Ataxia-telangiectasia-mutated (ATM) Is a T-antigen Kinase That Controls SV40 Viral Replication in Vivo

Abstract

. Our findings uncover a direct link between ATM and SV40 LTag that may have implications for understanding the replication cycle of oncogenic polyoma viruses.The eukaryotic DNA damage response represents a series of highly integrated and tightly regulated pathways that coordinate DNA repair, cell cycle, and homeostatic responses to abnormal DNA structures arising endogenously or following exposure to extrinsic genotoxic stimuli. Central to the DNA damage response are a pair of structurally and functionally related protein kinases, designated ATM 2 (ataxia-telangiectasia-mutated) and ATR (ATM-Rad3-related) belonging to the phosphoinositide 3-kinase-related kinase (PIKK) gene superfamily. ATM and ATR share a conserved carboxyl-terminal catalytic domain and display highly overlapping substrate specificities in vitro (1-3). Substrates for ATM and ATR include the p53 and BRCA1 tumor suppressors among many other proteins involved in cell cycle checkpoint activation, DNA repair, and transcriptional regulation (1, 3). Mutations in ATM cause the cancer susceptibility-neurodegeneration syndrome, ataxia-telangiectasia (1, 4). ATM-deficient cells are grossly defective in the ionizing radiation (IR)-induced G 1 /S, intra-S phase, and G 2 /M checkpoints and are profoundly sensitive to IR and other agents that induce DNA double-strand breaks (DSBs) (1). Although structurally and functionally related to ATM, the major functions of ATR pertain to its roles in DNA replication (5). ATR prevents premature firing of DNA replicons, couples the completion of S phase to mitosis, and is required for chromosome maintenance and stabilization of stalled DNA replication forks (6 -10). Although null mutations in ATR are lethal, hypomorphic splicing mutations that reduce ATR protein levels are associated with a rare congenital condition known as Seckel's syndrome (11-13).The catalytic activity of ATM is rapidly up-regulated in response to IR and other DSB-inducing agents. Catalytic activation involves the transautophosphorylation of inactive, dimeric ATM on Ser-1981, followed by dissociation into active monomers (14). The trimeric complex of MRE11, RAD50, and NBS1 (MRN) facilitates ATM activation and ATMdependent substrate phosphorylation through recruitment of ATM to DSBs and/or orientation of the ATM catalytic domain (15-18). Recent studies suggest that the recruitment of ATM is mediated by the carboxyl terminus of NBS1 (19,20). Although ATR isolated from DNA-damaged cells does not show enhanced kinase activity, its recruitment to regions of stalled DNA replication is regulated through binding to the ATRinteracting protein (ATRIP) and replication protein A (RPA) (19,21). Among many key substrates for ATR and ATM are the checkpoint effector kinases, CHK1 and CHK2, which are phosphorylated by ATM and ATR in response to DSBs and DNA replication stress, respectively (6,(22)(23)(24). CHK1 and CHK2 promote checkpoint arrest through phosphorylation and inactivation of CDC25 family phosphatases (25-28).Virus infection can also elicit ATM-dependent...

Baculoviruses Modulate a Proapoptotic DNA Damage Response To Promote Virus Multiplication

“…DDR kinases such as ATM may also phosphorylate baculovirus replicative factors to activate them for vDNA synthesis. This mechanism has been proposed for ATMdriven phosphorylation of simian virus 40 (SV40) large T-antigen, which is required for optimal SV40 replication (57). Indeed, we recently demonstrated that phosphorylation of the essential replicative factor IE1 of AcMNPV coincides with vDNA replication (62).…”

Phosphorylation of Sp1 in Response to DNA Damage by Ataxia Telangiectasia-Mutated Kinase

“…Studies comparing the expression of the insulin growth factor receptor-I in normal fibroblasts and AT-mutated fibroblasts showed decreased levels of insulin growth factor-I receptor in ATmutated cells and identified Sp1 as a potential mediator between ATM and insulin growth factor-I receptor expression (38). In addition, ATM is induced by infection of cells with herpes simplex virus-1 and SV40 (71,72), which also induce Sp1 phosphorylation (11,20). Kim and DeLuca have shown that phosphorylated Sp1 purified from herpes simplex virus-1 -infected cells has decreased ability to activate transcription in in vitro transcription assays and that the kinetics of the phosphorylation correlate with the expression of Sp1-independent viral late genes, suggesting a viral-mediated temporal regulation of gene expression.…”

Coronavirus Infection Induces DNA Replication Stress Partly through Interaction of Its Nonstructural Protein 13 with the p125 Subunit of DNA Polymerase δ

“…Human Papillomavirus 16 E7 oncoprotein attenuates DNA damage checkpoint control by increasing the proteolytic turnover of claspin (75). SV40 large T antigen is a target of ATM kinase, and this ATM-mediated phosphorylation of T-antigen is required for optimal viral DNA synthesis (77). Inhibition of ATM activity decreases SV40 DNA replication and delays recruitment of T-antigen and DNA repair proteins to viral replication foci (76 -78).…”