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

• Published in: Blood 2007-07, Vol.110 (2), p.651-660
• Main Authors: Rink, Lori, Slupianek, Artur, Stoklosa, Tomasz, Nieborowska-Skorska, Margaret, Urbanska, Katarzyna, Seferynska, Ilona, Reiss, Krzysztof, Skorski, Tomasz
• Format: Article
• Language: English
• Subjects: Acid Anhydride Hydrolases; Animals; Antineoplastic agents; Antineoplastic Agents - pharmacology; Antineoplastic Agents - therapeutic use; Benzamides; Biological and medical sciences; Cell Cycle Proteins - metabolism; Cell Survival - drug effects; DNA Repair; DNA Repair Enzymes - metabolism; DNA Replication - drug effects; DNA-Binding Proteins - metabolism; Fusion Proteins, bcr-abl; Gene Expression Regulation, Neoplastic; General aspects; Humans; Imatinib Mesylate; Leukemia - drug therapy; Medical sciences; Mice; MRE11 Homologue Protein; Neoplasia; Nuclear Proteins - metabolism; Pharmacology. Drug treatments; Phosphorylation; Piperazines - pharmacology; Piperazines - therapeutic use; Protein-Tyrosine Kinases - analysis; Pyrimidines - pharmacology; Pyrimidines - therapeutic use; Recombination, Genetic
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2006-08-042630

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/PDGFβR, 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.