Die Rolle von Ca 2+ -aktivierten K + -Kanälen für die Radioresistenz des Glioblastoms

Glioblastoma multiforme sind die häufigsten und gleichzeitig malignesten primären Neoplasien im Gehirn. Glioblastomzellen können innerhalb des Gehirns weite Strecken zurücklegen, eine diffuse Infiltration des Gehirns ist die Folge. Eine komplette operative Entfernung und Erfassung der residuellen Tumorzellen durch das Zielvolumen während der adjuvanten Strahlentherapie ist daher oft nicht möglich. Die Migration von Glioblastomzellen hängt sehr stark von hoch effizienten Zellvolumenänderungen ab, welche es der Zelle ermöglicht, sich durch die engen Zellzwischenräume hindurch zu zwängen. Diese Ab- und Zunahme des Zellvolumens schließt die Abgabe von KCl mit ein, welche von einem osmotisch bedingten Verlust an freiem Zellwasser gefolgt wird. Dieser Prozess wird bewerkstelligt durch Ca2+- regulierte K+- und Cl--Kanäle in der Plasmamembran. Eine Bestrahlung (IR) dieser Zellen scheint die Migration von Glioblastomzellen sogar noch weiter zu stimulieren. Ein Schlüsselereignis in diesem Vorgang ist die Aktivierung von BK K+-Kanälen in den bestrahlten Zellen. Der erste Teil dieser Doktorarbeit analysierte das Signaling „down“- und „upstream“ der durch Bestrahlung induzierten BK K+-Kanal-Aktivierung. Eine Bestrahlung induzierte die Bildung des CXCR4 Agonisten SDF-1 und veränderte das Ca2+- Signaling, welches in einer Ca2+-abhängigen Aktivierung von BK K+-Kanälen resultierte. Wie bei einer Bestrahlung der Glioblastomzellen induzierte SDF-1 oder konditioniertes Medium von bestrahlten Zellen Ca2+-Signale, die eine Hypermigration von unbehandelten Glioblastomzellen stimulierte. Der CXCR4 Antagonist AMD3100 und der BK-Kanal Inhibitor Paxilline unterbanden die Signale, die eine Hypermigration ermöglichen. Die Ergebnisse deuten auf eine Stimulation der Hypermigration in bestrahlten Glioblastomzellen hin, ermöglicht durch ein Signaling via SDF-1, den CXCR4 Chemokinrezeptor, Ca2+-aktivierte BK K+-Kanäle und die Ca2+-aktivierte CaMKII Serin/Threoninkinase. Letztere aktiviert ClC-3 Cl--Kanäle, die zusammen mit BK K+- Kanälen und Aquaporinen die Zellvolumenänderungen bewerkstelligen, welche für die Migration notwendig sind.Neben BK-Kanälen überexprimieren Glioblastomzellen auch Ca2+-aktivierte IK K+-Kanäle. Der zweite Teil dieser Doktorarbeit untersuchte die Funktion dieser IK Kanäle für die Radioresistenz der Glioblastomzellen. Eine Bestrahlung von Glioblastomzellen erhöhte die Aktivität von TRAM34-sensitiven IK K+-Kanälen, welche zu einem veränderten Ca2+-Signaling und der Aktivierung von Ca2+/Calmodulin-abhängigen Kinase II (CaMKII) Isoformen führten. Diese Aktivierung resultierte anschließend in einer Inaktivierung des cdc2 „mitosis promoting factor“ und einem vorübergehenden G2/M Arrest. TRAM34 schwächte die IR-induzierte Aktivierung der CaMKII, eine cdc2 Dephosphorylierung und eine verringerte Akkumulierung der Zellen im G2/M Arrest waren die Folge. Des Weiteren erhöhte TRAM34 die Anzahl der gamma-H2AX Foci 24 Stunden nach Bestrahlung, welche auf einen durch TRAM34 induzierten Anstieg von residuellen DNA Doppelstrangbrüchen hindeutet. TRAM34 radiosensitivierte T98G und U87MG Glioblastomzellen in Koloniebildungstests. Zudem zeigte das klonogene Überleben zweier mit Retroviren transfizierten T98G Glioblastomzellklone, welche sich in ihrer IK-Kanal Expression unterscheiden, sowohl eine durch IK-Kanäle vermittelte Radioresistenz als auch eine IK-Spezifität des TRAM34-Effektes. Es konnte ebenso gezeigt werden, dass eine zeitgleiche TRAM34-Behandlung und Bestrahlung zu einem verzögerten ektopen Tumorwachstum im hinteren rechten Oberschenkel von immunkompromittierten Nacktmäusen führte. Zusammenfassend zeigen die Daten eine Zellzyklus-regulatorische Funktion von IK K+-Kanälen

Inhibition of HSP90 as a Strategy to Radiosensitize Glioblastoma: Targeting the DNA Damage Response and Beyond

Radiotherapy is an essential component of multi-modality treatment of glioblastoma (GBM). However, treatment failure and recurrence are frequent and give rise to the dismal prognosis of this aggressive type of primary brain tumor. A high level of inherent treatment resistance is considered to be the major underlying reason, stemming from constantly activated DNA damage response (DDR) mechanisms as a consequence of oncogene overexpression, persistent replicative stress, and other so far unknown reasons. The molecular chaperone heat shock protein 90 (HSP90) plays an important role in the establishment and maintenance of treatment resistance, since it crucially assists the folding and stabilization of various DDR regulators. Accordingly, inhibition of HSP90 represents a multi-target strategy to interfere with DDR function and to sensitize cancer cells to radiotherapy. Using NW457, a pochoxime-based HSP90 inhibitor with favorable brain pharmacokinetic profile, we show here that HSP90 inhibition at low concentrations with per se limited cytotoxicity leads to downregulation of various DNA damage response factors on the protein level, distinct transcriptomic alterations, impaired DNA damage repair, and reduced clonogenic survival in response to ionizing irradiation in glioblastoma cells in vitro. In vivo, HSP90 inhibition by NW457 improved the therapeutic outcome of fractionated CBCT-based irradiation in an orthotopic, syngeneic GBM mouse model, both in terms of tumor progression and survival. Nevertheless, in view of the promising in vitro results the in vivo efficacy was not as strong as expected, although apart from the radiosensitizing effects HSP90 inhibition also reduced irradiation-induced GBM cell migration and tumor invasiveness. Hence, our findings identify the combination of HSP90 inhibition and radiotherapy in principle as a promising strategy for GBM treatment whose performance needs to be further optimized by improved inhibitor substances, better formulations and/or administration routes, and fine-tuned treatment sequences

Three Eruptions Observed by Remote Sensing Instruments Onboard Solar Orbiter

On February 21 and March 21 – 22, 2021, the Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter observed three prominence eruptions. The eruptions were associated with coronal mass ejections (CMEs) observed by Metis, Solar Orbiter’s coronagraph. All three eruptions were also observed by instruments onboard the Solar–TErrestrial RElations Observatory (Ahead; STEREO-A), the Solar Dynamics Observatory (SDO), and the Solar and Heliospheric Observatory (SOHO). Here we present an analysis of these eruptions. We investigate their morphology, direction of propagation, and 3D properties. We demonstrate the success of applying two 3D reconstruction methods to three CMEs and their corresponding prominences observed from three perspectives and different distances from the Sun. This allows us to analyze the evolution of the events, from the erupting prominences low in the corona to the corresponding CMEs high in the corona. We also study the changes in the global magnetic field before and after the eruptions and the magnetic field configuration at the site of the eruptions using magnetic field extrapolation methods. This work highlights the importance of multi-perspective observations in studying the morphology of the erupting prominences, their source regions, and associated CMEs. The upcoming Solar Orbiter observations from higher latitudes will help to constrain this kind of study better

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Role of ion channels in ionizing radiation-induced cell death

AbstractNeoadjuvant, adjuvant or definitive fractionated radiation therapy are implemented in first line anti-cancer treatment regimens of many tumor entities. Ionizing radiation kills the tumor cells mainly by causing double strand breaks of their DNA through formation of intermediate radicals. Survival of the tumor cells depends on both, their capacity of oxidative defense and their efficacy of DNA repair. By damaging the targeted cells, ionizing radiation triggers a plethora of stress responses. Among those is the modulation of ion channels such as Ca2+-activated K+ channels or Ca2+-permeable nonselective cation channels belonging to the super-family of transient receptor potential channels. Radiogenic activation of these channels may contribute to radiogenic cell death as well as to DNA repair, glucose fueling, radiogenic hypermigration or lowering of the oxidative stress burden. The present review article introduces these channels and summarizes our current knowledge on the mechanisms underlying radiogenic ion channel modulation. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers

BK K+ channel blockade inhibits radiation-induced migration/brain infiltration of glioblastoma cells

Infiltration of the brain by glioblastoma cells reportedly requires Ca2+ signals and BK K+ channels that program and drive glioblastoma cell migration, respectively. Ionizing radiation (IR) has been shown to induce expression of the chemokine SDF-1, to alter the Ca2+ signaling, and to stimulate cell migration of glioblastoma cells. Here, we quantified fractionated IR-induced migration/brain infiltration of human glioblastoma cells in vitro and in an orthotopic mouse model and analyzed the role of SDF-1/CXCR4 signaling and BK channels. To this end, the radiation-induced migratory phenotypes of human T98G and far-red fluorescent U-87MG-Katushka glioblastoma cells were characterized by mRNA and protein expression, fura-2 Ca2+ imaging, BK patch-clamp recording and transfilter migration assay. In addition, U-87MG-Katushka cells were grown to solid glioblastomas in the right hemispheres of immunocompromised mice, fractionated irradiated (6 MV photons) with 5 x 0 or 5 x 2 Gy, and SDF-1, CXCR4, and BK protein expression by the tumor as well as glioblastoma brain infiltration was analyzed in dependence on BK channel targeting by systemic paxilline application concomitant to IR. As a result, IR stimulated SDF-1 signaling and induced migration of glioblastoma cells in vitro and in vivo. Importantly, paxilline blocked IR-induced migration in vivo. Collectively, our data demonstrate that fractionated IR of glioblastoma stimulates and BK K+ channel targeting mitigates migration and brain infiltration of glioblastoma cells in vivo. This suggests that BK channel targeting might represent a novel approach to overcome radiation-induced spreading of malignant brain tumors during radiotherapy