Biomedical subjects

Louise M C Webb

Publications and source records attributed to Louise M C Webb.

6 recordsLinked to original sources

PubMed2006

RhoG regulates the neutrophil NADPH oxidase.

RhoG is a Rho family small GTPase implicated in cytoskeletal regulation, acting either upstream of or in parallel to Rac1. The precise function(s) of RhoG in vivo has not yet been defined. We have identified a novel role for RhoG in signaling the neutrophil respiratory burst stimulated by G protein-coupled receptor agonists. Bone marrow-derived neutrophils from RhoG knockout (RhoG(-/-)) mice exhibited a marked impairment of oxidant generation in response to C5a or fMLP, but normal responses to PMA or opsonized zymosan and normal bacterial killing. Activation of Rac1 and Rac2 by fMLP was diminished in RhoG(-/-) neutrophils only at very early (5 s) time points (by 25 and 32%, respectively), whereas chemotaxis in response to soluble agonists was unaffected by lack of RhoG. Additionally, fMLP-stimulated phosphorylation of protein kinase B and p38MAPK, activation of phospholipase D, and calcium fluxes were equivalent in wild-type and RhoG(-/-) neutrophils. Our results define RhoG as a critical component of G protein-coupled receptor-stimulated signaling cascades in murine neutrophils, acting either via a subset of total cellular Rac relevant to oxidase activation and/or by a novel and as yet undefined interaction with the neutrophil NADPH oxidase.

Animals↗

PubMed2005

P-Rex1 regulates neutrophil function.

Rac GTPases regulate cytoskeletal structure, gene expression, and reactive oxygen species (ROS) production. Rac2-deficient neutrophils cannot chemotax, produce ROS, or degranulate upon G protein-coupled receptor (GPCR) activation. Deficiency in PI3Kgamma, an upstream regulator of Rac, causes a similar phenotype. P-Rex1, a guanine-nucleotide exchange factor (GEF) for Rac, is believed to link GPCRs and PI3Kgamma to Rac-dependent neutrophil responses. We have investigated the functional importance of P-Rex1 by generating a P-Rex1(-/-) mouse. P-Rex1(-/-) mice are viable and healthy, with apparently normal leukocyte development, but with mild neutrophilia. In neutrophils from P-Rex1(-/-) mice, GPCR-dependent Rac2 activation is impaired, whereas Rac1 activation is less compromised. GPCR-dependent ROS formation is absent in lipopolysaccharide (LPS)-primed P-Rex1(-/-) neutrophils, but less affected in unprimed or TNFalpha-primed cells. Recruitment of P-Rex1(-/-) neutrophils to inflammatory sites is impaired. Surprisingly, chemotaxis of isolated neutrophils is only slightly reduced, with a mild defect in cell speed, but normal polarization and directionality. Secretion of azurophil granules is unaffected. In conclusion, P-Rex1 is an important regulator of neutrophil function by mediating a subset of Rac-dependent neutrophil responses. However, P-Rex1 is not an essential regulator of neutrophil chemotaxis and degranulation.

Actins↗

PubMed2005

Cutting edge: T cell development requires the combined activities of the p110gamma and p110delta catalytic isoforms of phosphatidylinositol 3-kinase.

The role of PI3K activity in T lymphocyte development is obscure because mice deficient in single PI3K catalytic subunits either die before birth (p110alpha-/- and p110beta-/-) or lack a significant T cell developmental phenotype (p110gamma-/- and p110delta-/-). We have generated mice deficient in both p110gamma and p110delta and show that p110gamma/delta-/- mice have a profound block in T cell development that occurs at the beta-selection checkpoint. We show that pre-TCR-induced signaling is significantly reduced in p110gamma/delta-/- thymocytes and that this results in a concomitant lack of proliferative expansion and increased apoptosis. The survival defect in p110gamma/delta-/- thymocytes is associated with increased levels of the pro-apoptotic molecule Bcl2 interacting mediator of cell death. This work demonstrates that PI3K activity is critical for T cell development and depends on the combined function of p110gamma and p110delta.

Animals↗

PubMed2005

Virally encoded chemokine binding proteins.

Virus-encoded immune evasion mechanisms provide information on viral pathogenesis and offer a unique opportunity to identify new strategies of immune modulation. Secreted proteins that bind a broad range of chemokines have been identified in recent years in poxviruses and herpesviruses. We discuss the properties of these viral chemokine inhibitors and their potential as new therapeutics to treat human inflammatory diseases.

Animals↗

PubMed2004

The gammaherpesvirus chemokine binding protein can inhibit the interaction of chemokines with glycosaminoglycans.

Chemokines are small glycosaminoglycan (GAG) binding proteins that direct the migration of leukocytes by signaling through G protein coupled receptors (GPCR). Many viruses encode proteins that disrupt chemokine responses. The murine gammaherpesvirus-68 gene M3 encodes a chemokine binding protein (vCKBP-3), which has no sequence similarity to chemokine receptors. Initial characterization of vCKBP-3 showed that it inhibits receptor binding and chemokine-induced calcium influx. The structural requirements for the chemokines CXCL8 and CCL2 to bind to vCKBP-3 have been determined. Both chemokines bind to vCKBP-3 via their N-loop, a site that can participate in GAG binding for some chemokines. We have investigated the effect of vCKBP-3 on the interaction of chemokines with GAGs. We found that vCKBP-3 can prevent a range of chemokines from binding to GAGs. Moreover, we also found that vCKBP-3 can displace chemokines from a heparin-coated surface. Together, these data imply that vCKBP-3 can inhibit chemokine activity at two distinct levels. First, it inhibits chemokines from binding to their GPCR. Second, it inhibits their GAG binding and disrupts pre-formed chemokine gradients. This dual ability of vCKBP-3 makes it a more effective inhibitor of chemokine activity.

Animals↗

PubMed2003

The gammaherpesvirus chemokine binding protein binds to the N terminus of CXCL8.

Viruses encode proteins that disrupt chemokine responses. The murine gammaherpesvirus 68 gene M3 encodes a chemokine binding protein (vCKBP-3) which has no sequence similarity to chemokine receptors but inhibits chemokine receptor binding and activity. We have used a panel of CXCL8 analogs to identify the structural requirements for CXCL8 to bind to vCKBP-3 in a scintillation proximity assay. Our data suggest that vCKBP-3 acts by mimicking the binding of chemokine receptors to CXCL8.

Amino Acid Sequence↗