Cross-Species Analysis of Innate Immune Antagonism by Cytomegalovirus IE1 Protein

The human cytomegalovirus (CMV) immediate early 1 (IE1) protein has evolved as a multifunctional antagonist of intrinsic and innate immune mechanisms. In addition, this protein serves as a transactivator and potential genome maintenance protein. Recently, the crystal structures of the human and rat CMV IE1 (hIE1, rIE1) core domain were solved. Despite low sequence identity, the respective structures display a highly similar, all alpha-helical fold with distinct variations. To elucidate which activities of IE1 are either species-specific or conserved, this study aimed at a comparative analysis of hIE1 and rIE1 functions. To facilitate the quantitative evaluation of interactions between IE1 and cellular proteins, a sensitive NanoBRET assay was established. This confirmed the species-specific interaction of IE1 with the cellular restriction factor promyelocytic leukemia protein (PML) and with the DNA replication factor flap endonuclease 1 (FEN1). To characterize the respective binding surfaces, helix exchange mutants were generated by swapping hIE1 helices with the corresponding rIE1 helices. Interestingly, while all mutants were defective for PML binding, loss of FEN1 interaction was confined to the exchange of helices 1 and 2, suggesting that FEN1 binds to the stalk region of IE1. Furthermore, our data reveal that both hIE1 and rIE1 antagonize human STAT2; however, distinct regions of the respective viral proteins mediated the interaction. Finally, while PML, FEN1, and STAT2 binding were conserved between primate and rodent proteins, we detected that rIE1 lacks a chromatin tethering function suggesting that this activity is dispensable for rat CMV. In conclusion, our study revealed conserved and distinct functions of primate and rodent IE1 proteins, further supporting the concept that IE1 proteins underwent a narrow co-evolution with their respective hosts to maximize their efficacy in antagonizing innate immune mechanisms and supporting viral replication.

Inhibitors of Activin Receptor-like Kinase 5 Interfere with SARS-CoV-2 S-Protein Processing and Spike-Mediated Cell Fusion via Attenuation of Furin Expression

Screening of a protein kinase inhibitor library identified SB431542, targeting activin receptor-like kinase 5 (ALK5), as a compound interfering with SARS-CoV-2 replication. Since ALK5 is implicated in transforming growth factor β (TGF-β) signaling and regulation of the cellular endoprotease furin, we pursued this research to clarify the role of this protein kinase for SARS-CoV-2 infection. We show that TGF-β1 induces the expression of furin in a broad spectrum of cells including Huh-7 and Calu-3 that are permissive for SARS-CoV-2. The inhibition of ALK5 by incubation with SB431542 revealed a dose-dependent downregulation of both basal and TGF-β1 induced furin expression. Furthermore, we demonstrate that the ALK5 inhibitors SB431542 and Vactosertib negatively affect the proteolytic processing of the SARS-CoV-2 Spike protein and significantly reduce spike-mediated cell-cell fusion. This correlated with an inhibitory effect of ALK5 inhibition on the production of infectious SARS-CoV-2. Altogether, our study shows that interference with ALK5 signaling attenuates SARS-CoV-2 infectivity and cell-cell spread via downregulation of furin which is most pronounced upon TGF-β stimulation. Since a TGF-β dominated cytokine storm is a hallmark of severe COVID-19, ALK5 inhibitors undergoing clinical trials might represent a potential therapy option for COVID-19.

Dual signaling via interferon and DNA damage response elicits entrapment by giant PML nuclear bodies

PML nuclear bodies (PML-NBs) are dynamic interchromosomal macromolecular complexes implicated in epigenetic regulation as well as antiviral defense. During herpesvirus infection, PML-NBs induce epigenetic silencing of viral genomes, however, this defense is antagonized by viral regulatory proteins such as IE1 of human cytomegalovirus (HCMV). Here, we show that PML-NBs undergo a drastic rearrangement into highly enlarged PML cages upon infection with IE1-deficient HCMV. Importantly, our results demonstrate that dual signaling by interferon and DNA damage response is required to elicit giant PML-NBs. DNA labeling revealed that invading HCMV genomes are entrapped inside PML-NBs and remain stably associated with PML cages in a transcriptionally repressed state. Intriguingly, by correlative light and transmission electron microscopy (EM), we observed that PML cages also entrap newly assembled viral capsids demonstrating a second defense layer in cells with incomplete first line response. Further characterization by 3D EM showed that hundreds of viral capsids are tightly packed into several layers of fibrous PML. Overall, our data indicate that giant PML-NBs arise via combined interferon and DNA damage signaling which triggers entrapment of both nucleic acids and proteinaceous components. This represents a multilayered defense strategy to act in a cytoprotective manner and to combat viral infections.

Cytomegalovirus immediate-early 1 proteins form a structurally distinct protein class with adaptations determining cross-species barriers

Restriction factors are potent antiviral proteins that constitute a first line of intracellular defense by blocking viral replication and spread. During co-evolution, however, viruses have developed antagonistic proteins to modulate or degrade the restriction factors of their host. To ensure the success of lytic replication, the herpesvirus human cytomegalovirus (HCMV) expresses the immediate-early protein IE1, which acts as an antagonist of antiviral, subnuclear structures termed PML nuclear bodies (PML-NBs). IE1 interacts directly with PML, the key protein of PML-NBs, through its core domain and disrupts the dot-like multiprotein complexes thereby abrogating the antiviral effects. Here we present the crystal structures of the human and rat cytomegalovirus core domain (IE1_CORE). We found that IE1_CORE domains, also including the previously characterized IE1_CORE of rhesus CMV, form a distinct class of proteins that are characterized by a highly similar and unique tertiary fold and quaternary assembly. This contrasts to a marked amino acid sequence diversity suggesting that strong positive selection evolved a conserved fold, while immune selection pressure may have fostered sequence divergence of IE1. At the same time, we detected specific differences in the helix arrangements of primate versus rodent IE1_CORE structures. Functional characterization revealed a conserved mechanism of PML-NB disruption, however, primate and rodent IE1 proteins were only effective in cells of the natural host species but not during cross-species infection. Remarkably, we observed that expression of HCMV IE1 allows rat cytomegalovirus replication in human cells. We conclude that cytomegaloviruses have evolved a distinct protein tertiary structure of IE1 to effectively bind and inactivate an important cellular restriction factor. Furthermore, our data show that the IE1 fold has been adapted to maximize the efficacy of PML targeting in a species-specific manner and support the concept that the PML-NBs-based intrinsic defense constitutes a barrier to cross-species transmission of HCMV.

Cytomegaloviruses have evolved in very close association with their hosts resulting in a highly species-specific replication. Cell-intrinsic proteins, known as restriction factors, constitute important barriers for cross-species infection of viruses. All cytomegaloviruses characterized so far express an abundant immediate-early protein, termed IE1, that binds to the cellular restriction factor promyelocytic leukemia protein (PML) and antagonizes its repressive activity on viral gene expression. Here, we present the crystal structures of the PML-binding domains of rat and human cytomegalovirus IE1. Despite low amino-acid sequence identity both proteins share a highly similar and unique fold forming a distinct protein class. Functional characterization revealed a common mechanism of PML antagonization. However, we also detected that the respective IE1 proteins only interact with PML proteins of the natural host species. Interestingly, expression of HCMV IE1 allows rat cytomegalovirus infection in human cells. This indicates that the cellular restriction factor PML forms an important barrier for cross-species infection of cytomegaloviruses that might be overcome by adaptation of IE1 protein function. Our data suggest that the cytomegalovirus IE1 structure represents an evolutionary optimized protein fold targeting PML proteins via coiled-coil interactions.

Functional regulation of the structure-specific endonuclease FEN1 by the human cytomegalovirus protein IE1 suggests a role for the re-initiation of stalled viral replication forks

Flap endonuclease 1 (FEN1) is a member of the family of structure-specific endonucleases implicated in regulation of DNA damage response and DNA replication. So far, knowledge on the role of FEN1 during viral infections is limited. Previous publications indicated that poxviruses encode a conserved protein that acts in a manner similar to FEN1 to stimulate homologous recombination, double-strand break (DSB) repair and full-size genome formation. Only recently, cellular FEN1 has been identified as a key component for hepatitis B virus cccDNA formation. Here, we report on a novel functional interaction between Flap endonuclease 1 (FEN1) and the human cytomegalovirus (HCMV) immediate early protein 1 (IE1). Our results provide evidence that IE1 manipulates FEN1 in an unprecedented manner: we observed that direct IE1 binding does not only enhance FEN1 protein stability but also phosphorylation at serine 187. This correlates with nucleolar exclusion of FEN1 stimulating its DSB-generating gap endonuclease activity. Depletion of FEN1 and inhibition of its enzymatic activity during HCMV infection significantly reduced nascent viral DNA synthesis demonstrating a supportive role for efficient HCMV DNA replication. Furthermore, our results indicate that FEN1 is required for the formation of DSBs during HCMV infection suggesting that IE1 acts as viral activator of FEN1 in order to re-initiate stalled replication forks. In summary, we propose a novel mechanism of viral FEN1 activation to overcome replication fork barriers at difficult-to-replicate sites in viral genomes.

Crystal structure of cytomegalovirus IE1 protein reveals targeting of TRIM family member PML via coiled-coil interactions

PML nuclear bodies (PML-NBs) are enigmatic structures of the cell nucleus that act as key mediators of intrinsic immunity against viral pathogens. PML itself is a member of the E3-ligase TRIM family of proteins that regulates a variety of innate immune signaling pathways. Consequently, viruses have evolved effector proteins to modify PML-NBs; however, little is known concerning structure-function relationships of viral antagonists. The herpesvirus human cytomegalovirus (HCMV) expresses the abundant immediate-early protein IE1 that colocalizes with PML-NBs and induces their dispersal, which correlates with the antagonization of NB-mediated intrinsic immunity. Here, we delineate the molecular basis for this antagonization by presenting the first crystal structure for the evolutionary conserved primate cytomegalovirus IE1 proteins. We show that IE1 consists of a globular core (IE1_CORE) flanked by intrinsically disordered regions. The 2.3 Å crystal structure of IE1_CORE displays an all α-helical, femur-shaped fold, which lacks overall fold similarity with known protein structures, but shares secondary structure features recently observed in the coiled-coil domain of TRIM proteins. Yeast two-hybrid and coimmunoprecipitation experiments demonstrate that IE1_CORE binds efficiently to the TRIM family member PML, and is able to induce PML deSUMOylation. Intriguingly, this results in the release of NB-associated proteins into the nucleoplasm, but not of PML itself. Importantly, we show that PML deSUMOylation by IE1_CORE is sufficient to antagonize PML-NB-instituted intrinsic immunity. Moreover, co-immunoprecipitation experiments demonstrate that IE1_CORE binds via the coiled-coil domain to PML and also interacts with TRIM5α We propose that IE1_CORE sequesters PML and possibly other TRIM family members via structural mimicry using an extended binding surface formed by the coiled-coil region. This mode of interaction might render the antagonizing activity less susceptible to mutational escape.

Research of the last few years has revealed that microbial infections are not only controlled by innate and adaptive immune mechanisms, but also by cellular restriction factors, which give cells the capacity to resist pathogens. PML nuclear bodies (PML-NBs) are dot-like nuclear structures representing multiprotein complexes that consist of the PML protein, a member of the TRIM family of proteins, as well as a multitude of additional regulatory factors. PML-NB components act as a barrier against many viral infections; however, viral antagonistic proteins have evolved to modify PML-NBs, thus abrogating this cellular defense. Here, we delineate the molecular basis for antagonization by the immediate-early protein IE1 of the herpesvirus human cytomegalovirus. We present the first crystal structure for the evolutionary conserved core domain (IE1_CORE) of primate cytomegalovirus IE1, which exhibits a novel, unusual fold. IE1_CORE modifies PML-NBs by releasing other PML-NB proteins into the nucleoplasm which is sufficient to antagonize intrinsic immunity. Importantly, IE1_CORE shares secondary structure features with the coiled-coil domain (CC) of TRIM factors, and we demonstrate strong binding of IE1 to the PML-CC. We propose that IE1_CORE sequesters PML and possibly other TRIM family members via an extended binding surface formed by the coiled-coil domain.

Efficacy of daily bedside chest radiography as visualized by digital luminescence radiography

To determine the diagnostic impact of daily bedside chest radiography in comparison with digital luminescence technique (DLR; storage phosphor radiography) and conventional film screen radiography, a prospective randomized study was completed in 210 mechanically ventilated patients with a total of 420 analysed radiographs. The patients were allocated to two groups: 150 patients underwent DLR, and 60 patients underwent conventional film screen radiography. Radiological analysis was performed consensually and therapeutic efficacy was assessed by the clinicians. There was no statistical significant difference between the frequency of abnormal findings seen on DLR and conventional film screen radiography. In total, 448 abnormal findings were present in 249 of 300 DLR and 97 of 120 conventional film screen radiographs. The most common findings were signs of overhydration (41%), pleural effusion (31%), partial collapse of the lung (11%) and pneumothorax (2%). One hundred and twenty-three of 448 (27%) of these abnormal findings were thought to have a considerable impact on patient management. The high rate of abnormal findings with significant impact on patient management suggests that the use of daily bedside chest radiography may be reasonable.

["Phtisis atra"--a now seldom disease picture as a special disease course of silicosis]

Progressive massive fibrosis (PMF) of the lung is caused by coalescence of fibrotic nodules. The center of the PMF often displays necrotic areas. If the necrosis gets in contact to the bronchial system cavitation may occur. We report on a 68 year old patient suffering from severe silicosis of the lung and metastatic spread of a histologically proven lung cancer into the brain. The patient who was administered to the hospital under the intention of cerebral radiotherapy showed a colliquative PMF in the right upper lobe with cavitation and expectoration of large amounts of black-stained sputum (melanoptysis).

[Virtual bronchoscopy in the child using multi-slice CT: initial clinical experiences]

PURPOSE

Virtual bronchoscopy of the pediatric patient has been reported to be more difficult because of artifacts due to breathing or motion. We demonstrate the benefit of the accelerated examination based on multislice spiral CT (MSCT) in the pediatric patient which has not been reported so far.

MATERIAL AND METHODS

MSCT (tube voltage 120 kV, tube current 110 mA, 4 x 1 mm Slice thickness, 500 ms rotation time, Pitch 6) was performed on a CT scanner of the latest generation (Volume Zoom, Siemens Corp. Forchheim, Germany). In totally we examined 11 patients (median age 48 months, range 2-122 months) suspected of having tracheoesophageal fistula (n = 2), tracheobronchial narrowing (n = 8) due to intrinsic or extrinsic factors or injury of the bronchial system (n = 1).

RESULTS

In all patients we obtained sufficient data for 3D reconstruction avoiding general anesthesia. 6/11 examinations were described to be without pathological finding. A definite diagnosis was obtained in 10 patients. Virtual bronchoscopy could avoid other invasive diagnostic examination in 8/11 patients (73%).

CONCLUSION

Helical CT provides 3D-reconstruction and virtual bronchoscopy in the newborn as well as the infant. It avoids additional diagnostic bronchoscopy in a high percentage of all cases.

A pilot study on the effects of exercise in patients with systemic lupus erythematosus

OBJECTIVE

A pilot study was designed to assess the efficacy and safety of different exercise therapies on patient-reported fatigue and functional status.

METHODS

Ten patients with systemic lupus erythematosus (SLE) were randomly placed in either an aerobic exercise group (group 1: n = 5) or a range of motion/muscle strengthening (ROM/MS) exercise group (group 2: n = 5). Outcome measures assessed at baseline and the end of the study were fatigue, functional status, disease activity, cardiovascular fitness, isometric strength, bone mineral density (BMD) of the lumbar spine and femoral neck, and parathyroid hormone and osteocalcin as representative bone biochemical markers for bone resorption and bone formation, respectively.

RESULTS

Both aerobic and ROM/MS types of exercise were safe and did not worsen SLE disease activity. Patients in both exercise groups showed some improvement in fatigue, functional status, cardiovascular fitness, and muscle strength. Both groups showed increased bone turnover, but BMD was unchanged. Eighty percent of the patients met the compliance standard for the study.

CONCLUSIONS

This pilot study shows the feasibility of exercise for SLE patients. The potential value of this approach shows promise in the routine management of these patients.

[Computerized tomography detection of portal vein air accumulation in severe gastroenteritis during chemotherapy]

Portal venous gas is caused by various pathological processes, both iatrogenic (complications of endoscopy) and non-iatrogenic (bowel ischemia, obstruction, perforated gastric ulcer, septicaemia). We report an immunocompromised patient suffering from metastatic cancer of the breast who developed severe gastroenteritis. Plain radiographs of the abdomen showed branching tubular lucencies that extended from the porta hepatis widely over the liver. A computed tomography performed to exclude air in the biliary tract demonstrated portal venous gas. Although the finding of portal venous gas has been associated with a high mortality rate and usually necessitates surgery, our patient survived without surgical intervention.

Measurement of impulsivity: construct coherence, longitudinal stability, and relationship with externalizing problems in middle childhood and adolescence

This study focused on the assessment of impulsivity in nonreferred school-aged children. Children had been participants since infancy in the Bloomington Longitudinal Study. Individual differences in impulsivity were assessed in the laboratory when children were 6 (44 boys, 36 girls) and 8 (50 boys, 39 girls) years of age. Impulsivity constructs derived from these assessments were related to parent and teacher ratings of externalizing problems across the school-age period (ages 7-10) and to parent and self-ratings of these outcomes across adolescence (ages 14-17). Consistent with prior research, individual measures of impulsivity factor-analyzed into subdimensions reflecting children's executive control capabilities, delay of gratification, and ability or willingness to sustain attention and compliance during work tasks. Children's performance on the main interactive task index, inhibitory control, showed a signficant level of stability between ages 6 and 8. During the school-age years, children who performed impulsively on the laboratory measures were perceived by mothers and by teachers as more impulsive, inattentive, and overactive than others, affirming the external validity of the impulsivity constructs. Finally, impulsive behavior in the laboratory at ages 6 and 8 predicted maternal and self-ratings of externalizing problem behavior across adolescence, supporting the long-term predictive value of the laboratory-derived impulsivity measures.

CTF-guided puncture of an unenhanced isodense liver lesion during continuous intravenous injection of contrast medium

CT fluoroscopy (CTF) facilitates guidance of percutaneous biopsies and other interventional procedures. We wished to demonstrate the usefulness of CTF for the puncture of an unenhanced isodense liver lesion during continuous injection of intravenous contrast medium. We performed CTF-guided puncture of a 2-cm lesion in the liver of a patient suffering from lung cancer. CTF enables puncture of liver foci even if they are unenhanced and isodense with the surrounding parenchyma.

First experiences in percutaneous arterial chemoembolization of malignant liver lesions by means of real-time CT fluoroscopy

Computed tomography fluoroscopy (CTF) allows real-time display (continuous imaging) and has been increasingly used in interventional procedures. We wished to demonstrate the usefulness of CTF in chemoembolization of the liver. Twenty-one patients with primary or secondary malignant lesions of the liver underwent CTF-guided chemoembolization after angiographic positioning of a catheter in the hepatic artery. Embolization materials such as Lipiodol and mitomycin C were administered under continuous CT scanning. CTF led to a change of the method (correction of catheter position, application of norepinephrine) in nine of 21 cases. There were no fatal complications.

[Rothmund-Thomson syndrome and osteosarcoma]

Until now less than 200 cases of Rothmund Thomson syndrome (RTS) also called Poikiloderma atrophicans have been reported. RTS is an autosomal recessive dermatosis characterized by athropy and teleangiectasia of the skin, juvenile cataract, hypogonadism and sceletal abnormalities. These osseous disorders include cortical hyperostosis mimicking rickets or chondrodysthropy and may mask early signs of malignant disorders. This seems to be a problem due to the fact that there is an association between osteosarcoma and RTS. The radiologic findings of both RTS and osteosarcoma in a 7 year old female are discussed.

Retroviral risk factors in patients with autoimmune disease

OBJECTIVE

Retroviruses can cause immunoregulatory disturbances and may play a role in the pathogenesis of autoimmune disorders. Little is known about the frequency of behavioral risk factors for exogenous retroviral infections in patients with autoimmune diseases. We compare the frequency of recognized risk factors for retroviral infections among patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and controls.

METHODS

Patients with SLE and RA from a university rheumatology clinic and control patients were enrolled in this study. The presence of retroviral risk factors (intravenous drug use, prostitution, increased number of sex partners, sexually transmitted diseases, high risk sex partners, blood transfusion) was determined by a self-administered questionnaire.

RESULTS

We surveyed 81 patients with SLE and 117 with RA and 100 healthy controls. Patients in all groups reported similar exposure to all risk factors surveyed for retroviral infection except sexually transmitted disease, which was reported more often in patients with SLE (25% of SLE versus 11% of RA and 11% of controls, p = 0.013).

CONCLUSION

Self-reported retroviral risk factors were generally not increased in patients with autoimmune disease compared to healthy controls; the role of exogenous retroviruses in the pathogenesis of SLE and RA remains unclear.