Cargo binding promotes KDEL receptor clustering at the mammalian cell surface

TL;DR

This study reveals how cargo binding induces clustering of KDEL receptors on mammalian cell surfaces, involving transport mechanisms that are elucidated through combined experimental and theoretical approaches.

Contribution

It provides a mechanistic understanding of receptor clustering driven by cargo binding, integrating experimental data with modeling to uncover underlying processes.

Findings

Cargo binding causes dose-dependent receptor clustering.

Receptor clusters are internalized and transported via microtubules.

Transport dynamics are causative for receptor cluster formation.

Abstract

Transmembrane receptor clustering is a ubiquitous phenomenon in pro- and eukaryotic cells to physically sense receptor/ligand interactions and subsequently translate an exogenous signal into a cellular response. Despite that receptor cluster formation has been described for a wide variety of receptors, ranging from chemotactic receptors in bacteria to growth factor and neurotransmitter receptors in mammalian cells, a mechanistic understanding of the underlying molecular processes is still puzzling. In an attempt to fill this gap we followed a combined experimental and theoretical approach by dissecting and modulating cargo binding, internalization and cellular response mediated by KDEL receptors (KDELRs) at the mammalian cell surface after interaction with a model cargo/ligand. Using a fluorescent variant of ricin toxin A chain as KDELR-ligand, eGFP-RTA (H/KDEL), we demonstrate that cargo binding induces dose-dependent receptor cluster formation at and subsequent internalization from the membrane which is associated and counteracted by anterograde and microtubule-assisted receptor transport to preferred docking sites at the plasma membrane. By means of analytical arguments and extensive numerical simulations we show that cargo-synchronized receptor transport from and to the membrane is causative for KDELR/cargo cluster formation at the mammalian cell surface.