Tyrosine hydroxylase phosphorylation: regulation and consequences

Abstract

The rate-limiting enzyme in catecholamine synthesis is tyrosine hydroxylase. It is phosphorylated at serine (Ser) residues Ser8, Ser19, Ser31 and Ser40 in vitro, in situ and in vivo. A range of protein kinases and protein phosphatases are able to phosphorylate or dephosphorylate these sites in vitro. Some of these enzymes are able to regulate tyrosine hydroxylase phosphorylation in situ and in vivo but the identity of the kinases and phosphatases is incomplete, especially for physiologically relevant stimuli. The stoichiometry of tyrosine hydroxylase phosphorylation in situ and in vivo is low. The phosphorylation of tyrosine hydroxylase at Ser40 increases the enzyme's activity in vitro, in situ and in vivo. Phosphorylation at Ser31 also increases the activity but to a much lesser extent than for Ser40 phosphorylation. The phosphorylation of tyrosine hydroxylase at Ser19 or Ser8 has no direct effect on tyrosine hydroxylase activity. Hierarchical phosphorylation of tyrosine hydroxylase occurs both in vitro and in situ, whereby the phosphorylation at Ser19 increases the rate of Ser40 phosphorylation leading to an increase in enzyme activity. Hierarchical phosphorylation depends on the state of the substrate providing a novel form of control of tyrosine hydroxylase activation. Keywords: activity, catecholamine synthesis, phosphorylation, protein kinases, protein phosphatases, tyrosine hydroxylase. The catecholamines (CAs) dopamine (DA), noradrenaline and adrenaline are physiologically important neurotransmitters and hormones. It has been established that when the CAs are secreted there is generally no decrease in their levels within tissues (Zigmond et al. 1989). This is because there is a concomitant increase in the rate of CA synthesis that is closely coupled to secretion. Tyrosine hydroxylase (TH; tyrosine 3-monooxygenase; E.C. 1.14.16.2) is the first and rate-limiting enzyme in CA synthesis and it catalyses the hydroxylation of L-tyrosine to DOPA. The activity of TH can be modulated by two mechanisms: medium-to long-term regulation of gene expression (enzyme stability, transcriptional regulation, RNA stability, alternative RNA splicing and translational regulation) and short-term regulation of enzyme activity (feedback inhibition, allosteric regulation and phosphorylation) (Kumer and Vrana 1996). TH activation by phosphorylation is the primary mechanism responsible for the maintenance of CA levels in tissues after CA secretion. TH can be phosphorylated at serine residues (Ser) 8, 19, 31 and 40 by a variety of protein kinases. The regulation of the phosphorylation of these sites and the consequences in terms of TH activity in vitro have been extensively investigated. In situ and in vivo it is less clear which protein kinase(s), and/or phosphatase(s), modulates TH phosphorylation and which mechanism(s) leads to the activation of TH and CA synthesis. The major focus of this review is therefore the regulation and consequences of the (Kaufman 1995;Nagatsu 1995;Kappock and Caradonna 1996;Kumer and Vrana 1996;...

Transcription factors FOXA1 and FOXA2 maintain dopaminergic neuronal properties and control feeding behavior in adult mice

“…2B). The activity of TH can be modulated by phosphorylation, and phospho-serine 40 TH (pSer40 TH) represents an active form of the enzyme (28). We found that, in Foxa1/2 cKO mice, there was also a small but significant reduction in the amount of pSer40 TH, normalized to the total amount of TH ) Quantification of FOXA1/2 colocalization with TH+ neurons, and efficiency of deletion is shown in the graph (C) (proportion of TH+ neurons that coexpresses FOXA1/2; control VTA = 95.8% ± 2.9, control SNc = 95.8% ± 3.6; Foxa1/2 cKO VTA = 10.4% ± 3.6*, Foxa1/2 cKO SNc = 1.4% ± 1.6*; n = 3; mean ± SEM; *P < 0.001 vs. control, t test).…”

Amphetamine Self-Administration Attenuates Dopamine D2 Autoreceptor Function

“…Ser31 and Ser40 of TH are believed to be directly involved in DA synthesis because increases in the phosphorylation of TH at these two sites enhance the catalytic activity of TH (Colby et al, 1989;Dunkley et al, 2004). Compared with control animals, AMPH self-administration did not change the expression of TH, but significantly reduced the level of TH phosphorylation at serine 31 (N ¼ 5-6, two-tailed unpaired t-test, t 9 ¼ 3.054, Po0.05) and serine 40 (t 9 ¼ 2.427, Po0.05) as shown in Figure 3.…”

Differential Regulation of the Human Tyrosine Hydroxylase Isoforms via Hierarchical Phosphorylation

“…This result is consistent with previous work where attempts to demonstrate the phosphorylation of hTH2 Ser 35 in intact human neuroblastoma cells (prelabeled with 32 P i , treated with veratridine, forskolin, or phorbol ester, immunoprecipitated with isoform-specific antibodies, trypsinized, and analyzed by HPLC with radiochemical detection) indicated, rather, that hTH2 Ser 35 was essentially not phosphorylated under any of the conditions. 3 Effect of ERK Phosphorylation on the Human TH Isoforms-We examined the effect of ERK phosphorylation on the rate of activation of the dopamine-bound human TH isoforms by PKA. The data is shown in Fig.…”

“…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).…”