Enzymes related to catecholamine biosynthesis in Tetrahymena pyriformis. Presence of GTP cyclohydrolase I

Catecholaminergic System of Invertebrates: Comparative and Evolutionary Aspects in Comparison With the Octopaminergic System

In this review we examined the catecholaminergic system of invertebrates, starting from protists and getting to chordates. Different techniques used by numerous researchers revealed, in most examined phyla, the presence of catecholamines dopamine, noradrenaline, and adrenaline or of the enzymes involved in their synthesis. The catecholamines are generally linked to the nervous system and they can act as neurotransmitters, neuromodulators, and hormones; moreover they play a very important role as regards the response to a large number of stress situations. Nevertheless, in some invertebrate phyla belonging to Protostoma, the monoamine octopamine is the main biogenic amine. The presence of catecholamines in some protists suggests a role as intracellular or interorganismal signaling molecules and an ancient origin of their synthetic pathways. The catecholamines appear also involved in the regulation of bioluminescence and in the control of larval development and metamorphosis in some marine invertebrate phyla.

Pharmacological characterization of N-methyl-d-aspartic acid (NMDA)-like receptors in the single-celled organism Paramecium primaurelia

Paramecium primaurelia is a unicellular eukaryote that moves in freshwater by ciliary beating and responds to environmental stimuli by altering motile behaviour. The movements of the cilia are controlled by the electrical changes of the cell membrane: when the intraciliary Ca2+ concentration associated with plasma membrane depolarization increases, the ciliary beating reverses its direction, and consequently the swimming direction changes. The ciliary reversal duration is correlated with the amount of Ca2+ influx. Here we evaluated the effects due to the activation or blockade of NMDA receptors on swimming behaviour in Paramecium. Paramecia normally swim forward drawing almost linear tracks. We observed that the simultaneous administration of NMDA and glycine induced a partial ciliary reversal (PaCR) leading to a continuous spiral-like swim. Furthermore, the duration of continuous ciliary reversal (CCR), triggered by high external KCl concentrations, was longer in NMDA/glycine treated cells. NMDA action required the presence of Ca2+, as the normal forward swimming was restored when the ion was omitted from the extracellular milieu. The PaCR and the enhancement of CCR duration significantly decreased when the antagonists of the glutamate site D-AP5 or CGS19755, the NMDA channel blocker MK-801, or the glycine site antagonist DCKA were added. The action of NMDA/glycine was also abolished by Zn2+ or ifenprodil, the GluN2A and the GluN2B NMDA-containing subunit blockers, respectively. Searches of the Paramecium genome database currently available indicate that the NMDA-like receptor with ligand binding characteristics of an NMDA receptor-like complex, purified from rat brain synaptic membranes and found in some metazoan genome, is also present in Paramecium. These results provide evidence that functional NMDA receptors similar to those typical of mammalian neuronal cells are present in the single-celled organism Paramecium and thus suggest that the glutamatergic NMDA system is a phylogenetically old behaviour-controlling mechanism.

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.

Chemoprevention of breast cancer, proteomic discovery of genistein action in the rat mammary gland

Genistein, the primary isoflavone component of soy, consumed in the diet during the prepubertal period only, and the combined prepubertal and adult periods, suppresses chemically induced mammary cancer in rats. Gestational or adult-only exposures do not provide protection. An inverse relation exists between cancer susceptibility and mammary gland differentiation. The current study used proteomic technology to investigate genistein mechanisms of action as related to programming against chemically induced mammary cancer. Rats were injected subcutaneously with 500 microg genistein/g body weight on d 16, 18, and 20 postpartum. At d 21, mammary glands were subjected to 2-dimensional polyacrylamide gel electrophoresis. After gel scanning, image analysis, and MS, 6 proteins were determined to be differentially regulated and identified. One protein, GTP-cyclohydrolase 1 (GTP-CH1), was confirmed as being significantly upregulated at d 21 by immunoblot analysis. Investigation of downstream signaling from GTP-CH1 showed that tyrosine hydroxylase was upregulated and vascular endothelial growth factor receptor 2 (VEGFR2) was downregulated in the mammary glands of 50-d-old rats treated with genistein in the prepubertal period. This and previous work suggest that early prepubertal exposure to genistein enhances cell proliferation by upregulating GTP-CH1 and the epidermal growth factor (EGF)-signaling pathway, and hence cell differentiation and gland maturation. This unique developmental maturation leads to a new biochemical blueprint, whereby the cells have reduced EGF signaling and VEGFR2, which renders the mature mammary gland less proliferative and less susceptible to cancer. This study demonstrated the usefulness of proteomics for the discovery of novel pathways that may be involved in cancer prevention.

cAMP inhibits cytokine-induced biosynthesis of tetrahydrobiopterin in human umbilical vein endothelial cells

We studied the effects of cAMP on cytokine (interferon-gamma plus tumor necrosis factor-alpha)-induced stimulation of tetrahydrobiopterin (BH4) synthesis in human umbilical vein endothelial cells (HUVEC). The cytokine mixture caused a marked increase in the biosynthesis and release of BH4 by HUVEC. Dibutyryl-cAMP produced a dose-dependent inhibition of this cytokine-induced stimulation of synthesis and release of BH4 by these cells. 8-Bromo-cAMP also caused a significant inhibition, although the effects were less marked than those of dibutyryl-cAMP. Both forskolin and the stable analog of prostacyclin, iloprost, caused cAMP accumulation and a concomitant diminution of the cytokine-induced BH4 synthesis in HUVEC. Dibutyryl-cAMP and iloprost also significantly inhibited the cytokine-induced stimulation of GTP cyclohydrolase I (GCHI) activity and mRNA production. We concluded that the suppression by the cAMP messenger system of cytokine-induced stimulation of synthesis and release of BH4 by HUVEC can be attributed to the inhibition of the activity of GCHI, the rate-limiting enzyme in BH4 biosynthetic pathway, in HUVEC. The data also suggest that the cAMP-mediated reduction in the GCHI mRNA level may at least partially explain the decline in GCHI activity. It is reasoned that under inflammatory conditions, cAMP-elevating agents such as prostacyclin exert regulatory effects on circulation by inhibiting cytokine-induced synthesis and release of BH4 by HUVEC.

Immunoanalogue of vertebrate beta-adrenergic receptor in the unicellular eukaryote Paramecium

Cell fractionation, SDS-PAGE, quantitative Western blot, confocal immunolocalization and immunogold labelling were performed to find an interpretation of the physiological response of the unicellular eukaryote Paramecium to beta-adrenergic ligands. The 69 kDa polypeptide separated by SDS-PAGE in S2 and P2 Paramecium subcellular fractions cross-reacted with antibody directed against human beta2-adrenergic receptor. This was detected by Western blotting followed by chemiluminescent detection. Quantitative image analysis showed that beta-selective adrenergic agonist (-)-isoproterenol--previously shown to enhance phagocytic activity--evoked redistribution of the adrenergic receptor analogue from membraneous (P2) to cytosolic (S2) fraction. The relative increase in immunoreactive band intensity in S2 reached 80% and was paralleled by a 59% decrease in P2 fraction. Confocal immunofluorescence revealed beta2-adrenergic receptor sites on the cell surface and at the ridge of the cytopharynx--where nascent phagosomes are formed. This localization was confirmed by immunoelectron microscopy. These results indicate that the 69 kDa Paramecium polypeptide immunorelated to vertebrate beta2-adrenergic receptor appeared in this evolutionary ancient cell as a nutrient receptor.

GTP cyclohydrolase I from Tetrahymena pyriformis: cloning of cDNA and expression

A full-length cDNA clone for GTP cyclohydrolase I (EC 3.5.4.16) was isolated from a Tetrahymena pyriformis cDNA library by plaque hybridization. The nucleotide sequence determination revealed that the length of the cDNA insert was 1516 bp. The coding region encoded a protein of 223 amino acid residues with a calculated molecular mass of 25 416 Da. The deduced amino acid sequence of Tetrahrymena GTP cyclohydrolase I showed sequence identity with that of Escherichia coli (55%). The identity of T. pyriformis GTP cyclohydrolase I with sequences of Dictyostelium discoideum, Saccharomyces cerevisiae, Drosophila melanogaster, mouse, rat, and human enzymes was less marked and was 30, 30, 25, 28, 28, and 27%, respectively. RNA blot analysis showed a single mRNA species of 2.1 kb in this protozoan. The mRNA level of GTP cyclohydrolase I increased during synchronous cell division induced by intermittent heat treatment. The results suggest that the mRNA expression is associated with the cell cycle of T. pyriformis.