ATM induces MacroD2 nuclear export upon DNA damage

ADP-ribosylation is a dynamic post-translation modification that regulates the early phase of various DNA repair pathways by recruiting repair factors to chromatin. ADP-ribosylation levels are defined by the activities of specific transferases and hydrolases. However, except for the transferase PARP1/ARDT1 little is known about regulation of these enzymes. We found that MacroD2, a mono-ADP-ribosylhydrolase, is exported from the nucleus upon DNA damage, and that this nuclear export is induced by ATM activity. We show that the export is dependent on the phosphorylation of two SQ/TQ motifs, suggesting a novel direct interaction between ATM and ADP-ribosylation. Lastly, we show that MacroD2 nuclear export temporally restricts its recruitment to DNA lesions, which may decrease the net ADP-ribosylhydrolase activity at the site of DNA damage. Together, our results identify a novel feedback regulation between two crucial DNA damage-induced signaling pathways: ADP-ribosylation and ATM activation.

Poly-ADP-ribosylation signaling during DNA damage repair

Poly-ADP-ribosylation is a post-translational modification generated in high amounts by poly-ADP-ribose polymerases (PARPs) in response to cellular stress, especially genotoxic stimuli. DNA damage-induced PARylation significantly changes local chromatin structure and triggers the accumulation of several DNA damage response (DDR) proteins at the DNA lesions. In this review, we will discuss the regulation of chromatin structure and DNA damage repair machineries by DNA damage-induced poly-ADP-ribosylation.

Deficiency of terminal ADP-ribose protein glycohydrolase TARG1/C6orf130 in neurodegenerative disease

Adenosine diphosphate (ADP)-ribosylation is a post-translational protein modification implicated in the regulation of a range of cellular processes. A family of proteins that catalyse ADP-ribosylation reactions are the poly(ADP-ribose) (PAR) polymerases (PARPs). PARPs covalently attach an ADP-ribose nucleotide to target proteins and some PARP family members can subsequently add additional ADP-ribose units to generate a PAR chain. The hydrolysis of PAR chains is catalysed by PAR glycohydrolase (PARG). PARG is unable to cleave the mono(ADP-ribose) unit directly linked to the protein and although the enzymatic activity that catalyses this reaction has been detected in mammalian cell extracts, the protein(s) responsible remain unknown. Here, we report the homozygous mutation of the c6orf130 gene in patients with severe neurodegeneration, and identify C6orf130 as a PARP-interacting protein that removes mono(ADP-ribosyl)ation on glutamate amino acid residues in PARP-modified proteins. X-ray structures and biochemical analysis of C6orf130 suggest a mechanism of catalytic reversal involving a transient C6orf130 lysyl-(ADP-ribose) intermediate. Furthermore, depletion of C6orf130 protein in cells leads to proliferation and DNA repair defects. Collectively, our data suggest that C6orf130 enzymatic activity has a role in the turnover and recycling of protein ADP-ribosylation, and we have implicated the importance of this protein in supporting normal cellular function in humans.

[Electrocardiographic findings in a school-age population using a computerized system: calculation of standard norms for heart rate and PR, QRS, and QT intervals]

We evaluated some ECG parameters (HR, P-R, Q-R-S, Q-T) in a healthy school-age population. One-thousand-eight-hundred and ninety children ranging in age from 5 to 12 coming from different zones of the city of Naples were studied. On physical examination all subjects were free from cardiac disease. A computerized ECG (Muse 12SL System Marquette) was performed on every subject. One-hundred and seventy-four of the 1890 children were excluded from statistical analysis because of ectopic rhythm (junctional rhythm or wandering pacemaker) or poor quality of the recording. Of the 1716 children included in the study, 837 were male and 879 were female. The computerized ECG 12SL System Marquette registers an ECG record consisting of all 12 classical ECG leads acquired simultaneously over a 10 second period. Each individual complex can be analyzed in all leads by the computer. An interpretation using this extended record, along with an ECG record of conventional length, is presented to the physician for review. The first step in computerized ECG analysis is Q-R-S identification, then P wave identification, beat classification, rhythm analysis, morphology analysis, complex alignment and computation of median complex. All parameters were divided for sex and age and gathered into tables. The variability of P-R, Q-R-S, Q-T versus HR were also evaluated. The following conclusions were drawn: 1) Sex is a very important variable in the parameters examined. Males have a much slower HR, greater Q-R-S duration, and longer Q-T interval when compared to females. 2) As age increases, HR slowly decreases, while P-R, Q-R-S and Q-T intervals increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-invasive electrophysiological evaluation of calcium antagonist long-term therapy

The evaluated effects of oral administration of verapamil, diltiazem, and nifedipine in patients with first degree A-V block by using a new noninvasive technique: signal averaged ECG. The study group consists of 5 females and 3 males ranging from 52 to 70 years old. All patients showed a first degree A-V block at surface ECG and an abnormal A-V time (suprahisian lengthening) during signal averaged ECG (SAECG). Verapamil 240 mg/daily, diltiazem 180 mg/day and nifedipine 30 mg/day were given separately for a week followed by a wash out period of 5 days before giving next drugs. An ECG and SAECG were performed before and after every administration. PR, A-H and H-V interval were evaluated in every recording. Verapamil and diltiazem induced a significant lengthening of A-V conduction (PR increase was 15.4% and 15.1%, respectively). No significant modification appeared after nifedipine. Our data, using a noninvasive technique, agreed with values of previous invasive evaluations. We suggest precaution in using verapamil and diltiazem in patients with BAV 1 degree and advise a selective use of calcium antagonist therapy.

Amiodarone treatment in cardiac preexcitation syndrome: use of signal averaged electrocardiogram

Amiodarone effectiveness to prevent reentrant arrhythmia in Wolff-Parkinson-White (WPW) syndrome is well known. Authors tried to evaluate the results of long-term therapy in a group of 11 patients (mean age 39 +/- years) suffering from WPW syndrome. Before amiodarone treatment, a conventional ECG and a high resolution ECG (a new noninvasive technique) were performed in order to define Hisian activity. After 50 days of therapy (600 mg daily for the first week, 400 mg daily for the second week, 200 mg daily for 5 days in the following period), a second recording revealed the evidence a a lengthening of PR segment (p less than 0.05) and a disappearance of delta wave (1 patient) and arrhythmia. Before treatment, His deflection was defined only in 2 patients. After amiodarone therapy the H-V time was clearly evaluated in 9 patients. Probably the drug has induced a lengthening of AV node refractoriness and primarily an increase of accessory pathway refractoriness.

[Ventricular tachycardia]

Various electrocardiographic forms of ventricular tachycardia are described. After a discussion of the different pathogenetic mechanisms about this arrhythmia, the various types of pharmacological and electrical treatment are examined.