Ataxia-telangiectasia mutated (ATM) is a high molecular weight protein serine/threonine kinase that plays a central role in the maintenance of genomic integrity by activating cell cycle checkpoints and promoting repair of DNA double-strand breaks. Little is known about the regulatory mechanisms for ATM expression itself. MicroRNAs are naturally existing regulators that modulate gene expression in a sequence-specific manner. Here, we show that a human microRNA, miR-421, suppresses ATM expression by targeting the 3′-untranslated region (3′UTR) of ATM transcripts. Ectopic expression of miR-421 resulted in S-phase cell cycle checkpoint changes and an increased sensitivity to ionizing radiation, creating a cellular phenotype similar to that of cells derived from ataxiatelangiectasia (A-T) patients. Blocking the interaction between miR-421 and ATM 3′UTR with an antisense morpholino oligonucleotide rescued the defective phenotype caused by miR-421 overexpression, indicating that ATM mediates the effect of miR-421 on cell cycle checkpoint and radiosensitivity. Overexpression of the N-Myc transcription factor, an oncogene frequently amplified in neuroblastoma, induced miR-421 expression, which, in turn, downregulated ATM expression, establishing a linear signaling pathway that may contribute to N-Myc-induced tumorigenesis in neuroblastoma. Taken together, our findings implicate a previously undescribed regulatory mechanism for ATM expression and ATMdependent DNA damage response and provide several potential targets for treating neuroblastoma and perhaps A-T.neuroblastoma | S-phase checkpoint | radiosensitivity | DNA repair

Large numbers of genetic disorders are caused by nonsense mutations for which compound-induced readthrough of premature termination codons (PTCs) might be exploited as a potential treatment strategy. We have successfully developed a sensitive and quantitative high-throughput screening (HTS) assay, protein transcription/translation (PTT)–enzyme-linked immunosorbent assay (ELISA), for identifying novel PTC-readthrough compounds using ataxia-telangiectasia (A-T) as a genetic disease model. This HTS PTT-ELISA assay is based on a coupled PTT that uses plasmid templates containing prototypic A-T mutated (ATM) mutations for HTS. The assay is luciferase independent. We screened ∼34,000 compounds and identified 12 low-molecular-mass nonaminoglycosides with potential PTC-readthrough activity. From these, two leading compounds consistently induced functional ATM protein in ATM-deficient cells containing disease-causing nonsense mutations, as demonstrated by direct measurement of ATM protein, restored ATM kinase activity, and colony survival assays for cellular radiosensitivity. The two compounds also demonstrated readthrough activity in mdx mouse myotube cells carrying a nonsense mutation and induced significant amounts of dystrophin protein.

Cells were irradiated with 10 Gy and were incubated for 45 min at 37°C before fixation on coverslips. ATM pS1981 IRIFs were not observed in untreated cells; maximum intensity of staining was seen in the nuclei of cells exposed to 75 g͞ml. Nonirradiated cells, untreated or exposed to comparable concentrations of geneticin, showed only occasional foci. A taxia-telangiectasia (A-T) is an autosomal recessive neurodegenerative disorder with onset in early childhood, resulting from mutations in the A-T mutated (ATM) gene (1). The ATM protein is a hierarchical serine-threonine kinase, phosphorylating many substrates involved in repair of doublestranded DNA breaks, control of cell cycle checkpoints, and responses to oxidative stress, as well as in radiosensitivity, cancer susceptibility, immune function, and neurological development (2). ATM protein levels are undetectable in the cells of most A-T patients by conventional testing. However a few patients, often with a milder phenotype, have some detectable ATM protein (3,4). This finding encouraged us to seek compounds, such as aminoglycosides, that have the potential to read through premature termination codons and restore ATM protein function (5, 6).To test these effects, we selected 13 lymphoblastoid cell lines (LCLs) with primary premature termination codon (PTC) mutations from a repository of Ͼ400 lines derived from A-T patients. Herein, we show representative data from 5 of the 13 LCLs. Using protein truncation testing (PTT) driven by plasmid templates containing PTC mutations in the ATM gene (7), we observed in vitro read-through effects of various magnitudes with three of four aminoglycosides tested. Full-length ATM protein was also documented ex vivo by immunoprecipitation. Correction of radioresistant DNA synthesis and radiosensitivity, as well as autophosphorylation of ATM, suggested that this readthrough produces functional ATM protein. Experimental ProceduresCell Lines. Lymphoblastoid cell lines were maintained in RPMI medium 1640 (Invitrogen) with 15% FBS (HyClone) and 1% penicillin͞streptomycin (Invitrogen) at 37°C and 5% CO 2 . In ex vivo experiments, aminoglycosides were added daily into culture media at the indicated doses and times. Because streptomycin is also an aminoglycoside that can perturb proofreading by binding to another ribosomal site, ex vivo experiments were performed with or without streptomycin; no differences were noted.Mutations. We selected only PTC mutations that resulted directly from the mutation, i.e., primary PTC mutations, and not those caused indirectly by upstream mutations or aberrant splicing, because the latter would have no potential therapeutic benefits. The LCLs carried the following mutations (www.benaroyaresearch.org͞bri investigators͞atm.htm): AT185LA, homozygous 3673C 3 T (a UAA G stop codon in PTT fragment 4); TAT51, homozygous 5623C 3 T (a UGA C stop codon in PTT fragment 5); AT187LA, homozygous 5908C 3 T (a UAA G stop codon in PTT fragment 6); AT153LA, homozygous 8977C 3 T (a UGA A stop codon in fragment 8); and AT...

The enhancing rim fraction score, a quantitative DCE MR imaging lncRNA radiogenomic biomarker, is associated with early metastasis and expression of the known predictor of metastatic progression, HOTAIR.