University of Rijeka

About: University of Rijeka is a education organization based out in Rijeka, Croatia. It is known for research contribution in the topics: Population & Tourism. The organization has 3471 authors who have published 7993 publications receiving 110386 citations. The organization is also known as: Rijeka University & Sveučilište u Rijeci.

Herpesviruses induce aggregation and selective autophagy of host signalling proteins NEMO and RIPK1 as an immune-evasion mechanism

Abstract: Viruses manipulate cellular signalling by inducing the degradation of crucial signal transducers, usually via the ubiquitin-proteasome pathway. Here, we show that the murine cytomegalovirus (Murid herpesvirus 1) M45 protein induces the degradation of two cellular signalling proteins, the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) essential modulator (NEMO) and the receptor-interacting protein kinase 1 (RIPK1), via a different mechanism: it induces their sequestration as insoluble protein aggregates and subsequently facilitates their degradation by autophagy. Aggregation of target proteins requires a distinct sequence motif in M45, which we termed 'induced protein aggregation motif'. In a second step, M45 recruits the retromer component vacuolar protein sorting 26B (VPS26B) and the microtubule-associated protein light chain 3 (LC3)-interacting adaptor protein TBC1D5 to facilitate degradation of aggregates by selective autophagy. The induced protein aggregation motif is conserved in M45-homologous proteins of several human herpesviruses, including herpes simplex virus, Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, but is only partially conserved in the human cytomegalovirus UL45 protein. We further show that the HSV-1 ICP6 protein induces RIPK1 aggregation and degradation in a similar fashion to M45. These data suggest that induced protein aggregation combined with selective autophagy of aggregates (aggrephagy) represents a conserved viral immune-evasion mechanism.

Exergy analysis of marine steam turbine labyrinth (gland) seals

Abstract: The paper presents an exergy analysis of marine steam turbine labyrinth (gland) seals - an inevitable component of any marine steam turbine cylinder, in three different operating regimes. Throughout labyrinth seals, steam specific enthalpy can be considered as a constant because the results obtained by this assumption do not deviate significantly from the results of complex numerical models. Changes in labyrinth seals exergy efficiency and specific exergy destruction are reverse proportional. The analyzed labyrinth seals have high exergy efficiencies in each observed operating regime at the ambient temperature of 298 K (above 92%), what indicates seals proper operation. An increase in the ambient temperature resulted with a decrease in labyrinth seals exergy efficiency, but even at the highest observed ambient temperature of 318 K, seals exergy efficiency did not fall below 90.5% in each observed operating regime.

“Activated” STAT Proteins: A Paradoxical Consequence of Inhibited JAK-STAT Signaling in Cytomegalovirus-Infected Cells

Abstract: We have previously characterized mouse CMV (MCMV)-encoded immune-evasive IFN signaling inhibition and identified the viral protein pM27 as inducer of proteasomal degradation of STAT2. Extending our analysis to STAT1 and STAT3, we found that MCMV infection neither destabilizes STAT1 protein nor prevents STAT1 tyrosine Y701 phosphorylation, nuclear translocation, or the capability to bind γ-activated sequence DNA-enhancer elements. Unexpectedly, the analysis of STAT3 revealed an induction of STAT3 Y705 phosphorylation by MCMV. In parallel, we found decreasing STAT3 protein amounts upon MCMV infection, although STAT3 expression normally is positive autoregulative. STAT3 phosphorylation depended on the duration of MCMV infection, the infectious dose, and MCMV gene expression but was independent of IFNAR1, IL-10, IL-6, and JAK2. Although STAT3 phosphorylation did not require MCMV immediate early 1, pM27, and late gene expression, it was restricted to MCMV-infected cells and not transmitted to bystander cells. Despite intact STAT1 Y701 phosphorylation, IFN-γ-induced target gene transcription (e.g., IRF1 and suppressor of cytokine signaling [SOCS] 1) was strongly impaired. Likewise, the induction of STAT3 target genes (e.g., SOCS3) by IL-6 was also abolished, indicating that MCMV antagonizes STAT1 and STAT3 despite the occurrence of tyrosine phosphorylation. Consistent with the lack of SOCS1 induction, STAT1 phosphorylation was prolonged upon IFN-γ treatment. We conclude that the inhibition of canonical STAT1 and STAT3 target gene expression abrogates their intrinsic negative feedback loops, leading to accumulation of phospho-tyrosine-STAT3 and prolonged STAT1 phosphorylation. These findings challenge the generalization of tyrosine-phosphorylated STATs necessarily being transcriptional active and document antagonistic effects of MCMV on STAT1/3-dependent target gene expression.

Genetic Susceptibility and Caspase Activation in Mouse and Human Macrophages Are Distinct for Legionella longbeachae and L. pneumophila

Abstract: Legionella longbeachae belongs to the family Legionellaceae, which causes a severe and fatal pneumonia known as Legionnaires' disease. In the United States, more than 90% of cases of Legionnaires' disease are caused by Legionella pneumophila (6). Interestingly, the most predominant species responsible for Legionnaires' disease in Western Australia is L. longbeachae (15). In addition, infection due to L. longbeachae has been reported in New Zealand, Germany, Japan, Denmark, Sweden, Canada, and The Netherlands. Unlike L. pneumophila, which inhabits mostly aquatic environments, L. longbeachae is commonly isolated from moist potting soil (29). In aquatic environments, amoeba serves as a reservoir for the amplification and dissemination of L. pneumophila and is considered the natural host for the bacterium (34). In addition, amoeba has been shown to resuscitate viable nonculturable L. pneumophila after disinfection by biocides, which may account for the reemergence of Legionella in water systems after disinfection (24). L. pneumophila replicates in alveolar macrophages, which is necessary for the manifestation of Legionnaires' disease. After phagocytosis, L. pneumophila is localized in a unique phagosome that is isolated from the endocytic pathway (26, 41, 43). The L. pneumophila-containing phagosome excludes endocytic markers, including the lysosome-associated membrane glycoproteins lysosome-associated membrane protein 1 (LAMP-1) and LAMP-2 as well as the lysosomal acid protease cathepsin D (10). While the L. pneumophila-containing phagosome does not interact with the dynamic endocytic traffic, the L. longbeachae-containing phagosome interacts with the endocytic traffic and its biogenesis exhibits some maturation within the endocytic pathway (5). Recent studies have shown that within human macrophages, the L. longbeachae-containing phagosome is trafficked into a nonacidified late endosome-like phagosome that acquires the LAMPs and the mannose-6-phosphate receptor late endosomal markers but excludes the vacuolar ATPase proton pump and lysosomal markers (5). In addition, the L. longbeachae-containing phagosome is remodeled by the rough endoplasmic reticulum and bacterial replication occurs within the rough endoplasmic reticulum-remodeled late endosome-like phagosomes (5). Thus, there is a divergence in the mechanisms of pathogenesis of L. longbeachae and L. pneumophila in human macrophages (5). Further studies are needed to dissect further the host-parasite interaction of L. longbeachae, which is lagging behind that of most other intracellular pathogens, including the closely related species L. pneumophila. Many intracellular pathogens, including L. pneumophila, have been shown to modulate the intrinsic and extrinsic apoptotic pathways of apoptosis that converge on the activation of caspase 3, resulting in apoptosis/programmed cell death (20). L. pneumophila induces the activation of caspase 3 in human macrophages during early stages of infection, which is thought to be essential for evasion of vesicle traffic, since inhibition of caspase 3 in human macrophages results in fusion of the phagosomes to lysosomes (18, 35). The activation of caspase 3 and the subsequent isolation of the phagosome from the endocytic pathway are mediated by the Dot/Icm type IV secretion system (47). Although caspase 3 is induced robustly during early stages of infection in human macrophages, apoptosis is not triggered until late stages of infection, concomitant with the termination of intracellular replication (2, 3, 35). The delay in apoptosis is associated with the induction of antiapoptotic signaling through the activation of NF-κB-dependent and -independent pathways (3, 30). In contrast, caspase 3 is not activated and is not required for the intracellular infection of mouse-derived macrophages (36, 45). Whether L. longbeachae also triggers caspase 3 and subsequent apoptosis in human macrophages is not known. Among inbred mouse strains, A/J is the only inbred mouse strain susceptible to infection by L. pneumophila, while all the other strains are resistant (31). In contrast, many inbred strains of mice are susceptible to infection by many Legionella species (31). Only one study of permissiveness of mouse macrophages in vitro to L. longbeachae has been reported using a single isolate and indicated that the isolate replicates in both A/J and C57BL/6 thioglycolate-elicited mouse peritoneal macrophages, but whether the growth kinetics are similar to those of L. pneumophila is not known (27). Whether L. longbeachae can replicate in mouse lungs in vivo and whether mice are a suitable animal model for L. longbeachae are not known. The genetic susceptibility of mice has been attributed to a polymorphism in the neuronal apoptosis inhibitory protein 5 (naip5)-birc1e gene (13). At least eight murine homologues of naip genes have been identified (25), and naip5 has been identified as the gene responsible for the differential susceptibilities of A/J mice to L. pneumophila infection (13). The family of Naips is expressed abundantly in macrophage-rich tissues in mice, and their collective expression is increased after phagocytosis by murine macrophages (14), but whether Naip5 is one of the induced Naips is not known. The differential susceptibilities of different inbred mouse strains to infection by L. pneumophila are due to the rapid activation of caspase 1 in C57BL/6 versus A/J mice, resulting in early macrophage pyropoptosis-mediated cell death in C57BL/6 mice (36, 45). The L. pneumophila product that is responsible for the activation of caspase 1 is flagellin, but it is not known how Naip5 contributes to the process (36). Whether L. pneumophila triggers caspase 1 activation in human macrophages is not known, and whether L. longbeachae is capable of activating caspase 1 in mouse or human macrophages is also not known. Some Naips have been shown to possess antiapoptotic activity (40) due to inhibition of caspase 3, caspase 7, and caspase 9 (17). The role of Naip5 in the activation of caspase 3 and apoptosis has not been determined, although it has been shown that the differential susceptibilities of mice to L. pneumophila are not related to the activation of caspase 3 (36, 45). Here, we show that polymorphism of the naip5 allele does not play a role in the susceptibility of inbred mouse strains to infection by L. longbeachae. Both in vitro and in vivo studies show that L. longbeachae replicates efficiently in bone marrow-derived macrophages and in the lungs of A/J, C57BL/6, and BALB/c mice. In addition, we show that the induction of naip5 transcription in both L. pneumophila- and L. longbeachae-infected A/J mouse macrophages is less compared to that in C57BL/6 mice. We show that unlike what was observed with L. pneumophila, caspase 3 activation and late-stage apoptosis are triggered only at very low levels in both mouse and human macrophages infected by L. longbeachae. Flagellated L. longbeachae does not trigger caspase 1-mediated pyropoptosis in mouse macrophages, which correlates with the lack of detectable pore-forming activity in this species. Neither species activates caspase 1 in human macrophages.