Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The purpose of this study is to examine whether monosodium L-glutamate (MSG) influences the function of pinealocytes in female rats. MSG was administered at a does of 4 mg/g body weight to rat pups on days 1 and 3 postnatally. As the rats matured, sexual receptivity as well as proceptivity were observed by testing the lordosis quotient (LQ), rejection quotient (RQ) and solicitation. Pineal function was estimated by measuring the serum level of melatonin and the activity of protein kinase A (PKA) in the pineal gland. Blood samples were withdrawn at light and dark phases for four consecutive days, respectively. The serum concentration of melatonin was determined by radioimmunoassay and the data of each phase were pooled together. The results showed that both the receptivity and proceptivity of MSG-treated female rats were significantly lower than that of the control ones. Melatonin levels during the dark phase were significantly higher than those during the light phase in both control and MSG-treated groups, but whenever in the light or dark phase, the levels of melatonin were the same in both groups. There was no significant difference in PKA activity in the pineal gland between the control and MSG-treated group. These results indicate that MSG used as a neurotoxin to induce hypogonadal status affected neither the PKA activity of pineal gland nor the serum level of melatonin in young female rats. Thus, the decrease in receptivity and proceptivity of MSG-treated female rats was not caused by the alteration of pineal function.
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PMID:[The effect of monosodium L-glutamate (MSG) treatment during neonatal period on the pineal function in young female rats]. 146 41

The pineal hormone melatonin modulates constitutive protein secretion from melanoma M2R cells. Nanomolar concentrations of melatonin inhibited protein secretion early after plating or at low cell density, but facilitated it late after plating or at high cell density. Inhibition by melatonin of adenylate cyclase is the best known downstream response to melatonin. We have therefore examined the involvement of cAMP in the melatonin-mediated modulation of protein secretion from the melanoma cells. Melatonin slightly but significantly reduced cell cAMP content when effecting inhibition and marginally increased cAMP levels when effecting facilitation of protein secretion. Dibutyryl cAMP abrogated the melatonin-mediated inhibition but not facilitation of protein secretion without affecting basal secretion. Accordingly, forskolin prevented the inhibitory action of melatonin on protein secretion without affecting basal secretion. The selective protein kinase A inhibitor H-89 did not alter the inhibitory effect of melatonin at low cell density and slightly facilitated secretion at high cell density with or without melatonin. Thus, melatonin's effects on protein secretion may not be mediated via cAMP. Nevertheless, changes in cAMP or protein kinase A activity can abrogate, or mask, the melatonin-mediated responses.
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PMID:Modulation by melatonin of protein secretion from melanoma cells: is cAMP involved? 748 20

The pars tuberalis (PT) of the anterior pituitary is notable for the expression of levels of melatonin receptors that consistently exceed those in all other tissues in mammals. For this reason and because of its anatomical position, it has been suggested that the PT may play a role in seasonal reproductive responsiveness. However, no data have been forthcoming on the nature of the melatonin-responsive cells in this tissue or on the interaction of melatonin with other hormonal signals in the control of PT cells. A number of recent studies have reported that the tubero-infundibular region of the pituitary in several species contains binding sites for insulin-like growth factor-1 (IGF-1). The present study, therefore, sought to address the question of whether functional receptors for IGF-1 exist in the ovine PT (oPT). Primary cultures of cells from the oPT contained a widespread distribution of cells staining positively with a monoclonal antibody to the human IGF-1 receptor, with the strongest staining occurring over the small phase-bright cells that predominate in this culture system and are thought to constitute the melatonin-responsive cell type. As a functional assay for responsiveness to IGF-1, primary cultures of oPT cells were assayed for activation of mitogen-activated protein kinase (MAPK) using a previously validated phosphotransferase assay. Cytosolic extracts from PT cells treated with IGF-1 (100 pM-10 nM) caused a dose-dependent increase in the rate of phosphorylation of myelin basic protein; in contrast, treatment with melatonin had no significant effect on myelin basic protein phosphorylation. Immunostaining of Western blots of PT cell extracts with a pan-extracellular regulated kinase antibody demonstrated that both p42 and p44 MAPK are strongly expressed in this tissue. To confirm that the effects observed in the cytosol assay were indeed attributable to increased activation of p42/p44, gel renaturation assays of protein kinase activity were performed. These experiments revealed that IGF-1 (10 nM) and forskolin (1 microM) were both potent activators of 42- and 44-kDa moeities; however, neither of these agents had any significant effect on the phosphotransferase activity associated with several other higher molecular weight kinases also detected by the gel-renaturation assay procedure. Melatonin (10 nm) was consistently found to be a highly potent inhibitor of the activation of MAPK induced by forskolin; in contrast, melatonin did not inhibit the activation of MAPK induced by IGF-1.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulation of mitogen-activated protein kinase in the pars tuberalis of the ovine pituitary: interactions between melatonin, insulin-like growth factor-1, and forskolin. 853 15

Melatonin release by chick cultured pineal cells increases during the dark periods and decreases during the light periods under light-dark cycles, and this rhythmic secretion is maintained under constant conditions with a period of almost 24 hr. The mechanisms by which the circadian oscillator drives the melatonin rhythm under constant conditions have not been elucidated enough. We examined the possibility that cyclic AMP-dependent protein kinase A is involved in the subjective nocturnal increase in melatonin release by chick pineal cells cultured under constant darkness. The subjective nocturnal increase of melatonin release was suppressed dose dependently by H8 (protein kinase inhibitor) and H89 (specific protein kinase A inhibitor), but not by calphostin C (specific protein kinase C inhibitor) in static cell cultures. In a cell perfusion experiment, 9 hr pulses of H8 and H89 starting at ZT 9 (CT 11.2) hr suppressed the subjective nocturnal increase in melatonin rhythm in dose-dependent manner without causing a phase shift. An intracellular Ca2+ chelator, O,O'-bis(2-aminophenoxy)ethyleneglycol-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM), and extracellular Ca2+ chelators, O,O'-bis(2-aminophenoxy)ethyleneglycol-N,N,N',N'-tetraacetic acid tetrapotassium salt hydrate (BAPTA) and ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), suppressed both the subjective nocturnal increases in melatonin release and cAMP levels dose dependently. This direct evidence strongly supports the hypothesis that cAMP-dependent protein kinase A may be involved in the subjective nocturnal increase in melatonin release by chick pineal cells and that intracellular Ca2+ plays an important role in pineal adenylate cyclase activation.
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PMID:Involvement of protein kinase A in the subjective nocturnal rise of melatonin release by chick pineal cells in constant darkness. 946 54

Knowledge about intracellular signal transduction cascades is largely based on investigations of cultured cells whose responses to different stimuli are typically quantified via RIA, ELISA, or immunoblots. These techniques, which require relatively large amounts of biological material, are performed with homogenized cells and therefore do not allow localization of the molecules under investigation. We describe a protocol for recording dose-response curves directly from immunocytochemical preparations using rat pinealocytes as a model system. The cells were exposed to beta-adrenergic stimuli inducing the phosphorylation of the transcription factor CREB (mediated by PKA), an increase in ICER protein levels, and synthesis and release of melatonin. Melatonin concentrations were determined by ELISA. cPKA, phosphorylated CREB, and ICER were demonstrated by immunocytochemistry and immunoblots. Dose-response curves were recorded by measuring the integrated density of the immunoreactive sites with an image analysis program. Dose-response curves from immunoblots and immunocytochemical preparations showed almost identical dynamics, validating the immunocytochemical approach, which minimizes the amount of biological material needed for such studies, allows combined quantification and localization of biomolecules, and may even be more sensitive than immunoblotting.
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PMID:A semiquantitative image-analytical method for the recording of dose-response curves in immunocytochemical preparations. 1002 43

Melatonin, secreted nocturnally by the pineal gland, can bind to human benign prostate epithelial cells and attenuate their growth and viability. In the present study, melatonin binding and responses were explored in the human steroid-independent PC3 prostatic tumor cells. PC3 cells bound 125I-melatonin with low affinity (Kd ca. 0.9 nM) at high as well as low cell density. Melatonin enhanced cGMP and 3H-thymidine incorporation at low, but attenuated them at high cell density. In addition, melatonin inhibited cAMP at low, but augmented it at high cell density. These effects were associated with an increase in cell count at low- but not high-density cultures. Pertussis toxin treatment suppressed 125I-melatonin binding and ablated all the effects of melatonin on 3H-thymidine incorporation, cAMP, and cGMP at both cell densities. Cholera toxin treatment failed to block the effects of melatonin on 3H-thymidine incorporation, but prevented the modulation by melatonin of cAMP at low and cGMP at high cell density. The cGMP analog 8-Br-cGMP, inhibited melatonin's effects on 3H-thymidine incorporation at both cell densities. H89, a protein kinase A inhibitor, prevented melatonin's effects on 3H-thymidine incorporation at low but not high cell density. These results provide the first demonstration of direct interaction of melatonin with hormone-insensitive prostate tumor cells. The melatonin receptors in the PC3 cells are coupled to pertussis toxin-sensitive G proteins to induce cell density-dependent changes in cGMP, cAMP, and cell growth.
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PMID:Melatonin receptors in PC3 human prostate tumor cells. 1034 Jul 23

Melatonin inhibits GnRH-induced release of LH and FSH from the neonatal, but not the adult, rat anterior pituitary gland. This action of melatonin is mediated by the specific high-affinity membrane-bound receptors that are absent in adult rats. The intracellular mechanism of melatonin action involves a decrease in intracellular calcium [Ca2+]i in the gonadotrophs; melatonin inhibits GnRH-induced Ca2+ release from endoplasmic reticulum as well as Ca2+ influx through voltage-sensitive channels. Melatonin also inhibits GnRH-induced accumulation of cAMP, which may result in the decreased influx of Ca2+, because cAMP, acting through protein kinase A, stimulates Ca2+ influx into the gonadotrophs. This age-dependent effect of melatonin on gonadotrophin release from the pituitary may be involved in the timing of puberty.
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PMID:Inhibitory effect of melatonin on GnRH-induced LH release. 1035 93

Pigment aggregation in melanophores of Labrus ossifagus is controlled by an alpha2-adrenoceptor and is somehow modulated by melatonin. The signal transduction mechanisms seem to involve both an attenuation of cAMP and an increase in intracellular Ca2+, inhibiting protein kinase A or activating a phosphatase, respectively. These effects result in dephosphorylation, which in turn induces aggregation. Various alpha2-adrenoceptor agonists attenuate cAMP levels or increase the concentration of intracellular Ca2+. Noradrenaline, for example, lowers cAMP but does not affect the calcium signal whereas B-HT 920, an alpha2-adrenoceptor specific agonist, does not induce a cAMP decrease but does appear to induce an increase in intracellular Ca2+. This later inference is drawn from experiments with BAPTA/AM, an intracellular calcium chelator, which counteracts the aggregation induced by B-HT 920. Interestingly, the very potent alpha2-adrenoceptor agonist medetomidine apparently activates both signal transduction pathways, which could explain its high efficacy in producing aggregation. Melatonin itself does not cause pigment aggregation, but it potentiates noradrenaline-induced aggregation. It has been suggested that melatonin receptors and alpha2-adrenoceptors follow the same signal transduction pathway, i.e. an attenuation of cAMP. In our experiments, melatonin did not reduce cAMP levels; instead it appears to increase Ca2+ concentration, since melatonin-potentiated aggregation was inhibited by BAPTA/AM. Thus, aggregation amplified by melatonin is probably not mediated by a further decrease in cAMP, but by the same signal transduction mechanism as B-HT 920, i.e. an increase in Ca2+. This further strengthens the suggestion that melatonin and B-HT 920 bind to the same site, but it is unclear if that particular site is on the melatonin receptor or the alpha2-adrenoceptor.
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PMID:Is Ca2+ the second messenger in the response to melatonin in cuckoo wrasse melanophores? 1072 47

Melatonin has gained recent popularity as a treatment for insomnia and other sleep disorders; however, its cellular effects are unknown. We report the effects of melatonin on the cellular morphology of Chinese hamster ovary (CHO) cells transformed to express the human melatonin receptors, mt1 and MT2. Our results show that melatonin exerts a strong influence on cellular shape and cytoskeletal organization in a receptor-dependent and possibly subtype-selective manner. The cell shape change that we see after a 5-h treatment of these non-neuronal cells with a pharmacological concentration of melatonin consists of the formation of long filamentous outgrowths that are reminiscent of the neurite processes produced by differentiating nerve cells. This morphological change occurs exclusively in cells expressing the mt1 receptor. We find that the microtubule and microfilament organization within these outgrowths is similar to that of neurites. Microtubules are required for the shape change to occur as Colcemid added in combination with melatonin completely blocks outgrowth formation. We demonstrate that the number of cells showing the altered cell shape is dependent on melatonin concentration, constant exposure to melatonin and that outgrowth frequencies increase when protein kinase A (PKA) is inhibited. Concomitant melatonin-dependent increases in MEK 1/2 and ERK 1/2 phosphorylation are noted in mt1-CHO cells only. The production of filamentous outgrowths is dependent on the translation of new protein but not the transcription of new mRNA. Outgrowth number is not controlled by centrosomes but is instead controlled by the polymerization state of the actin cytoskeleton. The results of this work show that the organization of the cytoskeleton is affected by processes specifically mediated or regulated by the mt1 receptor and may represent a novel alternative mechanism for the stimulation of process formation.
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PMID:Melatonin induction of filamentous structures in non-neuronal cells that is dependent on expression of the human mt1 melatonin receptor. 1084 31

Melanophores, brown to black pigment cells from, for example, Xenopus laevis, contain mobile melanin filled organelles, and are well suited for studies on organelle movement. The intracellular regulation of the movement seems to be controlled by serine and threonine phosphorylations and dephosphorylations. Melatonin induces aggregation of the melanosomes to the cell centre through a G(i/o)-protein-coupled receptor, Mel1c, which leads to an inhibition of PKA and a stimulation of PP2A. However, this study shows that the melatonin-induced aggregation of melanosomes is also accompanied by tyrosine phosphorylation of a protein with a molecular weight of approximately 280 kDa. Cells pre-incubated with genistein, an inhibitor of tyrosine phosphorylations, showed inhibited melanosome movement after melatonin stimulation, and a lower degree of tyrosine phosphorylation of the approximately 280 kDa protein. The adenylyl cyclase activator forskolin, and the G(i/o) protein inhibitor pertussis toxin, also inhibited tyrosine phosphorylation of the approximately 280 kDa protein. The results indicate that melatonin stimulation generates tyrosine phosphorylation of a high molecular weight protein, an event that seems to be essential for melanosome aggregation.
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PMID:Melatonin-induced organelle movement in melanophores is coupled to tyrosine phosphorylation of a high molecular weight protein. 1098 82


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