Journal of Neuroscience, Vol 10, 2649-2659, Copyright © 1990 by Society for Neuroscience
Identification of MARPP-58, a morphine- and cyclic AMP-regulated phosphoprotein of 58 kDa, as tyrosine hydroxylase: evidence for regulation of its expression by chronic morphine in the rat locus coeruleus
X Guitart, M Hayward, LK Nisenbaum, DB Beitner-Johnson, JW Haycock and EJ Nestler
Laboratory of Molecular Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06508.
Previously, we have identified a number of morphine- and cyclic AMP-
regulated phosphoproteins (MARPPs) in the rat locus coeruleus (LC) and
other brain regions. We now show that one of these phosphoproteins, a 58
kDa protein designated MARPP-58, is tyrosine hydroxylase. First, MARPP-58
comigrates with immunolabeled, immunoprecipitated, and purified tyrosine
hydroxylase on 1- and 2-dimensional electrophoresis. Second, MARPP-58,
immunoprecipitated tyrosine hydroxylase, and purified tyrosine hydroxylase
yield identical 1-dimensional phosphopeptide maps. Third, MARPP-58 exhibits
a regional and subcellular distribution in brain consistent with tyrosine
hydroxylase. Identification of MARPP-58 as tyrosine hydroxylase made it
possible to determine whether increases in MARPP-58 phosphorylation induced
by chronic morphine in the LC reported previously are associated with
alterations in enzyme activity and expression in this brain region. We show
that chronic treatment of rats with morphine increases levels of tyrosine
hydroxylase activity, immunoreactivity, and mRNA in the LC. Induction of
the enzyme by chronic morphine was blocked by concomitant treatment of rats
with the opiate receptor antagonist naltrexone, indicating that morphine
produces this effect through the activation of opiate receptors. Consistent
with previous observations that the chronic morphine-induced change in
MARPP-58 phosphorylation is specific to the LC, changes observed in enzyme
activity, immunoreactivity, and mRNA were not observed in a number of other
brain regions studied. The results indicate that chronic morphine regulates
the expression of tyrosine hydroxylase specifically in the LC and suggest
that such regulation reflects long-term adaptations of LC neurons to
chronic morphine at the level of gene expression.
Previous Article | Next Article
