Isolation and characterization of the kininogen-binding protein p33 from endothelial cells. Identity with the gC1q receptor

Role of gC1qR as a modulator of endothelial cell permeability and contributor to post-stroke inflammation and edema formation

Ischemic stroke is a leading cause of death and disability worldwide. A serious risk of acute ischemic stroke (AIS) arises after the stroke event, due to inflammation and edema formation. Inflammation and edema in the brain are mediated by bradykinin, the formation of which is dependent upon a multi-ligand receptor protein called gC1qR. There are currently no preventive treatments for the secondary damage of AIS produced by inflammation and edema. This review aims to summarize recent research regarding the role of gC1qR in bradykinin formation, its role in inflammation and edema following ischemic injury, and potential therapeutic approaches to preventing post-stroke inflammation and edema formation.

Interaction of von Willebrand factor with blood cells in flow models: a systematic review

The presence of blood flow influences the interaction between von Willebrand factor (VWF) and blood cells, affecting characteristics of forming blood clots. The interactions between coagulation and inflammation have mainly been studied in thrombosis models, but it remains unclear whether these interactions might also play a role in reduced bleeding in patients with bleeding disorders. In this systematic review, we provide an overview of the literature investigating the interactions between VWF and blood cells in flow models. For article selection, a systematic search was performed in Embase, Medline-Ovid, Cochrane Library, Web of Science databases, and Google Scholar. After selection, 24 articles were included. These articles describe direct or platelet-dependent interactions between VWF and neutrophils, monocytes, erythrocytes, or lymphocytes under different flow conditions. Almost all the described interactions required the presence of activated platelets. Only erythrocytes, monocytes, and natural killer cells were capable of directly binding the VWF multimers. Overall, interactions between VWF and blood cells mainly occurred in the presence of platelets. Because of the large variation in study design and used flow rates, further research is necessary to compare the results between studies and draw firm conclusions on when and under what conditions these interactions can occur. After our findings, many questions remained unanswered. This review might provide a starting point for future research. Extended knowledge on the influence of blood flow on VWF and blood cell interactions can contribute to improved understanding of the variation in bleeding in patients with bleeding disorders.

An approach to p32/gC1qR/HABP1: a multifunctional protein with an essential role in cancer

P32/gC1qR/HABP1 is a doughnut-shaped acidic protein, highly conserved in eukaryote evolution and ubiquitous in the organism. Although its canonical subcellular localization is the mitochondria, p32 can also be found in the cytosol, nucleus, cytoplasmic membrane, and it can be secreted. Therefore, it is considered a multicompartmental protein. P32 can interact with many physiologically divergent ligands in each subcellular location and modulate their functions. The main ligands are C1q, hyaluronic acid, calreticulin, CD44, integrins, PKC, splicing factor ASF/SF2, and several microbial proteins. Among the functions in which p32 participates are mitochondrial metabolism and dynamics, apoptosis, splicing, immune response, inflammation, and modulates several cell signaling pathways. Notably, p32 is overexpressed in a significant number of epithelial tumors, where its expression level negatively correlates with patient survival. Several studies of gain and/or loss of function in cancer cells have demonstrated that p32 is a promoter of malignant hallmarks such as proliferation, cell survival, chemoresistance, angiogenesis, immunoregulation, migration, invasion, and metastasis. All of this strongly suggests that p32 is a potential diagnostic molecule and therapeutic target in cancer. Indeed, preclinical advances have been made in developing therapeutic strategies using p32 as a target. They include tumor homing peptides, monoclonal antibodies, an intracellular inhibitor, a p32 peptide vaccine, and p32 CAR T cells. These advances are promising and will allow soon to include p32 as part of targeted cancer therapies.

Baicalin Targets HSP70/90 to Regulate PKR/PI3K/AKT/eNOS Signaling Pathways

Baicalin is a major active ingredient of traditional Chinese medicine Scutellaria baicalensis, and has been shown to have antiviral, anti-inflammatory, and antitumor activities. However, the protein targets of baicalin have remained unclear. Herein, a chemical proteomics strategy was developed by combining baicalin-functionalized magnetic nanoparticles (BCL-N3@MNPs) and quantitative mass spectrometry to identify the target proteins of baicalin. Bioinformatics analysis with the use of Gene Ontology, STRING and Ingenuity Pathway Analysis, was performed to annotate the biological functions and the associated signaling pathways of the baicalin targeting proteins. Fourteen proteins in human embryonic kidney cells were identified to interact with baicalin with various binding affinities. Bioinformatics analysis revealed these proteins are mainly ATP-binding and/or ATPase activity proteins, such as CKB, HSP86, HSP70-1, HSP90, ATPSF1β and ACTG1, and highly associated with the regulation of the role of PKR in interferon induction and the antiviral response signaling pathway (P = 10-6), PI3K/AKT signaling pathway (P = 10-5) and eNOS signaling pathway (P = 10-4). The results show that baicalin exerts multiply pharmacological functions, such as antiviral, anti-inflammatory, antitumor, and antioxidant functions, through regulating the PKR and PI3K/AKT/eNOS signaling pathways by targeting ATP-binding and ATPase activity proteins. These findings provide a fundamental insight into further studies on the mechanism of action of baicalin.

Identification of the factor XII contact activation site enables sensitive coagulation diagnostics

Contact activation refers to the process of surface-induced activation of factor XII (FXII), which initiates blood coagulation and is captured by the activated partial thromboplastin time (aPTT) assay. Here, we show the mechanism and diagnostic implications of FXII contact activation. Screening of recombinant FXII mutants identified a continuous stretch of residues Gln317-Ser339 that was essential for FXII surface binding and activation, thrombin generation and coagulation. Peptides spanning these 23 residues competed with surface-induced FXII activation. Although FXII mutants lacking residues Gln317-Ser339 were susceptible to activation by plasmin and plasma kallikrein, they were ineffective in supporting arterial and venous thrombus formation in mice. Antibodies raised against the Gln317-Ser339 region induced FXII activation and triggered controllable contact activation in solution leading to thrombin generation by the intrinsic pathway of coagulation. The antibody-activated aPTT allows for standardization of particulate aPTT reagents and for sensitive monitoring of coagulation factors VIII, IX, XI.

SLE: Novel Postulates for Therapeutic Options

Genetic deficiency in C1q is a strong susceptibility factor for systemic lupus erythematosus (SLE). There are two major hypotheses that potentially explain the role of C1q in SLE. The first postulates that C1q deficiency abrogates apoptotic cell clearance, leading to persistently high loads of potentially immunogenic self-antigens that trigger autoimmune responses. While C1q undoubtedly plays an important role in apoptotic clearance, an essential biological process such as removal of self- waste is so critical for host survival that multiple ligand-receptor combinations do fortunately exist to ensure that proper disposal of apoptotic debris is accomplished even in the absence of C1q. The second hypothesis is based on the observation that locally synthesized C1q plays a critical role in regulating the earliest stages of monocyte to dendritic cell (DC) differentiation and function. Indeed, circulating C1q has been shown to keep monocytes in a pre-dendritic state by silencing key molecular players and ensuring that unwarranted DC-driven immune responses do not occur. Monocytes are also able to display macromolecular C1 on their surface, representing a novel mechanism for the recognition of circulating "danger." Translation of this danger signal in turn, provides the requisite "license" to trigger a differentiation pathway that leads to adaptive immune response. Based on this evidence, the second hypothesis proposes that deficiency in C1q dysregulates monocyte-to-DC differentiation and causes inefficient or defective maintenance of self-tolerance. The fact that C1q receptors (cC1qR and gC1qR) are also expressed on the surface of both monocytes and DCs, suggests that C1q/C1qR may regulate DC differentiation and function through specific cell-signaling pathways. While their primary ligand is C1q, C1qRs can also independently recognize a vast array of plasma proteins as well as pathogen-associated molecular ligands, indicating that these molecules may collaborate in antigen recognition and processing, and thus regulate DC-differentiation. This review will therefore focus on the role of C1q and C1qRs in SLE and explore the gC1qR/C1q axis as a potential target for therapy.

The C1q Receptors: Focus on gC1qR/p33 (C1qBP, p32, HABP-1)1

In the past several years, a number of C1q binding surface proteins or receptors have been described. This is not of course surprising considering the complexity of the C1q molecule and its ability to bind to a wide range of cellular and plasma proteins via both its collagen-like [cC1q] region and its heterotrimeric globular heads [gC1q] each of which in turn is capable of binding a specific ligand. However, while each of these "receptor" molecules undoubtedly plays a specific function within its restricted microenvironment, and therefore merits full attention, this review nonetheless, will singularly focus on the structure and function of gC1qR-a multi-functional and multi-compartmental protein, which plays an important role in inflammation, infection, and cancer. Although first identified as a receptor for C1q, gC1qR has been shown to bind to a plethora of proteins found in plasma, on the cell surface and on pathogenic microorganisms. The plasma proteins that bind to gC1qR are mostly blood coagulation proteins and include high molecular weight kininogen [HK], Factor XII [Hageman factor], fibrinogen, thrombin [FII], and multimeric vitronectin. This suggests that gC1qR can play an important role in modulating not only of fibrin formation, particularly at local sites of immune injury and/or inflammation, but by activating the kinin/kallikrein system, it is also able to generate, bradykinin, a powerful vasoactive peptide that is largely responsible for the swelling seen in angioedema. Another important function of gC1qR is in cancer, where it has been shown to play a role in tumor cell survival, growth and metastatic invasion by interacting with critical molecules in the tumor cell microenvironment including those of the complement system and kinin system. Finally, by virtue of its ability to interact with a growing list of pathogen-associated molecules, including bacterial and viral ligands, gC1qR is becoming recognized as an important pathogen recognition receptor [PRR]. Given the numerous roles it plays in a growing list of disease settings, gC1qR has now become a potential target for the development of monoclonal antibody-based and/or small molecule-based therapies.

p32 is a negative regulator of p53 tetramerization and transactivation

p53 is a sequence-specific transcription factor, and proper regulation of p53 transcriptional activity is critical for orchestrating different tumor-suppressive mechanisms. p32 is a multifunctional protein which interacts with a large number of viral proteins and transcription factors. Here, we investigate the effect of p32 on p53 transactivation and identify a novel mechanism by which p32 alters the functional characteristics of p53. Specifically, p32 attenuates p53-dependent transcription through impairment of p53 binding to its response elements on target genes. Upon p32 expression, p53 levels bound at target genes are decreased, and p53 target genes are inactivated, strongly indicating that p32 restricts p53 occupancy and function at target genes. The primary mechanism contributing to the observed action of p32 is the ability of p32 to interact with the p53 tetramerization domain and to block p53 tetramerization, which in turn enhances nuclear export and degradation of p53, leading to defective p53 transactivation. Collectively, these data establish p32 as a negative regulator of p53 function and suggest the therapeutic potential of targeting p32 for cancer treatment.

Systematic Multiomics Analysis of Alterations in C1QBP mRNA Expression and Relevance for Clinical Outcomes in Cancers

C1QBP (Complement Component 1 Q Subcomponent-Binding Protein), a multicompartmental protein, participates in various cellular processes, including mRNA splicing, ribosome biogenesis, protein synthesis in mitochondria, apoptosis, transcriptional regulation, and infection processes of viruses. The correlation of C1QBP expression with patient survival and molecular function of C1QBP in relation to cancer progression has not been comprehensively studied. Therefore, we sought to systematically investigate the expression of C1QBP to evaluate the change of C1QBP expression and the relationship with patient survival and affected pathways in breast, lung, colon, and bladder cancers as well as lymphoma. Relative expression levels of C1QBP were analyzed using the Oncomine, Gene Expression Across Normal and Tumor Tissue (GENT), and The Cancer Genome Atlas (TCGA) databases. Mutations and copy number alterations in C1QBP were also analyzed using cBioPortal, and subsequently, the relationship between C1QBP expression and survival probability of cancer patients was explored using the PrognoScan database and the R2: Kaplan Meier Scanner. Additionally, the relative expression of C1QBP in other cancers, and correlation of C1QBP expression with patient survival were investigated. Gene ontology and pathway analysis of commonly differentially coexpressed genes with C1QBP in breast, lung, colon, and bladder cancers as well as lymphoma revealed the C1QBP-correlated pathways in these cancers. This data-driven study demonstrates the correlation of C1QBP expression with patient survival and identifies possible C1QBP-involved pathways, which may serve as targets of a novel therapeutic modality for various human cancers.

Cell Receptor and Cofactor Interactions of the Contact Activation System and Factor XI

The contact activation system (CAS) or contact pathway is central to the crosstalk between coagulation and inflammation and contributes to diverse disorders affecting the cardiovascular system. CAS initiation contributes to thrombosis but is not required for hemostasis and can trigger plasma coagulation via the intrinsic pathway [through factor XI (FXI)] and inflammation via bradykinin release. Activation of factor XII (FXII) is the principal starting point for the cascade of proteolytic cleavages involving FXI, prekallikrein (PK), and cofactor high molecular weight kininogen (HK) but the precise location and cell receptor interactions controlling these reactions remains unclear. FXII, PK, FXI, and HK utilize key protein domains to mediate binding interactions to cognate cell receptors and diverse ligands, which regulates protease activation. The assembly of contact factors has been demonstrated on the cell membranes of a variety of cell types and microorganisms. The cooperation between the contact factors and endothelial cells, platelets, and leukocytes contributes to pathways driving thrombosis yet the basis of these interactions and the relationship with activation of the contact factors remains undefined. This review focuses on cell receptor interactions of contact proteins and FXI to develop a cell-based model for the regulation of contact activation.

Globular C1q receptor (p33) binds and stabilizes pro-inflammatory MCP-1: a novel mechanism for regulation of MCP-1 production and function

The protein gC1qR (globular C1q receptor), also named p33, was originally identified as a binding partner of the globular heads of C1q in the complement system. gC1qR/p33 is abundantly expressed in many cell types, but the functional importance of this protein is not completely understood. Here, we investigate the impact of gC1qR/p33 on the production and function of the pathophysiologically important chemokine monocyte chemoattractant protein-1 (MCP-1) and the underlying molecular mechanisms. Knockdown of gC1qR/p33 negatively regulated the production of MCP-1, but had no effect on the expression of transcript for MCP-1 in human periodontal ligament cells, suggesting a translational/post-translational mechanism of action. Laser scanning confocal microscopy showed considerable cytosolic co-localization of gC1qR/p33 and MCP-1, and co-immunoprecipitation disclosed direct physical interaction between gC1qR/p33 and MCP-1. Surface plasmon resonance analysis revealed a high-affinity binding (K_D = 10.9 nM) between gC1qR/p33 and MCP-1. Using a transwell migration assay, we found that recombinant gC1qR/p33 enhances MCP-1-induced migration of human THP-1 monocytes, pointing to a functional importance of the interaction between gC1qR/p33 and MCP-1. An in vitro assay revealed a rapid turnover of the MCP-1 protein and that gC1qR/p33 stabilizes MCP-1, hence preventing its degradation. We propose that endogenous gC1qR/p33 physically interacts with MCP-1 causing stabilization of the MCP-1 protein and stimulation of its activity in human periodontal ligament cells, suggesting a novel gC1qR/p33-mediated pro-inflammatory mechanism of action.

Haemostasis and innate immunity - a complementary relationship: A review of the intricate relationship between coagulation and complement pathways

Coagulation and innate immunity are linked evolutionary processes that orchestrate the host defence against invading pathogens and injury. The complement system is integral to innate immunity and shares numerous interactions with components of the haemostatic pathway, helping to maintain physiological equilibrium. The term 'immunothrombosis' was introduced in 2013 to embrace this process, and has become an area of much recent interest. What is less apparent in the literature however is an appreciation of the clinical manifestations of the coagulation-complement interaction and the consequences of dysregulation of either system, as seen in many inflammatory and thrombotic disease states, such as sepsis, trauma, atherosclerosis, antiphospholipid syndrome (APS), paroxysmal nocturnal haemoglobinuria (PNH) and some thrombotic microangiopathies to name a few. The growing appreciation of this immunothrombotic phenomenon will foster the drive for novel therapies in these disease states, including anticoagulants as immunomodulators and targeted molecular therapies.

Immunoregulation of Neutrophil Extracellular Trap Formation by Endothelial-Derived p33 (gC1q Receptor)

The formation of neutrophil extracellular traps (NETs) is a host defence mechanism, known to facilitate the entrapment and growth inhibition of many bacterial pathogens. It has been implicated that the translocation of myeloperoxidase (MPO) from neutrophilic granules to the nucleus is crucial to this process. Under disease conditions, however, excessive NET formation can trigger self-destructive complications by releasing pathologic levels of danger-associated molecular pattern molecules (DAMPs). To counteract such devastating immune reactions, the host has to rely on precautions that help circumvent these deleterious effects. Though the induction of DAMP responses has been intensively studied, the mechanisms that are used by the host to down-regulate them are still not understood. In this study, we show that p33 is an endothelial-derived protein that has the ability to annul NET formation. We found that the expression of human p33 is up-regulated in endothelial cells upon infections with Streptococcus pyogenes bacteria. Using tissue biopsies from a patient with streptococcal necrotising fasciitis, we monitored co-localisation of p33 with MPO. Further in vitro studies revealed that p33 is able to block the formation of DAMP-induced NET formation by inhibiting the enzymatic activity of MPO. Additionally, mice challenged with S. pyogenes bacteria demonstrated diminished MPO activity when treated with p33. Together, our results demonstrate that host-derived p33 has an important immunomodulating function that helps to counterbalance an overwhelming DAMP response.

Factor XII-Driven Inflammatory Reactions with Implications for Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction. It is triggered by the release of pro-inflammatory cytokines and mediators from mast cells and basophils in response to immunologic or non-immunologic mechanisms. Mediators that are released upon mast cell activation include the highly sulfated polysaccharide and inorganic polymer heparin and polyphosphate (polyP), respectively. Heparin and polyP supply a negative surface for factor XII (FXII) activation, a serine protease that drives contact system-mediated coagulation and inflammation. Activation of the FXII substrate plasma kallikrein leads to further activation of zymogen FXII and triggers the pro-inflammatory kallikrein-kinin system that results in the release of the mediator bradykinin (BK). The severity of anaphylaxis is correlated with the intensity of contact system activation, the magnitude of mast cell activation, and BK formation. The main inhibitor of the complement system, C1 esterase inhibitor, potently interferes with FXII activity, indicating a meaningful cross-link between complement and kallikrein-kinin systems. Deficiency in a functional C1 esterase inhibitor leads to a severe swelling disorder called hereditary angioedema (HAE). The significance of FXII in these disorders highlights the importance of studying how these processes are integrated and can be therapeutically targeted. In this review, we focus on how FXII integrates with inflammation and the complement system to cause anaphylaxis and HAE as well as highlight current diagnosis and treatments of BK-related diseases.

G Protein-Coupled Kinin Receptors and Immunity Against Pathogens

For decades, immunologists have considered the complement system as a paradigm of a proteolytic cascade that, acting cooperatively with the immune system, enhances host defense against infectious organisms. In recent years, advances made in thrombosis research disclosed a functional link between activated neutrophils, monocytes, and platelet-driven thrombogenesis. Forging a physical barrier, the fibrin scaffolds generated by synergism between the extrinsic and intrinsic (contact) pathways of coagulation entrap microbes within microvessels, limiting the systemic spread of infection while enhancing the clearance of pathogens by activated leukocytes. Insight from mice models of thrombosis linked fibrin formation via the intrinsic pathway to the autoactivation of factor XII (FXII) by negatively charged "contact" substances, such as platelet-derived polyphosphates and DNA from neutrophil extracellular traps. Following cleavage by FXIIa, activated plasma kallikrein (PK) initiates inflammation by liberating the nonapeptide bradykinin (BK) from an internal domain of high molecular weight kininogen (HK). Acting as a paracrine mediator, BK induces vasodilation and increases microvascular permeability via activation of endothelial B2R, a constitutively expressed subtype of kinin receptor. During infection, neutrophil-driven extravasation of plasma fuels inflammation via extravascular activation of the kallikrein-kinin system (KKS). Whether liberated by plasma-borne PK, tissue kallikrein, and/or microbial-derived proteases, the short-lived kinins activate immature dendritic cells via B2R, thus linking the infection-associated innate immunity/inflammation to the adaptive arm of immunity. As inflammation persists, a GPI-linked carboxypeptidase M removes the C-terminal arginine from the primary kinin, converting the B2R agonist into a high-affinity ligand for B1R, a GPCR subtype that is transcriptionally upregulated in injured/inflamed tissues. As reviewed here, lessons taken from studies of kinin receptor function in experimental infections have shed light on the complex proteolytic circuits that, acting at the endothelial interface, reciprocally couple immunity to the proinflammatory KKS.

The complement and contact activation systems: partnership in pathogenesis beyond angioedema

The blood plasma contains four biologically important proteolytic cascades, which probably evolved from the same ancestral gene. This in part may explain why each cascade has very similar "initiating trigger" followed by sequential and cascade-like downstream enzymatic activation pattern. The four cascades are: the complement system, the blood clotting cascade, the fibrinolytic system, and the kallikrein-kinin system. Although much has been written about the interplay between all these enzymatic cascades, the cross-talk between the complement and the kinin generating systems has become particularly relevant as this interaction results in the generation of nascent molecules that have significant impact in various inflammatory diseases including angioedema and cancer. In this review, we will focus on the consequences of the interplay between the two systems by highlighting the role of a novel molecular link called gC1qR. Although this protein was first identified as a receptor for C1q, it is now recognized as a multiligand binding cellular protein, which serves not only as C1q receptor, but also as high affinity (K_D  ≤ 0.8 nM) binding site for both high molecular weight kininogen (HK) and factor XII (FXII). At inflammatory sites, where atherogenic factors such as immune complexes and/or pathogens can activate the endothelial cell into a procoagulant and proinflammatory surface, the two pathways are activated to generate vasoactive peptides that contribute in various ways to the inflammatory processes associated with numerous diseases. More importantly, since recent observations strongly suggest an important role for both pathways in cancer, we will focus on how a growing tumor cluster can employ the byproducts derived from the two activation systems to ensure not only its survival and growth, but also its escape into distal sites of colonization.

HAE Pathophysiology and Underlying Mechanisms

Remarkable progress in understanding the pathophysiology and underlying mechanisms of hereditary angioedema has led to the development of effective treatment for this disorder. Progress in three separate areas has catalyzed our understanding of hereditary angioedema. The first is the recognition that HAE type I and type II result from a deficiency in the plasma level of functional C1 inhibitor. This observation has led to a detailed understanding of the SERPING1 mutations responsible for this deficiency as well as the molecular regulation of C1 inhibitor expression and function. The second is that the fundamental cause of swelling is enhanced contact system activation leading to increased generation of bradykinin. Substantial progress has been made in defining the parameters regulating bradykinin generation and catabolism as well as the receptors that transduce the biologic effects of kinins. The third is the understanding that tissue swelling in hereditary angioedema primarily involves the function of endothelial cell adherens junctions. This knowledge is driving increased attention to the role of endothelial biology in determining disease activity in hereditary angioedema. While there has been considerable progress made, large gaps still remain in our knowledge. Important areas that remain poorly understood include the factors that lead to very low plasma functional C1 inhibitor levels, the triggers of contact system activation in hereditary angioedema, and the role of the bradykinin B1 receptor. The phenotypic variability of hereditary angioedema has been extensively documented but never understood. The mechanisms discussed in this chapter likely contribute to this variability. Future progress in understanding these mechanisms should provide new means to improve the diagnosis and treatment of hereditary angioedema.

Review: The plasma kallikrein/kinin and renin angiotensin systems in blood pressure regulation in sepsis

The hemodynamics of septic shock after endotoxinemiai s influenced by the plasma kallikrein/kinin and the renin angiotensin systems. In recent years, new information has improved understanding of the protein/biologically active peptide interactions between these two systems. The plasma kallikrein/kinin system, more commonly known as the contact system, has undergone a re-evaluation as to how it assembles on cell membranes for physiological and pathophysiological activation and as to its role in Gram-negative sepsis. It has been proposed that it counterbalances the plasma renin angiotensin system. Furthermore, more knowledge about the renin angiotensin system has become available on how it either opposes the actions of the kallikrein/kinin system or, in some cases, summates with it. Understanding the interactions between these two systems may lead to development of better pharmacological treatments for endotoxin-induced shock.

Novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis

Previous studies have demonstrated that cleaved high-molecular-weight kininogen (HKa) induces endothelial apoptosis and inhibits angiogenesis and have suggested that this occurs through inhibition of Src family kinases. This study assessed the role of tyrosine-protein kinase Lck (p56/Lck) in this pathway. We analyzed early events leading to apoptosis of human endothelial cells exposed to HKa. The role of p56/Lck was investigated using short interfering (si) RNA knockdown and lentivirus expression in assays of endothelial tube formation, sprouting of neovessels from murine aorta, and angiogenesis in Matrigel plugs. HKa stimulated expression and phosphorylation of p56/Lck. siRNA knockdown of p56/Lck promoted endothelial proliferation and blocked HKa-induced apoptosis and activation of p53, Bax, and Bak. Lentivirus expression of p56/Lck in endothelial cells induced apoptosis and blocked tube formation. Expression of p56/Lck in murine aortic rings blocked sprouting angiogenesis. Lentivirus expressing p56/Lck blocked angiogenesis in Matrigel plugs, while p56/Lck short hairpin RNA inhibited the antiangiogenic effect of HKa. Scrambled siRNAs and empty lentiviral vectors were used in all experiments. Apoptosis of proliferating endothelial cells and inhibition of angiogenesis by HKa requires p56/Lck. This suggests a novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis.-Betapudi, V., Shukla, M., Alluri, R., Merkulov, S., McCrae, K. R. Novel role for p56/Lck in regulation of endothelial cell survival and angiogenesis.

The role of complement activation in thrombosis and hemolytic anemias

OBJECTIVE

The objective of this study was to describe complement activation in hemostatic and pathologic states of coagulation and in the acquired and congenital hemolytic anemias.

METHODS AND RESULTS

We review published and emerging data on the involvement of the classic, alternative and lectin-based complement pathways in coagulation and the hemolytic anemias. The alternative pathway in particular is always "on," at low levels, and is particularly sensitive to hyper-activation in a variety of physiologic and pathologic states including infection, autoimmune disorders, thrombosis and pregnancy, requiring tight control predicated on a variety of soluble and membrane bound regulatory proteins. In acquired hemolytic anemias such as paroxysmal nocturnal hemoglobinuria (PNH) and cold agglutinin disease (CAD), the complement system directly induces red blood cell injury, resulting in intravascular and extravascular hemolysis. In congenital hemolytic anemias such as sickle cell disease and β-thalassemia, the complement system may also contribute to thrombosis and vascular disease. Complement activation may also lead to a storage lesion in red blood cells prior to transfusion.

CONCLUSION

Complement pathways are activated in hemolytic anemias and are closely linked with thrombosis. In acquired disorders such as PNH and possibly CAD, inhibition of the alternative complement pathway improves clinical outcomes and reduces thrombosis risk. Whether complement inhibition has a similar role in congenital hemolytic anemias apart from the atypical hemolytic-uremic (aHUS)-type thrombotic microangiopathies remains to be determined.

Analysis of the Interaction between Globular Head Modules of Human C1q and Its Candidate Receptor gC1qR

The heterotrimeric globular head (gC1q) domain of human C1q is made up of the C-terminal ends of the three individual chains, ghA, ghB, and ghC. A candidate receptor for the gC1q domain is a multi-functional pattern recognition protein, gC1qR. Since understanding of gC1qR and gC1q interaction could provide an insight into the pleiotropic functions of gC1qR, this study was undertaken to identify the gC1qR-binding site on the gC1q domain, using the recombinant ghA, ghB, and ghC modules and their substitution mutants. Our results show that ghA, ghB, and ghC modules can interact with gC1qR independently, thus reinforcing the notion of modularity within the gC1q domain of human C1q. Mutational analysis revealed that while Arg162 in the ghA module is central to interaction between gC1qR and C1q, a single amino acid substitution (arginine to glutamate) in residue 114 of the ghB module resulted in enhanced binding. Expression of gC1qR and C1q in adherent monocytes with or without pro-inflammatory stimuli was also analyzed by qPCR; it showed an autocrine/paracrine basis of C1q and gC1qR interaction. Microscopic studies revealed that C1q and gC1qR are colocalized on PBMCs. Cell proliferation assays indicated that ghA, ghB, and ghC modules were able to attenuate phytohemagglutinin-stimulated proliferation of PBMCs. Addition of gC1qR had an additive effect on the anti-proliferative effect of globular head modules. In summary, our results identify residues involved in C1q-gC1qR interaction and explain, to a certain level, their involvement on the immune cell surface, which is relevant for C1q-induced functions including inflammation, infection, and immunity.

LL-37-induced host cell cytotoxicity depends on cellular expression of the globular C1q receptor (p33)

It is unclear how human host cells cope with cytotoxic effects caused by the host-defence peptide (HDP) LL-37. Our findings show that LL-37-induced cytotoxicity is counteracted by intracellular p33, suggesting that p33 protects against deleterious activities of the innate immune system.

[Kallikrein-Kinin System. Long History and Present. (To 90th Anniversary of Discovery of the System)]

The kallikrein-kinin system (KKS) is the key proteolytic system participating in control of a wide spectrum of physiological functions and the development of many pathological conditions. This explains great interest in structures, functions and molecular biology of separate components of the system, molecular mechanisms of their interaction and relationship with other regulatory systems. The information in this field for the last two decades clarifies the role of KKS in morphogenesis of cells, regulation of smooth muscular contractility of some organs, decrease of blood pressure, increase of vascular permeability, the development of inflammation, transformation of cells and the other functions of both physiological and pathological processes. Essential progress in understanding of functions KKS was made by the discovery and study of bradykinin receptors, cloning of kininogen and kallikrein encoding genes, revealing of domain structure of kininogen, prekallikrein and some kininases and decoding of mechanisms of contact phase of proteolytic system activation in blood plasma.

Soluble gC1qR in Blood and Body Fluids: Examination in a Pancreatic Cancer Patient Cohort

BACKGROUND

gC1qR is a multifunctional cellular protein that has been linked to inflammation and cancer. gC1qR is highly upregulated in adenocarcinomas as compared to normal tissue counterparts, and soluble gC1qR (sgC1qR) has been detected in vitro in the pericellular milieu of proliferating malignant cells.

AIM

The present study explored the tissue expression of gC1qR in pancreatic cancer by immunohistochemistry, and the presence of sgC1qR in vivo, by examining blood and malignant effusions from patients with metastatic pancreatic adenocarcinoma.

METHODS

Tissue expression of gC1qR by pancreatic adenocarcinoma was visualized by immunohistochemistry. SgC1qR was quantified in serum from healthy volunteers (n=20) and pancreatic cancer patients (n=34), as well as in malignant pleural (n=23) and peritoneal effusions (n=27), using a newly developed, sensitive immunocapture sandwich ELISA.

RESULTS

Overexpression of gC1qR was confirmed in pancreatic adenocarcinoma compared to nonmalignant pancreatic tissue. Moreover, increased serum levels of sgC1qR (0.29 ± 0.22 ng/ml) were noted in patients with metastatic pancreatic cancer compared to healthy controls (0.15 ± 0.10 ng/ml) (mean ± S.D.) (p=0.035). In 11 of 16 patients for whom sequential samples were available, serum sgC1qR levels rose with disease progression, and paralleled changes in tumor biomarkers, CEA and CA19.9. In addition to blood, sgC1qR was detected in malignant pleural (0.55 ± 0.47 ng/ml) and peritoneal effusions (0.57 ± 0.38 ng/ml).

CONCLUSION

This study provides the first evidence for the presence of sgC1qR in vivo. The ability to detect sgC1qR in blood and body fluids will enable further studies to elucidate its pathophysiology in malignancy.

Human endogenous peptide p33 inhibits detrimental effects of LL-37 on osteoblast viability

BACKGROUND AND OBJECTIVE

High levels of the antimicrobial peptide, LL-37, are detected in gingival crevicular fluid from patients with chronic periodontitis. LL-37 not only shows antimicrobial activity but also affects host-cell viability. The objective of the present study was to identify endogenous mechanisms that antagonize the detrimental effects of LL-37 on osteoblast viability, focusing on the human peptide p33 expressed on the surface of various cell types.

MATERIAL AND METHODS

Human osteoblast-like MG63 cells and human hFOB1.19 osteoblasts were treated with or without LL-37 in the presence or absence of p33. Recombinant human p33 was expressed in an Escherichia coli expression system. Lactate dehydrogenase (LDH) was assessed using an enzymatic spectrophotometric assay. DNA synthesis was determined by measuring [(3) H]-thymidine incorporation. Cell number was assessed by counting cells in a Bürker chamber. Intracellular Ca(2+) was monitored by recording Fluo 4-AM fluorescence using a laser scanning confocal microscope. Cellular expression of p33 was determined by western blotting.

RESULTS

LL-37 caused a concentration-dependent release of LDH from human osteoblasts, showing a half-maximal response value (EC50 ) of 4 μm and a rapid and sustained rise in the intracellular Ca(2+) concentration of osteoblasts, suggesting that LL-37 forms pores in the cell membrane. p33 (10 μm) inhibited the LL-37-induced LDH release and LL-37-evoked rise in intracellular Ca(2+) concentration, suggesting that p33 prevents LL-37-induced permeabilization of the cell membrane. Moreover, p33 blocked LL-37-induced attenuation of osteoblast numbers. Also, mucin antagonized, at concentrations representative for nonstimulated whole saliva, LL-37-evoked LDH release, whilst cationic endogenous polyamines had no impact on LL-37-induced LDH release from osteoblasts.

CONCLUSIONS

The endogenous peptide p33 prevents LL-37-induced reduction of human osteoblast viability. Importantly, this mechanism may protect the osteoblasts from LL-37-induced cell damage in patients suffering from chronic periodontitis associated with high levels of LL-37 locally.

Soluble gC1qR is an autocrine signal that induces B1R expression on endothelial cells

Bradykinin (BK) is one of the most potent vasodilator agonists known and belongs to the kinin family of proinflammatory peptides. BK induces its activity via two G protein-coupled receptors: BK receptor 1 (B1R) and BK receptor 2. Although BK receptor 2 is constitutively expressed on endothelial cells (ECs), B1R is induced by IL-1β. The C1q receptor, receptor for the globular heads of C1q (gC1qR), which plays a role in BK generation, is expressed on activated ECs and is also secreted as soluble gC1qR (sgC1qR). Because sgC1qR can bind to ECs, we hypothesized that it may also serve as an autocrine/paracrine signal for the induction of B1R expression. In this study, we show that gC1qR binds to ECs via a highly conserved domain consisting of residues 174-180, as assessed by solid-phase binding assay and deconvolution fluorescence microscopy. Incubation of ECs (24 h, 37 °C) with sgC1qR resulted in enhancement of B1R expression, whereas incubation with gC1qR lacking aa 174-180 and 154-162 had a diminished effect. Binding of sgC1qR to ECs was through surface-bound fibrinogen and was inhibited by anti-fibrinogen. In summary, our data suggest that, at sites of inflammation, sgC1qR can enhance vascular permeability by upregulation of B1R expression through de novo synthesis, as well as rapid translocation of preformed B1R.

Role of the B1 bradykinin receptor and gC1qR/p33 in angioedema

Patients affected by angioedema (AE) are subject to asymmetric, nonerythematous, nonpruritic, localized, transient, episodic swelling of deeper layers or submucosal tissues of the skin, oropharyngolaryngeal tissue, and/or gastrointestinal wall. The nonapeptide bradykinin (BK) may be largely responsible for the vascular permeability seen in most AE. During AE attacks, activation of the serine proteases leads to the release of BK. Enzymes expressed on the endothelial cell membrane can metabolize BK, producing the agonist of the B1R, which can then be upregulated by proinflammatory stimuli, suggesting that the blockade of B1R and B2R, or gC1q/p33, may provide novel therapeutic targets.

Crosstalk of the plasma contact system with bacteria

Activation of the plasma contact system triggers several cascade systems such as the kallikrein-kinin system, the intrinsic pathway of coagulation, the classical complement cascade and the fibrinolytic system. Recent studies have shown a critical role of the contact system for arterial and venous thrombus formation and thromboembolic disease. In contrast, the function of the contact system for host-defense reactions and its physiological functions have remained enigmatic. Experimental animal studies and clinical data have linked the contact system to bacterial infections with implications for sepsis disease. The present review summarizes the role of the contact system and its activation for bacterial infections.

Inhibition of Rho and Rac geranylgeranylation by atorvastatin is critical for preservation of endothelial junction integrity

Background

Small GTPases (guanosine triphosphate, GTP) are involved in many critical cellular processes, including inflammation, proliferation, and migration. GTP loading and isoprenylation are two important post-translational modifications of small GTPases, and are critical for their normal function. In this study, we investigated the role of post-translational modifications of small GTPases in regulating endothelial cell inflammatory responses and junctional integrity.

Methods and Results

Confluent human umbilical vein endothelial cell (HUVECs ) treated with atorvastatin demonstrated significantly decreased lipopolysaccharide (LPS)-mediated IL-6 and IL-8 generation. The inhibitory effect of atorvastatin (Atorva) was attenuated by co-treatment with 100 µM mevalonate (MVA) or 10 µM geranylgeranyl pyrophosphate (GGPP), but not by 10 µM farnesyl pyrophosphate (FPP). Atorvastatin treatment of HUVECs produced a time-dependent increase in GTP loading of all Rho GTPases, and induced the translocation of small Rho GTPases from the cellular membrane to the cytosol, which was reversed by 100 µM MVA and 10 µM GGPP, but not by 10 µM FPP. Atorvastatin significantly attenuated thrombin-induced HUVECs permeability, increased VE-cadherin targeting to cell junctions, and preserved junction integrity. These effects were partially reversed by GGPP but not by FPP, indicating that geranylgeranylation of small GTPases plays a major role in regulating endothelial junction integrity. Silencing of small GTPases showed that Rho and Rac, but not Cdc42, play central role in HUVECs junction integrity.

Conclusions

In conclusion, our studies show that post-translational modification of small GTPases plays a vital role in regulating endothelial inflammatory response and endothelial junction integrity. Atorvastatin increased GTP loading and inhibited isoprenylation of small GTPases, accompanied by reduced inflammatory response and preserved cellular junction integrity.

gC1qR expression in normal and pathologic human tissues: differential expression in tissues of epithelial and mesenchymal origin

The gC1qR (i.e., gC1q receptor, gC1q binding protein, p32, p33) is a multifunctional cellular protein that interacts with components of the complement, kinin, and coagulation cascades and select microbial pathogens. Enhanced gC1qR expression has been reported in adenocarcinomas arising in a variety of organs. The present study compared gC1qR expression in normal, inflammatory, dysplastic, and malignant tissue of epithelial and mesenchymal origin. gC1qR expression was visualized in tissue sections by immunohistochemistry using the 60.11 monoclonal antibody (i.e., IgG(1) mouse monoclonal antibody directed against gC1qR) and the UltraVision LP Detection System. Sections were counterstained with hematoxylin and examined by light microscopy. Strongest gC1qR expression was noted in epithelial tumors of breast, prostate, liver, lung, and colon, as well as in squamous and basal cell carcinoma of the skin. However, increased gC1qR staining was appreciated also in inflammatory and proliferative lesions of the same cell types, as well as in normal continuously dividing cells. In contrast, tumors of mesenchymal origin generally stained weakly, with the exception of osteoblasts, which stained in both benign and malignant tissues. The data suggest that increased gC1qR expression may be a marker of benign and pathologic cell proliferation, particularly in cells of epithelial origin, with potential diagnostic and therapeutic applications.

DC-SIGN, C1q, and gC1qR form a trimolecular receptor complex on the surface of monocyte-derived immature dendritic cells

C1q modulates the differentiation and function of cells committed to the monocyte-derived dendritic cell (DC) lineage. Because the 2 C1q receptors found on the DC surface-gC1qR and cC1qR-lack a direct conduit into intracellular elements, we postulated that the receptors must form complexes with transmembrane partners. In the present study, we show that DC-SIGN, a C-type lectin expressed on DCs, binds directly to C1q, as assessed by ELISA, flow cytometry, and immunoprecipitation experiments. Surface plasmon resonance analysis revealed that the interaction was specific, and both intact C1q and the globular portion of C1q bound to DC-SIGN. Whereas IgG reduced this binding significantly, the Arg residues (162-163) of the C1q-A chain, which are thought to contribute to the C1q-IgG interaction, were not required for C1q binding to DC-SIGN. Binding was reduced significantly in the absence of Ca(2+) and by preincubation of DC-SIGN with mannan, suggesting that C1q binds to DC-SIGN at its principal Ca(2+)-binding pocket, which has increased affinity for mannose residues. Antigen-capture ELISA and immunofluorescence microscopy revealed that C1q and gC1qR associate with DC-SIGN on blood DC precursors and immature DCs. The results of the present study suggest that C1q/gC1qR may regulate DC differentiation and function through the DC-SIGN-mediated induction of cell-signaling pathways.

Binding of cellular p32 protein to the rubella virus P150 replicase protein via PxxPxR motifs

A proline-rich region (PRR) within the rubella virus (RUBV) P150 replicase protein that contains three SH3 domain-binding motifs (PxxPxR) was investigated for its ability to bind cell proteins. Pull-down experiments using a glutathione S-transferase-PRR fusion revealed PxxPxR motif-specific binding with human p32 protein (gC1qR), which could be mediated by either of the first two motifs. This finding was of interest because p32 protein also binds to the RUBV capsid protein. Binding of p32 to P150 was confirmed and was abolished by mutation of the first two motifs. When mutations in the first two motifs were introduced into a RUBV cDNA infectious clone, virus replication was significantly impaired. However, virus RNA synthesis was found to be unaffected, and subsequent immunofluorescence analysis of RUBV-infected cells revealed co-localization of p32 and P150 but little overlap of p32 with RNA replication complexes, indicating that p32 does not participate directly in virus RNA synthesis. Thus, the role of p32 in RUBV replication remains unresolved.

The many faces of the contact pathway and their role in thrombosis

Understanding inherent differences between thrombosis and hemostasis in the vascular system are critical to developing safe and effective anticoagulants. To this end, constituents of the contact activated and intrinsic pathway of coagulation appear to be involved in pathological thrombus formation, but are not required for normal hemostasis. In addition to coagulation, activation of the contact system is involved in fibrinolytic, inflammatory, and angiogenic processes that can also contribute to the thrombotic environment. This review discusses the role of the contact system in these processes, and highlights the potential of FXII and FXI as safer targets for antithrombotic therapy.

Cross-talk between the complement and the kinin system in vascular permeability

The endothelium is a continuous physical barrier that regulates coagulation and selective passage of soluble molecules and circulating cells through the vessel wall into the tissue. Due to its anatomic localization, the endothelium may establish contact with components of the complement, the kinin and the coagulation systems which are the main, though not exclusive, inducers of vascular leakage. Although the complement and the kinin systems may act independently, increasing evidence suggest that there is a crosstalk that involve different components of both systems. Activation is required for the function of the two systems which are involved in pathological conditions such as hereditary and acquired angioedema (AE) and vasculitidis. The aim of this review is to discuss the contribution of complement and kinin systems to vascular leakage and the cross-talk between the two systems in the development of AE. This clinical condition is characterized by episodic and recurrent local edema of subcutaneous and submucosal tissues and is due to inherited or acquired C1-INH deficiency. Although the pathogenesis of the swelling in patients with AE was originally thought to be mediated by C2, ample evidence indicate bradykinin (BK) as the most effective mediator even though the possibility that both the complement and the kinin-forming systems may contribute to the edema has not been completely excluded. BK induces endothelial leakage interacting with B2 receptors but other molecules may be involved in the onset and maintenance of AE. In this review we shall discuss the role of B1 receptors and gC1qR/p33 in addition to that of B2 receptors in the onset of AE attacks and the importance of these receptors as new possible molecular targets for therapy.

Kinin system activation in vasculitis

Vasculitis is a systemic autoimmune inflammatory disease, characterized by inflammation in and around vessel walls leading to perturbed vessel patency and tissue damage. Many different organs may be involved. In this review, pathogenetic mechanisms of vasculitis are discussed, with special reference to activation of the kinin system. Mechanisms of kinin system activation are described, ultimately leading to release of kinins from high molecular weight kininogen. These vasoactive peptides promote inflammation.

CONCLUSION

  Kinin system activation during vasculitis promotes inflammation.

Structure-function studies using deletion mutants identify domains of gC1qR/p33 as potential therapeutic targets for vascular permeability and inflammation

The endothelial cell receptor complex for kininogen (HK) comprises gC1qR, cytokeratin 1, and urokinase-type plasminogen activator receptor and is essential for activation of the kinin system that leads to bradykinin (BK) generation. Of these, gC1qR/p33 constitutes a high affinity site for HK – the BK precursor – and is therefore critical for the assembly of the kinin-generating cascade. Previous studies have identified a putative HK site within the C-terminal domain (residues 204–218) of gC1qR recognized by mAb 74.5.2. In these studies, we used information from the crystal structure of gC1qR, to engineer several deletion (Δ) mutants and test their ability to bind and/or support BK generation. While deletion of residues 204–218 (gC1qRΔ204–218), showed significantly reduced binding to HK, BK generation was not affected when tested by a sensitive bradykinin immunoassay. In fact, all of the gC1qR deletion mutants supported BK generation with the exception of gC1qRΔ154–162 and a point mutation in which Trp 233 was substituted with Gly. Binding studies also identified the existence of two additional sites at residues 144–162 and 190–202. Moreover, binding of HK to a synthetic peptide 190–202 was inhibited by mAbs 48 and 83, but not by mAb 74.5.2. Since a single residue separates domains 190–202 and 204–218, they may be part of a highly stable HK binding pocket and therefore a potential target for drug design to prevent vascular permeability and inflammation.

Streptococcal inhibitor of complement-mediated lysis (SIC): an anti-inflammatory virulence determinant

Since the late 1980s, a worldwide increase of severe Streptococcus pyogenes infections has been associated with strains of the M1 serotype, strains which all secrete the streptococcal inhibitor of complement-mediated lysis (SIC). Previous work has shown that SIC blocks complement-mediated haemolysis, inhibits the activity of antibacterial peptides and has affinity for the human plasma proteins clusterin and histidine-rich glycoprotein; the latter is a member of the cystatin protein family. The present work demonstrates that SIC binds to cystatin C, high-molecular-mass kininogen (HK) and low-molecular-mass kininogen, which are additional members of this protein family. The binding sites in HK are located in the cystatin-like domain D3 and the endothelial cell-binding domain D5. Immobilization of HK to cellular structures plays a central role in activation of the human contact system. SIC was found to inhibit the binding of HK to endothelial cells, and to reduce contact activation as measured by prolonged blood clotting time and impaired release of bradykinin. These results suggest that SIC modifies host defence systems, which may contribute to the virulence of S. pyogenes strains of the M1 serotype.

Contact system activation in severe infectious diseases

Hemostasis is a sensitive and tightly regulated process, involving vascular endothelium and blood cells, as well as factors of the coagulation and fibrinolytic cascades. In severe and invasive infectious diseases, the equilibrium between the procoagulant and anticoagulant status of the host may change dramatically and can induce life-threatening complications. A growing body of evidence suggests that the contact system, also known as the intrinsic pathway of coagulation or kallikrein/kinin system, participate in these processes. Contact activation leads to the release of the highly potent proinflammatory peptide bradykinin and initiates the intrinsic pathway of coagulation. Several studies have shown a systemic activation of the contact system in animal models of severe bacterial infections, and similar findings were also reported when monitoring patients suffering from sepsis, severe sepsis, or septic shock. Complications resulting from a systemic activation of the contact system are pathologically high levels of bradykinin, consumption of contact factors, and a subsequent induction of inflammatory reactions. These conditions may contribute to serious complications such as hypotension and vascular leakage. Here, we summarize the state of the art in this field of research with a focus on the contact system, and we also discuss a potential role for the contact system as a target for the development of novel antimicrobial strategies.

Structure of the Trypanosoma brucei p22 protein, a cytochrome oxidase subunit II-specific RNA-editing accessory factor

Kinetoplastid RNA (k-RNA) editing is a complex process in the mitochondria of kinetoplastid protozoa, including Trypanosoma brucei, that involves the guide RNA-directed insertion and deletion of uridines from precursor-mRNAs to produce mature, translatable mRNAs. k-RNA editing is performed by multiprotein complexes called editosomes. Additional non-editosome components termed k-RNA-editing accessory factors affect the extent of editing of specific RNAs or classes of RNAs. The T. brucei p22 protein was identified as one such accessory factor. Here we show that p22 contributes to cell growth in the procyclic form of T. brucei and functions as a cytochrome oxidase subunit II-specific k-RNA-editing accessory factor. To gain insight into its functions, we solved the crystal structure of the T. brucei p22 protein to 2.0-A resolution. The p22 structure consists of a six-stranded, antiparallel beta-sheet flanked by five alpha-helices. Three p22 subunits combine to form a tight trimer that is primarily stabilized by interactions between helical residues. One side of the trimer is strikingly acidic, while the opposite face is more neutral. Database searches show p22 is structurally similar to human p32, which has a number of functions, including regulation of RNA splicing. p32 interacts with a number of target proteins via its alpha1 N-terminal helix, which is among the most conserved regions between p22 and p32. Co-immunoprecipitation studies showed that p22 interacts with the editosome and the k-RNA accessory protein, TbRGG2, and alpha1 of p22 was shown to be important for the p22-TbRGG2 interaction. Thus, these combined studies suggest that p22 mediates its role in k-RNA editing by acting as an adaptor protein.

C1q induces a rapid up-regulation of P-selectin and modulates collagen- and collagen-related peptide-triggered activation in human platelets

Blood platelets are emerging as important immunomodulatory cells, but complement interaction with platelets is not well understood. Several platelet structures have been described as complement protein 1q (C1q) binding receptors, such as C1qRp/CD93 and gC1qR. However, there are conflicting results whether these receptors are C1q binding structures, or even at all expressed on the cell surface. Recently, the collagen-binding integrin αIIβI was reported to bind C1q on mast cells, and this receptor is also present on platelets. The aim of this study was to further characterize the effects of C1q on platelets, by quantifying the platelet surface expression of P-selectin (CD62P) and monitoring the formation of platelet-neutrophil aggregates. Using flow cytometry, we found that C1q dose-dependently triggered a rapid but moderate and transient up-regulation of P-selectin already within 5s of C1q exposure. Pre-incubation with an antibody directed against gC1qR significantly inhibited (with 57% compared to control) the up-regulation, whereas an antibody towards the αIIβI-integrin showed no effect. Stimulation with C1q did not change the cytosolic calcium-levels, as measured with the fluorescent ratiometric probe Fura-2, however, a protein kinase C inhibitor (GF109203x) blocked the C1q-induced P-selectin expression. Furthermore, pre-incubation of platelets with C1q diminished both the collagen as well as the collagen-related peptide-induced up-regulation of P-selectin, most evident after 90s of stimulation. This indicates that C1q may regulate platelet activation via the GPVI receptor, which is a novel finding. Moreover, C1q antagonized the collagen-induced formation of platelet-neutrophil aggregates, indicating a reduced interaction between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1(PSGL-1/CD162). In summary, C1q induces a moderate rapid platelet P-selectin expression, modulates subsequent collagen and collagen-related peptide stimulation of platelets, and inhibits the formation of platelet-neutrophil aggregates. These immuno-regulatory effects of C1q may have a crucial role in innate immunity and inflammation.

Mitochondrial p32 protein is a critical regulator of tumor metabolism via maintenance of oxidative phosphorylation

p32/gC1qR/C1QBP/HABP1 is a mitochondrial/cell surface protein overexpressed in certain cancer cells. Here we show that knocking down p32 expression in human cancer cells strongly shifts their metabolism from oxidative phosphorylation (OXPHOS) to glycolysis. The p32 knockdown cells exhibited reduced synthesis of the mitochondrial-DNA-encoded OXPHOS polypeptides and were less tumorigenic in vivo. Expression of exogenous p32 in the knockdown cells restored the wild-type cellular phenotype and tumorigenicity. Increased glucose consumption and lactate production, known as the Warburg effect, are almost universal hallmarks of solid tumors and are thought to favor tumor growth. However, here we show that a protein regularly overexpressed in some cancers is capable of promoting OXPHOS. Our results indicate that high levels of glycolysis, in the absence of adequate OXPHOS, may not be as beneficial for tumor growth as generally thought and suggest that tumor cells use p32 to regulate the balance between OXPHOS and glycolysis.

Novel pathogenic mechanism and therapeutic approaches to angioedema associated with C1 inhibitor deficiency

BACKGROUND

Activation of bradykinin-mediated B2 receptor has been shown to play an important role in the onset of angioedema associated with C1 inhibitor deficiency. This finding has led to the development of novel therapeutic drugs such as the B2 receptor antagonist icatibant. However, it is unclear whether other receptors expressed on endothelial cells contribute to the release of kinins and vascular leakage in these patients. The recognition of their role may have obvious therapeutic implications.

OBJECTIVE

Our aim was to investigate the involvement of B1 and gC1q receptors in in vitro and in vivo models of vascular leakage induced by plasma samples obtained from patients with C1 inhibitor deficiency.

METHODS

The vascular leakage was evaluated in vitro on endothelial cells by a transwell model system and in vivo on rat mesentery microvessels by intravital microscopy.

RESULTS

We observed that the attack phase plasma from C1 inhibitor-deficient patients caused a delayed fluorescein-labeled albumin leakage as opposed to the rapid effect of bradykinin, whereas remission plasma elicited a modest effect compared with control plasma. The plasma permeabilizing effect was prevented by blocking the gC1q receptor-high-molecular-weight kininogen interaction, was partially inhibited by B2 receptor or B1 receptor antagonists, and was totally prevented by the mixture of the 2 antagonists. Involvement of B1 receptor was supported by the finding that albumin leakage caused by attack phase plasma was enhanced by IL-1beta and was markedly reduced by brefeldin A.

CONCLUSION

Our data suggest that both B1 receptor and gC1q receptor are involved in the vascular leakage induced by hereditary and acquired angioedema plasma.

Identification of novel cell migration-promoting genes by a functional genetic screen

Here we describe the identification of novel cell migration-promoting genes based on an unbiased functional genetic screen in cultured cells. After the introduction of the retroviral mouse brain cDNA library into NIH3T3 mouse fibroblast cells, migration-promoted cells were selected by a 3-dimensional migration assay using cell culture inserts. After 5 rounds of enrichment, cDNAs were retrieved from the cells with a selected phenotype. Cell migration-promoting activity was confirmed by independent migration assays for the retrieved cDNAs, among which further investigation was focused on coiled-coil-helix-coiled-coil-helix domain-containing protein 2 (chchd2). Whereas overexpression of chchd2 promoted cell migration, knockdown of endogenous chchd2 expression reduced cell migration. Chchd2-induced cell migration was associated with augmented formation of actin stress fibers and focal adhesion, which was mediated through Akt, RhoA/ROCK, and Jnk pathways. CHCHD2 protein directly interacted with hyaluronic acid-binding protein 1 (HABP1) that possessed migration-suppressing activity. Intracellular localization and further functional studies suggested that CHCHD2 and HABP1 may mutually regulate each other to balance cell migration. Thus, chchd2 is a novel cell migration determinant identified by an in vitro functional genetic selection strategy. The selection method can also be useful for the isolation of genes that give other phenotypes of interest.

Cleaved high molecular weight kininogen, a novel factor in the regulation of matrix metalloproteinases in vascular smooth muscle cells

We previously reported that Brown Norway Katholiek rats, which feature a deficiency of plasma kininogens, develop severe abdominal aortic aneurysm. Increased activity of matrix metalloproteinases (MMPs) in the aortic wall, leading to degradation of extracellular matrix components, is considered to play a crucial role in aneurysm formation. Using an in vitro model of vascular smooth muscle cells (VSMCs), cultured from the rat aorta, we investigated whether the cleaved form of high molecular weight kininogen, designated HKa, affects the expression of MMP-9 and MMP-2 and their tissue inhibitors (TIMPs). Treatment of VSMCs with HKa reduced in a concentration-dependent manner IL-1alpha-induced release of MMP-9 and MMP-2, associated with decreased MMP enzymatic activity levels in conditioned media, as demonstrated by gelatin zymography and fluorescein-labeled gelatin substrate assay, respectively. Real-time PCR revealed that HKa reduced corresponding MMP-9 mRNA levels. Further investigations showed that this effect did not result from a modified rate of MMP-9 mRNA degradation. TIMP-1 mRNA levels, already increased as a result of cytokine-stimulation, were significantly enhanced by HKa. Furthermore, we found elevated basal mRNA expression levels of MMP-2 and TIMP-2 in VSMCs derived from kininogen-deficient Brown Norway Katholiek rats. These results demonstrate for the first time that HKa affects the regulation of MMPs in VSMCs.