Regulation of mouse oocyte maturation: effect of elevating cumulus cell cAMP on oocyte cAMP levels

We have reexamined the possibility that cumulus cell cAMP can enter the oocyte via the gap junctions connecting the two cell types (Schultz et al., 1983a). Since our recent results indicate that the mouse oocyte possesses a very active cyclic nucleotide phosphodiesterase (PDE) (Bornslaeger et al., 1984), we have altered our experimental protocol to ensure that mouse oocyte PDE activity is inhibited throughout the duration of an experiment. Our results demonstrate the apparent transfer of cAMP from cumulus cells to the oocyte; these results are discussed in terms of current models for regulation of mammalian oocyte maturation.     

Regulation of phosphodiesterase and ornithine decarboxylase by cAMP is cell cycle independent.

Cyclic AMP (cAMP) causes growth arrest in G1 and induction of cAMP phosphodiesterase and decrease of ornithine decarboxylase in S49 mouse lymphoma cells. Dibutyryl cAMP treatment of partially synchronized cells causes similar changes in activities of both enzymes, regardless of position in the cell cycle. This suggests that cAMP regulation of these enzymes is not mediated by growth perturbation.     

Changes in cAMP levels in bacterial cells during the cell cycle

The changes in the cAMP level during the cell cycle in the synchronous cultures of E. coli were demonstrated. Two maxima in the cAMP level were revealed during each generation period. In the cell cycle of 40-45 min duration the first increase was observed approximately in the middle of the cycle, i. e., it was coincident with the initiation of DNA synthesis. Under these conditions the cAMP level increased 8-10 times (from 0.5 to 5.0 pmole per ml of cell suspension). The second, less pronounced increase in the cAMP level was observed immediately before or during the cell division and was probably related to the regulation of the cell wall formation.     

Effect of leukoagglutinating phytohemagglutinin on cAMP and cGMP levels in lymphocytes

In concentrations which do not affect the cellular concentrations of the cyclic nucleotides cAMP and cGMP, phytohemagglutinin (PHA) (crystalline, kidney-bean leukoagglutinin) can activate adenoidal lymphocytes. High concentrations of leukoagglutinin caused an increase in cAMP without stimulating mitosis in lymphocytes. Our results do not support the concept that cyclic nucleotides act as mediators for lymphocyte activation by lectins. Previous contradictory reports on the role of cyclic nucleotides may have been due to the use of impure bean extracts and lymphocytes.     

Staphylococcus aureus promotes autophagy by decreasing intracellular cAMP levels

Staphylococcus aureus is an intracellular bacterium responsible for serious infectious processes. This pathogen escapes from the phagolysosomal pathway into the cytoplasm, a strategy that allows intracellular bacterial replication and survival with the consequent killing of the eukaryotic host cell and spreading of the infection. S. aureus is able to secrete several virulence factors such as enzymes and toxins. Our recent findings indicate that the main virulence factor of S. aureus, the pore-forming toxin α-hemolysin (Hla), is the secreted factor responsible for the activation of an alternative autophagic pathway. We have demonstrated that this noncanonical autophagic response is inhibited by artificially elevating the intracellular levels of cAMP. This effect is mediated by RAPGEF3/EPAC (Rap guanine nucleotide exchange factor (GEF)3/exchange protein activated by cAMP), a cAMP downstream effector that functions as a GEF for the small GTPase Rap. We have presented evidence that RAPGEF3 and RAP2B, through calpain activation, are the proteins involved in the regulation of Hla and S. aureus-induced autophagy. In addition, we have found that both, RAPGEF3 and RAP2B, are recruited to the S. aureus–containing phagosome. Of note, adding purified α-toxin or infecting the cells with S. aureus leads to a decrease in intracellular cAMP levels, which promotes autophagy induction, a response that favors pathogen intracellular survival, as previously demonstrated. We have identified some key signaling molecules involved in the autophagic response upon infection with a bacterial pathogen, which have important implications in understanding innate immune defense mechanisms.     

Increasing intracellular cAMP and cGMP inhibits cadmium-induced oxidative stress in rat submandibular saliva

The effect of cadmium on induction of oxidative stress in rat submandibular saliva and protective role of increasing intracellular cAMP and cGMP by use of specific phosphodiesterase inhibitors, theophylline and sildenafil were investigated. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Acute administration of cadmium (10 mg/kg) caused significant oxidative stress by increasing lipid peroxidation by-products (thiobarbituric reactive substances, TBARS) and decreasing total thiols and total antioxidant power of the saliva. Concurrent therapy of rats by theophylline (25 mg/kg) and sildenafil (5 mg/kg) prevented cadmium-induced oxidative stress in saliva. Theophylline and sildenafil inhibited cadmium-induced increase in lipid peroxidation and decrease in total thiols and antioxidant power. It is concluded that cadmium administration results in oxidative stress in rat submandibular saliva, which can be protected by concurrent administration of specific cyclic nucleotide phosphodiesterase inhibitors.     

The increase in cAMP and cGMP levels in the oestrogenized rat hypophysis.

Male and female rats were given oestradiol benzoate (1 mg s.c. twice a week for 3 weeks) and/or sodium nitroprusside (SN), a donor of nitric oxide (NO), which was administered in their food in amounts of 0.2 or 0.6 mg/rat/day. Neither oestradiol-induced hypertrophy of the hypophysis, nor the serum prolactin (PRL) level, was affected by the simultaneous administration of SN. The PRL content of the hypophysis rose after oestradiol in the males, but the increase was again uninfluenced by the simultaneous administration of SN and the cAMP content of the hypophysis--raised after oestradiol--was likewise unaffected. The amount of cGMP in the hypophysis after oestradiol rose only in males. Both the serum and the hypophyseal prolactin level were found to be correlated to the cAMP and the cGMP content of the hypophysis. It was found that the simultaneous administration of SN together with oestradiol slightly reduced the increase in the cGMP content of the hypophysis elicited with oestradiol treatment only.     

Regulation of the starfish sperm acrosome reaction by cGMP, pH, cAMP and Ca2+

In the starfish, Asterias amurensis, three components in the jelly coat of eggs, namely acrosome reaction-inducing substance (ARIS), Co-ARIS and asterosap, act in concert on homologous spermatozoa to induce the acrosome reaction (AR). Molecular recognition between the sperm surface molecules and the egg jelly molecules must underlie signal transduction events triggering the AR. Asterosap is a sperm-activating molecule, which stimulates rapid synthesis of intracellular cGMP, pH and Ca(2+). This transient elevation of Ca(2+) level is caused by a K(+)-dependent Na(+)/Ca(2+) exchanger, and the increase of intracellular pH is sufficient for ARIS to induce the AR. The concerted action of ARIS and asterosap could induce elevate intracellular cAMP levels in starfish sperm and the sustained increase in [Ca(2+)], which is essential for the AR. The signaling pathway induced by these factors seems to be synergistically regulated to trigger the AR in starfish sperm.     

The effects of valproate and phenytoin on the cAMP and cGMP levels in nervous tissue

Earlier studies have demonstrated that valproic acid (VPA) and phenytoin (PHT) influence the excitability properties of crayfish axons through different mechanisms. PHT was found to antagonize the electrophysiologic effects of VPA. The purpose of the present study was to determine if the electrophysiologic effects of VPA and PHT are correlated with changes in the cellular levels of either cAMP or cGMP as these substances are known to influence membrane excitability. It was found that PHT (0.1 mM) has no effect on the levels of either cAMP or cGMP within crayfish neural tissue. VPA (4.0 mM) also has no effect on cAMP levels. However, it does significantly reduce the levels of cGMP. Pretreatment of neural tissue with PHT has been shown to eliminate the effects of VPA on membrane excitability. It was found that this pretreatment has no influence on VPA's ability to reduce cGMP levels. The effect of VPA on cGMP levels is observed in the absence of spontaneous activity. Therefore, it is concluded that the observed reduction in cGMP levels does not represent the modulation of cGMP levels that is known to accompany activity. Two experiments demonstrate that the 4-mV depolarization of membranes by VPA can not account for its effect on cGMP levels. In the first, pretreatment with PHT abolished the depolarizing effect on VPA but not its effect on cGMP. In the second, a concentration of ouabain which depolarizes crayfish neural tissue by 8-10 mV without producing spike activity had no effect on either cAMP or cGMP levels. These experiments effectively dissociate the electrophysiologic response to VPA and PHT from changes in cyclic nucleotide levels.     

Decrease in cAMP levels and increase in cGMP levels in the small intestine mucosa after treatment with fluoride

Sodium fluoride was studied for its effect on the cAMP and cGMP amount in the small intestine mucosa of rats under conditions of acute and chronic experiments. A significant decrease in the cAMP level and an increase in the cGMP level were revealed in both cases. Changes in the content of cyclic nucleotides were followed by marked changes in their physiologically important ratios.     

Effect of adenylyl cyclase activation on intracellular and extracellular cAMP and cGMP in preimplantation cattle blastocysts

The effects of direct and indirect activation of adenylyl cyclase on the production of intracellular and extracellular cAMP and cGMP by 13- to 16-day-old cattle embryos were determined. Embryos were incubated for 2 h in a Krebs Ringer bicarbonate medium containing the phosphodiesterase inhibitor isobutyl-methylxanthine, to which stimulating agents forskolin (100 mumol l-1), cholera toxin (2 micrograms ml-1), or both were added. Total (intra- and extracellular) basal cAMP and cGMP concentrations ranged from 6.65 +/- 0.895 to 3.4 +/- 0.708 fmol microgram-1 protein in 13-day-old embryos and from 4.05 +/- 1.151 to 0.19 +/- 0.041 fmol microgram-1 protein in 16-day-old embryos. Forskolin induced an increase (P < 0.001) in cAMP that ranged from 5.4-fold on day 13 to 2.7-fold on day 16, whereas cholera toxin induced an increase (P < 0.001) that ranged from 30-fold at day 13 to 21-fold at day 16, similar to the effect of forskolin and cholera toxin combined. Individually, forskolin and cholera toxin had no effect on cGMP concentrations, but together they induced an increase (P < 0.05). cAMP (P < 0.01) and cGMP (P < 0.001) concentrations decreased with embryo age from day 13 to day 16 for all treatments; the decrease was greater for cGMP than cAMP (5-24-fold versus 1.6-3.3-fold, respectively). It is concluded that inducible adenylyl cyclase is present in 13- to 16-day-old cattle embryos and that the embryos secrete cAMP and cGMP into the incubation medium. In addition, basal and inducible concentrations of cAMP and cGMP decrease with embryo age from day 13 to day 16. These observations indicate that cAMP and cGMP may have a role in the rapid embryonic cell proliferation that occurs at this time or in signalling to the endometrium.     

泛素化途径与细胞周期的关系

泛素化途径(the ubiquitin pathway)是一种有高度选择性的蛋白水解途径,是细胞周期调控的基础。本文主要论述了依赖SCF(skp-cullin-F-boxprotein)和APC／C(anaphase-promoting complexor cyclosome)的两种泛素化途径对细胞周期不同时期的调控作用及其研究进展。     

Regulation of cGMP production by intracellular alkalinization in cultured rat inner medullary collecting duct cells

We evaluated the relationship between cell pH and cGMP production in cultured rat renal inner medullary collecting duct cells. The cGMP level, 21 +/- 6, was not different in control vs. alkalinized cells, 49 +/- 17 fmol/mg protein (p greater than 0.5). 10(-11) M atrial natriuretic peptide (ANF) enhanced cGMP production in alkalinized cells, 426 +/- 34 vs. 141 +/- 9*. Conversely, alkalinization inhibited 10(-4)M nitroprusside (SNP) induced cGMP formation, 29 +/- 9 vs. 332 +/- 67*. Phosphodiesterase inhibition abolished the difference in cGMP production by ANF but did not reverse the inhibitory effect of alkalinization on SNP induced cGMP production. In rat renal inner medullary collecting duct cells, cellular alkalinization plays a significant role in the regulation of guanylate cyclase mediated cGMP production. * = p less than 0.05).