10 research outputs found
Aminoglycoside-driven biosynthesis of selenium-deficient Selenoprotein P
Selenoprotein biosynthesis relies on the co-translational insertion of
selenocysteine in response to UGA codons. Aminoglycoside antibiotics interfere
with ribosomal function and may cause codon misreading. We hypothesized that
biosynthesis of the selenium (Se) transporter selenoprotein P (SELENOP) is
particularly sensitive to antibiotics due to its ten in frame UGA codons. As
liver regulates Se metabolism, we tested the aminoglycosides G418 and
gentamicin in hepatoma cell lines (HepG2, Hep3B and Hepa1-6) and in
experimental mice. In vitro, SELENOP levels increased strongly in response to
G418, whereas expression of the glutathione peroxidases GPX1 and GPX2 was
marginally affected. Se content of G418-induced SELENOP was dependent on Se
availability, and was completely suppressed by G418 under Se-poor conditions.
Selenocysteine residues were replaced mainly by cysteine, tryptophan and
arginine in a codon-specific manner. Interestingly, in young healthy mice,
antibiotic treatment failed to affect Selenop biosynthesis to a detectable
degree. These findings suggest that the interfering activity of
aminoglycosides on selenoprotein biosynthesis can be severe, but depend on the
Se status, and other parameters likely including age and general health.
Focused analyses with aminoglycoside-treated patients are needed next to
evaluate a possible interference of selenoprotein biosynthesis by the
antibiotics and elucidate potential side effects
Regulation of selenoproteins after synthetic selenocompound exposure and during the acute phase inflammatory response
Selen ist ein essentielles Spurenelement, das ĂĽber den Einbau als 21-ste
proteinogene Aminosäure Selenocystein einer kleinen Gruppe von Selenoproteinen
den Namen gibt und als Bestandteil des aktiven Zentrums dieser Proteine die
enzymatische Katalyse bestimmter Reaktionen ermöglicht. In der Evolution haben
sich eine komplexe Synthesemaschinerie zur Biosynthese von Selenoproteinen und
besondere Regulationsmechanismen zur Kontrolle der Expressionsraten
entwickelt. Selenoproteine sind von besonderer Bedeutung fĂĽr den
Energiestoffwechsel, die SchilddrĂĽse und das Immunsystem. In der Klinik wird
Selen als Supplement zur UnterstĂĽtzung des Immunsystems und zum Ausgleich des
Selenverlustes bei Sepsis eingesetzt. Allerdings sind die molekularen
Mechanismen des Selenverlustes in Sepsis nicht verstanden, und es herrscht
Uneinigkeit ĂĽber die Wirkung verschiedener Formen selenhaltiger Supplemente.
Diese beiden Punkte stehen im Zentrum meiner Arbeit. In einem murinen Sepsis-
Modell wurde durch Endotoxin eine Akutphasenreaktion hervorgerufen. Es zeigte
sich eine streng hierarchische Verteilung des verfĂĽgbaren Selens auf die
Biosynthese der unterschiedlichen Selenoproteine, die darĂĽber hinaus auch
geschlechterspezifisch war. Der Selentransporter SePP erwies sich als stabiler
Selenbiomarker und als Negativ-Akutphase-Protein, während das ER-residente
Selenoprotein SepS als Positiv-Akutphase-Protein eingeordnet werden konnte.
Auf molekularer Ebene konnten mit der Regulation geschwindigkeitsbestimmender
Proteine des Selenmetabolismus und der Charakterisierung von Hypoxie als
starker Modulator der Biosynthese wichtige Mechanismen identifiziert werden,
die zu einer Verschiebung der Selenoprotein-Expression in schweren
Erkrankungen beitragen. Diese Studien zur Grundlage des Selenstoffwechsels
wurden durch Versuche zur Intervention mit neuen selenhaltigen Präparaten
ergänzt. Hier konnte mit der Gruppe der Imidoselenocarbamate eine
Substanzklasse charakterisiert werden, die therapeutisch vielversprechende
Effekte spezifisch in Tumorzellen induzierte und als besonders aktive
Induktoren der selenabhängigen Dejodasen wirkt, ohne dabei toxisch zu sein.
Zusammenfassend wurden in dieser Arbeit somit neue klinisch relevante
Regulationsmechanismen der Expression von Selenoproteinen charakterisiert und
mit den Imidoselenocarbamaten eine vielversprechende Substanzklasse fĂĽr eine
zukĂĽnftige pharmakologische Intervention identifiziert.The view on selenium (Se) changed from a toxic substance to an essential trace
element with the discovery of the 21st aminoacid selenocysteine (Sec). Se
exerts its biological function as part of Sec-containing selenoproteins. Sec
synthesis is mediated by a complex molecular machinery and depends on an
optimal selenium status. Se is essential for cellular functions and energy
metabolism, thyroid gland and immune system. Se research gained interest by
being linked to several diseases through animal and clinical studies. Se is a
supplement in the clinics to support the immune system and replenish loss of
Se in critical illness. Still, the function of several selenoproteins and the
underlying physiological mechanisms controlling Se metabolism are not
completely understood or have not even been explored. The present work
includes experimental studies on the role and regulation of Se and
selenoproteins in inflammatory diseases. To this end, an endotoxin
(LPS)-challenged mouse model with different Se status was analysed, and Se-
containing carbamates were characterized in tumor and non-transformed cells.
Using LPS-injected mice as sepsis model, our work highlighted a hierarchical
distribution of the available Se for the biosyntheses of the selenoproteome.
In addition, these regulatory principles acted in a sex-specific way. The
secreted SePP proved as stabile Se biomarker in blood. In inflammation, SePP
qualified as a hepatic negative acute phase protein whereas SepS was regulated
as a positive acute phase protein. SepS is located in the ER membrane and is
part of the protein quality control and therefore reduces cellular ER stress.
The second part of my work based on the interesting phenomenon that humans in
Se deficient areas are diagnosed more often with cancer than others. In fact,
several studies indicate an anticarcinogenic effect of Se. The relevant
selenoproteins and physiological mechanisms are unknown. Comparative studies
with the chemical class of imidoselenocarbamates using tumor-derived and non-
transformed cells showed different effects on translation of different
selenoproteins. The specific modulation of the selenoproteome expressed
reflects substance- and cell-specific effects of selenocarbamates on specific
selenoproteins, but not a general activation of the selenoprotein biosynthesis
machinery. Especially methyl-carrying selenocarbamates proved to be efficient
modulators. Moreover, this substance class proved to be effective modulators
of deiodinase activities without showing toxic effects. A further
characterization of the interaction of selenocompounds with specific
selenoproteins and their role in inflammation, cancer and the immune system is
needed to provide a better insight into underlying mechanisms needed to
optimize Se supplementation
Hypoxia reduces and redirects selenoprotein biosynthesis
Selenium deficiency constitutes a risk factor for the incidence and negative course of severe diseases including sepsis, stroke, autoimmune diseases or cancer. In this study, hypoxia is identified as a powerful stimulus to redirect selenoprotein biosynthesis causing reduced selenoprotein P expression and diminished selenium export from hepatocytes in favour of increased biosynthesis of the essential protective intracellular phospholipid hydroperoxide glutathione peroxidase GPX4. Specifically, hypoxia decreases transcript concentrations of central factors controlling selenium and selenocysteine metabolism including selenophosphate synthetase-2, phosphoseryl-tRNASerSec kinase and selenocysteine lyase, which are all proven to be rate-limiting enzymes in selenoprotein biosynthesis. These effects are paralleled by a general decline of selenoprotein expression; however, not all selenoproteins are affected to the same extent by hypoxia, and GPX4 constitutes an exception as its expression becomes slightly increased. Supplemental selenium is able to overcome the hypoxia-dependent down regulation of selenoprotein expression in our cell culture model system, supporting the concept of using selenium as an adjuvant treatment option in severe diseases. Although it remains to be tested whether these effects constitute a hepatocyte-specific response, the selenium-dependent decline of selenoprotein P biosynthesis under hypoxic conditions may explain the progressive selenium deficit developing in severe diseases.Peer Reviewe
Hypoxia reduces and redirects selenoprotein biosynthesis
Selenium deficiency constitutes a risk factor for the incidence and negative course of severe diseases including sepsis, stroke, autoimmune diseases or cancer. In this study, hypoxia is identified as a powerful stimulus to redirect selenoprotein biosynthesis causing reduced selenoprotein P expression and diminished selenium export from hepatocytes in favour of increased biosynthesis of the essential protective intracellular phospholipid hydroperoxide glutathione peroxidase GPX4. Specifically, hypoxia decreases transcript concentrations of central factors controlling selenium and selenocysteine metabolism including selenophosphate synthetase-2, phosphoseryl-tRNASerSec kinase and selenocysteine lyase, which are all proven to be rate-limiting enzymes in selenoprotein biosynthesis. These effects are paralleled by a general decline of selenoprotein expression; however, not all selenoproteins are affected to the same extent by hypoxia, and GPX4 constitutes an exception as its expression becomes slightly increased. Supplemental selenium is able to overcome the hypoxia-dependent down regulation of selenoprotein expression in our cell culture model system, supporting the concept of using selenium as an adjuvant treatment option in severe diseases. Although it remains to be tested whether these effects constitute a hepatocyte-specific response, the selenium-dependent decline of selenoprotein P biosynthesis under hypoxic conditions may explain the progressive selenium deficit developing in severe diseases.Peer Reviewe
Selenoprotein P status correlates to cancer-specific mortality in renal cancer patients.
Selenium (Se) is an essential trace element for selenoprotein biosynthesis. Selenoproteins have been implicated in cancer risk and tumor development. Selenoprotein P (SePP) serves as the major Se transport protein in blood and as reliable biomarker of Se status in marginally supplied individuals. Among the different malignancies, renal cancer is characterized by a high mortality rate. In this study, we aimed to analyze the Se status in renal cell cancer (RCC) patients and whether it correlates to cancer-specific mortality. To this end, serum samples of RCC patients (n = 41) and controls (n = 21) were retrospectively analyzed. Serum Se and SePP concentrations were measured by X-ray fluorescence and an immunoassay, respectively. Clinical and survival data were compared to serum Se and SePP concentrations as markers of Se status by receiver operating characteristic (ROC) curve and Kaplan-Meier and Cox regression analyses. In our patients, higher tumor grade and tumor stage at diagnosis correlated to lower SePP and Se concentrations. Kaplan-Meier analyses indicated that low Se status at diagnosis (SePP<2.4 mg/l, bottom tertile of patient group) was associated with a poor 5-year survival rate of 20% only. We conclude that SePP and Se concentrations are of prognostic value in RCC and may serve as additional diagnostic biomarkers identifying a Se deficit in kidney cancer patients potentially affecting therapy regimen. As poor Se status was indicative of high mortality odds, we speculate that an adjuvant Se supplementation of Se-deficient RCC patients might be beneficial in order to stabilize their selenoprotein expression hopefully prolonging their survival. However, this assumption needs to be rigorously tested in prospective clinical trials
Box Plot analysis of serum SePP concentration in RCC patients and controls.
<p>RCC patients were stratified using pathologic tumor characteristics <b>A</b>) non metastatic versus metastatic <b>B</b>) G1/G2 versus G3/G4 and <b>C</b>) pT<sub>1</sub>/pT<sub>2</sub> versus pT<sub>3</sub>/pT<sub>4.</sub> The corresponding significance levels between groups are given in the graph.</p
Serum concentrations of Se and SePP in RCC patients<sup>*</sup> and controls.
*<p>Patients were classified by diagnosis; the serum data are presented as median, range, and percentile.</p>#<p>Mann-Whitney U-Test.</p