In vitro phosphorylation of bovine adrenal chromaffin cell tyrosine hydroxylase by endogenous protein kinases

Myeloid adrenergic signaling via CaMKII forms a feedforward loop of catecholamine biosynthesis

Type 2 immune response has been shown to facilitate cold-induced thermogenesis and browning of white fat. However, whether alternatively activated macrophages produce catecholamine and substantially promote adaptive thermogenesis in adipose tissue remains controversial. Here, we show that tyrosine hydroxylase (TyrH), a rate-limiting enzyme of catecholamine biosynthesis, was expressed and phosphorylated in adipose-resident macrophages. In addition, the plasma level of adrenaline was increased by cold stress in mice, and treatment of macrophages with adrenaline stimulated phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and TyrH. Genetic and pharmacological inhibition of CaMKII or PKA signaling diminished adrenaline-induced phosphorylation of TyrH in primary macrophages. Consistently, overexpression of constitutively active CaMKII upregulated basal TyrH phosphorylation, while suppressing the stimulatory effect of adrenaline on TyrH in macrophages. Myeloid-specific disruption of CaMKIIγ suppressed both the cold-induced production of norepinephrine and adipose UCP1 expression in vivo and the stimulatory effect of adrenaline on macrophage-dependent activation of brown adipocytes in vitro. Lack of CaMKII signaling attenuated catecholamine production mediated by cytokines IL-4 and IL-13, key inducers of type 2 immune response in primary macrophages. Taken together, these results suggest a feedforward mechanism of adrenaline in adipose-resident macrophages, and that myeloid CaMKII signaling plays an important role in catecholamine production and subsequent beige fat activation.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Identification by hydrogen/deuterium exchange of structural changes in tyrosine hydroxylase associated with regulation

The activity of tyrosine hydroxylase is regulated by reversible phosphorylation of serine residues in an N-terminal regulatory domain and catecholamine inhibition at the active site. Catecholamines such as dopamine bind very tightly to the resting enzyme; phosphorylation of Ser40 decreases the affinity for catecholamines by 3 orders of magnitude. The effects of dopamine binding and phosphorylation of Ser40 on the kinetics of deuterium incorporation into peptide bonds were examined by mass spectrometry. When dopamine is bound, three peptic peptides show significantly slower deuterium incorporation, 35-41 and 42-71 in the regulatory domain and 295-299 in the catalytic domain. In the phosphorylated enzyme, peptide 295-299 shows more rapid incorporation of deuterium, while 35-41 and 42-71 can not be detected. These results are consistent with tyrosine hydroxylase existing in two different conformations. In the closed conformation, the regulatory domain lies across the active site loop containing residues 295-298; this is stabilized when dopamine is bound in the active site. In the open conformation, the regulatory domain has moved out of the active site, allowing substrate access; this conformation is favored by phosphorylation of Ser40.

Melatonin inhibits amphetamine-induced increase in alpha-synuclein and decrease in phosphorylated tyrosine hydroxylase in SK-N-SH cells

alpha-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegeneration disorders. Understanding alpha-synuclein function in dopaminergic cells could add to our knowledge of this key protein which is implicated in Parkinson's disease. Chronic or intermittent amphetamine (AMPH) abuse may create temporary or permanent disturbances in the dopaminergic system of the brain that may predispose individuals to Parkinsonism. Our previous studies showed that neurotoxicity induced by AMPH was mediated by enhanced oxidative stress and these effects were abolished by melatonin, a main secretory product of pineal gland. The present study was conducted to investigate the effect of AMPH on alpha-synuclein in regulating tyrosine hydroxylase (TH), a rate limiting enzyme for dopamine synthesis, in cultured human dopaminergic SK-N-SH cells. Of these, phosphorylation of Ser40 (pSer40) contributes significantly to TH activation and dopamine synthesis. Our data indicated that AMPH significantly increased the level of alpha-synuclein to 183% of the control value while reducing the levels of phosphorylated TH (TH-pSer40) enzyme and mitochondrial complex I to 78 and 52.9% of the control values, respectively and these effects were attenuated by melatonin. Further studies are needed to explore the mechanism by which alpha-synuclein contributes to TH-pSer40 dephosphorylation and the mechanism by which melatonin contributes to this interaction.

Alpha-synuclein aggregation alters tyrosine hydroxylase phosphorylation and immunoreactivity: lessons from viral transduction of knockout mice

Tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis, is frequently used as a marker of dopaminergic neuronal loss in animal models of Parkinson's disease (PD). We have been exploring the normal function of the PD-related protein alpha-synuclein (alpha-Syn) with regard to dopamine synthesis. TH is activated by the phosphorylation of key seryl residues in the TH regulatory domain. Using in vitro models, our laboratory discovered that alpha-Syn inhibits TH by acting to reduce TH phosphorylation, which then reduces dopamine synthesis [X.-M. Peng, R. Tehranian, P. Dietrich, L. Stefanis, R.G. Perez, Alpha-synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells, J. Cell. Sci. 118 (2005) 3523-3530; R.G. Perez, J.C. Waymire, E. Lin, J.J. Liu, F. Guo, M.J. Zigmond, A role for alpha-synuclein in the regulation of dopamine biosynthesis, J. Neurosci. 22 (2002) 3090-3099]. We recently began exploring the impact of alpha-Syn on TH in vivo, by transducing dopaminergic neurons in alpha-Syn knockout mouse (ASKO) olfactory bulb using wild type human alpha-Syn lentivirus. At 3.5-21 days after viral delivery, alpha-Syn expression was transduced primarily in periglomerular dopaminergic neurons. Cells with modest levels of alpha-Syn consistently co-labeled for Total-TH. However, cells bearing aggregated alpha-Syn, as revealed by proteinase K or Thioflavin-S treatment had significantly reduced Total-TH immunoreactivity, but high phosphoserine-TH labeling. On immunoblots, we noted that Total-TH immunoreactivity was equivalent in all conditions, although tissues with alpha-Syn aggregates again had higher phosphoserine-TH levels. This suggests that aggregated alpha-Syn is no longer able to inhibit TH. Although the reason(s) underlying reduced Total-TH immunoreactivity on tissue sections await(s) confirmation, the dopaminergic phenotype was easily verified using phosphorylation-state-specific TH antibodies. These findings have implications not only for normal alpha-Syn function in TH regulation, but also for measuring cell loss that is associated with synucleinopathy.

α-Synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells

α-Synuclein is an abundant presynaptic protein implicated in neuronal plasticity and neurodegenerative diseases. Although the function of α-synuclein is not thoroughly elucidated, we found that α-synuclein regulates dopamine synthesis by binding to and inhibiting tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis. Understanding α-synuclein function in dopaminergic cells should add to our knowledge of this key protein, which is implicated in Parkinson's disease and other disorders. Herein, we report a mechanism by which α-synuclein diminishes tyrosine hydroxylase phosphorylation and activity in stably transfected dopaminergic cells. Short-term regulation of tyrosine hydroxylase depends on the phosphorylation of key seryl residues in the amino-terminal regulatory domain of the protein. Of these, Ser40 contributes significantly to tyrosine hydroxylase activation and dopamine synthesis. We observed that α-synuclein overexpression caused reduced Ser40 phosphorylation in MN9D cells and inducible PC12 cells. Ser40 is phosphorylated chiefly by the cyclic AMP-dependent protein kinase PKA and dephosphorylated almost exclusively by the protein phosphatase, PP2A. Therefore, we measured the impact of α-synuclein overexpression on levels and activity of PKA and PP2A in our cells. PKA was unaffected by α-synuclein. PP2A protein levels also were unchanged, however, the activity of PP2A increased in parallel with α-synuclein expression. Inhibition of PP2A dramatically increased Ser40 phosphorylation only in α-synuclein overexpressors in which α-synuclein was also found to co-immunoprecipitate with PP2A. Together the data reveal a functional interaction between α-synuclein and PP2A that leads to PP2A activation and underscores a key role for α-synuclein in protein phosphorylation.

Effects of erythropoietin on neuronal activity

Recently, erythropoietin (EPO) receptors and synthesis of EPO have been identified in the brain. To clarify the effects of EPO on neuronal cells, we investigated the effects of EPO on Ca2+ uptake, intracellular Ca2+ concentration, membrane potential, cell survival, release and biosynthesis of dopamine, and nitric oxide (NO) production in differentiated PC12 cells, which possess EPO receptors. EPO (10(-12)-10(-10) M) increased 45Ca2+ uptake and intracellular Ca2+ concentration in PC12 cells in a dose-related manner; these increases were inhibited by nicardipine (1 microM) or anti-EPO antibody (1:100 dilution). EPO induced membrane depolarization in PC12 cells. After a 5-day culture without serum and nerve growth factor (NGF), viable cell number decreased to 50% of that of the control cells cultured with serum and NGF. EPO (10(-13)-10(-10) M) increased the number of viable cells cultured without serum and NGF; this increase was blunted by nicardipine or anti-EPO antibody. Incubation with EPO (10(-13)-10(-10) M) stimulated mitogen-activated protein kinase activity in PC12 cells. EPO (10(-13)-10(-10) M) increased dopamine release from PC12 cells and tyrosine hydroxylase activity; these increases were sensitive to nicardipine or anti-EPO antibody. Following a 4-h incubation with EPO (10(-14)-10(-10) M), NO production was increased, which was blunted by nicardipine and anti-EPO antibody. In contrast, maximal NO synthase activity was not changed by EPO. These results suggest that EPO stimulates neuronal function and viability via activation of Ca2+ channels.

Effects of sodium nitroprusside on the catecholamine synthetic pathway in the adrenal medulla of rats

We studied the effect of sodium nitroprusside (SNP), a nitric oxide (NO) donor, on tyrosine hydroxylase (TH) activity and epinephrine and norepinephrine levels in the adrenal medulla of rats. TH activity and the levels of epinephrine and norepinephrine in the adrenal medulla of the SNP+nicotine (Nic)-treated group were increased significantly compared to those in the control, Nic-treated and SNP-treated groups. Furthermore, methylene blue inhibited this increase in TH activity. The data suggest that the NO derived from SNP may increase TH through the guanylyl cyclase pathway in the presence of Nic.

Activation of tyrosine hydroxylase by histamine in bovine chromaffin cells

Acute activation of tyrosine hydroxylase by histamine has been studied in cultured bovine chromaffin cells. Tyrosine hydroxylase activity was determined in situ by measuring 14CO2 release following the hydroxylation and rapid decarboxylation of 14C-tyrosine offered to the cells. Histamine increased tyrosine hydroxylase activity 2-fold over 10 min with an EC50 of 0.3 microM and maximal response at 10 microM. Tyrosine hydroxylase activation was detectable within 1-2 min and maintained for at least 10 min. The effect of histamine was fully blocked by the H1 antagonist mepyramine, but unaffected by H2 (cimetidine) and H3 (thioperamide) antagonists. It was mimicked by Nalpha-methylhistamine and the H1 agonist 2-thiazolylethylamine, but not by H2 (dimaprit) or H3 (R)alpha-methylhistamine) agonists. The response to histamine was reduced by 70% by removing extracellular Ca2+ and abolished by removing extracellular Ca2+ and chelating intracellular Ca2+ with BAPTA. Tyrosine hydroxylase activation by histamine was unaffected by the protein kinase C inhibitor Ro 31-8220 but was completely blocked by the protein kinase A inhibitor H89. The results indicate that histamine activates tyrosine hydroxylase and that this effect is mediated through H1 receptors by a mechanism that depends on both extracellular and intracellular Ca2+ and that requires protein kinase A.

Activation of tyrosine hydroxylase by pituitary adenylate cyclase-activating polypeptide (PACAP-27) in bovine adrenal chromaffin cells

The effect of pituitary adenylate cyclase-activating polypeptide (PACAP-27) on tyrosine hydroxylase activity has been studied in intact, cultured, bovine adrenal chromaffin cells. Tyrosine hydroxylase activity was determined in situ by measuring the production of 14CO2 following the hydroxylation and rapid decarboxylation of [14C]tyr offered to the cells. PACAP-27 increased tyrosine hydroxylase activity 3-fold over 10 min. With an EC50 of 10-20 nM. PACAP-38 was approximately 2-fold less potent. Removing extracellular Ca2+ reduced basal tyrosine hydroxylase activity and the activation produced by both PACAP-27 and forskolin by about 20%. In the absence of extracellular Ca2+, chelation of intracellular Ca2+ by treating cells with BAPTA-AM (50 microM) caused a consistent 40-50% reduction in basal tyrosine hydroxylase activity and in the responses to forskolin and PACAP-27. The tyrosine hydroxylase activation produced by PACAP-27 was unaffected by the protein kinase C inhibitor Ro 3l-8220 (3 microM), but was reduced by 85% by the protein kinase A inhibitor H89 (10 microM). PACAP-27 increased cellular cyclic AMP levels 3-fold at 100 nM. The results suggest that PACAP-27 activates tyrosine hydroxylase in bovine chromaffin cells through cyclic AMP formation and protein kinase A activation, and that both extracellular and intracellular Ca2+ modulate the effect of the adenylate cyclase/cyclic AMP/protein kinase A signalling pathway on tyrosine hydroxylase activity.

The role of protein kinase C in nicotinic responses of bovine chromaffin cells

The effects of the protein kinase C inhibitor CGP 41251 (31-benzoyl-staurosporine) on nicotinic responses of cultured bovine adrenal chromaffin cells have been investigated. CGP 41251 inhibited tyrosine hydroxylase activation by phorbol 12,13-dibutyrate, with an IC50 of < 0.3 microM and complete inhibition at 1 microM. In contrast, it had little effect on nicotine-stimulated tyrosine hydroxylase activity up to 1 microM, and did not fully inhibit it even at 10 microM. From 1 to 10 microM, CGP 41251 caused a similar concentration-dependent inhibition of tyrosine hydroxylase activity stimulated by nicotine, K+, forskolin and 8-Br-cyclic AMP. CGP 42700 (19,31-dibenzoyl-staurosporine), a structural analogue of CGP 41251 that lacks activity as a protein kinase C inhibitor, had no effect on tyrosine hydroxylase activity stimulated by any of the agonists. CGP 41251 had no effect on catecholamine secretion induced by nicotine. The results suggest phorbol ester-sensitive protein kinase C isozymes do not play a major role in nicotinic stimulation of tyrosine hydroxylase activity or catecholamine secretion in chromaffin cells.

Inhibition of nicotinic responses of bovine adrenal chromaffin cells by the protein kinase C inhibitor, Ro 31-8220

1. The effects of the protein kinase C inhibitor, Ro 31-8220, on the responses of cultured bovine adrenal chromaffin cells to nicotine, phorbol 12, 13-dibutyrate (PDBu) and K+ have been investigated. 2. Tyrosine hydroxylase activity was measured in situ in intact cells by measuring 14CO2 evolved following the hydroxylation and rapid decarboxylation of [14C]-tyrosine offered to the cells. Secretion of endogenous adrenaline and noradrenaline was measured by use of h.p.l.c. with electrochemical detection. Cyclic AMP levels were measured in cell extracts by RIA. 3. Ro 31-8220 produced a concentration-dependent inhibition of 300 nM PDBu-stimulated tyrosine hydroxylase activity with an IC50 of < 2 microM and complete inhibition at 10 microM. It had no effect on the responses to forskolin. 4. Ro 31-8220 produced a concentration-dependent inhibition of 5 microM nicotine-stimulated tyrosine hydroxylase activity, adrenaline and noradrenaline secretion and cellular cyclic AMP levels, with an IC50 of about 3 microM and complete inhibition by 10 microM. At concentrations up to 10 microM, Ro 31-8220 had little or no effect on the corresponding responses to 50 mm K+. 5. A structural analogue of Ro 31-8220, bisindolylmaleimide V, that lacks activity as a protein kinase C inhibitor, had no effect up to 10 microM on PDBu-stimulated tyrosine hydroxylase activity or on nicotine-stimulated cyclic AMP levels or noradrenaline secretion and only marginal inhibitory effects on nicotine-stimulated tyrosine hydroxylase activity and adrenaline secretion. 6. A structurally related protein kinase C inhibitor, bisindolylmaleimide I, inhibited PDBu-stimulated tyrosine hydroxylase activity with an IC50 of < 1 microM and complete inhibition by 3 microM, but had essentially no effect on nicotine stimulated tyrosine hydroxylase activity or catecholamine secretion. 7. The results suggest that Ro 31-8220 is not only a protein kinase C inhibitor but is also a potent inhibitor of nicotinic receptor responses in adrenal chromaffin cells by a mechanism unrelated to protein kinase C inhibition. The results are consistent with Ro 31-8220 being a nicotinic receptor antagonist.

Phosphorylation of chromogranin A and catecholamine secretion stimulated by elevation of intracellular Ca2+ in cultured bovine adrenal medullary cells

We have recently isolated a new endogenous substrate of 70 kDa for Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) from bovine adrenal medullary cells (Yanagihara, N., Toyohira, Y., Yamamoto, H., Ohta, Y., Tsutsui, M., Miyamoto, E., and Izumi, F. (1994) Mol. Pharmacol. 46, 423-430). Here we report the sequence analysis of the 70-kDa protein and examine its phosphorylation by various protein kinases in vitro and by depolarization of the cultured cells. Protein sequencing and immunoblotting revealed that the 70-kDa protein is chromogranin A (CgA) or a closely related protein. Partially purified CgA was phosphorylated by cyclic AMP-dependent protein kinase and protein kinase C as well as CaM kinase II. Tryptic phosphopeptide mapping patterns of CgA differed among these protein kinases. In 32P-labeled bovine adrenal medullary cells, 56 mM K+ increased the phosphorylation of CgA and catecholamine secretion in similar time- and concentration-dependent manners, both of which were inhibited by 20 mM MgSO4, an inhibitor of voltage-dependent Ca2+ channels. These findings suggest that CgA serves as a substrate for several multifunctional protein kinases and that the elevation of the intracellular Ca2+ stimulates the phosphorylation of CgA associated with catecholamine secretion in cultured adrenal medullary cells.

Tyrosine hydroxylase phosphorylation in bovine adrenal chromaffin cells. Clonidine stimulates basal but inhibits nicotinic receptor evoked phosphorylation

Clonidine inhibited the uptake of calcium and the overall phosphorylation of tyrosine hydroxylase induced by nicotinic receptor activation in bovine adrenal medullary chromaffin cells in culture. However, clonidine did not inhibit the increase in these parameters that accompanied K+ depolarisation of the cells. There was also no effect of clonidine on the overall phosphorylation of tyrosine hydroxylase when cells were stimulated by muscarine. Nicotinic receptor activation increased the phosphorylation of Ser-19, Ser-31, and Ser-40 on tyrosine hydroxylase, and this was inhibited by clonidine in a concentration-dependent manner. On the other hand, clonidine had no effect on calcium uptake, yet increased the phosphorylation of Ser-19 under basal conditions. Using calcium and calmodulin-stimulated protein kinase II obtained from rat brain clonidine increased the autophosphorylation of the alpha-subunit of the kinase by 37%, and also its activity against an exogenous peptide substrate by 29%. These data are consistent with the hypothesis that clonidine inhibits nicotinic receptor-induced tyrosine hydroxylase phosphorylation by decreasing calcium influx into chromaffin cells, perhaps by an action at the nicotinic receptor. Clonidine also increases the basal phosphorylation of tyrosine hydroxylase at Ser-19, perhaps by directly activating calcium and calmodulin-stimulated protein kinase II.

Protein kinase A and nicotinic activation of bovine adrenal tyrosine hydroxylase

1. Stimulation of nicotinic cholinoceptors on bovine chromaffin cells increases phosphorylation of three serine residues in tyrosine hydroxylase (TOH) and activates TOH. One of the serines is a target for protein kinase A phosphorylation, and phosphorylation of this serine is adequate alone to cause TOH activation. The role of protein kinase A in nicotinic activation of TOH was therefore investigated. 2. TOH activity was studied in situ in intact, cultured, bovine adrenal chromaffin cells, by measuring 14CO2 evolved following the hydroxylation and rapid decarboxylation of [14C]-tyrosine offered to the cells. 3. Nicotine (5 microM), forskolin (1 microM) and 8-bromo-cyclic AMP (8-Br-cyclic AMP, 1 mM) each increased TOH activity by up to 200% over 10 min. The effect of nicotine was completely abolished by removal of extracellular Ca2+. 4. TOH activation by all three drugs was blocked by H89 (3-20 microM), which inhibits protein kinase A by competing for the ATP binding site on the kinase. Adenosine 3':5'-cyclic monophosphorothioate Rp-diastereomer (Rp-cAMPS) (1 mM), an inhibitor of protein kinase A that competes with cyclic AMP for the regulatory subunit of the kinase, abolished the activation of TOH by nicotine, and reduced that by forskolin and 8-Br-cyclic AMP. Both H89 and Rp-cAMPS inhibited basal TOH activity by 50-80%. 5. A structural analogue of H89, H85 (3-20 microM), which lacks activity as a protein kinase A inhibitor, did not inhibit either the activation of TOH by nicotine (5 microM) or basal TOH activity. Neither sodium nitroprusside (0.3-1O microM) nor 8-Br-cyclic GMP (1 mM) increased TOH activity.6. In digitonin-permeabilized chromaffin cells, forskolin (3 microM), cyclic AMP (10 microM) and Ca2+ (approx.2 micro M free Ca2+) each increased TOH activity. The response to all three drugs was blocked by H89(10 microM), which also reduced basal TOH activity in the permeabilized cells.7. Maximal activation of TOH by forskolin was achieved with 10 micro M forskolin. This concentration was less than the EC50 for forskolin-induced cyclic AMP accumulation in these cells. The activations of TOH by forskolin (1O microM) and nicotine (5 microM) were additive.8. The results indicate that both basal TOH activity and nicotinic activation of TOH in bovine chromaffin cells require protein kinase A activity. However, it is unlikely that nicotinic activation of TOH is directly mediated by an activation of protein kinase A in response to elevated cyclic AMP levels.It is possible that protein kinase A plays a permissive role in allowing nicotinic cholinoceptors to activate TOH by another signalling pathway.

Dephosphorylation of tyrosine hydroxylase by brain protein phosphatases: a predominant role for type 2A

Extracts from rat corpus striatum, or striatal proteins resolved by chromatography on DE-52, were tested for protein phosphatase activity using tyrosine hydroxylase, phosphorylated by cAMP-dependent protein kinase, as substrate. The predominant dephosphorylating activity was independent of divalent cations and was inhibited by low concentrations (100 nM) of okadaic acid, defining the phosphatase as type 2A. Phosphatase type 2C (Mg2+ and Mn2+ stimulated) was evident in the presence of okadaic acid but at a level of approximately 10% of type 2A activity. Phosphatase 2B (Ca2+ and calmodulin dependent) mediated dephosphorylation of tyrosine hydroxylase was not apparent. The dephosphorylation of [32P]-tyrosine hydroxylase was not modulated by tetrahydrobiopterin, ATP, or GTP. These results indicate that tyrosine hydroxylase which has been phosphorylated by cAMP dependent protein kinase is dephosphorylated predominantly by phosphatase type 2A in brain, and the activity of this phosphatase is not modulated by pteridines or nucleotides.

Vasoactive intestinal polypeptide-related peptides modulate tyrosine hydroxylase gene expression in PC12 cells through multiple adenylate cyclase-coupled receptors

We investigated the receptor mechanisms by which vasoactive intestinal polypeptide (VIP) and related peptides exert their effects on tyrosine hydroxylase (TH) gene expression. VIP, secretin, and peptide histidine isoleucine (PHI) each produced increases in TH gene expression, as measured by increases in TH mRNA levels and TH activity. The concentrations at which the effects of these peptides were maximal differed for TH activity and TH mRNA. Moreover, maximal increases in TH activity were 130-140% of control, whereas maximal increases in TH mRNA were 250% of control. The concentration dependence of the increases in TH mRNA in response to the three peptides was analyzed by fitting the data to nonlinear regression models that assume either one or two components to the response. The data for secretin fit best to a model that assumes a single component to the increase in TH mRNA levels. The data derived for PHI and VIP fit best to models that assumed two components to the TH mRNA response. These data suggested that there may be more than one receptor or signal transduction mechanism involved in the response to the various peptides. We examined whether the peptides exerted their effects through common or multiple second messenger systems. The ability of maximally active concentrations of these peptides to stimulate increases in TH mRNA was not additive, indicating that the peptides work through a common receptor or signal transduction pathway. Each peptide stimulated increases in protein kinase A (PKA) activity. Secretin and VIP were ineffective in increasing TH mRNA levels in a PKA-deficient mutant PC12 cell line (A126-1B2). Moreover, the adenylate cyclase antagonist 2',5'-dideoxyadenosine prevented the increase in TH mRNA produced by each peptide. Thus, each peptide requires an intact cyclic AMP second messenger pathway to produce changes in TH gene expression, suggesting that the complex pattern of response to VIP and PHI revealed by concentration-response analysis was due to the actions of these peptides at multiple receptors. To evaluate this possibility, we examined the effect of several peptide receptor antagonists on the increase in TH gene expression elicited by VIP, PHI, and secretin. The secretin antagonist secretin (5-27) (20 microM) had no significant effect on VIP or PHI stimulation of TH gene expression, but reduced the effect of secretin. The VIP antagonist VIP (10-28) (20 microM) reduced the effect of VIP on increasing TH mRNA, but had no significant effect on the response of TH mRNA to secretin or PHI.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of cyclic AMP levels by phorbol esters in bovine adrenal medullary cells

Cyclic AMP responses to phorbol esters were studied in cultured bovine adrenal medullary cells. Phorbol esters that activate protein kinase C (PKC: phorbol 12,13-dibutyrate, phorbol 12,13-didecanoate) increased cellular cyclic AMP levels by up to 100% over 5 min, and this was maintained for up to 3 h. The effect was mimicked by 1,2-dioctanoyl-sn-glycerol but not by inactive phorbol esters. The effect of active phorbol esters was concentration dependent over the range 50-500 nM, and was abolished by the PKC inhibitor, Ro 31-8220 (10 microM). The response was enhanced by 3-isobutyl-1-methylxanthine (1 mM) and by forskolin (0.3 microM), was enhanced following pertussis toxin pretreatment (100 ng/ml, 7.5 h) and was unaffected by removing extracellular Ca2+. The phorbol ester cyclic AMP response was additive with that to K+ depolarisation, and synergised with those to prostaglandin E1 and dimaprit. The results indicate PKC activation increases cyclic AMP formation in bovine adrenal medullary cells, probably by a direct action on adenylate cyclase or Gs.

Multiple signaling pathways in bovine chromaffin cells regulate tyrosine hydroxylase phosphorylation at Ser19, Ser31, and Ser40

Intact bovine adrenal medullary chromaffin cells were preincubated with 32PO4, and the multiple-site phosphorylation of tyrosine hydroxylase (TH) was studied. Up to eight 32P-labeled peptides were produced by tryptic hydrolysis of TH; however, all of the tryptic phosphopeptides were derived from four phosphorylation sites--Ser8, Ser19, Ser31 and Ser40. In situ regulation of 32P incorporation into the latter three sites was demonstrated with a diverse set of pharmacological agents. 32P incorporation into Ser19 was preferentially increased by brief exposures to depolarizing secretagogues. Longer treatments also increased Ser31 and Ser40 phosphorylation. Nicotine, muscarine and vasoactive intestinal polypeptide--reflecting cholinergic and non-cholinergic components of sympatho-adrenal transmission--each produced different patterns of multiple-site phosphorylation of TH. Nicotine, bradykinin and histamine increased 32P incorporation at each of the three sites whereas muscarine, angiotensin II, endothelin III, prostaglandin E1, GABA and ATP selectively increased Ser31 phosphorylation. Nerve growth factor did not influence TH phosphorylation in chromaffin cells from adult adrenal glands but selectively increased Ser31 phosphorylation in chromaffin cells isolated from calf adrenal glands. 32P incorporation into Ser40 was selectively increased by forskolin and other cAMP-acting agents whereas vasoactive intestinal polypeptide increased Ser31 and Ser40 phosphorylation. Thus, the phosphorylation of TH in bovine chromaffin cells appears to be regulated at three sites by three separate intracellular signaling pathways--Ser19 via Ca2+/calmodulin-dependent protein kinase II; Ser31 via ERK (MAP2 kinases); and Ser40 via cAMP-dependent protein kinase. These signaling pathways, as well as the extracellular signals that were effective in stimulating them, are similar to those previously described for TH in rat pheochromocytoma cells. However, several of the pharmacological agents produced different patterns of multiple-site TH phosphorylation in the bovine chromaffin cells. These differences between tissues could be accounted for by differences in the coupling/access between the extracellular signal transduction systems and the intracellular signaling pathways as opposed to differences in the intracellular signaling pathways per se.

Protein Phosphorylation in Bovine Adrenal Medullary Chromaffin Cells: Histamine-Stimulated Phosphorylation of Tyrosine Hydroxylase

Histamine can cause the release of catecholamines from bovine adrenal medullary chromaffin cells by a mechanism distinct from that of the depolarizing agents nicotine or high K+ buffer. It was the aim of this study to determine the protein phosphorylation responses to histamine in these cells and to compare them with those induced by depolarization. A number of proteins showed increases in phosphorylation in response to histamine especially when analyzed on two-dimensional polyacrylamide gel electrophoresis or by phosphopeptide mapping; one protein of 20,000 daltons was markedly dephosphorylated. Emphasis was given to the effects of histamine on tyrosine hydroxylase (TOH) phosphorylation, because this protein showed the most prominent changes on one-dimensional gels. Histamine acted via H1 receptors to increase TOH phosphorylation; the response was blocked by the H1 antagonist mepyramine and could be mimicked by the H1 agonist thiazolylethylamine, but not by the H2 agonist dimaprit. The H3 agonist (R) alpha-methylhistamine increased TOH phosphorylation at high concentrations, but the response was blocked entirely by mepyramine. Histamine rapidly increased the phosphorylation of TOH, with a maximum reached within 5 s and maintained for at least 30 min. This was in marked contrast to nicotine-stimulated protein phosphorylation of TOH, which was rapidly desensitized. The initial phosphorylation response to histamine was independent of extracellular Ca2+ for at least 3 min, but the sustained response required extracellular Ca2+. This was in contrast to the situation with both nicotine and high K+ buffer, which under the conditions used here caused a response which was dependent on extracellular Ca2+ at all times investigated. In the presence of histamine, the phosphopeptide profiles for TOH were essentially the same with or without Ca2+, suggesting that the same protein kinases were involved, but at longer times there was evidence of new phosphorylation sites. The mechanism or mechanisms whereby histamine modulates TOH phosphorylation are discussed with emphasis on the differences from depolarizing agents.

Cholinoceptor regulation of cyclic AMP levels in bovine adrenal medullary cells

1. The regulation of adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels by cholinoceptors has been studied in cultured bovine adrenal medullary cells. 2. Acetylcholine (100 microM), nicotine (10 microM) and dimethylphenylpiperazinium (20 microM) each increased cellular cyclic AMP levels 2 to 4 fold over 5 min in the absence of phosphodiesterase inhibitors. The muscarinic agonist acetyl-beta-methylcholine (100 microM) had no effect either on its own or on the response to nicotine. The responses to acetylcholine and nicotine were unaffected by atropine (1 microM) but were abolished by mecamylamine (5 microM). 3. Cellular cyclic AMP increased transiently during continuous exposure to nicotine (1-20 microM), with the largest response seen after 5 min, a smaller response after 20 min, and no change in cyclic AMP levels seen after 90 or 180 min. The maximal response after 5 min stimulation was seen with 5-10 microM nicotine and the EC50 was about 2 microM. In contrast, extracellular cyclic AMP levels did not change after 5 or 20 min stimulation with nicotine, but increased slightly after 90 min and further after 180 min. 4. The cellular cyclic AMP response to nicotine (10 microM) was unchanged or weakly enhanced in the presence of the unselective phosphodiesterase inhibitor, isobutylmethylxanthine, and was unchanged in the presence of rolipram. Nicotine did not interact synergistically with low concentrations of forskolin. The response was however completely abolished in the absence of extracellular Ca2+.

Activation of tyrosine hydroxylase by nicotine in rat adrenal gland

The administration of nicotine activates tyrosine hydroxylase in the rat adrenal gland. This activation is apparently maximal 25 min after a single subcutaneous injection of nicotine at 2.3 mg/kg. Repeated injections of nicotine (seven injections once every 30 min) are associated with a persistent activation of adrenal tyrosine hydroxylase for at least 3 h. The nicotinic receptor antagonist hexamethonium does not significantly inhibit the nicotine-mediated activation of tyrosine hydroxylase in innervated adrenal glands. However, hexamethonium completely blocks the activation of adrenal tyrosine hydroxylase by nicotine in denervated adrenal glands. Furthermore, even though a single injection of nicotine activates tyrosine hydroxylase in both innervated and denervated adrenal glands, repeated injections of nicotine do not activate tyrosine hydroxylase in denervated adrenal glands. Our results suggest that the systemic administration of nicotine activates adrenal tyrosine hydroxylase by two mechanisms: (1) via direct interaction with adrenal chromaffin cell nicotinic receptors; and (2) via stimulation of the CNS leading to the release from the splanchnic nerve of substances that interact with adrenal chromaffin cell receptors other than the nicotinic receptor.

Regulation of cyclic AMP levels by calcium in bovine adrenal medullary cells

Both nicotine and histamine have been reported to increase cyclic AMP levels in chromaffin cells by Ca(2+)-dependent mechanisms. The present study investigated whether Ca2+ was an adequate and sufficient signal for increasing cyclic AMP in cultured bovine adrenal medullary cells. Depolarization with 50 mM K+ caused a two- to three-fold increase in cellular cyclic AMP levels over 5 min, with no change in extracellular cyclic AMP. This response was abolished by omission of extracellular Ca2+ and by 100 microM methoxyverapamil, and was unaffected by 1 microM tetrodotoxin and by 1 mM isobutylmethylxanthine. Veratridine (40 microM) also increased cellular cyclic AMP levels by two- to fourfold. This response was abolished by either methoxyverapamil or tetrodotoxin. The Ca2+ ionophore A23187 (10-50 microM) had little or no effect on cellular cyclic AMP levels. When the concentration of K+ used to depolarize the cells was reduced to 12-15 mM, the catecholamine release was similar to that induced by 50 microM A23187, and the cyclic AMP response was almost abolished. The results suggest that Ca2+ entry into chromaffin cells is a sufficient stimulus for increasing cellular cyclic AMP production. The possible involvement of a Ca2+/calmodulin-dependent isozyme of adenylate cyclase is discussed.

Vasoactive intestinal peptide stimulates catecholamine biosynthesis in isolated adrenal chromaffin cells: evidence for a cyclic AMP-dependent phosphorylation and activation of tyrosine hydroxylase

Vasoactive intestinal peptide (VIP) increased catecholamine biosynthesis in bovine adrenal chromaffin cells by 50-200%. Six related peptides produced no effects. In addition, VIP increased tyrosine hydroxylase (TH) activity measured in gel-filtered supernatants prepared from homogenates of treated cells. The hypothesis that cyclic AMP is the second messenger involved in these effects of VIP was also evaluated. VIP led to an elevation of cyclic AMP levels, and this increase occurred over a similar concentration range and time course as the activation of TH and the increase in catecholamine biosynthesis. Each measure reached maximal levels at 10-20 microM VIP within 1 min and remained elevated for at least 16 min. These changes produced by VIP were paralleled by enhanced phosphorylation of TH, and this phosphorylation occurred on a single tryptic peptide that was the same peptide whose phosphorylation has been previously shown to be stimulated by forskolin. In contrast to VIP and forskolin, 12-O-tetradecanoylphorbol 13-acetate, a phorbol ester known to activate protein kinase C, increased the phosphorylation on a total of three tryptic peptides of TH. Our results indicate that VIP stimulates catecholamine biosynthesis in chromaffin cells through the phosphorylation and activation of TH and support the conclusion that a cyclic AMP-dependent phosphorylation of TH is responsible for these effects.

Is prolactin playing a role in the regulation of catecholamine synthesis and release from male rat adrenal medulla?

Previous evidence allows one to suspect that prolactin (PRL) may be a physiological regulator of catecholamine (CA) synthesis and release in the adrenal gland of rodents. To explore this possibility, we studied the in vivo and in vitro metabolism and release of noradrenaline (NA) and adrenaline (A) in the adrenal gland of male rats. The study was carried out with animals exhibiting a moderate increase in plasma PRL levels induced by grafting of additional pituitaries or a severe hyperprolactinemia produced by diethylstilbestrol (DES)-induced pituitary hyperplasia. The latter animals exhibited a significant increase in adrenal weight, associated with decrease in tyrosine hydroxylase (TH) activity and in NA content. Moreover, the adrenal activity of phenylethanolamine-N-methyl transferease (PNMT) was decreased in DES-treated animals. Pituitary-grafted rats also displayed an increased adrenal weight, together with decreases in the activities of PNMT, catechol-O-methyl transferase and monoamine oxidase. These in vivo observations were followed by in vitro studies, which showed a decrease in the basal release of both CAs from incubated adrenals of DES-treated rats, with no changes in pituitary-grafted rats. In addition, exposure to PRL of the incubated adrenals of animals exhibiting normal PRL levels produced decreases in A release and storage and in TH activity. These observations allow us to conclude that: i) PRL appears to exert an inhibitory influence on the catecholaminergic activity in the adrenal gland; and ii) its effect seems to be exerted by a direct action on this gland.

Effects of peptides of the secretin-glucagon family and cyclic nucleotides on tyrosine hydroxylase activity in sympathetic nerve endings

Previous studies have shown that certain peptides of the secretin-glucagon family stimulate tyrosine hydroxylase activity in sympathetic neurons of the superior cervical ganglion and three of its end organs, i.e., the iris, pineal gland, and submaxillary gland. To determine whether a similar regulation occurs in other sympathetic neurons, the effects of two of these peptides, secretin and vasoactive intestinal peptide, were examined in the right cardiac ventricle of the rat, a tissue innervated primarily by the middle and inferior cervical ganglia. Both peptides stimulated tyrosine hydroxylase activity, measured in situ, in this tissue. In addition, several second messenger systems were investigated as possible mediators of this peptidergic stimulation of tyrosine hydroxylase activity in autonomic end organs. 8-Bromoadenosine 3',5'-cyclic monophosphate and forskolin elevated tyrosine hydroxylase activity in slices of both the right ventricle and the submaxillary gland. 8-Bromoguanosine 3',5'-cyclic monophosphate also stimulated tyrosine hydroxylase activity in both tissues, whereas nitroprusside stimulated activity only in the submaxillary slices. Furthermore, the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine and/or Ro 20-1724 potentiated the stimulation by secretin, as well as the stimulations by forskolin and nitroprusside. Phorbol 12,13-dibutyrate also stimulated tyrosine hydroxylase activity in cardiac and submaxillary slices; however, no potentiation of these effects was seen following addition of either phosphodiesterase inhibitor. These data, taken together with those of previous studies, suggest a role for a cyclic nucleotide, probably adenosine 3',5'-cyclic monophosphate, in the peptidergic stimulation of tyrosine hydroxylase activity in sympathetic nerve terminals.

Stimulatory action of Ba2+ on catecholamine biosynthesis in cultured bovine adrenal chromaffin cells: possible relation to protein kinase C

The effect of Ba2+ on the catecholamine biosynthetic activity was studied by measuring the formation of [14C]catecholamines from L-[14C]tyrosine in cultured adrenal chromaffin cells. In the absence of Ca2+, [14C]catecholamine formation was markedly stimulated by Ba2+, and this stimulation was observed in a manner dependent on its concentration. The stimulation of [14C]catecholamine formation by relatively low concentrations of Ba2+ was suppressed by polymyxin B, a typical inhibitor of Ca2+/phospholipid-dependent protein kinase (protein kinase C); and this inhibitory action of polymyxin B was attenuated by increasing the Ba2+ concentration. On the other hand, a tendency toward the enhancement of Ba2+-stimulated [14C]catecholamine formation was observed by a protein kinase C activator, 12-O-tetradecanoylphorbol 13-acetate (TPA). In contrast to the acute effect of TPA, [14C]catecholamine formation stimulated by Ba2+ was reduced by long-term exposure of chromaffin cells to a high concentration of TPA, which has already been reported to cause the reduction of protein kinase C activity as a result of the down-regulation of this enzyme. These findings suggest that Ba2+ stimulates catecholamine biosynthesis, probably through its direct action on protein kinase C in adrenal chromaffin cells.

Phosphorylation of the multicatalytic proteinase complex from bovine pituitaries by a copurifying cAMP-dependent protein kinase

The multicatalytic proteinase complex (MPC) constitutes a major nonlysosomal proteolytic system that may play an important role in the processing of biologically active peptides and enzymes, as well as in intracellular metabolism. We report that at least two of its subunits of MW 28,800 (S2) and 27,000 (S3) are phosphorylated by a cAMP-dependent protein kinase (PK-A) that copurifies with the complex isolated from bovine pituitaries. The cAMP-induced phosphorylation was time dependent and inhibited by a PK-A inhibitor. Although not an integral part of the complex, PK-A activity was still present even in 1700-fold-purified and apparently homogeneous preparations by criteria of nondissociating polyacrylamide gel electrophoresis. Furthermore, we present evidence that the copurification of the two enzymes is not species or tissue specific, or dependent on a single method of purification. The copurifying kinase was stimulated 10-fold by cAMP (10 microM) and 2- to 3-fold by a peptide substrate of the MPC, but was unaffected by protein kinase C activators (calcium and a phospholipid mixture). These findings suggest that protein phosphorylation may represent a mechanism for regulating the activity of the multicatalytic proteinase complex.

Prolactin inhibits the activity of tyrosine hydroxylase in cultured bovine adrenal chromaffin cells in a dose-dependent manner

Prolactin can modulate the adrenal medulla function, but it has not yet been established whether its action is directly exerted on the adrenal medulla cells. In this work, we have studied the effect of several concentrations of prolactin on the synthesis, storage and release of norepinephrine and epinephrine using cultured bovine adrenal chromaffin cells. In these cells, prolactin inhibited the activity of tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine synthesis, in a dose-dependent manner, from a concentration above 50 ng/ml of prolactin in the incubation medium. Surprisingly, this dose-dependent decrease was not accompanied by changes in the catecholamine release, since the secretion of both norepinephrine and epinephrine as well as the total catecholamine secretion were not significantly altered by the different prolactin concentrations. Moreover, the cellular content of both catecholamines was not altered by prolactin. In summary, these observations allow us to conclude that prolactin exerts a direct inhibitory effect on the tyrosine hydroxylase activity in cultured adrenal chromaffin cells without altering catecholamine release.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Calcium/calmodulin-dependent protein kinase II

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