PubMed · 3538974
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C A Alper. 1986. Genetics of the complement system.. https://doi.org/10.1111/j.1749-6632.1986.tb20854.x
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Factor J (FJ) is an inhibitor of the classical and alternative complement pathways. On the classical pathway factor J disrupts the C1 component, and on the alternative pathway, factor J disrupts the C3 convertase (C3b,Bb) by a direct interaction of FJ with the components C3b and Bb. The aim of this work was to verify whether FJ could have any effect on factor D proteolytic activity since previous experiments could not rule out an eventual inhibition by factor J on factor D enzymatic activity. For this purpose, the reactivity of serine proteinase factor D was determined by using two peptide thioester substrates, Z-Lys-SBzl.HCl and Z-Lys-Arg-SBzl.2HCl, in the presence and in the absence of factor J. Kinetic studies evidenced that FJ did not affect the enzymatic activity of factor D in any case.
C1 inhibitor (C1 INH) is the major inhibitor of the proteolytically active subcomponents of C1, kallikrein, activated forms of factor XII, and factor XIa in plasma. We determined the mechanism(s) how interferon-gamma (IFN-gamma) regulates C1 INH mRNA expression in HepG2 cells. Cycloheximide or anisomycin treatment alone did not increase C1 INH mRNA nor did it potentiate C1 INH mRNA expression after IFN-gamma stimulation. C1 INH mRNA levels on Northern blot from untreated and IFN-gamma-treated cells did not change for more than 20 hours after actinomycin D treatment. Actinomycin D and 5,6-dichloro-1-beta-ribofuranosylbenzimidazole abolished IFN-gamma-induced C1 INH mRNA expression. Relatively more C1 INH mRNA precursor (heterogeneous nuclear RNA [hnRNA]) was detected in total RNA from IFN-gamma-treated HepG2 cells than unstimulated cells. Treatment of HepG2 cells with the phosphatase 1 and 2A inhibitors, okadaic acid (> or = 50 nmol/L) and calyculin (> or = 25 nmol/L), decreased IFN-gamma's ability to upregulated C1 INH mRNA. The phosphatase 2A inhibitor, cantharidin (> or = 10 micromol/L), also blocked the IFN-gamma induction of the C1 INH gene. In HepG2 cells total phosphatase 2A activity was significantly increased by C6 ceramide but not IFN-gamma. However, C6 ceramide itself did not increase C1 INH mRNA expression. These data indicate that phosphatase 2A is required to dephosphorylate a substrate in order for IFN-gamma to induce the transcriptional upregulation of C1 INH mRNA, but phosphatase 2A is not a direct stimulator of C1 INH gene expression.
An enzyme immuno assay was developed to measure complexes of tissue-type plasminogen activator (t-PA) with C1-inhibitor in order to study the role of C1-inhibitor as an inhibitor of t-PA in plasma. In vitro experiments with melanoma and recombinant t-PA learned that purified C1-inhibitor reacts with both single chain t-PA and two chain t-PA. The rate constants ranged from 3.0 to 5.2 M-1s-1. In plasma, melanoma and recombinant two chain t-PA were hardly inhibited by C1-inhibitor, in contrast to melanoma and recombinant single chain t-PA which were inhibited to the same extent by endogenous C1-inhibitor as they were by purified C1-inhibitor. In vivo, t-PA/C1-inhibitor complex could be measured in plasma in a few cases in healthy volunteers (0.62 +/- 0.43 ng/ml t-PA equivalents), after exercise (0.84 +/- 0.25 ng/ml t-PA equivalents) and after a desmopression infusion (0.26 +/- 0.04 ng/ml t-PA equivalents). However, t-PA/C1-inhibitor complex was found in plasma in all cases after venous occlusion (1.7 +/- 0.5 ng/ml t-PA equivalents), in peritoneal fluid from patients suffering from peritoneal inflammatory disease (2.2 +/- 1.3 ng/ml t-PA equivalents) and in plasma from healthy volunteers during a t-PA infusion (27.7 +/- 18.5 ng/ml t-PA equivalents at peak level). In the last case, about 8% of the infused dose of recombinant t-PA (alteplase) was inhibited by C1-inhibitor at peak level.(ABSTRACT TRUNCATED AT 250 WORDS)