Formation of a ternary complex among NHERF1, beta-arrestin, and parathyroid hormone receptor.

ß-Arrestins are crucial regulators of G-protein coupled receptor (GPCR) signaling, desensitization, and internalization. Despite the long-standing paradigm that agonist-promoted receptor phosphorylation is required for ß-arrestin2 recruitment, emerging evidence suggests that phosphorylation-independent mechanisms play a role in ß-arrestin2 recruitment by GPCRs. Several PDZ proteins are known to interact with GPCRs and serve as cytosolic adaptors to modulate receptor signaling and trafficking. Na(+)/H(+) exchange regulatory factors (NHERFs) exert a major role in GPCR signaling. By combining imaging and biochemical and biophysical methods we investigated the interplay among NHERF1, ß-arrestin2, and the parathyroid hormone receptor type 1 (PTHR). We show that NHERF1 and ß-arrestin2 can independently bind to the PTHR and form a ternary complex in cultured human embryonic kidney cells and Chinese hamster ovary cells. Although NHERF1 interacts constitutively with the PTHR, ß-arrestin2 binding is promoted by receptor activation. NHERF1 interacts directly with ß-arrestin2 without using the PTHR as an interface. Fluorescence resonance energy transfer studies revealed that the kinetics of PTHR and ß-arrestin2 interactions were modulated by NHERF1. These findings suggest a model in which NHERF1 may serve as an adaptor, bringing ß-arrestin2 into close proximity to the PTHR, thereby facilitating ß-arrestin2 recruitment after receptor activation.