@phdthesis{Engelmann2023, author = {Engelmann, Daria Marie}, title = {Regulation of Mammalian Phosphoglycolate Phosphatase}, doi = {10.25972/OPUS-19957}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-199577}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {Mammalian phoshoglycolate phosphatase (PGP, also known as AUM) belongs to the ubiquitous HAD superfamily of phosphatases. As several other members of HAD phosphatases, the Mg2+-dependent dephosphorylation is conducted via a nucleophilic attack from a conserved aspartate residue in the catalytic cleft. The protein structure of PGP could not yet be solved entirely. Only a hybrid consisting of the PGP cap and the PDXP core (pyridoxal phosphatase, closest enzyme paralog) was crystallizable so far. PGP is able to efficiently dephosphorylate 2-phosphoglycolate, 2-phospho-L-lactate, 4-phospho-D-erythronate, and glycerol-3-phosphate in vitro which makes them likely physiological substrates. The first three substrates can be derived from metabolic side reactions (during glycolysis) and inhibit key enzymes in glycolysis and pentose phosphate pathway, the latter is situated at the intersection between glycolysis and lipogenesis. 2-phosphoglycolate can also be released in the context of repair of oxidative DNA damage. The activity of purified PGP can be reversibly inhibited by oxidation - physiologically likely in association with epidermal growth factor (EGF) signal transduction. In fact, an association between persistently lacking PGP activity (via downregulation) and the presence of hyperphosphorylated proteins after EGF stimulation has been identified. Reversible oxidation and transient inactivation of PGP may be particularly important for short-term and feedback regulatory mechanisms (as part of the EGF signaling). Furthermore, cellular proliferation in PGP downregulated cells is constantly reduced. Whole-body PGP inactivation in mice is embryonically lethal. Despite the many well-known features and functions, the knowledge about PGP is still incomplete. In the present work the influence of reactive oxygen species (ROS) on PGP activity in cells und a possible connection between oxidative stress and the proliferation deficit of PGP downregulated cells was investigated. For the experiments, a spermatogonial cell line was used (due to the high PGP expression in testis). PGP activity can be reversibly inhibited in cellular lysates by H2O2 (as a ROS representative). Reversible oxidation could thus indeed be physiologically important. More oxidative DNA damage (by bleomycin) showed no PGP-dependent effects here. EGF stimulation (as an inducer of transient and well-controlled ROS production), low concentrations of menadione (as an oxidant) and N-acetylcysteine (as an antioxidant) were able to approximate the proliferation rate in PGP downregulated cells to that of control cells. The redox regulation of PGP could thus have an influence on cellular proliferation as a feedback mechanism - a mechanism that could not take place in PGP downregulated cells. However, the connections are probably even more complex and cannot be elucidated by a sole examination of the proliferation rate. The present results can thus only be regarded as preliminary experiments. For a better understanding of the features and functions of PGP, this work then focused on specific regulation of enzyme activity by pharmacologically applicable small molecules. Four potent inhibitors had previously been identified in a screening campaign. In this work, three of these four inhibiting compounds could be further characterized in experiments with highly purified, recombinant murine and human PGP. Compounds \#2 and \#9 showed competitive inhibition properties with a markedly rising KM value with little or no change in vmax. The results were consistent for all tested protein variants: the murine and the human PGP as well as a PGP/PDXP hybrid protein. Compound \#1 was the most potent and interesting PGP-inhibitory molecule: less change in KM and a constant decrease in vmax as well as a lower impact on the PGP/PDXP hybrid hint at a mixed mode of inhibition as a combination of competitive and non-competitive inhibition. The characterization of the potential inhibitors can serve as a basis for further structural analysis and studies on the complex physiological role of PGP.}, subject = {Phosphoglykolatphosphatase}, language = {en} } @phdthesis{Laesker2023, author = {L{\"a}sker, Katharina}, title = {The influence of the short-chain fatty acid butyrate on "Signal transducer and activator of transcription 3" (STAT3) and selected inflammatory genes in the colon carcinoma cell line CACO-2 cultured in 2D and 3D}, doi = {10.25972/OPUS-30038}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300389}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {A disturbance in the symbiotic mutualism between the intestinal microbiome and the human host's organism (syn. dysbiosis) accompanies the development of a variety of inflammatory and metabolic diseases that comprise the Metabolic Syndrome, chronic inflammatory gut diseases like Crohn's disease, Non-alcoholic fatty liver disease (NAFLD) and cardiovascular diseases, among others. The changed uptake and effectiveness of short chain fatty acids (SCFAs) as well as an increase of the intestinal permeability are common, interdependent disease elements in this regard. Short chain fatty acids are end-products of intestinal bacterial fermentation and affect the mucosal barrier integrity via numerous molecular mechanisms. There is evidence to suggest, that SCFAs have a modulating influence on Signal transducer and activator of transcription 3 (STAT3) in intestinal epithelial cells. STAT3 is a central gene-transcription factor in signaling pathways of proliferation and inflammation. It can be activated by growth factors and other intercellular signaling molecules like the cytokine Oncostatin M (OSM). The mode of STAT3's activation exhibits, finally, a decisive influence on the immunological balance at the intestinal mucosa. Therefore, the posttranslational modification of STAT3 under the influence of SCFAs is likely to be a very important factor within the development and -progression of dysbiosis-associated diseases. In this study, a clear positive in vitro-effect of the short chain fatty acid butyrate on the posttranslational serine727-phosphorylation of STAT3 and its total protein amount in the human adenocarcinoma cell line CACO2 is verified. Moreover, an increased gene expression of the OSM-receptor subunit OSMRβ can be observed after butyrate incubation. Histone deacetylase inhibition is shown to have a predominant role in these effects. Furthermore, a subsequent p38 MAPK-activation by Butyrate is found to be a key molecular mechanism regarding the STAT3-phosphorylation at serine727-residues. To consider the portion of butyrate receptor signaling in this context in future assays, a CACO-2 cell 3D-culture model is introduced in which an improvement of the GPR109A-receptor expression in CACO-2 cells is accomplished.}, subject = {Butyrate }, language = {en} } @phdthesis{Wagner2020, author = {Wagner, Leonard}, title = {Zinc homeostasis in megakaryocytes}, doi = {10.25972/OPUS-21452}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214526}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Zinc is an essential trace element for all living organisms. In mammals, including humans and mice, it is required for normal growth, development, hematopoiesis and immune defense. This thesis investigates the influence of zinc on the development of megakaryocytes (MKs), the cells responsible for bone marrow-derived platelet production. Furthermore, a detailed analysis of the expression of zinc import and export transporters (Slc39a/Slc30a genes) is carried out, firstly over the course of MK differentiation and secondly dependent on extracellular zinc.}, subject = {Zink}, language = {en} }