Increased site-specific phosphorylation of tyrosine hydroxylase accompanies stimulation of enzymatic activity induced by cessation of dopamine neuronal activity
Jy. Lew et al., Increased site-specific phosphorylation of tyrosine hydroxylase accompanies stimulation of enzymatic activity induced by cessation of dopamine neuronal activity, MOLEC PHARM, 55(2), 1999, pp. 202-209
Activation of striatal dopamine (DA) neurons by neuroleptic treatment or by
electrical stimulation of the nigrostriatal pathway increases the activity
of tyrosine hydroxylase (TH). The increase is mediated by phosphorylation
of the enzyme. However, abolition of DA neuronal activity [by gamma-butyrol
actone (GBL) treatment or transection of the nigrostriatal pathway] also in
creases TH activity. Quantitative blot immunolabeling experiments using sit
e- and phosphorylation state-specific antibodies to TH demonstrated that GE
L treatment (750 mg/kg, 35 min) significantly increased phosphorylation at
Ser19 (+40%) and Ser40 (+217%) without altering Ser31 phosphorylation. Conc
omitantly, GEL treatment [along with the 3,4-dihydroxyphenylalanine (dopa)
decarboxylase inhibitor NSD-1015, 100 mg/kg, 30 min] increased in vivo stri
atal dopa accumulation and in vitro TH activity 3-fold. Likewise, cerebral
hemitransection of the nigrostriatal pathway significantly increased phosph
orylation of TH at Ser19 (+89%) and Ser40 (+158%) but not at Ser31; dopa le
vels were increased accordingly (+191%). Kinetic analysis of TM activity es
tablished that GEL treatment and hemitransection primarily decreased the K-
m for the cofactor tetrahydrobiopterin (3-fold). The effects of GEL and hem
itransection were abolished or attenuated by pretreatment with the DA agoni
st R-(-)-N-n-propylnorapomorphine (NPA; 30 mu g/ kg, 40 min), presumably vi
a stimulation of inhibitory presynaptic DA autoreceptors, NPA dose-response
curves for reversal of GEL-induced dopa accumulation and Ser40 phosphoryla
tion were identical; however, only the highest dose of NPA reversed the sma
ll and variable increase in Ser19 phosphorylation, Thus, TH activity seems
to be regulated by phosphorylation in both hyper- and hypoactive striatal D
A neurons; in the latter case, activation seems to be caused by selective p
hosphorylation of Ser40.