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Vol. 60, Issue 6, 1168-1172, December 2001
s:
Characterization of G
s-Insensitive Mutants of
Adenylyl Cyclase V
Department of Medicinal Chemistry and Molecular Pharmacology,
Purdue University, West Lafayette, Indiana (V.J.W.); Department of
Biological Chemistry, University of Michigan, Ann Arbor, Michigan
(R.T.); Department of Psychiatry, Harvard Medical School and McLean
Hospital, Belmont, Massachusetts (R.L.N.); Department of Behavioral
Neuroscience, Oregon Health Sciences University, Portland, Oregon
(K.A.N); and Medical Research Service, Veterans Affairs Medical Center,
Portland, Oregon (K.A.N.)
Whereas acute stimulation of G
i/o-coupled receptors
inhibits the activity of adenylyl cyclase, a delayed consequence of
persistent activation of the receptors is heterologous sensitization,
an enhanced responsiveness of adenylyl cyclase to activators such as
forskolin or agonists of G
s-coupled receptors.
G
s-insensitive mutants of adenylyl cyclase type V were
used to test the hypothesis that heterologous sensitization requires
G
s-dependent activation of adenylyl cyclase. When
adenylyl cyclase was stably expressed in human embryonic kidney (HEK)
293 cells with the D2L dopamine receptor, basal,
forskolin-stimulated, and isoproterenol-stimulated cyclic AMP
accumulation were all enhanced by 2-h pretreatment with the
D2 receptor agonist quinpirole. Transient expression of
wild-type adenylyl cyclase and three G
s-insensitive
mutants (F379L, R1021Q, and F1093S) in HEK293 cells stably expressing the D2L receptor demonstrated that all three mutants had
little or no responsiveness to
-adrenergic receptor-mediated
activation of G
s but that the mutants retained
sensitivity to forskolin and to D2L receptor-mediated
inhibition. Transiently expressed adenylyl cyclase V was robustly
sensitized by 2-h pretreatment with quinpirole. In contrast, the
G
s-insensitive mutants displayed no sensitization of
forskolin-stimulated cyclic AMP accumulation, indicating that
responsiveness to G
s is required for the expression of
heterologous sensitization.
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