RT Journal Article SR Electronic T1 δ-Opioid Receptor Gene: Effect of Sp1 Factor on Transcriptional Regulation in Vivo JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 331 OP 340 DO 10.1124/mol.60.2.331 VO 60 IS 2 A1 Dmitri Smirnov A1 Hee-Jeong Im A1 Horace H. Loh YR 2001 UL http://molpharm.aspetjournals.org/content/60/2/331.abstract AB δ-Opioid receptor (DOR) promoter exhibited a cell-type–specific expression pattern. Protein-DNA interactions in this promoter were identified by dimethyl sulfate in vivo footprinting analysis of NG108-15 cells, expressing endogenous DOR. Complete protection of the putative Sp1 cis-element and partial protection of the sequence defined as X-NotI in the basal promoter were observed only in the G0/G1 phase of the cell cycle. No protection was detected in Neuro2A cells that do not express DOR. In vivo formaldehyde cross-linking confirmed Sp1 factor binding to its cis-acting element during the G0/G1 phase. The functional significance of these Sp1 and X-NotI sites was evaluated by transient transfection analysis. Northern blot analysis and nuclear run-off assays revealed maximum DOR mRNA level and transcription rate, respectively, during the G0/G1 phase of NG108-15 cells. In summary, the protein-DNA interactions at the Sp1 and X-NotI sites are necessary for cell cycle-dependent and cell-type–specific up-regulated DOR gene expression.