Cellular effects of olomoucine, an inhibitor of cyclin-dependent kinases

Triaging between post-translational modification of cell cycle regulators and their therapeutics in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, present challenges in healthcare because of their complicated etiologies and absence of healing remedies. Lately, the emerging role of post-translational modifications (PTMs), in the context of cell cycle regulators, has garnered big interest as a potential avenue for therapeutic intervention. The review explores the problematic panorama of PTMs on cell cycle regulators and their implications in neurodegenerative diseases. We delve into the dynamic phosphorylation, acetylation, ubiquitination, SUMOylation, Glycation, and Neddylation that modulate the key cell cycle regulators, consisting of cyclins, cyclin-dependent kinases (CDKs), and their inhibitors. The dysregulation of these PTMs is related to aberrant cell cycle in neurons, which is one of the factors involved in neurodegenerative pathologies. Moreover, the effect of exogenous activation of CDKs and CDK inhibitors through PTMs on the signaling cascade was studied in postmitotic conditions of NDDs. Furthermore, the therapeutic implications of CDK inhibitors and associated alteration in PTMs were discussed. Lastly, we explored the putative mechanism of PTMs to restore normal neuronal function that might reverse NDDs.

DrugSim2DR: systematic prediction of drug functional similarities in the context of specific disease for drug repurposing

BACKGROUND

Traditional approaches to drug development are costly and involve high risks. The drug repurposing approach can be a valuable alternative to traditional approaches and has therefore received considerable attention in recent years.

FINDINGS

Herein, we develop a previously undescribed computational approach, called DrugSim2DR, which uses a network diffusion algorithm to identify candidate anticancer drugs based on a drug functional similarity network. The innovation of the approach lies in the drug-drug functional similarity network constructed in a manner that implicitly links drugs through their common biological functions in the context of a specific disease state, as the similarity relationships based on general states (e.g., network proximity or Jaccard index of drug targets) ignore disease-specific molecular characteristics. The drug functional similarity network may provide a reference for prediction of drug combinations. We describe and validate the DrugSim2DR approach through analysis of data on breast cancer and lung cancer. DrugSim2DR identified some US Food and Drug Administration-approved anticancer drugs, as well as some candidate drugs validated by previous studies in the literature. Moreover, DrugSim2DR showed excellent predictive performance, as evidenced by receiver operating characteristic analysis and multiapproach comparisons in various cancer datasets.

CONCLUSIONS

DrugSim2DR could accurately assess drug-drug functional similarity within a specific disease context and may more effectively prioritize disease candidate drugs. To increase the usability of our approach, we have developed an R-based software package, DrugSim2DR, which is freely available on CRAN (https://CRAN.R-project.org/package=DrugSim2DR).

Differential effects of the cell cycle inhibitor, olomoucine, on functional recovery and on responses of peri-infarct microglia and astrocytes following photothrombotic stroke in rats

Background

Following stroke, changes in neuronal connectivity in tissue surrounding the infarct play an important role in both spontaneous recovery of neurological function and in treatment-induced improvements in function. Microglia and astrocytes influence this process through direct interactions with the neurons and as major determinants of the local tissue environment. Subpopulations of peri-infarct glia proliferate early after stroke providing a possible target to modify recovery. Treatment with cell cycle inhibitors can reduce infarct volume and improve functional recovery. However, it is not known whether these inhibitors can influence neurological function or alter the responses of peri-infarct glia without reducing infarction. The present study aimed to address these issues by testing the effects of the cell cycle inhibitor, olomoucine, on recovery and peri-infarct changes following photothrombotic stroke.

Methods

Stroke was induced by photothrombosis in the forelimb sensorimotor cortex in Sprague-Dawley rats. Olomoucine was administered at 1 h and 24 h after stroke induction. Forelimb function was monitored up to 29 days. The effects of olomoucine on glial cell responses in peri-infarct tissue were evaluated using immunohistochemistry and Western blotting.

Results

Olomoucine treatment did not significantly affect maximal infarct volume. Recovery of the affected forelimb on a placing test was impaired in olomoucine-treated rats, whereas recovery in a skilled reaching test was substantially improved. Olomoucine treatment produced small changes in aspects of Iba1 immunolabelling and in the number of CD68-positive cells in cerebral cortex but did not selectively modify responses in peri-infarct tissue. The content of the astrocytic protein, vimentin, was reduced by 30% in the region of the lesion in olomoucine-treated rats.

Conclusions

Olomoucine treatment modified functional recovery in the absence of significant changes in infarct volume. The effects on recovery were markedly test dependent, adding to evidence that skilled tasks requiring specific training and general measures of motor function can be differentially modified by some interventions. The altered recovery was not associated with specific changes in key responses of peri-infarct microglia, even though these cells were considered a likely target for early olomoucine treatment. Changes detected in peri-infarct reactive astrogliosis could contribute to the altered patterns of functional recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02208-w.

Design, Synthesis, and In Vitro Antiproliferative Activity of Hydantoin and Purine Derivatives with the 4-Acetylphenylpiperazinylalkyl Moiety

Cancer represents one of the most serious health problems and the second leading cause of death around the world. Heterocycles, due to their prevalence in nature as well as their structural and chemical diversity, play an immensely important role in anti-cancer drug discovery. In this paper, a series of hydantoin and purine derivatives containing a 4-acetylphenylpiperazinylalkyl moiety were designed, synthesized, and biologically evaluated for their anticancer activity on selected cancer cell lines (PC3, SW480, SW620). Compound 4, a derivative of 3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione, was the most effective against SW480, SW620, and PC3 cancer cell lines. Moreover, 4 has high tumor-targeting selectivity. Based on docking studies, it was concluded that R isomers of 3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione could be further studied as promising scaffolds for the development of thymidine phosphorylase inhibitors.

Room-Temperature Amination of Chloroheteroarenes in Water by a Recyclable Copper(II)-Phosphaadamantanium Sulfonate System

Buchwald-Hartwig amination of chloroheteroarenes has been a challenging synthetic process, with very few protocols promoting this important transformation at ambient temperature. The current report discusses about an efficient copper-based catalytic system (Cu/PTABS) for the amination of chloroheteroarenes at ambient temperature in water as the sole reaction solvent, a combination that is first to be reported. A wide variety of chloroheteroarenes could be coupled efficiently with primary and secondary amines as well as selected amino acid esters under mild reaction conditions. Catalytic efficiency of the developed protocol also promotes late-stage functionalization of active pharmaceutical ingredients (APIs) such as antibiotics (floxacins) and anticancer drugs. The catalytic system also performs efficiently at a very low concentration of 0.0001 mol % (TON = 980,000) and can be recycled 12 times without any appreciable loss in activity. Theoretical calculations reveal that the π-acceptor ability of the ligand PTABS is the main reason for the appreciably high reactivity of the catalytic system. Preliminary characterization of the catalytic species in the reaction was carried out using UV-VIS and ESR spectroscopy, providing evidence for the Cu(II) oxidation state.

Steroid resistance in Diamond Blackfan anemia associates with p57Kip2 dysregulation in erythroid progenitors

Despite the effective clinical use of steroids for the treatment of Diamond Blackfan anemia (DBA), the mechanisms through which glucocorticoids regulate human erythropoiesis remain poorly understood. We report that the sensitivity of erythroid differentiation to dexamethasone is dependent on the developmental origin of human CD34+ progenitor cells, specifically increasing the expansion of CD34+ progenitors from peripheral blood (PB) but not cord blood (CB). Dexamethasone treatment of erythroid-differentiated PB, but not CB, CD34+ progenitors resulted in the expansion of a newly defined CD34+CD36+CD71hiCD105med immature colony-forming unit-erythroid (CFU-E) population. Furthermore, proteomics analyses revealed the induction of distinct proteins in dexamethasone-treated PB and CB erythroid progenitors. Dexamethasone treatment of PB progenitors resulted in the specific upregulation of p57Kip2, a Cip/Kip cyclin-dependent kinase inhibitor, and we identified this induction as critical; shRNA-mediated downregulation of p57Kip2, but not the related p27Kip1, significantly attenuated the impact of dexamethasone on erythroid differentiation and inhibited the expansion of the immature CFU-E subset. Notably, in the context of DBA, we found that steroid resistance was associated with dysregulated p57Kip2 expression. Altogether, these data identify a unique glucocorticoid-responsive human erythroid progenitor and provide new insights into glucocorticoid-based therapeutic strategies for the treatment of patients with DBA.

Dietary Walnut Supplementation Alters Mucosal Metabolite Profiles During DSS-Induced Colonic Ulceration

Walnuts contain a complex array of natural compounds and phytochemicals that exhibit a wide range of health benefits, including protection against inflammation and colon cancer. In this study, we assess the effects of dietary supplementation with walnuts on colonic mucosal injury induced in mice by the ulcerogenic agent, dextran sodium sulfate (DSS). C57Bl/6J mice were started on the Total Western Diet supplemented with freshly-ground whole walnuts (0, 3.5, 7 and 14% g/kg) 2 weeks prior to a 5-day DSS treatment and walnut diets were continued throughout the entire experimental period. Mice were examined at 2 days or 10 days after withdrawal of DSS. In a separate study, a discovery-based metabolite profiling analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) was performed on fecal samples and colonic mucosa following two weeks of walnut supplementation. Dietary walnut supplementation showed significant effects in the 10-day post-DSS recovery-phase study, in which the extent of ulceration was significantly reduced (7.5% vs. 0.3%, p < 0.05) with 14% walnuts. In the metabolite-profiling analysis, walnuts caused a significant increase in several polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid (DHA) and 9-oxo-10(E),12(E)-octadecadienoic acid (9-oxoODA), as well as kynurenic acid. In colon tissue samples, walnuts caused a significant increase in the levels of S-adenosylhomocysteine (SAH) and betaine, important components of fatty acid β-oxidation. These metabolite changes may contribute in part to the observed protection against DSS-induced inflammatory tissue injury.

CDK5 inhibitors prevent astroglial apoptosis and reactive astrogliosis by regulating PKA and DRP1 phosphorylations in the rat hippocampus

Status epilepticus (SE) results in the unique pattern of dynamin-related protein 1 (DRP1)-mediated mitochondrial dynamics, which is associated with astroglial apoptosis and reactive astrogliosis in the regional-specific pattern representing the differential astroglial properties. However, less defined are the epiphenomena/upstream effecters for DRP1 phosphorylation in this process. Since cyclin-dependent kinase 5 (CDK5) is involved in reactive astrogliosis, CDK5 is one of the possible upstream regulators for DRP1 phosphorylation. In the present study, both olomoucine and roscovitine (CDK5 inhibitors) effectively ameliorated SE-induced astroglial apoptosis in the dentate gyrus without changed seizure susceptibility. In addition, they inhibited reactive astrogliosis in the CA1 region independent of neuronal death induced by SE. These effects of CDK5 inhibitors were relevant to abrogation of altered DRP1 phosphorylation ratio and mitochondrial length induced by SE. CDK5 inhibitors also negatively regulated protein kinase A (PKA) activity in astrocytes. Therefore, our findings suggest that CDK5 inhibitors may mitigate astroglial apoptosis and reactive astrogliosis accompanied by modulations of DRP1-mediated mitochondrial dynamics.

Radioiodination of cyclin dependent kinase inhibitor Olomoucine loaded Fe@Au nanoparticle and evaluation of the therapeutic efficacy on cancerous cells

Magnetic nanoparticles have promising biomedical applications such as drug delivery, novel therapeutics and diagnostic imaging. Magnetic drug delivery combination works on the delivery of magnetic nanoparticles loaded with drug to the target tissue by means of an external magnetic field. Gold coated iron oxide (Fe@Au) nanoparticles can provide useful surface chemistry and biological reactivity. Covalent conjugation to the Fe@Au nanoparticles through cleavable linkages can be used to deliver drugs to tumor cells, then the drug can be released by an external. In this paper, purine based cyclin dependent kinases (CDKs) inhibitor Olomoucine (Olo) [2-(Hydroxyethylamino)-6-benzylamino-9-methylpurine] was loaded on gold coated iron oxide (Fe@Au) nanoparticles and radiolabeled with 131I to combine magnetic targeted drug delivery and radiotherapy. Fe@Au nanoparticles were synthesized by microemulsion method. The characterization of nanoparticles was examined by TEM, VSM and XRD. Amine activation was utilized by cysteamine hydrochloride and then CDI was used for conjugation of Olomoucine. Antiproliferative effect and cytotoxicity of Olomoucine loaded Fe@Au nanoparticles (Fe@Au-Olo) were investigated on MCF7 and A549 cell lines. Proliferation rate was decreased while uptake of Fe@Au-Olo on both cell lines was high in comparison with Olomoucine. Also, enhanced incorporation ratio was observed under external magnetic field.

Amyloid beta modulators and neuroprotection in Alzheimer's disease: a critical appraisal

Multiple cellular changes have been identified as being involved in Alzheimer's disease (AD) pathogenesis, including mitochondrial damage, synaptic loss, amyloid beta (Aβ) production and/or accumulation, inflammatory responses, and phosphorylated tau formation and/or accumulation. Studies have established that Aβ-induced synaptic dysfunction is dependent on abnormal amyloid precursor protein (APP) processing caused by β- and γ-secretases, resulting in the generation of Aβ. The Aβ formed as a result of abnormal APP processing induces phosphorylated tau and activates glycogen synthase kinase-3β (GSK3β) and cyclin-dependent kinase-5 (CDK5). Here, we review the latest research on the development of Aβ modulators for neuroprotection in AD. We also review the use of molecular inhibitors as therapeutic targets in AD.

CDK INHIBITORY NUCLEOSIDE ANALOGS PREVENT TRANSCRIPTION FROM VIRAL GENOMES

Targeting viral proteins has lead to many successful antivirals. Yet, such antivirals rapidly select for resistance, tend to be active against only a few related viruses, and require previous characterization of the target proteins. Alternatively, antivirals may be targeted to cellular proteins. Replication of many viruses requires cellular CDKs and pharmacological CDK inhibitors (PCIs), such as the purine-based roscovitine (Rosco), are proving safe in clinical trials against cancer. Rosco inhibits replication of wild-type or (multi-)drug resistant HIV, HCMV, EBV, VZV, and HSV-1 and 2. However, the antiviral mechanisms of purine PCIs remain unknown. Our objective is to characterize these mechanisms using HSV as a model We have shown that Rosco prevents initiation of transcription from viral, but not cellular, genomes. This inhibition is promoter independent, but genome dependent, and requires no viral proteins. This is a novel antiviral mechanism and a previously unknown activity for purine PCIs.

Cell cycle activation and spinal cord injury

Traumatic spinal cord injury (SCI) evokes a complex cascade of events with initial mechanical damage leading to secondary injury processes that contribute to further tissue loss and functional impairment. Growing evidence suggests that the cell cycle is activated following SCI. Up-regulation of cell cycle proteins after injury appears to contribute not only to apoptotic cell death of postmitotic cells, including neurons and oligodendrocytes, but also to post-traumatic gliosis and microglial activation. Inhibition of key cell cycle regulatory pathways reduces injury-induced cell death, as well as microglial and astroglial proliferation both in vitro and in vivo. Treatment with cell cycle inhibitors in rodent SCI models prevents neuronal cell death and reduces inflammation, as well as the surrounding glial scar, resulting in markedly reduced lesion volumes and improved motor recovery. Here we review the effects of SCI on cell cycle pathways, as well as the therapeutic potential and mechanism of action of cell cycle inhibitors for this disorder.

Cell cycle arrest and cytochrome c-mediated apoptotic induction by MCS-5A is associated with up-regulation of p16(INK4a) in HL-60 cells

MCS-5A, an analog of sangivamycin, selectively inhibits the cyclin-dependent kinases CDK1 and 4 in HL-60 cells in vitro (IC(50): 9.6 and 8.8 1V, respectively), while weakly inhibiting other housekeeping protein kinases. MCS-5A effectively induces HL-60 cell cycle arrest at the G(1) and G(2)/M phases through direct inhibition of CDK1 and 4 activity. In addition, elevated expression of p16(INK4a) and a reduction in the level of hyperphosphorylated pRb showed that 3 1V MCS-5A also induces p16(INK4a)-mediated cell cycle arrest at the G(1) phase. Furthermore, apoptotic induction in MCS-5A-treated HL-60 cells is associated with the release of cytochrome c from mitochondria, which, in turn, results in the activation of procaspase-8, -9 and -3, and the cleavage of poly(ADP-ribose) polymerase (PARP). In addition, the involvement of p16(INK4a) in this apoptotic induction was demonstrated using A549 cells with a homozygous deletion of p16(INK4a). Based on these results, we conclude that MCS-5A is a candidate therapeutic agent for the treatment of human promyelocytic leukemia via the up-regulation of p16(INK4a).

The influence of bioactive oxylipins from marine diatoms on invertebrate reproduction and development

Diatoms are one of the main primary producers in aquatic ecosystems and occupy a vital link in the transfer of photosynthetically-fixed carbon through aquatic food webs. Diatoms produce an array of biologically-active metabolites, many of which have been attributed as a form of chemical defence and may offer potential as candidate marine drugs. Of considerable interest are molecules belonging to the oxylipin family which are broadly disruptive to reproductive and developmental processes. The range of reproductive impacts includes; oocyte maturation; sperm motility; fertilization; embryogenesis and larval competence. Much of the observed bioactivity may be ascribed to disruption of intracellular calcium signalling, induction of cytoskeletal instability and promotion of apoptotic pathways. From an ecological perspective, the primary interest in diatom-oxylipins is in relation to the potential impact on energy flow in planktonic systems whereby the reproductive success of copepods (the main grazers of diatoms) is compromised. Much data exists providing evidence for and against diatom reproductive effects; however detailed knowledge of the physiological and molecular processes involved remains poor. This paper provides a review of the current state of knowledge of the mechanistic impacts of diatom-oxylipins on marine invertebrate reproduction and development.

PI3K and ERK 1-2 regulate early stages during head regeneration in hydra

Different signaling systems coordinate and regulate the development of a multicellular organism. In hydra, the canonical Wnt pathway and the signal transduction pathways mediated by PKC and Src regulate early stages of head formation. In this paper, we present evidence for the participation of a third pathway, the PI3K-PKB pathway, involved in this process. The data presented here are consistent with the participation of ERK 1-2 as a point of convergence for the transduction pathways mediated by PKC, Src and PI3K for the regulation of the regeneration of the head in hydra. The specific developmental point regulated by them appears to be the commitment of tissue at the apical end of the regenerate to form the head organizer.

Multifunctional drug treatment in neurotrauma

Although the concepts of secondary injury and neuroprotection after neurotrauma are experimentally well supported, clinical trials of neuroprotective agents in traumatic brain injury or spinal cord injury have been disappointing. Most strategies to date have used drugs directed toward a single pathophysiological mechanism that contributes to early necrotic cell death. Given these failures, recent research has increasingly focused on multifunctional (i.e., multipotential, pluripotential) agents that target multiple injury mechanisms, particularly those that occur later after the insult. Here we review two such approaches that show particular promise in experimental neurotrauma: cell cycle inhibitors and small cyclized peptides. Both show extended therapeutic windows for treatment and appear to share at least one important target.

Maize D4;1 and D5 cyclin proteins in germinating maize. Associated kinase activity and regulation by phytohormones

We have previously reported the expression of four different maize D cyclins during seed germination and showed that cytokinins and auxins stimulate the expression of every cyclin in a differential way. In this paper we characterize the behavior at the protein level of two of these cyclins, CycD5 and CycD4;1. Antibodies were raised against CycD5;2 (which very likely also recognizes D5;1) and CycD4;1 and Western blot studies demonstrated that neither BA nor indol-3 acetic acid (IAA) stimulate cyclin accumulation during germination, compared with control levels. However, phytohormones, particularly IAA, modify the kinase activity associated to D cyclins preferentially at early hours of germination. The associated kinase moiety to D cyclins appears to be of a Cdk-A type because this protein immunoprecipitates with D cyclins and because kinase activity is strongly inhibited by both olomoucine and also by a peptide corresponding to the carboxy end of a maize kip related protein (KRP) protein. There is thus no correlation between mRNA and protein expression for these maize D cyclins during seed germination, although phytohormones may stimulate a signaling cascade that stimulates activation of protein kinase activity in cyclin-Cdk complexes.

A tyrosine kinase inhibitor, beta-hydroxyisovalerylshikonin, induced apoptosis in human lung cancer DMS114 cells through reduction of dUTP nucleotidohydrolase activity

Apoptotic cell death was induced in human lung cancer DMS114 cells by treatment with beta-hydroxyisovalerylshikonin (beta-HIVS), an ATP-noncompetitive inhibitor of protein tyrosine kinases. Changes in phosphoprotein profiles were analyzed by two-dimensional-polyacrylamide gel electrophoresis (2D-PAGE) after the cells were treated with beta-HIVS. One spot on the 2D gel showed a marked decrease in intensity and the corresponding protein was identified by mass spectrometry as dUTP nucleotidohydrolase (dUTPase). The beta-HIVS-induced decrease of dUTPase in the phosphoprotein fraction of DMS114 cells was confirmed using immunoblotting. Treatment of the cells with beta-HIVS-induced rapid reduction of dUTPase activity. An antioxidant N-acetyl-cysteine inhibited both the reduction of phosphorylated dUTPase and the induction of apoptosis by beta-HIVS treatment of DMS114 cells. Introduction of siRNA directed against dUTPase mRNA into DMS114 cells enhanced the susceptibility of beta-HIVS-induced apoptosis. Treatment of DMS114 cells with beta-HIVS and 5-fluorouracil, a specific inhibitor of thymidylate synthase used as a chemotherapeutic drug, revealed the synergistic effects of these drugs on the inhibition of cell growth. These results suggest that dUTPase activity is one of the crucial factors involved in apoptotic cell death in lung cancer cells.

Role of Cell Cycle Proteins in CNS Injury

Following trauma or ischemia to the central nervous system (CNS), there is a marked increase in the expression of cell cycle-related proteins. This up-regulation is associated with apoptosis of post-mitotic cells, including neurons and oligodendrocytes, both in vitro and in vivo. Cell cycle activation also induces proliferation of astrocytes and microglia, contributing to the glial scar and microglial activation with release of inflammatory factors. Treatment with cell cycle inhibitors in CNS injury models inhibits glial scar formation and neuronal cell death, resulting in substantially decreased lesion volumes and improved behavioral recovery. Here we critically review the role of cell cycle pathways in the pathophysiology of experimental stroke, traumatic brain injury and spinal cord injury, and discuss the potential of cell cycle inhibitors as neuroprotective agents.

Differing mechanisms of cAMP- versus seawater-induced oocyte maturation in marine nemertean worms I. The roles of serine/threonine kinases and phosphatases

Unlike in most animals, oocytes of marine nemertean worms initiate maturation (=germinal vesicle breakdown, GVBD) following an increase, rather than a decrease, in intraoocytic cAMP. To analyze how serine/threonine (Ser/Thr) kinase cascades involving mitogen-activated protein kinase (MAPK), maturation-promoting factor (MPF), cAMP-dependent protein kinase (PKA), and phosphatidylinositol 3-kinase (PI3K) regulate nemertean GVBD, oocytes of Cerebratulus sp. were treated with pharmacological modulators and stimulated with cAMP-elevating drugs or seawater (SW) alone. Both cAMP elevators and SW triggered GVBD while activating MAPK, its target p90Rsk, and MPF. Similarly, neither cAMP- nor SW-induced GVBD was affected by several Ser/Thr phosphatase inhibitors, and both stimuli apparently accelerated GVBD via a MAPK-independent, PI3K-dependent mechanism. However, inhibitors of Raf-1, a kinase that activates MAPK kinase, blocked GVBD and MAPK activation during SW-, but not cAMP-induced maturation. In addition, MPF blockers more effectively reduced GVBD and MAPK activity in SW versus in cAMP-elevating treatments. Moreover, the two maturation-inducing stimuli yielded disparate patterns of PKA-related MAPK activations and phosphorylations of putative PKA substrates. Collectively, such findings suggest that in maturing oocytes of Cerebratulus sp., Ser/Thr kinase cascades differ during cAMP- versus SW-induced GVBD in several ways, including MAPK activation modes, MPF-feedback loops, and PKA-related signaling pathways. Additional differences in cAMP- versus SW-induced oocyte maturation are also described in the accompanying study that deals with the roles of tyrosine kinase signaling during GVBD.

Cyclin dependent kinase inhibitors prevent apoptosis of postmitotic mouse motoneurons

Recent evidence suggests that apoptosis in post-mitotic neurons involves an aborted attempt of cells to re-enter the cell cycle which is characterized by increased expression of cyclins, such as cyclin D1, prior to death. However, such cyclins activation prior to apoptotic cell death remains controversial. Many neurological disorders are characterized by neuronal loss, particularly amyotrophic lateral sclerosis (ALS). ALS is a motoneuronal degenerative condition in which motoneuron loss could be due to an inappropriate return of these cells in the cell cycle. In the present study, we observed that deprivation of neurotrophic factor in purified motoneuron cultures induces an apoptotic pathway. After neurotrophic factor withdrawal, DAPI (4,6-diamidin-2-phenylindol dichlorohydrate) staining revealed the presence of nuclear condensation, DNA fragmentation, and perinuclear apoptotic body. Similarly, release of apoptotic microparticles and activation of caspases-3 and -9 were observed within the first hours following neurotrophic factor withdrawal. Next, we tested whether inhibition of cell cycle-related cyclin-dependent kinases (cdks) can prevent motoneuronal cell death. We showed that three cdk inhibitors, olomoucine, roscovitine and flavopiridol, suppress the death of motoneurons. Finally, we observed early increases in cyclin D1 and cyclin E expression after withdrawal of neurotrophic factors. These findings support the hypothesis that after removal of trophic support, post-mitotic neuronal cells die due to an attempt to re-enter the cell cycle in an uncoordinated and inappropriate manner.

Involvement of Bcl-XL deamidation in E1A-mediated cisplatin sensitization of ovarian cancer cells

The adenovirus E1A protein has been shown to be involved in the potentiation of apoptosis induced by chemotherapeutic agents, yet the molecular events of E1A-mediated apoptosis are not very clear. A recent report has suggested that deamidation of the Bcl-X(L) protein inhibits its antiapoptotic ability and leads to apoptosis induced by alkylating agents in Rb-deficient tumor cells. Since Rb is known to interact with E1A, which interrupts Rb's normal function, we examined Bcl-X(L) deamidation and cell death induced by cisplatin in E1A transfectants. We found that the E1A transfectants became sensitive to cisplatin-induced apoptosis compared to the parental cells, SKOV3.ip1. Our data show that cisplatin treatment induced the modification of Bcl-X(L) in the E1A transfectants in dosage and time-dependent manner. Furthermore, phosphatase treatment had no effect on the level of Bcl-X(L) modification, whereas alkaline lysis buffer appeared to induce the same modification of Bcl-X(L). Ectopic expression of the deamidated forms of Bcl- X(L) in SKOV3.ip1 cells revealed that the modification to the Bcl- X(L) protein molecules was deamidation. Expression of the E1A mutant (dl1108) which contains deletion at CR2 domain suppressed Bcl-X(L) deamidation and apoptosis induced by cisplatin. We also found that expression of the nondeamidated Bcl-X(L) protected E1A transfectants from apoptosis. These findings suggest that Bcl-X(L) deamidation contributes to E1A-mediated cisplatin sensitization in SKOV3.ip1 cells.

Cdk2 activity is dispensable for triggering replicon initiation after transient hypoxia in T24 cells

We examined whether the fast release of replicon initiation after sudden O2 recovery of hypoxically incubated mammalian cells depends on kinase activity of Cdk2. We used a system based on starved/refed T24 cells elaborated previously for such investigations [van Betteraey-Nikoleit M, Eisele KH, Stabenow D and Probst H (2003) Eur J Biochem270, 3880-3890]. Cells subjected to hypoxia concurrently with refeeding accumulate the G1 DNA content within 5-6 h. In this state they are ready to perform, within 1-2 min after O2 recovery, a burst of replicon initiations that marks the start of a synchronous S-phase. We found that Cdk2 binds to the chromatin fraction within 4-6 h after refeeding with fresh medium, irrespective of whether the cells were incubated normoxically or hypoxically. However, inhibition of Cdk2 by olomoucine, roscovitine or the Cdk2/cyclin inhibitory peptide II had no influence on the synchronous burst of replicon initiations. Cdc6 and pRb, possible targets of Cdk2 phosphorylation, behaved differentially. Inhibition did not affect phosphorylation of Cdc6 after reoxygenation, whilst chromatin bound pRb remained hypophosphorylated beyond the initiation burst. Thus, neither Cdk2 activity, though present at the end of the hypoxic period, nor pRb phosphorylation are necessary for releasing the burst of replicon initiations upon oxygen recovery. Consequentially, Cdk2 dependent phosphorylation(s) cannot be a critical trigger of replicon initiation in response to reoxygenation after several hours of hypoxia, at least in the T24 cells studied.

The therapeutic potential of targeting the cell cycle

With the advent of modern molecular genetics, molecular biology and biochemistry has come a revolution in oncology drug discovery research. We are rapidly developing an increased understanding in the mechanisms driving cellular proliferation, transformation, differentiation and metastasis. The hope is that from these advances will emerge novel therapeutics that are more specific, more efficacious and less toxic than their predecessors. Uncontrolled proliferation is a hallmark of a cancer cell. Over the past two decades it has become increasingly clear that molecules that directly control cell cycle progression accumulate defects during tumourigenesis. These defects can result in the loss of checkpoint control and/or the inappropriate activation of the 'drivers' of cell cycle progression, the cyclin-dependent kinases (cdks). This review will describe the recent advances in our understanding of cell cycle regulation and its relation to tumourigenesis, and highlight the potential for the development of novel anticancer therapeutics.

New antiproliferative benzoindolinothiazepines derivatives

New benzoindolinothiazepines containing a piperazine moiety are described as potent antiproliferative agents against PC3 human prostatic cell lines. This activity could be explained by an accumulation of cells in G1 phase.

Changes in the amount of cytoplasmic inclusions in mouse oocytes during meiotic maturation in vivo and in vitro

Background and aims: The changes in cytoplasmic inclusions during meiotic maturation have only been examined in porcine oocytes. In the present study, the amount and the number of cytoplasmic inclusions (glycogen granules, lipid droplets and fibrous structures) were examined in mouse oocytes in the process of in vivo and in vitro maturation. For those inclusions that changed in amount during maturation, we also examined their content in oocytes treated with olomoucine, an inhibitor of cyclin-dependent kinase, in order to clarify the relationship between nuclear maturation and changes in the inclusions. Methods: Nuclear maturation in the oocytes cultured for various periods and those collected from antral follicles and oviducts was examined after staining with aceto-orcein. For the demonstration of glycogen granules and lipid droplets, oocytes were stained with periodic acid-Schiff or Sudan IV. Fibrous structures in the oocytes were observed under an electron microscope. Results: The amount of glycogen granules, Sudanophilic lipid droplets and fibrous structures did not change in the oocytes matured in vivo and in vitro, whereas the number of the lipid droplets increased during maturation. In the oocytes treated with olomoucine, the resumption of nuclear maturation was inhibited, whereas the increase in the number of Sudanophilic lipid droplets was not inhibited. Conclusion: Present findings suggest that the increase in the number of Sudanophilic lipid droplets occurs in the cytoplasm of mouse oocytes during maturation, regardless of in vivo or in vitro maturation, and that such the change in the inclusion is not related to nuclear maturation. (Reprod Med Biol 2004; 3: 231-236).

Isolation of a dinoflagellate mitotic cyclin by functional complementation in yeast

Dinoflagellates are protists with permanently condensed chromosomes that lack histones and whose nuclear membrane remains intact during mitosis. These unusual nuclear characters have suggested that the typical cell cycle regulators might be slightly different than those in more typical eukaryotes. To test this, a cyclin has been isolated from the dinoflagellate Gonyaulax polyedra by functional complementation in cln123 mutant yeast. This GpCyc1 sequence contains two cyclin domains in its C-terminal region and a degradation box typical of mitotic cyclins. Similar to other dinoflagellate genes, GpCyc1 has a high copy number, with approximately 5000 copies found in the Gonyaulax genome. An antibody raised against the N-terminal region of the GpCYC1 reacts with a 68kDa protein on Western blots that is more abundant in cell cultures enriched for G2-phase cells than in those containing primarily G1-phase cells, indicating its cellular level follows a pattern expected for a mitotic cyclin. This is the first report of a cell cycle regulator cloned and sequenced from a dinoflagellate, and our results suggest control of the dinoflagellate cell cycle will be very similar to that of other organisms.

Changes in the activities of hydroxysteroid dehydrogenases in mouse oocytes during meiotic maturation

The activities of hydroxysteroid dehydrogenases (HSDs) were histochemically demonstrated in mouse oocytes in the process of maturation in vivo and in vitro, and the changes in steroid metabolism during meiotic maturation and also the relationship between nuclear maturation and changes in steroid metabolism in the cytoplasm were examined. In mouse oocytes 0 h after human chorionic gonadotrophin (hCG) injection, the activities of Delta(5)-3beta-HSD (with DHA, pregnenolone and 17alpha-hydroxypregnenolone as the substrates), 17beta-HSD (estradiol-17beta and testosterone) and 20beta-HSD (17alpha-hydroxyprogesterone and 20beta-hydroxyprogesterone) were observed in 87 to 97% of those, but that of 20alpha-HSD (20alpha-hydroxyprogesterone) was not. The percentages of oocytes showing the activities of Delta(5)-3beta-HSD, 17beta-HSD and 20beta-HSD did not change during maturation in vivo or in vitro. Oocytes with 20alpha-HSD activity appeared 4 h after the hCG injection or after culture for 4 h and the rates of those reached 92 and 100%, respectively, 14 h after the hCG injection or after culture for 14 h. In oocytes cultured for 8 h with olomoucine or 3-isobutyl-1-methylxanthine, nuclei were almost all in the germinal vesicle stage, and activity of 20alpha-HSD was observed in 84 and 89% of the treated oocytes, respectively. On the other hand, 81% of control oocytes showed 20alpha-HSD activity, with no significant difference from the rate for the olomoucine- or 3-isobutyl-1-methylxanthine-treated oocytes. The present findings suggested that the metabolic abilities of progesterone, 17alpha-hydroxyprogesterone, 17alpha,20beta-dihydroxyprogesterone, 20beta-hydroxyprogesterone, androgen and estradiol-17beta in the cytoplasm are constantly present in mouse oocytes in the process of maturation in vivo and in vitro. The results also suggested that the metabolic ability of 20alpha-hydroxyprogesterone in mouse oocytes increases during maturation, but the change in the metabolic ability of such a steroid is not related to nuclear maturation.

PEP8-TAT2, a membrane-permeable peptide, inhibits cyclin-Cdk2 activity in HeLa cells

Here we show that the PEP8-TAT2 peptide is effectively transduced into HeLa cells and that it inhibits cellular cyclin-Cdk2 activity. Like the PEP8 peptide, the PEP8-TAT2 peptide inhibits Cdk2 activity in vitro with an IC50 value of 5 nM, as determined by an immuno-complex kinase assay. It also inhibits DNA synthesis in and proliferation of cultured HeLa cells by arresting cell cycle at the G1/S transition. Further, the PEP8-TAT2 peptide inhibits cell death-associated Cdk2 activity and thereby prevents apoptotic progression in paclitaxel-treated cells. We propose that this inhibitor peptide is an effective agent to suppress the proliferation of human cancer cells, as well as apoptotic progression, by blocking cellular cyclin-dependent Cdk kinase activity.

Synthesis and biological activity of N-aryl-2-aminothiazoles: potent pan inhibitors of cyclin-dependent kinases

N-Aryl aminothiazoles 6-9 were prepared from 2-bromothiazole 5 and found to be CDK inhibitors. In cells they act as potent cytotoxic agents. Selectivity for CDK1, CDK2, and CDK4 was dependent of the nature of the N-aryl group and distinct from the CDK2 selective N-acyl analogues. The N-2-pyridyl analogues 7 and 19 showed pan CDK inhibitory activity. Elaborated analogues 19 and 23 exhibited anticancer activity in mice against P388 murine leukemia. The solid-state structure of 7 bound to CDK2 shows a similar binding mode to the N-acyl analogues.

An inhibition of cyclin-dependent kinases that lengthens, but does not arrest, neuroepithelial cell cycle induces premature neurogenesis

The G1 phase of the cell cycle of neuroepithelial cells, the progenitors of all neurons of the mammalian central nervous system, has been known to lengthen concomitantly with the onset and progression of neurogenesis. We have investigated whether lengthening of the G1 phase of the neuroepithelial cell cycle is a cause, rather than a consequence, of neurogenesis. As an experimental system, we used whole mouse embryo culture, which was found to exactly reproduce the temporal and spatial gradients of the onset of neurogenesis occurring in utero. Olomoucine, a cell-permeable, highly specific inhibitor of cyclin-dependent kinases and G1 progression, was found to significantly lengthen, but not arrest, the cell cycle of neuroepithelial cells when used at 80 microM. This olomoucine treatment induced, in the telencephalic neuroepithelium of embryonic day 9.5 to 10.5 mouse embryos developing in whole embryo culture to embryonic day 10.5, (i) the premature up-regulation of TIS21, a marker identifying neuroepithelial cells that have switched from proliferative to neuron-generating divisions, and (ii) the premature generation of neurons. Our data indicate that lengthening G1 can alone be sufficient to induce neuroepithelial cell differentiation. We propose a model that links the effects of cell fate determinants and asymmetric cell division to the length of the cell cycle.

Phosphorylation of human Fen1 by cyclin-dependent kinase modulates its role in replication fork regulation

Cyclin-dependent kinase (Cdk) Cdk1-Cyclin A can phosphorylate Flap endonuclease 1 (Fen1), a key-enzyme of the DNA replication machinery, in late S phase. Cdk1-cyclin A forms a complex in vitro and in vivo with Fen1. Furthermore, Fen1 phosphorylation is detected in vivo and depends upon Cdks activity. As a functional consequence of phosphorylation by Cdk1-Cyclin A in vitro, endo- and exonuclease activities of Fen1 are reduced whereas its DNA binding is not affected. Moreover, phosphorylation of Fen1 by Cdk1-Cyclin A abrogates its proliferating cell nuclear antigen (PCNA) binding thus preventing stimulation of Fen1 by PCNA. Concomitantly, human cells expressing the S187A mutant defective for Cdk1-Cyclin A phosphorylation accumulate in S phase consistent with a failure in cell cycle regulation through DNA replication. Our results suggest a novel regulatory role of Cdks onto the end of S phase by targeting directly a key enzyme involved in DNA replication.

Roscovitine and other purines as kinase inhibitors. From starfish oocytes to clinical trials

This article reviews the steps that have led us from very fundamental research on the cell division cycle, investigated with the starfish oocyte model, to the identification of drugs now being evaluated against cancer in the clinic. Among protein kinases activated during entry in M phase, the cyclin-dependent kinase CDK1/cyclin B was initially identified as a universal M-phase promoting factor. It was then used as a screening target to identify pharmacological inhibitors. The first inhibitors to be discovered were 6-dimethylaminopurine and isopentenyladenine, from which more potent and selective inhibitors were optimized (olomoucine, roscovitine, and purvalanols). All were cocrystallized with CDK2 and found to localize in the ATP-binding pocket of the kinase. Their selectivity and cellular effects have been thoroughly investigated. Following encouraging results obtained in preclinical tests and favorable pharmacological properties, one of these purines, roscovitine (CYC202), is now entering phase II clinical trials against cancers and phase I clinical tests against glomerulonephritis. CDK inhibitors are also being evaluated, at the preclinical level, for therapeutic use against neurodegenerative diseases, cardiovascular disorders, viral infections, and parasitic protozoa. This initially unexpected scope of potential applications and the large number and chemical diversity of pharmacological inhibitors of CDKs now available constitute a very encouraging stimulus to pursue the search for optimization and characterization of protein kinase inhibitors, from which we expect numerous therapeutic applications.

The cell cycle: a review of regulation, deregulation and therapeutic targets in cancer

The cell cycle is controlled by numerous mechanisms ensuring correct cell division. This review will focus on these mechanisms, i.e. regulation of cyclin-dependent kinases (CDK) by cyclins, CDK inhibitors and phosphorylating events. The quality checkpoints activated after DNA damage are also discussed. The complexity of the regulation of the cell cycle is also reflected in the different alterations leading to aberrant cell proliferation and development of cancer. Consequently, targeting the cell cycle in general and CDK in particular presents unique opportunities for drug discovery. This review provides an overview of deregulation of the cell cycle in cancer. Different families of known CDK inhibitors acting by ATP competition are also discussed. Currently, at least three compounds with CDK inhibitory activity (flavopiridol, UCN-01, roscovitine) have entered clinical trials.

Synthesis and biological evaluations of pyrazolo[3,4-d]pyrimidines as cyclin-dependent kinase 2 inhibitors

A series of 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines 15-19, 30-38 capable of selectively inhibiting CDK2 activity were synthesized by derivatization at C-4, C-6 and N-1 with various amines and lower alkyl groups. For above synthetic compounds, biological evaluation was carried out and structure-activity relationship was examined. In our series, 4-anilino compounds exhibited better CDK2 inhibitory activity and antitumor activity compared to 4-benzyl compounds. The compounds 33a,b having a 3-fluoroaniline group at C-4 showed comparable or superior CDK2 inhibitory activity to those of olomoucine and roscovitine as reference compounds. In general, the unsubstituted compounds (30a,b, 33a,b, 36a,b) at N-1 possessed higher potency than the substituted compounds (32a,b, 34a,b) for the CDK2 inhibitory activity. As for EGFR inhibitory activity, most compounds didnot have a significant activity. The compounds 32a,b exhibited potent cell growth inhibitory activity against human cancer cell lines, but their CDK2 inhibitory activities were slightly poorer than olomoucine.

1H-Pyrazolo[3,4-b]pyridine inhibitors of cyclin-dependent kinases

1H-Pyrazolo[3,4-b]pyridine 3 (SQ-67563) has been shown to be a potent, selective inhibitor of CDK1/CDK2 in vitro. In cells 3 acts as a cytotoxic agent with the ability to block cell cycle progression and/or induce apoptosis. The solid state structure of 3 bound to CDK2 shows 3 resides coincident with the ATP purine binding site and forms important H-bonding interactions with Leu83 on the protein backbone.

Studies of the cell cycle of in vitro cultured skin fibroblasts in goats: work in progress

The effect of serum starvation and olomoucine treatment on the cell cycle and apoptosis of goat skin fibroblasts cultured in vitro is reported in this paper. The cells were obtained from the ear of a female goat 1.5 years of age. Analysis of cell cycle distribution by fluorescence-activated cell sorting (FACS) showed that 3.4, 60.8 and 15.1% of normally cycling cells were at G1, G0 and S phase, respectively. Serum starvation for 1, 3 and 5 days arrested 70.1, 70.2 and 83.4% cells, respectively, at G0/G1 phase. Seventy-eight percent of confluent cells were at G0/G1 stage, but in contrast to the serum starved group, this high percentage of G0/G1 cells was mainly associated with G1 cells. Of cells not deprived of serum, 73.6% were arrested at G1/G0 when treated with 100 microM olomoucine for 9 h compared to 85.5% of cells that had been starved of serum for 2 days (co-inhibition) (P<0.01). After co-inhibition, 45% of cells entered S phase when re-cultured in normal medium for 5 h, indicating that the inhibition was reversible. Under normal culture conditions, 1.2% of cells underwent apoptosis. Serum starvation for 1, 2, 3, 5 and 10 days caused apoptosis in 1.7, 3.9, 4.5, 11.7 and 90.3% of cells, respectively. Treatment with 100 microM olomoucine for 9h did not increase the number of apoptotic cells significantly (1.9%, P>0.05). When cells were co-inhibited, 4.1% of cells underwent apoptosis. In conclusion, although serum withdrawal for 5 days or more effectively arrested cells at G0/G1 stages, it increased apoptosis of cells significantly. However, co-inhibition by serum withdrawal and olomoucine treatment was found to be an appropriate treatment to obtain more healthy G0/G1 cells based on the low percentage of apoptotic cells after treatment.

In vitro and in vivo antitumor properties of the cyclin dependent kinase inhibitor CYC202 (R-roscovitine)

CDK2 inhibitors have been proposed as effective anti-cancer therapeutics. We show here that CYC202 (R-roscovitine) is a potent inhibitor of recombinant CDK2/cyclin E kinase activity (IC(50) = 0.10 microM) with an average cytotoxic IC(50) of 15.2 microM in a panel of 19 human tumour cell lines, and we also demonstrate selectivity for rapidly proliferating cells over non-proliferating cells. A study of the cell cycle effects of CYC202 in Lovo colorectal carcinoma cells showed that the major effect was not the predicted arrest in one part of the cycle, but rather an induction of cell death from all compartments of the cell cycle. The maximum tolerated dose given intravenously to mice was in excess of 20 mg/kg. Doses up to 2,000 mg/kg were tolerated when administered orally in mice. Following repeated intraperitoneal administration (3 times daily for 5 days) of 100 mg/kg to nude mice bearing the Lovo human colorectal tumour, CYC202 induced a significant antitumour effect with a 45% reduction in tumour growth compared to controls. A second experiment using the human uterine xenograft MESSA-DX5 treated with orally administered CYC202 (500 mg/kg 3 times daily for 4 days) also exhibited a significant reduction in the rate of growth of the tumour (62%). These data, showing enzyme and cellular potency together with antitumour activity, confirm the potential of CDK2 inhibitors such as CYC202 as anticancer drugs.

Synthetic inhibitors of CDKs induce different responses in androgen sensitive and androgen insensitive prostatic cancer cell lines

AIMS

Because of the high prevalence of prostatic cancer and the limitations of its treatment, enormous effort has been put into the development of new therapeutic modalities. One potential tool is the use of cyclin dependent kinase (CDK) inhibitors, which are based on the trisubstituted derivatives of purine. The aim of this study was to analyse alterations of the regulatory pathways in both androgen sensitive and androgen insensitive prostatic cancer cell lines (LNCaP and DU-145, respectively) after blockage of the cell cycle by the synthetic CDK inhibitors, olomoucine and bohemine.

METHODS

The effects of olomoucine and bohemine were studied on the following parameters: (1) cell proliferation, by measurement of DNA content; (2) viability, by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) and/or XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) test; and (3) the expression of p53, pRB, Bcl-2, Bax, p16, p21, p27, cyclins A, B, D1, E, p34(cdc2), and the androgen receptor (AR), by western blot analysis.

RESULTS

Both olomoucine and bohemine were potent inhibitors of growth and viability; however, bohemine was two to three times more effective than olomoucine. The sensitivity of LNCaP cells to both agents was significantly higher. After treatment, both cell lines revealed quite different spectra of protein expression.

CONCLUSIONS

These results indicate the existence of specific cell cycle regulating pathways in both cell lines, which may be associated with both p53 and AR status. CDK inhibitors exhibited valuable secondary effects on the expression of numerous regulators and thus may modulate the responsiveness of tumour cells to treatment, including treatment with hormone antagonists.

Inhibition of MEK or cdc2 kinase parthenogenetically activates mouse eggs and yields the same phenotypes as Mos(-/-) parthenogenotes

Mammalian eggs are arrested in metaphase II of meiosis until fertilization. Arrest is maintained by cytostatic factor (CSF) activity, which is dependent on the MOS-MEK-MAPK pathway. Inhibition of MEK1/2 with a specific inhibitor, U0126, parthenogenetically activated mouse eggs, producing phenotypes similar to Mos(-/-) parthenogenotes (premature, unequal cleavages and large polar bodies). U0126 inactivated MAPK in eggs within 1 h, in contrast to the 5 h required after fertilization, while the time course of MPF inactivation was similar in U0126-activated and fertilized eggs. We also found that inactivation of MPF by the cdc2 kinase inhibitor roscovitine induced parthenogenetic activation. Inactivation of MPF by roscovitine resulted in the subsequent inactivation of MAPK with a time course similar to that following fertilization. Notably, roscovitine also produced some Mos(-/-)-like phenotypes, indistinguishable from U0126 parthenogenotes. Simultaneous inhibition of both MPF and MAPK in eggs treated with roscovitine and U0126 produced a very high proportion of eggs with the more severe phenotype. These findings confirm that MEK is a required component of CSF in mammalian eggs and imply that the sequential inactivation of MPF followed by MAPK inactivation is required for normal spindle function and polar body emission.

A potential role for AMP-activated protein kinase in meiotic induction in mouse oocytes

Cyclic adenosine monophosphate (cAMP) has been implicated as an important regulator of meiotic maturation in mammalian oocytes. A decrease in cAMP, brought about by the action of cAMP phosphodiesterase (PDE), is thought to initiate germinal vesicle breakdown (GVB) by the inactivation of cAMP-dependent protein kinase. However, the product of PDE activity, 5'-AMP, is a potent activator of an important regulatory enzyme, AMP-activated protein kinase (AMPK). The aim of this study was to evaluate a possible role for AMPK in meiotic induction, using oocytes obtained from eCG-primed, immature mice. Alpha-1 and -2 isoforms of the catalytic subunit of AMPK were detected in both oocytes and cumulus cells. When 5-aminoimidazole-4-carboxamide 1-beta-d-ribofuranoside (AICA riboside), an activator of AMPK, was tested on denuded oocytes (DO) and cumulus cell-enclosed oocytes (CEO) maintained in meiotic arrest by dbcAMP or hypoxanthine, GVB was dose-dependently induced. Meiotic induction by AICA riboside in dbcAMP-supplemented medium was initiated within 3 h in DO and 4 h in CEO and was accompanied by increased AMPK activity in the oocyte. AICA riboside also triggered GVB when meiotic arrest was maintained with hypoxanthine, 8-AHA-cAMP, guanosine, or milrinone, but was ineffective in olomoucine- or roscovitine-arrested oocytes, indicating that it acts upstream of maturation-promoting factor. Adenosine monophosphate dose-dependently stimulated GVB in DO when meiotic arrest was maintained with dbcAMP or hypoxanthine. This effect was not mimicked by other monophosphate or adenosine nucleotides and was not affected by inhibitors of ectophosphatases. Combined treatment with adenosine and deoxycoformycin, an adenosine deaminase inhibitor, stimulated GVB in dbcAMP-arrested CEO, suggesting AMPK activation due to AMP accumulation. It is concluded that phosphodiesterase-generated AMP may serve as a transducer of the meiotic induction process through activation of AMPK.