A semiquantitative image-analytical method for the recording of dose-response curves in immunocytochemical preparations

Trehalose Activates CRE-Dependent Transcriptional Signaling in HT22 Mouse Hippocampal Neuronal Cells: A Central Role for PKA Without cAMP Elevation

Cyclic adenosine 3′,5′monophosphate (cAMP) regulated element binding protein (CREB) is a transcription factor involved in many different signaling processes including memory storage and retrieval. The mouse hippocampal neuronal cell line HT22 is widely used as a model system for neuronal cell death and cellular signal pathway investigations. For the present work a variant of HT22 with a stably expressed CRE-luciferase (CRE-luc) reporter (HT22CRE) is introduced, characterized and used to investigate cAMP-dependent and independent CRE-dependent signal processes. Trehalose (Mykose or 1-α-Glucopyranosyl-1-α-glucopyranosid) is a naturally occurring disaccharide consisting of two α,α′,1,1-glycosidic connected glucose molecules in a wide range of organisms but usually not found in mammals. Trehalose has been shown to activate autophagy, a process which regulates the degradation and recycling of proteins and organelles. The exact processes how trehalose application works on mammalian neuronal cells is not yet understood. The present work shows that trehalose application dose-dependently elevates CRE-luc activity in HT22 cells and acts synergistically with cAMP-elevating agents. In this pathway cAMP-dependent protein kinase (PKA) appears to be the most important factor and the stress kinase p38 and protein tyrosine kinases (PTKs) act as modulators.

Expression and functional relevance of cannabinoid receptor 1 in Hodgkin lymphoma

Background

Cannabinoid receptor 1 (CB₁) is expressed in certain types of malignancies. An analysis of CB₁ expression and function in Hodgkin lymphoma (HL), one of the most frequent lymphomas, was not performed to date.

Design and Methods

We examined the distribution of CB₁ protein in primary cases of HL. Using lymphoma derived cell lines, the role of CB₁ signaling on cell survival was investigated.

Results

A predominant expression of CB₁ was found in Hodgkin-Reed-Sternberg cells in a vast majority of classical HL cases. The HL cell lines L428, L540 and KM-H2 showed strong CB₁-abundance and displayed a dose-dependent decline of viability under CB₁ inhibition with AM251. Further, application of AM251 led to decrease of constitutively active NFκB/p65, a crucial survival factor of HRS-cells, and was followed by elevation of apoptotic markers in HL cells.

Conclusions

The present study identifies CB₁ as a feature of HL, which might serve as a potential selective target in the treatment of Hodgkin lymphoma.

Phosphorylation of cyclic AMP-response element-binding protein (CREB) is influenced by melatonin treatment in pancreatic rat insulinoma β-cells (INS-1)

The pineal hormone melatonin exerts its influence on the insulin secretion of pancreatic islets by a variety of signalling pathways. The purpose of the present study was to analyse the impact of melatonin on the phosphorylated transcription factor cAMP-response element-binding protein (pCREB). In pancreatic rat insulinoma β-cells (INS-1), pCREB immunofluorescence intensities in cell nuclei using digitised confocal image analysis were measured to semi-quantify differences in the pCREB immunoreactivity (pCREB-ir) caused by different treatments. Increasing concentrations of forskolin or 3-isobutyl-1-methylxanthine (IBMX) resulted in a dose-dependent rise of the mean fluorescence intensity in pCREB-ir nuclear staining. Concomitant melatonin application significantly decreased pCREB-ir in INS-1 cells after 30-min, 1-hr and 3-hr treatment. The melatonin receptor antagonists luzindole and 4-phenyl-2-propionamidotetraline (4P-PDOT) completely abolished the pCREB phosphorylation-decreasing effect of melatonin, indicating that both melatonin receptor isoforms (MT(1) and MT(2)) are involved. In a transfected INS-1 cell line expressing the human MT(2) receptor, melatonin caused the greatest reduction in pCREB after IBMX treatment compared with nontransfected INS-1 cells, indicating a crucial influence of melatonin receptor density on pCREB regulation. Furthermore, the downregulation of pCREB by melatonin is concomitantly associated with a statistically significant downregulation of Camk2d transcript levels, as measured after 3 hr. In conclusion, the present study provides evidence that the phosphorylation level of CREB is modulated in pancreatic β-cells by melatonin. Mediated via CREB, melatonin regulates the expression of genes that play an important functional role in the regulation of β-cell signalling pathways.

Early growth response-1 induction by fibroblast growth factor-1 via increase of mitogen-activated protein kinase and inhibition of protein kinase B in hippocampal neurons

BACKGROUND AND PURPOSE

The transcription factor early growth response-1 (Egr-1) and the acidic fibroblast growth factor (FGF-1) are involved in many regulatory processes, including hippocampus-associated learning and memory. However, the intracellular signalling mechanisms regulating Egr-1 in hippocampal cells are not entirely understood.

EXPERIMENTAL APPROACH

We used primary mouse hippocampal neurons and the mouse hippocampal neuronal cell line HT22 to investigate how FGF-1 transiently induces Egr-1 protein. This was accomplished by a range of techniques including Western blotting, immunofluorescence, specific protein kinase inhibitors and transfectable constitutively active protein kinase constructs.

KEY RESULTS

Protein kinase B (PKB) and mitogen-activated protein kinase (MAPK) were both initially phosphorylated and activated by FGF-1 treatment, but when phosphorylated MAPK reached maximal activation, phosphorylated PKB was at its lowest levels, suggesting an interaction between MAPK kinase (MEK-1/2) and phosphatidyl inositol-3-kinase (PI3K) during Egr-1 induction. Interestingly, pharmacological inhibition of MEK-1/2 resulted in a robust increase in the phosphorylation of PKB, which was repressed in the presence of increasing doses of a PI3K inhibitor. FGF-1-mediated Egr-1 induction was impaired by inhibition of MEK-1/2, but not of PI3K. However, elevated levels of PKB, induced by transfection of constitutively active PKB (myrAkt) into hippocampal neuronal HT22 cells, led to reduced levels of Egr-1 after FGF-1 application.

CONCLUSIONS AND IMPLICATIONS

Our data indicate a contribution of inactive (dephosphorylated) PKB to FGF-1-mediated induction of Egr-1, and strongly suggest a functionally and pharmacologically interesting cross-talk between MEK-1/2 and PI3K signalling in hippocampal neurons after FGF-1 stimulation that may play a role in hippocampal synaptic plasticity.

NDRG1 protein overexpression in malignant thyroid neoplasms

OBJECTIVES

The aim of this study was to examine the expression of the N-myc downstream-regulated gene 1 protein in benign and malignant lesions of the thyroid gland by immunohistochemistry.

INTRODUCTION

N-myc downstream-regulated gene 1 encodes a protein whose expression is induced by various stimuli, including cell differentiation, exposure to heavy metals, hypoxia, and DNA damage. Increased N-myc downstream-regulated gene 1 expression has been detected in various types of tumors, but the role of N-myc downstream-regulated gene 1 expression in thyroid lesions remains to be determined.

METHODS

A tissue microarray paraffin block containing 265 tissue fragments corresponding to normal thyroid, nodular goiter, follicular adenoma, papillary thyroid carcinoma (classical pattern and follicular variant), follicular carcinoma, and metastases of papillary and follicular thyroid carcinomas were analyzed by immunohistochemistry using a polyclonal anti- N-myc downstream-regulated gene 1 antibody.

RESULTS

The immunohistochemical expression of N-myc downstream-regulated gene 1 was higher in carcinomas compared to normal thyroid glands and nodular goiters, with higher expression in classical papillary thyroid carcinomas and metastases of thyroid carcinomas (P < 0.001). A combined analysis showed higher immunohistochemical expression of NDRG1 in malignant lesions (classical pattern and follicular variant of papillary thyroid carcinomas, follicular carcinomas, and metastases of thyroid carcinomas) compared to benign thyroid lesions (goiter and follicular adenomas) (P = 0.043). In thyroid carcinomas, N-myc downstream-regulated gene 1 expression was significantly correlated with a more advanced TNM stage (P = 0.007) and age, metastasis, tumor extent, and size (AMES) high-risk group (P = 0.012).

CONCLUSIONS

Thyroid carcinomas showed increased immunohistochemical N-myc downstream-regulated gene 1 expression compared to normal and benign thyroid lesions and is correlated with more advanced tumor stages.

Prognostic value of survivin in locally advanced prostate cancer: study based on RTOG 8610

PURPOSE

To examine the prognostic value of nuclear and cytoplasmic survivin expression in men with locally advanced prostate cancer who were enrolled in Radiation Therapy Oncology Group (RTOG) protocol 8610.

METHODS AND MATERIALS

RTOG 8610 was a Phase III randomized study comparing the effect of radiotherapy plus short-term androgen deprivation with radiotherapy alone. Of the 456 eligible patients, 68 patients had suitably stained tumor material for nuclear survivin analysis and 65 patients for cytoplasmic survivin.

RESULTS

Compared with patients with nuclear survivin intensity scores of <or=191.2, those with intensity scores >191.2 had significantly improved prostate cancer survival (hazard ratio [HR], 0.45; 95% confidence interval [CI], 0.20-1.00, p = 0.0452). On multivariate analysis, nuclear survivin intensity scores >191.2 were significantly associated with improved overall survival (HR, 0.46; 95% CI, 0.25-0.86; p = 0.0156) and prostate cancer survival (HR, 0.36; 95% CI, 0.16-0.84; p = 0.0173). On univariate analysis, compared with patients with cytoplasmic survivin integrated optical density <or=82.7, those with an integrated optical density >82.7 showed a significantly increased risk of local progression (HR, 2.49; 95% CI, 1.03-6.01; p = 0.0421).

CONCLUSION

Nuclear overexpression of survivin was associated with improved overall and prostate cancer survival on multivariate analysis, and cytoplasmic overexpression of survivin was associated with increased rate of local progression on univariate analysis in patients with locally advanced prostate cancer treated on RTOG 8610. Our results might reflect the different functions of survivin and its splice variants, which are known to exist in distinct subcellular compartments.

Clock gene expression in the retina of melatonin-proficient (C3H) and melatonin-deficient (C57BL) mice

In several mammalian species, the retina contains an autonomous circadian clock and is capable of synthesizing melatonin. The function of circadian clocks depends on interlocking transcriptional/translational feedback loops involving several clock genes. Here we investigated the expression of two clock genes (Per1, Cry2) and the level of phosphorylated (p) cyclic AMP response element binding protein (CREB) in retinae of melatonin-deficient (C57BL) with an intact retina and melatonin-proficient (C3H) mice with degenerated outer nuclear layer. RNase protection assay and in situ hybridization revealed in both strains a rhythm in transcript levels for Per1 with a peak at zeitgeber time (ZT) 08, but not for Cry2. Immunoreactions for PER1, CRY2 and pCREB were localized to the nuclei of cells in the inner nuclear layer (INL) and ganglion cell layer (GC) of both strains and to the outer nuclear layer of C57BL. In C3H, protein levels of PER1 and CRY2 followed a clear day/night rhythm in the INL and the GC with a peak at the end of the day (ZT14). pCREB levels peaked at the beginning of the day. Noteably, in melatonin-deficient C57BL mice, protein levels of PER1, CRY2 and pCREB did not show significant changes over a 16L/8D cycle. These data suggest that melatonin influences PER1 and CRY2 protein levels via post-transcriptional mechanisms and also plays a role in rhythmic regulation of pCREB levels in the mammalian retina.

Cannabinoids attenuate norepinephrine-induced melatonin biosynthesis in the rat pineal gland by reducing arylalkylamine N-acetyltransferase activity without involvement of cannabinoid receptors

Cannabinoids modulate neuronal and neuroendocrine circuits by binding to cannabinoid receptors acting upon cAMP/Ca(2+)-mediated intracellular signaling cascades. The rat pineal represents an established model to investigate intracellular signaling processes because a well defined input, the neurotransmitter norepinephrine, is transformed via cAMP/Ca(2+)-dependent mechanisms into an easily detectable output signal, the biosynthesis of melatonin. Here we investigated the impact of cannabinoids on norepinephrine-regulated melatonin biosynthesis in the rat pineal. We demonstrated that treatment of cultured rat pineals with 9-carboxy-11-nor-delta-9-tetrahydrocannabinol (THC), cannabidiol or cannabinol significantly reduced norepinephrine-induced arylalkylamine N-acetyltransferase (AANAT) activity and melatonin biosynthesis. These effects were not mimicked by the cannabinoid receptor agonist WIN55,212-2 and were not blocked by cannabinoid 1 and 2 receptor antagonists. The cannabinoids used did not affect norepinephrine-induced increases in cAMP/Ca(2+) levels. Notably, cannabinoids were found to directly inhibit AANAT activity in lysates of the pineal gland. This effect was specific in so far as cannabinoids did not influence the activity of hydroxyindole-O-methyltransferase (HIOMT), the last enzyme in melatonin biosynthesis. Taken together, our data strongly suggest that cannabinoids inhibit AANAT activity and attenuate melatonin biosynthesis through intracellular actions without involvement of classical cannabinoid receptor-dependent signaling cascades.

Immunocytochemical demonstration of day/night changes of clock gene protein levels in the murine adrenal gland: differences between melatonin-proficient (C3H) and melatonin-deficient (C57BL) mice

The circadian system comprises several peripheral oscillators and a central rhythm generator that, in mammals, is located in the suprachiasmatic nucleus of the hypothalamus. Expression of clock genes is a characteristic feature of the central rhythm generator and the peripheral oscillators. With regard to the rhythmic production of glucocorticoids, the adrenal gland can be considered as peripheral oscillator, but little is known about clock gene expression in this tissue. Therefore, the present study investigates the levels of three clock gene proteins PER1, BMAL1 and CRY2 in the murine adrenal cortex and medulla at seven different time points of a 12-hr light/12-hr dark cycle. To determine a potential role of melatonin we compared the patterns of clock gene proteins in the adrenal gland of melatonin-proficient mice (C3H) with those of melatonin-deficient mice (C57BL). In C3H mice, both, the adrenal cortex and medulla displayed day/night variation in PER1-, CRY2- and BMAL1-protein levels. PER1 and CRY2 peaked in the middle of the light phase, whereas BMAL1 peaked in the dark phase. This pattern was also observed in the adrenal medulla of C57BL, but in the adrenal cortex of C57BL clock gene protein levels did not change with time and were consistently lower than in C3H mice. These results support the hypothesis that the adrenal gland is a peripheral oscillator and raise the possibility that melatonin may be involved in the control of clock gene protein levels in the adrenal cortex of mice.

Rhythmic expression of adenylyl cyclase VI contributes to the differential regulation of serotonin N-acetyltransferase by bradykinin in rat pineal glands

The rhythmic nocturnal production of melatonin in pineal glands is controlled by the periodic release of norepinephrine from the superior cervical ganglion. Norepinephrine binds to the beta-adrenergic receptor and stimulates an increase in intracellular cAMP levels, leading to the transcriptional activation of serotonin N-acetyltransferase, which in turn promotes melatonin production. In the present study, we report that bradykinin inhibits basal- and forskolin-stimulated adenylyl cyclase activity, norepinephrine-induced cAMP generation, and N-acetyltransferase expression in a calcium-dependent manner. These effects were blocked by pretreatment with U73122 (a selective phospholipase C inhibitor), and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (a Ca(2+) chelator), but not pertussis toxin. The calcium ionophore, ionomycin, inhibited isoproterenol-mediated cAMP generation, similar to bradykinin. Interestingly, the inhibitory effect of bradykinin was evident only during the daytime. At midday, bradykinin inhibited the cAMP level by approximately 50% but markedly stimulated cAMP production (by approximately 50%) at night. Northern blotting and immunoblotting data disclosed circadian expression of calcium-inhibitable adenylyl cyclase type 6. Expression of adenylyl cyclase type 6 was maximal at Zeitgeber Time (ZT) 01 and very low at ZT 13. Our results suggest that bradykinin-induced calcium inhibits melatonin synthesis through the mediation of adenylyl cyclase type 6 expression.

Clock gene mRNA and protein rhythms in the pineal gland of mice

In vertebrates, the rhythmic transcription of clock genes, regulated by their own gene products, provides the basis for self-sustaining circadian clockworks. These endogenous clocks are lost in most mammalian tissues, but not in the central pacemaker of the hypothalamic suprachiasmatic nucleus (SCN). An interesting model system to understand this phylogenetic shift in function of clock gene products is the rodent pineal gland, as its intrinsic clockwork was replaced during evolution by an input-dependent oscillator. By means of immunohistochemistry, immunoblotting and real time PCR, we investigated the day/night expression profiles of all major clock genes and their products in the pineal gland of one melatonin-proficient and one melatonin-deficient mouse strain. All clockwork elements known to be indispensable for a sustained rhythm generation in the SCN were also found in the pineal organ of both mouse strains. Only mPer1 mRNA and PER1 protein accumulation coincides with timecourses of many other pineal genes and their products, which are cyclicAMP inducible. Here, presented data together with the known mechanisms for regulation of the mPer1 gene in the rodent pineal gland forward the idea that in this tissue PER1 may have a trigger function for initiating the cycles of the clockwork's transcriptional/translational feedback loops.

Light does not degrade the constitutively expressed BMAL1 protein in the mouse suprachiasmatic nucleus

Biological rhythms in mammals are driven by a central circadian clock located in the suprachiasmatic nucleus (SCN). At the molecular level the biological clock is based on the rhythmic expression of clock genes. Two basic helix-loop-helix (bHLH)/PAS-containing transcription factors, CLOCK and BMAL1 (MOP3), provide the basic drive to the system by activating transcription of negative regulators through E box enhancer elements. A critical feature of circadian timing is the ability of the clockwork to be entrained to the environmental light/dark cycle. The light-resetting mechanism of the mammalian circadian clock is poorly understood. Light-induced phase shifts are correlated with the induction of the clock genes mPer1 and mPer2 and a subsequent increase in mPER1 protein levels. It has previously been suggested that rapid degradation of BMAL1 protein in the rat SCN is part of the resetting mechanism of the central pacemaker. Our study shows that BMAL1 and CLOCK proteins are continuously expressed at high levels in the mouse SCN, supporting the hypothesis that rhythmic negative feedback plays the major role in rhythm generation in the mammalian pacemaker. Using both immunocytochemistry and immunoblot analysis, our studies demonstrate that BMAL1 protein in the mouse SCN is not affected by a phase-resetting light pulse. These results indicate that rapid degradation of BMAL1 protein is not a consistent feature of resetting mechanisms in rodents.

Dephosphorylation of pCREB by protein serine/threonine phosphatases is involved in inactivation of Aanat gene transcription in rat pineal gland

The rat pineal gland is a suitable model to investigate neurotransmitter-controlled gene expression, because it is well established that the stimulation of melatonin biosynthesis by norepinephrine (NE) depends on the activation of the gene that encodes arylalkylamine N-acetyltransferase (AANAT), the melatonin rhythm enzyme. The mechanisms responsible for downregulation of Aanat transcription are less clear. In this in vitro study we investigated the role of pCREB dephosphorylation for termination of Aanat gene transcription. Immunosignals for pCREB, strongly induced after NE stimulation, rapidly decreased after withdrawal of NE. The immunoreactivity of the inhibitory transcription factor ICER increased twofold after NE treatment for 6 h, but did not change within 30 min after removal of the stimulus. Application of protein serine/threonine phosphatase (PSP) inhibitors prevented pCREB dephosphorylation and blocked the decreases in Aanat mRNA levels, AANAT protein amount and melatonin biosynthesis all of which occurred rapidly after NE withdrawal. PSPs in the rat pineal gland were characterized by immunocytochemistry and immunoblotting. NE-stimulation for 8 h induced accumulation of PSP1-catalytic subunit (CSU) in pinealocyte nuclei, but did not affect the distribution of PSP2A-CSU. The results identify dephosphorylation of pCREB by PSPs as an essential mechanism for downregulation of Aanat transcription in the rat pineal gland.

Norepinephrine-dependent phosphorylation of the transcription factor cyclic adenosine monophosphate responsive element-binding protein in bovine pinealocytes

Norepinephrine (NE)-dependent activation of transcription factors is of central importance for the rhythmic production of melatonin in the rodent pineal gland. At variance with rodents, NE regulates melatonin biosynthesis through post-translational mechanisms in ungulates, and it is not yet known whether transcription factors play any role in ungulate pineal functions. Here, we investigated in isolated bovine pinealocytes the NE-dependent phosphorylation of the transcription factor cyclic adenosine monophosphate (cAMP) responsive element-binding protein (CREB) and compared the effects of NE with those of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). Treatment with 10(-7) m NE for 30 min induced a strong nuclear phosphorylated CREB (pCREB) immunoreaction in cells that were identified as pinealocytes by immunocytochemical demonstration of serotonin, a pinealocyte-specific marker. Immunoblots showed that the NE-induced immunoreaction was due to phosphorylation of the transcription factor CREB and another protein, presumably the activating transcription factor 1 (ATF-1). 10(-7) m isoproterenol (ISO) or 10(-5) m forskolin mimicked the response to NE indicating that NE acts through the beta-adrenergic/cAMP pathway. Also 10(-7) m PACAP, but not 10(-7) m VIP-enhanced CREB phosphorylation; however, only a subpopulation of cells was responsive to PACAP. Our results suggest that, irrespective of whether or not melatonin production is controlled via transcriptional mechanisms, NE-induced CREB phosphorylation represents a very conserved element in pineal physiology of mammals because NE increases pCREB levels in all mammalian species investigated so far. However, the genes targeted by pCREB may vary from one mammalian species to the other. Our results also suggest that transcription factors other than pCREB, like ATF-1, may play a role in pineal functions of mammals.

Protein kinase G I immunoreaction is colocalized with arginine-vasopressin immunoreaction in the rat suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) contains the primary mammalian circadian clock. This clock is entrained to environmental rhythms by external stimuli called zeitgebers. This entrainment is accomplished by the activation of specific, interacting signal transduction cascades. Since a cyclic guanosine monophosphate-dependent mechanism play a crucial functional role for light entrainment in the late night and for transmission of cholinergic stimuli, we examined the expression of protein kinase (PKG) in the rat SCN by means of qualitative and semi-quantitative immunocytochemistry. Immunoreaction (IR) for the isozyme protein kinase G I (PKG I) was found in the dorsomedial part of the SCN considered as an important relay in the output pathways of the clock. Within the SCN, PKG-I IR was colocalized with arginine-vasopressin-IR. The intensities of the PKG-I-IR did not vary between day and night.

Quantitative and qualitative immunofluorescence studies of neoplastic cells transfected with a construct encoding p53-EGFP

The p53 protein is a major regulator of cell cycle progression and apoptosis. We used a p53-enhanced green fluorescent protein (EGFP) construct for transfections into human breast cancer (MCF-7) cells. Cells expressing p53-EGFP showed an increased apoptotic index compared to cells transfected with EGFP alone. Interestingly, apoptotic cells showed localization of p53-EGFP to both nuclei and cytoplasm, whereas non-apoptotic cells usually only showed nuclear localization of p53-EGFP. This result is in agreement with the hypothesis that p53 induces apoptosis by interaction with both nuclear and cytoplasmic targets. Transfected p53-deficient osteosarcoma cells were used for immunofluorescence quantitation. The intensity of immunofluorescence for either p53 or EGFP showed excellent linear correlation to the EGFP autofluorescence, proving that measurements of immunofluorescence intensities can be used for determining endogenous protein levels.

Synchronous recording of load-deformation behaviour and polarized light-microscopic images of the rabbit incisor periodontal ligament during tensile loading

Tooth-periodontal ligament-bone segments were cut in the form of rectangular prisms (1.5 mm wide, 0.65 mm thick, and long enough to allow anchorage of the bone and tooth-end portions in a stretching jig) from the mandibular incisors of 10 rabbits. The experimental set-up enabled simultaneous recording, on video, of the changing image brightness under polarizing optics together with extension across the periodontal ligament. Specimens were stretched until failure at a velocity of 0.5 mm/min. The tensile load-deformation curve of the ligament exhibited an initial, non-linear region that was followed by a linear region, a subsequent yielding region preceding the maximum point, and a final descending region. Gradual increases in the intensity of birefringence in the linear and yielding regions indicated that stress concentrations occur in the supporting fibres attached to mineralized tissues. In the final descending region of the curve, progressive breakages of individual fibre bundles occurred, mainly in the middle zone of the ligament. Analysis of the polarized light-microscopic images showed that the increases in brightness and area of birefringent collagen fibre bundles occurred in parallel with the stress generated. These results suggest that the collagen fibre bundles became aligned with the direction of loading and the intensity of their birefringence increased according to the applied tensile force.

The dispersed cell culture as model for functional studies of the subcommissural organ: preparation and characterization of the culture system

The subcommissural organ (SCO) is an enigmatic secretory gland of the brain, which is believed to be derived from ependymal (glial) precursor cells. We here developed a dispersed cell culture system of the bovine SCO as an approach to functional analyses of this brain gland. Tissue of the bovine SCO obtained from the slaughterhouse was papain dissociated either directly after dissection or after preparation of SCO explants. The latter had been maintained for 4-6 weeks in organ culture. The dispersed cells were cultured for up to 14 days and continuously tested for their secretory state by immunostaining of their secretory product. With respect to the morphology of the SCO cells (shape, processes, nucleus), no difference was found between the culture of freshly dissociated SCOs and that of dissociated SCO explants. In all cases, the dissociation caused a dedifferentiation; typical elongated cells were formed increasingly after 1 day of culture. Thereafter, only the cellular size increased, whereas the shape and the viability of the cells remained unchanged. Proliferating SCO cells were never observed. The culture obtained from fresh SCO tissue contained more glia cells and fibrocytes than the culture prepared from SCO explants. The proliferation of glia cells and fibrocytes was suppressed by blocking the mitotic activity with cytosine-beta-D-arabino furanoside (CAF). The cytophysiological features of the cultured dispersed cells of both origins did not differ as demonstrated by classical histology, by immunocytochemistry for the secretory products of the SCO, by the characteristics of calcium influx into the cytoplasm ([Ca2+]i) and cyclic adenosine monophosphate (cAMP) after stimulation with adenosine-5-triphosphate, substance P or serotonin, and by the activation of the transcription factor cAMP-responsive element-binding protein. Because of the maintenance of their viability, their capacity to release the secretory product into the culture medium, their receptive capacity, and their signal transduction pathways, we conclude that the dispersed cell culture system, especially that obtained from SCO explants, represents an appropriate and useful model for functional studies of the mammalian SCO.

Clock gene protein mPER1 is rhythmically synthesized and under cAMP control in the mouse pineal organ

The mammalian clock gene Per1 is an important element of endogenous oscillators that control daily rhythms in central and peripheral tissues. Although such autonomous clock function is lost in the mammalian pineal gland during evolution, mPer1 mRNA and mPER1 protein were found to be strongly elevated in the mouse pineal organ during the dark period compared to daytime values. In vitro studies showed that mPer1 mRNA and mPER1 protein in mouse pineal gland are induced following the activation of a signalling pathway of fundamental importance for pineal physiology, the norepinephrine/cAMP/phosphoCREB cascade. mPER1 may function in the mouse pineal gland as a time-measuring molecule to participate in regulating rhythmic cellular responses in vivo.

Selective adrenergic/cyclic AMP-dependent switch-off of proteasomal proteolysis alone switches on neural signal transduction: an example from the pineal gland

The molecular processes underlying neural transmission are central issues in neurobiology. Here we describe a novel mechanism through which noradrenaline (NA) activates its target cells, using the mammalian pineal organ as a model. In this neuroendocrine transducer, NA stimulates arylalkylamine N:-acetyltransferase (AANAT; EC 2.3.1. 87), the key enzyme regulating the nocturnal melatonin production. In rodents, AANAT protein accumulates as a result of enhanced transcription, but in primates and ungulates, the AANAT mRNA level fluctuates only marginally, indicating that other mechanisms regulate AANAT protein and activity. These were investigated in cultured bovine pinealocytes. AANAT mRNA was readily detectable in unstimulated pinealocytes, and levels did not change following NA treatment. In contrast, NA increased AANAT protein levels in parallel with AANAT activity, apparently through a cyclic AMP-mediated mechanism. Immunocytochemistry revealed that the changes in AANAT protein levels occurred in virtually all pinealocytes. Inhibition of AANAT degradation by proteasomal proteolysis alone was found to switch-on enzyme activity by increasing AANAT protein levels five- to 10-fold. Accordingly, under unstimulated conditions AANAT protein is continually synthesized and immediately destroyed by proteasomal proteolysis. NA appears to act via cyclic AMP to protect AANAT from proteolytic destruction, resulting in accumulation of the protein. These findings show that tightly regulated control of proteasomal proteolysis of a specific protein alone can play a pivotal role in neural regulation.

Cyclic nucleotide analogs as biochemical tools and prospective drugs

Cyclic AMP (cAMP) and cyclic GMP (cGMP) are key second messengers involved in a multitude of cellular events. From the wealth of synthetic analogs of cAMP and cGMP, only a few have been explored with regard to their therapeutic potential. Some of the first-generation cyclic nucleotide analogs were promising enough to be tested as drugs, for instance N(6),O(2)'-dibutyryl-cAMP and 8-chloro-cAMP (currently in clinical Phase II trials as an anticancer agent). Moreover, 8-bromo and dibutyryl analogs of cAMP and cGMP have become standard tools for investigations of biochemical and physiological signal transduction pathways. The discovery of the Rp-diastereomers of adenosine 3',5'-cyclic monophosphorothioate and guanosine 3',5'-cyclic monophosphorothioate as competitive inhibitors of cAMP- and cGMP-dependent protein kinases, as well as subsequent development of related analogs, has proven very useful for studying the molecular basis of signal transduction. These analogs exhibit a higher membrane permeability, increased resistance against degradation, and improved target specificity. Furthermore, better understanding of signaling pathways and ligand/protein interactions has led to new therapeutic strategies. For instance, Rp-8-bromo-adenosine 3',5'-cyclic monophosphorothioate is employed against diseases of the immune system. This review will focus mainly on recent developments in cyclic nucleotide-related biochemical and pharmacological research, but also highlights some historical findings in the field.

Calculation of maximal hybridization capacity (Hmax) for quantitative in situ hybridization: a case study for multiple calmodulin mRNAs

In estimations of mRNA copy numbers, quantitative in situ hybridization (ISH) is expected to be performed at saturating probe concentration. In practice, however, this condition can rarely be fulfilled when medium to high amounts of transcripts exist and/or in large-scale experiments. To resolve this problem, we developed and tested a double-step procedure involving the use of calmodulin (CaM) I, II, and III [(35)S]-cRNA probes on adult rat brain sections; the hybridization signals were detected with a phosphorimager. By means of hybridization at increasing probe concentrations for a time sufficient for saturation, saturation curves were created for and maximal hybridization capacity (Hmax) values were assigned to selected brain areas. The Kd values of these various brain areas did not differ significantly, which allowed the creation and use of one calibration graph of Hmax vs hybridized [(35)S]-cRNA values for all brain areas for a given probe concentration. Large-scale ISH experiments involving a subsaturating probe concentration were performed to estimate Hmax values for multiple CaM mRNAs. A calibration graph corresponding to this probe concentration was created and Hmax values (expressed in ISH copy no/mm(2) units) were calculated for several brain regions via the calibration. The value of the method was demonstrated by simultaneous quantification of the total accessible multiple CaM mRNA contents of several brain areas in a precise and economical way.

Analyses of signal transduction cascades reveal an essential role of calcium ions for regulation of melatonin biosynthesis in the light-sensitive pineal organ of the rainbow trout (Oncorhynchus mykiss)

Signal transduction processes regulating melatonin production in the light-sensitive trout pineal organ were investigated by immunocytochemical and immunochemical demonstration of phosphorylated cyclic AMP-responsive element-binding protein (pCREB) and measurements of cyclic AMP, melatonin, and calcium levels. Melatonin levels were tightly controlled by light and darkness. Elevation of cyclic AMP levels by 8-bromo-cyclic AMP, forskolin, and 3-isobutyl-1-methylxanthine increased the levels of pCREB and melatonin in light- or dark-adapted pineal organs in vitro. Without pharmacological treatment, the levels of pCREB and cyclic AMP remained constant for several hours before and after light onset. Inhibition of cyclic AMP-dependent proteasomal proteolysis by lactacystin, MG 132, and calpain inhibitor I did not prevent the rapid, light-induced suppression of melatonin biosynthesis. However, changes in the intracellular calcium concentration by drugs affecting voltage-gated calcium channels of the L type and intracellular calcium oscillations (cobalt chloride, nifedipine, Bay K 8644) had dramatic effects on the rapid, light-dependent changes in melatonin levels. These effects were not accompanied by changes in cyclic AMP levels. Thus, the rapid, light-dependent changes in melatonin levels in the trout pineal organ are regulated apparently by a novel calcium signaling pathway and do not involve changes in cyclic AMP levels, cyclic AMP-dependent proteasomal proteolysis, or phosphorylation of cyclic AMP-responsive element-binding protein.

Transcription factor dynamics and neuroendocrine signalling in the mouse pineal gland: a comparative analysis of melatonin-deficient C57BL mice and melatonin-proficient C3H mice

In rodents, the nocturnal rise and fall of arylalkylamine N-acetyltransferase (AANAT) activity controls the rhythmic synthesis of melatonin, the hormone of the pineal gland. This rhythm involves the transcriptional regulation of the AANAT by two norepinephrine (NE)-inducible transcription factors, e.g. the activator pCREB (phosphorylated Ca2+/cAMP-response element binding protein) and the inhibitor ICER (inducible cAMP early repressor). Most inbred mouse strains do not produce melatonin under standard laboratory light/dark conditions. As melatonin-deficient mice are often the founders for transgenic animals used for chronobiological experimentations, molecular components of neuroendocrine signalling in the pineal gland as an integral part of clock entrainment mechanisms have to be deciphered. We therefore compared calcium signalling, transcriptional events and melatonin synthesis in the melatonin-deficient C57BL mouse and the melatonin-proficient C3H mouse. Pineal glands and primary pinealocytes were cultured and stimulated with NE or were collected at various times of the light/dark (LD) cycle. Changes in intracellular calcium concentrations, the phosphorylation of CREB, and ICER protein levels follow similar dynamics in the pineal glands of both mouse strains. pCREB levels are high during the early night and ICER protein shows elevated levels during the late night. In the C57BL pineal gland, a low but significant increase in melatonin synthesis could be observed upon NE stimulation, and, notably, also when animals were exposed to long nights. We conclude that the commonly used C57BL mouse is not completely melatonin-deficient and that this melatonin-deficiency does not affect molecular details involved in regulating transcriptional events of melatonin synthesis.

CREB phosphorylation and melatonin biosynthesis in the rat pineal gland: involvement of cyclic AMP dependent protein kinase type II

Phosphorylation of cyclic AMP response element binding protein (CREB) at amino acid serine 133 appears as an important link between the norepinephrine (NE)-induced activation of second messenger systems and the stimulation of melatonin biosynthesis. Here we investigated in the rat pineal gland: 1) the type of protein kinase that mediates CREB phosphorylation: and 2) its impact on melatonin biosynthesis. Immunochemical or immunocytochemical demonstration of serine133-phosphorylated cyclic AMP regulated element binding protein (pCREB) and radioimmunological detection of melatonin revealed that only cyclic AMP-dependent protein kinase (PKA) inhibitors suppressed NE-induced CREB phosphorylation and stimulation of melatonin biosynthesis, whereas inhibitors of cyclic GMP-dependent protein kinase (PKG), mitogen-activated protein kinase kinase, protein kinase C, or calcium-calmodulin-dependent protein kinase (CaMK) were ineffective. Investigations with cyclic AMP-agonist pairs that selectively activate either PKA type I or II link NE-induced CREB phosphorylation and stimulation of melatonin biosynthesis to the activation of PKA type II. Our data suggest that PKA type II plays an important role in the transcriptional control of melatonin biosynthesis in the rat pineal organ.

Inducible cyclic AMP early repressor protein in rat pinealocytes: a highly sensitive natural reporter for regulated gene transcription

Rhythmic activity of arylalkylamine N-acetyltransferase (AANAT) determines melatonin synthesis in rat pineal gland. The transcriptional regulation of AANAT involves the activating and inhibiting transcription factors of the cyclic AMP (cAMP)-signaling pathway, cAMP response element-binding protein and inducible cAMP early repressor (ICER), respectively. Activation of this pathway is centered around norepinephrine, stimulating beta(1)-adrenergic receptors, but various other transmitters can modulate melatonin biosynthesis. To compare the transcriptional impact of norepinephrine with that of other neurotransmitters on melatonin synthesis, we determined ICER protein levels in pinealocytes and, in parallel, hormone secretion. The dose-dependent inductions of ICER protein by norepinephrine, the beta(1)-adrenergic receptor agonist isoproterenol, vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, and adenosine are correlated to regulatory dynamics in melatonin production. Importantly, ICER protein induction required lower ligand concentrations than the induction of melatonin biosynthesis. Although neuropeptide Y, glutamate, and vasopressin altered norepinephrine-stimulated hormone production without affecting ICER levels, the activation of voltage-gated cation channels increased ICER without affecting hormone synthesis. Sensitivity and versatility of ICER induction in pinealocytes make these neuroendocrine cells a valuable model system in which to study molecular interactions determining a regulated gene expression.

Analyses of signal transduction cascades in rat pinealocytes reveal a switch in cholinergic signaling during postnatal development

In the rat pineal gland, norepinephrine activates alpha1- and beta-adrenergic receptors and triggers melatonin production through an increase in the intracellular calcium concentration ([Ca2+]i) and stimulation of the cAMP/cAMP responsive element-binding protein (CREB) cascade. VIP and PACAP also elevate the intracellular cAMP level and promote melatonin formation. Finally, ACh antagonizes the norepinephrine-induced hormone synthesis via nicotinic acetylcholine receptors and subsequent activation of voltage-gated calcium channels. By immuno(cyto)chemical demonstration of phosphorylated CREB and calcium imaging we have investigated the temporal relationship between the maturation of these signaling pathways and the rhythmic onset of melatonin biosynthesis in developing rat pinealocytes. Norepinephrine-regulated calcium signaling and phosphorylation of CREB are already fully developed at birth, i.e., prior to ingrowth of the sympathetic innervation into the pineal parenchyma, and appear to develop in an innervation-independent manner. VIP- and PACAP-induced CREB phosphorylation is restricted to subpopulations of neonatal cells and thus also displays an adult pattern. Cholinergic calcium signaling exhibits a developmental switch within the first three postnatal weeks. In neonatal pinealocytes, acetylcholine elevates [Ca2+]i via muscarinic rather than nicotinic acetylcholine receptors. In the second postnatal week, pinealocytes gain responsiveness to nicotine and gradually lose responsiveness to muscarinic cholinergic stimuli. Voltage-gated calcium channels are absent in neonatal cells and develop during the first postnatal days. ACh-evoked cellular events may be diversified depending on the functional subclass of receptor that is present. The transient existence of muscarinic acetylcholine receptors and the subsequent switch to nicotinic receptors would permit ACh to elicit temporary effects in early pineal development.

Transcription factors in neuroendocrine regulation: rhythmic changes in pCREB and ICER levels frame melatonin synthesis

Neurotransmitter-driven activation of transcription factors is important for control of neuronal and neuroendocrine functions. We show with an in vivo approach that the norepinephrine cAMP-dependent rhythmic hormone production in rat pineal gland is accompanied by a temporally regulated switch in the ratio of a transcriptional activator, phosphorylated cAMP-responsive element-binding protein (pCREB), and a transcriptional inhibitor, inducible cAMP early repressor (ICER). pCREB accumulates endogenously at the beginning of the dark period and declines during the second half of the night. Concomitant with this decline, the amount of ICER rises. The changing ratio between pCREB and ICER shapes the in vivo dynamics in mRNA and, thus, protein levels of arylalkylamine-N-acetyltransferase, the rate-limiting enzyme of melatonin synthesis. Consequently, a silenced ICER expression in pinealocytes leads to a disinhibited arylalkylamine-N-acetyltransferase transcription and a primarily enhanced melatonin synthesis.