Biosynthesis Of Tyrosine Hydroxylase Research Articles

P53 Inactivation leads to enhancement of tyrosine hydroxylase biosynthesis in brain dopaminergic neurons

In this paper we address a possibility of interaction among protein 53, members of the ERK1/2 signaling pathway, and the CREB transcription factor in regulation of activity of dopaminergic neurons. Nerve cells in the substantia nigra and zona incerta have been studied in control rats and in rats with pifithrin-alpha, a transcriptional inhibitor of p53, administered intraperitoneally. We have shown that p53 inhibition leads to an increased tyrosine hydroxylase content both in cell bodies and axon terminals. The CREB transcription factor activity is also enhanced in brain dopaminergic neurons. However, there have been observed no significant differences in phospho-ERK1/2 kinase content between cell bodies from pifithrin-alpha injected group and the control. It has been shown therefore that p53 exerts an inhibitory effect on tyrosine hydroxylase biosynthesis which may be mediated by the CREB.

Involvement of alpha 7 nicotinic acetylcholine receptors in gene expression of dopamine biosynthetic enzymes in rat brain.

Brain dopaminergic systems are critical in mediating the physiological responses to nicotine. The effects of several concentrations of nicotine (0.08, 0.17, or 0.33 mg/kg body weight) and involvement of alpha7 nicotinic acetylcholine receptors (nAChRs) in gene expression of key enzymes in dopamine biosynthesis were evaluated in the ventral tegmental area (VTA) and substantia nigra (SN), cell bodies of the mesocorticolimbic and nigrostriatal pathways. Nicotine elicited a dose-dependent elevation of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis in VTA and SN. The VTA was more sensitive to lower concentrations of nicotine with maximal response observed with the lowest dose of nicotine. Nicotine also elevated mRNA levels of GTP cyclohydrolase I (GTPCH), rate limiting in biosynthesis of TH's essential cofactor tetrahydrobiopterin in both dopaminergic locations. The changes in TH and GTPCH mRNAs were correlated. Pretreatment with the alpha7 nAChR antagonist methyllycaconitine prevented the nicotine-induced rise in TH or GTPCH mRNA in VTA and SN. Administration of alpha7 nAChR agonist 3-[2,4-dimethoxybenzilidene]anabaseine at 1 to 10 mg/kg or (E,E-3-(cinnamylidene)anabaseine at 0.3 to 1 mg/kg increased TH mRNA in VTA and SN, but not in peripheral catecholaminergic cells. Thus, agonists of alpha7 nAChRs have therapeutic potential for increasing TH gene expression in dopaminergic regions without some of nicotine's disadvantages, such as its harmful effects on the cardiovascular system. The findings indicate that nicotine may regulate dopamine biosynthesis by alterations in gene expression of TH and its cofactor. The alpha7 nAChRs are involved in mediating these effects of nicotine.

A denaturant-insoluble form of tyrosine hydroxylase in PC12 pheochromocytoma cells

A 6M urea-insoluble form of tyrosine hydroxylase (THi) was detected in PC12 pheochromocytoma cells by western blotting immunodetection methods, and the characteristics and mechanisms of formation of this insoluble species were investigated. THi accounts for about 4% of the immunodetectable tyrosine hydroxylase in exponentially dividing pheochromocytoma cells. It is unlikely that a subpopulation of dead or dying cells is the source of THi since essentially no changes in THi levels were detected when cell death was intentionally increased. To measure the kinetics of formation of cellular THi, exponentially dividing cells were metabolically labeled first with [3H]leucine and then with [14C]leucine, and though both 3H and 14C were incorporated into soluble tyrosine hydroxylase, the near absence of 14C in THi demonstrated that a lag period of at least a day exists between biosynthesis of tyrosine hydroxylase and the accumulation of measurable THi. The cellular accumulation of THi can evidently be regulated by the cell, since upon nerve growth factor (NGF) treatment of cells the total content of tyrosine hydroxylase increased and the content of THi decreased to yield, overall, a fivefold lower proportion of THi after 4 days. A large increase in urea-insoluble enzyme was found upon sublethal exposure of cells to ferrous ion and hydrogen peroxide, indicating that oxidative damage via metal-ion-catalyzed formation of hydroxide free radical can yield an enzyme that is similar in its insolubility to THi.

Repeated amphetamine evokes biphasic alterations in the tyrosine hydroxylase mRNA level in the rat adrenal medulla: an in situ hybridization study.

In the present study we estimated the effects of single and repeated administration of d-amphetamine (5 mg/kg, i.p., twice a day for 14 days) on tyrosine hydroxylase (TH) mRNA levels in the rat adrenal medulla. In situ hybridization experiments, conducted using a [35S]d-ATP-labelled deoxyoligonucleotide probe and a densitometric analysis of autoradiograms, showed that repeated d-amphetamine moderately increased the TH mRNA level (by ca. 24%) in the adrenal medulla at 2 h after the last injection. In contrast, after 48 h the TH mRNA level was decreased (by ca. 21%). No significant changes in the TH mRNA level in the adrenal medulla were found following single administration of d-amphetamine. These results suggest that repeated d-amphetamine administration leads to biphasic changes in the adrenal TH biosynthesis, which may reflect an adaptive response to chronic drug treatment.

Molecular aspects of the regulation of tyrosine hydroxylase by testosterone

Previous studies have demonstrated that the sympathetic hypogastric ganglia (HG) are dependent upon the continued presence of testosterone for normal development and maintenance of tyrosine hydroxylase (TH) activity. The regulation of TH by testosterone has been examined further to determine whether the reduction in TH activity following castration is associated with changes in levels of TH protein and mRNA. TH protein was measured by immunotitration of HG homogenates using a TH-specific antibody, and TH-specific mRNA was detected by hybridization of dot blots of total RNA isolated from HG with a cDNA probe coding for TH. The results show that tyrosine hydroxylase activity, protein and mRNA are coordinately reduced in a graded fashion at 1, 2 and 4 weeks following castration. Testosterone replacement therapy immediately following castration prevents the decrease in TH levels. The results indicate that gonadal steroids regulate the biosynthesis of TH in the HG. Testosterone may control TH either directly by interacting with neurons of the HG, or indirectly by altering levels of trophic factors in the target tissues.

Catecholamine synthesizing enzymes in 70 cases of functioning and non-functioning phaeochromocytoma and extra-adrenal paraganglioma.

Immunohistochemical localization of the catecholamine synthesizing enzymes, tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT), was investigated in 70 cases of functioning and non-functioning phaeochromocytomas comprising 52 of adrenal and 18 of extra-adrenal origin. Of 59 functioning tumours, 30 were mixed epinephrine and norepinephrine-producing (mixed type) and 29 were norepinephrine-producing tumours. TH, AADC and DBH were detected in all functioning phaeochromocytomas, but PNMT was limited to the mixed-type phaeochromocytomas. Non-functioning phaeochromocytomas were divided into two groups, comprising a complete type, which induced neither elevated plasma catecholamines nor their metabolites in urine, and an incomplete type which exhibited no elevated plasma catecholamines, but showed a slightly high urinary vanillylmandelic acid level. In the non-functioning complete-type tumours, immunoreactive TH was negative, but the incomplete tumours of the adrenal medulla had all four enzymes, and corresponded to a mixed-type phaeochromocytoma. AADC and DBH were present universally in all functioning and non-functioning tumours, including TH-negative tumours. TH is a rate-limiting enzyme of catecholamine biosynthesis and deficiency of TH is an important feature of extra-adrenal non-functioning phaeochromocytomas.

Tyrosine hydroxylase and POMC mRNA in the arcuate region are increased by castration and hyperprolactinemia

We have examined the changes which occur in neuronal expression of tyrosine hydroxylase (TH) and proopiomelanocortin (POMC) mRNA in response to castration and hyperprolactinemia (HP) in male rats. Steady-state mRNA levels were determined by quantitative in situ hybridization histochemistry (ISHH) using 35S-labeled synthetic 48-base oligodeoxynucleotide probes. Castration produced a 27% increase in TH mRNA in the periventricular and arcuate nuclei. PRL-exposed rats exhibited a further 27% increase in the level of TH mRNA and a striking 48% increase in POMC mRNA in periarcuate region cell bodies. These results indicate that gonadal steroids and PRL are involved, either directly or indirectly, in regulating the biosynthesis of TH and POMC in the hypothalamus.

Biosynthesis of Tyrosine Hydroxylase in Rat Adrenal Medulla after Exposure to Cold

Exposure of rats to cold increases the content of tyrosine hydroxylase [EC 1.14.16.2; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating)] in adrenal medulla, causing a long-lasting enhancement of the enzymatic activity. We have used an antibody specific to tyrosine hydroxylase to study the molecular mechanisms involved in the trans-synaptic induction of adrenal tyrosine hydroxylase. The rate of [(3)H]-leucine incorporation into adrenal tyrosine hydroxylase was measured by specific immunoprecipitation at various times after exposure to cold (4 hr). This enhanced rate of incorporation was evident between 11 and 30 hr after the beginning of exposure to cold, but not at 7 and 50 hr. The increase of (3)H incorporation preceded the maximal enhancement of adrenal tyrosine hydroxylase activity, which occurred about 30 hr after stimulation. Neither the activity of tyrosine hydroxylase nor the rate of (3)H incorporation into tyrosine hydroxylase in cervical sympathetic ganglia was changed by 4 hr of exposure to cold. The rate of degradation of tyrosine hydroxylase was estimated at 26 and 50 hr after the beginning of cold stress, as determined by the technique of double-isotope labeling. The data indicate that the tyrosine hydroxylase degradation rate was not reduced by exposure to cold. Thus, the induction of adrenal tyrosine hydroxylase appears to be due to an increased rate of its synthesis.