Interactions with PDZ Domain Proteins PIST/GOPC and PDZK1 Regulate Intracellular Sorting of the Somatostatin Receptor Subtype 5

Abstract

By yeast two-hybrid screening we have identified interaction partners for the intracellular C-terminal tail of the human and rodent somatostatin receptor subtype 5 (SSTR5). Interactions with the PDZ domain-containing proteins PIST and PDZK1 are mediated by the PDZ ligand motif at the C terminus of the receptor; in case of the human and mouse (but not the rat) receptors, a slight sequence variation of this motif also allows for binding of the peroxisomal receptor PEX5. PIST is Golgi-associated and retains SSTR5 in the Golgi apparatus when coexpressed with the receptor; PDZK1 on the other hand associates with the SSTR5 at the plasma membrane. Endogenous SSTR5 in the neuroendocrine AtT-20 tumor cell line is colocalized with PIST in the Golgi apparatus. On a functional level, removal of the PDZ ligand motif of the receptor does not interfere with agonist-dependent internalization of the receptor or its targeting to a Golgi-associated compartment; however, recycling of the receptor to the plasma membrane after washout of the agonist is inhibited, suggesting that the PDZ-mediated interaction of SSTR5 is required for postendocytic sorting.In recent years it has been appreciated that the signaling and the subcellular distribution of G-protein-coupled receptors may be influenced by proteins that interact with the intracellular regions of the receptors, most notably the C termini (1, 2). Several interactions have been mapped to the membrane proximal domain of the C terminus, including the so-called helix 8, which encompasses the palmitoylation motifs found in most receptors of the rhodopsin-related type I family (3-5). These contacts especially involve proteins that act in the postendocytic, intracellular sorting of multiple receptors, i.e. the sorting nexin SNX1, N-ethylmaleimide sensitive factor and the G-protein-coupled receptor-associated sorting protein GASP. A second type of interactions involves the distal C termini of GPCRs, 4 which in many cases contain motifs for the interaction with PDZ domains. PDZ domain proteins frequently act as scaffold molecules because of their multiple protein interaction motifs (6). Thus this type of interaction has the potential to target a receptor to specific subcellular domains and into specific signaling complexes. Interaction of the ␤ 1 -adrenergic receptor with the third PDZ domain of PSD-95, for example, is believed to anchor this receptor at the postsynaptic density of excitatory synapses (7). The interaction of the parathyroid hormone receptor with Na ϩ /H ϩ exchanger regulatory factor/EBP-50 on the other hand physically links the receptor to phospholipase C␤, thereby shifting the second messenger response from adenylate cyclase activation to the hydrolysis of phospholipids (8).We have recently initiated a search for intracellular interaction partners for the various members of the somatostatin receptor (SSTR) family (9, 10). There are five SSTR subtypes in mammalian species, which form a rather homogeneous subfamily within the larger family of GPCRs, as they all preferential...

Intracellular trafficking of somatostatin receptors

“…Wente et al identified two PDZ-domain containing proteins PIST and PDZK1, which interact with the C-terminus of sst 5 and seem to regulate its intracellular transport (Wente et al, 2005). Remarkably, all sst subtypes have a PDZ-binding motif in the C-terminal tail (Wente et al, 2005).…”

“…Remarkably, all sst subtypes have a PDZ-binding motif in the C-terminal tail (Wente et al, 2005). PIST is a Golgi apparatus associated protein and colocalizes with sst 5 in mouse pituitary AtT-20 cells.…”

Identification of a Postendocytic Sorting Sequence in CCR5

“…However, the similar characteristics between the last four amino acids of ␤2AR and CCR5 led us to suggest that the SVGL motif of CCR5 could act as a "recycling signal." Such a "recycling signal" is also found in other GPCRs, such as human lutropin receptor (Galet et al, 2004), -opioid receptor (Tanowitz and von Zastrow, 2003), D1 dopamine receptor (Vargas and Von Zastrow, 2004), endothelin receptor A (Paasche et al, 2005), and somatostatin receptor 5 (Wente et al, 2005). Whatever the recycling signal, they all share a leucine and/or a phosphate acceptor.…”

“…Likewise, the sorting protein is also different from one GPCR to another (Cao et al, 1999;Whistler et al, 2002;Wente et al, 2005). Many PDZ domain-containing proteins interact with GPCR C termini (Bockaert et al, 2003); some of them have been identified as being involved in GPCR postendocytic trafficking (Trejo, 2005).…”

Fine Tuning of CFTR Traffic and Function by PDZ Scaffolding Proteins

“…Comparable to CFTR, both the beta1-adrenergic receptor and cadherin 23 interact with CAL, leading to their intracellular accumulation and/or degradation (Fig.2); these interactions can be competitively counteracted by binding with other PDZ domain-containing proteins (He et al, 2004;Xu et al, 2010). Likewise, CAL is an intracellular retention partner for the somatostatin receptor subtype 5 and the metabotropic glutamate receptor subtypes 1a (Wente et al, 2005;Zhang et al, 2008).…”