Sustained activation of phosphatidylinositol 3-kinase/Akt/ nuclear factor κB signaling mediates G protein-coupled δ-opioid receptor gene expression

Expression of the δ-opioid receptor gene (dor) is tightly controlled during neuronal differentiation and developmental stages. Such distinct temporal and spatial expression of dor during development suggests a role for the δ-opioid receptor in early developmental events. However, little is known about intracellular signaling pathways that control dor expression.Awell established cell line model for the study of gene expression during neuronal differentiation is the rat adrenal pheochromocytoma PC12 cell line. Here we found that the constitutively activated TrkA/phosphatidylinositol 3-kinase/Akt (protein kinase B)/NF-κB survival cascade mediates dor expression during nerve growth factor (NGF)-induced differentiation of PC12h cells. Biochemical experiments showed that constitutive phosphorylation of Akt and IκBα correlates with NGF-induced dor expression. Overexpression of the transcriptional activator NF-κB/p65 increased dor promoter activity. Overexpression of the NF-κB signaling super inhibitor mutant IκBα (S32A/S36A) abolished the effect of p65 and blocked NGF-induced activation of NF-κB signaling, resulting in a significant reduction in dor promoter activity. Treatment with SN50, an NF-κB-specific nuclear translocation peptide inhibitor, inhibited the translocation of NF-κB, resulting in a reduction of dor mRNA. The gel shift assay supported the fact that there exists an NF-κB-binding site on the dor promoter. RNA interference experiments using NF-κB/p65 small interfering RNA confirmed that NF-κB signaling is required for dor expression. Our findings not only provide a new mechanistic explanation for NGF-induced dor expression but also shed some light on the molecular mechanism of the temporal and spatial expression of dor and the roles of the δ-opioid receptor during neuronal differentiation.