Interaction of suppressor of cytokine signalling 3 with cavin-1 links SOCS3 function and cavin-1 stability

Current Update on Transcellular Brain Drug Delivery

It is well known that the presence of a blood-brain barrier (BBB) makes drug delivery to the brain more challenging. There are various mechanistic routes through which therapeutic molecules travel and deliver the drug across the BBB. Among all the routes, the transcellular route is widely explored to deliver therapeutics. Advances in nanotechnology have encouraged scientists to develop novel formulations for brain drug delivery. In this article, we have broadly discussed the BBB as a limitation for brain drug delivery and ways to solve it using novel techniques such as nanomedicine, nose-to-brain drug delivery, and peptide as a drug delivery carrier. In addition, the article will help to understand the different factors governing the permeability of the BBB, as well as various formulation-related factors and the body clearance of the drug delivered into the brain.

Deciphering the relationship between caveolae-mediated intracellular transport and signalling events

The caveolae-mediated transport across polarized epithelial cell barriers has been largely deciphered in the last decades and is considered the second essential intracellular transfer mechanism, after the clathrin-dependent endocytosis. The basic cell biology knowledge was supplemented recently, with the molecular mechanisms beyond caveolae generation implying the key contribution of the lipid-binding proteins (the structural protein Caveolin and the adapter protein Cavin), along with the bulb coat stabilizing molecules PACSIN-2 and Eps15 homology domain protein-2. The current attention is focused also on caveolae architecture (such as the bulb coat, the neck, the membrane funnel inside the bulb, and the associated receptors), and their specific tasks during the intracellular transport of various cargoes. Here, we resume the present understanding of the assembly, detachment, and internalization of caveolae from the plasma membrane lipid raft domains, and give an updated view on transcytosis and endocytosis, the two itineraries of cargoes transport via caveolae. The review adds novel data on the signalling molecules regulating caveolae intracellular routes and on the transport dysregulation in diseases. The therapeutic possibilities offered by exploitation of Caveolin-1 expression and caveolae trafficking, and the urgent issues to be uncovered conclude the review.

Neuronal STAT3/HIF-1α/PTRF axis-mediated bioenergetic disturbance exacerbates cerebral ischemia-reperfusion injury via PLA2G4A

Ischemic stroke is an acute and severe neurological disease with high mortality and disability rates worldwide. Polymerase I and transcript release factor (PTRF) plays a pivotal role in regulating cellular senescence, glucose intolerance, lipid metabolism, and mitochondrial bioenergetics, but its mechanism, characteristics, and functions in neuronal cells following the cerebral ischemia-reperfusion (I/R) injury remain to be determined. Methods: Transcription factor motif analysis, chromatin immunoprecipitation (ChIP), luciferase and co-Immunoprecipitation (co-IP) assays were performed to investigate the mechanisms of PTRF in neuronal cells after I/R injury. Lentiviral-sgRNA against PTRF gene was introduced to HT22 cells, and adeno-associated virus (AAV) encoding a human synapsin (hSyn) promoter-driven construct was transduced a short hairpin RNA (shRNA) against PTRF mRNA in primary neuronal cells and the cortex of the cerebral I/R mice for investigating the role of PTRF in neuronal damage and PLA2G4A change induced by the cerebral I/R injury. Results: Here, we reported that neuronal PTRF was remarkably increased in the cerebral penumbra after I/R injury, and HIF-1α and STAT3 regulated the I/R-dependent expression of PTRF via binding to its promoter in neuronal cells. Moreover, overexpression of neuronal PTRF enhanced the activity and stability of PLA2G4A by decreasing its proteasome-mediated degradation pathway. Subsequently, PTRF promoted reprogramming of lipid metabolism and altered mitochondrial bioenergetics, which could lead to oxidative damage, involving autophagy, lipid peroxidation, and ferroptosis via PLA2G4A in neuronal cells. Furthermore, inhibition of neuronal PTRF/PLA2G4A-axis markedly reduced the neurological deficits, cerebral infarct volumes, and mortality rates in the mice following cerebral I/R injury. Conclusion: Our results thus identify that the STAT3/HIF-1α/PTRF-axis in neurons, aggravating cerebral I/R injury by regulating the activity and stability of PLA2G4A, might be a novel therapeutic target for ischemic stroke.

Cavin-1 promotes M2 macrophages/microglia polarization via SOCS3

PURPOSE

Our study aimed to investigate the function of Cavin-1 and SOCS3 in macrophages/microglia M2 polarization and further explored the relevant mechanism.

METHODS

Expression levels of Cavin-1 and SOCS3 in macrophages/microglia were measured by western blotting and RT-PCR, respectively. Then, Cavin-1 or SOCS3 was gene silenced by a siRNA approach, and gene silencing efficiency was determined by western blotting. Next, co-immunoprecipitation (Co-IP) was employed to further analyze the interaction between Cavin-1 and SOCS3. Finally, the activation of STAT6/PPAR-γ signaling was evaluated using western blotting, and the M2 macrophages/microglia polarization was validated by measuring the mRNA expression of M2 markers by RT-PCR.

RESULTS

In the polarization process of macrophages/microglia to M2 phenotype, both Cavin-1 and SOCS3 increased synchronously at protein and mRNA level, reached the peak at the 6 h, and then decreased. After Cavin-1 or SOCS3 silencing, the expression of Cavin-1 and SOCS3 declined. These results suggested that Cavin-1 and SOCS3 were positively correlated in macrophages/microglia, and this conjecture was verified by Co-IP. Besides, Cavin-1 silencing not only suppressed the activation of STAT6/PPAR-γ pathway, but also suppressed the release of anti-inflammatory factors. Finally, we found that SOCS3 overexpression reversed the inhibitory effect of Cavin-1 silencing on the release of anti-inflammatory factors in M2 macrophages/microglia.

CONCLUSIONS

Cavin-1 and SOCS3 are actively involved in the process of M2 macrophages/microglia polarization. As a SOCS3 interacting protein, Cavin-1 can promote M2 macrophages/microglia polarization via SOCS3.

Approaches to Visualising Endocytosis of LDL-Related Lipoproteins

Endocytosis is the process by which molecules are actively transported into cells. It can take on a variety of forms depending on the cellular machinery involved ranging from specific receptor-mediated endocytosis to the less selective and actin-driven macropinocytosis. The plasma lipoproteins, which deliver lipids and other cargo to cells, have been intensely studied with respect to their endocytic uptake. One of the first molecules to be visualised undergoing endocytosis via a receptor-mediated, clathrin-dependent pathway was low-density lipoprotein (LDL). The LDL molecule has subsequently been shown to be internalised through multiple endocytic pathways. Dissecting the pathways of lipoprotein endocytosis has been crucial to understanding the regulation of plasma lipid levels and how lipids enter cells in the arterial wall to promote atherosclerosis. It has also aided understanding of the dysregulation that occurs in plasma lipid levels when molecules involved in uptake are defective, as is the case in familial hypercholesterolemia (FH). The aim of this review is to outline the many endocytic pathways utilised for lipoprotein uptake. It explores the various experimental approaches that have been applied to visualise lipoprotein endocytosis with an emphasis on LDL and its more complex counterpart, lipoprotein(a) [Lp(a)]. Finally, we look at new developments in lipoprotein visualisation that hold promise for scrutinising endocytic pathways to finer detail in the future.

Proteomimetics of Natural Regulators of JAK-STAT Pathway: Novel Therapeutic Perspectives

The JAK-STAT pathway is a crucial cellular signaling cascade, including an intricate network of Protein-protein interactions (PPIs) responsible for its regulation. It mediates the activities of several cytokines, interferons, and growth factors and transduces extracellular signals into transcriptional programs to regulate cell growth and differentiation. It is essential for the development and function of both innate and adaptive immunities, and its aberrant deregulation was highlighted in neuroinflammatory diseases and in crucial mechanisms for tumor cell recognition and tumor-induced immune escape. For its involvement in a multitude of biological processes, it can be considered a valuable target for the development of drugs even if a specific focus on possible side effects associated with its inhibition is required. Herein, we review the possibilities to target JAK-STAT by focusing on its natural inhibitors as the suppressor of cytokine signaling (SOCS) proteins. This protein family is a crucial checkpoint inhibitor in immune homeostasis and a valuable target in immunotherapeutic approaches to cancer and immune deficiency disorders.

The IL6/sIL-6Rα trans-signaling increases PGE2 production in human granulosa cells

As a potent autocrine regulator, the proinflammatory cytokine interleukin 6 (IL6) is expressed in granulosa cells and follicular fluid and is involved in the modulation of various follicular functions, including follicular development and ovulation. At present, the detailed molecular mechanisms by which IL6 regulates the event of ovulation remain to be elucidated. In the present study, primary and immortalized (SVOG) human granulosa-lutein (hGL) cells were used to investigate the effects of IL6 on the expression of prostaglandin-endoperoxide synthase 2 (PTGS2) and the subsequent synthesis of prostaglandin E2 (PGE2) and to investigate the underlying molecular mechanisms. We found that instead of classic signaling, IL6/sIL-6Rα trans-signaling induced the expression of PTGS2 and production of PGE2 in both SVOG cells and primary hGL cells. Moreover, IL6/sIL-6Rα activated the phosphorylation of Janus activated kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), which in turn induced STAT3 nuclear translocation. Additionally, these effects were suppressed by the addition of inhibitors (AG490 for JAK2 and C188-9 for STAT3) and by the siRNA-mediated knockdown of STAT3. Additionally, suppressor of cytokine signaling 3 (SOCS3) acts as a negative-feedback regulator in IL6/sIL-6Rα-induced cellular activities, including the activation and nuclear translocation of STAT3, upregulation of PTGS2 expression, and increase in PGE2 production in SVOG cells. In conclusion, IL6 trans-signaling upregulates the expression of PTGS2 and increases the production of PGE2 via the JAK2/STAT3/SOCS3 signaling pathway in hGL cells. Our findings provide insights into the molecular mechanisms by which IL6 trans-signaling may potentially modulate the event of ovulation in human ovaries.

Endosomes as Signaling Platforms for IL-6 Family Cytokine Receptors

Interleukin-6 (IL-6) is the name-giving cytokine of a family of eleven members, including IL-6, CNTF, LIF, and IL-27. IL-6 was first recognized as a B-cell stimulating factor but we now know that the cytokine plays a pivotal role in the orchestration of inflammatory processes as well as in inflammation associated cancer. Moreover, IL-6 is involved in metabolic regulation and it has been shown to be involved in major neural activities such as neuroprotection, which can help to repair and to reduce brain damage. Receptor complexes of all members formed at the plasma membrane contain one or two molecules of the signaling receptor subunit GP130 and the mechanisms of signal transduction are well understood. IL-6 type cytokines can also signal from endomembranes, in particular the endosome, and situations have been reported in which endocytosis of receptor complexes are a prerequisite of intracellular signaling. Moreover, pathogenic GP130 variants were shown to interfere with spatial activation of downstream signals. We here summarize the molecular mechanisms underlying spatial regulation of IL-6 family cytokine signaling and discuss its relevance for pathogenic processes.

The miR-155 regulates cytokines expression by SOSC1 signal pathways of fish in vitro and in vivo

MiR-155 is reported as immune regulated miRNA in mammalian corresponding to immunity, antibacterial and antiviral effects regulation. However, the roles and mechanisms of the miRNA have remained largely undefined. We herein comprehensively investigated the functions of miR-155 in vitro and in vivo by miR-155 mimics, agomir and antagomir in Cyprinus carpio and Ictalurus punctatus, with the target genes in the SOSC1 pathway certified in I. punctatus via luciferase reporter assays. Results showed that the miR-155 regulated the expressions of cytokines, including TNF-α, IFN-γ, IL-1β, IL-6 and IL-10. Further research confirmed SOSC1 as one of the targets of the miRNA, and the JAK1/STAT3/SOSC1 signal pathway involved in the miR-155 effects on the expression of immune cytokines as well. Additionally, the changes of TLR2 in fish may also be related to miR-155 along with its target SOCS1, and the TLR2/MyD88 pathway may partly participate in the effects of the miR-155 on the cytokines. The research here confirmed that the miR-155 can regulate cytokines expression by SOSC1 signal pathways of fish in vitro and in vivo, which would provide resources for understanding and studying about immune regulation in fish.

SOCS Proteins Participate in the Regulation of Innate Immune Response Caused by Viruses

The host immune system has multiple innate immune receptors that can identify, distinguish and react to viral infections. In innate immune response, the host recognizes pathogen-associated molecular patterns (PAMP) in nucleic acids or viral proteins through pathogen recognition receptors (PRRs), especially toll-like receptors (TLRs) and induces immune cells or infected cells to produce type I Interferons (IFN-I) and pro-inflammatory cytokines, thus when the virus invades the host, innate immunity is the earliest immune mechanism. Besides, cytokine-mediated cell communication is necessary for the proper regulation of immune responses. Therefore, the appropriate activation of innate immunity is necessary for the normal life activities of cells. The suppressor of the cytokine signaling proteins (SOCS) family is one of the main regulators of the innate immune response induced by microbial pathogens. They mainly participate in the negative feedback regulation of cytokine signal transduction through Janus kinase signal transducer and transcriptional activator (JAK/STAT) and other signal pathways. Taken together, this paper reviews the SOCS proteins structures and the function of each domain, as well as the latest knowledge of the role of SOCS proteins in innate immune caused by viral infections and the mechanisms by which SOCS proteins assist viruses to escape host innate immunity. Finally, we discuss potential values of these proteins in future targeted therapies.

Potential Molecular Mechanism of the NPPB Gene in Postischemic Heart Failure with and without T2DM

Background

This study is aimed at investigating natriuretic peptide B (NPPB) coexpression genes and their pathways involved in heart failure (HF) among patients both with and without type 2 diabetes mellitus (T2DM).

Methods

The microarray dataset GSE26887, containing 19 postischemic HF patients' peripheral blood samples (7 with T2DM and 12 without T2DM), was examined to detect the genes coexpressed with NPPB using the corr.test function in the R packet. Furthermore, using online analytical tools, we determined the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, Gene Ontology (GO) annotation, and protein-protein interaction (PPI) network of the coexpression genes. The modules and hub genes of the PPI network were then identified using the Cytoscape software.

Results

In patients with T2DM, a total of 41 biological processes (BP), 20 cellular components (CC), 13 molecular functions (MF), and 41 pathways were identified. Furthermore, a total of 61 BPs, 16 CCs, 13 MFs, and 22 pathways in patients without T2DM were identified. In both groups of patients, 17 BPs, 10 CCs, 6 MFs, and 13 pathways were enriched. We also identified 173 intersectional coexpression genes (63 positively, 106 negatively, and 4 differently coexpressed in patients with and without T2DM, respectively) in both types of patients, which were enriched in 16 BPs, 8 CCs, 3 MFs, and 8 KEGG pathways. Moreover, the PPI network (containing 237 edges and 170 nodes) with the top module significantly enriched in 4 BPs (tricarboxylic acid metabolic process, citrate metabolic process, tricarboxylic acid cycle, and aerobic respiration) and 3 pathways (citrate cycle, malaria parasite metabolic pathway, and AGE-RAGE signaling pathway in diabetic complications) was constructed. DECR1, BGN, TIMP1, VCAN, and CTCF are the top hub genes.

Conclusions

Our findings may elucidate the functions and roles of the NPPB gene in patients with postischemic HF and facilitate HF management.

Stromal CAVIN1 Controls Prostate Cancer Microenvironment and Metastasis by Modulating Lipid Distribution and Inflammatory Signaling

Lipid uptake occurs through caveolae, plasma membrane invaginations formed by caveolins (CAV) and caveolae-associated protein 1 (CAVIN1). Genetic alterations of CAV1N1 and CAV1 modify lipid metabolism and underpin lipodystrophy syndromes. Lipids contribute to tumorigenesis by providing fuel to cancer metabolism and supporting growth and signaling. Tumor stroma promotes tumor proliferation, invasion, and metastasis, but how stromal lipids influence these processes remain to be defined. Here, we show that stromal CAVIN1 regulates lipid abundance in the prostate cancer microenvironment and suppresses metastasis. We show that depletion of CAVIN1 in prostate stromal cells markedly reduces their lipid droplet accumulation and increases inflammation. Stromal cells lacking CAVIN1 enhance prostate cancer cell migration and invasion. Remarkably, they increase lipid uptake and M2 inflammatory macrophage infiltration in the primary tumors and metastasis to distant sites. Our data support the concept that stromal cells contribute to prostate cancer aggressiveness by modulating lipid content and inflammation in the tumor microenvironment. IMPLICATIONS: This study showed that stromal CAVIN1 suppresses prostate cancer metastasis by modulating tumor microenvironment, lipid content, and inflammatory response.

Overview of Crosstalk Between Multiple Factor of Transcytosis in Blood Brain Barrier

Blood brain barrier (BBB) conserves unique regulatory system to maintain barrier tightness while allowing adequate transport between neurovascular units. This mechanism possess a challenge for drug delivery, while abnormality may result in pathogenesis. Communication between vascular and neural system is mediated through paracellular and transcellular (transcytosis) pathway. Transcytosis itself showed dependency with various components, focusing on caveolae-mediated. Among several factors, intense communication between endothelial cells, pericytes, and astrocytes is the key for a normal development. Regulatory signaling pathway such as VEGF, Notch, S1P, PDGFβ, Ang/Tie, and TGF-β showed interaction with the transcytosis steps. Recent discoveries showed exploration of various factors which has been proven to interact with one of the process of transcytosis, either endocytosis, endosomal rearrangement, or exocytosis. As well as providing a hypothetical regulatory pathway between each factors, specifically miRNA, mechanical stress, various cytokines, physicochemical, basement membrane and junctions remodeling, and crosstalk between developmental regulatory pathways. Finally, various hypotheses and probable crosstalk between each factors will be expressed, to point out relevant research application (Drug therapy design and BBB-on-a-chip) and unexplored terrain.

Sarcopenic Obesity, Insulin Resistance, and Their Implications in Cardiovascular and Metabolic Consequences

The prevalence of sarcopenic obesity is increasing worldwide, particularly amongst aging populations. Insulin resistance is the core mechanism of sarcopenic obesity and is also associated with variable cardiometabolic diseases such as cardiovascular disease, type 2 diabetes mellitus, and non-alcoholic fatty liver disease. Fat accumulation in muscle tissue promotes a proinflammatory cascade and oxidative stress, leading to mitochondrial dysfunction, impaired insulin signaling, and muscle atrophy. To compound the problem, decreased muscle mass aggravates insulin resistance. In addition, the crosstalk between myokines and adipokines leads to negative feedback, which in turn aggravates sarcopenic obesity and insulin resistance. In this review, we focus on the molecular mechanisms linking sarcopenic obesity and insulin resistance with various biological pathways. We also discuss the impact and mechanism of sarcopenic obesity and insulin resistance on cardiometabolic disease.

Molecular characterization, expression pattern and evolution of nine suppressors of cytokine signaling (SOCS) gene in the swamp eel (Monopterus albus)

Suppressors of cytokine signaling (SOCS) family members have negative effects on cytokine signaling pathways involved in immunity, growth and development. Owing to their typical feature, they have been extensively studied in mammalians, but they have not offered systematic studies among teleosts. In the present study, nine SOCS family genes were identified in the swamp eel genome and analyzed regulation mechanisms of SOCS family members in swamp eels. The open reading frames of MaSOCS1a, MaSOCS1b, MaSOCS2, MaSOCS3a, MaSOCS3b, MaSOCS4, MaSOCS5, MaSOCS6 and MaSOCS7 were 663 bp, 603 bp, 717 bp, 618 bp, 645 bp, 1188 bp, 1488 bp, 1611 bp and 1998 bp and encoded 220, 238, 200, 205, 214, 395, 496, 536 and 655 amino acids, respectively. All SOCS proteins have no signal peptides. Multiple alignment revealed that MaSOCS family members possessed a typical conserved SOCS box and SH2 region. Phylogenetic analyses showed that all SOCS proteins were divided into two main clusters. Taken together with the similarity and identity of SOCS protein amino acids, these results indicated that MaSOCS family members shared conserved with other homologous genes, in which MaSOCS7 was more conserved. Further syntenic analysis confirmed the phylogenetic analysis results and annotation of SOCS protein, suggesting that MaSOCS5 shared a common ancestor gene with that of fish and humans. MaSOCS family members were constitutively expressed in a wide range of tissues with different levels. In particular, spleen and head kidneys play an important role in immune-related pathways. After Aeromonas veronii and polyinosinic-polycytidylic acid (poly I:C) challenge in the spleen and head kidney, MaSOCS family members exhibit different expression profiles. These expression patterns indicated that MaSOCS family members could make acute responses after pathogen invasion. Taken together, these results indicate that MaSOCS family members participate in the immune response against pathogens and offer a solid foundation for future studies of SOCS function.

Investigation of Novel Cavin-1/Suppressor of Cytokine Signaling 3 (SOCS3) Interactions by Coimmunoprecipitation, Peptide Pull-Down, and Peptide Array Overlay Approaches

The ability of inducible regulator suppressor of cytokine signaling 3 (SOCS3) to inhibit Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling requires interaction with specific cytokine receptors, JAKs, and components of the cellular ubiquitylation machinery. However, it is now clear that additional protein interactions are essential for effective inhibition of JAK-STAT signaling that have also identified new roles for SOCS3. For example, we have demonstrated that SOCS3 interaction with cavin-1, a core component of caveolae essential for their formation, is required for effective inhibition of interleukin (IL)-6 signaling and maintenance of cellular levels of caveolae. This is achieved through cavin-1 interaction with a discrete motif within the SOCS3 SH2 domain. Here, we describe in detail three methods (coimmunoprecipitation; peptide pull-down; peptide array overlay) we have used to validate and characterize cavin-1/SOCS3 interactions in vitro.

Identification of the Toxoplasma gondii mitochondrial ribosome, and characterisation of a protein essential for mitochondrial translation

Apicomplexan parasites cause diseases such as malaria and toxoplasmosis. The apicomplexan mitochondrion shows striking differences from common model organisms, including fundamental processes such as mitochondrial translation. Despite evidence that mitochondrial translation is essential for parasite survival, it is largely understudied. Progress has been restricted by the absence of functional assays to detect apicomplexan mitochondrial translation, a lack of knowledge of proteins involved in the process and the inability to identify and detect mitoribosomes. We report the localization of 12 new mitochondrial proteins, including 6 putative mitoribosomal proteins. We demonstrate the integration of three mitoribosomal proteins in macromolecular complexes, and provide evidence suggesting these are apicomplexan mitoribosomal subunits, detected here for the first time. Finally, a new analytical pipeline detected defects in mitochondrial translation upon depletion of the small subunit protein 35 (TgmS35), while other mitochondrial functions remain unaffected. Our work lays a foundation for the study of apicomplexan mitochondrial translation.

Systems Network Genomic Analysis Reveals Cardioprotective Effect of MURC/Cavin-4 Deletion Against Ischemia/Reperfusion Injury

Background

Ischemia/reperfusion (I/R) injury is a critical issue in the development of treatment strategies for ischemic heart disease. MURC (muscle‐restricted coiled‐coil protein)/Cavin‐4 (caveolae‐associated protein 4), which is a component of caveolae, is involved in the pathophysiology of dilated cardiomyopathy and cardiac hypertrophy. However, the role of MURC in cardiac I/R injury remains unknown.

Methods and Results

The systems network genomic analysis based on PC‐corr network inference on microarray data between wild‐type and MURC knockout mouse hearts predicted a network of discriminating genes associated with reactive oxygen species. To demonstrate the prediction, we analyzed I/R‐injured mouse hearts. MURC deletion decreased infarct size and preserved heart contraction with reactive oxygen species–related molecule EGR1 (early growth response protein 1) and DDIT4 (DNA‐damage‐inducible transcript 4) suppression in I/R‐injured hearts. Because PC‐corr network inference integrated with a protein–protein interaction network prediction also showed that MURC is involved in the apoptotic pathway, we confirmed the upregulation of STAT3 (signal transducer and activator of transcription 3) and BCL2 (B‐cell lymphoma 2) and the inactivation of caspase 3 in I/R‐injured hearts of MURC knockout mice compared with those of wild‐type mice. STAT3 inhibitor canceled the cardioprotective effect of MURC deletion in I/R‐injured hearts. In cardiomyocytes exposed to hydrogen peroxide, MURC overexpression promoted apoptosis and MURC knockdown inhibited apoptosis. STAT3 inhibitor canceled the antiapoptotic effect of MURC knockdown in cardiomyocytes.

Conclusions

Our findings, obtained by prediction from systems network genomic analysis followed by experimental validation, suggested that MURC modulates cardiac I/R injury through the regulation of reactive oxygen species–induced cell death and STAT3‐meditated antiapoptosis. Functional inhibition of MURC may be effective in reducing cardiac I/R injury.

Dystrophy-associated caveolin-3 mutations reveal that caveolae couple IL6/STAT3 signaling with mechanosensing in human muscle cells

Caveolin-3 is the major structural protein of caveolae in muscle. Mutations in the CAV3 gene cause different types of myopathies with altered membrane integrity and repair, expression of muscle proteins, and regulation of signaling pathways. We show here that myotubes from patients bearing the CAV3 P28L and R26Q mutations present a dramatic decrease of caveolae at the plasma membrane, resulting in abnormal response to mechanical stress. Mutant myotubes are unable to buffer the increase in membrane tension induced by mechanical stress. This results in impaired regulation of the IL6/STAT3 signaling pathway leading to its constitutive hyperactivation and increased expression of muscle genes. These defects are fully reversed by reassembling functional caveolae through expression of caveolin-3. Our study reveals that under mechanical stress the regulation of mechanoprotection by caveolae is directly coupled with the regulation of IL6/STAT3 signaling in muscle cells and that this regulation is absent in Cav3-associated dystrophic patients.

Caveolae are mechanosensors and mutations of their coat proteins are implicated in muscle disorders, but molecular mechanisms are unclear. Here, the authors show that caveolae can regulate IL6/STAT3 signaling in muscle cells under stress, and that dystrophy related Cav3 mutant myotubes have reduced caveolae and upregulated IL6 signaling.

SOCS and Herpesviruses, With Emphasis on Cytomegalovirus Retinitis

Suppressor of cytokine signaling (SOCS) proteins provide selective negative feedback to prevent pathogeneses caused by overstimulation of the immune system. Of the eight known SOCS proteins, SOCS1 and SOCS3 are the best studied, and systemic deletion of either gene causes early lethality in mice. Many viruses, including herpesviruses such as herpes simplex virus and cytomegalovirus, can manipulate expression of these host proteins, with overstimulation of SOCS1 and/or SOCS3 putatively facilitating viral evasion of immune surveillance, and SOCS suppression generally exacerbating immunopathogenesis. This is particularly poignant within the eye, which contains a diverse assortment of specialized cell types working together in a tightly controlled microenvironment of immune privilege. When the immune privilege of the ocular compartment fails, inflammation causing severe immunopathogenesis and permanent, sight-threatening damage may occur, as in the case of AIDS-related human cytomegalovirus (HCMV) retinitis. Herein we review how SOCS1 and SOCS3 impact the virologic, immunologic, and/or pathologic outcomes of herpesvirus infection with particular emphasis on retinitis caused by HCMV or its mouse model experimental counterpart, murine cytomegalovirus (MCMV). The accumulated data suggests that SOCS1 and/or SOCS3 can differentially affect the severity of viral diseases in a highly cell-type-specific manner, reflecting the diversity and complexity of herpesvirus infection and the ocular compartment.

Targeting SOCS Proteins to Control JAK-STAT Signalling in Disease

Defective regulation of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signalling pathway in cancers, haematological diseases, and chronic inflammatory conditions highlights its clinical significance. While several biologic and small molecule therapeutics targeting this pathway have been developed, these have several limitations. Therefore, there is a need to identify new targets for intervention. Suppressor of cytokine signalling (SOCS) proteins are a family of inducible inhibitors of cytokine receptors that activate the JAK-STAT pathway. Here we propose that newly identified mechanisms controlling SOCS function could be exploited to develop molecularly targeted drugs with unique modes of action to inhibit JAK-STAT signalling in disease.

Understanding SOCS protein specificity

The development and activity of our immune system are largely controlled by the action of pleiotropic cytokines and growth factors, small secreted proteins, which bind to receptors on the surface of immune cells to initiate an appropriate physiological response. Cytokine signalling is predominantly executed by intracellular proteins known as the Janus kinases (JAKs) and the signal transducers and activators of transcriptions (STATs). Although the 'nuts and bolts' of cytokine-activated pathways have been well established, the nuanced way in which distinct cellular outcomes are achieved and the precise molecular details of the proteins that regulate these pathways are still being elucidated. This is highlighted by the intricate role of the suppressor of cytokine signalling (SOCS) proteins. The SOCS proteins act as negative feedback inhibitors, dampening specific cytokine signals to prevent excessive cellular responses and returning the cell to a homeostatic state. A great deal of study has demonstrated their ability to inhibit these pathways at the receptor complex, either through direct inhibition of JAK activity or by targeting the receptor complex for proteasomal degradation. Detailed analysis of individual SOCS proteins is slowly revealing the complex and highly controlled manner by which they can achieve specificity for distinct substrates. However, for many of the SOCS, a level of detail is still lacking, including confident identification of the full suite of tyrosine phosphorylated targets of their SH2 domain. This review will highlight the general mechanisms which govern SOCS specificity of action and discuss the similarities and differences between selected SOCS proteins, focusing on CIS, SOCS1 and SOCS3. Because of the functional and sequence similarities within the SOCS family, we will also discuss the evidence for functional redundancy.