We also tested whether chemical inhibition or mutation of ATM would block dCK activation by IR. (2.5M) GUID:?208A859C-1A0A-4CCB-9C9A-37A0559DBF74 Physique S3: dCK is localized and activated after IR in the cytoplasm. (A) Western blot of nuclear (N) and cytoplasmic (C) fractions of CHOC6 (WT LCL) before and 2 hours after 3 Gy exposure. (B) dCK kinase assay using CHOC6 nuclear ABT-888 (Veliparib) and cytoplasmic fraction lysates, [3H]-dC as substrate and performed 2 hours after exposure to 3 Gy (*, P?=?0.0049, N?=?3). (C) Western blot of nuclear (N) and cytoplasmic (C) fractions of L1210 cell line before and 2 hours after 3 Gy exposure. (D) dCK kinase assay using L1210 nuclear and cytoplasmic fraction lysates, [3H]-dC as substrate and performed 2 hours after exposure to 3 Gy (*, P?=?0.0008, N?=?3).(TIF) pone.0104125.s003.tif (337K) GUID:?72E596CD-8491-42F1-8F9C-3C721423C727 Abstract Efficient and adequate generation of deoxyribonucleotides is critical to successful DNA repair. We show that ataxia telangiectasia mutated (ATM) integrates the DNA damage Rabbit polyclonal to Src.This gene is highly similar to the v-src gene of Rous sarcoma virus.This proto-oncogene may play a role in the regulation of embryonic development and cell growth.The protein encoded by this gene is a tyrosine-protein kinase whose activity can be inhibited by phosphorylation by c-SRC kinase.Mutations in this gene could be involved in the malignant progression of colon cancer.Two transcript variants encoding the same protein have been found for this gene. response with DNA metabolism by regulating the salvage of deoxyribonucleosides. Specifically, ATM phosphorylates and activates deoxycytidine kinase (dCK) at serine 74 in response to ionizing radiation (IR). Activation of dCK shifts its substrate specificity toward deoxycytidine, increases intracellular dCTP pools post IR, and enhances the rate of DNA repair. Mutation of a single serine 74 residue has profound effects on murine T and B lymphocyte development, suggesting that post-translational regulation of dCK may be important in maintaining genomic stability during hematopoiesis. Using [18F]-FAC, a dCK-specific positron emission tomography (PET) probe, we visualized and quantified dCK activation in tumor xenografts after IR, indicating that dCK activation could serve as a biomarker for ATM function and DNA damage response in vivo. In addition, dCK-deficient leukemia cell lines and ABT-888 (Veliparib) murine embryonic fibroblasts exhibited increased sensitivity to IR, indicating that pharmacologic inhibition of dCK may be an effective radiosensitization strategy. Introduction Intracellular concentrations of deoxyribonucleotide triphosphates (dNTPs) are tightly regulated to avoid mutagenesis during DNA replication and repair . Mammalian cells synthesize dNTPs by two mechanisms: 1) the pathway converts glucose and amino acids to deoxyribonucleotides via ribonucleotide reductase (RNR); 2) the deoxyribonucleoside (dN) salvage pathway generates dNTPs through sequential phosphorylation of recycled deoxyribonucleosides . Deoxycytidine kinase (dCK) is usually a rate-limiting enzyme in the dN salvage pathway, capable of phosphorylating deoxycytidine (dC), deoxyadenosine (dA) and deoxyguanosine (dG) , . Indirectly, dCK can also contribute to dTTP pools via the actions of deoxycytidylate deaminase and thymidylate synthase. Several studies have exhibited increased dCK activity under various genotoxic conditions, including chemotherapy C, ionizing C and UV  radiation, and inhibition of several protein kinases C. The potentiation of dCK activity was attributed to post-translational modifications that induced a conformational change of the enzyme C. Phosphorylation of serine 74 (Ser74) was shown to be critical in regulating enzyme activity C. dCK can adopt an open state, capable of substrate binding, or a closed, catalytically active, state , . Serine to glutamic acid (S74E) substitution mimicking Ser74 phosphorylation favors the open state and dramatically reduces phosphorylation of purines (dA and dG) but not pyrimidine dC . Ataxia telangiectasia mutated (ATM) serine/threonine protein kinase is at the center of DNA double-strand break (DSB) repair . ATM is usually a member of phosphoinositide 3-kinase (PI3K)-related protein kinase family, which also includes ataxia telangiectasia and Rad3-related protein (ATR) and catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) . ATM phosphorylates multiple substrates in the nucleus in response to DNA ABT-888 (Veliparib) DSBs , and regulates several metabolic pathways which counteract oxidative stress and DNA damage C. In ABT-888 (Veliparib) particular, ATM regulates NADPH and ribose-5-phosphate production via the pentose phosphate pathway by promoting phosphorylation of Hsp27, which binds and activates G6PD . ATM also phosphorylates Ser72 in the RNR subunit p53R2, which stabilizes the enzyme against degradation and promotes.