PubMed Health⌕ Search

Biomedical subjects

F Frischknecht

Publications and source records attributed to F Frischknecht.

12 recordsLinked to original sources
PubMed2004

Umbilical endometriosis.

We report two women who presented with a recurrent, mildly painful, bluish nodule in the umbilicus. Both patients complained of local tenderness and occasional bleeding that increased during menstruation. Neither patient had had previous pelvic surgery. Excision of the lesions revealed a primary umbilical endometriosis; in one case, a simultaneous laparoscopy showed a pelvic endometriosis. We review the current literature and discuss the possible etiopathogenesis and when a laparoscopy is indicated to diagnose a concomitant pelvic endometriosis. Umbilical endometriosis is a very rare disease but should be considered in the differential diagnosis of umbilical lesions.

Adult↗
PubMed2001

Surfing pathogens and the lessons learned for actin polymerization.

A number of unrelated bacterial species as well as vaccinia virus (ab)use the process of actin polymerization to facilitate and enhance their infection cycle. Studies into the mechanism by which these pathogens hijack and control the actin cytoskeleton have provided many interesting insights into the regulation of actin polymerization in migrating cells. This review focuses on what we have learnt from the actin-based motilities of Listeria, Shigella and vaccinia and discusses what we would still like to learn from our nasty friends, including enteropathogenic Escherichia coli and Rickettsia

Actin-Related Protein 2↗
PubMed2001

Kinesin-dependent movement on microtubules precedes actin-based motility of vaccinia virus.

Vaccinia virus, a close relative of the causative agent of smallpox, exploits actin polymerization to enhance its cell-to-cell spread. We show that actin-based motility of vaccinia is initiated only at the plasma membrane and remains associated with it. There must therefore be another form of cytoplasmic viral transport, from the cell centre, where the virus replicates, to the periphery. Video analysis reveals that GFP-labelled intracellular enveloped virus particles (IEVs) move from their perinuclear site of assembly to the plasma membrane on microtubules. We show that the viral membrane protein A36R, which is essential for actin-based motility of vaccinia, is also involved in microtubule-mediated movement of IEVs. We further show that conventional kinesin is recruited to IEVs via the light chain TPR repeats and is required for microtubule-based motility of the virus. Vaccinia thus sequentially exploits the microtubule and actin cytoskeletons to enhance its cell-to-cell spread.

3T3 Cells↗
PubMed2000

[Prevalence of diagnoses in ambulatory and hospitalized patients].

Prevalence and distribution of different clinical presentations were analyzed in 6000 hospitalized and ambulatory patients. One medical University clinic and three further hospital units, two university outpatient clinics and four practitioners participated. 6000 main diagnoses and 2560 additional diagnoses had been recorded. The mean age was 64 for the hospitalized patients, 50 years for the outpatient clinic and 47 years at the doctors' office. Cardiovascular diseases were most common. This group of diagnoses was twice as common in hospitalized patients (40.9%) than in the ambulatory group: 19.5% (outpatient clinic) and 15.2% (private practice). In contrast, psychiatric diagnoses were 5 times more frequent in the practice than in the hospital (11.6% vs. 2.4%) and musculoskeletal diseases were even 7 times more common in the practice (13.3% vs. 1.9). 93% of the hospitalized patients had one of the 25 most prevalent diagnoses. This percentage was substantially lower in patients of the outpatient clinic (73%) and of private practice (64%). An additional diagnosis was posed for every other patient in the hospital or at the outpatient clinic, in the practitioners office only for every fourth patient. The analysis shows that hospitalized patients often have a different set of diagnoses than ambulatory ones. To guarantee a broad internistic training outpatient clinics are of great importance. A part of internistic education, however, can also be obtained by cooperation with practitioners.

Adult↗
PubMed2000

A complex of N-WASP and WIP integrates signalling cascades that lead to actin polymerization.

Wiskott-Aldrich syndrome protein (WASP) and N-WASP have emerged as key proteins connecting signalling cascades to actin polymerization. Here we show that the amino-terminal WH1 domain, and not the polyproline-rich region, of N-WASP is responsible for its recruitment to sites of actin polymerization during Cdc42-independent, actin-based motility of vaccinia virus. Recruitment of N-WASP to vaccinia is mediated by WASP-interacting protein (WIP), whereas in Shigella WIP is recruited by N-WASP. Our observations show that vaccinia and Shigella activate the Arp2/3 complex to achieve actin-based motility, by mimicking either the SH2/SH3-containing adaptor or Cdc42 signalling pathways to recruit the N-WASP-WIP complex. We propose that the N-WASP-WIP complex has a pivotal function in integrating signalling cascades that lead to actin polymerization.

Actin Cytoskeleton↗
PubMed1999

Actin-based motility of vaccinia virus mimics receptor tyrosine kinase signalling.

Studies of the actin-based motility of the intracellular pathogens Listeria monocytogenes and Shigella flexneri have provided important insight into the events occurring at the leading edges of motile cells. Like the bacteria Listeria and Shigella, vaccinia virus, a relative of the causative agent of smallpox, uses actin-based motility to spread between cells. In contrast to Listeria or Shigella, the actin-based motility of vaccinia is dependent on an unknown phosphotyrosine protein, but the underlying mechanism remains obscure. Here we show that phosphorylation of tyrosine 112 in the viral protein A36R by Src-family kinases is essential for the actin-based motility of vaccinia. Tyrosine phosphorylation of A36R results in a direct interaction with the adaptor protein Nck and the recruitment of the Ena/VASP family member N-WASP to the site of actin assembly. We also show that Nck and N-WASP are essential for the actin-based motility of vaccinia virus. We suggest that vaccinia virus spreads by mimicking the signalling pathways that are normally involved in actin polymerization at the plasma membrane.

Actins↗
PubMed1999

Tyrosine phosphorylation is required for actin-based motility of vaccinia but not Listeria or Shigella.

Studies of the actin-based motility of pathogens have provided important insights into the events occurring at the leading edge of motile cells [1] [2] [3]. To date, several actin-cytoskeleton-associated proteins have been implicated in the motility of Listeria or Shigella: vasodilator-stimulated phosphoprotein (VASP), vinculin and the actin-related protein complex of Arp2 and Arp3 [4] [5] [6] [7]. To further investigate the underlying mechanism of actin-tail assembly, we examined the localization of components of the actin cytoskeleton including Arp3, VASP, vinculin and zyxin during vaccinia, Listeria and Shigella infections. The most striking difference between the systems was that a phosphotyrosine signal was observed only at the site of vaccinia actin-tail assembly. Micro-injection experiments demonstrated that a phosphotyrosine protein plays an important role in vaccinia actin-tail formation. In addition, we observed a phosphotyrosine signal on clathrin-coated vesicles that have associated actin-tail-like structures and on endogenous vesicles in Xenopus egg extracts which are able to nucleate actin tails [8] [9]. Our observations indicate that a host phosphotyrosine protein is required for the nucleation of actin filaments by vaccinia and suggest that this phosphoprotein might be associated with cellular membranes that can nucleate actin.

Actins↗
PubMed1999

Leucine 255 of Src couples intramolecular interactions to inhibition of catalysis.

The activity of the c-Src tyrosine kinase is regulated through intramolecular interactions between the catalytic and SH2/SH3 domains. However, the exact mechanism by which this occurs remains obscure. In the crystal structure of c-Src, the peptide that links the SH2 and catalytic domain (SH2-CD linker) is sandwiched between the latter and the SH3 domain. A residue in the linker, Leu 255, inserts its side chain into a deep hydrophobic pocket present on the surface of the catalytic domain. To investigate the possible regulatory role of this prominent interaction, we mutated Leu 255 to different hydrophobic residues. We found that the length and 'bulkiness' of the side chain had a profound influence on c-Src regulation. Src-L255V was highly active but showed reduced SH3 accessibility in vitro as well as an altered localization in vivo when compared to other deregulated forms of Src. Our analyses lead us to suggest that the Leu 255-pocket interaction is a critical component of the intramolecular inhibition mechanism of Src family kinases.

Catalysis↗
PubMed1999

Interactions between vaccinia virus IEV membrane proteins and their roles in IEV assembly and actin tail formation.

The intracellular enveloped form of vaccinia virus (IEV) induces the formation of actin tails that are strikingly similar to those seen in Listeria and Shigella infections. In contrast to the case for Listeria and Shigella, the vaccinia virus protein(s) responsible for directly initiating actin tail formation remains obscure. However, previous studies with recombinant vaccinia virus strains have suggested that the IEV-specific proteins A33R, A34R, A36R, B5R, and F13L play an undefined role in actin tail formation. In this study we have sought to understand how these proteins, all of which are predicted to have small cytoplasmic domains, are involved in IEV assembly and actin tail formation. Our data reveal that while deletion of A34R, B5R, or F13L resulted in a severe reduction in IEV particle assembly, IEVs formed by the DeltaB5R and DeltaF13L deletion strains, but not DeltaA34R, were still able to induce actin tails. The DeltaA36R deletion strain produced normal amounts of IEV particles, although these were unable to induce actin tails. Using several different approaches, we demonstrated that A36R is a type Ib membrane protein with a large, 195-amino-acid cytoplasmic domain exposed on the surface of IEV particles. Finally, coimmunoprecipitation experiments demonstrated that A36R interacts with A33R and A34R but not with B5R and that B5R forms a complex with A34R but not with A33R or A36R. Using extracts from DeltaA34R- and DeltaA36R-infected cells, we found that the interaction of A36R with A33R and that of A34R with B5R are independent of A34R and A36R, respectively. We conclude from our observations that multiple interactions between IEV membrane proteins exist which have important implications for IEV assembly and actin tail formation. Furthermore, these data suggest that while A34R is involved in IEV assembly and organization, A36R is critical for actin tail formation.

Actins↗
PubMed1998

Voltage- and ligand-gated ion channels in floor plate neuroepithelia of the rat.

Whole-cell patch-clamp recordings were used to characterize the membrane properties and ion channel complement of floor plate neuroepithelia in embryonic and neonatal rats. The average resting potential was close to -60 mV, the capacitance was approximately 7 pS and the membrane time constant averaged 31 ms, in both neonates and embryos. Two types of K+ current were identified (i) a slowly activating, slowly inactivating current that was present in all cells, and (ii) a rapidly inactivating current that was present in 39% of cells from neonates and 64% of cells from embryos. K+ currents were significantly larger in neonates than embryos. Na+ currents were absent from all neuroepithelial cells examined. In contrast, the majority of floor plate cells exhibited a significant Ca2+ current. Biophysically this current activated at potentials positive to 60 mV and exhibited fast, voltage-dependent, inactivation. The Ca2+ current was equipermeant to Ca2+ and Ba2+, sensitive to 40-120 microM Ni2+ and only slightly inhibited by 100 microM Cd2+. These and other observations indicated this current is mediated by low-voltage-activated (i.e. T-type) Ca2+ channels. The majority of floor plate cells tested also exhibited responses to the neurotransmitter GABA which produced robust inward currents at negative membrane potentials, in chloride-loaded cells. Both the pharmacology and voltage-dependence of the GABA-activated currents indicated they arose from activation of GABA(A) receptors.

Animals↗
PubMed1998

Roles of vaccinia virus EEV-specific proteins in intracellular actin tail formation and low pH-induced cell-cell fusion.

During vaccinia virus (VV) morphogenesis intracellular mature virus (IMV) is wrapped by two additional membranes to form intracellular enveloped virus (IEV). IEV particles can nucleate the formation of actin tails which aid movement of IEVs to the cell surface where the outer IEV membrane fuses with the plasma membrane forming cell-associated enveloped virus (CEV) which remains attached to the cell, or extracellular enveloped virus (EEV) which is shed from the cell. In this report, we have used a collection of VV mutants lacking individual EEV-specific proteins to compare the roles of these proteins in the formation of IEV and IEV-associated actin tails and fusion of infected cells after a low pH shock. Data presented here show that p45-50 (A36R) is not required for IEV formation or for acid-induced cell-cell fusion, but is required for formation of IEV-associated actin tails. In contrast, gp86 (A56R), the virus haemagglutinin, is not required for formation of either IEV or IEV-associated actin tails. Data presented also confirm that p37 (gene F13L), gp42 (B5R) and gp22-24 (A34R) are needed for formation of IEV-associated actin tails and for cell-cell fusion after low pH shock. The phenotypes of these mutants were not affected by the host cell type as similar results were obtained in a range of different cells. Lastly, comparisons of the phenotypes of VV strains Western Reserve, deltaA34R and deltaA36R demonstrate that actin tails are not required for low pH-induced cell-cell fusion.

Actins↗