Unveiling the Multifaceted Roles of ISG15: From Immunomodulation to Therapeutic Frontiers

The Interferon Stimulated Gene 15 (ISG15), a unique Ubiquitin-like (Ubl) modifier exclusive to vertebrates, plays a crucial role in the immune system. Primarily induced by interferon (IFN) type I, ISG15 functions through diverse mechanisms: (i) covalent protein modification (ISGylation); (ii) non-covalent intracellular action; and (iii) exerting extracellular cytokine activity. These various roles highlight its versatility in influencing numerous cellular pathways, encompassing DNA damage response, autophagy, antiviral response, and cancer-related processes, among others. The well-established antiviral effects of ISGylation contrast with its intriguing dual role in cancer, exhibiting both suppressive and promoting effects depending on the tumour type. The multifaceted functions of ISG15 extend beyond intracellular processes to extracellular cytokine signalling, influencing immune response, chemotaxis, and anti-tumour effects. Moreover, ISG15 emerges as a promising adjuvant in vaccine development, enhancing immune responses against viral antigens and demonstrating efficacy in cancer models. As a therapeutic target in cancer treatment, ISG15 exhibits a double-edged nature, promoting or suppressing oncogenesis depending on the tumour context. This review aims to contribute to future studies exploring the role of ISG15 in immune modulation and cancer therapy, potentially paving the way for the development of novel therapeutic interventions, vaccine development, and precision medicine.

ISG15 Is Required for the Dissemination of Vaccinia Virus Extracellular Virions

Viruses have developed many different strategies to counteract immune responses, and Vaccinia virus (VACV) is one of a kind in this aspect. To ensure an efficient infection, VACV undergoes a complex morphogenetic process resulting in the production of two types of infective virions: intracellular mature virus (MV) and extracellular enveloped virus (EV), whose spread depends on different dissemination mechanisms. MVs disseminate after cell lysis, whereas EVs are released or propelled in actin tails from living cells. Here, we show that ISG15 participates in the control of VACV dissemination. Infection of Isg15-/- mouse embryonic fibroblasts with VACV International Health Department-J (IHD-J) strain resulted in decreased EV production, concomitant with reduced induction of actin tails and the abolition of comet-shaped plaque formation, compared to Isg15+/+ cells. Transmission electron microscopy revealed the accumulation of intracellular virus particles and a decrease in extracellular virus particles in the absence of interferon-stimulated gene 15 (ISG15), a finding consistent with altered virus egress. Immunoblot and quantitative proteomic analysis of sucrose gradient-purified virions from both genotypes reported differences in protein levels and composition of viral proteins present on virions, suggesting an ISG15-mediated control of viral proteome. Lastly, the generation of a recombinant IHD-J expressing V5-tagged ISG15 (IHD-J-ISG15) allowed us to identify several viral proteins as potential ISG15 targets, highlighting the proteins A34 and A36, which are essential for EV formation. Altogether, our results indicate that ISG15 is an important host factor in the regulation of VACV dissemination. IMPORTANCE Viral infections are a constant battle between the virus and the host. While the host's only goal is victory, the main purpose of the virus is to spread and conquer new territories at the expense of the host's resources. Along millions of years of incessant encounters, poxviruses have developed a unique strategy consisting in the production two specialized "troops": intracellular mature virions (MVs) and extracellular virions (EVs). MVs mediate transmission between hosts, and EVs ensure advance on the battlefield mediating the long-range dissemination. The mechanism by which the virus "decides" to shed from the primary site of infection and its significant impact in viral transmission is not yet fully established. Here, we demonstrate that this process is finely regulated by ISG15/ISGylation, an interferon-induced ubiquitin-like protein with broad antiviral activity. Studying the mechanism that viruses use during infection could result in new ways of understanding our perpetual war against disease and how we might win the next great battle.

Development of colorimetric sensors based on gold nanoparticles for SARS-CoV-2 RdRp, E and S genes detection

We present a fast, reliable and easy to scale-up colorimetric sensor based on gold nanoparticles (AuNPs) to detect the sequences coding for the RdRp, E, and S proteins of SARS-CoV-2. The optimization of the system (so-called “the sensor”) includes the evaluation of different sizes of nanoparticles, sequences of oligonucleotides and buffers. It is stable for months without any noticeable decrease in its activity, allowing the detection of SARS-CoV-2 sequences by the naked eye in 15 min. The efficiency and selectivity of detection, in terms of significative colorimetric changes in the solution upon target recognition, are qualitatively (visually) and quantitatively (absorbance measurements) assessed using synthetic samples and samples derived from infected cells and patients. Furthermore, an easy and affordable amplification approach is implemented to increase the system's sensitivity for detecting high and medium viral loads (≥10³ - 10⁴ viral RNA copies/μl) in patient samples. The whole process (amplification and detection) takes 2.5 h. Due to the ease of use, stability and minimum equipment requirements, the proposed approach can be a valuable tool for the detection of SARS-CoV-2 at facilities with limited resources.

Amplification-free detection of SARS-CoV-2 using gold nanotriangles functionalized with oligonucleotides

Gold nanotriangles (AuNTs) functionalized with dithiolated oligonucleotides have been employed to develop an amplification-free electrochemical biosensor for SARS-CoV-2 in patient samples. Gold nanotriangles, prepared through a seed-mediated growth method and exhaustively characterized by different techniques, serve as an improved electrochemical platform and for DNA probe immobilization. Azure A is used as an electrochemical indicator of the hybridization event. The biosensor detects either single stranded DNA or RNA sequences of SARS-CoV-2 of different lengths, with a low detection limit of 22.2 fM. In addition, it allows to detect point mutations in SARS-CoV-2 genome with the aim to detect more infective SARS-CoV-2 variants such as Alpha, Beta, Gamma, Delta, and Omicron. Results obtained with the biosensor in nasopharyngeal swab samples from COVID-19 patients show the possibility to clearly discriminate between non-infected and infected patient samples as well as patient samples with different viral load. Furthermore, the results correlate well with those obtained by the gold standard technique RT-qPCR, with the advantage of avoiding the amplification process and the need of sophisticated equipment.

The structure of native influenza virion ribonucleoproteins

The influenza viruses cause annual epidemics of respiratory disease and occasional pandemics, which constitute a major public-health issue. The segmented negative-stranded RNAs are associated with the polymerase complex and nucleoprotein (NP), forming ribonucleoproteins (RNPs), which are responsible for virus transcription and replication. We describe the structure of native RNPs derived from virions. They show a double-helical conformation in which two NP strands of opposite polarity are associated with each other along the helix. Both strands are connected by a short loop at one end of the particle and interact with the polymerase complex at the other end. This structure will be relevant for unraveling the mechanisms of nuclear import of parental virus RNPs, their transcription and replication, and the encapsidation of progeny RNPs into virions.

Genetic trans-complementation establishes a new model for influenza virus RNA transcription and replication

The influenza A viruses genome comprises eight single-stranded RNA segments of negative polarity. Each one is included in a ribonucleoprotein particle (vRNP) containing the polymerase complex and a number of nucleoprotein (NP) monomers. Viral RNA replication proceeds by formation of a complementary RNP of positive polarity (cRNP) that serves as intermediate to generate many progeny vRNPs. Transcription initiation takes place by a cap-snatching mechanism whereby the polymerase steals a cellular capped oligonucleotide and uses it as primer to copy the vRNP template. Transcription termination occurs prematurely at the polyadenylation signal, which the polymerase copies repeatedly to generate a 3′-terminal polyA. Here we studied the mechanisms of the viral RNA replication and transcription. We used efficient systems for recombinant RNP transcription/replication in vivo and well-defined polymerase mutants deficient in either RNA replication or transcription to address the roles of the polymerase complex present in the template RNP and newly synthesised polymerase complexes during replication and transcription. The results of trans-complementation experiments showed that soluble polymerase complexes can synthesise progeny RNA in trans and become incorporated into progeny vRNPs, but only transcription in cis could be detected. These results are compatible with a new model for virus RNA replication, whereby a template RNP would be replicated in trans by a soluble polymerase complex and a polymerase complex distinct from the replicative enzyme would direct the encapsidation of progeny vRNA. In contrast, transcription of the vRNP would occur in cis and the resident polymerase complex would be responsible for mRNA synthesis and polyadenylation.

The influenza A viruses produce annual epidemics and occasional pandemics of respiratory disease. There is great concern about a potential new pandemic being caused by presently circulating avian influenza viruses, and hence increasing interest in understanding how the virus replicates its genome. This comprises eight molecules of RNA, each one bound to a polymerase complex and encapsidated by multiple copies of the nucleoprotein, in the form of ribonucleoprotein complexes (RNPs). These structures are responsible for virus RNA replication and transcription but the detailed mechanisms of these processes are not fully understood. We report here the results of genetic complementation experiments using proficient in vitro and in vivo recombinant systems for transcription and replication, and polymerase point mutants that are either transcription-defective or replication-defective. These results are compatible with a new model for virus replication whereby a polymerase distinct from that present in the parental RNP is responsible for RNA replication in trans and the progeny RNP is associated to a polymerase distinct from that performing replication. In contrast, transcription is carried out in cis by the polymerase resident in the RNP.

The structural basis for cap binding by influenza virus polymerase subunit PB2

Influenza virus mRNAs are synthesized by the trimeric viral polymerase using short capped primers obtained by a 'cap-snatching' mechanism. The polymerase PB2 subunit binds the 5' cap of host pre-mRNAs, which are cleaved after 10-13 nucleotides by the PB1 subunit. Using a library-screening method, we identified an independently folded domain of PB2 that has specific cap binding activity. The X-ray structure of the domain with bound cap analog m(7)GTP at 2.3-A resolution reveals a previously unknown fold and a mode of ligand binding that is similar to, but distinct from, other cap binding proteins. Binding and functional studies with point mutants confirm that the identified site is essential for cap binding in vitro and cap-dependent transcription in vivo by the trimeric polymerase complex. These findings clarify the nature of the cap binding site in PB2 and will allow efficient structure-based design of new anti-influenza compounds inhibiting viral transcription.

[Brain haemodynamics in obstructive sleep apnea syndrome]

The obstructive sleep apnea syndrome (OSAS) is associated to a increased risk of cardiovascular diseases, including stroke. However, it is not known the cause of this last association. In this work the authors carry out a brief review of the theories that explain the relationship between OSAS and stroke and comment the potential alterations in cerebral hemodynamics of sleep apnea syndrome patients. The results of a recent case control study show that there are relevant differences in cerebral blood flow between OSAS patients and healthy subjects even in wakefulness. This fact could help to explain why OSAS causes a higher risk for suffering ischaemic strokes.

Sicca syndrome and silicoproteinosis in a dental technician

Secondary sicca syndrome has been described in silicotic and exposed nonpneumoconiotic individuals. Systemic autoimmune pathogenic mechanisms have been thought to be responsible. Salivary gland mineral deposition has not so far been implicated. We describe the case of a dental technician who sand-blasted dental prostheses and developed silicoproteinosis and sicca syndrome. Immunological studies were negative. Scanning electron microscopy study and energy-dispersive X-ray analysis were carried out in the patient's lung and salivary gland and in two salivary glands from nonexposed individuals diagnosed with sicca syndrome. High peaks of silicon and aluminium were detected in the patient's lung and salivary gland. Silicon/sulphur and aluminium/sulphur ratios were higher in the patient's glands (0.612 and 0.402, respectively) than in the two control salivary glands (0.193 and 0 and 0.127 and 0, respectively). We suggest that, in this case, sicca syndrome could have been caused by inorganic deposition.

Sicca syndrome and silicoproteinosis in a dental technician

Secondary sicca syndrome has been described in silicotic and exposed nonpneumoconiotic individuals. Systemic autoimmune pathogenic mechanisms have been thought to be responsible. Salivary gland mineral deposition has not so far been implicated. We describe the case of a dental technician who sand-blasted dental prostheses and developed silicoproteinosis and sicca syndrome. Immunological studies were negative. Scanning electron microscopy study and energy-dispersive X-ray analysis were carried out in the patient's lung and salivary gland and in two salivary glands from nonexposed individuals diagnosed with sicca syndrome. High peaks of silicon and aluminium were detected in the patient's lung and salivary gland. Silicon/sulphur and aluminium/sulphur ratios were higher in the patient's glands (0.612 and 0.402, respectively) than in the two control salivary glands (0.193 and 0 and 0.127 and 0, respectively). We suggest that, in this case, sicca syndrome could have been caused by inorganic deposition.

[Paroxysmal melanoptysis secondary to the cavitation of pulmonary pneumoconiosis conglomerate]

Progressive massive fibrosis (PMF) secondary to pneumoconiosis involves the formation of fibrotic masses that eventually cause death from multiple complications. We present a rare but potentially serious complication in a patient with coal pneumoconiosis with PMF, in whom the appearance of paroxysmal melanoptysis was attributed to the cavitation of one of the pneumoconiotic masses. We emphasize the need for differential diagnosis to exclude other more common causes, as well as the use of bronchoscopy for diagnosis and confirmation. Strict control is needed to prevent possible respiratory failure when melanoptysis is massive.

[Experience of a single center in liver transplantation in adults and children]

Orthotopic liver transplantation (THO) is the treatment of choice for a variety of liver diseases. The national experience before 1993 has been scarce. In November 1993 we started our experience in THO at Clínica Las Condes, as part of a multiorgan transplant program (liver, kidney, pancreas). Until January 1995 we have performed 14 THO in 13 recipients (one retransplantation), of which 5 were in pediatric cases. The recipients range of age fluctuated between 1 and 61 years. In two pediatric cases a liver allograft reduction was performed. Six recipients (46%) required treatment for acute cellular rejection. One recipient had an hepatic artery thrombosis and had to be retransplanted. There was no operative mortality up to 30 days in cases of primary liver transplants. The retransplanted adult recipient, and another pediatric recipient that died from a late recurrence of a hepatoblastoma, accounted for the mortality of this experience. After an average follow up of 10 months, the actual patient survival in 85%. Of the 11 surviving recipients, 9 are in excellent conditions with a very good quality of life. This experience shows that an active liver transplant program in our country can be successful in obtaining results comparable to those published by very experienced foreign transplant centers.

[The prevalence of tuberculous infection in the 6- to 7-year-old schoolchild population in Albacete]

To analyze the prevalence of tuberculosis infection, tuberculin tests were given to 3,292 elementary school children in the first and second grades in the environs of Albacete (Spain) in 1992. There were 1,532 children aged 6 (122 vaccinated with BCG) and 1,760 children aged 7 (162 vaccinated); 51 children tested positive (20 who had been vaccinated and 31 who had not been). The prevalence of infection was 0.78% at 6 years of age and 1.25 at 7 years of age in non vaccinated children, a rate similar to that found by earlier national surveys. One case of active pulmonary tuberculosis was identified. Inclusion of the 8.6% who had been vaccinated caused significant distortion of the initial prevalences. The annual rate of infection, estimated based on an annual decline of 4%, was 0.143 %. Differences in tuberculosis infection by family socioeconomic level, as indicted by level of parental studies or place of residence, were not statistically significant, although we did observe a slightly greater rate among children living in poorer areas and with parents with only elementary school education. Our results confirm a downward trend in the prevalence of tuberculosis infection in the population studied, as well as the importance of carrying out this type of survey to provide a reference for active control and for taking an active stand.

[Pneumonitis secondary to the inhalation of isocyanates. An analysis of 2 cases]

We present two patients with diffuse interstitial lung disease attributed to two different forms of presentation of pneumonitis due to inhalation of isocyanates. The first case was acute and accidental and the second was due to longer workplace exposure. In both cases, clinical, radiological and lung function findings as well as results of bronchoalveolar lavage were similar to those of hypersensitivity pneumonitis triggered by organic agents.

[Acute non-cardiogenic pulmonary edema secondary to upper airway obstruction. Clinical case]

Noncardiogenic pulmonary edema is a well recognized complication of upper airway obstruction. We report the case of a previously healthy 18-year-old male who presented this complication following laryngospasm after anesthesia. He developed severe pulmonary edema with hypoxemia, high cardiac output and low pulmonary capillary pressures. He was managed with mechanical ventilation and PEEP. Pulmonary edema resolved within 24 hours. The clinical picture, etiology, differential diagnosis and prevention are also discussed.