RETINOIC ACID-INDUCED INCREASE IN DELTA-OPIOID RECEPTOR AND N-METHYL-D-ASPARTATE RECEPTOR MESSENGER-RNA LEVELS IN NEUROBLASTOMA X GLIOMA (NG108-15) CELLS

We determined the effects of all-trans retinoic acid (RA) on the level s of delta opioid receptor (DOR) mRNA and N-Methyl-D-Aspartate recepto r (NMDAR1) mRNA in neuroblastoma x glioma hybrid cells (NG108-15) by u se of quantitative solution hybridization assays. The assays utilized riboprobes complementary to major portions of the coding region of the DOR and NMDAR1 cDNAs. At 10 mu M RA a 3-fold increase in DOR mRNA at 48 h, and later (144 h) alterations were observed in NMDAR1 mRNA level s. Northern blot analysis revealed six transcripts for DOR mRNA rangin g in size from 8.7 to 2.0 Kb, and three transcripts for NMDAR1 mRNA ra nging in size from 4.1 to 3.5 Kb, Neither the size nor the fractional band intensity was affected by RA treatment. The delayed induction of DOR mRNA suggests an indirect mechanism by which RA acts on transcript ion of this gene. A surprising induction of DOR mRNA by the protein sy nthesis inhibitor cycloheximide (CHX) suggests that either a repressor molecule or degrading enzymes/proteases may regulate basal levels of this mRNA. Treatment with RA resulted in a concentration- and time-dep endent morphological differentiation characterized by increased size o f the cell body and the appearance of numerous short and long processe s.