Intermolecular Interaction between Anchoring Subunits Specify Subcellular Targeting and Function of RGS Proteins in Retina ON-Bipolar Neurons

• Published in: The Journal of neuroscience Vol. 36; no. 10; pp. 2915 - 2925
• Main Authors: Sarria, Ignacio, Orlandi, Cesare, McCall, Maureen A, Gregg, Ronald G, Martemyanov, Kirill A
• Format: Journal Article
• Language: English
• Published: United States Society for Neuroscience 09.03.2016
• Subjects: Animals; Cadmium Chloride - pharmacology; DNA-Binding Proteins - metabolism; Female; Gene Expression Regulation - genetics; Gene Expression Regulation - physiology; HEK293 Cells; Humans; Light; Macromolecular Substances - metabolism; Male; Membrane Proteins - deficiency; Membrane Proteins - genetics; Mice; Mice, Transgenic; Models, Molecular; Phosphoproteins - metabolism; Receptors, G-Protein-Coupled - genetics; Receptors, G-Protein-Coupled - metabolism; Receptors, Metabotropic Glutamate - metabolism; Retina - cytology; Retinal Bipolar Cells - physiology; RGS Proteins - genetics; RGS Proteins - metabolism; Synaptic Transmission - physiology; vision; RGS proteins; synaptic transmission; retina; G-protein signaling
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/jneurosci.3833-15.2016

In vertebrate retina, light responses generated by the rod photoreceptors are transmitted to the second-order neurons, the ON-bipolar cells (ON-BC), and this communication is indispensible for vision in dim light. In ON-BCs, synaptic transmission is initiated by the metabotropic glutamate receptor, mGluR6, that signals via the G-protein Go to control opening of the effector ion channel, TRPM1. A key role in this process belongs to the GTPase Activating Protein (GAP) complex that catalyzes Go inactivation upon light-induced suppression of glutamate release in rod photoreceptors, thereby driving ON-BC depolarization to changes in synaptic input. The GAP complex has a striking molecular complexity. It contains two Regulator of G-protein Signaling (RGS) proteins RGS7 and RGS11 that directly act on Go and two adaptor subunits: RGS Anchor Protein (R9AP) and the orphan receptor, GPR179. Here we examined the organizational principles of the GAP complex in ON-BCs. Biochemical experiments revealed that RGS7 binds to a conserved site in GPR179 and that RGS11 in vivo forms a complex only with R9AP. R9AP and GPR179 are further integrated via direct protein-protein interactions involving their cytoplasmic domains. Elimination of GPR179 prevents postsynaptic accumulation of R9AP. Furthermore, concurrent knock-out of both R9AP and RGS7 does not reconfigure the GAP complex and completely abolishes synaptic transmission, resulting in a novel mouse model of night blindness. Based on these results, we propose a model of hierarchical assembly and function of the GAP complex that supports ON-BCs visual signaling.