Biomedical subjects

Susanne Schmidt

Publications and source records attributed to Susanne Schmidt.

11 recordsLinked to original sources

PubMed2007

Effective treatment of kaposiform hemangioendotheliomas associated with Kasabach-Merritt phenomenon using four-drug regimen.

We report a case of a 6-month-old girl suffering from a kaposiform hemangioendothelioma of the chest wall, associated with Kasabach-Merritt phenomenon. Despite rapid intervention with cortisone and interferon alpha the tumor led to a life-threatening clinical condition with progressive growth and consumption coagulopathy under therapy. Because therapy for kaposiform hemangioendotheliomas with a single anti-angiogenic or anti-proliferative agent has not been reported to be very successful, we administered vincristine, combined with cyclophosphamide, actinomycin D, and methotrexate in a critically ill patient. After six cycles of the applied four-drug regiment, the infant was in remission, which has been maintained for 5 months since stopping therapy.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2006

Identification of TRIO-GEFD1 chemical inhibitors using the yeast exchange assay.

BACKGROUND INFORMATION: Rho GTPases are involved in many biological processes and participate in cancer development. Their activation is catalysed by exchange factors [RhoGEFs (Rho GTPase guanine nucleotide-exchange factor)] of the Dbl family. RhoGEFs display proto-oncogenic features, thus appearing as candidate targets for anticancer drugs. Dominant-negative Rho GTPase mutants have been widely used to block RhoGEF signalling. However, these tools suffer from limitations, due to the high number of RhoGEFs and the complex mechanisms that control Rho GTPase activation. RESULTS: RhoG-T17N is a poor inhibitor of its exchange factor TRIO-GEFD1 (first exchange domain of the exchange factor TRIO) in vivo: although it binds to TRIO-GEFD1, RhoG-T17N does not block the downstream signalling. Using the yeast exchange assay, we show that in the presence of TRIO-GEFD1, RhoG-T17N can bind to its effectors, which illustrates how negative mutants may produce misleading interpretations and emphasizes the need for new types of RhoGEF inhibitors. In that prospect, we adapted the yeast exchange assay method to identify RhoGEF inhibitors. Using this novel approach, we screened a 3500-chemical-compound library and identified a potential inhibitor of TRIO-GEFD1. This molecule inhibited TRIO-GEFD1 in vitro. Among the chemical analogues of this compound, we identified two molecules with better inhibitory activity. The three TRIO-GEFD1 inhibitors had no effect on ARHGEF17 and ARNO [ARF (ADP-ribosylation factor) nucleotide-binding-site opener], two exchange factors for RhoA and Arf1 respectively. CONCLUSIONS: The development of RhoGEF inhibitors appears as a valuable tool for the study of Rho GTPase signalling pathways. The yeast exchange assay adaptation we present here is suitable to screen for chemical or peptide libraries and identify candidate inhibitors.

Biological Assay↗

PubMed2005

Eph-dependent tyrosine phosphorylation of ephexin1 modulates growth cone collapse.

Ephs regulate growth cone repulsion, a process controlled by the actin cytoskeleton. The guanine nucleotide exchange factor (GEF) ephexin1 interacts with EphA4 and has been suggested to mediate the effect of EphA on the activity of Rho GTPases, key regulators of the cytoskeleton and axon guidance. Using cultured ephexin1-/- mouse neurons and RNA interference in the chick, we report that ephexin1 is required for normal axon outgrowth and ephrin-dependent axon repulsion. Ephexin1 becomes tyrosine phosphorylated in response to EphA signaling in neurons, and this phosphorylation event is required for growth cone collapse. Tyrosine phosphorylation of ephexin1 enhances ephexin1's GEF activity toward RhoA while not altering its activity toward Rac1 or Cdc42, thus changing the balance of GTPase activities. These findings reveal that ephexin1 plays a role in axon guidance and is regulated by a switch mechanism that is specifically tailored to control Eph-mediated growth cone collapse.

Actins↗

PubMed2005

Linkage of familial hemophagocytic lymphohistiocytosis (FHL) type-4 to chromosome 6q24 and identification of mutations in syntaxin 11.

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disorder characterized by hyperactive phagocytes and defects in natural killer cell function. It has been shown previously that mutations in the perforin 1 gene (PRF1) and in UNC13D are associated with FHL2 and FHL3, respectively, indicating genetic heterogeneity. We performed genome-wide homozygosity mapping in a large consanguineous Kurdish kindred with five children affected with FHL. Linkage to a 10 cM region on chromosome 6q24 between D6S1569 and D6S960 defined a novel FHL locus. By screening positional candidate genes, we identified a homozygous deletion of 5 bp in the syntaxin 11 gene (STX11) in this family. We could demonstrate that syntaxin 11 protein was absent in the mononuclear cell fraction of patients with the homozygous 5 bp deletion. In addition to this family, we found homozygous mutations in STX11 in five consanguineous Turkish/Kurdish FHL kindreds including two families with the 5 bp deletion, one family with a large 19.2 kb genomic deletion spanning the entire coding region of STX11 (exon 2) and two families with a nonsense mutation that leads to a premature stop codon in the C-terminal end of the protein. As both STX11 and UNC13D are involved in vesicle trafficking and membrane fusion, we conclude that, besides mutations in perforin 1, defects in the endocytotic or the exocytotic pathway may be a common mechanism in FHL.

Chromosomes, Human, Pair 6↗

PubMed2004

Severe respiratory syncytial virus bronchiolitis in infancy and asthma and allergy at age 13.

We have prospectively studied wheezing disorder and allergy in 47 children hospitalized with respiratory syncytial virus (RSV) bronchiolitis in infancy and 93 matched control subjects. Subjects with at least three episodes of wheezing were defined as recurrent wheezers and as having asthma if the episodes were doctor verified. Here we report the outcome at age 13 years in 46/47 children with RSV and 92/93 control subjects. Wheezing disorder and clinical allergy were estimated using a questionnaire. Skin prick tests were performed and serum IgE antibodies measured. Spirometry was undertaken at rest, after dry air challenge, and after beta2-agonist inhalation. The occurrence of symptoms over the previous 12 months was significantly higher in the RSV group than among the control subjects, 43% versus 8% for asthma/recurrent wheezing and 39% versus 15% for allergic rhinoconjunctivitis. Sensitization to common inhaled allergens was more frequent in the RSV group than in the control subjects, judged by skin prick tests (50% versus 28%; p = 0.022), or by serum IgE antibodies (45% versus 26%; p = 0.038). Compared with the control subjects, the RSV group showed mild airway obstruction both at rest and after bronchodilation, and had slightly more reactive airways. RSV bronchiolitis in infancy severe enough to cause hospitalization is a risk factor for allergic asthma in early adolescence.

Adolescent↗

PubMed2002

Identification of the first Rho-GEF inhibitor, TRIPalpha, which targets the RhoA-specific GEF domain of Trio.

The Rho-guanine nucleotide exchange factors (Rho-GEFs) remodel the actin cytoskeleton via their Rho-GTPase targets and affect numerous physiological processes such as transformation and cell motility. They are therefore attractive targets to design specific inhibitors that may have therapeutic applications. Trio contains two Rho-GEF domains, GEFD1 and GEFD2, which activate the Rac and RhoA pathways, respectively. Here we have used a genetic screen in yeast to select in vivo peptides coupled to thioredoxin, called aptamers, that could inhibit GEFD2 activity. One aptamer, TRIAPalpha (TRio Inhibitory APtamer), specifically blocks GEFD2-exchange activity on RhoA in vitro. The corresponding peptide sequence, TRIPalpha, inhibits TrioGEFD2-mediated activation of RhoA in intact cells and specifically reverts the neurite retraction phenotype induced by TrioGEFD2 in PC12 cells. Thus TRIPalpha is the first Rho-GEF inhibitor isolated so far, and represents an important step in the design of inhibitors for the expanding family of Rho-GEFs.

Amino Acid Sequence↗

PubMed2002

The Human Rho-GEF trio and its target GTPase RhoG are involved in the NGF pathway, leading to neurite outgrowth.

Rho-GTPases control a wide range of physiological processes by regulating actin cytoskeleton dynamics. Numerous studies on neuronal cell lines have established that Rac, Cdc42, and RhoG activate neurite extension, while RhoA mediates neurite retraction. Guanine nucleotide exchange factors (GEFs) activate Rho-GTPases by accelerating GDP/GTP exchange. Trio displays two Rho-GEF domains, GEFD1, activating the Rac pathway via RhoG, and GEFD2, acting on RhoA, and contains numerous signaling motifs whose contribution to Trio function has not yet been investigated. Genetic analyses in Drosophila and in Caenorhabditis elegans indicate that Trio is involved in axon guidance and cell motility via a GEFD1-dependent process, suggesting that the activity of its Rho-GEFs is strictly regulated. Here, we show that human Trio induces neurite outgrowth in PC12 cells in a GEFD1-dependent manner. Interestingly, the spectrin repeats and the SH3-1 domain of Trio are essential for GEFD1-mediated neurite outgrowth, revealing an unexpected role for these motifs in Trio function. Moreover, we demonstrate that Trio-induced neurite outgrowth is mediated by the GEFD1-dependent activation of RhoG, previously shown to be part of the NGF (nerve growth factor) pathway. The expression of different Trio mutants interferes with NGF-induced neurite outgrowth, suggesting that Trio may be an upstream regulator of RhoG in this pathway. In addition, we show that Trio protein accumulates under NGF stimulation. Thus, Trio is the first identified Rho-GEF involved in the NGF-differentiation signaling.

Animals↗

PubMed2002

Human p63RhoGEF, a novel RhoA-specific guanine nucleotide exchange factor, is localized in cardiac sarcomere.

The Rho small GTPases are crucial proteins involved in regulation of signal transduction cascades from extracellular stimuli to cell nucleus and cytoskeleton. It has been reported that these GTPases are directly associated with cardiovascular disorders. In this context, we have searched for novel modulators of Rho GTPases, and here we describe p63RhoGEF a new Db1-like guanine nucleotide exchange factor (GEF). P63RhoGEF encodes a 63 kDa protein containing a Db1 homology domain in tandem with a pleckstrin homology domain and is most closely related to the second Rho GEF domain of Trio. Northern blot and in situ analysis have shown that p63RhoGEF is mainly expressed in heart and brain. In vitro guanine nucleotide exchange assays have shown that p63RhoGEF specifically acts on RhoA. Accordingly, p63RhoGEF expression induces RhoA-dependent stress fiber formation in fibroblasts and in H9C2 cardiac myoblasts. Moreover, we show that p63RhoGEF activation of RhoA in intact cells is dependent on the presence of the PH domain. Using a specific anti-p63RhoGEF antibody, we have detected the p63RhoGEF protein by immunocytochemistry in human heart and brain tissue sections. Confocal microscopy shows that p63RhoGEF is located in the sarcomeric I-band mainly constituted of cardiac sarcomeric actin. Together, these results show that p63RhoGEF is a RhoA-specific GEF that may play a key role in actin cytoskeleton reorganization in different tissues, especially in heart cellular morphology.

Amino Acid Sequence↗

PubMed2002

Can the nitrogenous composition of xylem sap be used to assess salinity stress in Casuarina glauca?

It is predicted that dryland salinity will affect up to 17 Mha of the Australian landscape by 2050, and therefore, monitoring the health of tree plantings and remnant native vegetation in saline areas is increasingly important. Casuarina glauca Sieber ex Spreng. has considerable salinity tolerance and is commonly planted in areas with a shallow, saline water table. To evaluate the potential of using the nitrogenous composition of xylem sap to assess salinity stress in C. glauca, the responses of trees grown with various soil salinities in a greenhouse were compared with those of trees growing in field plots with different water table depths and groundwater salinities. In the greenhouse, increasing soil salinity led to increased allocation of nitrogen (N) to proline and arginine in both stem and root xylem sap, with coincident decreases in citrulline and asparagine. Although the field plots were ranked as increasingly saline-based on ground water salinity and depth-only the allocation of N to citrulline differed significantly between the field plots. Within each plot, temporal variation in the composition of the xylem sap was related to rainfall, rainfall infiltration and soil salinity. Periods of low rainfall and infiltration and higher soil salinity corresponded with increased allocation of N to proline and arginine in the xylem sap. The allocation of N to citrulline and asparagine increased following rainfall events where rain was calculated to have infiltrated sufficiently to decrease soil salinity. The relationship between nitrogenous composition of the xylem sap of C. glauca and soil salinity indicates that the analysis of xylem sap is an effective method for assessing changes in salinity stress in trees at a particular site over time. However, the composition of the xylem sap proved less useful as a comparative index of salinity stress in trees growing at different sites.

Arginine↗

PubMed1998

Transport, storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia.

Xylem sap from woody species in the wet/dry tropics of northern Australia was analyzed for N compounds. At the peak of the dry season, arginine was the main N compound in sap of most species of woodlands and deciduous monsoon forest. In the wet season, a marked change occurred with amides becoming the main sap N constituents of most species. Species from an evergreen monsoon forest, with a permanent water source, transported amides in the dry season. In the dry season, nitrate accounted for 7 and 12% of total xylem sap N in species of deciduous and evergreen monsoon forests, respectively. In the wet season, the proportion of N present as nitrate increased to 22% in deciduous monsoon forest species. These results suggest that N is taken up and assimilated mainly in the wet season and that this newly assimilated N is mostly transported as amide-N (woodland species, monsoon forest species) and nitrate (monsoon forest species). Arginine is the form in which stored N is remobilized and transported by woodland and deciduous monsoon forest species in the dry season. Several proteins, which may represent bark storage proteins, were detected in inner bark tissue from a range of trees in the dry season, indicating that, although N uptake appears to be limited in the dry season, the many tree and shrub species that produce flowers, fruit or leaves in the dry season use stored N to support growth. Nitrogen characteristics of the studied species are discussed in relation to the tropical environment.

Journal Article↗

PubMedDate not supplied

Root adaptation and nitrogen source acquisition in natural ecosystems.

The capacity for nitrate reduction, as measured by nitrate reductase activity (NRA), was generally low for a range of plant communities in Australia (coastal heathland, rainforest, savanna woodland, monsoon forest, mangrove, open Eucalyptus forest, coral cay open forest) and only a loose relationship existed between NRA and leaf nitrogen concentration. This suggests that nitrate ions are not the sole nitrogen source in these communities. Based on (15)N labeling experiments, we found a range of tree species exhibiting a pronounced preference for uptake of ammonium over nitrate. Analysis of soil solutions from several forest and heathland communities indicated that ammonium ions were more prevalent than nitrate ions and that soluble forms of organic nitrogen (amino acids and protein) were present in concentrations similar to those of mineral nitrogen. To determine the extent to which root adaptations and associations might broaden nitrogen source utilization to include organic nitrogen, we assessed the effects of various nitrogen sources on seedling growth in sterile culture. Non-mycorrhizal seedlings of Eucalyptus grandis W. Hill ex Maiden and Eucalyptus maculata Hook. grew well on mineral sources of nitrogen, but did not grow on organic sources of nitrogen other than glutamine. Mycorrhizal seedlings grew well on a range of organic nitrogen sources. When offered a mixture of inorganic and organic nitrogen sources at low concentrations, mycorrhizal seedlings derived a significant proportion of their nitrogen budget from organic sources. We also demonstrated that a species of the obligately non-mycorrhizal genus Hakea, a heathland proteaceous shrub possessing cluster roots, had the ability to incorporate (15)N-labeled organic sources (e.g., glycine). We conclude that mycorrhizal associations and root adaptations confer the ability to substantially broaden the nitrogen source base on some plant species.

Journal Article↗