title: Genomic instability in Gadd45a-/- cells is coupled with S-phase checkpoint defects.
abstract: Gadd45a is a p53-regulated gene whose protein product, like p53, is involved in maintenance of genome stability. Specifically, deletion of Gadd45a leads to extensive aneuploidy as a consequence of centrosome amplification and subsequent abnormal segregation of chromosomes during mitosis. S-phase checkpoints were investigated in Gadd45a(-/-) cells to determine possible defects contributing to the uncoupling of centrosome duplication and DNA replication. In the presence of hydroxyurea, Gadd45a(-/-) mouse embryo fibroblasts show increased centrosome amplification coupled with loss of a sustained S-phase checkpoint. Gadd45a deletion allows another form of genomic instability, gene amplification, when p21 (Cdkn1a gene product) is deleted also. Gene amplification in Gadd45a(-/-)p21(-/-) cells correlated with loss of both G(1) and S-phase checkpoints. Multiple conditions of nutrient deprivation failed to prevent DNA synthesis in Gadd45a(-/-) cells. Gadd45a is therefore required for proper S-phase control and checkpoints under multiple conditions of nutrient deprivation. It is proposed that loss of S-phase control may account for both the uncoupling of DNA replication and centrosome duplication, and conferring gene amplification proficiency in cells lacking Gadd45a(-/-). This is of particular importance for solid tumors, which may lack sufficient nutrients yet are unable to elicit checkpoints preventing genomic instability under these conditions.
authors.affiliation: Cancer Therapeutics Branch, National Cancer Institute, Bethesda, Maryland 20889, USA. ch96b@nih.gov
authors.forename: M C
authors.initials: MC
authors.lastname: Hollander
authors.forename: R T
authors.initials: RT
authors.lastname: Philburn
authors.forename: A D
authors.initials: AD
authors.lastname: Patterson
authors.forename: M A
authors.initials: MA
authors.lastname: Wyatt
authors.forename: A J
authors.initials: AJ
authors.lastname: Fornace
mesh_terms: D000782:Aneuploidy; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000502:physiology*; D002460:Cell Line; D018385:Centrosome / Q000187:drug effects / Q000502:physiology; D020090:Chromosome Segregation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000502:physiology; D004247:DNA / Q000096:biosynthesis; D004261:DNA Replication; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D005784:Gene Amplification; D017353:Gene Deletion; D005786:Gene Expression Regulation; D018816:Genes, cdc / Q000187:drug effects; D016158:Genes, p53; D042822:Genomic Instability; D006918:Hydroxyurea / Q000494:pharmacology; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics* / Q000502:physiology*; D010746:Phosphonoacetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D016196:S Phase / Q000187:drug effects / Q000235:genetics*; D000097642:GADD45 Proteins
chemical_list: D001224:Aspartic Acid; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004247:DNA; D006918:Hydroxyurea; D009687:Nuclear Proteins; D010746:Phosphonoacetic Acid; C493957:Cdkn1a protein, mouse; C499072:Gadd45a protein, mouse; D000097642:GADD45 Proteins; C013195:sparfosic acid