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Dysfunctional cystic fibrosis transmembrane conductance regulator inhibits phagocytosis of apoptotic cells with proinflammatory consequences.

Cystic fibrosis (CF) is caused by mutated CF transmembrane conductance regulator (CFTR) and is characterized by robust airway inflammation and accumulation of apoptotic cells. Phagocytosis of apoptotic cells (efferocytosis) is a pivotal regulator of inflammation, because it prevents postapoptotic necrosis and actively suppresses release of a variety of proinflammatory mediators, including IL-8. Because CF is associated with accumulation of apoptotic cells, inappropriate levels of IL-8, and robust inflammation, we sought to determine whether CFTR deficiency specifically impairs efferocytosis and its regulation of inflammatory mediator release.

Inactivation of rho GTPases by statins attenuates anthrax lethal toxin activity.

Anthrax lethal factor (LF), secreted by Bacillus anthracis, interacts with protective antigen to form a bipartite toxin (lethal toxin [LT]) that exerts pleiotropic biological effects resulting in subversion of the innate immune response. Although the mitogen-activated protein kinase kinases (MKKs) are the major intracellular protein targets of LF, the pathology induced by LT is not well understood. The statin family of HMG-coenzyme A reductase inhibitors have potent anti-inflammatory effects independent of their cholesterol-lowering properties, which have been attributed to modulation of Rho family GTPase activity.

Peptide inhibitors MAP the way towards fighting anthrax pathogenesis.

The pathogenesis of anthrax is such that unless antibiotic treatment is initiated at an early stage in the disease, it is ineffective against the bacteria-induced toxaemia that subverts the immune response, inflicts massive tissue damage and is ultimately the major factor contributing to death during anthrax infection. As current events have demonstrated the feasibility of the use of anthrax as a bioterrorism agent, and exemplified the difficulty of treating the ensuing infection, inhibition of anthrax toxin has become a major focus of research for the design of antitoxin therapeutics. In this issue of Biochemical Journal, Bracci and co-workers describe the discovery by competitive screening of a phage-display library of a peptide inhibitor of anthrax toxin assembly that shows great promise towards the treatment of anthrax.

Rac2D57N, a dominant inhibitory Rac2 mutant that inhibits p38 kinase signaling and prevents surface ruffling in bone-marrow-derived macrophages.

Rac2 is a Rho GTPase that is expressed in cells of hematopoietic origin, including neutrophils and macrophages. We recently described an immunodeficient patient with severe, recurrent bacterial infections that had a point mutation in one allele of the Rac2 gene, resulting in the substitution of aspartate 57 with asparagine. To ascertain further the effects of Rac2D57N in leukocytes, Rac2D57N was expressed in primary murine bone-marrow-derived macrophages (cells that we show express approximately equal amounts of Rac1 and Rac2).

The final step in programmed cell death: phagocytes carry apoptotic cells to the grave.

As cells undergo apoptosis, they are recognized and removed from the body by phagocytes. This oft-overlooked yet critical final step in the cell-death programme protects tissues from exposure to the toxic contents of dying cells and also serves to prevent further tissue damage by stimulating production of anti-inflammatory cytokines and chemokines. The clearance of apoptotic-cell corpses occurs throughout the lifespan of multicellular organisms and is important for normal development during embryogenesis, the maintenance of normal tissue integrity and function, and the resolution of inflammation.

Phosphatidylserine (PS) induces PS receptor-mediated macropinocytosis and promotes clearance of apoptotic cells.

Efficient phagocytosis of apoptotic cells is important for normal tissue development, homeostasis, and the resolution of inflammation. Although many receptors have been implicated in the clearance of apoptotic cells, the roles of these receptors in the engulfment process have not been well defined. We developed a novel system to distinguish between receptors involved in tethering of apoptotic cells versus those inducing their uptake.

C1q and mannose binding lectin engagement of cell surface calreticulin and CD91 initiates macropinocytosis and uptake of apoptotic cells.

Removal of apoptotic cells is essential for maintenance of tissue homeostasis, organogenesis, remodeling, development, and maintenance of the immune system, protection against neoplasia, and resolution of inflammation. The mechanisms of this removal involve recognition of the apoptotic cell surface and initiation of phagocytic uptake into a variety of cell types. Here we provide evidence that C1q and mannose binding lectin (MBL), a member of the collectin family of proteins, bind to apoptotic cells and stimulate ingestion of these by ligation on the phagocyte surface of the multifunctional protein, calreticulin (also known as the cC1qR), which in turn is bound to the endocytic receptor protein CD91, also known as the alpha-2-macroglobulin receptor.

Loss of phospholipid asymmetry and surface exposure of phosphatidylserine is required for phagocytosis of apoptotic cells by macrophages and fibroblasts.

Removal of apoptotic cells during tissue remodeling or resolution of inflammation is critical to the restoration of normal tissue structure and function. During apoptosis, early surface changes occur, which trigger recognition and removal by macrophages and other phagocytes. Loss of phospholipid asymmetry results in exposure of phosphatidylserine (PS), one of the surface markers recognized by macrophages.

The Rib43a protein is associated with forming the specialized protofilament ribbons of flagellar microtubules in Chlamydomonas.

Ciliary and flagellar microtubules contain a specialized set of three protofilaments, termed ribbons, that are composed of tubulin and several associated proteins. Previous studies of sea urchin sperm flagella identified three of the ribbon proteins as tektins, which form coiled-coil filaments in doublet microtubules and which are associated with basal bodies and centrioles. To study the function of tektins and other ribbon proteins in the assembly of flagella and basal bodies, we have begun an analysis of ribbons from the unicellular biflagellate, Chlamydomonas reinhardtii, and report here the molecular characterization of the ribbon protein rib43a.