The PDZ Protein Mupp1 Promotes Gi Coupling and Signaling of the Mt1 Melatonin Receptor

Abstract

The concept of organized networks has emerged in the field of cellular signaling in the last few years. Assembling the different partners in close proximity optimizes the spatial and temporal organization and the specificity of the cellular response. The assembly of these multimolecular complexes occurs through the interaction of modular domains recognizing their target counterparts. PDZ domains are widely spread modules exhibiting this function. Data bank exploration with SMART (1) identifies 584 PDZ domains in 328 different proteins in the human genome.G protein-coupled receptors (GPCRs) 5 constitute the largest family of membrane receptors, and many of the more than 750 members have been shown to interact with PDZ domain-containing proteins, either constitutively or upon agonist activation (2). Binding of PDZ proteins to GPCRs has been reported to primarily regulate subcellular localization, trafficking, and stability of receptors (3). For instance, binding of MUPP1 and syntrophins to the ␥-aminobutyric acid type B (GABA B ) receptor and the ␣ 1D -adrenergic receptor, respectively, significantly increases receptor stability (4, 5). In other cases, PDZ scaffolds determine the subcellular localization of GPCRs (6) and receptor endocytosis as shown for PSD-95 and the 5-HT 2A serotonin and ␤ 1 -adrenergic receptors (7,8). PDZ proteins, such as NHERF and hScrib, are also important for the recycling of receptors to the cell surface (9 -11).Binding of PDZ proteins to GPCRs also modulates receptor signaling by assembling proteins involved in signal transduction. NHERF family proteins are known to regulate the activity of the Na ϩ /H ϩ exchanger through association with NHERF-1 (12) and to form a ternary complex with phospholipase C␤3 and GPCRs, which enhances the signaling efficiency of the receptor-mediated activation of the phospholipase C␤/Ca 2ϩ pathway (13-15). Binding of GIPC (GAIP-interacting protein, COOH terminus) to the COOH terminus of the D3 dopamine and the ␤ 1 -adrenergic receptor (16) decreased G␣ i -mediated signaling of these receptors most likely through RGS19, which binds to GIPC (17). Further examples of PDZ scaffolds that regulate GPCR signaling include a ternary complex formation around the PDZ scaffold MAGI-3, which binds to the GPCR frizzled-4 and Ltap to regulate the JNK signaling cascade (18), as well as PDZ-domain-containing Rho guanine nucleotide exchange factors that interact with lysophosphatidic acid 1 and 2 receptors to activate RhoA (19).

Rapid modulation of spine morphology by the 5-HT 2A serotonin receptor through kalirin-7 signaling

“…In agreement with these previous studies, here we found that in cultured cortical neurons, 5-HT 2A receptors colocalize with both PSD-95 and MUPP1 in the dendrites and dendritic spines of cortical pyramidal neurons, and when coexpressed in COS-7 cells, MUPP1 facilitates the membrane targeting of 5-HT 2A receptors which can be prevented by mutating the receptor PDZ binding motif. Importantly, MUPP1 is a scaffold for a growing list of synaptic proteins that are involved in GPCR and small GTPase signaling (27,(39)(40)(41). Our data, along with previous studies, are consistent with the roles of both MUPP1 and PSD-95 as protein scaffolds that may integrate signals through GPCRs at the synapse, provide avenues for crosstalk between signaling pathways, and function in the membrane localization of some receptors and signaling proteins.…”

Role of SAP97 Protein in the Regulation of Corticotropin-releasing Factor Receptor 1 Endocytosis and Extracellular Signal-regulated Kinase 1/2 Signaling

“…Second, MAGI-2 overexpression was found to have no effect on ␤ 1 AR-mediated cAMP signaling and to promote agonist-induced ␤ 1 AR internalization (40), but it was found to reduce vasoactive intestinal polypeptide type-1 receptor-mediated cAMP signaling and suppress agonist-induced receptor internalization (41). Finally, although MUPP1 enhances GABA B receptor signaling, it functions to uncouple the melatonin-1 receptor from G␣ i (42,43). Similarly, this study demonstrates that SAP97 regulates CRFR1 trafficking, because overexpression of GFP-SAP97 prevents CRFR1 endocytosis and knockdown of endogenous SAP97 promotes CRFR1 endocytosis.…”

Convergence of Melatonin and Serotonin (5-HT) Signaling at MT2/5-HT2C Receptor Heteromers

“…125 I]iodomelatonin as described previously (15). Receptors were solubilized with 1% digitonin and precipitated with a mixture of three anti-5-HT 2C rabbit antibodies (18461-10656, 18461-10657, and 18003-42961, Genway) or a pool of control preimmune serum, and immunoprecipitated radioactivity was determined.…”