title: CCAR2/DBC1 is required for Chk2-dependent KAP1 phosphorylation and repair of DNA damage.
abstract: Cell cycle and apoptosis regulator 2 (CCAR2, formerly known as DBC1) is a nuclear protein largely involved in DNA damage response, apoptosis, metabolism, chromatin structure and transcription regulation. Upon DNA lesions, CCAR2 is phosphorylated by the apical kinases ATM/ATR and this phosphorylation enhances CCAR2 binding to SIRT1, leading to SIRT1 inhibition, p53 acetylation and p53-dependent apoptosis. Recently, we found that also the checkpoint kinase Chk2 and the proteasome activator REGγ are required for efficient CCAR2-mediated inhibition of SIRT1 and induction of p53-dependent apoptosis.Here, we report that CCAR2 is required for the repair of heterochromatic DNA lesions, as cells knock-out for CCAR2 retain, at late time-points after genotoxic treatment, abnormal levels of DNA damage-associated nuclear foci, whose timely resolution is reinstated by HP1β depletion. Conversely, repair of DNA damages in euchromatin are not affected by CCAR2 absence.We also report that the impairment in heterochromatic DNA repair is caused by defective Chk2 activation, detectable in CCAR2 ablated cells, which finally impacts on the phosphorylation of the Chk2 substrate KAP1 that is required for the induction of heterochromatin relaxation and DNA repair.These studies further extend and confirm the role of CCAR2 in the DNA damage response and DNA repair and illustrate a new mechanism of Chk2 activity regulation. Moreover, the involvement of CCAR2 in the repair of heterochromatic DNA breaks suggests a new role for this protein in the maintenance of chromosomal stability, which is necessary to prevent cancer formation.
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Magni
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.|Current address: Max Planck Institute for Developmental Biology, Tubingen, Germany.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Ruscica
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Restelli
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Fontanella
authors.affiliation: Department of Biosciences, University of Milan, Milan, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Buscemi
authors.affiliation: Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Zannini
mesh_terms: D015153:Blotting, Western; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D064447:Checkpoint Kinase 2 / Q000378:metabolism*; D000090266:Chromobox Protein Homolog 5; D004249:DNA Damage / Q000502:physiology*; D004260:DNA Repair / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D055786:Gene Knockout Techniques; D006801:Humans; D047468:Immunoprecipitation; D009419:Nerve Tissue Proteins; D010766:Phosphorylation; D034741:RNA, Small Interfering; D012097:Repressor Proteins / Q000378:metabolism*; D014162:Transfection; D000076183:Tripartite Motif-Containing Protein 28; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: C112308:BRINP1 protein, human; C000715593:CBX1 protein, human; D018797:Cell Cycle Proteins; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; D000090266:Chromobox Protein Homolog 5; C101116:TRIM28 protein, human; D000076183:Tripartite Motif-Containing Protein 28; D064447:Checkpoint Kinase 2; C578634:CHEK2 protein, human
keywords: DNA damage; DNA repair; chromatin relaxation; phosphorylation