title: Geminin functions downstream of p53 in K-ras-induced gene amplification of dihydrofolate reductase.
abstract: DNA strand breakage and perturbation of cell-cycle progression contribute to gene amplification events that can drive cancer. In cells lacking p53, DNA damage does not trigger an effective cell-cycle arrest and in this setting promotes gene amplification. This is also increased in cells harboring oncogenic Ras, in which cell-cycle arrest is perturbed and ROS levels that cause DNA single strand breaks are elevated. This study focused on the effects of v-K-ras and p53 on Methotrexate (MTX)-mediated DHFR amplification. Rat lung epithelial cells expressing v-K-ras or murine lung cancer LKR cells harboring active K-ras continued cell-cycle progression when treated with MTX. However, upon loss of p53, amplification of DHFR and formation of MTX-resistant colonies occurred. Expression levels of cyclin A, Geminin, and Cdt1 were increased in v-K-ras transfectants. Geminin was sufficient to prevent the occurrence of multiple replications via interaction with Cdt1 after MTX treatment, and DHFR amplification proceeded in v-K-ras transfectants that possess a functional p53 in the absence of geminin. Taken together, our findings indicate that p53 not only regulates cell-cycle progression, but also functions through geminin to prevent DHFR amplification and protect genomic integrity.
authors.affiliation: Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Shen
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishioka
authors.forename: Jinjin
authors.initials: J
authors.lastname: Guo
authors.forename: Changyan
authors.initials: C
authors.lastname: Chen
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D004249:DNA Damage; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics; D064248:Geminin; D005784:Gene Amplification; D055785:Gene Knockdown Techniques; D016158:Genes, p53; D011905:Genes, ras; D042822:Genomic Instability; D008168:Lung / Q000187:drug effects / Q000502:physiology; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D018797:Cell Cycle Proteins; D064248:Geminin; C577997:Gmnn protein, mouse; D009687:Nuclear Proteins; D017382:Reactive Oxygen Species; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate