Interaction of the mu-opioid receptor with GPR177 (Wntless) inhibits Wnt secretion: potential implications for opioid dependence

Abstract

BackgroundOpioid agonist drugs produce analgesia. However, long-term exposure to opioid agonists may lead to opioid dependence. The analgesic and addictive properties of opioid agonist drugs are mediated primarily via the mu-opioid receptor (MOR). Opioid agonists appear to alter neuronal morphology in key brain regions implicated in the development of opioid dependence. However, the precise role of the MOR in the development of these neuronal alterations remains elusive. We hypothesize that identifying and characterizing novel MOR interacting proteins (MORIPs) may help to elucidate the underlying mechanisms involved in the development of opioid dependence.ResultsGPR177, the mammalian ortholog of Drosophila Wntless/Evi/Sprinter, was identified as a MORIP in a modified split ubiquitin yeast two-hybrid screen. GPR177 is an evolutionarily conserved protein that plays a critical role in mediating Wnt protein secretion from Wnt producing cells. The MOR/GPR177 interaction was validated in pulldown, coimmunoprecipitation, and colocalization studies using mammalian tissue culture cells. The interaction was also observed in rodent brain, where MOR and GPR177 were coexpressed in close spatial proximity within striatal neurons. At the cellular level, morphine treatment caused a shift in the distribution of GPR177 from cytosol to the cell surface, leading to enhanced MOR/GPR177 complex formation at the cell periphery and the inhibition of Wnt protein secretion.ConclusionsIt is known that chronic morphine treatment decreases dendritic arborization and hippocampal neurogenesis, and Wnt proteins are essential for these processes. We therefore propose that the morphine-mediated MOR/GPR177 interaction may result in decreased Wnt secretion in the CNS, resulting in atrophy of dendritic arbors and decreased neurogenesis. Our results demonstrate a previously unrecognized role for GPR177 in regulating cellular response to opioid drugs.

Regulation of M3 Muscarinic Receptor Expression and Function by Transmembrane Protein 147

“…In particular, the authors identified GPR177, the mammalian ortholog of Drosophila melanogaster Wntless, as a novel MOR-interacting protein. Additional experiments indicated that morphine treatment led to enhanced MOR/GPR177 complex formation at the cell periphery and inhibition of Wnt protein secretion, perhaps resulting in decreased neurogenesis (Jin et al, 2010).…”

“…After completion of this study, Jin et al (2010) reported the usefulness of the split ubiquitin two-hybrid screen to identify proteins that can associate with the -opioid receptor (MOR). In particular, the authors identified GPR177, the mammalian ortholog of Drosophila melanogaster Wntless, as a novel MOR-interacting protein.…”

WNT secretion and signalling in human disease

“…WLS might be another promising therapeutic candidate, although very little is known about its mechanism of action. Recently, Jin et al [72] reported an interaction between Wls and the m-opioid receptor in neurons: upon opioid treatment Wls is localised primarily to the plasma membrane and Wnt ligand secretion is reduced. Wnt signalling in the brain, however, was shown to be essential for hippocampal development and the arborisation of dendrites in mice [73].…”

A Wntless–SEC12 complex on the ER membrane regulates early Wnt secretory vesicle assembly and mature ligand export

“…We hypothesized that a proteomic analysis comparing wildtype Wls and this trafficking-defective Wls 1-491 might shed light on cellular machineries that regulate Wls trafficking. An N-terminally Flag-tagged full-length Wls has been described in biochemical and functional Wnt secretion studies in cultured cells (Jin et al, 2010). Using an anti-Flag antibody, we performed immunoprecipitation (IP) on HeLa cells stably expressing 3×Flag-tagged full-length Wls or Wls .…”