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N Zisapel

Publications and source records attributed to N Zisapel.

At least 37 records · Page 2Linked to original sources
PubMed1999

Hormonal interactions in human prostate tumor LNCaP cells.

Melatonin, the hormone secreted by the pineal gland at night, has recently been found to attenuate growth and viability of benign human prostate epithelial cells. Estradiol suppressed these responses by efflecting a protein kinase C mediated inactivation of melatonin receptors. In the present study, the effects of melatonin on growth and viability of the human androgen-sensitive prostatic tumor cell line-LNCaP and the influence of estradiol on these responses were explored. Melatonin inhibited 3H-thymidine incorporation into LNCaP cells at physiological concentrations. This response decayed within 24 h. The inactivation of the response slowed down in the presence of the protein kinase C inhibitor GF-109203X. Estradiol also inhibited 3H-thymidine incorporation and its effects were additive to those of melatonin. Suppression of DNA content was observed in cells treated for 2 days with melatonin (0.1 nM); this suppression was maintained for longer periods in the presence than in the absence of estradiol. In addition, estradiol and melatonin slightly and additively decreased cell viability. These results demonstrate for the first time a direct interaction of melatonin with androgen-sensitive prostate tumor cells leading to attenuation of cell growth. They also show that unlike in benign prostate epithelial cells, estrogen attenuates LNCaP cell growth and supports rather than inactivates melatonin's action.

Androgens↗
PubMed1999

Melatonin receptors in PC3 human prostate tumor cells.

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.

Binding Sites↗
PubMed1999

Involvement of cGMP in cellular melatonin responses.

Melatonin can enhance and suppress constitutive protein secretion from murine melanoma M2R cells in vitro in a cholera-toxin (CTX) sensitive process. In a number of tissues melatonin has been shown to modulate cGMP levels. The involvement of cGMP in melatonin responses in the melanoma cells was investigated. The effects of melatonin on melanoma cells cGMP and cGMP-phosphodiesterase activity and the effects of cGMP analogs on the melatonin-mediated modulation of protein secretion were studied. Melatonin reduced cGMP levels in the melanoma cells. CTX treatment had a similar and non-additive effect. The effects of melatonin on protein secretion were abrogated by activation of cGMP-dependent protein kinases. In addition, melatonin inhibited cGMP phosphodiesterase activity in these cells. The data presented indicate that inhibition of cGMP via a CTX sensitive G protein may be a major signal transduction pathway used by melatonin in melanoma cells.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1998

Melatonin receptors in benign prostate epithelial cells: evidence for the involvement of cholera and pertussis toxins-sensitive G proteins in their signal transduction pathways.

BACKGROUND: Melatonin, the hormone secreted nocturnally by the pineal gland, binds to epithelial cells from the human benign prostate, and can reduce their growth and viability. The possible involvement of GTP binding proteins cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in melatonin responses in these cells were investigated. METHODS: The effects of melatonin on cAMP and cGMP were assessed in prostate cells untreated or pretreated with pertussis toxin (PTX) or cholera toxin (CTX). RESULTS: Melatonin augmented cAMP but reduced cGMP in the epithelial cells (maximal responses at 10 nM). The increase in cAMP was attenuated by PTX, but not by CTX, whereas the decrease in cGMP was attenuated by CTX, but not by PTX. CTX, but not PTX, abolished the melatonin-mediated suppression of 3H-thymidine incorporation. In addition, melatonin facilitated the CTX- and PTX-mediated ADP ribosylation of 44- and 41-kilodalton proteins, respectively. The cGMP analogue 8-bromo-cGMP, negated the melatonin-mediated decrease in 3H-thymidine incorporation, whereas H89, a protein kinase A inhibitor, did not inhibit melatonin's effect. CONCLUSIONS: Melatonin receptors in the human benign prostate epithelial cells enhance cAMP and inhibit cGMP through PTX- and CTX-sensitive G proteins, respectively. The decrease in DNA synthesis may be secondary to the melatonin-mediated decrease in cGMP.

Adenosine Diphosphate Ribose↗
PubMed1998

Involvement of the pineal gland in daily scheduling of the golden spiny mouse.

The light-dark cycle is the major time cue for daily and seasonal scheduling of physiological activities. However, non-photic cues (e.g. environmental and social constraints) may also play a significant role. A natural model exists in the golden spiny mouse (Acomys russatus) which is nocturnal when maintained alone but diurnal when sharing a habitat with its congener, the common spiny mouse (A. cahirinus). We have recently observed that the presence of A. cahirinus provokes a major change in the daily rhythms of body temperature (Tb), and urine volume without affecting the melatonin rhythm and photoperiod-induced responses. The apparent lack of interaction between the daily and photoperiodic scheduling was further investigated by studying the significance of the pineal to the modification of A. russatus daily rhythms induced by the presence of A. cahirinus. Lesion of A. russatus pineal gland resulted in diminution of urinary 6-sulfatoxymelatonin (6-SMT) and modification of Tb and urine volume rhythms. However, the modification of Tb and urine volume rhythms provoked by the presence of A. cahirinus were similar in pineal lesioned and sham-operated A. russatus. The non-photic signals released by A. cahirinus did not significantly affect glucose utilization in the suprachiasmatic nucleus of pineal- as well as sham-lesioned A. russatus. Thus, the modification of the daily scheduling of A. russatus by the photoperiod involves the pineal and/or the melatonin rhythm whereas non-photic cues effect a direct (perhaps masking), pineal-independent response to the competitor.

Animals↗
PubMed1998

Body temperature daily rhythms in the striped mouse Rhabdomys pumilio: the effects of alpha and beta blockade.

Body temperature (Tb) daily rhythms and the effects of alpha and beta blockade were studied in the South African diurnal striped mouse Rhabdomys pumilio. Eleven mice (8 males and 3 females) with a body mass of 42.7+/-7.8 g (mean +/- SD) were tested. Mice were acclimated to a 13 h:11 h light-dark photoperiod at an ambient temperature of 25 degrees C. To assess the daily rhythm of pineal melatonin secretion, urinary 6-sulfatoxymelatonin (6-SMT) was determined. Mice displayed a robust Tb daily rhythm with an acrophase in the dark period, which is unexpected for a diurnal species. The nocturnal increase in Tb was accompanied by a significant rise in urinary 6-SMT. The beta blocker propranolol (4.5 mg/kg), injected 1 h before lights-off, resulted in a higher Tb value, whereas the alpha blocker prazosin (1 mg/kg) blocked the increase of Tb during the dark period. Prazosin also significantly attenuated the nocturnal increase of urinary 6-SMT. These results are in agreement with those obtained from the golden spiny mouse Acomys russatus and support the idea that small diurnal mammals retain the Tb rhythm of a nocturnal rodent. They also suggest that pineal melatonin secretion in these rodents is regulated by alpha rather than by beta receptors.

Adrenergic alpha-Antagonists↗
PubMed1998

A role for NAD+ and cADP-ribose in melatonin signal transduction.

The hormone melatonin modulates constitutive protein secretion and inhibits cGMP in melanoma M2R cells via cholera-toxin (CTX) sensitive pathways. Activation by melatonin of CTX-substrates is due to enhancement of their ADP ribosylation. The possibility that ADP ribosylation was enhanced by elevation of NAD+ was studied. Melatonin enhanced NAD+ and decreased cADP-ribose in the cells, in a CTX independent pathway, indicating inhibition of nicotinamide adenine dinucleotide glycohydrolase (NADase). Dibutyryl cGMP (db-cGMP), which obviates the melatonin-induced decrease in cGMP and prevents the modulation of protein secretion, abrogated the enhancement of NAD+. cADP-ribose is involved in calcium homeostasis and its decrease may reduce intracellular Ca2+. The intracellular Ca2+ chelator BAPTA/AM mimicked and Ca2+ ionophores prevented the melatonin-induced inhibition of protein secretion. These data indicate for the first time hormonal modulation of NADase resulting in two signals: (1) enhancement of NAD+ which may explain the increase in ADP ribosylation and activation of CTX substrates leading to facilitation of protein secretion; (2) suppression of cell cADP-ribose and consequently intracellular Ca2+ which may explain the melatonin-induced inhibition of protein secretion.

Adenosine Diphosphate Ribose↗
PubMed1998

Evidence for a local action of melatonin on the rat prostate.

PURPOSE: Melatonin, secreted by the pineal gland at night, inhibits pubertal development in rats and possibly humans. We have recently found functional specific binding sites for 125I-labeled melatonin (125I-melatonin) in human benign prostate tissue, localized in the microsomal fraction of the glandular epithelium. The aim of the present study was to set up an animal (rodent) model for the growth inhibitory effects of melatonin on the prostate. MATERIALS AND METHODS: Putative melatonin in the rat ventral prostate were explored by means of autoradiography and receptor binding assays and the ability of melatonin to inhibit stimulated prostate growth was tested in vivo. RESULTS: In vitro autoradiography and equilibrium binding experiments demonstrated specific binding sites for 125I-labeled melatonin (125I-melatonin) associated with the microsomal fraction of the rat ventral prostate cells (apparent dissociation constant 0.9 nM). 125I-melatonin binding was inhibited by 2-iodomelatonin > 6-hydroxy-melatonin > melatonin = N-(2,4 dinitrophenyl)-5-methoxytryptamine whereas similar concentrations of serotonin, 5-methoxytryptamine, and tryptamine were less potent. The guanine nucleotide analogs, guanosine 5'-0-[3-thiotriphosphate] and guanosine 5'-0-[2-thio-diphosphate], inhibited specific 125I-melatonin binding whereas 5'-guanylyl imido-diphosphate was less potent. Daily injections of testosterone to castrated rats induced regrowth of the prostate and increased the weight of the seminal vesicles. Administration of melatonin to the rats through drinking water prevented the testosterone-mediated regrowth of the prostate but had no effect on the seminal vesicles' weight. CONCLUSIONS: The results demonstrate putative melatonin receptors in the rat prostate and suggest a direct suppression by melatonin of testosterone-dependent prostate growth.

Animals↗
PubMed1997

Putative melatonin receptors in the blind mole rat harderian gland.

The blind mole rat (Spalax ehrenbergi) displays daily and seasonal rhythms. Melatonin, secreted nocturnally by the pineal gland, is also produced in the harderian gland and affects its morphology in rodents. We report here on the presence of putative melatonin receptors in the blind mole rat harderian gland, located in the microsome-enriched fraction of the cells. Equilibrium 125I-melatonin binding studies indicated high- and low-affinity melatonin binding sites in the female (apparent Kd 10 pM and 2.4 nM, respectively) and low-affinity sites in the male (apparent Kd 2.6 nM) mole rat. The binding sites were not significantly affected by season. Castration increased the density of high-affinity binding sites in males and low-affinity binding in females. 125I-melatonin binding to the gonadectomized mole rat preparation was inhibited by serotonin > 2-iodomelatonin > or = memelatonin > 5-methoxytryptamine. The guanine nucleotide analogs, guanosine 5'-O-[3-thio-triphosphate] and guanosine 5'-O-[2-thio-diphosphate], inhibited specific 125I-melatonin binding, whereas 5'-guanylyl imido-diphosphate was less potent. These results indicate for the first time the presence of GTP-sensitive melatonin binding sites in the blind mole rat harderian gland, and suggest that their expression is under control of sex steroids.

Animals↗
PubMed1997

The impact of beta-adrenergic blockade on daily rhythms of melatonin and body temperature of golden spiny mice Acomys russatus.

Beta-adrenergic stimulation induces melatonin synthesis and non-shivering thermogenesis (NST) in rodents. The golden spiny mouse, Acomys russatus is a nocturnal species capable of diurnal activity when coexisting with its congenitor the common spiny mouse A. cahirinus. We have investigated the impact of beta-adrenergic blockade on 6-sulphatoxymelatonin (6-SMT--a metabolite and index of melatonin production) and body temperature (Tb) daily rhythms in male A. russatus. Mice were acclimated to an ambient temperature (Ta) of 28 degrees C, under two photoperiod regimes (16L:8D; 8L:16D). The daily rhythms of Tb and urinary 6-SMT were measured for a period of 30 h at intervals of 4 h. Propranolol (4.5 mg/kg, i.p.) was administered one hour before lights went off (i.e. when beta blockade does not affect NST in this species) and both variables were measured for another 30 h. The beta blocker markedly augmented melatonin output of A. russatus under both photoperiod regimes. The elevation in melatonin secretion was accompanied with an increase in Tb of only 16L:8D-acclimated mice (i.e. shorten duration of melatonin peak). However, in 8L:16D-acclimated mice, a phase advance of about 4 h was noted in 6-SMT daily rhythm. These results indicate that the role of sympathetic innervation in regulation of melatonin synthesis in A. russatus differs from that in the rat. In addition, these data are compatible with the hyperthermic action of melatonin in this species. Therefore, it is suggested that in A. russatus, other neural pathways are involved in its pineal regulation.

Adrenergic alpha-Agonists↗
PubMed1997

Temporal segregation in coexisting spiny mice (genus Acomys): role of photoperiod and heterospecific odor.

Daily rhythms of activity and body temperature were measured in golden spiny mice Acomys russatus, acclimated for 2 weeks, at least, to 2 different photoperiod regimes (16L:8D; 8L:16D) at a constant ambient temperature of 28 degrees C. For recording body temperature, VM-FM (Mini-Mitter Co. Inc., Sunriver, OR) transmitters were implanted. For activity measurements, an infrared sensor (Hengstar BL 68 907F, Japan, using a Lodestar PS-303 power supply, Taiwan) mounted on each cage. Both rhythms were also measured in the same individuals exposed to chemical signals released in the urine of A. cahirinus. The results of this study show that both rhythms of A. russatus correlate and respond to changes in photoperiod regimens, as well as to the chemical signals. However, the correlation changes under the 2 photoperiod regimens. Under LD acclimation, a decrease in the correlation is noted, as a response to the addition of chemical signals. Our results suggest that the different responses due to the different light regimens represent 2 seasons in nature, where presumably each season demands a different physiological response.

Animals↗
PubMed1997

Rapid reversal of tolerance to benzodiazepine hypnotics by treatment with oral melatonin: a case report.

A 43 year old woman had suffered from insomnia for the past 11 years and was being treated with benzodiazepines. All attempts to stop benzodiazepine treatment resulted in withdrawal symptoms and a renewal of the insomnia. Treatment with 1 mg of controlled release melatonin enabled the patient to completely cease any benzodiazepine use within two days, with an improvement in sleep quality and no side effects. Examination of urinary 6-sulphatoxymelatonin levels before the melatonin treatment indicated that the levels were very low and lacked the typical circadian rhythm of excretion. Reexamination of 6-sulphatoxymelatonin levels during melatonin treatment revealed the existence of a normal circadian rhythm of excretion. This case may suggest that some of the people suffering from insomnia and addicted to benzodiazepines may successfully undergo withdrawal from these drugs and improve their sleep by means of treatment with melatonin. The results of this single case study warrant further investigation of a larger population by means of a double-blind placebo-drug study.

Adult↗
PubMed1997

Inactivation of melatonin receptors by protein kinase C in human prostate epithelial cells.

The pineal hormone melatonin regulates seasonal reproduction and pubertal development in mammals. We recently found melatonin receptors in the human benign prostate tissue, primarily associated with the microsome-enriched fraction of the epithelial cells. In cultured benign prostate epithelial cells, melatonin, at physiological concentrations, suppressed [3H]thymidine incorporation and cGMP levels. The effects of melatonin were transient, suggesting inactivation of the receptors. In the present study, the possibility of inactivation of the prostate melatonin receptors by protein kinase C (PKC) was explored. Treatment of the microsome-enriched fraction with crude rat brain PKC in the presence of phorbol 12-myristate 13-acetate (TPA) or CaCl2 abolished the specific [125I]melatonin binding. This effect was prevented by the PKC inhibitor bisindolylmaleimide (GF-109203). [125I]Melatonin binding could be reinstated by iodoacetamide treatment. In benign prostate epithelial cells in culture, TPA pretreatment markedly reduced the apparent affinity of [125I]melatonin binding. In addition, TPA ablated the cells responses to melatonin, namely the suppression of [3H]thymidine incorporation and cGMP levels. Pretreatment with GF-109203 prevented the TPA effects on [125I]melatonin binding and responses. In addition, GF-109203 slowed down the inactivation of the melatonin-mediated inhibition of [3H]thymidine incorporation. Taken together, these data show that melatonin receptors are desensitized by PKC and imply that the transient response to melatonin may be the outcome of a direct or indirect melatonin-mediated activation of endogenous PKC.

Aged↗
PubMed1997

Interplay between sex steroids and melatonin in regulation of human benign prostate epithelial cell growth.

Human benign prostatic epithelial cells contain functional melatonin receptors that can suppress cell growth and viability. The development of benign prostatic hyperplasia in men is assumed to result from androgen-estrogen imbalance. The impact of sex steroids on melatonin receptors in human benign prostate epithelial cells was investigated. The suppression by melatonin of [3H]thymidine incorporation and cGMP, and the enhancement of cAMP levels in the cells were used as markers of melatonin responses. Dihydrotestosterone (DHT) and 17 beta-estradiol (E2) separately increased [3H]thymidine incorporation into the cells, but suppressed it when combined. In cells grown with DHT, melatonin responses were extenuated. E2 greatly reduced the apparent affinity of [125I]melatonin binding in these cells without affecting binding site density. In parallel, the ability of melatonin to suppress [3H]thymidine incorporation into the cells was ablated within 1 h after the addition of E2. The melatonin-mediated increase in cAMP and decrease in cGMP concentrations were also ablated by E2. Preincubation of the cells with bis-indolylmaleimide (GF 102903X), a specific inhibitor of protein kinase C, prevented the E2-mediated inactivation of melatonin binding and the inhibitory action on [3H]thymidine incorporation. Prolonged (18-h) incubation of the cells with phorbol 12-myristate 13-acetate to down regulate protein kinase activity, partially restored [125I]melatonin binding and responsiveness in the E2-treated cells. These data indicate that 1) DHT and E2 enhance prostate epithelial cells growth, but reduce cell growth when combined; 2) DHT extenuates the inhibitory effects of melatonin on epithelial cell growth; and 3) E2 acts to inactivate melatonin receptors and consequently responses in human epithelial benign prostatic hyperplasia cells. This process is probably mediated by protein kinase C. Together, these results show an interplay between melatonin and sex steroids in the regulation of benign prostatic epithelial cell growth.

Aged↗
PubMed1996

Enhancement by melatonin of GTP exchange and ADP ribosylation reactions.

The pineal hormone melatonin modulates constitutive protein secretion from murine melanoma M2R cells in vitro, in a cholera-toxin (CTX)-sensitive process, without effecting major changes in cAMP. The effects of melatonin on GTP binding proteins and putative CTX substrates in these cells were investigated. Melatonin enhanced GTP gamma 35S binding and the incorporation of 32P-P3-(4-azidoanilido)-P1-5'-guanosine triphosphate (Az-32P-GTP) into 94, 40 and 28 kilodalton proteins. Similar changes were induced by CTX treatment. In addition, melatonin enhanced ADP ribosylation of several proteins, among them 94 and 40 kilodalton bands, apparently at arginyl residues. CTX catalyzed the ADP ribosylation of 45 and 40 (both recognized by antibodies specific to the C-terminal peptide of the Gs alpha subunit) and 94 kilodalton proteins and attenuated melatonin's effect. The melatonin-mediated ADP ribosylation reactions were attenuated by nicotinamide which inhibits mono(ADP ribosyl)transferases and poly(ADP-ribose)synthetase, but not by 3-amino benzamide, a specific inhibitor of poly(ADP-ribose)synthetase. Nicotinamide but not 3-amino benzamide prevented the enhancement by melatonin of GTP gamma 35S binding. These results indicate that melatonin enhances protein ADP ribosylation and consequently GTP exchange in a number of CTX-sensitive G proteins. They demonstrate a novel route for concerted activation of multiple GTP binding proteins by a single hormone.

Adenosine Diphosphate↗