Differential Regulation of the Human Tyrosine Hydroxylase Isoforms via Hierarchical Phosphorylation

Abstract

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of the catecholamines dopamine, noradrenaline, and adrenaline. In response to short term stimuli TH activity is primarily controlled by phosphorylation of serine 40. We have previously shown that phosphorylation of serine 19 in TH can indirectly activate TH via a hierarchical mechanism by increasing the rate of phosphorylation of serine 40. Here we show that phosphorylation of serine 31 in rat TH increases the rate of serine 40 phosphorylation 9-fold in vitro. Phosphorylation of serine 31 in intact bovine chromaffin cells potentiated the forskolin-induced increase in serine 40 phosphorylation and TH activity more than 2-fold. Humans are unique in that they contain four TH isoforms but to date no significant differences have been shown in the regulation of these isoforms. Phosphorylation of the human TH isoform 1 at serine 31 by extracellular signal-regulated protein kinase (ERK) also produced a 9-fold increase in the rate of phosphorylation of serine 40, whereas little effect was seen in the TH isoforms 3 and 4. ERK did not phosphorylate human TH isoform 2. The effect of serine 19 phosphorylation on serine 40 (44 in TH2) phosphorylation is stronger in TH2 than in TH1. Thus hierarchical phosphorylation provides a mechanism whereby the two major human TH isoforms (1 and 2) can be differentially regulated with only isoform 1 responding to the ERK pathway, whereas isoform 2 is more sensitive to calcium-mediated events.Tyrosine hydroxylase (TH) 2 [EC1.14.16.2] is the rate-limiting enzyme in the biosynthesis of the catecholamines dopamine, noradrenaline, and adrenaline (1). Short term regulation of TH is accomplished by dynamic changes in the phosphorylation state of the enzyme (2, 3). Although four serine residues have been shown to be phosphorylated in TH, only three of these serine residues (Ser 19 , Ser 31 , and Ser 40 ) are regulated in vivo (4). The most important mechanism of TH activation is phosphorylation of Ser 40 , which decreases the feedback inhibition by the catecholamines (5-7). Phosphorylation of dopamine bound TH at Ser 40 by protein kinase A (PKA) can activate TH by up to 20-fold (5). The direct effect of Ser 19 and Ser 31 phosphorylation on TH activation is much more modest. Phosphorylation of Ser 19 by calcium calmodulindependent protein kinase (CaMKII) will only increase TH activity in the presence of the 14-3-3 protein (8 -10), and this results only in a 2-fold increase in the activity. The phosphorylation of Ser 31 by extracellular signal-regulated protein kinase (ERK) produces less than a 2-fold increase in TH activity, primarily by decreasing the affinity of the cofactor tetrahydrobiopterin (BH 4 ) (11-13). Phosphorylation of Ser 31 in TH has also been shown to increase the stability of TH (14).Humans have four TH protein isoforms, whereas anthropoids have two, and other mammalian species only have one (15). TH is encoded by a single gene, and the multiple isoforms are because of multiple mRNAs generated by alternativ...

AAV2-mediated gene transfer of GDNF to the striatum of MPTP monkeys enhances the survival and outgrowth of co-implanted fetal dopamine neurons

“…Alternatively, since the relationship between GDNF concentration, time of GDNF exposure and TH activity has not been defined, it may be that down-regulation of the enzyme will not occur over time if exposure to GDNF does not exceed a certain threshold. In addition, as TH in primate brain exists in multiple isoforms (Haycock, 2002) which may be differentially regulated (Lehmann et al, 2006), it is feasible that the effect of high GDNF concentrations over time will be different in the primate and rodent brain. Finally, the different parkinsonian models used here and in the rodent study (Georgievska et al, 2004a) may have a bearing on the effects of GDNF on TH.…”

Prion Protein Modulates Monoaminergic Systems and Depressive-like Behavior in Mice

“…Consistent with these findings, we also found a significant increase of total dopamine levels in PrP C -null cerebral cortex. Although phosphorylation of TH is the primary regulator of the production of dopamine in synapses (74), it is likely that the increased level of total TH, rather than a shift in phosphorylation, explains the chronically increased dopamine content.…”

Differential Expression of the B′β Regulatory Subunit of Protein Phosphatase 2A Modulates Tyrosine Hydroxylase Phosphorylation and Catecholamine Synthesis

“…Best characterized is Ser 40 phosphorylation by cyclic AMP-dependent protein kinase (PKA), which markedly enhances TH catalytic activity both in vitro and in vivo by relieving feedback inhibition by the catecholamines (4 -9). Phosphorylation at Ser 19 by calcium/calmodulin-dependent kinase II (CaMKII) and at Ser 31 by proline-directed kinases has comparatively moderate effects on TH activity but can facilitate subsequent Ser 40 phosphorylation (10,11). Although the kinases that regulate catecholamine synthesis have been studied extensively, little is know about inactivation of TH by protein Ser/Thr phosphatases.…”