Characterization of the 5' flanking region of the human complement factor H gene

Complement factor H gene (CFH) polymorphisms C-257T, G257A and haplotypes are associated with protection against severe dengue phenotype, possible related with high CFH expression

Four genetic polymorphisms located at the promoter (C-257T) and coding regions of CFH gene (exon 2 G257A, exon 14 A2089G and exon 19 G2881T) were investigated in 121 dengue patients (DENV-3) in order to assess the relationship between allele/haplotypes variants and clinical outcomes. A statistical value was found between the CFH-257T allele (TT/TC genotypes) and reduced susceptibility to severe dengue (SD). Statistical associations indicate that individuals bearing a T allele presented significantly higher protein levels in plasma. The -257T variant is located within a NF-κB binding site, suggesting that this variant might have effect on the ability of the CFH gene to respond to signals via the NF-κB pathway. The G257A allelic variant showed significant protection against severe dengue. When CFH haplotypes effect was considered, the ancestral CG/CG promoter-exon 2 SNP genotype showed significant risk to SD either in a general comparison (ancestral × all variant genotypes), as well as in individual genotypes comparison (ancestral × each variant genotype), where the most prevalent effect was observed in the CG/CG × CA/TG comparison. These findings support the involvement of -257T, 257A allele variants and haplotypes on severe dengue phenotype protection, related with high basal CFH expression.

Interleukin 27 induces the expression of complement factor H (CFH) in the retina

Complement factor H (CFH) is a central regulator of the complement system and has been implicated in the etiology of age-related macular degeneration (AMD), a leading cause of blindness in the elderly. In view of previous studies showing that reduced expression of CFH in the retina is a risk factor for developing AMD, there is significant interest in understanding how CFH expression is regulated in the retina. In this study, we have shown that the anti-inflammatory cytokine, IL-27, induced CFH expression in mouse retinal cells and human retinal pigmented epithelial cells (RPE) through STAT1-mediated up-regulation of Interferon Regulatory Factor-1 (IRF-1) and IRF-8. We further show that cells in the ganglion and inner-nuclear layers of the retina constitutively express IRF-1 and IRF-8 and enhanced CFH expression in the retina during ocular inflammation correlated with significant increase in the expression of IRF-1, IRF-8 and IL-27 (IL-27p28 and Ebi3). Our data thus reveal a novel role of IL-27 in regulating complement activation through up-regulation of CFH and suggest that defects in IL-27 signaling or expression may contribute to the reduction of CFH expression in the retina of patients with AMD.

c-Jun and c-Fos regulate the complement factor H promoter in murine astrocytes

The complement system is a critical component of innate immunity that requires regulation to avoid inappropriate activation. This regulation is provided by many proteins, including complement factor H (CFH), a critical regulator of the alternative pathway of complement activation. Given its regulatory function, mutations in CFH have been implicated in diseases such as age-related macular degeneration and membranoproliferative glomerulonephritis, and central nervous system diseases such as Alzheimer's disease, Parkinson's disease, and a demyelinating murine model, experimental autoimmune encephalomyelitis (EAE). There have been few investigations on the transcriptional regulation of CFH in the brain and CNS. Our studies show that CFH mRNA is present in several CNS cell types. The murine CFH (mCFH) promoter was cloned and examined through truncation constructs and we show that specific regions throughout the promoter contain enhancers and repressors that are positively regulated by inflammatory cytokines in astrocytes. Database mining of these regions indicated transcription factor binding sites conserved between different species, which led to the investigation of specific transcription factor binding interactions in a 241 base pair (bp) region at -416 bp to -175 bp that showed the strongest activity. Through supershift analysis, it was determined that c-Jun and c-Fos interact with the CFH promoter in astrocytes in this region. These results suggest a relationship between cell cycle and complement regulation, and how these transcription factors and CFH affect disease will be a valuable area of investigation.

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.

Constitutive expression of murine decay-accelerating factor 1 is controlled by the transcription factor Sp1

The complement regulatory protein decay-accelerating factor (DAF or CD55) protects host tissue from complement-mediated injury by inhibiting the classical and alternative complement pathways. Besides its role in complement regulation, DAF has also been shown to be a key player in T cell immunity. Modulation of DAF expression could therefore represent a critical regulatory mechanism in both innate and adaptive immune responses. To identify and characterize key transcriptional regulatory elements controlling mouse Daf1 expression, a 2.5-kb fragment corresponding to the 5' flanking region of the mouse Daf1 gene was cloned. Sequence analysis showed that the mouse Daf1 promoter lacks conventional TATA and CCAAT boxes and displays a high guanine and cytosine content. RACE was used to identify one major and two minor transcription start sites 47, 20, and 17 bp upstream of the translational codon. Positive and negative regulatory regions were identified by transiently transfecting sequential 5'deletion constructs of the 5'flanking region into NIH/3T3, M12.4, and RAW264.7 cells. Mutational analyses of the promoter region combined with Sp1-specific ELISA showed that the transcription factor Sp1 is required for basal transcription and LPS-induced expression of the Daf1 gene. These findings provide new information on the regulation of the mouse Daf1 promoter and will facilitate further studies on the expression of Daf1 during immune responses.

Release of endogenous anti-inflammatory complement regulators FHL-1 and factor H protects synovial fibroblasts during rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory disease of unknown aetiology predominantly affecting cells and tissues of synovial joints. Here we show that the two important complement regulators FHL-1 and factor H play a protective anti-inflammatory role in rheumatoid arthritis. Expression analyses at the mRNA- and protein level show in vitro expression and secretion of both regulators by synovial fibroblasts derived from patients with rheumatoid arthritis. Similarly the two regulators are synthesized in vivo in diseased synovial tissue, and in particular synovial lining cells express high levels of FHL-1. The anti-inflammatory role of these regulators in rheumatoid arthritis is highlighted by their induction with IFN-gamma and dexamethasone, whilst the pro-inflammatory cytokine TNF-alpha had no effect. Transient transfection experiments with various FHL-1/factor H promoter-luciferase reporter constructs into cells of distinct origin show independent cell and tissue specific promoter regulated transcription of these two regulators. The inducible expression, specifically of FHL-1 has physiological consequences. By binding directly to surfaces the released proteins protect cells from inflammatory damage and complement-mediated cell lysis. This study shows a novel protective and anti-inflammatory role of the two important complement regulators FHL-1 and factor H in rheumatoid arthritis and suggests a disease controlling role of the two proteins.

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.

Cancer and diabetes: two pathological conditions in which adrenomedullin may be involved

Adrenomedullin (AM) is a regulatory peptide involved in several physiological processes. Among them, AM has been implicated in the regulation of growth, both with mitogenic and antiproliferative activities on normal cells. AM is widely expressed during embryogenesis and may have a significant role in the proliferation and differentiation processes associated with development. AM is also expressed by cancer cell lines and tumors and has been implicated in the growth of malignant cells. Some additional activities associated with AM (antiapoptotic capabilities, angiogenic potential, and upregulation in hypoxic conditions), together with its wide distribution in cancer, suggest that AM may be an important factor in carcinogenesis. Besides its implication in growth, embryogenesis and tumor biology, AM is also involved in pancreatic regulation and diabetes. AM regulates insulin secretion and is overexpressed in the plasma of diabetic patients. Several findings indicate that AM may participate in the pathogenesis and/or clinical complications of this disease.

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.

FHL-1/reconectin and factor H: two human complement regulators which are encoded by the same gene are differently expressed and regulated

FHL-1/reconectin and factor H are two human complement regulators which are encoded by a single gene. FHL-1/reconectin contains the first 7 of 20 SCR protein domains of factor H and has four unique residues attached to its C-terminal end. The overlapping region of 445 amino acids explains the related complement regulatory functions of the two proteins. However, unique biological functions have also been reported for FHL-1/reconectin, such as cell adhesion and binding to microbial surfaces. Both proteins are synthesised and secreted by the liver. Extrahepatic synthesis occurs in a wide variety of cells, e.g. in monocytes, fibroblasts or neuronal cells. Unexpectedly, FHL-1/reconectin and factor H exhibit distinct expression patterns. This is also observed in disease situations such as in rheumatoid arthritis or malignancies. In rheumatoid arthritis a potentially protective role is suggested by the local synthesis of both FHL-1/reconectin and factor H in synovial fibroblasts and their induction by the anti-inflammatory agent dexamethasone and the cytokine IFN-gamma, but not by TNF-alpha. FHL-1/reconectin is overexpressed in certain tumor cells such as glioblastoma, conferring an exceptional resistance to such cells against complement mediated lysis. Although FHL-1/reconectin and factor H are encoded by a single gene, regulated by the same gene promoter and initiate transcription at the same start site, their transcripts are differently regulated. The putative control levels, which are responsible for this complex regulation, include transcript elongation, RNA processing, alternative splicing and differential poly(A) site selection.

Regulation of complement factor H expression in L cells

The luciferase system was used to assay basal promoter activity of the murine factor H gene in the fibroblast cell line L929 (L cells). Thirteen nested deletion constructs were tested, and a region between -811 and -344 was found to have enhancer activity in the context of a heterologous promoter. This fragment was subdivided further and each of the two resulting subfragments also had enhancer activity. These subfragments each were shifted in electrophoretic mobility shift assays and were able to cross-inhibit each other in binding to a nuclear factor. Sequence analysis of these subfragments revealed the presence of an octamer in each subfragment, and a synthetic oligomer containing this octamer sequence was able to block binding in the mobility shift assay. Thus, this octamer sequence appears to play a major role in the basal expression of the factor H gene in L cells.

Complement receptor type 1 gene regulation: retinoic acid and cytosine arabinoside increase CR1 expression

Complement receptor type 1 (CR1) is expressed principally on erythrocytes, monocytes, neutrophils and B cells, where it acts as a negative regulator of the complement cascade and as a clearance mechanism for immune complexes. As CR1 expression occurs in a number of lineages, its regulation may parallel other steps in haematopoiesis. Several leucocyte-cell lines (including K-562, THP-1, U-937 and HL-60) and B-cell lines, as well as peripheral blood cells (PBCs), were tested for the ability of various compounds to up-regulate their CR1 expression. While most of the compounds tested had minimal effects on CR1 message level, retinoic acid induced increases in mRNA levels in nearly all cell lines studied. Furthermore, in K-562 cells, the cytosine analogue Ara-C, an inducer of erythroid differentiation, caused the highest increases in CR1 mRNA levels as compared to untreated cells. Ara-C also induced significant increases in CR1 message in PBCs. These data suggest that induction of specific CR1 expression could be an integral part of blood cell differentiation and that the identified cell induction systems may be useful as models to study the regulation of CR1 gene expression.