Essential role of Hrs in a recycling mechanism mediating functional resensitization of cell signaling.

Hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) is well known to terminate cell signaling by sorting activated receptors to the MVB/lysosomal pathway. Here we identify a distinct role of Hrs in promoting rapid recycling of endocytosed signaling receptors to the plasma membrane. This function of Hrs is specific for receptors that recycle in a sequence-directed manner, in contrast to default recycling by bulk membrane flow, and is distinguishable in several ways from previously identified membrane-trafficking functions of Hrs/Vps27p. In particular, Hrs function in sequence-directed recycling does not require other mammalian Class E gene products involved in MVB/lysosomal sorting, nor is receptor ubiquitination required. Mutational studies suggest that the VHS domain of Hrs plays an important role in sequence-directed recycling. Disrupting Hrs-dependent recycling prevented functional resensitization of the beta(2)-adrenergic receptor, converting the temporal profile of cell signaling by this prototypic G protein-coupled receptor from sustained to transient. These studies identify a novel function of Hrs in a cargo-specific recycling mechanism, which is critical to controlling functional activity of the largest known family of signaling receptors.