title: Enhanced phosphorylation of Nbs1, a member of DNA repair/checkpoint complex Mre11-RAD50-Nbs1, can be targeted to increase the efficacy of imatinib mesylate against BCR/ABL-positive leukemia cells.
abstract: Nbs1, a member of the Mre11-RAD50-Nbs1 complex, is phosphorylated by ATM, the product of the ataxia-telangiectasia mutated gene and a member of the phosphatidylinositol 3-kinase-related family of serine-threonine kinases, in response to DNA double-strand breaks (DSBs) to regulate DNA damage checkpoints. Here we show that BCR/ABL stimulated Nbs1 expression by induction of c-Myc-dependent transactivation and protection from caspase-dependent degradation. BCR/ABL-related fusion tyrosine kinases (FTKs) such as TEL/JAK2, TEL/PDGFbetaR, TEL/ABL, TEL/TRKC, BCR/FGFR1, and NPM/ALK as well as interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) also stimulated Nbs1 expression. Enhanced ATM kinase-dependent phosphorylation of Nbs1 on serine 343 (S343) in response to genotoxic treatment was detected in leukemia cells expressing BCR/ABL and other FTKs in comparison to normal counterparts stimulated with IL-3, GM-CSF, and SCF. Expression of Nbs1-S343A mutant disrupted the intra-S-phase checkpoint, decreased homologous recombinational repair (HRR) activity, down-regulated XIAP expression, and sensitized BCR/ABL-positive cells to cytotoxic drugs. Interestingly, inhibition of Nbs1 phosphorylation by S343A mutant enhanced the antileukemia effect of the combination of imatinib and genotoxic agent.
authors: Department of Microbiology and Immunology, Temple University, Philadelphia, PA 19140, USA.
authors: Lori
authors: L
authors: Rink
authors: Artur
authors: A
authors: Slupianek
authors: Tomasz
authors: T
authors: Stoklosa
authors: Margaret
authors: M
authors: Nieborowska-Skorska
authors: Katarzyna
authors: K
authors: Urbanska
authors: Ilona
authors: I
authors: Seferynska
authors: Krzysztof
authors: K
authors: Reiss
authors: Tomasz
authors: T
authors: Skorski
mesh_terms: D017766:Acid Anhydride Hydrolases; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001549:Benzamides; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016044:Fusion Proteins, bcr-abl; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000068877:Imatinib Mesylate; D007938:Leukemia / Q000188:drug therapy*; D000076228:MRE11 Homologue Protein; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology* / Q000627:therapeutic use; D011505:Protein-Tyrosine Kinases / Q000032:analysis*; D011743:Pyrimidines / Q000494:pharmacology* / Q000627:therapeutic use; D011995:Recombination, Genetic
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes