Constitutive Expression and Regulation of Rat Complement Factor H in Primary Cultures of Hepatocytes, Kupffer Cells, and Two Hepatoma Cell Lines

Abstract

SUMMARY: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-␣, IL-1␤, and IFN-␥, only IFN-␥ 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-␥, 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 g LPS/ml did not show any effect on HC. Our data suggest that LPS does not regulate the expression of FH in HC. (Lab Invest 2002, 82:183-192).T he regulation of complement activation at the level of C3 and C4 is mediated by several receptors and soluble regulatory proteins. These include complement receptor 1 (CD35), complement receptor 2 (CD21), decay-accelerating factor (CD55), membrane cofactor protein (CD46), factor I (FI), and factor H (FH). These proteins, with the exception of FI, form the "regulators of complement activation" family (Hourcade et al, 1989). Their genes are closely linked on chromosome 1 in man and mouse. This illustrates that this region on the long arm of chromosome 1 in humans is analogous to that region in mice (Klickstein et al, 1985). The serine protease FI could be located to chromosome 4 in man (Goldberger et al, 1987) and to chromosome 3 in mouse (Minta et al, 1996).The potentially deleterious complement system is strictly regulated to prevent damage in the absence of pathologic situations Mulligan et al, 1992;Piddlesden et al, 1994;Smith et al, 1993). On some host cell surfaces, membrane-bound complement regulatory factors are expressed only at low levels. Thus, reduced protection against complement attack may be compensated by the soluble regulator FH, which has a critical role in complement inactivation in the fluid phase (Meri and Pangburn, 1990; Pangburn and Müller-Eberhardt, 1978) and acts in concert with FI. FH is a single-chain protein...

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

“…These data were in accordance with previous studies that described IFN‐γ‐dependent up‐regulation of FH in two human cell lines of hepatocellular origin and some other primary cells 21–24. LPS is, on the one hand, a potent activator of the alternative pathway of the complement system thereby generating the highly potent anaphylatoxin C5a and, on the other hand, has turned out to up‐regulate expression of the complement inhibitory FH 20. Therefore, the present study was performed to investigate the possibility that excessive activation of the complement system may be controlled by direct C5a‐mediated up‐regulation of FH in the liver.…”

“…In contrast to FI, which is restricted to hepatocytes (HC), FH was shown to be expressed in HC and Kupffer cells (KC). Furthermore, the proinflammatory cytokine IFN‐γ turned out to be a potent up‐regulator of FH‐specific mRNA and protein expression both in KC and HC 11, 20, whereas LPS up‐regulated the expression of FH only in KC 20. These data were in accordance with previous studies that described IFN‐γ‐dependent up‐regulation of FH in two human cell lines of hepatocellular origin and some other primary cells 21–24.…”

“…The primary site of FH synthesis is the liver 18, 19, although there are several extrahepatic cell types that have also been reported to express FH and may function as local sources of the protein, thereby reducing tissue damage caused by local complement activation. In a recent study 20, the constitutive expression of FH in primary cultured liver cells was investigated. In contrast to FI, which is restricted to hepatocytes (HC), FH was shown to be expressed in HC and Kupffer cells (KC).…”

Human complement factor H is a novel diagnostic marker for lung adenocarcinoma

“…This central fluid phase protein regulates the alternative pathway of the complement system (17)(18)(19). cfH was expressed in various malignant cell lines including ovarian, colon, bladder, liver and lung cancer cell lines (6,10,(20)(21)(22). it binds to c3b and blocks the alternative pathway of complement by i) acting as cofactor for c3b cleavage, ii) accelerating the decay of the alternative c3 convertase, and iii) preventing binding of factor B to c3.…”

Properdin and Factor H: Opposing Players on the Alternative Complement Pathway “See-Saw”

“…The 4.3 kb mRNA is more abundant than the 1.8 kb. The factor H secretion by Kupffer cells and hepatocytes is up-regulated by IFN-γ in rats (Schlaf et al, 2002). The extrahepatic synthesis of factor H in humans is also up-regulated by IFN-γ (Gasque et al, 1995; Friese et al, 1999, 2003; Schlaf et al, 2001).…”