The Transient Pore Formed by Homologous Terminal Complement Complexes Functions as a Bidirectional Route for the Transport of Autocrine and Paracrine Signals across Human Cell Membranes

Abstract

Background: We have previously shown that the membrane attack complex (MAC) of complement stimulates cell proliferation and that insertion of homologous MAC into the membranes of endothelial cells results in the release of potent mitogens, including basic fibroblast growth factor (bFGF). The mechanism of secretion of bFGF and other polypeptides devoid of signal peptides, such as interleukin 1 (IL-1) is still an open problem in cell biology. We have hypothesized that the homologous MAC pore itself could constitute a transient route for the diffusion of biologically active macromolecules in and out of the target cells. Materials and Methods: Human red blood cell ghosts and artificial lipid vesicles were loaded with labeled growth factors, cytokines and IgG, and exposed to homologous MAC. The release of the '25I-macromolecules was followed as a function of time. The incorporation of labeled polypeptides and fluorescent dextran (MW: 10,000) was measured in MAC-impacted human red blood cells and human umbilical endothelial cells (HUVEC), respectively. Results: Homologous MAC insertion into HUVEC resulted in the massive uptake of 10-kD dextran and induced the release of bFGF, in the absence of any measurable lysis. Red blood cell ghosts preloaded with bFGF, IL-l1,3, and the a-chain of interferon-y (IFN-'y) released the polypeptides upon MAC insertion, but they did not release preloaded IgG. MAC-impacted ghosts took up radioactive IFN-,y from the extracellular medium. Vesicles loaded with IL-1 released the polypeptide when exposed to NAC. Conclusions: The homologous MAC pore in its nonlytic form allows for the export of cytosolic proteins devoid of signal peptides that are not secreted through the classical endoplasmic reticulum/Golgi exocytotic pathways. Our results suggest that the release, and perhaps the uptake, of biologically active macromolecules through the homologous MAC pore is a novel biological function of the complement system in mammals.

The NLRP3 Inflammasome Contributes to Brain Injury in Pneumococcal Meningitis and Is Activated through ATP-Dependent Lysosomal Cathepsin B Release

“…Moreover, we observed in a previous study that complement activation is a key factor in IL-1b production during pneumococcal meningitis (43). Both the anaphylatoxin C5a and the terminal complement complex C5b-9, which can form pores in host membranes (44), were also reported to stimulate IL-1b release by human mononuclear cells (45,46). In this study, we contribute to clarification of the role of pneumolysin and complement in pneumococci-induced IL-1b release by exposing cells to a pneumolysin-deficient strain and challenging cells in the absence of C5.…”

Increased All-Cause Mortality in Patients With Type 1 Diabetes and High-Expression Mannan-Binding Lectin Genotypes: A 12-Year Follow-up Study

“…On the basis of the present and previous results, we hypothesize that diabetesinduced alternations in enzymatic glycosylations and/or increased formation of advanced glycation end products lead to formation of patterns recognized by MBL. As shown in vitro, complement activation and sublytic formation of the terminal complement complex on mammalian cells may induce release of growth factors, leading to vascular alternations (26)(27)(28)(29)(30)(31). In addition, glycation of complement regulatory proteins has been shown to decrease their regulatory capacity and increase complement activation in diabetes (32,33).…”

Glycation Inactivation of the Complement Regulatory Protein CD59

“…Consistent with a key role of CD59 in protecting cells from MAC-mediated attack is the increased MAC deposition observed in cell membranes after deletion (31), absence (34), or inhibition (35) of CD59. In endothelium, absence or inhibition of CD59 results in increased MACinduced phenomena, including the release of growth factors and proinflammatory and prothrombotic cytokines that may, respectively, promote cell proliferation, inflammation, and thrombosis in the vascular wall (12). The (24).…”