Phosphatidylethanolamine‐Binding Protein Regulates Mu Opioid Receptor Induced βarrestin2 Recruitment and Downstream Signaling

Abstract

The signaling regulators and pathways of the mu‐opioid receptor (MOR) are being studied to develop functionally selective MOR ligands. Such novel analgesic drugs may alleviate pain without the side effects and drawbacks of typical opioids. We have analyzed proteomics databases available in the literature to find candidate proteins that are regulated in the brain by chronic opioid treatment. One such candidate, phosphatidylethanolamine‐binding protein (PEBP), is a cytoplasmic protein with a highly conserved structure that has been shown to regulate GPCR signaling through both the Raf/MEK/ERK pathway and G protein‐coupled receptor kinase 2 (GRK2), a major feedback inhibitor of GPCRs which has been implicated in a number of neurological disorders including chronic pain. The expression of PEBP was also found to be regulated by chronic morphine treatment in a proteomic study of rodent brain, suggesting that PEBP may regulate MOR signaling, however PEBP has not yet been associated with MOR signaling. We have knocked down PEBP in MOR‐ expressing HEK, U2OS, N2a and SH‐SY5Y cells using specific siRNA to determine changes in either MOR‐induced ERK signaling or βarrestin2 (βarr2) recruitment and receptor internalization, with and without GRK2 overexpression. PEBP knockdown does not change MOR agonist induced ERK signaling efficacy or potency, but βarr2 recruitment, MOR internalization, and chronic morphine desensitization potency is increased. This suggests a role for PEBP in regulating MOR induced βarr2 recruitment and attendant opioid induced side effects. We will continue to study the role of PEBP in pain and opioid response in vivo, and are developing in vitro drug discovery screens with PEBP as a target.