Receptor for endogenous opioids such as beta-endorphin and endomorphin. Receptor for natural and synthetic opioids including morphine, heroin, DAMGO, fentanyl, etorphine, buprenorphin and methadone. Agonist binding to the receptor induces coupling to an inactive GDP-bound heterotrimeric G-protein complex and subsequent exchange of GDP for GTP in the G-protein alpha subunit leading to dissociation of the G-protein complex with the free GTP-bound G-protein alpha and the G-protein beta-gamma dimer activating downstream cellular effectors. The agonist-and cell type-specific activity is predominantly coupled to pertussis toxin-sensitive G(i) and G(o) G alpha proteins, GNAI1, GNAI2, GNAI3 and GNAO1 isoforms Alpha-1 and Alpha-2, and to a lesser extend to pertussis toxin-insensitive G alpha proteins GNAZ and GNA15. They mediate an array of downstream cellular responses, including inhibition of adenylate cyclase activity and both N-type and L-type calcium channels, activation of inward rectifying potassium channels, mitogen-activated protein kinase (MAPK), phospholipase C (PLC), phosphoinositide/protein kinase (PKC), phosphoinositide 3-kinase (PI3K) and regulation of NF-kappa-B. Also couples to adenylate cyclase stimulatory G alpha proteins. The selective temporal coupling to G-proteins and subsequent signaling can be regulated by RGSZ proteins, such as RGS9, RGS17 and RGS4. Phosphorylation by members of the GPRK subfamily of Ser/Thr protein kinases and association with beta-arrestins is involved in short-term receptor desensitization. Beta-arrestins associate with the GPRK-phosphorylated receptor and uncouple it from the G-protein thus terminating signal transduction. The phosphorylated receptor is internalized through endocytosis via clathrin-coated pits which involves beta-arrestins. The activation of the ERK pathway occurs either in a G-protein-dependent or a beta-arrestin-dependent manner and is regulated by agonist-specific receptor phosphorylation. Acts as a class A G-protein coupled receptor (GPCR) which dissociates from beta-arrestin at or near the plasma membrane and undergoes rapid recycling. Receptor down-regulation pathways are varying with the agonist and occur dependent or independent of G-protein coupling. Endogenous ligands induce rapid desensitization, endocytosis and recycling whereas morphine induces only low desensitization and endocytosis. Heterooligomerization with other GPCRs can modulate agonist binding, signaling and trafficking properties. Involved in neurogenesis. Isoform 12 couples to GNAS and is proposed to be involved in excitatory effects. Isoform 16 and isoform 17 do not bind agonists but may act through oligomerization with binding-competent OPRM1 isoforms and reduce their ligand binding activity.

• GO:0007191 : adenylate cyclase-activating dopamine receptor signaling pathway
• GO:0007193 : adenylate cyclase-inhibiting G-protein coupled receptor signaling pathway
• GO:0048149 : behavioral response to ethanol
• GO:0033554 : cellular response to stress
• GO:0007187 : G-protein coupled receptor signaling pathway, coupled to cyclic nucleotide second messenger
• GO:0007626 : locomotory behavior
• GO:0007194 : negative regulation of adenylate cyclase activity
• GO:0043951 : negative regulation of cAMP-mediated signaling
• GO:0008285 : negative regulation of cell proliferation
• GO:0051481 : negative regulation of cytosolic calcium ion concentration
• GO:0045019 : negative regulation of nitric oxide biosynthetic process
• GO:0061358 : negative regulation of Wnt protein secretion
• GO:0007200 : phospholipase C-activating G-protein coupled receptor signaling pathway
• GO:0043950 : positive regulation of cAMP-mediated signaling
• GO:0007204 : positive regulation of cytosolic calcium ion concentration
• GO:0070374 : positive regulation of ERK1 and ERK2 cascade
• GO:0050769 : positive regulation of neurogenesis
• GO:0045429 : positive regulation of nitric oxide biosynthetic process
• GO:0050795 : regulation of behavior
• GO:2000310 : regulation of N-methyl-D-aspartate selective glutamate receptor activity
• GO:0019233 : sensory perception of pain

Source: The Gene Ontology Consortium. Gene ontology: tool for the unification of biology. Nat. Genet.. May 2000;25(1):25-9.
World Wide Web URL: http://www.geneontology.org/

Source: Online Mendelian Inheritance in Man, OMIM®. McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University (Baltimore, MD), May, 2012.
World Wide Web URL: http://omim.org/