Background-Common causative agents in the development of inflammatory cardiomyopathy include cardiotropic viruses such as coxsackievirus B3 (CVB3). Here, we investigated the role of the ubiquitin-like modifier interferon-stimulated gene of 15 kDa (ISG15) in the pathogenesis of viral cardiomyopathy. Methods and Results-In CVB3-infected mice, the absence of protein modification with ISG15 was accompanied by a profound exacerbation of myocarditis and by a significant increase in mortality and heart failure. We found that ISG15 in cardiomyocytes contributed significantly to the suppression of viral replication. In the absence of an intact ISG15 system, virus titers were markedly elevated by postinfection day 8, and viral RNA persisted in ISG15 −/− mice at postinfection day 28. Ablation of the ISG15 protein modification system in CVB3 infection predisposed mice to long-term disease with deposition of collagen fibers, all leading to inflammatory cardiomyopathy. We found that ISG15 acts as part of the intrinsic immunity in cardiomyocytes and detected no significant effects of ISG15 modification on the cellular immune response. ISG15 modification of CVB3 2A protease counterbalanced CVB3-induced cleavage of the host cell eukaryotic initiation factor of translation eIF4G in cardiomyocytes, thereby counterbalancing the shutoff of host cell translation in CVB3 infection. We demonstrate that ISG15 suppressed infectious virus yield in human cardiac myocytes and the induction of ISG15 in patients with viral cardiomyopathy. Conclusions-The ISG15 conjugation system represents a critical innate response mechanism in cardiomyocytes to fight the battle against invading pathogens, limiting inflammatory cardiomyopathy, heart failure, and death. Interference with the ISG15 system might be a novel therapeutic approach in viral cardiomyopathy. response. Type I IFNs contribute to the suppression of viral titers and thereby ameliorate invasion of immune cells into the heart, contributing to improved survival in CVB3 infection. [6][7][8] Type I IFN-dependent processes resulted in improved cardiac function during viral cardiomyopathy 7,9 and ensured long-term survival in CVB3-positive dilated cardiomyopathy patients. 10Binding of type I IFNs to their cognate receptors results in the induction of IFN-stimulated gene of 15 kDa (ISG15), a small ubiquitin family protein consisting of 2 ubiquitinlike folds.11 ISG15 is involved in the struggle against pathogens.12-16 ISG15 modification, the process by which ISG15 is covalently attached to lysine residues of target proteins, is mediated through the sequential action of a type I IFN-induced E1-E2-E3 enzymatic cascade, 17 involving the E1-activating enzyme Ube1L, 18 E2-conjugating enzyme Ube2L6, 19 and E3 ligases Herc5 and Herc6 20 in humans and mice, respectively. The isopeptidase USP18 specifically removes ISG15 from ISG15-modified substrates. 21Pursuing the aim to define host determinants that influence the pathogenesis of viral cardiomyopathy, we provide the first evidence for the impact of the ...

Human SNM1B/Apollo is involved in the cellular response to DNA-damage, however, its precise role is unknown. Recent reports have implicated hSNM1B in the protection of telomeres. We have found hSNM1B to interact with TRF2, a protein which functions in telomere protection and in an early response to ionizing radiation. Here we show that endogenous hSNM1B forms foci which colocalize at telomeres with TRF1 and TRF2. However, we observed that additional hSNM1B foci could be induced upon exposure to ionizing radiation (IR). In live-cell-imaging experiments, hSNM1B localized to photoinduced double-strand breaks (DSBs) within 10s post-induction. Further supporting a role for hSNM1B in the early stages of the cellular response to DSBs, we observed that autophosphorylation of ATM, as well as the phosphorylation of ATM target proteins in response to IR, was attenuated in cells depleted of hSNM1B. These observations suggest an important role for hSNM1B in the response to IR damage, a role that may be, in part, upstream of the central player in maintenance of genome integrity, ATM.