Actin dynamics rapidly reset chemoattractant receptor sensitivity following adaptation in neutrophils

Abstract

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.

Mechanics regulates ATP-stimulated collective calcium response in fibroblast cells

“…We interpret results from our two-dimensional cultures as cells cultured on a soft PA substrate form fewer actin fibres and therefore are not anchored as strongly to the substrate. A related observation in the literature is made in neutrophils, where actin dynamics are necessary to reset the sensitivity of receptors, thus enabling the neutrophils to respond repetitively to chemoattractants [66]. Similarly, we hypothesize that a softer PA gel or hydrogel influences the actin filaments' structure and dynamics, giving fibroblasts higher sensitivity to ATP, thus more oscillation peaks during a calcium response.…”

The Directional Response of Chemotactic Cells Depends on a Balance between Cytoskeletal Architecture and the External Gradient

“…They argued that receptor resensitization required cytoskeletal dynamics and therefore JLY-treatment led to termination of the response (Dandekar et al, 2013). The difference might due to the steepness of the applied gradient and the time period assessed.…”

“…JLY-treated HL-60 neutrophils stop migrating and maintain their shape, although Rac activity seen at the leading edge of moving cells disappears (Dandekar et al, 2013; Peng et al, 2011). Thus a dynamic cytoskeleton appears to be necessary to maintain polarization in the signal transduction system.…”

Moving towards a paradigm: common mechanisms of chemotactic signaling in Dictyostelium and mammalian leukocytes

“…In addition, there is a significant decrease in the amplification of internal PIP3 gradients in neutrophil cells in a gradient [332]. Moreover, when actin dynamics are stabilized using several pharmacological inhibitors, the actin cytoskeleton positively regulates receptor desensitization in neutrophil fMLP responses [333]. …”