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Biomedical subjects

Darcy B Gill

Publications and source records attributed to Darcy B Gill.

5 recordsLinked to original sources
PubMed2005

Engagement of CD46 and alpha5beta1 integrin by group A streptococci is required for efficient invasion of epithelial cells.

Membrane cofactor protein (MCP or CD46), a widely distributed complement regulatory human protein, is a cell surface receptor for many pathogens including group A streptococci (GAS). The surface M protein of GAS binds CD46 and mediates GAS adherence to keratinocytes. In the present study, we studied the role of CD46 in GAS invasion of human lung epithelial cells, A549. Anti-CD46 antibody which specifically blocks the domain to which M protein binds inhibited adherence to and invasion of A549 cells by GAS. Moreover, downregulation of CD46 expression on A549 by RNA interference resulted in reduced invasion of these cells by GAS. A mutant form of CD46 with a deletion in the cytoplasmic domain was overexpressed in A549 cells, which resulted in partial inhibition of invasion. This indicates that the cytoplasmic tail is required for CD46 to promote invasion by GAS. Invasion assays with Lactococcus lactis that express M protein demonstrated the dependence of CD46-promoted invasion on interaction with M protein. In addition, CD46-mediated invasion was also found to be dependent on the extracellular matrix protein fibronectin.

Antigens, Bacterial↗
PubMed2005

Release of host-derived membrane vesicles following pilus-mediated adhesion of Neisseria gonorrhoeae.

Following attachment of Neisseria gonorrhoeae to human epithelial cell lines, the cellular pilus receptor CD46 is shed from the cell and accumulates in the media. In this report, we assess Neisseria-induced alterations in CD46 surface distribution and characterize this complement regulatory protein following its release from the infected cell. Within 3 h of attachment of gonococci to human epithelial cell lines, CD46 is enriched beneath sites of microcolony adhesion. By 6 h post infection, differential ultracentrifugation of culture media from ME-180 monolayers resulted in sedimentation of structurally and functionally intact CD46. Electron microscopy of these 100,000 g pellets revealed 30-200 nm vesicles. These vesicles likely originated from the host cell as they contained additional host cell surface proteins including CD55 and the epidermal growth factor receptor. Further, these vesicles were visualized by quick-freeze, deep-etch electron microscopy in association with the surface of infected ME-180 cells and with pili of adherent gonococci. Like CD46 shedding, CD46 redistribution and vesicle release were insensitive to colchicine and cytochalasin-D but dependent on expression of the pilus retraction protein PilT. This vesiculation may represent a host cell defence response in which surface proteins that are commonly exploited by pathogens, such as CD46, are removed from the cell.

Adenosine Triphosphatases↗
PubMed2004

CD46: expanding beyond complement regulation.

During the 1980s CD46 was discovered in a search for C3b binding proteins of human peripheral blood cells. Its role as an inactivator of C3b and C4b deposited on self-tissue is highlighted by the observation that partial deficiency of CD46 is a predisposing factor to hemolytic uremic syndrome. This discovery has an impact on the treatment options for these patients. Other new findings have expanded the role of CD46 in immunity and disease. For example, signaling through CD46 on human T lymphocytes drives them to become regulatory cells, indicating a novel link between the complement system and cellular immunity. Also, CD46 interacts with at least seven human pathogens and participates in reproduction/fertilization, further suggesting that dissecting its multi-faceted activities will have important clinical implications.

Anemia, Hemolytic↗
PubMed2003

Down-regulation of CD46 by piliated Neisseria gonorrhoeae.

Human membrane cofactor protein (CD46) protects host cells against complement attack and may function as a receptor for pathogenic Neisseriae. We assessed CD46 expression in the human cervical cell line ME-180 after exposure to Neisseria gonorrhoeae. Piliated but not nonpiliated gonococci adhered to cells and produced up to an 80% reduction in CD46 surface expression by 6 h that persisted for at least 24 h. This response required a minimum multiplicity of infection of 10 and was not prevented by antibodies to CD46. CD46 down-regulation was not attributable to intracellular retention or a global or specific shutdown of mRNA or protein synthesis. Substantial quantities of CD46 were found in the supernatants, indicating a specific shedding of this protein. Adherent gonococci lacking the pilus retraction protein PilT did not down-regulate CD46 but de-repression of pilT expression restored CD46 down-regulation. After experimental infection of human volunteers with a gonococcal variant incapable of inducing CD46 down-regulation, variants of this strain were reisolated that exhibited CD46 down-regulation. Pilus-mediated interactions of gonococci with human epithelial cells results in a pathogen-induced manipulation of the host cell environment in which a membrane protein is removed from epithelial cells by liberation into the surrounding milieu.

Antigens, CD↗