Pyruvate Kinase M2 Expression,but Not Pyruvate Kinase Activity,Is Up-Regulated in a Grade-Specific Manner in Human Glioma

Normal tissues express the M1 isoform of pyruvate kinase (PK) that helps generate and funnel pyruvate into the mitochondria for ATP production. Tumors, in contrast, express the less active PKM2 isoform, which limits pyruvate production and spares glycolytic intermediates for the generation of macromolecules needed for proliferation. Although high PKM2 expression and low PK activity are considered defining features of tumors, very little is known about how PKM expression and PK activity change along the continuum from low grade to high grade tumors, and how these changes relate to tumor growth. To address this issue, we measured PKM isoform expression and PK activity in normal brain, neural progenitor cells, and in a series of over 100 astrocytomas ranging from benign grade I pilocytic astrocytomas to highly aggressive grade IV glioblastoma multiforme (GBM). All glioma exhibited comparably reduced levels of PKM1 expression and PK activity relative to normal brain. In contrast, while grade I-III gliomas all had modestly increased levels of PKM2 RNA and protein expression relative to normal brain, GBM, regardless of whether they arose de novo or progressed from lower grade tumors, showed a 3–5 fold further increase in PKM2 RNA and protein expression. Low levels of PKM1 expression and PK activity were important for cell growth as PKM1 over-expression and the accompanying increases in PK activity slowed the growth of GBM cells. The increased expression of PKM2, however, was also important, because shRNA-mediated PKM2 knockdown decreased total PKM2 and the already low levels of PK activity, but paradoxically also limited cell growth in vitro and in vivo. These results show that pyruvate kinase M expression, but not pyruvate kinase activity, is regulated in a grade-specific manner in glioma, but that changes in both PK activity and PKM2 expression contribute to growth of GBM.     

Enzymatic defences against photooxidative stress induced by ultraviolet radiation in Arctic marine macroalgae

The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT), as well as the content of the antioxidant compound ascorbic acid, were determined in five green, seven red and ten brown macroalgal species from the Kongsfjord (Spitsbergen, Svalbard, Norway). In general, higher antioxidant enzyme activities and a higher content of ascorbic acid were measured in green algae in comparison to red and brown algae. Species from the eulittoral and upper sublittoral (Acrosiphonia penicilliformis, Monostroma arcticum, Chaetomorpha linum, Chaetomorpha melagonium, Devaleraea ramentacea, Palmaria palmata) showed higher antioxidant enzyme activities compared to species from the lower sublittoral, indicating a more efficient biochemical protection in algae exposed to higher stress conditions in the field. The activity of GR was stimulated by artificial ultraviolet radiation in the green alga M. arcticum, and in the red algae Coccotylus truncatus and Phycodrys rubens after 84 h under continuous exposure. GR activity was even higher when the UV exposure was followed by incubation in darkness for 24 h, indicating a higher elimination rate of toxic oxygen radicals under these conditions. D. ramentacea, P. palmata and A. penicilliformis did not show any significant effect of UV radiation on CAT, APX and SOD activities after 8 days of culture under laboratory conditions. However, a significant reduction in activities of GR and SOD was observed in A. penicilliformis when solar UV radiation was cut off by selective filter foils in the field, indicating a lower oxidative stress in the absence of UV radiation. Overall, the ecological success of macroalgae in the eulittoral and upper sublittoral is supported by an enhanced oxygen-reactive scavenging system, allowing fast acclimation to the changes in environmental radiation conditions.     

Grazing and UV radiation effects on an Antarctic intertidal microalgal assemblage: a long-term field study

A 15 week field experiment (austral summer Nov–Mar) was carried out in an intertidal hard bottom platform in Antarctica (King George Island). To test whether grazing and ultraviolet radiation (UVR) influenced the succession of a benthic microalgal assemblage, a two-factorial design was used (1) ambient radiation, >280 nm; (2) ambient minus UV-B, >320 nm; (3) ambient minus UVR, >400 nm versus grazer–no grazer). On four sampling occasions microalgae were identified, counted and carbon contents were calculated. The assemblage was dominated by the diatom genera Navicula and Cocconeis. Biomass was generally low in all treatments but was significantly reduced by grazing throughout the experiment. No significant UV effects were found. Grazer absence particularly favoured diatoms of the genus Cocconeis. We conclude that the Antarctic microalgal assemblage was unaffected by present day UVR whereas grazers acted as important drivers on the intertidal microalgal community structure.     

The life history of Porphyra endiviifolium from the South Shetland Islands, Antarctica

This paper describes the reproduction and life history of an intertidal species, Porphyra endiviifolium, from Antarctica. Field specimens were examined microscopically, prepared for electron microscopy and used to establish cultures. Wild populations comprised two kinds of leafy thalli, morphologically similar but distinguished by their mode of reproduction, either sexual or asexual. Carpospores from monoecious leafy gametophytes developed into conchocelis filaments in culture, and under “winter-spring” conditions these formed conchospores that germinated to produce leafy thalli. Monospores from asexual leafy thalli developed directly into two different forms of leafy thalli. Only one of the cultured morphotypes became fertile, reproducing asexually by monospores. We conclude that the phases of the life history of P. endiviifolium show different ecological strategies, the conchocelis phase reproducing in response to short days unlike the leafy thalli in which growth and reproduction respond primarily to irradiance. Received: 2 May 1997 / Accepted: 11 October 1997     

New records of temperate and sub-Antarctic marine benthic macroalgae from Antarctica

 During visits to several localities on the South Shetland Islands and the Antarctic Peninsula in summer 1994 we made collections of marine benthic algae. Among the algae we collected were three new records for Antarctica [Petalonia fascia (OF Müller) Kuntze; Enteromorpha intestinalis (L.) Nees; Rhodymenia subantarctica Ricker] and seven other species [Scytosiphon simplicissimus (Clemente) Cremades; Chordaria linearis (Hooker et Harvey) Cotton; Halopteris obovata (Hooker et Harvey) Sauvageau; Acrosiphonia arcta (Dillwyn) J. Agardh; Enteromorpha compressa (L.) Nees; Bangia atropurpurea (Roth) C. Agardh; Porphyra plocamiestris Ricker] that had been reported on only one or two previous occasions (or, in one case, three). The ten species detailed in this paper fall into two groups: four species previously known from sub-Antarctic islands and/or locations in southern South America, and six species having a wider distribution in temperate regions. We discuss the possibility that the less accessible subtidal habitats of some species may have prevented earlier discovery. Other species may be comparatively recent adventives, most likely introduced with shipping. In view of possible global climate changes, species of this latter group are regarded as suitable organisms for monitoring changes of water temperature. Received: 12 December 1995/Accepted: 14 April 1996     

Photosynthetic performance of Arctic macroalgae after transplantation from deep to shallow waters

Transplantation experiments conducted in the Arctic Kongsfjord (Spitsbergen) in summer 1997 investigated the effects of various types of filtered natural radiation (solar, solar without UV-B, solar without UV-A/B) on photosynthesis of various macroalgae. Two brown algal species (Laminaria solidungula, Saccorhiza dermatodea) and four red algal species (Palmaria palmata, Phycodrys rubens, Phyllophora truncata, Ptilota plumosa) were collected from deeper waters, kept in UV-transparent plexiglass tubes wrapped with different spectral cut-off filter foils and positioned at fixed depths in shallow waters for 7-9 days. At regular intervals, chlorophyll fluorescence of photosystem II (optimum quantum yield, F_v/F_m) was determined, as an indicator of photosynthetic performance. The data demonstrate that shallow-water species such as P. palmata are much less affected by natural photosynthetically active radiation (PAR) and UV radiation near the surface than extremely sensitive deep-water species such as Phyc. rubens which exhibited strong decreases in photosynthetic performance, as well as photobleaching of part of the thallus. The other species showed intermediate response patterns. In most species investigated inhibition of photosynthesis was mainly caused by the UV-B wavelengths. Interpretation of the data clearly indicates species-specific tolerances of photosynthesis to ambient solar radiation which can be explained by broad physiological acclimation potentials and/or genetic adaptation to certain (low or high) irradiances. The species-specific photosynthetic performance under radiation stress is in good accordance with the vertical distribution of the macroalgae on the shore.     

Inhibition of the adaptive response of human lymphocytes to very low doses of ionizing radiation by the protein synthesis inhibitor cycloheximide

When human lymphocytes are preirradiated with 1 cGy of X-rays, the cells become less sensitive to subsequent exposures to high doses of about 150 cGy in that approximately one-half as many chromatid aberrations are induced as expected. This adaptation has been attributed to the induction of repair enzymes (proteins) some 4-6 h after the initial low-dose exposure. Experiments have now been carried out showing that application of the protein synthesis inhibitor cycloheximide at this time, but not earlier, prevents the adaptive response.     

DNA methylation arrays as surrogate measures of cell mixture distribution

ABSTRACT: BACKGROUND: There has been a long-standing need in biomedical research for a method that quantifies the normally mixed composition of leukocytes beyond what is possible by simple histological or flow cytometric assessments. The latter is restricted by the labile nature of protein epitopes, requirements for cell processing, and timely cell analysis. In a diverse array of diseases and following numerous immune-toxic exposures, leukocyte composition will critically inform the underlying immuno-biology to most chronic medical conditions. Emerging research demonstrates that DNA methylation is responsible for cellular differentiation, and when measured in whole peripheral blood, serves to distinguish cancer cases from controls. RESULTS: Here we present a method, similar to regression calibration, for inferring changes in the distribution of white blood cells between different subpopulations (e.g. cases and controls) using DNA methylation signatures, in combination with a previously obtained external validation set consisting of signatures from purified leukocyte samples. We validate the fundamental idea in a cell mixture reconstruction experiment, then demonstrate our method on DNA methylation data sets from several studies, including data from a Head and Neck Squamous Cell Carcinoma (HNSCC) study and an ovarian cancer study. Our method produces results consistent with prior biological findings, thereby validating the approach. CONCLUSIONS: Our method, in combination with an appropriate external validation set, promises new opportunities for large-scale immunological studies of both disease states and noxious exposures.