Status and trends of RGS16 based on data visualization analysis: A review

G-protein signaling regulator 16 (RGS16) has been confirmed that RGS16 is associated with cancer, neurodegenerative diseases, and cardiovascular diseases. Moreover, many studies have shown that RGS16 can be used as a biomarker for cancer diagnosis and prognosis. We used CiteSpace and VOS viewer software to perform a bibliometric analysis of 290 publications in the core collection of Web of Science. All the articles come from 399 institutions, including 618 authors, 179 journals, 40 countries, 115 keywords, 1 language, two types of papers, and reviews. The United States has the largest number of publications. The Research Center of Allergy and Infectious Diseases (NIAID) publishes the most papers, Emory University is the most recent of all institutions with the most recent results in the RGS16 study. Cell biology is the most studied discipline, and the most studied topic is migration. Drury published RGS16-related articles with the most citations (n = 15), and Berman published articles with the most citations (n = 106). The biological applications of RGS16 are currently a hot area of RGS16 research, including inflammation, cancer, ulcerative colitis, metabolic acidosis, platelet activation, and thrombosis. The current scientometrics study provides an overview of RGS16 research from 1995 to 2022. This study provides an overview of current and potential future research hotspots in the field of RGS16 and can be used as a resource for interested researchers.

Phosphorylation of RGS16 at Tyr168 promote HBeAg-mediated macrophage activation by ERK pathway to accelerate liver injury

Liver injury is closely associated with macrophage activation following HBV infection. Our previous study showed that only HBeAg, but not HBsAg and HBcAg, stably enhances inflammatory cytokine production in macrophages. And we also indicated that HBeAg could induce macrophage activation via TLR2 and thus aggravate the progression of liver fibrosis. However, the specific molecular mechanism of HBeAg in macrophage activation is not clear. We screened significantly overexpressed RGS16 from RNASeq results of HBeAg-stimulated macrophages and validated them with cellular assays, GSE83148 microarray dataset, and in clinical samples. Meanwhile, small interference, plasmid, and lentivirus transfection assays were used to establish cell models for knockdown and overexpression of RGS16, and q-PCR, ELISA, Transwell, and CCK-8 assays were used to analyze the role of RGS16 in HBeAg-induced macrophage activation. In addition, the upstream and downstream mechanisms of RGS16 in HBeAg-treated macrophage activation were explored using inhibitors, phostag gels, and RGS16 phosphorylation mutant plasmids. Finally, the effect of RGS16 on hepatic inflammation in murine tissues was evaluated by H&E staining, liver enzyme assay and immunofluorescence. RGS16 was significantly upregulated in HBeAg-induced macrophage activation, and its expression was enhanced with increasing HBeAg content and treatment time. Functional experiments showed that overexpression of RGS16 promoted the production of inflammatory factors TNF-α and IL-6 and boosted macrophage proliferation and migration, while knockdown of RGS16 exhibited the opposite effect. Mechanistically, we discovered that RGS16 is regulated by the TLR2/P38/STAT5 signaling pathway. Meanwhile, RGS16 enhanced ERK phosphorylation via its own Tyr168 phosphorylation to contribute to macrophage activation, thereby accelerating liver injury. Finally, in mice, overexpression of RGS16 markedly strengthened liver inflammation. HBeAg upregulates RGS16 expression through the TLR2-P38-STAT5 axis, and the upregulated expression of RGS16 enhances macrophage activation and accelerates liver injury by promoting ERK phosphorylation. In this process, phosphorylation of Tyr168 is necessary for RGS16 to function. KEY MESSAGES: RGS16 boosted HBeAg-induced macrophage inflammation, proliferation, and migration. Tyr168 phosphorylation of RGS16 affected by ERK promoted macrophage activation. HBeAg upregulated the expression of RGS16 through TLR2/P38/STAT5 signal pathway. RGS16 promoted liver injury by regulating macrophage functions in mouse model.

Interaction between host cell proteins and open reading frames of porcine circovirus type 2

Postweaning multisystemic wasting syndrome (PMWS) is caused by a systemic inflammation after porcine circovirus type 2 (PCV2) infection. It was one of the most economically important pathogens affecting pig production worldwide before PCV2 vaccine was first introduced in 2006. After the development of a vaccine against PCV2a type, pig farms gradually restored enormous economic losses from PMWS. However, vaccine against PCV2a type could not be fully effective against several different PCV2 genotypes (PCV2b - PCV2h). In addition, PCV2a vaccine itself could generate antigenic drift of PCV2 capsid. Therefore, PCV2 infection still threats pig industry worldwide. PCV2 infection was initially found in local tissues including reproductive, respiratory, and digestive tracks. However, PCV2 infection often leads to a systemic inflammation which can cause severe immunosuppression by depleting peripheral lymphocytes in secondary lymphoid tissues. Subsequently, a secondary infection with other microorganisms can cause PMWS. Eleven putative open reading frames (ORFs) have been predicted to encode PCV2 genome. Among them, gene products of six ORFs from ORF1 to ORF6 have been identified and characterized to estimate its functional role during PCV2 infection. Acquiring knowledge about the specific interaction between each PCV2 ORF protein and host protein might be a key to develop preventive or therapeutic tools to control PCV2 infection. In this article, we reviewed current understanding of how each ORF of PCV2 manipulates host cell signaling related to immune suppression caused by PCV2.

Functions of regulators of G protein signaling 16 in immunity, inflammation, and other diseases

Regulators of G protein signaling (RGS) act as guanosine triphosphatase activating proteins to accelerate guanosine triphosphate hydrolysis of the G protein α subunit, leading to the termination of the G protein-coupled receptor (GPCR) downstream signaling pathway. RGS16, which is expressed in a number of cells and tissues, belongs to one of the small B/R4 subfamilies of RGS proteins and consists of a conserved RGS structural domain with short, disordered amino- and carboxy-terminal extensions and an α-helix that classically binds and de-activates heterotrimeric G proteins. However, with the deepening of research, it has been revealed that RGS16 protein not only regulates the classical GPCR pathway, but also affects immune, inflammatory, tumor and metabolic processes through other signaling pathways including the mitogen-activated protein kinase, phosphoinositide 3-kinase/protein kinase B, Ras homolog family member A and stromal cell-derived factor 1/C-X-C motif chemokine receptor 4 pathways. Additionally, the RGS16 protein may be involved in the Hepatitis B Virus -induced inflammatory response. Therefore, given the continuous expansion of knowledge regarding its role and mechanism, the structure, characteristics, regulatory mechanisms and known functions of the small RGS proteinRGS16 are reviewed in this paper to prepare for diagnosis, treatment, and prognostic evaluation of different diseases such as inflammation, tumor, and metabolic disorders and to better study its function in other diseases.

PDZK1 upregulates nitric oxide production through the PI3K/ERK2 pathway to inhibit porcine circovirus type 2 replication

Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus-associated disease. Changes in host cell gene expression are induced by PCV2 infection. Here, we showed that porcine PDZ Domain-Containing 1 (PDZK1) expression was enhanced during PCV2 infection and that overexpression of PDZK1 inhibited the expression of PCV2 Cap protein. PCV2 genomic DNA copy number and viral titers were decreased in PDZK1-overexpressing PK-15B6 cells. PDZK1 knockdown enhanced the replication of PCV2. Overexpression of PDZK1 activated the phosphoinositide 3-kinase (PI3K)/ERK2 signaling pathway to enhance nitric oxide (NO) levels, while PDZK1 knockdown had the opposite effects. A PI3K inhibitor (LY294002) and a NO synthase inhibitor (L-NAME hydrochloride) decreased the activity of PDZK1 in restricting PCV2 replication. ERK2 knockdown enhanced the proliferation of PCV2 by decreasing levels of NO. Levels of interleukin (IL)- 4 mRNA were reduced in PDZK1 knockdown and ERK2 knockdown PK-15B6 cells. Increased IL-4 mRNA levels were unable to decrease NO production in PDZK1-overexpressing cells. Thus, we conclude that PDZK1 affected PCV2 replication by regulating NO production via PI3K/ERK2 signaling. PDZK1 affected IL-4 expression through the PI3K/ERK2 pathway, but PDZK1 modulation of PCV2 replication occurred independently of IL-4. Our results contribute to understanding the biological functions of PDZK1 and provide a theoretical basis for the pathogenic mechanisms of PCV2.

Advances in Crosstalk between Porcine Circoviruses and Host

Porcine circoviruses (PCVs), including PCV1 to PCV4, are non-enveloped DNA viruses with a diameter of about 20 nm, belonging to the genus Circovirus in the family Circoviridae. PCV2 is an important causative agent of porcine circovirus disease or porcine circovirus-associated disease (PCVD/PCVAD), which is highly prevalent in pigs and seriously affects the swine industry globally. Furthermore, PCV2 mainly causes subclinical symptoms and immunosuppression, and PCV3 and PCV4 were detected in healthy pigs, sick pigs, and other animals. Although the pathogenicity of PCV3 and PCV4 in the field is still controversial, the infection rates of PCV3 and PCV4 in pigs are increasing. Moreover, PCV3 and PCV4 rescued from infected clones were pathogenic in vivo. It is worth noting that the interaction between virus and host is crucial to the infection and pathogenicity of the virus. This review discusses the latest research progress on the molecular mechanism of PCVs–host interaction, which may provide a scientific basis for disease prevention and control.

Coinfection of Porcine Circovirus 2 and Pseudorabies Virus Enhances Immunosuppression and Inflammation through NF-κB, JAK/STAT, MAPK, and NLRP3 Pathways

Porcine circovirus 2 (PCV2) and pseudorabies virus (PRV) are economically important pathogens in swine. PCV2 and PRV coinfection can cause more severe neurological and respiratory symptoms and higher mortality of piglets. However, the exact mechanism involved in the coinfection of PRV and PCV2 and its pathogenesis remain unknown. Here, porcine kidney cells (PK-15) were infected with PCV2 and/or PRV, and then the activation of immune and inflammatory pathways was evaluated to clarify the influence of the coinfection on immune and inflammatory responses. We found that the coinfection of PCV2 and PRV can promote the activation of nuclear factor-κB (NF-κB), c-Jun N-terminal protein kinases (JNK), p38, and nod-like receptor protein 3 (NLRP3) pathways, thus enhancing the expression of interferon-γ (IFN-γ), interferon-λ1 (IFN-λ1), interferon-stimulated gene (ISG15), interleukin 6 (IL6), and interleukin 1β (IL1β). Meanwhile, PCV2 and PRV also inhibit the expression and signal transduction of IFN-β, tumor necrosis factor α (TNFα), and the Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway. In addition, PCV2 and PRV infection can also weaken extracellular-signal-regulated kinase (ERK) activity. These results indicate that the regulations of cellular antiviral immune responses and inflammatory responses mediated by NF-κB, JAK/STAT, mitogen-activated protein kinase (MAPK), and NLRP3 pathways, contribute to immune escape of PCV2 and PRV and host antiviral responses.

Open reading frame 5 protein of porcine circovirus type 2 induces RNF128 (GRAIL) which inhibits mRNA transcription of interferon-β in porcine epithelial cells

A previous study has indicated that mRNA transcript of Rnf128 (Grail) is significantly increased in porcine epithelial cells expressing porcine circovirus type 2 (PCV2) open reading frame 5 (ORF5). RNF128 is an E3 ubiquitin ligase that can modulate the activity of target protein via ubiquitination of specific lysine residues. However, the function of RNF128 in PCV2-infected epithelial cells has not been well studied yet. Thus, the objective of the present study was to examine the functional role of RNF128 in porcine epithelial cells (PK15 cells) after PCV2 infection. Results clearly indicated that PCV2 ORF5 increased the expression of RNF128 which inhibited type I IFN production and enhanced viral replication of PCV2 in PK15 cells. Therefore, up-regulating RNF128 by PCV2 ORF5 can help PCV2 circumvent initial immune surveillance of porcine epithelial cells.

Porcine circovirus 2 capsid protein produced in N. benthamiana forms virus-like particles that elicit production of virus-neutralizing antibodies in guinea pigs

Porcine circovirus type 2 (PCV2) is a non-enveloped, icosahedral virus of the Circoviridae family, with a small, circular, single-stranded DNA genome. PCV2 infections cause substantial economic losses in the pig industry worldwide. Currently, commercially produced PCV2 vaccines are expensive, whereas plant-based expression systems can produce recombinant proteins at low cost for use as vaccines. In this study, recombinant PCV2 capsid protein (rCap) was transiently expressed in Nicotiana benthamiana and purified by metal affinity chromatography, with a yield of 102 mg from 1 kg plant leaves. Electron microscopy confirmed that purified rCap self-assembled into virus-like particles (VLPs) at neutral pH. It was shown to provoke a strong immune response in guinea pigs. The results indicate that plant systems can enable production of large amounts of proteins to serve as candidates for subunit vaccines.

Apoptosis Triggered by ORF3 Proteins of the Circoviridae Family

Apoptosis, a form of the programmed cell death, is an indispensable defense mechanism regulating cellular homeostasis and is triggered by multiple stimuli. Because of the regulation of apoptosis in cellular homeostasis, viral proteins with apoptotic activity are particular foci of on antitumor therapy. One representative viral protein is the open reading frame 3 (ORF3) protein, also named as apoptin in the Circoviridae chicken anemia virus (CAV), and has the ability to induce tumor-specific apoptosis. Proteins encoded by ORF3 in other circovirus species, such as porcine circovirus (PCV) and duck circovirus (DuCV), have also been reported to induce apoptosis, with subtle differences in apoptotic activity based on cell types. This article is aimed at reviewing the latest research advancements in understanding ORF3 protein-mediated apoptosis mechanisms of Circoviridae from three perspectives: subcellular localization, interactions with host proteins, and participation in multiple apoptotic signaling pathways, providing a scientific basis for circovirus pathogenesis and a reference on its potential anticancer function.

The Monoclonal Antibody Recognized the Open Reading Frame Protein in Porcine Circovirus Type 2-Infected Peripheral Blood Mononuclear Cells

The purpose of this study in the context of the open reading frame 3 (ORF3) protein of porcine circovirus type 2 (PCV2) was especially its location and its relation to the capsid protein and the apoptosis protein in PCV2-infected porcine peripheral blood mononuclear cells (PBMCs). To detect the ORF3 protein, monoclonal antibodies (mAbs) were generated in this study. The mAb 7D3 binds to the ORF3 peptide (residues 35–66) and the native ORF3 protein in PCV2-infected PBMCs, as shown by immunofluorescence assay (IFA). The data show that 3–5% of PBMCs were positive for ORF3 protein or p53 protein. Further, 78–82% of PBMCs were positive for the capsid. This study confirmed the ORF3 protein not only colocalized with the capsid protein but also colocalized with the p53 protein in PBMCs. Immunoassays were conducted in this study to detect the capsid protein, the ORF3 protein, anti-capsid IgG, and anti-ORF3 IgG. The data show the correlation (r = 0.758) of the ORF3 protein and the capsid protein in the blood samples from the PCV2-infected herd. However, each anti-viral protein IgG had a different curve of the profile in the same herd after vaccination. Overall, this study provides a blueprint to explore the ORF3 protein in PCV2-infected PBMCs.

Inhibitory effect of polysaccharide of Sargassum weizhouense on PCV2 induced inflammation in mice by suppressing histone acetylation

Seaweeds are excellent source of bioactive compounds and seaweed-derived polysaccharides have demonstrated an array of biological effects. Here, we investigated the effect of polysaccharide of Sargassum weizhouense (PSW) on the inflammatory response in porcine circovirus type 2 (PCV2) infected mice and the underlying mechanism was studied according to the histone acetylation. After PCV2 infection, the levels of TNF-α, IL-1β, IL-6, IL-8, IL-10, MCP-1, COX-1, COX-2 and HAT in both serum and spleen were significantly increased (P <0.05). The mRNA expression of TNF-α, IL-6, IL-10 and NF-κB p65 were elevated in PCV2 infected mice (P <0.05). The HDAC content in both serum and spleen as well the mRNA expression of HDAC1 were greatly decreased (P <0.05). PSW treatment dramatically inhibited the secretions of inflammatory cytokines and HATs, reduced mRNA expression of TNF-α, IL-6, IL-10 and NF-κB p65, but promoted HDAC secretion and mRNA expression of HDAC1 in PCV2-infected mice. The acetylation of both H3 and H4 was significantly up-regulated in PCV2-infected mice, and strongly inhibited by PSW treatment (P <0.01). These results suggested that PCV2 mediate the equilibrium between HATs and HDACs, alternate the histone acetylation and thus DNA packaging, and then activate the transcription of inflammatory cytokines. PSW could inhibit the histone acetylation and the production of inflammatory cytokines, showing excellent potentials in improving the resistance of host against PCV2 infection.

A Host Factor GPNMB Restricts Porcine Circovirus Type 2 (PCV2) Replication and Interacts With PCV2 ORF5 Protein

Porcine circovirus type 2 (PCV2) is the infectious agent of postweaning multisystemic wasting syndrome (PMWS). The recently discovered open reading frame 5 (ORF5) in PCV2 genome encodes a non-structural protein. Previous study revealed that ORF5 protein inhibits cell proliferation and may interact with host transmembrane glycoprotein NMB (GPNMB). However, whether the GPNMB affects PCV2 replication and the underlying molecular mechanisms are still unknown. In this study, the transcriptome maps of PCV2-infected and ORF5-transfected porcine alveolar macrophages 3D4/2 (PAM) cells were profiled. The GPNMB gene was down-regulated in PCV2-infected and ORF5-transfected PAMs. By using glutathione S-transferase (GST) pull-down, co-immunoprecipitation (co-IP) and confocal microscopy approaches, we convincingly showed that PCV2 ORF5 protein interacts with GPNMB. Furthermore, by utilizing lentivirus mediated overexpression or knockdown approach, we showed that the cellular GPNMB significantly inhibits PCV2 replication and ORF5 expression. Moreover, GPNMB overexpressing leads to an increased Cyclin A expression and a reduced S phase, whereas GPNMB knockdown causes a decreased Cyclin A expression and a prolonged S phase. In conclusion, we identified a novel host factor GPNMB that interacts with PCV2 ORF5 protein and restricts PCV2 replication.

Sargassum polysaccharide inhibits inflammatory response in PCV2 infected-RAW264.7 cells by regulating histone acetylation

Toxic inflammatory response is frequently introduced upon virus infection. In this study, RAW264.7 cells were infected with porcine circovirus type 2 (PCV2) and treated with Sargassum polysaccharide SP. It was found that PCV2 infection induced increased significant inflammation response represented with increased secretion of inflammatory cytokines, corresponding with promoted HAT activity, inhibited HDAC activity, elevated HDAC1 mRNA levels, and up-regulated acetylation levels of H3 and H4 in RAW264.7 cells. SP treatment significantly inhibited the increase of inflammatory cytokines, HAT activity and the acetylation of histones, but dramatically increased the HDAC activity and the expression of HDAC1. From these results, SP might be able to protect immune cells from virus induced damages through inhibiting the inflammatory responds by maintaining an equilibrium between the activity of HATs and HDACs which contributes to an appropriate level of histone acetylation.

Immunogenicity evaluation of inactivated virus and purified proteins of porcine circovirus type 2 in mice

Background

Vaccination is considered as an effective and economical way to against PCV2 infection. However, some of commercial available vaccines are based on inactivated viruses, while the others are based on purified protein of PCV2. In the present study, we aimed to compare the immunogenicity of inactivated virus and purified proteins of porcine circovirus type 2 in mice.

Results

The results showed that positive antiserum titers were significantly increased after second, third and fourth immunization using inactivated PCV2 or purified proteins as coating antigen. Moreover, the inactivated PCV2 induced significantly higher levels of PCV2-specific antibodies than that of PCV2 subunit proteins. After PCV2 wild strain challenged, the average daily gain was comparable with that of mice in the mock group, and the sera from both inactivated PCV2-immunized animals and subunit protein Cap+ORF3 + Rep immunized animals had significantly higher neutralizing antibody titers than that of the PBS group. As expected, the neutralizing antibody in the inactivated PCV2 group was significantly higher than that of the subunit protein group. These results indicated that positive antiserum induced by the inactivated PCV2 had a better reactivity and specificity than that of the positive antiserum induced by the purified proteins.

Conclusions

The results in the present study demonstrated inactivated PCV2 is more effective than PCV2 subunit proteins in stimulating immune response to against PCV2 infection.

Genetic analysis of porcine circovirus type 2 from pigs affected with PMWS in Chile reveals intergenotypic recombination

Background

Porcine circovirus type 2 (PCV2) is a very small, non-enveloped and icosahedral virus, with circular single stranded DNA genome. This virus is the most ubiquitous and persistent pathogen currently affecting the swine industry worldwide. PCV2 has been implicated as the major causative agent of postweaning multisystemic wasting syndrome (PMWS), a disease which is characterized by severe immunosuppressive effects in the porcine host. Worldwide PCV2 isolates have been classified into four different genotypes, PCV2a, PCV2b, PCV2c and PCVd. The goal of this work was to conduct the first phylogenetic analysis of PCV2 in Chile.

Methods

PCV2 partial ORF2 sequences (462 nt) obtained from 29 clinical cases of PMWS in 22 Chilean intensive swine farms, covering over the 90% of the local pork-production, were analyzed.

Results

14% and 52% of sequences belonged to the genotypes PCV2a and PCV2b, respectively. Surprisingly, 34% of sequences were PCV2a/PCV2d recombinant viruses.

Conclusions

Our findings suggested that a novel cluster of Chilean sequences emerged resulting from intergenotypic recombination between PCV2a and PCV2d.

Porcine circovirus type 2 activates PI3K/Akt and p38 MAPK pathways to promote interleukin-10 production in macrophages via Cap interaction of gC1qR

Porcine circovirus type 2 (PCV2) infection caused PCV2-associated diseases (PCVAD) is one of the major emerging immunosuppression diseases in pig industry. In this study, we investigated how PCV2 inoculation increases interleukin (IL)-10 expression in porcine alveolar macrophages (PAMs). PCV2 inoculation significantly upregulated IL-10 expression compared with PCV1. Upon initial PCV2 inoculation, PI3K/Akt cooperated with NF-κB pathways to promote IL-10 transcription via p50, CREB and Ap1 transcription factors, whereas inhibition of PI3K/Akt activation blocked Ap1 and CREB binding to the il10 promoter, and decreased the binding level of NF-κB1 p50 with il10 promoter, leading to great reduction in early IL-10 transcription. In the later phase of inoculation, PCV2 further activated p38 MAPK and ERK pathways to enhance IL-10 production by promoting Sp1 binding to the il10 promoter. For PCV2-induced IL-10 production in macrophages, PCV2 capsid protein Cap, but not the replicase Rep or ORF3, was the critical component. Cap activated PI3K/Akt, p38 MAPK, and ERK signaling pathways to enhance IL-10 expression. In the whole process, gC1qR mediated PCV2-induced PI3K/Akt and p38 MAPK activation to enhance IL-10 induction by interaction with Cap. Depletion of gC1qR blocked PI3K/Akt and p38 MAPK activation, resulting in significant decrease in IL-10 production in PCV2-inoculated cells. Thus, gC1qR might be a critical functional receptor for PCV2-induced IL-10 production. Taken together, these data demonstrated that Cap protein binding with host gC1qR induction of PI3K/Akt and p38 MAPK signalings activation is a critical process in enhancing PCV2-induced IL-10 production in porcine alveolar macrophages.

Suppressor of cytokine signaling 3 plays an important role in porcine circovirus type 2 subclinical infection by downregulating proinflammatory responses

Porcine circovirus type 2 (PCV2) causes porcine circovirus-associated diseases and usually evokes a subclinical infection, without any obvious symptoms, in pigs. It remains unclear how PCV2 leads to a subclinical infection. In this study, we found that peripheral blood mononuclear cells (PBMCs) from PCV2-challenged piglets with no significant clinical symptoms exhibited increased expression of suppressor of cytokine signaling (SOCS) 3, but no significant changes in the expression of the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α; this differed from piglets that displayed significant clinical symptoms. IL-6- and TNF-α-mediated signalings were inhibited in PBMCs from subclinical piglets. Elevated SOCS3 levels inhibited IL-6- and TNF-α-mediated NF-kappa-B inhibitor alpha degradation in PBMCs and PK-15 cells. SOCS3 production was also increased in PCV2-infected PK-15 porcine kidney cells, and IL-6 and TNF-α production that was induced by PCV2 in PK-15 cells was significantly increased when SOCS3 was silenced by a small interfering RNA. SOCS3 interacted with signal transducer and activator of transcription 3 and TNF-associated receptor-associated factor 2, suggesting mechanisms by which SOCS3 inhibits IL-6 and TNF-α signaling. We conclude that SOCS3 plays an important role in PCV2 subclinical infection by suppressing inflammatory responses in primary immune cells.

The ORF4 protein of porcine circovirus type 2 antagonizes apoptosis by stabilizing the concentration of ferritin heavy chain through physical interaction

Porcine circovirus type 2 (PCV2) is the primary aetiological agent of porcine circovirus-associated disease in swine. The mechanism of PCV2 pathogenesis remains largely unknown. A newly identified viral protein of PCV2, ORF4, has been suggested to be involved in virus-induced apoptosis. However, there is still no information regarding the molecular mechanism by which ORF4 regulates apoptosis. In this study, we reveal that a physical interaction between the PCV2 ORF4 protein and ferritin heavy chain (FHC) in the cytoplasm of host cells reduced the cellular concentration of FHC. The ORF4-mediated reduction of FHC inhibited reactive oxygen species accumulation in PCV2-infected cells. Consequently, the ORF4 protein inhibited apoptosis in host cells. This may be the first report to describe the mechanism of ORF4 cytoprotection against apoptosis during the early stages of PCV2 infection.

R4 Regulator of G Protein Signaling (RGS) Proteins in Inflammation and Immunity

G protein-coupled receptors (GPCRs) have important functions in both innate and adaptive immunity, with the capacity to bridge interactions between the two arms of the host responses to pathogens through direct recognition of secreted microbial products or the by-products of host cells damaged by pathogen exposure. In the mid-1990s, a large group of intracellular proteins was discovered, the regulator of G protein signaling (RGS) family, whose main, but not exclusive, function appears to be to constrain the intensity and duration of GPCR signaling. The R4/B subfamily--the focus of this review--includes RGS1-5, 8, 13, 16, 18, and 21, which are the smallest RGS proteins in size, with the exception of RGS3. Prominent roles in the trafficking of B and T lymphocytes and macrophages have been described for RGS1, RGS13, and RGS16, while RGS18 appears to control platelet and osteoclast functions. Additional G protein independent functions of RGS13 have been uncovered in gene expression in B lymphocytes and mast cell-mediated allergic reactions. In this review, we discuss potential physiological roles of this RGS protein subfamily, primarily in leukocytes having central roles in immune and inflammatory responses. We also discuss approaches to target RGS proteins therapeutically, which represents a virtually untapped strategy to combat exaggerated immune responses leading to inflammation.