OPRL1 and glioblastoma: Studies have also indicated that nociceptin receptor (NOPr), a G protein-coupled receptor that is significantly expressed in GBM, mediates nociceptin through the β-arrestin 2/PKC/extracellular signal-regulated kinase 1/2 (Erk1/2) pathway to hinder proliferation, migration, and inflammatory signaling in lipopolysaccharide-stimulated U87 cells [52].