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M Kann

Publications and source records attributed to M Kann.

24 records · Page 2Linked to original sources
PubMed1993

Characterization of the endogenous protein kinase activity of the hepatitis B virus.

During the assembly of the nucleocapsid of the hepatitis B virus a protein kinase, probably of cellular origin, is encapsidated. This enzyme phosphorylates serine residue(s) localized within the lumen of the particle. By using purified, liver-derived core particles, we characterized the protein kinase activity in the presence of different ions and inhibitors. Controls were performed with cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) and recombinant core particles. We showed that the endogenous protein kinase of the core particles was not inhibited by H89, a specific inhibitor of PKA. Staurosporine, a selective inhibitor of PKC inhibited the endogenous kinase activity only within the first minutes of the reaction. In contrast, quercetine, a selective inhibitor of the protein kinase M (PKM) did not inhibit during the first minutes but inhibited efficiently during later phases of incubation. PKM represents an enzymatically active proteolytic fragment of PKC. These results suggest that PKC is encapsidated into human core particles and is converted to PKM during the in vitro reaction. This conclusion implies the association of a protease activity localized with the HBV nucleocapsid inside liver-derived core particles.

Cyclic AMP-Dependent Protein Kinases↗
PubMed1991

Identification of a binding site in the hepatitis B virus RNA pregenome for the viral Pol gene product.

The hepatitis B virus, although containing a DNA genome, replicates by reverse transcription of an RNA pregenome. The viral Pol gene encodes the reverse transcriptase which catalyzes viral DNA synthesis. To study the interaction of this protein with HBV RNA, the entire Pol gene product was expressed except its eight amino-terminal codons in Escherichia coli as fusion protein with beta-galactosidase. In the absence of competing nucleic acids full-length expression products were able to nonspecifically bind in vitro synthesized HBV RNAs of different polarity and length. However, if competed with an excess of unspecific RNA, only those HBV RNAs were bound which contained besides the direct repeats 1 and 2 nucleotide sequences downstream of direct repeat 1. The corresponding binding site was found to be located within the adjacent 134 nucleotides downstream of DR1. We conclude from our data that this region which is in part homologous to the U5 region of retroviral genomes may be important for the binding of the HBV Pol gene product to the viral pregenome.

Binding Sites↗
PubMed1990

The effect of acetazolamide on hypercapnic and eucapnic/poikilocapnic hypoxic ventilatory responses in normal subjects.

We have studied the effect of acetazolamide 500 mg bd for three days on ventilatory response to CO2 (HCVR) and hypoxia under both isocapnic and poikilocapnic conditions (isocapnic and poikilocapnic HVR) in five normal subjects. Although acetazolamide reduced calculated arterial pH (7.41 [SEM] 0.01 to 7.37 [SEM] 0.01: p less than 0.01) there was no significant change in either isocapnic HVR (with PetCO2 held at the post-drug resting level) or poikilocapnic HVR in terms of slope and ventilation at SaO2 = 80%. HCVR slope rose slightly (+1.82 [SEM] 0.43 to +2.2 [SEM] 0.29 l/min/mmHg: NS) and there was a significant increase in ventilation at Pet-CO2 = 50 mmHg (9.42 [SEM] 3.3 to 31.4 [SEM] 6.31/min: p less than 0.01). These findings are consistent with the claim that acetazolamide stimulates central chemoreceptors and inhibits peripheral chemoreceptors. Increased sensitivity to CO2 would reverse the suppressive effect of respiratory alkalosis on hypoxic ventilatory drive following rapid ascent to high altitude, and this probably accounts for the efficacy of acetazolamide in the prophylaxis of acute mountain sickness. However, inhibition of peripheral chemoreceptors may also result in symptomatic benefit by reducing sleep disturbance due to periodic breathing.

Acetazolamide↗
PubMedDate not supplied

Cell-based delivery of cytokines allows for the differentiation of a doxycycline inducible oligodendrocyte precursor cell line in vitro.

BACKGROUND: Stem cells, having the property of self renewal, offer the promise of lifelong repair of damaged tissue. However, somatic tissue-committed primary stem cells are rare and difficult to expand in vitro. Genetically modified stem-like cells with the ability to expand conditionally provide a valuable tool with which to study stem cell biology, especially the cellular events of proliferation and differentiation. In addition, stem cells may be appropriate candidates for therapeutic applications. METHODS: Double transgenic mice possesing SV40 T antigen (Tag) under the control of the reverse tetracycline-transactivator (rtTA) were used to establish cell lines. One brain cell line was partially characterized by DNA sequencing, morphology, antigen expression using flow cytometry, confocal microscopy, and electrophysiology using the patch clamp technique. Cell cycle analysis was performed using propidium iodide staining; cell viability and H3-thymidine incorporation assays. The ability of this cell line to differentiate was assessed by confocal microscopy following co-culture with stem cells secreting cytokines. RESULTS: We report here the establishment and partial characterization of a cell line derived from the brain tissue of rtTA-SV40 Tag transgenic mice. Analysis of the morphology and antigen markers has shown that this cell line mimics some aspects of primary glial precursors. The results of electrophysiology are consistent with this and suggest that the cell line is derived from O2A glial precursor cells. Cell cycle progression of this cell line is doxycycline-dependent. In the absence of doxycycline, cells become apoptotic. Differentiation into mature type 2 astrocytes and (precursor) oligodendrocytes can be induced upon withdrawal of doxycycline and addition of epithelial stem cells secreting cytokine, such as hIL3 (human Interleukine 3) or hIL6 to the culture. In contrast, co-culturing with hCNTF (human Ciliary NeuroTrophic Factor)-secreting epithelial stem cells did not induce them to mature into progeny cell types. CONCLUSION: The differentiation of this O2A glial precursor line does not occur automatically in culture. Additional external help is required from the cell-based delivery of appropriate transgenic cytokines. Withdrawal of doxycycline from the culture medium removes the proliferation signals and induces a fatal outcome.

Animals↗
PubMedDate not supplied

Changes in the spectrum of fungal isolates: results from clinical specimens gathered in 1987/88 compared with those in 1991/92 in the University Hospital Göttingen, Germany.

In the University Hospital in Göttingen, the spectra of fungal species in clinical specimens of respiratory secretions, bronchial secretions and urine were compared over periods of 15 months (10/87 to 12/88 and 1/91 to 3/92) before and after the introduction of fluconazole. The following changes could be demonstrated: 1. In all specimens analysed the number of Candida albicans isolates decreased, while the number of Candida tropicalis isolates remained almost unchanged. 2. During the observation period the number of Candida glabrata isolates doubled. In 1991 C. glabrata was second to C. albicans as the most common of all fungal isolates, appearing in 8.6% of all specimens. 3. The total number of Candida krusei isolates increased only slightly, but the rise in the number of isolates in bronchial secretions was statistically significant. 4. The prevalence of rarely isolated Candida yeasts, such as Candida guilliermondii, Candida lipolytica and Candida kefyr, and Candida isolates which were not further differentiated increased. 5. During the observation period the number of mixed cultures showed a fourfold increase. C. glabrata and C. krusei were associated in more than 75% of all isolates with C. albicans or C. tropicalis respectively. 6. The number of mould isolates increased. These changes in the spectra of fungal isolates are discussed with respect to the broad therapeutic and prophylactic usage of fluconazole in the University Hospital of Göttingen.

Candida↗