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CELLULAR AND MOLECULAR

Morphine and Endomorphins Differentially Regulate µ-Opioid Receptor mRNA in SHSY-5Y Human Neuroblastoma Cells

Department of Biology, Seton Hall University, South Orange, New Jersey (X.Y., A.D.B., S.L.C.); and Department of Virology, Wuhan University, Wuhan, China (X.M., W.X.L.)

A sensitive quantitative-competitive reverse transcriptase-polymerase chain reaction method was developed to measure µ-opioid receptor (MOR) mRNA expression in SHSY-5Y neuroblastoma cells. Differentiation of SHSY-5Y cells with either retinoic acid (RA) or 12-o-tetradecanoyl-phorbol-13-acetate (TPA) significantly increased MOR mRNA levels. Morphine treatment (10 µM) for 24 h decreased MOR mRNA levels in control, as well as RA- and TPA-differentiated cells. In contrast, chronic exposure to the opioid peptides endomorphin-1 or endomorphin-2 significantly increased MOR mRNA levels in undifferentiated and RA-differentiated cells. An opioid antagonist, naloxone, reversed the morphine and endomorphin-1 and -2 effects on MOR mRNA levels in undifferentiated SHSY-5Y cells, but naloxone had differential reversing effects on the agonists' regulation of MOR mRNA in RA- or TPA-differentiated cells. To investigate whether the changes in MOR mRNA expression paralleled changes in MOR receptor function, intracellular cAMP accumulation in SHSY-5Y cells was measured. After chronic treatment with morphine, forskolin-induced cAMP levels in SHSY-5Y cells were significantly higher than those of untreated control cells. In contrast, forskolin-induced cAMP accumulation levels were lower in cells treated with endomorphin-1 or -2 than in untreated control cells. Together, our studies indicate that the opioid alkaloid morphine and the opioid peptides endomorphin-1 and -2 differentially regulate MOR mRNA expression and MOR function in SHSY-5Y cells.

Address correspondence to: Dr. Sulie L. Chang, Department of Biology, Seton Hall University, 400 South Orange Ave., South Orange, NJ 07079. E-mail: changsul{at}shu.edu