Regulation of taurine transport in Ehrlich ascites tumor cells

Summary Taurine influx is inhibited and taurine efflux accelerated when the cell membrane of Ehrlich ascites tumor cells is depolarized. Taurine influx is inhibited at acid pH partly due to the concomitant depolarization of the cell membrane partly due to a reduced availability of negatively charged free carrier. These results are in agreement with a 2Na, 1Cl, 1taurine cotransport system which is sensitive to the membrane potential due to a negatively charged empty carrier. Taurine efflux from Ehrlich cells is stimulated by addition of LTD4 and by swelling in hypotonic medium. Cell swelling in hypotonic medium is known to result in stimulation of the leukotriene synthesis and depolarization of the cell membrane. The taurine efflux, activated by cell swelling, is dramatically reduced when the phospholipase A₂ is inhibited indirectly by addition of the anti-calmodulin drug pimozide, or directly by addition of RO 31-4639. The inhibition is in both cases lifted by addition of LTD₄. The swelling-induced taurine efflux is also inhibited by addition of the 5-lipoxygenase inhibitors ETH 615-139 and NDGA. It is concluded that the swelling-induced activation of the taurine leak pathway involves a release of arachidonic acid from the membrane phospholipids and an increased oxidation of arachidonic acid into leukotrienes via the 5-lipoxygenase pathway. LTD₄ seems to act as a second messenger for the swelling induced activation of the taurine leak pathway either directly or indirectly via its activation of the Cl^– channels, i.e., via a depolarization of the cell membrane.     

Phosphorylation and activation of human cdc25-C by cdc2--cyclin B and its involvement in the self-amplification of MPF at mitosis.

We have investigated the mechanisms responsible for the sudden activation of the cdc2-cyclin B protein kinase before mitosis. It has been found previously that cdc25 is the tyrosine phosphatase responsible for dephosphorylating and activating cdc2-cyclin B. In Xenopus eggs and early embryos a cdc25 homologue undergoes periodic phosphorylation and activation. Here we show that the catalytic activity of human cdc25-C phosphatase is also activated directly by phosphorylation in mitotic cells. Phosphorylation of cdc25-C in mitotic HeLa extracts or by cdc2-cyclin B increases its catalytic activity. cdc25-C is not a substrate of the cyclin A-associated kinases. cdc25-C is able to activate cdc2-cyclin B1 in Xenopus egg extracts and to induce Xenopus oocyte maturation, but only after stable thiophosphorylation. This demonstrates that phosphorylation of cdc25-C is required for the activation of cdc2-cyclin B and entry into M-phase. Together, these studies offer a plausible explanation for the rapid activation of cdc2-cyclin B at the onset of mitosis and the self-amplification of MPF observed in vivo.     

The unexpected long period of elevated CH4 emissions from an inundated fen meadow ended only with the occurrence of cattail (Typha latifolia)

Drainage and agricultural use transform natural peatlands from a net carbon (C) sink to a net C source. Rewetting of peatlands, despite of high methane (CH₄) emissions, holds the potential to mitigate climate change by greatly reducing CO₂ emissions. However, the time span for this transition is unknown because most studies are limited to a few years. Especially, nonpermanent open water areas often created after rewetting, are highly productive. Here, we present 14 consecutive years of CH₄ flux measurements following rewetting of a formerly long-term drained peatland in the Peene valley. Measurements were made at two rewetted sites (non-inundated vs. inundated) using manual chambers. During the study period, significant differences in measured CH₄ emissions occurred. In general, these differences overlapped with stages of ecosystem transition from a cultivated grassland to a polytrophic lake dominated by emergent helophytes, but could also be additionally explained by other variables. This transition started with a rapid vegetation shift from dying cultivated grasses to open water floating and submerged hydrophytes and significantly increased CH₄ emissions. Since 2008, helophytes have gradually spread from the shoreline into the open water area, especially in drier years. This process was periodically delayed by exceptional inundation and eventually resulted in the inundated site being covered by emergent helophytes. While the period between 2009 and 2015 showed exceptionally high CH₄ emissions, these decreased significantly after cattail and other emergent helophytes became dominant at the inundated site. Therefore, CH₄ emissions declined only after 10 years of transition following rewetting, potentially reaching a new steady state. Overall, this study highlights the importance of an integrative approach to understand the shallow lakes CH₄ biogeochemistry, encompassing the entire area with its mosaic of different vegetation forms. This should be ideally done through a study design including proper measurement site allocation as well as long-term measurements.     

Dephosphorylation of cdc25-C by a type-2A protein phosphatase: specific regulation during the cell cycle in Xenopus egg extracts.

We have examined the roles of type-1 (PP-1) and type-2A (PP-2A) protein-serine/threonine phosphatases in the mechanism of activation of p34cdc2/cyclin B protein kinase in Xenopus egg extracts. p34cdc2/cyclin B is prematurely activated in the extracts by inhibition of PP-2A by okadaic acid but not by specific inhibition of PP-1 by inhibitor-2. Activation of the kinase can be blocked by addition of the purified catalytic subunit of PP-2A at a twofold excess over the activity in the extract. The catalytic subunit of PP-1 can also block kinase activation, but very high levels of activity are required. Activation of p34cdc2/cyclin B protein kinase requires dephosphorylation of p34cdc2 on Tyr15. This reaction is catalysed by cdc25-C phosphatase that is itself activated by phosphorylation. We show that, in interphase extracts, inhibition of PP-2A by okadaic acid completely blocks cdc25-C dephosphorylation, whereas inhibition of PP-1 by specific inhibitors has no effect. This indicates that a type-2A protein phosphatase negatively regulates p34cdc2/cyclin B protein kinase activation primarily by maintaining cdc25-C phosphatase in a dephosphorylated, low activity state. In extracts containing active p34cdc2/cyclin B protein kinase, dephosphorylation of cdc25-C is inhibited, whereas the activity of PP-2A (and PP-1) towards other substrates is unaffected. We propose that this specific inhibition of cdc25-C dephosphorylation is part of a positive feedback loop that also involves direct phosphorylation and activation of cdc25-C by p34cdc2/cyclin B. Dephosphorylation of cdc25-C is also inhibited when cyclin A-dependent protein kinase is active, and this may explain the potentiation of p34cdc2/cyclin B protein kinase activation by cyclin A. In extracts supplemented with nuclei, the block on p34cdc2/cyclin B activation by unreplicated DNA is abolished when PP-2A is inhibited or when stably phosphorylated cdc25-C is added, but not when PP-1 is specifically inhibited. This suggests that unreplicated DNA inhibits p34cdc2/cyclin B activation by maintaining cdc25-C in a low activity, dephosphorylated state, probably by keeping the activity of a type-2A protein phosphatase towards cdc25-C at a high level.     

Induction of phagocytic behaviour in human epithelial cells by Escherichia coli cytotoxic necrotizing factor type1

Cytotoxic necrotizing factor type 1 (CNF1) from strains of pathogenic Escherichia coli induces in human epithelial HEp-2 cells, a profound reorganization of the actin cytoskeleton into prominent stress fibres and membrane ruffles. We report here that this process is associated with induction of phagocytic-like activity. CNF1-treated cells acquired the ability to ingest latex beads as well as non-invasive bacteria such as Listeria innocua, which were taken as a model system. Uptake of bacteria was similar to pathogen-induced phagocytosis, since L. innocua transformed with DNA coding for the pore-forming toxin listeriolysln O behaved, with respect to intracellular growth, like the invasive, pathogenic species L. monocytogenes. Our results raise the possibility that, in vivo, pathogenic CNF1 -producing E. coli may invade epithelia by this novel induced phagocytic-like mechanism.     

Insulin-like growth factors: Putative muscle-derived trophic agents that promote motoneuron survival

Treatment of chick embryos in ovo with IGF-I during the period of normal, developmentally regulated neuronal death (embryonic days 5–10) resulted in a dose-dependent rescue of a significant number of lumbar motoneurons from degeneration and death. IGF-II and two variants of IGF-I with reduced affinity for IGF binding proteins, des(1-3) IGF-I and long R³ IGF-I, also elicited enhanced survival of motoneurons equal to that seen in IGF-I-treated embryos. IGF-I did not enhance mitogenic activity in motoneuronal populations when applied to embryos during the period of normal neuronal proliferation (E2-5). Treatment of embryos with IGF-I also reduced two types of injury-induced neuronal death. Following either deafferentation or axotomy, treatment of embryos with IGF-I rescued approximately 75% and 50%, respectively, of the motoneurons that die in control embryos as a result of these procedures. Consistent with the survival-promoting activity on motoneurons in ovo, IGF-I, -II, and des(1-3) IGF-I elevated choline acetyltransferase activity in embryonic rat spinal cord cultures, with des (1-3) IGF-I demonstrating 2.5 times greater potency than did IGF-I. A single addition of IGF-I at culture initiation resulted in the maintenance of 80% of the initial ChAT activity for up to 5 days, during which time ChAT activity in untreated control cultures fell to 9%. In summary, these results demonstrate clear motoneuronal trophic activity for the IGFs. These findings, together with previous reports that IGFs are synthesized in muscle and may participate in motoneuron axonal regeneration and sprouting, indicate that these growth factors may have an important role in motoneuron development, maintenance, and recovery from injury. © 1993 John Wiley & Sons, Inc.     

Image-guided navigation for the control interstitial laser therapy of vascular malformations in the head and neck region]

Laser-induced interstitial thermal therapy (LITT) is a proven minimally invasive surgical technique for the treatment of haemangiomas and vascular malformations, and various tumours. The intra-lesion application of thermal energy destroys regional tissue. The percutaneous placement of the laser fibre for photocoagulation is done without the benefit of direct visual control. Image-data-based LITT was performed in patients (five procedures) with extensive venous malformations in the maxillofacial area. The system comprised a specially developed Nd:YAG laser fibre introducer set used in conjunction with fused high-resolution computed tomography, and magnetic resonance image-data--based surgical navigation. In all cases, follow-up examination clearly showed a diminishment in tumour volume, and all patients reported significant subjective improvement. The results suggest that navigation-guided LITT can be performed safely, preserving vital structures from collateral thermal damage.     

DAYLENGTH AND LIGHT RESPONSES IN GROWTH AND FERTILITY OF GLOSSOPHORA KUNTHII (PHAEOPHYTA,DICTYOTALES) FROM PACIFIC SOUTH AMERICA1

Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4–24 h and photon fluence rates of 10–75 μmol.m^?2.s^?1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long-day regimens with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short-day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short-day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short-day regimes and low irradiances; differentiation was completely inhibited at long-day conditions and high irradiance.     

Soil algae from acid rain impacted forest areas of the Krušné hory Mts. 1. Algal communities

The soil algal communities of forested and reforested, limed and unlimed plots were compared in the acid rain impacted Kru sné hory Mountains. The floristic composition of unlimed plots is similar to that found in acid forest soils with a naturally low pH and no effect of the acid rain on these communities can be detected. Chlorophyceae are the only group present in these soils. In limed areas with a higher soil pH, algal diversity is significantly increased while algal densities remain similar. Chlorophyceae, while still the dominant group, are accompanied in these soils by Bacillariophyceae, Xanthophyceae, Eustigmatophyceae and Cyanophyceae. Total vegetation cover and thus light hitting the soil surface seems to be most important in determining the algal biomass.     

Genetic structure of Halotydeus destructor and Penthaleus major populations in Victoria (Acari: Penthaleidae)

The redlegged earth mite (Halotydeus destructor) and the blue oat mite (Penthaleus major) are major pests of pastures and crops in southern Australia. Reproductive modes, migration rates and levels of differentiation between populations were investigated using allozyme electrophoresis. Collections were made throughout Victoria and a sample was also obtained from Western Australia. Three enzyme loci were polymorphic in H. destructor (Mdh-1, Mdh-2 and Idh). Genotype frequencies of these loci did not differ between phenotypic males and females, providing no evidence for haplodiploidy. Allele frequencies were in Hardy-Weinberg equilibrium, indicating that H. destructor is diploid and sexual. This was confirmed via crosses between males and females. Allele frequencies differed between Victorian sites, although F statistics indicated little differentiation over all loci. A sample from Western Australia did not differ in allele frequencies from the Victorian sites. Four polymorphic loci were found in P. major (Mdh-1, Mdh-2, Idh and Gpi). Only a few multilocus genotypes occurred in a sample, indicating that P. major is parthenogenic. No male P. major were found in this study. A number of colour morphs were also identified and a genetic association between genital plate colour and clonal type was found in one population of P. major. Two different body colour morphs were associated with different clonal types.