TY - JOUR
T1 - μ Opioid Transactivation and Down-Regulation of the Epidermal Growth Factor Receptor in Astrocytes
T2 - Implications for Mitogen-Activated Protein Kinase Signaling
AU - Belcheva, Mariana M.
AU - Tan, Yun
AU - Heaton, Virginia M.
AU - Clark, Amy L.
AU - Coscia, Carmine J.
PY - 2003/12
Y1 - 2003/12
N2 - Astroglia are a principal target of long-term μ antiproliferative actions. The mitogen-activated protein (MAP) kinase known as extracellular signal-regulated kinase (ERK), is a key mediator of cell proliferation. In studies on the mechanism of short- and long-term μ opioid regulation of the ERK signaling pathway, we show that the μ opioid agonist [D-Ala 2,N-Me-Phe4,Gly5-ol]-enkepphalin (DAMGO), acting via the endogenous μ opioid receptor (MOR), induced sequential epidermal growth factor receptor (EGF) receptor (EGFR) Tyr phosphorylation, Ser phosphorylation, and down-regulation in immortalized rat cortical astrocytes. The short-term action of DAMGO resulted in the stimulation of ERK phosphorylation. 4(3-Chlorophenylamino)-6,7-dimethoxyquinazoline (Tyrphostin AG1478), a selective inhibitor of EGFR Tyr kinase activity, blocked EGFR and ERK activation by short-term DAMGO administration, implicating EGFR transactivation in its stimulation of ERK activity. Inhibitors of matrix metalloproteinases attenuated MOR-mediated ERK phosphorylation, suggesting that shedding of EGF-like ligands from the plasma membrane may be involved in the EGFR transactivation process. Prolonged DAMGO exposure induced EGFR internalization/down-regulation, did not activate ERK, and inhibited exogenous EGF-stimulated ERK phosphorylation. MOR-mediated EGFR down-regulation seems to be MAP kinase-dependent, because it was inhibited by the ERK kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio) butadiene (U0126), and tyrphostin AG1478. The κ opioid agonist (5α,7α,8β )-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl) benzeneacetamide (U69,593) induced Tyr and Ser phosphorylation of EGFR and activation of ERK. However, long-term application of U69,593 neither down-regulated EGFR nor inhibited EGF-induced ERK activation. Instead, it engendered a sustained activation of ERK. Collectively, our data suggest that long-term application of DAMGO initiates heterologous down-regulation of EGFR via a mechanism involving ERK in astrocytes.
AB - Astroglia are a principal target of long-term μ antiproliferative actions. The mitogen-activated protein (MAP) kinase known as extracellular signal-regulated kinase (ERK), is a key mediator of cell proliferation. In studies on the mechanism of short- and long-term μ opioid regulation of the ERK signaling pathway, we show that the μ opioid agonist [D-Ala 2,N-Me-Phe4,Gly5-ol]-enkepphalin (DAMGO), acting via the endogenous μ opioid receptor (MOR), induced sequential epidermal growth factor receptor (EGF) receptor (EGFR) Tyr phosphorylation, Ser phosphorylation, and down-regulation in immortalized rat cortical astrocytes. The short-term action of DAMGO resulted in the stimulation of ERK phosphorylation. 4(3-Chlorophenylamino)-6,7-dimethoxyquinazoline (Tyrphostin AG1478), a selective inhibitor of EGFR Tyr kinase activity, blocked EGFR and ERK activation by short-term DAMGO administration, implicating EGFR transactivation in its stimulation of ERK activity. Inhibitors of matrix metalloproteinases attenuated MOR-mediated ERK phosphorylation, suggesting that shedding of EGF-like ligands from the plasma membrane may be involved in the EGFR transactivation process. Prolonged DAMGO exposure induced EGFR internalization/down-regulation, did not activate ERK, and inhibited exogenous EGF-stimulated ERK phosphorylation. MOR-mediated EGFR down-regulation seems to be MAP kinase-dependent, because it was inhibited by the ERK kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio) butadiene (U0126), and tyrphostin AG1478. The κ opioid agonist (5α,7α,8β )-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl) benzeneacetamide (U69,593) induced Tyr and Ser phosphorylation of EGFR and activation of ERK. However, long-term application of U69,593 neither down-regulated EGFR nor inhibited EGF-induced ERK activation. Instead, it engendered a sustained activation of ERK. Collectively, our data suggest that long-term application of DAMGO initiates heterologous down-regulation of EGFR via a mechanism involving ERK in astrocytes.
UR - http://www.scopus.com/inward/record.url?scp=0346996807&partnerID=8YFLogxK
U2 - 10.1124/mol.64.6.1391
DO - 10.1124/mol.64.6.1391
M3 - Article
C2 - 14645669
AN - SCOPUS:0346996807
VL - 64
SP - 1391
EP - 1401
JO - Molecular Pharmacology
JF - Molecular Pharmacology
SN - 0026-895X
IS - 6
ER -