Macrophage motility requires distinct α5β1/FAK and α4β1/paxillin signaling events

Abstract

Macrophages function as key inflammatory mediators at sites of infection and tissue damage. Integrin and growth factor receptors facilitate recruitment of monocytes/macrophages to sites of inflammation in response to numerous extracellular stimuli. We have shown recently that FAK plays a role in regulating macrophage chemotaxis and invasion. As FAK is an established downstream mediator of integrin signaling, we sought to define the molecular circuitry involving FAK and the predominant β1 integrin heterodimers expressed in these cells-α4β1 and α5β1. We show that α4β1 and α5β1 integrins are required for efficient haptotactic and chemotactic invasion and that stimulation of these integrin receptors leads to the adoption of distinct morphologies associated with motility. FAK is required downstream of α5β1 for haptotaxis toward FN and chemotaxis toward M-CSF-1 and downstream of α4β1 for the adoption of a polarized phenotype. The scaffolding molecule paxillin functions independently of FAK to promote chemotaxis downstream of α4β1. These studies expand our understanding of β1 integrin signaling networks that regulate motility and invasion in macrophages and thus, provide important new insights into mechanisms by which macrophages perform their diverse functions.

Fibronectin induces macrophage migration through a SFK-FAK/CSF-1R pathway

“…19 Moreover, later evidences definitively linked FAK to macrophage migration. 20,21 In particular, experiments carried out using murine FAK ¡/¡ cells showed that FAK mediates haptotaxis elicited by the activation of a5b1 integrin, that binds a number of substrates including FN. 20 We therefore characterized the effects of FN on FAK activation in macrophages.…”

“…20,21 In particular, experiments carried out using murine FAK ¡/¡ cells showed that FAK mediates haptotaxis elicited by the activation of a5b1 integrin, that binds a number of substrates including FN. 20 We therefore characterized the effects of FN on FAK activation in macrophages. No previous data were indeed available on a possible link between FN-elicited signaling and FAK phosphorylation in macrophages.…”

“…20,21 To evaluate whether FAK is involved in macrophage migration toward FN, we silenced FAK using specific siRNA ( Fig. 2A).…”

Erythroid cells generated in the absence of specific 1-integrin heterodimers accumulate reactive oxygen species at homeostasis and are unable to mount effective antioxidant defenses

“…[43][44][45][46][47] Furthermore, in fibroblasts, neural cells or macrophages, migratory signals elicited by α4β1 are distinct from those elicited in the same cells by α5β1. [33][34][35][36] Their motility was dependent on α5/FAK signaling, but this was dispensable for α4β1-mediated signaling mediated through c-Src activation instead. In hematopoietic cells, integrin-dependent FAK signaling is thought to be important in integrating growth/survival signals, especially under stress.…”

“…33 For example, it has previously been shown that α5β1 and α4β1 integrins stimulate motility in fibroblasts, neural cells or macrophages through distinct mechanisms: an FAK/Pyk2 linkage is essential for α5-signaling, but not for α4-dependent signaling, which depends only on c-Src activation, 34,35 and paxillin can promote α4-mediated macrophage chemotaxis independently of FAK. 36 Consequently, it could be suggested that, for erythroid proliferative expansion in spleen, as occurs in α4 −/− mice, the α4/c-Src-dependent signaling is dispensable. If instead the α5/FAK-dependent signaling is responsible, then inhibition of this signaling should phenocopy the response of β1 D/D mice to stress.…”