title: Hypoxia-induced alterations of G2 checkpoint regulators.
abstract: Hypoxia promotes an aggressive tumor phenotype with increased genomic instability, partially due to downregulation of DNA repair pathways. However, genome stability is also surveilled by cell cycle checkpoints. An important issue is therefore whether hypoxia also can influence the DNA damage-induced cell cycle checkpoints. Here, we show that hypoxia (24 h 0.2% O2) alters the expression of several G2 checkpoint regulators, as examined by microarray gene expression analysis and immunoblotting of U2OS cells. While some of the changes reflected hypoxia-induced inhibition of cell cycle progression, the levels of several G2 checkpoint regulators, in particular Cyclin B, were reduced in G2 phase cells after hypoxic exposure, as shown by flow cytometric barcoding analysis of individual cells. These effects were accompanied by decreased phosphorylation of a Cyclin dependent kinase (CDK) target in G2 phase cells after hypoxia, suggesting decreased CDK activity. Furthermore, cells pre-exposed to hypoxia showed increased G2 checkpoint arrest upon treatment with ionizing radiation. Similar results were found following other hypoxic conditions (∼0.03% O2 20 h and 0.2% O2 72 h). These results demonstrate that the DNA damage-induced G2 checkpoint can be altered as a consequence of hypoxia, and we propose that such alterations may influence the genome stability of hypoxic tumors.
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Grete
authors.initials: G
authors.lastname: Hasvold
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Christin
authors.initials: C
authors.lastname: Lund-Andersen
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Malin
authors.initials: M
authors.lastname: Lando
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Patzke
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Sissel
authors.initials: S
authors.lastname: Hauge
authors.affiliation: Department of Pathology, Norwegian Radium Hospital, Oslo University Hospital, 0310 Oslo, Norway; Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
authors.forename: ZhenHe
authors.initials: Z
authors.lastname: Suo
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway.
authors.forename: Heidi
authors.initials: H
authors.lastname: Lyng
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, 0310 Oslo, Norway. Electronic address: randi.syljuasen@rr-research.no.
authors.forename: Randi G
authors.initials: RG
authors.lastname: Syljuåsen
mesh_terms: D045744:Cell Line, Tumor; D004249:DNA Damage; D016195:G2 Phase; D059565:G2 Phase Cell Cycle Checkpoints; D015972:Gene Expression Regulation, Neoplastic; D042822:Genomic Instability; D006801:Humans; D000860:Hypoxia / Q000150:complications* / Q000235:genetics*; D009369:Neoplasms / Q000150:complications* / Q000235:genetics*
keywords: DNA damage; G2 checkpoint; Genome stability; Hypoxia; Ionizing radiation