Phosphorylation of Galphas influences its association with the micro-opioid receptor and is modulated by long-term morphine exposure.
The recent biochemical demonstration of the association of the mu-opioid receptor (MOR) with Galpha(s) that increases after long-term morphine treatment (Mol Brain Res 135:217-224, 2005) provides a new imperative for studying MOR-Galpha(s) interactions and the mechanisms that modulate it. A persisting challenge is to elucidate those neurochemical parameters modulated by long-term morphine treatment that facilitate MOR-Galpha(s) association. This study demonstrates that 1) Galpha(s) exists as a phosphoprotein, 2) the stoichiometry of Galpha(s) phosphorylation decreases after long-term morphine treatment, and 3) in vitro dephosphorylation of Galpha(s) increases its association with MOR. Furthermore, our data suggest that increased association of Galpha(s) with protein phosphatase 2A is functionally linked to the long-term morphine treatment-induced reduction in Galpha(s) phosphorylation. These findings are observed in MOR-Chinese hamster ovary and F11 cells as well as spinal cord, indicating that they are not idiosyncratic to the particular cell line used or a "culture" phenomenon and generalize to complex neural tissue. Taken together, these results indicate that the phosphorylation state of Galpha(s) is a critical determinant of its interaction with MOR. Long-term morphine treatment decreases Galpha(s) phosphorylation, which is a key mechanism underlying the previously demonstrated increased association of MOR and Galpha(s) in opioid tolerant tissue.
Chakrabarti
Sumita
S
Department of Biochemistry, State University of New York, Downstate Medical Center, Brooklyn, NY 11203, USA.
Gintzler
Alan R
AR
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000032:analysis; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects; D013997:Time Factors
D010761:Phosphorus Radioisotopes; D017450:Receptors, Opioid, mu; D009020:Morphine; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D019205:GTP-Binding Protein alpha Subunits, Gs