title: Targeting protein for xenopus kinesin-like protein 2 (TPX2) regulates γ-histone 2AX (γ-H2AX) levels upon ionizing radiation.
abstract: The microtubule-associated protein targeting protein for Xenopus kinesin-like protein 2 (TPX2) plays a key role in spindle assembly and is required for mitosis in human cells. In interphase, TPX2 is actively imported into the nucleus to prevent its premature activity in microtubule organization. To date, no function has been assigned to nuclear TPX2. We now report that TPX2 plays a role in the cellular response to DNA double strand breaks induced by ionizing radiation. Loss of TPX2 leads to inordinately strong and transient accumulation of ionizing radiation-dependent Ser-139-phosphorylated Histone 2AX (γ-H2AX) at G(0) and G(1) phases of the cell cycle. This is accompanied by the formation of increased numbers of high intensity γ-H2AX ionizing radiation-induced foci. Conversely, cells overexpressing TPX2 have reduced levels of γ-H2AX after ionizing radiation. Consistent with a role for TPX2 in the DNA damage response, we found that the protein accumulates at DNA double strand breaks and associates with the mediator of DNA damage checkpoint 1 (MDC1) and the ataxia telangiectasia mutated (ATM) kinase, both key regulators of γ-H2AX amplification. Pharmacologic inhibition or depletion of ATM or MDC1, but not of DNA-dependent protein kinase (DNA-PK), antagonizes the γ-H2AX phenotype caused by TPX2 depletion. Importantly, the regulation of γ-H2AX signals by TPX2 is not associated with apoptosis or the mitotic functions of TPX2. In sum, our study identifies a novel and the first nuclear function for TPX2 in the cellular responses to DNA damage.
authors.affiliation: Department of Clinical Neurosciences, Hotchkiss Brain Institute, University of Calgary, Calgary T2N4N1, Canada.
authors.forename: Gernot
authors.initials: G
authors.lastname: Neumayer
authors.forename: Angela
authors.initials: A
authors.lastname: Helfricht
authors.forename: Su Yeon
authors.initials: SY
authors.lastname: Shim
authors.forename: Hoa Thi
authors.initials: HT
authors.lastname: Le
authors.forename: Cecilia
authors.initials: C
authors.lastname: Lundin
authors.forename: Camille
authors.initials: C
authors.lastname: Belzil
authors.forename: Mathieu
authors.initials: M
authors.lastname: Chansard
authors.forename: Yaping
authors.initials: Y
authors.lastname: Yu
authors.forename: Susan P
authors.initials: SP
authors.lastname: Lees-Miller
authors.forename: Oliver J
authors.initials: OJ
authors.lastname: Gruss
authors.forename: Haico
authors.initials: H
authors.lastname: van Attikum
authors.forename: Thomas
authors.initials: T
authors.lastname: Helleday
authors.forename: Minh Dang
authors.initials: MD
authors.lastname: Nguyen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000235:genetics / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D053903:DNA Breaks, Double-Stranded; D051747:DNA-Activated Protein Kinase / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000235:genetics / Q000528:radiation effects; D005720:Gamma Rays / Q000009:adverse effects*; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis / Q000235:genetics / Q000528:radiation effects*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000528:radiation effects; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; C413163:MDC1 protein, human; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; C122167:TPX2 protein, human; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases