Sterol dependent LDL-receptor gene transcription in lymphocytes from normal and CML patients

Sterol regulatory element (SRE) has been recognized to regulate various key genes coding for especially low density lipoprotein (LDL)-receptor, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and HMG-CoA synthase known to play a crucial role in the cholesterol feedback mechanism. The deranged cholesterol feedback mechanism has been widely recognised in initiation as well as progression of various types of cancers including chronic myeloid leukaemia (CML). Consequently, the present study was addressed to understand this phenomenon and revealed the existence of a unique 47 kDa protein factor having affinity for this SRE sequence in lymphocytes from normal subjects as well as its absence in lymphocytes from untreated CML patients. However, this factor appeared when the CML patients achieved complete haematological remission (CHR) through alpha-interferon therapy. Further, an inverse relationship was also observed between sterol modulated LDL-receptor gene transcription and the binding affinity of this 47 kDa factor to the SRE sequence. Based upon these results we propose that alpha-interferon through its receptor initiates phosphatidic acid dependent signalling which in turn regulates the affinity of 47 kDa sterol regulatory element binding factor as well as LDL-receptor gene transcription in lymphocytes from CML patients.

An expression system for the single-step production of recombinant human amidated calcitonin

Amidating mouse pituitary cells (AtT-20) have been engineered to secrete human calcitonin (hCT) in the fully active amidated form, without the need of additional enzymatic or chemical modifications. The 141-residue human calcitonin precursor has first been cloned in the eucaryotic expression vector pRc/RSV, and the resulting plasmid pRc/RSV/hCT introduced in AtT-20 cells. After transfection, 122 independent clones resistant to G-418 were selected and screened for calcitonin production using a competitive ELISA specifically designed to detect the amidated form of calcitonin. One of these clones was amplified and showed expression of 17 ng/ml of hCT, with a 70% increase in productivity after cAMP treatment. Calcitonin was partially purified from culture medium by two sequential steps of reverse-phase chromatography and characterized in terms of immunoreactivity and molecular weight by TOF-MALDI mass spectroscopy, which confirmed the intended chemical nature and the presence of the C-terminal amidated residue.

Effects of prostaglandins and cyclic AMP on cytokine production in rat leukocytes

Prostaglandins E1, prostaglandin E2, 3-oxa-methano-prostaglandin I1 (SM-10906), a stable prostaglandin I2 analog, and dibutyryl cyclic AMP suppressed the production of tumor necrosis factor and interleukin-1 in lipopolysaccharide-stimulated rat pleural resident monocytic cells, whereas they enhanced the production of interleukin-6 and cytokine-induced neutrophil chemoattractant (CINC), a rat interleukin-8-like chemokine, in these cells. SM-10906 also inhibited the in vivo production of tumor necrosis factor and interleukin-1 in pleural exudates, when injected into the rat pleural cavity concomitantly with carrageenin. The cyclic AMP (cAMP) level in the lipopolysaccharide-stimulated resident cells was increased when the cells were incubated in the presence of prostaglandin E1, prostaglandin E2 or SM-10906. Prostaglandin I2 showed only slight effects. The addition of pentoxifylline, a phosphodiesterase inhibitor, to the incubation mixture increased the cAMP level and also enhanced the effect of prostaglandins, indicating that these regulating actions of prostaglandins may be exerted partly through a mechanism involving an increased intracellular cAMP level.

Retinoic acid suppresses in-vitro decidualization of human endometrial stromal cells

All-trans retinoic acid (RA) has potent effects on cell differentiation and gene expression. Previous studies have demonstrated that human endometrial stromal cells express mRNA for retinoic acid receptors (RARs) and cellular RA-binding protein-II (CRABP-II). We examined whether RA regulates stromal cell differentiation (decidualization), a critical process in preparation of the uterus for blastocyst implantation. Decidualization was induced by incubating cultured stromal cells with medroxyprogesterone acetate (MPA) and oestradiol. Decidualization was defined by the induction of prolactin, insulin-like growth factor binding protein-1 (IGFBP-1), appearance of a differentiated phenotype and changes in fibronectin expression. RA treatment significantly (P < 0.05) suppressed prolactin and IGFBP-1 production associated with stromal cells decidualization. The formation of differentiated cells was inhibited by RA, and consistent with maintenance of the undifferentiated phenotype, fibronectin mRNA content was approximately 3.5-times greater than in the absence of RA. Upon induction of decidualization, the expression of mRNA for the major RA receptor sub-types (RAR-alpha, -beta and -gamma) was maintained while the relative amounts of CRABP-II mRNA progressively decreased with differentiation. With RA treatment, RAR-alpha and RAR-gamma mRNA concentrations were approximately 70 and 25% respectively of those in cells decidualized in the absence of RA. The effects of RA appear to be partially mediated by inhibition of cAMP action. RA suppressed intracellular cAMP concentrations induced by MPA and oestradiol to approximately 35% of those in cells without RA. Addition of 50 microM dibutyryl cAMP to stromal cells treated with MPA and oestradiol only partially reversed the suppression of decidualization and prolactin release by RA. In summary, we have demonstrated that in-vitro decidualization of human endometrial stromal cells induced by MPA and oestradiol treatment is suppressed by RA.

Quantitative estimation of potentiation and antagonism by dose ratios corrected for slopes of dose-response curves deviating from one

A shift of dose-response curves of a receptor agonist A by a receptor antagonist B to the right is frequently expressed or quantitated by calculating the dose ratio (DR) from the ED50 values obtained in the absence and presence of B. A comparison of ED50 values or a DR is also used in a more general way to express the effects of other antagonists or of potentiators. For this situation, where B is not competing with A for a binding site, slope-values may often deviate from one. Because the slope of shifted dose-response curves (deviating from one) affects the magnitude of enhancement or diminution at a given DR, we have to take it into account. For example, the same changes in effects are associated with DR = 10 at curves with slope = 1, but with DR = 2.15 in case of slope = 3. Enhancement and diminution expressed by dose ratios is more or less underestimated in case of curves with slope > 1. We therefore propose to quantitate potentiation and antagonism by a corrected DR (DRcorr), which can simply be calculated from the uncorrected DR at a given slope. Consequently, a DRcorr reflects a true measure of enhancement or diminution for curves with slope = 1, equivalent to that which would have been observed for curves with slope = 1. The practical value of this modification is exemplified and illustrated by analysis of experimental data.

Dibutyryl cyclic adenosine monophosphate stimulates the sodium pump in rabbit renal cortical tubules

The elevation in oxygen consumption (QO2) observed following addition of the sodium ionophore nystatin in suspensions of rabbit renal proximal tubules was significantly increased by 1 mM dibutyryl cyclic adenosine monophosphate (db-cAMP). The QO2 after subsequent addition of strophanthidin to block the sodium pump was unaffected by db-cAMP. However, 10 microM forskolin in the presence of 100 microM IBMX had no significant effect on the QO2 observed following addition of either nystatin or strophanthidin. Nevertheless, we can conclude that db-cAMP does stimulate the sodium pump activity independently of sodium transport mechanisms in the rabbit renal proximal tubule.

Effect of anoxia on isolated turtle tissues: is the response to anoxia mediated by protein kinase second messengers?

Organ slices from the turtle Trachemys scripta elegans were incubated under aerobic and anoxic conditions to examine the effect of protein kinase (PrK) second messengers in potentiating the biochemical responses to anoxia exposure. Incubating liver slices from aerobic animals under anoxic conditions produced biochemical changes exactly similar to those observed in vivo: phosphofructokinase (PFK) was more sensitive to citrate inhibition and the percentage of glycogen phosphorylase (GP) in the active a form increased. On the other hand, incubating brain and heart tissue slices under anoxic conditions produced no changes in PFK and GP kinetic constants. Addition of PrK second messengers (dibutyryl-cAMP or Ca2+ plus phorbol myristate acetate) to the incubated tissues did not promote anoxia-associated changes in aerobically incubated tissues nor did they prevent anoxia-associated changes in anaerobically incubated tissues. These results suggest that unidentified external hormonal signals mediate heart and brain responses to anoxia. It is also apparent that cAMP and Ca2+ plus phospholipid do not play a role in bringing about the anoxia-induced changes in PFK, GP and fructose 2,6-bisphosphate in liver of turtles.

Factors regulating sterol biosynthesis in the rat pineal gland in vitro

The effects of hormones, feeding and photoperiod on pineal sterol biosynthesis were studied in rat pineal glands incubated with 1-14C acetate. The rate of sterol biosynthesis was 7.1 nmol/g/2 h. A high synthesis rate was observed during mid-dark of a 12:12 LD cycle and under constant light. Melatonin, testosterone, and glucagon had no effect on sterol synthesis whereas estradiol increased it and insulin and norepinephrine treatments decreased it. Increased cAMP levels resulting from dibutyryl cAMP and theophylline were also found to be inhibitory. Dietary cholesterol did not alter the rate of sterol biosynthesis but 24 h fasting depressed sterol synthesis significantly. It can be concluded that hormones and substrate availability may be involved in the regulation of pineal sterol biosynthesis.

Interleukin 10 suppression of monocyte prostaglandin H synthase-2. Mechanism of inhibition of prostaglandin-dependent matrix metalloproteinase production

Monocytes/macrophages are associated with chronic inflammatory lesions, such as periodontal disease and rheumatoid arthritis, in which there is extensive connective tissue destruction. Stimulation of human monocytes results in the production of matrix metalloproteinases (MMPs) via a prostaglandin E2 (PGE2)-cAMP-dependent pathway. Modulation of many monocyte functions by interleukin 10 (IL-10) suggested that this cytokine may influence the signal transduction pathway leading to the production of MMPs by monocytes. Pre-incubation of monocytes with IL-10 for 1 h prior to stimulation with ConA resulted in significant inhibition of prostaglandin H synthase-2 (PGHS-2, the inducible form of prostaglandin synthase). In contrast, PGHS-1, the constitutive PGHS, was not affected by IL-10. Suppression of PGHS-2 mRNA and protein levels was detected at 1 ng/ml of IL-10 with maximal inhibition at 20 ng/ml. Nuclear run-on transcription assays performed on monocytes exposed to ConA or the combination of ConA and IL-10 indicated that IL-10 treatment suppressed PGHS-2 expression at the level of transcription. Attenuation of PGHS-2 by IL-10 was accompanied by decreased prostaglandin production, including PGE2. The decrease in prostaglandin production was primarily related to the effect of IL-10 on PGHS-2, since the release of arachidonic acid was unaffected by this cytokine. The inhibition of PGE2 production by IL-10 resulted in the suppression of mRNA and protein for interstitial collagenase and 92-kDa type IV collagenase/gelatinase (gelatinase B). This conclusion is supported by the ability of exogenously added PGE2 or dibutyryl cAMP to restore the production of MMPs in IL-10-treated monocytes. Additionally, PGHS-2 was also restored by PGE2 or dibutyryl cAMP, indicating that PGHS-2 is regulated through a PGE2-cAMP amplification pathway. These data add further support to the anti-inflammatory properties of IL-10.

Spontaneous Ca2+ release from a caffeine and ryanodine-sensitive intracellular Ca2+ store in freshly prepared hepatocytes

A considerable fraction of freshly prepared hepatocytes loaded with the fluorescent [Ca2+]i indicator fura-2 exhibited spontaneous rhythmic fluctuations that tended to decrease with increasing length of incubation after isolation. These oscillations were dependent on the external Ca2+. They could no longer be observed when a Ca2+ chelator-(ethylenebis [oxyethylenenitrilo]) tetraacetic acid--was added to medium. Addition of thapsigargin, which is known to release Ca2+ from inositol 1,4,5-trisphosphate-sensitive and -insensitive Ca2+ stores, induced a large transient increase in [Ca2+]i and abolished the fluctuations. When the cells were treated with 2 mmol/L caffeine, frequency was increased, whereas 10 mmol/L caffeine induced a single large peak followed by a persistent plateau. Moreover, addition of dibutyryl cAMP led to decreased frequency of fluctuations. Ryanodine caused larger fluctuations; thereafter the [Ca2+]i level became much higher and the spikes ceased. These results suggest that spontaneous rhythmic fluctuations in freshly prepared hepatocytes are driven by Ca2+ release from a caffeine- and ryanodine-sensitive calcium-induced calcium release pool.

Suppressed expression of the cytochrome P45017 alpha protein in the testicular feminized (Tfm) mouse testes

The testes of testicular feminized (Tfm) mice synthesize and secrete abnormally low amounts of testosterone, as a consequence of selectively decreased cytochrome P450(17 alpha) activity. To investigate the mechanism of this deficiency, three steroidogenic enzymes were immunolabeled in the testes of normal and Tfm adult (2.5-6 month old) mice. Cholesterol side-chain cleavage cytochrome P450 (P450scc) and delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) were detected in the Leydig cells of both normal and Tfm mice whereas, in contrast to normal mice, only a small proportion of Leydig cells were immunostained for cytochrome P450-17 alpha-hydroxylase, C17-->20 lyase (P450(17 alpha)) in the testes of Tfm mice. The numbers of cells differed from male to male and interestingly were markedly higher in the right testis. Explants of testes from Tfm mice were kept in organ culture at 32 degrees C for 45 h, with or without dibutyryl cyclic AMP (100 or 500 mumol/l). All Leydig cells remained positive for P450scc and 3 beta-HSD, and P450(17 alpha) became detectable in the majority of Leydig cells in both left and right testes, showing that the lack of expression of P450(17 alpha) protein in Tfm mouse testes in vivo is not structural but is a regulatory phenomenon.

Transcriptional modulation of platelet-activating factor receptor gene expression by cyclic AMP

We examined the effects of increasing intracellular cyclic AMP levels on the expression of human PAF receptor (hPAF-R). Peripheral blood monocytes constitutively expressed hPAF-R mRNA transcripts. A transiently elevated intracellular concentration of AMP induced with prostaglandin E2, cholera toxin, or forskolin was a sufficient signal to inhibit PAF-R expression. To determine the mechanisms of this inhibition, human monocytes were treated with dibutyryl cAMP, a cell-permeable cAMP analogue. cAMP reduced the expression of hPAF-R in a concentration- and a time-dependent manner. The effect was seen as early as 1 h and was essentially total by 4 h. Stability of hPAF-R mRNA was not markedly decreased by cAMP, as assessed by measuring the half-lives of the transcripts. Moreover, the nuclear transcription rate of the hPAF-R gene was reduced as early as 30 min after stimulation with cAMP. The inhibition of hPAF-R mRNA accumulation was associated with diminished responsiveness to PAF, as assayed by intracellular Ca2+ fluxes, decreased number of binding sites, and decreased hPAF-R protein expression on the cell surface, as assessed by flow cytometry using a polyclonal anti-hPAF-R antibody. These data indicate that PAF-R expression can be regulated at the transcriptional and possibly post-transcriptional levels by elevation of intracellular cAMP.

GLUT4 phosphorylation and inhibition of glucose transport by dibutyryl cAMP

To investigate the mechanism responsible for the inhibition of glucose transport by dibutyryl cAMP (Bt2cAMP), two different transporter isoforms (GLUT1 and GLUT4) and several GLUT1/4 chimeric transporters were expressed in Chinese hamster ovary (CHO) cells by using a Sindbis virus expression system. Bt2cAMP inhibited GLUT4-mediated 2-deoxy[3H]glucose (2DOG) uptake by 50% but was without effect on GLUT1-mediated uptake. When the subcellular distribution of GLUT4 was assessed by quantitative immunocytochemistry, neither the overall concentration of GLUT4 nor the regional distribution of GLUT-4 within the plasma membrane was found to be altered by Bt2cAMP. Thus, inhibition of 2DOG uptake by Bt2cAMP appears to be due to a decrease in transporter activity rather than a decrease in the number of transporters exposed at the plasma membrane. By using chimeric transporters, a region of GLUT4 necessary for the inhibitory effect of Bt2cAMP was localized to the last 29 amino acids in the COOH terminus. This intracellular region contains the site (Ser488) phosphorylated in vitro by cAMP-dependent protein kinase (cAdPK). Changing Ser488 to an Ala abolished phosphorylation of GLUT4; however, the inhibitory effect of Bt2cAMP on glucose transport was not diminished by this mutation. Therefore, phosphorylation of GLUT4 was not required for the inhibition. The effects of other nucleotides on GLUT4 transport activity were assessed to investigate the role of cAdPK. Uptake of 2DOG by GLUT4 was inhibited by 8-bromo-AMP, but not by 8-bromo-cAMP, suggesting that the inhibitory effect did not involve activation of cAdPK. Results consistent with this interpretation were obtained with CHO cells (line 10248), which express a cAdPK that is resistant to activation by cAMP. No difference in the concentrations of Bt2cAMP required to inhibit GLUT4-mediated transport was observed in normal CHO cells and 10248 cells. The results presented suggest that the inhibitory effects of Bt2cAMP could be mediated by direct binding of a nucleotide to GLUT4 at a site involving the intracellular COOH terminus of the transporter.

Single-cell [Ca2+]i analysis and biochemical characterization of pinealocytes immobilized with novel attachment peptide preparation

Single-cell image analysis of rat pinealocytes has been difficult because they do not attach readily to coated or uncoated surfaces and typically adhere in clusters to fibroblast-like cells. In the present report, a new method for the rapid attachment of rat pinealocytes is described. Cells were prepared using papain digestion and density centrifugation and then were placed on coverslips or slides coated with PepTite-2000, a preparation containing the attachment peptide sequence Arg-Gly-Asp. Cells immobilized with this preparation responded to norepinephrine treatment with an increase in cyclic AMP and melatonin production. Single-cell analysis of Fura-2-loaded cells revealed that norepinephrine increased [Ca2+]i. This development makes it possible to conduct routine single-cell image analysis and other studies of freshly isolated rat pinealocytes.

Immunohistochemical localization of basic fibroblast growth factor in cultured rat astrocytes and oligodendrocytes

The distribution of basic fibroblast growth factor in cultured astrocytes and oligodendrocytes was examined using immunocytochemistry. The results demonstrate a localization of basic fibroblast growth factor immunoreactivity predominantly in astrocyte nuclei at all stages of differentiation. Cytoplasmic and process staining was best detected during early stages of differentiation, under normal growth conditions or as a result of treatment with dibutyryl cyclic adenosine monophosphate. Astrocytes at all stages of differentiation bound antibody-complexed bFGF, suggesting the presence of cell-associated low affinity binding sites for the growth factor. Our studies also show the presence of immunoreactivity for basic fibroblast growth factor in process-bearing oligodendrocytes. These results suggest a role for endogenous basic fibroblast growth factor in astrocyte and oligodendrocyte growth and function.

Adhesion molecules involved in protein kinase A- and C-dependent lymphocyte adherence to microvascular endothelial cells

A twofold increase in lymphocyte adherence to rat microvascular endothelial cells (EC) was achieved by incubating EC for 4 h with IL-1 alpha or dibutyryl-cAMP (stimulators of protein kinase A, PKA) and PMA (stimulator of protein kinase C, PKC). Monoclonal antibodies anti-CD11a, anti-CD18 (LFA-1) and anti-CD49d (VLA-4 alpha) significantly inhibited the increased lymphocyte binding to IL-1 alpha-induced EC, anti-CD18 and to a lesser extent anti-CD11a and anti-CD49d to dibutyryl-cAMP-induced EC, whereas only anti-CD11a and anti-CD18 monoclonal antibodies inhibited PMA-induced lymphocyte binding. These findings suggest that stimulation of PKA and PKC induces lymphocyte binding to EC via different adhesion molecules.

Stage-dependent modulation of Sertoli cell steroid production in dogfish (Scyliorhinus canicula)

Seminiferous lobules of dogfish (Scyliorhinus canicula) testis comprise cysts formed by steroid-producing Sertoli cells associated with germ cells at an identical stage of spermatogenesis. These lobules were isolated in four populations corresponding to lobules with spermatogonia (A), spermatocytes (B), early spermatids (C) and late spermatids (D). They were used for steroid radioimmunoassay or incubated with 22 alpha-hydroxycholesterol or with dibutyryl cyclic AMP (dibutyryl cAMP) to measure steroid production. Our results indicate that progesterone was the major steroid in seminiferous lobules at all stages of spermatogenesis except in lobules A. Furthermore, marked changes in the distribution of steroids were observed according to the stage of spermatogenesis; progesterone, 4-androstenedione, testosterone and 17 alpha-hydroxy,20 beta-dihydroprogesterone concentrations were highest in lobules D, whereas dihydrotestosterone concentrations decreased during spermatogenesis. No significant stage-related change was observed for 3 alpha-diol and 3 beta-diol. Incubation experiments revealed that the isolated seminiferous lobules at all stages can synthesize steroids from hydroxycholesterol and that lobules D have the highest basal contents of androstenedione and testosterone. Furthermore, when dibutyryl cAMP and 10 mumol hydroxycholesterol l-1 were added together to the cultures, an enhancement of the steroid secretion was observed rather than a change in synthesis. Our results also indicated that the responsiveness of the lobules to dibutyryl cAMP varies according to the stage of spermatogenesis and to the steroid assayed. Overall, this study indicated that germ cells probably markedly influence Sertoli cell steroidogenesis in the adult dogfish testis.

Analysis of [1-13C]D-glucose metabolism in cultured astrocytes and neurons using nuclear magnetic resonance spectroscopy

The metabolism of [1-13C]D-glucose by astrocytes, neurons and mixed astroglial/neuronal cultures derived from the striatum of fetal rats was studied using NMR. Metabolic activity was studied in resting and depolarized cells (55 mM K+), with dibutyryl cyclic-AMP added to the medium to promote cell differentiation, and with glutamate (0.1 mM) included in the medium. Due to sample limitations the accumulation of 13C label in metabolites within the cells was not sufficient to quantitate. Of the metabolites released into the medium by the astrocyte cultures and the mixed astroglial/neuronal cultures, measurable amounts of label were present in lactate C-3 and C-2, glutamine C-2, C-3 and C-4, acetate C-2, citrate C-2 or C-4 and C-3, glycerol C-1 or C-3, succinate C-2 or C-3 and several unidentified metabolites. Of the labeled metabolites released into the medium, only succinate was markedly affected by K(+)-induced depolarization, dBcAMP, or glutamate. The label in succinate was increased, especially in the K(+)-depolarized astrocyte cultures (3- to 6-fold). The neuronal cultures consumed [1-13C]D-glucose much more slowly than the astrocyte cultures or the mixed cultures. Except for lactate C-3, there was no measurable 13C in metabolites in the medium of the neuronal cultures.

Insulin and noradrenaline independently stimulate the translocation of glucose transporters from intracellular stores to the plasma membrane in mouse brown adipocytes

The mechanism of the effect of noradrenaline on the transport of 3-O-methyl-D-[14C]glucose ([14C]-MG) was studied in mouse brown adipocytes. When cells were exposed to low concentrations (< 10(-8) M) of insulin, the [14C]-MG uptake by cells was enhanced by noradrenaline additively. The action of noradrenaline was mimicked by isoproterenol, and was completely blocked by propranolol. Exposing cells to noradrenaline induced both an increase in the transport activity of plasma membrane fractions and a decrease in that of microsomal fractions similar to insulin exposure, indicating that noradrenaline also induces the translocation of glucose transporters to the plasma membrane. The ratio of an increase in the transport activity of plasma membrane fraction to a decrease in the activity of microsomal fraction was lower in cells exposed to noradrenaline than in cells exposed to insulin. This quantitative disagreement suggests that there are at least two different modes involved in the regulation of the translocation of glucose transporters in mouse brown adipocytes.

Opposing influences of protein kinase activities on neurite outgrowth in human neuroblastoma cells: initiation by kinase A and restriction by kinase C

The respective roles of cAMP-dependent protein kinase (protein kinase A [PKA]) and protein kinase C (PKC) in the early stages of neurite outgrowth were examined in SH-SY-5Y human neuroblastoma cells. Forskolin or dbcAMP, agents that increase intracellular cAMP levels, and intracellular delivery of PKA catalytic subunit induced neurite outgrowth. The PKA inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), prevented the increases, and decreased further the percentage of cells possessing short, filopodia-like neurites in the absence of inducers. In contrast to effects on PKA activation, PKC activation by 12-0-tetradecanoylphorbol-13-acetate (TPA) reduced the percentage of filopodia-like neurites elaborated by otherwise untreated cells, and prevented neurite outgrowth induced by PKA activators. PKC inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), staurosporine, and sphingosine induced neurite outgrowth. Neurites induced by PKA activation contained higher levels of tubulin immunoreactivity than those induced by PKC inhibition. Furthermore, PKA-induced neurites rapidly retracted in the presence of colchicine, while those elaborated following PKC inhibition were more resistant. These data suggest that neurites elaborated in response to PKA activation are dependent upon microtubule polymerization, and that neurite induction following PKC inhibition is mediated by a different mechanism. PKA activators and PKC inhibitors exerted additive effects on neurite outgrowth, suggesting that the distinct pathways regulated by these two kinases function cooperatively during neuritogenesis.

Action site of the lethal Ay gene in the mouse embryo

We investigated the lethal effect of Ay gene in embryos at the preimplantation stage in vitro. First, the development until the blastocyst stage and the division of individual cells from 8-cell stage embryos were examined. No difference in development was detected between embryos from the experimental cross (Ay/a x Ay/a) and those from the control cross (a/a x a/a). Therefore, it seems that the abnormality of the Ay/Ay embryo does not appear until blastocyst formation in vitro. We subsequently examined the hatching from zona pellucida of the blastocysts. The hatching ratio of the embryos from the experimental cross was significantly lower than that of the control crosses (Ay/a x a/a, a/a x a/a: p < 0.05). Our observation indicates that deficiency of the Ay/Ay embryo can be detected in vitro at hatching. In order to elucidate the mechanism of the gene action of the Ay, we attempted to rescue the lethal embryos from decreased hatching ratio in vitro. When dbcAMP at the concentration of 1 mM was added to the culture medium, the hatching ratio of blastocysts from the experimental cross increased until the level of those from the control crosses. Since this result indicates that the cAMP content in Ay homozygote seemed to be lower than those in a/a and Ay/a, the cAMP content in individual blastocyst was quantified. It is found that Ay homozygosity was associated with lower level of cAMP. When adenylate cyclase was activated by forskolin and cholera toxin, the hatching ratio was increased. These results seem to suggest that Ay homozygote embryos possess a defect in signal transduction system mediated by adenylate cyclase during hatching.

Homocysteate and homocysteine sulfinate, excitatory transmitter candidates present in rat astroglial cultures

The presence of homocysteate and homocysteine sulfinate was demonstrated in extracts prepared from cultures of rat cortical and cerebellar astrocytes as well as from C6 glioblastoma cells by o-phthalaldehyde derivatization and subsequent HPLC analysis. Homocysteate-like immunoreactivity was found in cultured cortical astrocytes by postembedding immunocytochemistry at the level of light microscopy. These findings support the notion of a glial localization of the excitatory transmitter candidate homocysteate.

Norepinephrine-mediated protein phosphorylation in astrocytes

Studies were conducted to determine if norepinephrine activates both protein kinase C and the cyclic AMP-dependent protein kinase in cultured rat astrocytes using phosphoproteins as markers. Norepinephrine was found to decrease 32P incorporation into an acidic 80,000 M(R) protein. A similar response was observed with isoproterenol and cyclic AMP analogs. In contrast, phorbol myristate acetate (PMA) increased 32P incorporation into this protein. Further studies looked at phosphorylation sites on glial fibrillary acidic protein and vimentin using two-dimensional tryptic phosphopeptide maps. The pattern of phosphorylation of these two proteins by norepinephrine resembles that of 8-bromo cyclic AMP and isoproterenol, and not that of PMA. Additionally, the effect of norepinephrine on the phosphorylation of GFAP and vimentin was blocked by alprenolol. One difference noted between norepinephrine and isoproterenol was the phosphorylation of an 18,000 M(R) protein. Norepinephrine increased, and isoproterenol decreased, 32P incorporation into this protein; however, the mechanism which mediates the norepinephrine effect remains to be determined. Overall, these studies indicate that the most prominent phosphorylation events mediated by norepinephrine are the consequence of the activation of cyclic AMP-dependent protein kinase.

Isoproterenol-induced Mg2+ uptake in liver

Isoproterenol increased the Mg2+ content of hepatocytes after injection into rats or after addition to collagenase-dispersed hepatocytes. cAMP also the increased cellular Mg2+ content of isolated hepatocytes. This effect was prevented by staurosporine. Phorbol ester had no effect on the Mg2+ content of isolated hepatocytes, and after injection of isoproterenol into rats, protein kinase C of liver was not affected. It was concluded that isoproterenol induced long-term Mg2+ influx via the activation of protein kinase A which can be inhibited by staurosporine.