Plexin C1 engagement on mouse dendritic cells by viral semaphorin A39R induces actin cytoskeleton rearrangement and inhibits integrin-mediated adhesion and chemokine-induced migration.

The poxvirus A39R protein is a member of the semaphorin family previously reported to bind plexin C1. We show that, in the mouse, plexin C1 is expressed on dendritic cells (DCs) and neutrophils and is the only receptor for A39R on these cells. The biological effects of a recombinant form of A39R were examined in vitro on mouse DCs derived from wild-type or plexin C1(-/-) mice. A39R binding to plexin C1 on DCs inhibited integrin-mediated adhesion and spreading in vitro. This phenomenon was accompanied by a decrease in integrin signaling, measured by focal adhesion kinase phosphorylation, and a rearrangement of the actin cytoskeleton, without inducing DC maturation or affecting their viability. The A39R effect on DC adhesion was blocked by a specific inhibitor of cofilin phosphorylation, suggesting that the regulation of F-actin turnover by plexin C1 was essential to induce cellular retraction. Furthermore, A39R binding to plexin C1 inhibited chemokine-induced migration of DCs in vitro, suggesting that plexins and semaphorins could be involved in the regulation of leukocyte movement.