms. Furthermore, ALT may influence tumor growth, as experimental and clinical data suggest that telomerase expression may favor tumor progression. This review summarizes recent findings in mammalian cells and models, as well as clinical data, that identify the genetic mutations permissive to ALT, the DNA repair proteins involved in ALT mechanisms and the importance of telomere maintenance mechanisms for tumor progression. A comprehensive understanding of the mechanisms that permit tumor cell immortalization will be important for identifying novel therapeutic targets in cancer.
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States.
authors.forename: April Renee Sandy
authors.initials: ARS
authors.lastname: Gocha
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States.
authors.forename: Julia
authors.initials: J
authors.lastname: Harris
authors.affiliation: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States. Electronic address: joanna.groden@osumc.edu.
authors.forename: Joanna
authors.initials: J
authors.lastname: Groden
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D004260:DNA Repair; D018450:Disease Progression; D006801:Humans; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D016615:Telomere / Q000235:genetics* / Q000378:metabolism; D059505:Telomere Homeostasis
chemical_list: D019098:Telomerase