Cantharidin-induced mitotic arrest is associated with the formation of aberrant mitotic spindles and lagging chromosomes resulting, in part, from the suppression of PP2Aalpha.
(33/89)Cantharidin, a natural vesicant, inhibits the activity of several PPP family phosphatases, displays antitumor activity, and induces apoptosis in many types of tumor cells. However, the molecular mechanisms underlying the antitumor activity of cantharidin are not clear. Here, dose-response studies confirm a strong correlation between the suppression of phosphatase activity and cell death. Flow cytometry analysis indicates that before apoptosis, cantharidin delays cell cycle progression following DNA replication with no apparent effect on G(1)-S or S-G(2) phase progression. In contrast, studies with double thymidine-synchronized populations of cells indicate that cantharidin can rapidly arrest growth when added during G(2) or early M phase. Immunostaining indicates that cell cycle arrest occurs before the completion of mitosis and is associated with the appearance of aberrant mitotic spindles. Live cell imaging with time-lapse microscopy shows that cantharidin disrupts the metaphase alignment of chromosomes and produces a prolonged mitotic arrest, with the onset of apoptosis occurring before the onset of anaphase. To explore the contribution of individual phosphatases, antisense oligonucleotides and small interfering RNA were developed to suppress the expression of cantharidin-sensitive phosphatases. The suppression of PP2Aalpha, but not PP2Abeta, is sufficient to induce metaphase arrest, during which time lagging chromosomes are observed moving between the spindle poles and the metaphase plate. Immunostaining revealed slightly abnormal, yet predominately bipolar, mitotic spindles. Nonetheless, after a 10- to 15-hour delay, the cells enter anaphase, suggesting that an additional cantharidin-sensitive phosphatase is involved in the progression from metaphase into anaphase or to prevent the onset of apoptosis in cells arrested during mitosis. (+info)
Small-molecule inhibitors of ser/thr protein phosphatases: specificity, use and common forms of abuse.
(34/89)Natural product extracts have proven to be a rich source of small molecules that potently inhibit the catalytic activity of certain PPP-family ser/thr protein phosphatases. To date, the list of inhibitors includes okadaic acid (produced by marine dinoflagelates, Prorocentrum sp. and Dinophysis sp.), calyculin A, dragmacidins (isolated from marine sponges), microcystins, nodularins (cyanobacteria, Microcystis sp. and Nodularia sp.), tautomycin, tautomycetin, cytostatins, phospholine, leustroducsins, phoslactomycins, fostriecin (soil bacteria, Streptomyces sp.), and cantharidin (blister beetles, approx 1500 species). Many of these compounds share structural similarities, and several have become readily available for research purposes. Here we will review the specificity of available inhibitors and present methods for their use in studying sensitive phosphatases. Common mistakes in the employment of these compounds will also be addressed briefly, notably the widespread misconception that they only inhibit the activity of PP1 and PP2A. Inhibitors of PP2B (calcineurin) will only be mentioned in passing, except to state that, in our hands, cypermethrin, deltamethrin, and fenvalerate, which are sold as potent inhibitors of PP2B, do not inhibit the catalytic activity of PP2B. (+info)
Pharmacokinetics of dalbavancin in plasma and skin blister fluid.
(35/89)OBJECTIVES: Dalbavancin is a novel lipoglycopeptide antibiotic in development for the treatment of complicated skin and skin structure infections (cSSSIs) caused by Gram-positive bacteria. The aim of the present study was to assess the penetration of dalbavancin into skin blister fluid. METHODS: Nine healthy subjects (five males; ranging in age from 26 to 57 years) were administered a single 30 min intravenous infusion of dalbavancin at a dose of 1000 mg. Skin blisters were induced by application of cantharidin ointment. Plasma and blister fluid samples were collected over 7 days post-dose, and concentrations of dalbavancin were assessed by a validated LC/MS/MS assay. Pharmacokinetics were determined by non-compartmental methods, and drug penetration was assessed based on the ratio of area under the curve (AUC) in the blister fluid versus plasma for each subject. RESULTS: The mean (SD) peak concentration of dalbavancin in plasma and blister fluid was 285 (31.1) and 67.3 (18.2) mg/L, respectively; the corresponding AUC(Day 7) values were 10 806 (1926) and 6438 (1238) mg . h/L, respectively. The mean (SD) penetration of dalbavancin into blister fluid was 59.6% (6.3%). By Day 7, the mean concentration of dalbavancin in plasma and blister fluid was 46.5 and 30.3 mg/L, respectively. CONCLUSIONS: Dalbavancin concentrations in blister fluid remained well above the MIC90 values for pathogens commonly implicated in cSSSIs such as Staphylococcus aureus, including methicillin-resistant S. aureus (MIC90 = 0.06 mg/L) and beta-haemolytic streptococci (MIC90 = 0.03 mg/L) through Day 7. These pharmacokinetic data support the use of dalbavancin in the treatment of cSSSIs caused by susceptible Gram-positive pathogens. (+info)
Natural variation in the thermotolerance of neural function and behavior due to a cGMP-dependent protein kinase.
(36/89)Although it is acknowledged that genetic variation contributes to individual differences in thermotolerance, the specific genes and pathways involved and how they are modulated by the environment remain poorly understood. We link natural variation in the thermotolerance of neural function and behavior in Drosophila melanogaster to the foraging gene (for, which encodes a cGMP-dependent protein kinase (PKG)) as well as to its downstream target, protein phosphatase 2A (PP2A). Genetic and pharmacological manipulations revealed that reduced PKG (or PP2A) activity caused increased thermotolerance of synaptic transmission at the larval neuromuscular junction. Like synaptic transmission, feeding movements were preserved at higher temperatures in larvae with lower PKG levels. In a comparative assay, pharmacological manipulations altering thermotolerance in a central circuit of Locusta migratoria demonstrated conservation of this neuroprotective pathway. In this circuit, either the inhibition of PKG or PP2A induced robust thermotolerance of neural function. We suggest that PKG and therefore the polymorphism associated with the allelic variation in for may provide populations with natural variation in heat stress tolerance. for's function in behavior is conserved across most organisms, including ants, bees, nematodes, and mammals. PKG's role in thermotolerance may also apply to these and other species. Natural variation in thermotolerance arising from genes involved in the PKG pathway could impact the evolution of thermotolerance in natural populations. (+info)
Type 2A phosphoprotein phosphatase is required for asexual development and pathogenesis of Sclerotinia sclerotiorum.
(37/89)Sclerotinia sclerotiorum is a necrotrophic, omnivorous plant pathogen with worldwide distribution. Sclerotia of S. sclerotiorum are pigmented, multihyphal structures that play a central role in the life and infection cycles of this pathogen. Plant infection depends on the formation of melanin-rich infection cushions, and secretion of hydrolytic enzymes and oxalic acid. Type 2A Ser/Thr phosphatases (PP2As) are involved in the regulation of a variety of cellular process. In the presence of cantharidin, a PP2A-specific inhibitor, hyphal elongation and sclerotia numbers were impaired whereas sclerotial size increased. We partially inactivated PP2A by antisense expression of the gene (pph1) encoding the PP2A catalytic subunit. When antisense expression was induced, almost complete cessation of fungal growth was observed, indicative of a crucial role for PP2A in fungal growth. RNAi-based gene silencing was employed to alter the expression of the 55-kDa R2 (B regulatory subunit). Isolates in which rgb1 RNA levels were decreased were slow growing, but viable. Melanin biosynthesis, infection-cushion production, and pathogenesis were significantly impaired in the rgb1 mutants, yet theses mutants were pathogenic on wounded leaves. Reduced ERK (extracellular signal-regulated kinases)-like mitogen-activated protein kinase (MAPK) function conferred a reduction in NADPH oxidase and PP2A activity levels, suggesting a functional link between MAPK, reactive oxygen species, and PP2A activity in S. sclerotiorum. (+info)
Crystal structures of protein phosphatase-1 bound to nodularin-R and tautomycin: a novel scaffold for structure-based drug design of serine/threonine phosphatase inhibitors.
PINOID kinase regulates root gravitropism through modulation of PIN2-dependent basipetal auxin transport in Arabidopsis.
Effects of low-dose aspirin on acute inflammatory responses in humans.