Klaudia Brix

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Papers by Klaudia Brix

Thyroid functions of mouse cathepsins B, K, and L

by Klaudia Brix and V. Herzog

Journal of Clinical Investigation, 2003

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Effects of different space relevant environmental stressors including Lunar Dust on microorganisms and human cells of different tissues

by Klaudia Brix and Maren Rehders

40th International Conference on Environmental Systems, 2010

McInnes et al 2013 FEMS Published

by Klaudia Brix and Maren Rehders

The Saccharomyces cerevisiae strain CBS6412 has been shown to be able to grow in synthetic medium... more The Saccharomyces cerevisiae strain CBS6412 has been shown to be able to grow in synthetic medium containing glycerol as the sole carbon source, conditions under which laboratory strains such as CEN.PK and S288c cannot grow. Nonetheless, this strain exhibits a lag phase of c. 30-40 h following transition to glycerol medium. As mitochondria play a critical role in the dissimilation of the respiratory carbon source glycerol, we investigated mitochondrial function and dynamics throughout the lag phase using mitochondria-targeted roGFP, a redox-sensitive GFP variant. We found that following transition to glycerol medium, mitochondria become more oxidizing, accumulate near the bud neck, and exhibit decreased inheritance into daughter cells. Directly preceding entry into exponential growth phase, mitochondria become more reducing, mitochondrial accumulations at the bud neck decrease, and inheritance of mitochondria into daughter cells is restored.

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Modulation of monocarboxylate transporter 8 oligomerization by specific pathogenic mutations

by Klaudia Brix and Maren Rehders

Journal of molecular endocrinology, 2015

The monocarboxylate transporter 8 (MCT8) is a member of the major facilitator superfamily (MFS). ... more The monocarboxylate transporter 8 (MCT8) is a member of the major facilitator superfamily (MFS). These membrane-spanning proteins facilitate translocation of a variety of substrates, MCT8 specifically transports iodothyronines. Mutations in MCT8 are the underlying cause of severe X-linked psychomotor retardation. At the molecular level, such mutations led to deficiencies in substrate translocation due to reduced cell-surface expression, impaired substrate binding, or decreased substrate translocation capabilities. However, the causal relationships between genotypes, molecular features of mutated MCT8, and patient characteristics have not yet been comprehensively deciphered. We investigated the relationship between pathogenic mutants of MCT8 and their capacity to form dimers (presumably oligomeric structures) as a potential regulatory parameter of the transport function of MCT8. Fourteen pathogenic variants of MCT8 were investigated in vitro with respect to their capacity to form oli...

Proteolysis mediated by cysteine cathepsins and legumain-recent advances and cell biological challenges

by Klaudia Brix and Maren Rehders

Protoplasma, Jan 16, 2014

Proteases play essential roles in protein degradation, protein processing, and extracellular matr... more Proteases play essential roles in protein degradation, protein processing, and extracellular matrix remodeling in all cell types and tissues. They are also involved in protein turnover for maintenance of homeostasis and protein activation or inactivation for cell signaling. Proteases range in function and specificity, with some performing distinct substrate cleavages, while others accomplish proteolysis of a wide range of substrates. As such, different cell types use specialized molecular mechanisms to regulate the localization of proteases and their function within the compartments to which they are destined. Here, we focus on the cysteine family of cathepsin proteases and legumain, which act predominately within the endo-lysosomal pathway. In particular, recent knowledge on cysteine cathepsins and their primary regulator legumain is scrutinized in terms of their trafficking to endo-lysosomal compartments and other less recognized cellular locations. We further explore the mechanis...

Thyroid Cathepsin K: Roles in Physiology and Thyroid Disease

by Maren Rehders, Klaudia Brix, and Stephanie Dauth

The human genome encodes 11 cysteine cathepsins belonging to the papain-like family of cysteine p... more The human genome encodes 11 cysteine cathepsins belonging to the papain-like family of cysteine peptidases that are known predominantly as endo-lysosomal enzymes. However, it is now understood that the functions and activities of cysteine cathepsins are not limited to endo-lysosomal compartments, as they are also active in the peri-and extracellular space. The thyroid gland is an endocrine organ where such intra-and extracellular proteolytic activities are required to solubilize the

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Trafficking of lysosomal cathepsin B-green fluorescent protein to the surface of thyroid epithelial cells involves the endosomal/lysosomal compartment

Journal of Cell Science, 2002

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Molecules important for thyroid hormone synthesis and action - known facts and future perspectives

Thyroid Research, 2011

Thyroid hormones are of crucial importance for the functioning of nearly every organ. Remarkably,... more Thyroid hormones are of crucial importance for the functioning of nearly every organ. Remarkably, disturbances of thyroid hormone synthesis and function are among the most common endocrine disorders affecting approximately one third of the working German population. Over the last ten years our understanding of biosynthesis and functioning of these hormones has increased tremendously. This includes the identification of proteins involved in thyroid hormone biosynthesis like Thox2 and Dehal where mutations in these genes are responsible for certain degrees of hypothyroidism. One of the most important findings was the identification of a specific transporter for triiodothyronine (T3), the monocarboxylate transporter 8 (MCT8) responsible for directed transport of T3 into target cells and for export of thyroid hormones out of thyroid epithelial cells. Genetic disturbances of MCT8 in patients result in a biochemical constellation of high T3 levels in combination with low or normal TSH and thyroxine levels leading to a new syndrome of severe X-linked mental retardation. Importantly mice lacking MCT8 presented only with a mild phenotype, indicating that compensatory mechanisms exist in mice. Moreover, it has become clear that not only genomic actions of T3 exist. T3 is also capable to activate adhesion receptors and it signals via activation of PI3K and MAPK pathways. Most recently, thyroid hormone derivatives were identified, the thyronamines which are decarboxylated thyroid hormones initiating physiological actions like lowering body temperature and heart rate, thereby acting in opposite direction to the classical thyroid hormones. So far it is believed that thyronamines function via the activation of a G-protein coupled receptor, TAAR1. The objective of this review is to summarise the recent findings in thyroid hormone synthesis and action and to discuss their implications for diagnosis of thyroid disease and for treatment of patients.

Cathepsin B trafficking in thyroid carcinoma cells

Thyroid Research, 2011

Background: The cysteine peptidase cathepsin B is important in thyroid physiology by being involv... more Background: The cysteine peptidase cathepsin B is important in thyroid physiology by being involved in prohormone processing initiated in the follicle lumen and completed in endo-lysosomal compartments. However, cathepsin B has also been localized to the extrafollicular space in thyroid cancer tissue, and is therefore suggested to promote invasiveness and metastasis in thyroid carcinomas through e.g. extracellular matrix degradation.

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The endolysosomal cysteine cathepsins L and K are involved in macrophage-mediated clearance of Staphylococcus aureus and the concomitant cytokine induction

by Klaudia Brix and Stephanie Dauth

The FASEB Journal, 2014

Cysteine cathepsins are endolysosomal cysteine proteases highly expressed in macrophages; however... more Cysteine cathepsins are endolysosomal cysteine proteases highly expressed in macrophages; however, their individual contributions to the elimination of bacteria and bacteria-induced cytokine production by macrophages are unknown. We assessed the contribution of cysteine cathepsins to macrophage defense pathways against Staphylococcus aureus by using chemical inhibitors and by infecting primary bone marrow-derived macrophages deficient in 1 of 7 major macrophage-expressed endolysosomal cysteine proteases. We show that cysteine cathepsins are involved in the phagocytosis and killing of S. aureus. Cathepsin L was identified as an executor of nonoxidative killing. Moreover, microarray data revealed cysteine cathepsins to be important for the maximal induction of certain proinflammatory genes, such as IL6, in response to S. aureus. Cysteine cathepsin&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s contribution to IL6 production was dependent on phagocytosis, and cathepsin K was identified to be a critical protease in this process. Analysis of macrophages with impaired trafficking of endolysosomal Toll-like receptors (TLRs) to the acidic compartment revealed that they were not involved in cathepsin-dependent IL6 induction. Because IL6 production was completely dependent on the TLR-adaptor protein myeloid differentiation primary response gene 88 (MyD88), it appears that other TLRs are involved. In summary, lysosomal cysteine proteases are functionally linked to the complex bactericidal and inflammatory activities of macrophages.

A Potential New Pathway for Staphylococcus aureus Dissemination: The Silent Survival of S. aureus Phagocytosed by Human Monocyte-Derived Macrophages

by Klaudia Brix and Malgorzata Kubica

PLoS ONE, 2008

Although considered to be an extracellular pathogen, Staphylococcus aureus is able to invade a va... more Although considered to be an extracellular pathogen, Staphylococcus aureus is able to invade a variety of mammalian, nonprofessional phagocytes and can also survive engulfment by professional phagocytes such as neutrophils and monocytes. In both of these cell types S. aureus promptly escapes from the endosomes/phagosomes and proliferates within the cytoplasm, which quickly leads to host cell death. In this report we show that S. aureus interacted with human monocyte-derived macrophages in a very different way to those of other mammalian cells. Upon phagocytosis by macrophages, S. aureus persisted intracellularly in vacuoles for 3-4 days before escaping into the cytoplasm and causing host cell lysis. Until the point of host cell lysis the infected macrophages showed no signs of apoptosis or necrosis and were functional. They were able to eliminate intracellular staphylococci if prestimulated with interferon-c at concentrations equivalent to human therapeutic doses. S. aureus survival was dependent on the alternative sigma factor B as well as the global regulator agr, but not SarA. Furthermore, isogenic mutants deficient in a-toxin, the metalloprotease aureolysin, protein A, and sortase A were efficiently killed by macrophages upon phagocytosis, although with different kinetics. In particular a-toxin was a key effector molecule that was essential for S. aureus intracellular survival in macrophages. Together, our data indicate that the ability of S. aureus to survive phagocytosis by macrophages is determined by multiple virulence factors in a way that differs considerably from its interactions with other cell types. S. aureus persists inside macrophages for several days without affecting the viability of these mobile cells which may serve as vehicles for the dissemination of infection. Citation: Kubica M, Guzik K, Koziel J, Zarebski M, Richter W, et al (2008) A Potential New Pathway for Staphylococcus aureus Dissemination: The Silent Survival of S. aureus Phagocytosed by Human Monocyte-Derived Macrophages. PLoS ONE 3(1): e1409.

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Toxicity of cucurbit[7]uril and cucurbit[8]uril: an exploratory in vitro and in vivo study

Organic & Biomolecular Chemistry, 2010

Cucurbit[n]urils (CB[n]) are potential stabilizing, solubilizing, activating, and delivering agen... more Cucurbit[n]urils (CB[n]) are potential stabilizing, solubilizing, activating, and delivering agents for drugs. The toxicity of the macrocyclic host molecules cucurbit[7]uril (CB[7]), the most water-soluble homologue, as well as cucurbit[8]uril (CB[8]) has been evaluated. In vitro studies on cell cultures revealed an IC(50) value of 0.53 +/- 0.02 mM for CB[7], corresponding to around 620 mg of CB[7] per kg of cell material. Live-cell imaging studies performed on cells treated with subtoxic amounts of CB[7] showed no detrimental effects on the cellular integrity as assessed by mitochondrial activity. For CB[8], no significant cytotoxicity was observed within its solubility range. The bioadaptability of the compounds was further examined through in vivo studies on mice, where intravenous administration of CB[7] showed a maximum tolerated dosage of 250 mg kg(-1), while oral administration of a CB[7]/CB[8] mixture showed a tolerance of up to 600 mg kg(-1). The combined results indicate a sufficiently low toxicity to encourage further exploration of CB[n] as additives for medicinal and pharmaceutical use.

LRP1 modulates APP trafficking along early compartments of the secretory pathway

Neurobiology of Disease, 2008

The amyloid beta peptide (A beta) is a central player in Alzheimer&amp;amp;amp;amp;amp;amp;am... more The amyloid beta peptide (A beta) is a central player in Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease (AD) pathology. A beta liberation depends on APP cleavage by beta- and gamma-secretases. The low density lipoprotein receptor related protein 1 (LRP1) was shown to mediate APP processing at multiple steps. Newly synthesized LRP1 can interact with APP, implying an interaction between these two proteins early in the secretory pathway. We wanted to investigate whether LRP1 mediates APP trafficking along the secretory pathway, and, if so, whether it affects APP processing. Indeed, the early trafficking of APP within the secretory pathway is strongly influenced by its interaction with the C-terminal domain of LRP1. The LRP1-construct expressing an ER-retention motif, LRP-CT KKAA, had the capacity to retard APP traffic to early secretory compartments. In addition, we provide evidence that APP metabolism occurs in close conjunction with LRP1 trafficking, highlighting a new role of lipoprotein receptors in neurodegenerative diseases.

Watching proteases in action

Nature Chemical Biology, 2005

Activity-based probes can be used for monitoring enzyme activity based on their covalent reaction... more Activity-based probes can be used for monitoring enzyme activity based on their covalent reactions with active-site residues. A quenched activity-based probe has now been developed that becomes fluorescent only after labeling active proteases. The specificity of the fluorescent signal and cell permeability of the small molecule make this probe effective for monitoring protease activity in living cells.

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Altered Dye Diffusion and Upregulation of Connexin37 in Mouse Aortic Endothelium Deficient in Connexin40

Journal of Vascular Research, 2002

Connexin40 (Cx40), connexin37 (Cx37) and connexin43 (Cx43) are subunit proteins of gap junction c... more Connexin40 (Cx40), connexin37 (Cx37) and connexin43 (Cx43) are subunit proteins of gap junction channels in the vascular wall which are presumably involved in the propagation of vasomotor signals. In this study we have investigated in Cx40-deficient versus wild-type aortic endothelium to which extent loss of Cx40 impairs intercellular communication. We show in Cx40-deficient mice that expression of both Cx37 and Cx43 protein was increased approximately 3- and 2-fold over the level in wild-type endothelium, respectively. Furthermore, Cx37 immunosignals were distributed more homogeneously on contacting plasma membranes in Cx40-deficient versus with wild-type endothelium. Cx43 was not detected in endothelium but only in smooth muscle cells of the vessel wall. Iontophoretic injection of Lucifer Yellow or neurobiotin into aortic endothelium of Cx40-deficient mice showed extensive intercellular transfer of neurobiotin but not of Lucifer Yellow. In contrast, intercellular spreading of Lucifer Yellow was observed in endothelium of wild-type aorta. As shown by electron microscopy, gap junctions in Cx40-deficient endothelium were morphologically different from those of wild-type vessels. These results demonstrate that dye diffusibility of endothelial gap junctions is different in Cx40-deficient and wild-type mice, although Cx40-deficient mice retain the capability of intercellular communication. Apparently, Cx40-deficient endothelial cells upregulate and redistribute Cx37 as a molecular adaptation to the lack of Cx40.

Micro Raman spectroscopy for monitoring alterations between human skin keratinocytes HaCaT and their tumorigenic derivatives A5RT3-toward a Raman characterization of a skin carcinoma model

by Klaudia Brix and Maren Rehders

Journal of Raman Spectroscopy, 2010

We have monitored such changes for the human skin keratinocyte cell line HaCaT and its cancerogen... more We have monitored such changes for the human skin keratinocyte cell line HaCaT and its cancerogenic counterpart A5RT3 at 514.5 and 647 nm excitations, with either fixed-cell droplets or adherent fixed and living cells for repeated preparations over time in order to discriminate intrinsic characteristic changes. Cell droplets yielded average but rather reproducible information and helped to rapidly determine such changes. The Raman spectra show differences in the relative intensity ratios of the protein amide I band at 1656 cm −1 and amide III bands around 1250 cm −1 and of the phenylalanine ring mode at 1003.6 cm −1 to the CH 2 deformation band at 1448 cm −1 , which are considerably greater for HaCaT cells than A5RT3 cells. Interestingly, these observations were accompanied by severe and consistent changes in the amide III region and in the collagen marker region around 936 cm −1 , therefore providing an unambiguous evidence of

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