GABAB Receptor Association with the PDZ Scaffold Mupp1 Alters Receptor Stability and Function

Randy A. Hall,Sami R. Fam,Srividya Balasubramanian

doi:10.1074/jbc.m607695200

Abstract

gamma-Aminobutyric acid, type B (GABA(B)) receptors are heterodimeric G protein-coupled receptors that mediate slow inhibitory synaptic transmission in the central nervous system. To identify novel interacting partners that might regulate GABA(B) receptor (GABA(B)R) functionality, we screened the GABA(B)R2 carboxyl terminus against a recently created proteomic array of 96 distinct PDZ (PSD-95/Dlg/ZO-1 homology) domains. The screen identified three specific PDZ domains that exhibit interactions with GABA(B)R2: Mupp1 PDZ13, PAPIN PDZ1, and Erbin PDZ. Biochemical analysis confirmed that full-length Mupp1 and PAPIN interact with GABA(B)R2 in cells. Disruption of the GABA(B)R2 interaction with PDZ scaffolds by a point mutation to the carboxyl terminus of the receptor dramatically decreased receptor stability and attenuated the duration of GABA(B) receptor signaling. The effects of mutating the GABA(B)R2 carboxyl terminus on receptor stability and signaling were mimicked by small interference RNA knockdown of endogenous Mupp1. These findings reveal that GABA(B) receptor stability and signaling can be modulated via GABA(B)R2 interactions with the PDZ scaffold protein Mupp1, which may contribute to cell-specific regulation of GABA(B) receptors in the central nervous system.

Highlights

Family members such as the metabotropic glutamate receptors, calcium receptor, and vomeronasal receptors
We previously reported that association of GABAB receptors with the GABAA receptor ␥2S subunit confers agonist-mediated endocytosis on GABAB receptors expressed in heterologous cells (16)
We identified three PDZ proteins that interact with the GABABR2 carboxyl terminus: Mupp1, Erbin, and PAPIN

Summary

Introduction

Family members such as the metabotropic glutamate receptors, calcium receptor, and vomeronasal receptors. One possible explanation for such discrepancies is that GABAB receptor signaling and trafficking properties are highly dependent on cellular context This implies that interaction with differentially expressed cellular proteins might modulate GABAB receptor function. PDZ (PSD-95/Discs-large/ZO-1) domains are 90-amino acid protein-protein interaction modules that recognize and bind to specialized motifs in the distal carboxyl termini of target proteins such as G protein-coupled receptors and ion channels (22). The GABABR2 carboxyl-terminal motif of VSGL conforms to the preferred binding motif for Class I PDZ domains and may interact with PDZ proteins that could potentially regulate GABAB receptor function. We further studied the interactions of these proteins with GABABR2 in cells and examined the roles of these interactions in regulating GABAB receptor signaling, trafficking, and stability

Methods

Results

Conclusion