Effect of interferon-gamma on complement gene expression in different cell types

Complement system molecules: Expression and regulation at the maternal-conceptus interface during pregnancy in pigs

The complement system, composed of complement components and complement control proteins, plays an essential role in innate immunity. Complement system molecules are expressed at the maternal-conceptus interface, and inappropriate activation of the complement system is associated with various adverse pregnancy outcomes in humans and rodents. However, the expression, regulation, and function of the complement system at the maternal-conceptus interface in pigs have not been studied. In this study, we investigated the expression, localization, and regulation of complement system molecules at the maternal-conceptus interface in pigs. Complement components and complement control proteins were expressed in the endometrium, early-stage conceptus, and chorioallantoic tissues during pregnancy. The expression of complement components acting on the early stage of complement activation increased in the endometrium on Day 15 of pregnancy, with greater levels on that day compared with the estrous cycle. Localization of several complement components and complement control proteins was cell-type specific in the endometrium. The expression of C1QC, C2, C3, C4A, CFI, ITGB2, MASP1, and SERPING1 was increased by IFNG in endometrial explant tissues. Furthermore, cleaved C3 fragments were detected in endometrial tissues and uterine flushings on Day 15 of the estrous cycle and Day 15 of pregnancy, with greater levels on Day 15 of pregnancy. These results suggest that complement system molecules in pigs expressed at the maternal-conceptus interface play important roles in the establishment and maintenance of pregnancy by regulating innate immunity and modulating the maternal immune environment during pregnancy.

Myeloid lineage cells evince distinct steady-state level of certain gene groups in dependence on hereditary angioedema severity

Hereditary angioedema (HAE) is a rare genetic disorder with variable expressivity even in carriers of the same underlying genetic defect, suggesting other genetic and epigenetic factors participate in modifying HAE severity. Recent knowledge indicates the role of immune cells in several aspects of HAE pathogenesis, which makes monocytes and macrophages candidates to mediate these effects. Here we combined a search for HAE phenotype modifying gene variants with the characterization of selected genes' mRNA levels in monocyte and macrophages in a symptom-free period. While no such gene variant was found to be associated with a more severe or milder disease, patients revealed a higher number of dysregulated genes and their expression profile was significantly altered, which was typically manifested by changes in individual gene expression or by strengthened or weakened relations in mutually co-expressed gene groups, depending on HAE severity. SERPING1 showed decreased expression in HAE-C1INH patients, but this effect was significant only in patients carrying mutations supposedly activating nonsense-mediated decay. Pro-inflammatory CXC chemokine superfamily members CXCL8, 10 and 11 were downregulated, while other genes such as FCGR1A, or long non-coding RNA NEAT1 were upregulated in patients. Co-expression within some gene groups (such as an NF-kappaB function related group) was strengthened in patients with a severe and/or mild course compared to controls. All these findings show that transcript levels in myeloid cells achieve different activation or depression levels in HAE-C1INH patients than in healthy controls and/or based on disease severity and could participate in determining the HAE phenotype.

Effect of Avian Influenza Virus subtype H9N2 on the expression of complement-associated genes in chicken erythrocytes

The H9N2 subtype avian influenza virus can infect both chickens and humans. Previous studies have reported a role for erythrocytes in immunity. However, the role of H9N2 against chicken erythrocytes and the presence of complement-related genes in erythrocytes has not been studied. This research investigated the effect of H9N2 on complement-associated gene expression in chicken erythrocytes. The expression of complement-associated genes (C1s, C1q, C2, C3, C3ar1, C4, C4a, C5, C5ar1, C7, CD93 and CFD) was detected by reverse transcription-polymerase chain reaction (RT-PCR). Quantitative Real-Time PCR (qRT-PCR) was used to analyse the differential expression of complement-associated genes in chicken erythrocytes at 0 h, 2 h, 6 h and 10 h after the interaction between H9N2 virus and chicken erythrocytes in vitro and 3, 7 and 14 d after H9N2 virus nasal infection of chicks. Expression levels of C1q, C4, C1s, C2, C3, C5, C7 and CD93 were significantly up-regulated at 2 h and significantly down-regulated at 10 h. Gene expression levels of C1q, C3ar1, C4a, CFD and C5ar1 were seen to be different at each time point. The expression levels of C1q, C4, C1s, C2, C3, C5, C7, CFD, C3ar1, C4a and C5ar1 were significantly up-regulated at 7 d and the gene expression of levels of C3, CD93 and C5ar1 were seen to be different at each time point. The results confirmed that all the complement-associated genes were expressed in chicken erythrocytes and showed the H9N2 virus interaction with chicken erythrocytes and subsequent regulation of chicken erythrocyte complement-associated genes expression. This study reported, for the first time, the relationship between H9N2 and complement system of chicken erythrocytes, which will provide a foundation for further research into the prevention and control of H9N2 infection.

Preferential production and secretion of the complement regulator factor H-like protein 1 (FHL-1) by human myeloid cells

Factor H is a pivotal complement regulatory protein that is preferentially produced by the liver and circulates in high concentrations in serum. There has been an increasing interest in the extrahepatic production of complement factors, including by cells of the immune system, since this contributes to non-canonical functions of local complement activation and regulation. Here we investigated the production and regulation of factor H and its splice variant factor H-like protein 1 (FHL-1) by human myeloid cells. As validation, we confirmed the predominant presence of intact factor H in serum, despite a strong but comparable mRNA expression of CFH and FHL1 in liver. Comparable levels of CFH and FHL1 were also observed in renal tissue, although a dominant staining for FHL-1 was shown within the proximal tubules. Human in vitro generated pro- and anti-inflammatory macrophages both expressed and produced factor H/FHL-1, but this was strongest in pro-inflammatory macrophages. Production was not affected by LPS activation, but was increased upon stimulation with IFN-γ or CD40L. Importantly, in both macrophage subsets mRNA expression of FHL1 was significantly higher than CFH. Moreover, production of FHL-1 protein could be confirmed using precipitation and immunoblotting of culture supernatants. These data identify macrophages as producers of factor H and FHL-1, thereby potentially contributing to local complement regulation at sites of inflammation.

Coordinated local RNA overexpression of complement induced by interferon gamma in myositis

Complement proteins are deposited in the muscles of patients with myositis. However, the local expression and regulation of complement genes within myositis muscle have not been well characterized. In this study, bulk RNA sequencing (RNAseq) analyses of muscle biopsy specimens revealed that complement genes are locally overexpressed and correlate with markers of myositis disease activity, including the expression of interferon-gamma (IFNγ)-induced genes. Single cell and single nuclei RNAseq analyses showed that most local expression of complement genes occurs in macrophages, fibroblasts, and satellite cells, with each cell type expressing different sets of complement genes. Biopsies from immune-mediated necrotizing myopathy patients, who have the lowest levels of IFNγ-induced genes, also had the lowest complement gene expression levels. Furthermore, data from cultured human cells showed that IFNγ upregulates complement expression in macrophages, fibroblasts, and muscle cells. Taken together, our results suggest that in myositis muscle, IFNγ coordinates the local overexpression of complement genes that occurs in several cell types.

A novel pathogenetic factor of laryngeal attack in hereditary angioedema? Involvement of protease activated receptor 1

BACKGROUND

Hereditary angioedema (HAE) is a rare, life-threatening disease. The knowledge about the molecular pathogenesis of HAE has derived mainly from investigating blood samples. However, limited data are available on the role of the molecular mechanisms in the affected tissues during HAE attack.

OBJECTIVE

The aim of our study was to explore the histological changes occurring in HAE attacks.

METHODS

Post mortem macro-, microscopic and immunohistological assessment of upper airway tissues of a patient with HAE due to C1 inhibitor deficiency (C1-INH-HAE) type 2 who died from laryngeal HAE attack was compared with a non-HAE patient who died from other condition without any signs of angioedema.

RESULTS

Compared to the control patient, we demonstrated stronger T cell/monocyte infiltration and a more intense C1-INH staining in the C1-INH-HAE patient. The expression of both bradykinin receptors (B1/B2) was observed with a slightly lower level in the C1-INH-HAE patient than in the control patient. PAR1 expression was strongly reduced in the C1-INH-HAE patient suggesting overactivation of this hyperpermeability inducing receptor.

CONCLUSION

Our unique case and novel results correspond to the knowledge about C1-INH and BDKRs observed in plasma; however, it revealed new information about the pathomechanism of HAE attack focusing on the potential involvement of PAR1 in edema formation. This observation, if it is verified by subcutaneous biopsy studies, may designate a new therapeutic target in HAE.

Ex Vivo Test for Measuring Complement Attack on Endothelial Cells: From Research to Bedside

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Suppression of complement component 2 expression by hepatitis B virus contributes to the viral persistence in chronic hepatitis B patients

Previously, we identified rare missense mutations of complement component 2 (C2) to be associated with chronic hepatitis B (CHB) by exome sequencing. However, up to now, little is known about the role of C2 in CHB. In the present study, we aimed to perform preliminary exploration about the underlying role of C2 in CHB. Serum samples from 113 CHB patients and 30 healthy controls, and liver biopsy samples from 5 CHB patients and 3 healthy controls were obtained from the Third Affiliated Hospital of Sun Yat-sen University between January 2018 and January 2020. HepG2.2.15 and HepG2-NTCP cells infected with HBV were used to examine the influence of HBV infection on C2 expression. IFN-treated HepG2.2.15 cells were used to assess the effect of IFN on C2 expression. C2-overexpressing or C2-silencing HepG2.2.15 cells were constructed to evaluate the effect of C2 on HBV infection. Western blot and RT-qPCR were used to measure C2 expression in biopsy samples. HBeAg and HBsAg in culture medium and C2 of serum samples were measured by ELISA. HBV-DNA was measured by RT-qPCR. GSE84044, GSE54747 and GSE27555 were downloaded from GEO. C2 expression in liver tissue and serum was significantly lower in CHB patients compared to healthy controls, and significantly higher C2 expression was found in CHB patients with lower ALT, AST, Scheuer grade and stages compared to CHB patients with higher ALT, AST, Scheuer grades and Scheuer stage. Besides, HBV infection could decrease C2 expression by increasing expression of Sp1 and reducing expression of HDAC4. Moreover, C2 could enhance the anti-virus effect of IFN on HepG2.2.15 cells and also inhibit HBV replication in HepG2.2.15 cells by inhibition of p38-MAPK signalling pathway. In conclusion, HBV may promote viral persistence in CHB patients by inhibiting C2 expression.

Monocyte upregulation of podoplanin during early sepsis induces complement inhibitor release to protect liver function

Multiple organ failure in sepsis is a progressive failure of several interdependent organ systems. Liver dysfunction occurs early during sepsis and is directly associated with patient death; however, the underlying mechanism of liver dysfunction is unclear. Platelet transfusion benefits patients with sepsis, and inhibition of complement activation protects liver function in septic animals. Herein, we explored the potential link between platelets, complement activation, and liver dysfunction in sepsis. We found that deletion of platelet C-type lectin-like receptor 2 (CLEC-2) exacerbated liver dysfunction in early sepsis. Platelet CLEC-2-deficient mice exhibited higher complement activation, more severe complement attack in the liver, and lower plasma levels of complement inhibitors at early time points after E. coli infection. Circulating monocytes expressed the CLEC-2 ligand podoplanin in early sepsis, and podoplanin binding induced release of complement inhibitors from platelets. Injection of complement inhibitors released from platelets reduced complement attack and attenuated liver dysfunction in septic mice. These findings indicate a new function of platelets in the regulation of complement activation during sepsis.

SERPING1 exon 3 splicing variants using alternative acceptor splice sites

Mutations in the C1 inhibitor (C1INH) encoding gene, SERPING1, are associated with hereditary angioedema (HAE) which manifests as recurrent submucosal and subcutaneous edema episodes. The major C1INH function is the complement system inhibition, preventing its spontaneous activation. The presented study is focused on SERPING1 exon 3, an alternative and extraordinarily long exon (499 bp). Endogenous expression analysis performed in the HepG2, human liver, and human peripheral blood cells revealed several exon 3 splicing variants alongside exon inclusion: a highly prevalent exon skipping variant and less frequent +38 and -15 variants with alternative 3' splice sites (ss) located 38 and 15 nucleotides downstream and upstream from the authentic 3' ss, respectively. An exon skipping variant introducing a premature stop codon, represented nearly one third of all splicing variants and surprisingly appeared not to be degraded by NMD. The alternative -15 3' ss was used to a small extent, although predicted to be extremely weak. Its use was shown to be independent of its strength and highly sensitive to any changes in the surrounding sequence. -15 3' ss seems to be co-regulated with the authentic 3' ss, whose use is dependent mainly on its strength and less on the presence of intronic regulatory motifs. Subtle SERPING1 exon 3 splicing regulation can contribute to overall C1INH plasma levels and HAE pathogenesis.

Endothelial cells: source, barrier, and target of defensive mediators

Endothelium is strategically located at the interface between blood and interstitial tissues, placing thus endothelial cell as a key player in vascular homeostasis. Endothelial cells are in a dynamic equilibrium with their environment and constitute concomitantly a source, a barrier, and a target of defensive mediators. This review will discuss the recent advances in our understanding of the complex crosstalk between the endothelium, the complement system and the hemostasis in health and in disease. The first part will provide a general introduction on endothelial cells heterogeneity and on the physiologic role of the complement and hemostatic systems. The second part will analyze the interplay between complement, hemostasis and endothelial cells in physiological conditions and their alterations in diseases. Particular focus will be made on the prototypes of thrombotic microangiopathic disorders, resulting from complement or hemostasis dysregulation-mediated endothelial damage: atypical hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Novel aspects of the pathophysiology of the thrombotic microangiopathies will be discussed.

Production of complement components by cells of the immune system

The complement system is an important part of the innate immune defence. It contributes not only to local inflammation, removal and killing of pathogens, but it also assists in shaping of the adaptive immune response. Besides a role in inflammation, complement is also involved in physiological processes such as waste disposal and developmental programmes. The complement system comprises several soluble and membrane-bound proteins. The bulk of the soluble proteins is produced mainly by the liver. While several complement proteins are produced by a wide variety of cell types, other complement proteins are produced by only a few related cell types. As these data suggest that local production by specific cell types may have specific functions, more detailed studies have been employed recently analysing the local and even intracellular role of these complement proteins. Here we review the current knowledge about extrahepatic production and/or secretion of complement components. More specifically, we address what is known about complement synthesis by cells of the human immune system.

Expression of the SERPING1 gene is not regulated by promoter hypermethylation in peripheral blood mononuclear cells from patients with hereditary angioedema due to C1-inhibitor deficiency

SERPING1 mutations causing Hereditary Angioedema type I (HAE-I) due to C1-Inhibitor (C1-INH) deficiency display a dominant-negative effect usually resulting in protein levels far below the expected 50%. To further investigate mechanisms for its reduced expression, we analyzed the promoter DNA methylation status of SERPING1 and its influence on C1-INH expression. Global epigenetic reactivation correlated with C1-INH mRNA synthesis and protein secretion in Huh7 hepatoma cells. However, PBMCs extracted from controls, HAE-I and HAE-II patients presented identical methylation status of the SERPING1 promoter when analyzed by bisulphite sequencing; the proximal CpG island (exon 2) is constitutively unmethylated, while the most distant one (5.7Kb upstream the transcriptional start site) is fully methylated. These results correlate with the methylation profile observed in Huh7 cells and indicate that there is not a direct epigenetic regulation of C1-INH expression in PBMCs specific for each HAE type. Other indirect modes of epigenetic regulation cannot be excluded.

The complement system: history, pathways, cascade and inhibitors

Since its discovery in the 19th century, the complement system has developed into a clinically significant entity. The complement system has been implicated in a variety of clinical conditions, from autoimmune diseases to ischemia-reperfusion injury in transplantation. This article charts the historical progress of our understanding of the complement system and provides a synopsis on the activation pathways and its inherent regulators.

Molecular characterization and expression analysis of a complement component 3 in the sea cucumber (Apostichopus japonicus)

The complement system has been discovered in invertebrates and vertebrates, and plays a crucial role in the innate defense against common pathogens. As a central component in the complement system, complement component 3 (C3) is an intermediary between innate and adaptive immune system. In this study, a new isoform of C3 in the sea cucumber Apostichopus japonicus, termed AjC3-2 was identified. Its open reading frame (ORF) is 5085 bp and encodes for 1695 amino acids with a putative signal peptide of 20 amino acid residues. The mature protein molecular weight of AjC3-2 was 187.72 kDa. It has a conserved thioester site and a linker R(689)RRR(692) where AjC3-2 is splitted into β and α chain during posttranslational modification. The expression patterns of two distinct sea cucumber C3 genes, AjC3-2 and AjC3, were similar. During the different development stages from unfertilized egg to juvenile of the sea cucumber, the highest expression levels of AjC3-2 and AjC3 genes were both found in late auricularia. In the adult, the highest expression of these two genes was observed in the coelomocytes and followed by the body wall. AjC3-2 and AjC3 genes expression increased significantly at 6 h after the LPS challenge. These results indicated that these two C3 genes play a pivotal role in immune responses to the bacterial infection in sea cucumber.

Transcriptional control of genes for soluble complement cascade regulatory proteins

The complement cascade of the immune system is an important mediator of the inflammatory response to infection; however it is crucial that this pathway is tightly regulated to prevent uncontrolled activation, which can lead to damage to host tissues. The complement system has many regulators that control activation; both membrane-bound and soluble factors. This review will focus on what is currently known about the transcriptional regulation of the soluble complement regulatory genes C1-inhibitor, complement factor I, complement factor H and C4-binding protein. The absence or mutation of these regulators is all associated with specific disease, and yet their contribution to disease is often poorly understood. It is through full understanding of these genes that we can comprehend the diseases with which they are implicated, and thus prove why knowledge of the transcriptional regulation of these genes is valuable.

Primary human hepatocytes are protected against complement by multiple regulators

Inflammatory liver disorders are often associated with a potentially tissue damaging complement activation directly at the main site of complement protein synthesis. As hepatocytes may be the primary target of complement attack, we investigated the expression and protective capacity of soluble and membrane-bound complement regulatory proteins in primary human hepatocytes (PHH). Isolated PHHs were analyzed for their basal and cytokine-induced complement regulator expression by cytofluorometry, rtPCR, confocal laser microscopy and ELISA. Susceptibility to complement-mediated cell lysis was investigated with cytotoxicity tests. In contrast to previous reports, PHHs expressed CD46, CD55, CD59, soluble CD59 (sCD59) and factor H (fH), but not CD35. A low basal expression of CD55 was strongly enhanced by IFN-gamma, IL-1 beta and TNF-alpha. The expression of CD59 could be augmented by IL-1 beta, IL-6 and TNF-alpha but was suppressed by IFN-gamma. CD46 expression was not significantly altered. PHHs synthesized fH and sCD59 and fH was detected on PHH surface after exposure to IL-1 beta. Inhibition experiments revealed that CD59 was most effective in protecting PHHs from complement attack. These data clearly indicate that PHHs are protected by multiple complement regulatory proteins, which are controlled by proinflammatory cytokines. CD59 appears to be pivotal in protecting PHHs against complement-mediated lysis.

Interferon gamma in successful pregnancies

Interferon gamma (IFNG) is a proinflammatory cytokine secreted in the uterus during early pregnancy. It is abundantly produced by uterine natural killer cells in maternal endometrium but also by trophoblasts in some species. In normal pregnancies of mice, IFNG plays critical roles that include initiation of endometrial vasculature remodeling, angiogenesis at implantation sites, and maintenance of the decidual (maternal) component of the placenta. In livestock and in humans, deviations in these processes are thought to contribute to serious gestational complications, such as fetal loss or preeclampsia. Interferon gamma has broader roles in activation of innate and adaptive immune responses to viruses and tumors, in part through upregulating transcription of genes involved in cell cycle regulation, apoptosis, and antigen processing/presentation. Despite this, rodent and human trophoblast cells show dampened responses to IFNG that reflect the resistance of these cells to IFNG-mediated activation of major histocompatibility complex (MHC) class II transplantation antigen expression. Lack of MHC class II antigens on trophoblasts is thought to facilitate survival of the semiallogeneic conceptus in the presence of maternal lymphocytes. This review describes the dynamic roles of IFNG in successful pregnancy and briefly summarizes data on IFNG in gestational pathologies.

The relative importance of local and systemic complement production in ischaemia, transplantation and other pathologies

Besides a critical role in innate host defence, complement activation contributes to inflammatory and immunological responses in a number of pathological conditions. Many tissues outside the liver (the primary source of complement) synthesise a variety of complement proteins, either constitutively or response to noxious stimuli. The significance of this local synthesis of complement has become clearer as a result of functional studies. It revealed that local production not only contributes to the systemic pool of complement but also influences local tissue injury and provides a link with the antigen-specific immune response. Extravascular production of complement seems particularly important at locations with poor access to circulating components and at sites of tissue stress responses, notably portals of entry of invasive microbes, such as interstitial spaces and renal tubular epithelial surfaces. Understanding the relative importance of local and systemic complement production at such locations could help to explain the differential involvement of complement in organ-specific pathology and inform the design of complement-based therapy. Here, we will describe the lessons we have learned over the last decade about the local synthesis of complement and its association with inflammatory and immunological diseases, placing emphasis on the role of local synthesis of complement in organ transplantation.

IFN-gamma upregulates expression of the mouse complement C1rA gene in keratinocytes via IFN-regulatory factor-1

We examined the expression of the mouse complement component C1rA (mC1rA) in IFN-gamma-stimulated mouse keratinocytes (Pam 212) and found that it was upregulated. To analyze the mechanism involved, we cloned the 2,150 bp 5'-flanking region of mC1rA by the vectorette-PCR technique, and identified the transcription start site of mC1rA by rapid amplification of complementary DNA ends. Analysis of the 5' sequence revealed putative binding sites for activator protein 1, CCAAT/enhancer binding protein (C/EBP), signal transducer and activator of transcription 1 (STAT-1), IFN-regulatory factor-1 (IRF-1), and others. We detected transcriptional activation dependent on this upstream region in reporter gene assays and Northern blots. To identify the cis-acting regulatory elements involved, we analyzed serial deletion constructs of the promoter using luciferase reporters. The -80 to -19 bp region, which contains a putative IRF-1 binding site, was required for both basal promoter activity and responses to IFN-gamma. The use of site-directed point mutations, electrophoresis mobility shift assays, and supershift assays indicated that the putative IRF-1 binding site was essential for both IFN-gamma-dependent and -independent transcriptional activity of the mC1rA promoter. We conclude that IFN-gamma stimulates mC1rA gene expression via IRF-1 in mouse keratinocytes.

C5a anaphylatoxin as a product of complement activation up-regulates the complement inhibitory factor H in rat Kupffer cells

The 155-kDa complement regulator factor H (FH) is the predominant soluble regulatory protein of the complement system. It acts as a cofactor for the factor I-mediated conversion of the component C3b to iC3b, competes with factor B for a binding site on C3b and C3(H2O) and promotes the dissociation of the C3bBb complex. The primary site of synthesis is the liver, i.e. FH-specific mRNA and protein were identified in both hepatocytes (HC) and Kupffer cells (KC). Previous studies in rat primary HC and KC had shown that the proinflammatory cytokine IFN-gamma influences the balance between activation and inhibition of the complement system through up-regulation of the inhibitory FH. In this study we show that C5a, as a product of complement activation, stimulates the expression of FH-specific mRNA and protein in KC and thus induces a negative feedback. Quantitative-competitive RT-PCR showed an approximate threefold C5a-induced up-regulation of FH. ELISA analyses revealed a corresponding increase in FH protein in the supernatants of KC. The up-regulation of FH was completely inhibited by the C5a-blocking monoclonal antibody 6-9F. Furthermore, an involvement of LPS and IFN-gamma was excluded, which strongly indicates a direct effect of C5a on the expression of FH in KC.

Nuclear phosphatases and the proteasome in suppression of STAT1 activity in hepatocytes

IFN-gamma induction of C1 inhibitor (C1INH) is mediated by an IFN-gamma-activated sequence (GAS), via binding of signal transducer and activator of transcription 1 (STAT1). These studies focused on the factors responsible for down-regulation of nuclear STAT1 in hepatocytes, the primary site of synthesis of C1INH. The activity of nuclear STAT1 following stimulation with IFN-gamma was sustained with the phosphatase inhibitor, pervanadate, or the proteasome inhibitor, lactacystin. Pervanadate prolonged STAT1 activation and blocked the inactivation of nuclear STAT1. Binding of ubiquitin to phosphorylated STAT1 was detectable in cells treated with lactacystin. Staurosporine only moderately decreased the prolongation of nuclear phosphorylated STAT1 after pretreatment with pervanadate or lactacystin. An antisense mitogen-activated protein kinase phosphatase (MKP-1) oligonucleotide prolonged the accumulation of phosphorylated STAT1. These data are consistent with the hypothesis that down-regulation of IFN-gamma-mediated nuclear STAT1 binding in hepatocytes involves both dephosphorylation by MKP-1 and degradation via proteolysis by the ubiquitin-dependent proteasome pathway.

Constitutive expression and regulation of rat complement factor H in primary cultures of hepatocytes, Kupffer cells, and two hepatoma cell lines

The 155-kd soluble complement regulator factor H (FH), which consists of 20 short consensus repeats, increases the affinity of complement factor I (FI) for C3b by about 15 times. In addition to its cofactor activity, it prevents factor B from binding to C3b and promotes the dissociation of the C3bBb complex. The primary site of synthesis of FH, as well as of FI, is the liver, but the cell types responsible for the hepatic synthesis of both factors have not yet been clearly identified. In contrast to FI-mRNA, which was detectable only in hepatocytes (HC), FH-specific mRNA was identified in both HC and Kupffer cells (KC). As calculated for equal amounts of mRNA isolated from both cell types, FH-specific mRNA was found to be nearly 10-fold higher in KC than in HC, leading to the conclusion that KC are an abundant source of FH. Of the investigated proinflammatory cytokines IL-6, TNF-alpha, IL-1beta, and IFN-gamma, only IFN-gamma up-regulated FH-specific mRNA up to 6-fold in both primary HC and KC. This was also demonstrable on the protein level. However, FH-specific mRNA was not inducible in the rat hepatoma cell line H4IIE, which did not express FH-specific mRNA and could not be up-regulated in FAO cells that constitutively expressed FH-specific mRNA. This demonstrates that transformed cell lines do not reflect FH regulation in isolated primary HC. In addition to IFN-gamma, the endotoxin lipopolysaccharide (LPS) up-regulated FH-specific mRNA nearly 10-fold in KC after stimulation at concentrations of 10 or 1 ng/ml. In contrast, concentrations of up to 2 microg LPS/ml did not show any effect on HC. Our data suggest that LPS does not regulate the expression of FH in HC.

Cytokine-mediated up-regulation of CD55 and CD59 protects human hepatoma cells from complement attack

Hepatic parenchymal cells respond in many different ways to acute-phase cytokines. Some responses may protect against damage by liver-derived inflammatory mediators. Previous investigations have shown that cytokines cause increased secretion by hepatoma cells of soluble complement regulatory proteins, perhaps providing protection from complement attack. More important to cell protection are the membrane complement regulators. Here we examine, using flow cytometry and Northern blotting, the effects of different cytokines, singly or in combination, on expression of membrane-bound complement regulators by a hepatoma cell line. The combination of tumour necrosis factor-alpha, IL-1beta, and IL-6 caused increased expression of CD55 (three-fold) and CD59 (two-fold) and decreased expression of CD46 at day 3 post-exposure. Interferon-gamma reduced expression of CD59 and strongly antagonized the up-regulatory effects on CD59 mediated by the other cytokines. Complement attack on antibody-sensitized hepatoma cells following a 3-day incubation with the optimum combination of acute-phase cytokines revealed increased resistance to complement-mediated lysis and decreased C3b deposition. During the acute-phase response there is an increased hepatic synthesis of the majority of complement effector proteins. Simultaneous up-regulation of expression of CD55 and CD59 may serve to protect hepatocytes from high local concentrations of complement generated during the acute-phase response.

Expression of complement messenger RNAs by human endothelial cells

This study evaluated complement mRNA expression in human brain microvessel endothelial cells (HBMEC), human umbilical vein endothelial cells (HUVEC), and cells of the human derived ECV304 line. Cerebral endothelial cells and HUVEC expressed detectable levels of complement gene mRNAs for the C1q B-chain, C1r, C1s, C2, C3, C4, C5, C7, C8 gamma-subunit and C9. In addition to C6 mRNA, C1q and C9 were not detected in ECV304 cells. These results indicate that endothelial cells may be a source of complement proteins in brain and other organs of the body.

Interferon-gamma improves splicing efficiency of CYBB gene transcripts in an interferon-responsive variant of chronic granulomatous disease due to a splice site consensus region mutation

X-linked chronic granulomatous disease (CGD) derives from defects in the CYBB gene, which encodes the gp91-phox component of NADPH oxidase. We studied the molecular basis of the disease in a kindred with variant CGD, due to a single base substitution at the sixth position of CYBB first intron. The patients' phagocytes have been shown previously to greatly increase superoxide release in response to interferon-gamma (IFN-γ) in vitro and in vivo. We examined CYBB gene expression in an Epstein-Barr virus (EBV)-transformed B-cell line from 1 patient in this kindred. These cells showed markedly decreased levels of CYBB transcripts in total RNA (5% of normal) and nuclear RNA (1.4% of normal), despite equal CYBB transcription rates in the CGD and control cells. Incubation with IFN-γ produced a 3-fold increase in CYBBtotal messenger RNA (mRNA) levels in the patient's cells, and decreased nuclear transcripts to undetectable levels. Reverse transcriptase–polymerase chain reaction analysis of RNA splicing revealed a preponderance of unspliced CYBB transcripts in the patient's nuclear RNA. In vitro incubation with IFN-γ increased by 40% the ratio of spliced relative to unspliced CYBB mRNA in nuclei from the CGD B-cell line. Total RNA harvested from the same patient's monocytes, on and off therapy with IFN-γ, showed a similar improvement in splicing. We conclude that IFN-γ partially corrects a nuclear processing defect due to the intronic mutation in theCYBB gene in this kindred, most likely by augmentation of nuclear export of normal transcripts, and improvement in the fidelity of splicing at the first intron.

Interferon-gamma improves splicing efficiency of CYBB gene transcripts in an interferon-responsive variant of chronic granulomatous disease due to a splice site consensus region mutation

X-linked chronic granulomatous disease (CGD) derives from defects in the CYBB gene, which encodes the gp91-phox component of NADPH oxidase. We studied the molecular basis of the disease in a kindred with variant CGD, due to a single base substitution at the sixth position of CYBB first intron. The patients' phagocytes have been shown previously to greatly increase superoxide release in response to interferon-gamma (IFN-γ) in vitro and in vivo. We examined CYBB gene expression in an Epstein-Barr virus (EBV)-transformed B-cell line from 1 patient in this kindred. These cells showed markedly decreased levels of CYBB transcripts in total RNA (5% of normal) and nuclear RNA (1.4% of normal), despite equal CYBB transcription rates in the CGD and control cells. Incubation with IFN-γ produced a 3-fold increase in CYBBtotal messenger RNA (mRNA) levels in the patient's cells, and decreased nuclear transcripts to undetectable levels. Reverse transcriptase–polymerase chain reaction analysis of RNA splicing revealed a preponderance of unspliced CYBB transcripts in the patient's nuclear RNA. In vitro incubation with IFN-γ increased by 40% the ratio of spliced relative to unspliced CYBB mRNA in nuclei from the CGD B-cell line. Total RNA harvested from the same patient's monocytes, on and off therapy with IFN-γ, showed a similar improvement in splicing. We conclude that IFN-γ partially corrects a nuclear processing defect due to the intronic mutation in theCYBB gene in this kindred, most likely by augmentation of nuclear export of normal transcripts, and improvement in the fidelity of splicing at the first intron.

Counter-regulatory effect of sodium butyrate on tumour necrosis factor-alpha (TNF-alpha)-induced complement C3 and factor B biosynthesis in human intestinal epithelial cells

The various biological activities of butyrate have been well documented. In this study, we tested the effects of butyrate on TNF-alpha-induced complement C3 and factor B biosynthesis in human intestinal epithelial cells. The biosynthesis of C3, factor B and IL-8 was evaluated at the protein and mRNA levels. To evaluate transcriptional activation, the nuclear run-on assay was performed. The transcription factor-DNA binding activity was assessed by an electrophoretic gel mobility shift assay (EMSA). In the intestinal epithelial cell lines HT-29, T84 and Caco-2, sodium butyrate enhanced TNF-alpha-induced C3 secretion, but suppressed TNF-alpha-induced factor B and IL-8 secretion. Nuclear run-on assay revealed that transcriptional regulatory mechanisms are involved in the effects of sodium butyrate. The EMSAs indicated that sodium butyrate suppressed TNF-alpha-induced nuclear factor (NF)-kappaB- and activation protein (AP)-1-DNA binding activity, but enhanced TNF-alpha-induced activation of CCAAT/enhancer-binding protein (C/EBP)beta (NF-IL-6)-DNA binding activity. Sodium butyrate induced a counter-regulatory effect on TNF-alpha-induced C3 and factor B biosynthesis in human intestinal epithelial cells. Butyrate action has been discussed with its activity to induce histone hyperacetylation, but its counter-regulatory effect on complement biosynthesis may be closely associated with the modulation of transcription factor activation.

Sodium butyrate blocks interferon-gamma (IFN-gamma)-induced biosynthesis of MHC class III gene products (complement C4 and factor B) in human fetal intestinal epithelial cells

Human intestinal epithelial cells have been established as local sites for complement biosynthesis. In this study, we investigated the effects of IFN-gamma and sodium butyrate on biosynthesis of MHC class III gene products (complement C4 and factor B) in the human fetal intestinal epithelial cell line INT-407. IFN-gamma induced a dose- and time-dependent increase in C4 and factor B secretion. However, sodium butyrate dose-dependently inhibited IFN-gamma-induced C4 and factor B secretion. These effects were also observed at the mRNA level. Immunoblotting indicated that IFN-gamma induced a rapid activation of Stat1alpha, and fluorescence immunohistochemistry detected a translocation of Stat1alpha into the nucleus within 1 h. However, the translocation of Stat1alpha was not affected by the addition of sodium butyrate. Nuclear run-on assay indicated that IFN-gamma induced a weak increase in the transcription rate of factor B gene, and sodium butyrate did not affect this response. IFN-gamma and sodium butyrate induced a counter-regulatory effect on C4 and factor B secretion: IFN-gamma acted as a potent inducer, but sodium butyrate potently abrogated these responses. These are mainly regulated through the post-transcriptional mechanism.

The Promoter of the C1 Inhibitor Gene Contains a Polypurine·Polypyrimidine Segment that Enhances Transcriptional Activity

The C1 inhibitor (C1INH) promoter is unusual in two respects: 1) It contains no TATA sequence, but instead contains a TdT-like initiator element (Inr) at nucleotides −3 to +5; 2) it contains a polypurine·polypyrimidine tract between nucleotides −17 and −45. Disruption of the Inr by the introduction of point mutations reduced promoter activity by 40%. A TATA element inserted at nucleotide −30 in the wild-type promoter and in promoter constructs containing the mutated Inr led to a 2-fold increase in basal promoter activity. Previous studies suggested that the potential hinged DNA-forming polypurine·polypyrimidine tract might be important in the regulation of C1INH promoter activity. The present studies indicate that this region is capable of such intramolecular triple helix formation. Disruption of the polypurine·polypyrimidine sequence by substitution of 5 of the 23 cytosine residues with adenine prevented triple helix formation. Site-directed mutagenesis experiments demonstrate that the regulation of promoter activity is independent of hinged DNA-forming capacity but requires an intact AC box (ACCCTNNNNNACCCT) or the overlapping PuF binding site (GGGTGGG). The C1INH gene also contains a number of potential regulatory elements, including an Sp-1 and an hepatocyte nuclear factor-1 binding site and a CAAT box. The role of these elements in regulation of the C1INH promoter was examined. Elimination of the hepatocyte nuclear factor-1 site at nucleotides −94 to −81 by truncation reduced the activity of the promoter by ∼50%. Similarly, site-directed mutations that disrupt this site reduce promoter activity by 70%.

Regulation of C1 inhibitor synthesis

The primary biologic roles of C1 inhibitor (C1-INH) are the regulation of activation of the classical complement pathway and of the contact system of kinin formation. Heterozygosity for deficiency or dysfunction of C1-INH results in hereditary angioedema (HAE). This deficiency results in loss of homeostasis with unregulated complement and contact system activation. Due to the consequent C1-INH consumption, plasma levels of C1-INH in patients with HAE are decreased below 50% of normal. In addition, diminished synthesis contributes to the lowered levels in some patients. The hepatocyte is the primary source of C1-INH, although a number of other cell types, including peripheral blood monocytes, microglial cells, fibroblasts, endothelial cells, the placenta, and megakaryocytes also synthesize and secrete the protein both in vivo and in vitro. Interferon-gamma and alpha (IFN), colony stimulating factor-1, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) all induce C1-INH synthesis in a variety of cell types. The IFN-response elements in the 5'-flanking region and in the first intron have been partially characterized, as have several of the promoter elements that direct basal transcription of the gene. However, although androgen therapy, in vivo, results in an increase in C1-INH plasma levels, a direct effect of androgens on C1-INH synthesis has not been convincingly demonstrated. Although the C1-INH gene contains a potential glucocorticoid/androgen response element, this element does not appear to respond to androgen. Continued analysis of the transcriptional regulation of the C1-INH gene may lead to new approaches to therapy of HAE.

Endothelial cells cultured from human brain microvessels produce complement proteins factor H, factor B, C1 inhibitor, and C4

The inflammatory mediators, cytokines and complement proteins are believed to regulate the sequential events during the development of lesions secondary to ischaemia and reperfusion. The endothelial cell monolayer of the brain microvasculature is the critical interface between the blood-borne mediators and brain tissue. The involvement of these cells in complement production and regulation has not been well documented. In the present study, expression of complement proteins (C1 inhibitor, factor H, factor B, C4) by cultured endothelial cells obtained from human brain microvessels has been characterized. Interferon gamma upregulates the production of all the complement factors studied. Serine proteases, plasmin and miniplasmin induce the expression of C4, decrease the level of ELISA detectable C1 inhibitor, and do not affect the production of factors H and B. These data indicate that complement proteins are expressed locally by the brain microvessels, and may modulate the inflammatory responses of brain tissue.

Complement gene expression by rabbit heart: upregulation by ischemia and reperfusion

Activation of the complement system has been implicated in the pathogenesis of myocardial ischemia/reperfusion injury. It has always been assumed that liver is the primary source of complement components. In the present study, we used the reverse-transcriptase polymerase chain reaction technique to establish that the mRNAs for complement proteins C3 and C9 are expressed in rabbit heart. Rabbit liver, brain, spleen, and kidney were also shown to express C3 and C9 mRNAs. We used Western blotting to establish that these mRNAs in heart are translated into the corresponding proteins. We further established that dramatic upregulation of the mRNAs occurred in Langendorff-perfused isolated hearts subjected to ischemia and reperfusion. C3 mRNA was always expressed at higher levels than was C9 mRNA, but C9 mRNA showed greater upregulation under stress. Compared with levels in control hearts subjected to 5 minutes of normoxic perfusion, hearts subjected to 0.5 hours of ischemia followed by 1 hour of reperfusion had a 4.72-fold increase in C3 mRNA and a 19.5-fold increase in C9 mRNA. By contrast, C3 mRNA in hearts subjected to 3.5 hours of normoxic perfusion showed no change, and those subjected to 3.5 hours of ischemia showed only a 1.72-fold increase, whereas C9 mRNA levels increased by 5.17-fold after 3.5 hours of normoxic perfusion and 12.5-fold after 3.5 hours of ischemia. The results of this study demonstrate for the first time that heart tissue is capable of expressing genes and proteins of the complement system, although it is not yet known which cell types are responsible. They further demonstrate that ischemia and reperfusion of the heart promotes a rapid upregulation of the mRNAs encoding the complement proteins C3 and C9 and that these abnormal levels considerably exceed those of normal liver. These observations are consistent with the hypothesis that local production of complement proteins may contribute significantly to the degree of ischemic injury to the myocardium and that complement expression is augmented by reperfusion.

Analysis of the promoter region of the murine complement factor H gene

We have used the luciferase system to assay basal promoter activity of the murine factor H gene. Based on the results from luciferase assays with clones of 13 nested deletions, a 242-bp region that appeared to contain an enhancer element was subcloned upstream of a heterologous promoter and was shown to enhance transcription. A 26-bp fragment from this region was shifted in electrophoretic mobility assays, and this fragment contains a consensus sequence for the adenovirus major late transcription factor/upstream stimulatory factor (MLTF/USF). This fragment had enhancing activity in a minimal factor H promoter construct, demonstrating that it is a major enhancer of the factor H gene in murine liver cells.

Increased expression of complement component 3 in human ectopic endometrium compared with the matched eutopic endometrium

OBJECTIVE

To compare the gene expression of complement component 3 (C3) in human eutopic and ectopic endometrium.

DESIGN

A prospective, controlled study.

SETTING

Academic hospital.

PATIENT(S)

Women with documented endometriosis.

INTERVENTION(S)

Eutopic and ectopic endometrial tissues were collected simultaneously at laparoscopy.

MAIN OUTCOME MEASURE(S)

Detection of C3 messenger RNA (mRNA) by in situ hybridization and C3 protein by immunohistochemistry and Western blot.

RESULT(S)

Expression of C3 mRNA increased in ectopic endometrium compared with that in the matched eutopic endometrium. The quantitative analysis of C3 mRNA by grain count (mean +/- SE) showed 175.60 +/- 40.02 and 39.97 +/- 8.17 grains per micron2 in ectopic and eutopic glands, respectively, and 67.65 +/- 29.82 and 15.02 +/- 5.80 grains per micron2 in ectopic and eutopic stroma, respectively. Expression of C3 mRNA in ectopic glands was significantly higher than that in eutopic glands. The pattern of immunoreactive staining of C3 protein was consistent with that of C3 mRNA. A higher level of C3 protein in ectopic endometrium than eutopic endometrium was detected by immunohistochemistry and Western blot.

CONCLUSION(S)

Expression of C3 mRNA and protein significantly increased in human ectopic endometrium compared with that in the matched eutopic endometrium.

From housekeeper to microsurgeon: the diagnostic and therapeutic potential of ribonucleases

The RNA population in cells is controlled post-transcriptionally by ribonucleases (RNases) of varying specificity. Angiogenin, neurotoxins, and plant allergens are among many proteins with RNase activity or significant homology to known RNases. RNase activity in serum and cell extracts is elevated in a variety of cancers and infectious diseases. RNases are regulated by specific activators and inhibitors, including interferons. Many of these regulatory molecules are useful lead compounds for the design of drugs to control tumor angiogenesis, allergic reactions, and viral replication. One RNase (Onconase) and several RNase activators are now in clinical trials for cancer treatment or inhibition of chronic virus infections. Several others, alone or conjugated with specific cell binding molecules, are being developed for their antifungal, antiviral, and antitumor cell activity.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

C3 production of cultured human epidermal keratinocytes is enhanced by IFNgamma and TNFalpha through different pathways

We investigated the regulation of C3 production by human cultured epidermal keratinocytes by enzyme-linked immunosorbent assay. The results showed that IFNgamma and TNFalpha enhanced the synthesis of C3 by epidermal keratinocytes in a concentration-dependent manner. Moreover, a protein kinase C (PKC) inhibitor blocked C3 production, whereas PMA enhanced it. There was a synergistic effect between IFNgamma and TNFalpha. In experiments to investigate the role of protein tyrosine kinase (PTK) in C3 production, we found that treatment with herbimycin A, a specific inhibitor for the c-Src-related PTK, caused significant enhancement of the C3 production induced by IFNgamma or TNFalpha, suggesting that c-Src-type PTK(s) provides a negative signal to C3 production. Each competitive inhibitor of PTK, genistein or tyrphostin, substantially increased the C3 production by IFNgamma at lower concentrations, although each agent had little effect on TNFalpha-associated production of C3 at the same concentrations. The data show that pro-inflammatory cytokines IFNgamma and TNFalpha synergistically augment C3 production by epidermal keratinocytes by different pathways.

Production of the third and fourth component of complement (C3, C4) by smooth muscle cells

Production of the third and fourth components of complement (C3, C4) by smooth muscle cells was investigated by using normal human aortic smooth muscle cells (AoSMC), human smooth muscle cell line (G402) and vascular smooth muscle cells obtained from human umbilical cord vein (UVSMC). AoSMC spontaneously produced both C3 and C4 at 15 ng/10(6) cells/72 hr and 22 ng/10(6) cells/72 hr, respectively, and both were enhanced by interferon-gamma (IFN-gamma). Although phorbol 12-myristate 13-acetate (PMA) and tumour necrosis factor-alpha (TNF-alpha) enhanced C3 production, C4 production was reduced by these agents. On the other hand, G402 produced C4 but not C3 in a dose-dependent manner when cultured with IFN-gamma. UVSMC produced only a small amount of C3 and C4 compared with AoSMC or G402. C3 and C4 produced by AoSMC were confirmed to be identical with their human serum counterparts as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and measurement of haemolytic activity. Northern blotting analysis showed that the expression of mRNA of C3 and C4 was enhanced by TNF-alpha and IFN-gamma, respectively, in AoSMC. Our findings suggest the importance of smooth muscle cells as a source of components of complement in vascular diseases including vasculitis.

Regulation of early complement components C3 and C4 in the synovium

To determine the cytokine inducibility of early complement component (C3 and C4) expression in the synovium, explant tissue was maintained in culture for 7 days. C3 and C4 production was measured by specific enzyme-linked immunosorbent assay, and RNA was evaluated by semiquantitative PCR. The effects of leukemia inhibitory factor (LIF), gamma interferon (IFN-gamma), IFN-alpha, and estrogen on C3 and C4 expression were evaluated. C3 levels were unaffected by 7 days of LIF, IFN-gamma, or IFN-alpha treatment. In contrast, C4 levels were significantly induced in synovial samples treated for 7 days with either IFN-gamma or IFN-alpha. LIF had no effect on C4 levels in this system. Estrogen was found to down-modulate the induction of expression due to IFN-gamma. These data provide evidence for cytokine regulation of C4 expression in the synovium and for estrogen modulation of those effects.

Tissue synthesis of complement as an immune regulator

Evidence is accumulating that a variety of tissues produce complement components, and that production in each tissue is differentially regulated by inflammatory cytokines. This locally produced complement could have protective or injurious actions, depending upon local circumstances. Techniques for analysing separately the contributions of local complement synthesis and complement derived from the circulation are now becoming available. We argue that an appreciation of the role of local complement synthesis may help to explain many features of organ- and tissue-specific immunological disease.

Kinetic modeling and mathematical analysis indicate that acute phase gene expression in Hep 3B cells is regulated by both transcriptional and posttranscriptional mechanisms

To evaluate the possible role of posttranscriptional mechanisms in the acute phase response, we determined the kinetics of transcription (by nuclear run-on assay) and mRNA accumulation of five human acute phase genes in Hep 3B cells incubated with conditioned medium from LPS-stimulated monocytes. Increase in mRNA accumulation was comparable to increase in transcription rate for fibrinogen-alpha and alpha-1 protease inhibitor, suggesting largely transcriptional regulation. In contrast, mRNA accumulation was about 10-20-fold greater than transcriptional increase for serum amyloid A, C3, and factor B, suggesting participation of posttranscriptional mechanisms. Since finding a disparity between the magnitudes of increase in mRNA and transcription does not definitively establish involvement of posttranscriptional mechanisms, we subjected our data to modeling studies and dynamic mathematical analysis to evaluate this possibility more rigorously. In modeling studies, accumulation curves resembling those observed for these three mRNAs could be generated from the nuclear run-on results only if posttranscriptional regulation was assumed. Dynamic mathematical analysis of relative transcription rates and relative mRNA abundance also strongly supported participation of posttranscriptional mechanisms. These observations suggest that posttranscriptional regulation plays a substantial role in induction of some, but not all acute phase proteins.

Human complement protein C2. Alternative splicing generates templates for secreted and intracellular C2 proteins

Alternative splicing of the primary transcript for human complement protein C2 generates templates for translation of a secreted (C2 long) protein and an intracellular (C2 short) form in liver, bronchoalveolar macrophages, and fibroblasts. The approximate ratio of C2 long to C2 short mRNA is 2:1. The C2 short mRNA does not contain the 396-base pair encompassed by exons 2 and 3 of the full-length C2 long and thus lacks codons for the 5 carboxyl-terminal residues of the signal peptide. Synthesis of C2 in cells transfected with full-length RNA corresponding to each of the transcripts show that C2 long is secreted within a half-time of approximately 1 h and that C2 short is not secreted. Cell-free biosynthesis in the presence of microsomes demonstrate that this intracellular C2 protein (70 kDa) is apparently capable of traversing the membrane of the endoplasmic reticulum. Though the function of the intracellular C2 protein is unknown, it is abundant in all cell types that express the C2 gene.

Role of protein kinase C activation in synthesis of complement components C2 and factor B in interferon-gamma-stimulated human fibroblasts, glioblastoma cell line A172 and monocytes

The synthesis of C2 and factor B, the key components of complement system, is performed by various kinds of cells and is also up-regulated by interferon-gamma (IFN-gamma). By using human fibroblasts, human glioblastoma cell line A172 and monocytes, we investigated the signal-transduction mechanism for IFN-gamma-induced synthesis of C2 and factor B. The C2 and factor B synthesis induced by IFN-gamma in all three cell types was inhibited by a protein kinase C (PKC) inhibitor, 1-(5-isoquinolinyl-sulphonyl)-2-methylpiperazine (H-7). The depletion of PKC in these cell types after treatment with phorbol 12-myristate 13-acetate (PMA) resulted in inhibition of IFN-gamma-induced C2 production. In addition, IFN-gamma treatment elicited a decrease in cytoplasmic PKC in A172 cells, indicating that PKC is activated by IFN-gamma. These results suggest that PKC is crucial for IFN-gamma-induced C2 and factor B synthesis. Northern-blot analysis showed that the effects at H-7 were at least partly mediated by modulation of C2 and factor B mRNA abundance in A172 cells. Since treatment of fibroblasts and A172 cells with IFN-gamma had no effect on intracellular Ca2+ concentration, and since neither EGTA nor nifedipine inhibited C2 or factor B synthesis induced by IFN-gamma, we concluded that intracellular Ca2+ mobilization was not involved in the effect of IFN-gamma. In addition, genistein, herbimycin A and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W-7) had no inhibitory effect on IFN-gamma-mediated action in any of the three cell types, which suggests that IFN-gamma acts independently of tyrosine kinases and calmodulin-dependent protein kinases.