delta-Opioid receptor gene: Effect of Sp1 factor on transcriptional regulation in vivo

delta -Opioid receptor (DOR) promoter exhibited a cell-type-specific expres sion pattern. Protein-DNA interactions in this promoter were identified by dimethyl sulfate in vivo footprinting analysis of NG108-15 cells, expressin g endogenous DOR. Complete protection of the putative Spl cis-element and p artial protection of the sequence defined as X-Notl in the basal promoter w ere observed only in the G(0)/G(1) phase of the cell cycle. No protection w as detected in Neuro2A cells, that do not express DOR. In vivo formaldehyde cross-linking confirmed Sp1 factor binding to its cis-acting element durin g the G(0)/G(1) phase. The functional significance of these Sp1 and X-Notl sites was evaluated by transient transfection analysis. Northern blot analy sis and nuclear run-off assays revealed maximum DOR mRNA level and transcri ption rate, respectively, during the G(0)/G(1) phase of NG108-15 cells. In summary, the protein-DNA interactions at the Sp1 and X-Notl sites are neces sary for cell cycle-dependent and cell-type-specific up-regulated DOR gene expression.