title: Regulation of mitotic entry by microcephalin and its overlap with ATR signalling.
abstract: Ataxia-telangiectasia mutated and Rad3 related (ATR)-Seckel syndrome and autosomal recessive primary microcephaly (MCPH) syndrome share clinical features. RNA interference (RNAi) of MCPH1 have implicated the protein it encodes as a DNA-damage response protein that regulates the transcription of Chk1 and BRCA1, two genes involved in the response to DNA damage. Here, we report that truncating mutations observed in MCPH-syndrome patients do not impact on Chk1 or BRCA1 expression or early ATR-dependent damage-induced phosphorylation events. However, like ATR-Seckel syndrome cells, MCPH1-mutant cell lines show defective G2-M checkpoint arrest and nuclear fragmentation after DNA damage, and contain supernumerary mitotic centrosomes. MCPH1-mutant and ATR-Seckel cells also show impaired degradation of Cdc25A and fail to inhibit Cdc45 loading onto chromatin after replication arrest. Additionally, microcephalin interacts with Chk1. We conclude that MCPH1 has a function downstream of Chk1 in the ATR-signalling pathway. In contrast with ATR-Seckel syndrome cells, MCPH1-mutant cells have low levels of Tyr 15-phosphorylated Cdk1 (pY15-Cdk1) in S and G2 phases, which correlates with an elevated frequency of G2-like cells displaying premature chromosome condensation (PCC). Thus, MCPH1 also has an ATR-independent role in maintaining inhibitory Cdk1 phosphorylation, which prevents premature entry into mitosis.
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, East Sussex, BN1 9RQ, UK.
authors.forename: Gemma K
authors.initials: GK
authors.lastname: Alderton
authors.forename: Laura
authors.initials: L
authors.lastname: Galbiati
authors.forename: Elen
authors.initials: E
authors.lastname: Griffith
authors.forename: Katharina H
authors.initials: KH
authors.lastname: Surinya
authors.forename: Heidemarie
authors.initials: H
authors.lastname: Neitzel
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Jackson
authors.forename: Penny A
authors.initials: PA
authors.lastname: Jeggo
authors.forename: Mark
authors.initials: M
authors.lastname: O'Driscoll
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D003598:Cytoskeletal Proteins; D004249:DNA Damage / Q000502:physiology; D018816:Genes, cdc / Q000502:physiology; D006801:Humans; D008831:Microcephaly / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008938:Mitosis / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009421:Nervous System Malformations / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism
chemical_list: C113571:CDC45 protein, human; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C460645:MCPH1 protein, human; D009419:Nerve Tissue Proteins; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases