Actin dynamics rapidly reset chemoattractant receptor sensitivity following adaptation in neutrophils.

Neutrophils are cells of the innate immune system that hunt and kill pathogens using directed migration. This process, known as chemotaxis, requires the regulation of actin polymerization downstream of chemoattractant receptors. Reciprocal interactions between actin and intracellular signals are thought to underlie many of the sophisticated signal processing capabilities of the chemotactic cascade including adaptation, amplification and long-range inhibition. However, with existing tools, it has been difficult to discern actin's role in these processes. Most studies investigating the role of the actin cytoskeleton have primarily relied on actin-depolymerizing agents, which not only block new actin polymerization but also destroy the existing cytoskeleton. We recently developed a combination of pharmacological inhibitors that stabilizes the existing actin cytoskeleton by inhibiting actin polymerization, depolymerization and myosin-based rearrangements; we refer to these processes collectively as actin dynamics. Here, we investigated how actin dynamics influence multiple signalling responses (PI3K lipid products, calcium and Pak phosphorylation) following acute agonist addition or during desensitization. We find that stabilized actin polymer extends the period of receptor desensitization following agonist binding and that actin dynamics rapidly reset receptors from this desensitized state. Spatial differences in actin dynamics may underlie front/back differences in agonist sensitivity in neutrophils

Actin dynamics rapidly reset chemoattractant receptor sensitivity following adaptation in neutrophils.

Neutrophils are cells of the innate immune system that hunt and kill pathogens using directed migration. This process, known as chemotaxis, requires the regulation of actin polymerization downstream of chemoattractant receptors. Reciprocal interactions between actin and intracellular signals are thought to underlie many of the sophisticated signal processing capabilities of the chemotactic cascade including adaptation, amplification and long-range inhibition. However, with existing tools, it has been difficult to discern actin's role in these processes. Most studies investigating the role of the actin cytoskeleton have primarily relied on actin-depolymerizing agents, which not only block new actin polymerization but also destroy the existing cytoskeleton. We recently developed a combination of pharmacological inhibitors that stabilizes the existing actin cytoskeleton by inhibiting actin polymerization, depolymerization and myosin-based rearrangements; we refer to these processes collectively as actin dynamics. Here, we investigated how actin dynamics influence multiple signalling responses (PI3K lipid products, calcium and Pak phosphorylation) following acute agonist addition or during desensitization. We find that stabilized actin polymer extends the period of receptor desensitization following agonist binding and that actin dynamics rapidly reset receptors from this desensitized state. Spatial differences in actin dynamics may underlie front/back differences in agonist sensitivity in neutrophils

A chemokine receptor CCR-1 antagonist reduces renal fibrosis after unilateral ureter ligation

The expression of chemokines and their receptors is thought to contribute to leukocyte infiltration and progressive renal fibrosis after unilateral ureter obstruction (UUO). We hypothesized that blocking the chemokine receptor CCR1 using the nonpeptide antagonist BX471 could reduce leukocyte infiltration and renal fibrosis after UUO. UUO kidneys from BX471-treated mice (day 0–10 and day 6–10) revealed a 40–60% reduction of interstitial macrophage and lymphocyte infiltrate compared with controls. Treated mice also showed a marked reduction of CCR1 and CCR5 mRNA levels, and FACS analysis showed a comparable reduction of CD8(+)/CCR5(+) T cells. Markers of renal fibrosis, such as interstitial fibroblasts, interstitial volume, mRNA and protein expression for collagen I, were all significantly reduced by BX471-treatment compared with vehicle controls. By contrast treatment was ineffective when the drug was supplied only from days 0 to 5. In summary, blockade of CCR1 substantially reduces cell accumulation and renal fibrosis after UUO. Most interestingly, late onset of treatment is also effective. We therefore conclude that CCR1 blockade may represent a new therapeutic strategy for reducing cellular infiltration and renal fibrosis as major factors in the progression to end-stage renal failure

The first World Cell Race

In Authors: WCR participants World Wide, listed in Supplemental InformationInternational audienceMotility is a common property of animal cells. Cell motility is required for embryogenesis [1], tissue morphogenesis [2] and the immune response [3] but is also involved in disease processes, such as metastasis of cancer cells [4]. Analysis of cell migration in native tissue in vivo has yet to be fully explored, but motility can be relatively easily studied in vitro in isolated cells. Recent evidence suggests that cells plated in vitro on thin lines of adhesive proteins printed onto culture dishes can recapitulate many features of in vivo migration on collagen fibers [5,6]. However, even with controlled in vitro measurements, the characteristics of motility are diverse and are dependent on the cell type, origin and external cues. One objective of the first World Cell Race was to perform a large-scale comparison of motility across many different adherent cell types under standardized conditions. To achieve a diverse selection, we enlisted the help of many international laboratories, who submitted cells for analysis. The large-scale analysis, made feasible by this competition-oriented collaboration, demonstrated that higher cell speed correlates with the persistence of movement in the same direction irrespective of cell origin

Bacterial virulence proteins as tools to rewire kinase pathways in yeast and immune cells

Bacterial pathogens have evolved specific effector proteins that, by interfacing with host kinase signaling pathways, provide a mechanism to evade immune responses during infection(1,2). Although these effectors are responsible for pathogen virulence, we realized that they might also serve as valuable synthetic biology reagents for engineering cellular behavior. Here, we have exploited two effector proteins, the Shigella flexneri OspF protein(3) and Yersinia pestis YopH protein(4), to systematically rewire kinase-mediated responses in both yeast and mammalian immune cells. Bacterial effector proteins can be directed to selectively inhibit specific mitogen activated protein kinase (MAPK) pathways in yeast by artificially targeting them to pathway specific complexes. Moreover, we show that unique properties of the effectors generate novel pathway behaviors: OspF, which irreversibly inactivates MAPKs(4), was used to construct a synthetic feedback circuit that displays novel frequency-dependent input filtering. Finally, we show that effectors can be used in T cells, either as feedback modulators to precisely tune the T cell response amplitude, or as an inducible pause switch that can temporarily disable T cell activation. These studies demonstrate how pathogens could provide a rich toolkit of parts to engineer cells for therapeutic or biotechnological applications