The FcεRI signaling cascade and integrin trafficking converge at patterned ligand surfaces

Abstract

Surface-patterned ligands reveal spatially targeted signaling events mediated by FcεRI on mast cells. Distinctively clustered IgE-FcεRI recruits signaling proteins, including Syk, LAT, and activated PLCγ1. β1- and β3-integrins also colocalize at patterned sites, involving actin polymerization and stimulated trafficking from recycling endosomes.

Abstract

We examined the spatial targeting of early and downstream signaling mediated by the immunoglobulin E (IgE) receptor (FcεRI) in RBL mast cells using surface-patterned 2,4-dinitrophenyl (DNP) ligands. Micron-sized features of DNP are presented as densely immobilized conjugates of bovine serum albumin (DNP-BSA) or mobile in a supported lipid bilayer (DNP-SLB). Although soluble anti-DNP IgE binds uniformly across features for both pattern types, IgE bound to FcεRI on cells shows distinctive distributions: uniform for DNP-SLB and edge concentrated for DNP-BSA. These distributions of IgE-FcεRI propagate to the spatial recruitment of early signaling proteins, including spleen tyrosine kinase (Syk), linker for activation of T-cells (LAT), and activated phospholipase C gamma 1 (PLCγ1), which all localize with engaged receptors. We found stimulated polymerization of F-actin is not required for Syk recruitment but is progressively involved in the recruitment of LAT and PLCγ1. We further found β1- and β3-integrins colocalize with IgE-FcεRI at patterned ligand surfaces as cells spread. This recruitment corresponds to directed exocytosis of recycling endosomes (REs) containing these integrins and their fibronectin ligand. Together our results show targeting of signaling components, including integrins, to regions of clustered IgE-FcεRI in processes that depend on stimulated actin polymerization and outward trafficking of REs.