Intramembranous processing by γ-secretase regulates reverse signaling of ephrin-B2 in migration of microglia

The Eph-ephrin system plays pivotal roles in cell adhesion and migration. The receptor-like functions of the ephrin ligands allow the regulation of intracellular processes via reverse signaling. γ-Secretase mediated processing of ephrin-B has previously been linked to activation of Src, a kinase crucial for focal adhesion and podosome phosphorylation. Here, we analyzed the role of γ-secretase in the stimulation of reverse ephrin-B2 signaling in the migration of mouse embryonic stem cell derived microglia. The proteolytic generation of the ephrin-B2 intracellular domain (ICD) by γ-secretase stimulates Src and focal adhesion kinase (FAK). Inhibition of γ-secretase decreased the phosphorylation of Src and FAK, and reduced cell motility. These effects were associated with enlargement of the podosomal surface. Interestingly, expression of ephrin-B2 ICD could rescue these effects, indicating that this proteolytic fragment mediates the activation of Src and FAK, and thereby regulates podosomal dynamics in microglial cells. Together, these results identify γ-secretase as well as ephrin-B2 as regulators of microglial migration

Siglec-mediated regulation of immune cell function in disease

All mammalian cells display a diverse array of glycan structures that differ from those found on microbial pathogens. Siglecs are a family of sialic acid-binding immunoglobulin-like receptors that participate in the discrimination of ‘self’ and ‘non-self’ and regulate the functions of cells in the innate and adaptive immune systems through recognition of their glycan ligands. In this review, we describe the recent advances in our understanding of the roles of Siglecs in the regulation of immune cell functions in infectious diseases, inflammation, neurodegeneration, autoimmune diseases and cancer