title: p53-Dependent but ATM-independent inhibition of DNA synthesis and G2 arrest in cadmium-treated human fibroblasts.
abstract: This study focused on the activation of cell cycle checkpoint responses in diploid human fibroblasts that were treated with cadmium chloride and the potential roles of ATM and p53 signaling pathways in cadmium-induced responses. The alkaline comet assay indicated that cadmium caused a dose-dependent increase in DNA damage. Cells that were rendered p53-defective by expression of a dominant-negative p53 allele or knockdown of p53 mRNA were more resistant to cadmium-induced inactivation of colony formation than normal and ataxia telangiectasia (AT) cells. Synchronized fibroblasts in S were more sensitive to cadmium toxicity than cells in G1, suggesting that cadmium may target some element of DNA replication. Cadmium produced a dose- and time-dependent inhibition of DNA synthesis. An immediate inhibition was associated with severe delay in progression through S phase and a delayed inhibition seen 24 h after treatment was associated with accumulation of cells in G2. AT and normal cells displayed similar patterns of inhibition of DNA synthesis and G2 delay after treatment with cadmium, while p53-defective cells displayed significantly less of the delayed inhibition of DNA synthesis and accumulation in G2 post-treatment. Total p53 protein and ser15-phosphorylated p53 were induced by cadmium in normal and AT cells. The p53 transactivation target Gadd45alpha was induced in both p53-effective and p53-defective cells after 4 h cadmium treatment, and this was associated with an acute inhibition of mitosis. Cadmium produced a very unusual pattern of toxicity in human fibroblasts, inhibiting DNA replication and inducing p53-dependent growth arrest but without induction of p21(Cip1/Waf1) or activation of Chk1.
authors.affiliation: Department of Toxicology, School of Public Health, Medical Center of Fudan University, Shanghai, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Cao
authors.forename: Tong
authors.initials: T
authors.lastname: Zhou
authors.forename: Dennis
authors.initials: D
authors.lastname: Simpson
authors.forename: Yingchun
authors.initials: Y
authors.lastname: Zhou
authors.forename: Jayne
authors.initials: J
authors.lastname: Boyer
authors.forename: Bo
authors.initials: B
authors.lastname: Chen
authors.forename: Taiyi
authors.initials: T
authors.lastname: Jin
authors.forename: Marila
authors.initials: M
authors.lastname: Cordeiro-Stone
authors.forename: William
authors.initials: W
authors.lastname: Kaufmann
mesh_terms: D001260:Ataxia Telangiectasia / Q000235:genetics*; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D002104:Cadmium / Q000494:pharmacology / Q000633:toxicity*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D020552:Comet Assay; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis* / Q000235:genetics; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000187:drug effects*; D016193:G1 Phase / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects*; D006801:Humans; D010957:Plasmids / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D002104:Cadmium; D004247:DNA; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases