Tyrosine hydroxylase protein phosphorylation

Several key questions remain with regard to the regulation of tyrosine hydroxylase by phosphorylation. What is the precise effect of the phosphorylation of each of these serine residues on the catalytic activity of the enzyme How does the phosphorylation of multiple residues affect enzyme activity Does the phosphorylation of one residue affect the ability of the others to be phosphorylated Tyrosine hydroxylase provides a striking example as to how multiple intracellular messengers and protein kinases converge functionally through the phosphorylation of a single substrate protein. Phosphorylation of tyrosine hydroxylase by cAMP-dependent and Ca2+-dependent protein kinases and by MAPK cascades... 

Pigeon, D. Ferrara, P. Gros, E Thibault, J. Rat pheochromocytoma tyrosine hydroxylase is phosphorylated on serine 40 by an associated protein kinase. J. Biol. Chem., 262, 6155-6158 (1987)... 

The dopamine is then concentrated in storage vesicles via an ATP-dependent process. Here the rate-limiting step appears not to be precursor uptake, under normal conditions, but tyrosine hydroxylase activity. This is regulated by protein phosphorylation and by de novo enzyme synthesis. The enzyme requites oxygen, ferrous iron, and tetrahydrobiopterin (BH. The enzymatic conversion of the precursor to the active agent and its subsequent storage in a vesicle are energy-dependent processes. 

Sutherland, C., Alterio, J., Campbell, D. G., Le Bourdelles, B., Mallet, J., Haavik, J., and Cohen, P. (1993). Phosphorylation and activation of human tyrosine hydroxylase in vitro by mitogen-activated protein (MAP) kinase and MAP-kinase-activated kinases 1 and 2. Em.J. Biodiem. 217, 715-722. 

FIGURE 1 2-2 Schematic diagram of the phosphorylation sites on each of the four 60kDa subunits of tyrosine hydroxylase (TOHase). Serine residues at the N-terminus of each of the four subunits of TOHase can be phosphorylated by at least five protein kinases. (J), Calcium/calmodulin-dependent protein kinase II (CaM KII) phosphorylates serine residue 19 and to a lesser extent serine 40. (2), cAMP-dependent protein kinase (PKA) phosphorylates serine residue 40. (3), Calcium/phosphatidylserine-activated protein kinase (PKC) phosphorylates serine 40. (4), Extracellular receptor-activated protein kinase (ERK) phosphorylates serine 31. (5), A cdc-like protein kinase phosphorylates serine 8. Phosphorylation on either serine 19 or 40 increases the activity of TOHase. Serine 19 phosphorylation requires the presence of an activator protein , also known as 14-3-3 protein, for the expression of increased activity. Phosphorylation of serines 8 and 31 has little effect on catalytic activity. The model shown includes the activation of ERK by an ERK kinase. The ERK kinase is activated by phosphorylation by PKC. (With permission from reference [72].)... 

Waymire, J. C. and Craviso, G. L. Multiple site phosphorylation and activation of tyrosine hydroxylase. Adv. Protein Phosphatases 7 501-513,1993. 

TABLE 23-3 Examples of proteins regulated by phosphorylation Enzymes involved in neurotransmitter biosynthesis Tyrosine hydroxylase Tryptophan hydroxylase Neurotransmitter receptors Adrenergic receptors Dopamine receptors Opioid receptors Glutamate receptors Many others... 

FIGURE 23-5 Schematic diagram of tyrosine hydroxylase with sites of phosphorylation indicated (yellow) along with the protein kinases. 

The hereditary absence of phenylalanine hydroxylase, which is found principally in the liver, is the cause of the biochemical defect phenylketonuria (Chapter 25, Section B).430 4308 Especially important in the metabolism of the brain are tyrosine hydroxylase, which converts tyrosine to 3,4-dihydroxyphenylalanine, the rate-limiting step in biosynthesis of the catecholamines (Chapter 25), and tryptophan hydroxylase, which catalyzes formation of 5-hydroxytryptophan, the first step in synthesis of the neurotransmitter 5-hydroxytryptamine (Chapter 25). All three of the pterin-dependent hydroxylases are under complex regulatory control.431 432 For example, tyrosine hydroxylase is acted on by at least four kinases with phosphorylation occurring at several sites.431 433 4338 The kinases are responsive to nerve growth factor and epidermal growth factor,434 cAMP,435 Ca2+ + calmodulin, and Ca2+ + phospholipid (protein kinase C).436 The hydroxylase is inhibited by its endproducts, the catecholamines,435 and its activity is also affected by the availability of tetrahydrobiopterin.436... 

There are numerous data that peroxynitrite is involved in cell death and tissue injuries in many clinical conditions. An important mechanism underlying peroxynitrite toxicity is the reaction of tyrosine nitration. Tyrosine nitration inactivates certain enzymes, as was postulated for prostacyclin (PGI2) synthase (M14), cytochrome P450 2B1 (RIO), tyrosine hydroxylase (A 14), and MnSOD (Yl). Moreover, nitration blocks tyrosine phosphorylation, and thus interferes with the tyrosine kinase signaling pathways (K18). The peroxynitrite treatment of rat liver epithelial cells stimulates mitogen-activated protein kinases p38 MAPK, JNK1/2, and ERK1/2 the mechanism of this effect awaits elucidation (S9). 

Tyrosine hydroxylase is a substrate for protein kinases (see following section on second messengers), and once phosphorylated, the enzyme is less sensitive to end-product inhibition and thereby appears to have a greater affinity for hydroxylase cofactor. One study suggests that under physiologic... 

As with cAMP-stimulated protein kinase, the specific cellular responses to protein kinase C activation depend on the ensemble of target proteins that become phosphorylated in a given cell. Known target proteins include calmodulin, the insulin receptor, the adrenergic receptor (see here), the glucose transporter, HMG-CoA reductase, cytochrome P450, and tyrosine hydroxylase. 

Depolarization of the nerve terminal activates tyrosine hydroxylase. Depolarization also activates a number of protein kinases (including protein kinase C, protein kinase A [the cAMP-dependent protein kinase] and CAM kinases [Ca -calmodulin-dependent kinases]) that phosphorylate tyrosine hydroxylase. These activation steps result in an enzyme that binds BH4 more tightly, making it less sensitive to end-product inhibition. 

In addition to these short-term regulatory processes, a long-term process involves alterations in the amounts of tyrosine hydroxylase and dopamine (3-hydroxylase present in nerve terminals. When sympathetic neuronal activity is increased for a prolonged period, the amounts of mRNA coding for tyrosine hydroxylase and dopamine p-hydroxylase are increased in the neuronal perikarya (the cell body of the neuron). The increased gene transcription may be the result of phosphorylation of CREB (cAMP response element binding protein see Chapter 26) by... 

CaM kinase II participates in the phosphorylation of tau (Baudier and Cole, 1987 Steiner et al., 1990). It phosphorylates a nnmber of other substrates in vitro, including MAP-2, tyrosine hydroxylase, synapsin 1, APP, and varions intermediate filament proteins such as vimentin, desmin, and GFAP (Colbran et al., 1989). In vitro, CaM kinase Il-phosphorylated tau inhibits microtnbnle assembly (Yamamoto et al., 1983 Yamamoto et al., 1985, 1988). It phosphorylates tau in vitro in such a way to slow its electrophoretic mobility (Baudier and Cole, 1987). Serine " (numbered according to the longest human tau isoform) is one of the major phosphorylation sites for CaM kinase II in vitro (Steiner et al., 1990). Immnnostaining of AD brain showed serine " phosphorylation only in neuronal soma, bnt not in neuropil threads and dystrophic neurites (Yamamoto et al., 2005). Tau phosphorylation in glia cells is unlikely due to CaM kinase II. 

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