An intracellular signaling hierarchy determines direction of migration in opposing chemotactic gradients

Abstract

Neutrophils must follow both endogenous and bacterial chemoattractant signals out of the vasculature and through the interstitium to arrive at a site of infection. By necessity, in the setting of multiple chemoattractants, the neutrophils must prioritize, favoring end target chemoattractants (e.g., fMLP and C5a) emanating from the site of infection over intermediary endogenous chemoattractants (e.g., IL-8 and LTB4) encountered en route to sites of infection. In this study, we propose a hierarchical model of two signaling pathways mediating the decision-making process of the neutrophils, which allows end target molecules to dominate over intermediary chemoattractants. In an under agarose assay, neutrophils predominantly migrated toward end target chemoattractants via p38 MAPK, whereas intermediary chemoattractant-induced migration was phosphoinositide 3-kinase (PI3K)/Akt dependent. When faced with competing gradients of end target and intermediary chemoattractants, Akt activation was significantly reduced within neutrophils, and the cells migrated preferentially toward end target chemoattractants even at 1/1,000th that of intermediary chemoattractants. End target molecules did not require chemotactic properties, since the p38 MAPK activator, LPS, also inhibited Akt and prevented migration to intermediary chemoattractants. p38 MAPK inhibitors not only reversed this hierarchy, such that neutrophils migrated preferentially toward intermediary chemoattractants, but also allowed neutrophils to be drawn out of a local end target chemoattractant environment and toward intermediary chemoattractants unexpectedly in an exaggerated (two- to fivefold) fashion. This was entirely related to significantly increased magnitude and duration of Akt activation. Finally, end target chemoattractant responses were predominantly Mac-1 dependent, whereas nondominant chemoattractants used primarily LFA-1. These data provide support for a two pathway signaling model wherein the end target chemoattractants activate p38 MAPK, which inhibits intermediary chemoattractant-induced PI3K/Akt pathway, establishing an intracellular signaling hierarchy.

Hierarchy of eosinophil chemoattractants: role of p38 mitogen‐activated protein kinase

“…Interestingly, inhibition of p38 MAP kinase converted the inhibitory effect of 5-oxo-ETE on migration towards PGD 2 to enhancement, and this coincided with 5-oxo-ETE-induced p38 MAP kinase phosphorylation, which suggests that it is the MAP kinase pathway that determines the hierarchy of eosinophil chemoattractants. p38 MAP kinase has been shown to be essential for neutrophil orientation in opposing gradients of chemoattractants [36]. However, in contrast to the observations of Heit et al [36], where inhibition of p38 MAP kinase induced the activation PI-3 kinase and by that enhanced the chemotactic responsiveness of neutrophils, here we observed that p38 MAP kinase and PI-3 kinase acted in a consecutive manner in eosinophils.…”

“…p38 MAP kinase has been shown to be essential for neutrophil orientation in opposing gradients of chemoattractants [36]. However, in contrast to the observations of Heit et al [36], where inhibition of p38 MAP kinase induced the activation PI-3 kinase and by that enhanced the chemotactic responsiveness of neutrophils, here we observed that p38 MAP kinase and PI-3 kinase acted in a consecutive manner in eosinophils. This notion was based on the fact that inhibition of PI-3 kinase reversed the inhibitory effect of 5-oxo-ETE on eosinophil migration to enhancement, as did inhibition of p38 MAP kinase.…”

Soluble Fractalkine Prevents Monocyte Chemoattractant Protein-1-Induced Monocyte Migration via Inhibition of Stress-Activated Protein Kinase 2/p38 and Matrix Metalloproteinase Activities

“…Indeed, several reports have shown that SAPK2/p38 is involved in chemokine-induced chemotaxis of cells (16,34,70,71). Our study also presents evidence that SAPK2/p38 and SAPK1/JNK1, but not ERKs, intervene in the control of MCP-1-induced MonoMac6 migration.…”

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…Chemoattractant control of neutrophil migration is complex, not least because the effect on chemotaxis may depend on agonist concentration and context, but also the in vivo milieu is a dynamic environment comprising multiple chemokine signals. There is intracellular signalling hierarchy, with end-target chemoattractants signalling predominantly through p38 MAPK [4]. Neutrophils are avid phagocytes, which recognise and rapidly ingest bacteria.…”