NT5DC2 affects the phosphorylation of tyrosine hydroxylase regulating its catalytic activity

5'-Nucleotidase domain-containing protein 2 (NT5DC2) has been revealed by genome-wide association studies (GWAS) as a gene implicated in neuropsychiatric disorders related to the abnormality of dopamine (DA) activity in the brain. Based on its amino acid sequence, NT5DC2 is assumed to be a member of the family of haloacid dehalogenase-type phosphatases; although there is no information about its function and structural conformation. We recently reported that NT5DC2 binds to tyrosine hydroxylase (TH) and that the down-regulation of NT5DC2 tended to increase DA synthesis. In this study, we investigated whether NT5DC2 could regulate the catalytic activity of TH, which converts tyrosine to DOPA, because the phosphorylation level of TH, controlled by protein kinases and phosphatases, is well known to regulate its catalytic activity. The down-regulation of NT5DC2 by siRNA increased mainly DOPA synthesis by TH in PC12D cells, although this down-regulation tended to increase the conversion of DOPA to DA by aromatic L-amino acid decarboxylase. The increased DOPA synthesis should be attributed to the catalytic activity of TH controlled by its phosphorylation, because Western blot analysis revealed that the down-regulation of NT5DC2 tended to increase the level of TH phosphorylated at its Ser residues, but not that of the TH protein. Moreover, the induction of kinase activity by forskolin markedly potentiated the phosphorylation of TH at its Ser40 in PC12D cells having down-regulated NT5DC2. Immunocytochemical analysis of PC12D cells demonstrated that NT5DC2, TH protein, and TH phosphorylated at its Ser40 were predominantly localized in the cytoplasm and that the localization of NT5DC2 and TH proteins partially overlapped. Collectively, our results indicate that NT5DC2 could work to inhibit the DOPA synthesis by decreasing the phosphorylation of TH at its Ser40. We propose that NT5DC2 might decrease this phosphorylation of TH by promoting dephosphorylation or by inhibiting kinase activity.

Development of a PC12 Cell Based Assay for Screening Catechol-O-methyltransferase Inhibitors

The male rat adrenal pheochromocytoma cell-derived PC12 cell line can synthesize and release catecholamine neurotransmitters, and it has been widely used as a model system in cell biology and toxicology research. Catechol-O-methyltransferase (COMT) is involved in the inactivation of the catecholamine neurotransmitters, and it is particularly important for the regulation of dopamine. In this study, we explored the feasibility of using PC12 cells as an in vitro drug screening platform to compare the activity of multiple COMT inhibitors. Incubation of PC12 cells with tolcapone, a highly potent and selective COMT inhibitor, increased the concentrations of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) while reducing the metabolites 3-methoxytyramine (3-MT) and homovanillic acid (HVA) in the cell culture medium. LIBD-3, a novel, non-nitrocatechol COMT inhibitor, produced similar effects compared to tolcapone. LIBD-4, a less potent inhibitor, exhibited the expected right-shift in functional inhibition in the assay. These results match the known in vivo effects of COMT inhibition in rodents. Together, these data support the continued use of PC12 cells as an in vitro screen that bridges cell-free enzyme assays and more costly in vivo assays.

Catecholamine-Synthesizing Enzymes in Pheochromocytoma and Extraadrenal Paraganglioma

In chromaffin cells, tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) are mainly involved in catecholamine synthesis. In this study, we evaluated the association between the status of catecholamine-synthesizing enzymes and histopathological features of pheochromocytoma and extraadrenal paraganglioma with special emphasis upon their postoperative clinical behavior. Immunohistochemical evaluation of TH, DBH, AADC, PNMT, Ki 67, and S-100 was performed in 29 pheochromocytoma and 10 extraadrenal paraganglioma and one lymph node harboring metastatic pheochromocytoma. Among these cases, metastasis was subsequently developed in three cases. Urinary normetanephrine (U-NM) levels were significantly higher in clinical metastatic cases than non-metastatic ones. Ki 67 labeling index was significantly higher in both clinical metastatic cases and the Adrenal Gland Scaled Score (PASS) score of ≧ 4 cases than PASS < 4 cases, although this score was originally used in pheochromocytoma. H-score of AADC and DBH were significantly lower in PASS ≧ 4 cases than those with < 4 cases, and in the cases associated with intratumoral necrosis (n = 4), the presence of spindle shaped tumor cells (n = 4), and large nests of cells or diffuse growth (n = 5). Lower status of intratumoral AADC could be related to poor differentiation of tumor cells in both catecholamine production and morphology and could be related to aggressive biological behavior of both pheochromocytoma and extraadrenal paraganglioma.

Kai-Xin-San, a traditional Chinese medicine formula, induces neuronal differentiation of cultured PC12 cells: Modulating neurotransmitter regulation enzymes and potentiating NGF inducing neurite outgrowth

ETHNOPHARMACOLOGICAL RELEVANCE

Kai-Xin-San, an ancient formula composed of Ginseng Radix et Rhizoma, Polygalae Radix, Acori Tatarinowii Rhizoma and Poria, was frequently applied for major depression disorders for thousands of years. However, its molecular mechanism has not clearly been investigated.

AIM OF THE STUDY

We aimed to reveal the action mechanism of KXS on anti-depression on inducing neuronal differentiation on PC12 cells.

MATERIALS AND METHODS

A chemically standardized water extract of KXS was applied onto cultured PC12 cells in determining its effect on neurotransmitter regulation enzymes and neurite outgrowth.

RESULTS

Single KXS treatment showed obvious changes in the expression of neurofilament and neurotransmitter regulation enzymes, which in parallel to treatment of nerve growth factor (NGF). Although KXS by itself did not show significant inductive effect on neurite outgrowth of PC12 cells, KXS could potentiate the NGF induced neurite outgrowth. Among the three ratios, K-652 showed the most powerful effect and cAMP-dependent pathway might play the major role.

CONCLUSIONS

KXS might exert the anti-depressant-like action of be inducing neuronal differentiation, which supported the clinically usage of this decoction.

Enhanced tyrosine hydroxylase expression in PC12 cells co-cultured with feline mesenchymal stem cells

Mesenchymal stem cells (MSCs) secrete a variety of neuroregulatory molecules, such as nerve growth factor, brain-derived neurotrophic factor, and glial cell-derived neurotrophic factor, which upregulate tyrosine hydroxylase (TH) gene expression in PC12 cells. Enhancing TH gene expression is a critical step for treatment of Parkinson's disease (PD). The objective of this study was to assess the effects of co-culturing PC12 cells with MSCs from feline bone marrow on TH protein expression. We divided the study into three groups: an MSC group, a PC12 cell group, and the combined MSC + PC12 cell group (the co-culture group). All cells were cultured in DMEM-HG medium supplemented with 10% fetal bovine serum for three days. Thereafter, the cells were examined using western blot analysis and immunocytochemistry. In western blots, the co-culture group demonstrated a stronger signal at 60 kDa than the PC12 cell group (p<0.001). TH was not expressed in the MSC group, either in western blot or immunocytochemistry. Thus, the MSCs of feline bone marrow can up-regulate TH expression in PC12 cells. This implies a new role for MSCs in the neurodegenerative disease process.

PC3 potentiates NGF-induced differentiation and protects neurons from apoptosis

PC3TIS21/BTG2 is member of a novel family of antiproliferative genes (BTG1, ANA/BTG3, PC3B, TOB, and TOB2) that play a role in cellular differentiation. We have previously shown that PC3TIS21/BTG2 is induced by nerve growth factor (NGF) at the onset of neuronal differentiation in the neural crest-derived PC12 cell line, and is a marker for neuronal birth. We now observe that PC3TIS21/BTG2 ectopically expressed in PC12 cells synergises with NGF, similarly to the cyclin-dependent kinase inhibitor p21, potentiating the induction of the neuronal markers tyrosine hydroxylase and neurofilament 160 kDa. Furthermore, PC3TIS21/BTG2 protects from apoptosis elicited by NGF deprivation in terminally differentiated PC12 cultures. Such effects might be a consequence of the arrest of cell cycle exerted by PC3TIS21/BTG2, or expression of a sensitizing (neurogenic) property of the molecule.

Parallel modulation of striatal dopamine synthetic enzymes by second messenger pathways

The activity of tyrosine hydroxylase and aromatic L-amino acid decarboxylase in the striatum and their mRNA content in the midbrain were assayed in mice following the intracerebroventricular injection of forskolin or phorbol-12,13-myristic acid (PMA). Control and 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned animals were studied. Both forskolin and PMA induced a rapid and transient increase of tyrosine hydroxylase and aromatic L-amino acid decarboxylase activity in the striatum that lasted less than 45 and 60 min, respectively. A second belated increase of striatal tyrosine hydroxylase and aromatic L-amino acid decarboxylase activities was seen only after forskolin, and it was accompanied by a rise of tyrosine hydroxylase and aromatic L-amino acid decarboxylase mRNA in the midbrain. In the MPTP-lesioned mouse, the rise of tyrosine hydroxylase and aromatic L-amino acid decarboxylase following forskolin appeared exaggerated, while the response to PMA was not. These studies suggest that tyrosine hydroxylase and aromatic L-amino acid decarboxylase of striatum can be modulated in parallel by protein kinase A and protein kinase C, and that exaggerated responsiveness to protein kinase A is observed in the partially denervated striatum.