title: HIF mediated and DNA damage independent histone H2AX phosphorylation in chronic hypoxia.
abstract: The histone variant 2AX (H2AX) is phosphorylated at Serine 139 by the PI3K-like kinase family members ATM, ATR and DNA-PK. Genotoxic stress, such as tumor radio- and chemotherapy, is considered to be the main inducer of phosphorylated H2AX (γH2AX), which forms distinct foci at sites of DNA damage where DNA repair factors accumulate. γH2AX accumulation under severe hypoxic/anoxic (0.02% oxygen) conditions has recently been reported to follow replication fork stalling in the absence of detectable DNA damage. In this study, we found HIF-dependent accumulation of γH2AX in several cancer cell lines and mouse embryonic fibroblasts exposed to physiologically relevant chronic hypoxia (0.2% oxygen), which did not induce detectable levels of DNA strand breaks. The hypoxic accumulation of γH2AX was delayed by the RNAi-mediated knockdown of HIF-1α or HIF-2α and further decreased when both HIF-αs were absent. Conversely, basal phosphorylation of H2AX was increased in cells with constitutively stabilized HIF-2α. These results suggest that both HIF-1 and HIF-2 are involved in γH2AX accumulation by tumor hypoxia, which might increase a cancer cell's capacity to repair DNA damage, contributing to tumor therapy resistance.
authors.affiliation: Institute of Physiology and Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Wrann
authors.forename: Muriel R
authors.initials: MR
authors.lastname: Kaufmann
authors.forename: Renato
authors.initials: R
authors.lastname: Wirthner
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Stiehl
authors.forename: Roland H
authors.initials: RH
authors.lastname: Wenger
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D004249:DNA Damage / Q000235:genetics*; D005434:Flow Cytometry; D006657:Histones / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D010766:Phosphorylation; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D006657:Histones; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000099162:Endothelial PAS Domain-Containing Protein 1; C468783:H2AX protein, human; C497442:HIF1A protein, human