PubMed Health⌕ Search

Biomedical subjects

K Krause

Publications and source records attributed to K Krause.

At least 37 records · Page 2Linked to original sources
PubMed2000

NF-Y mediates the transcriptional inhibition of the cyclin B1, cyclin B2, and cdc25C promoters upon induced G2 arrest.

During normal cell cycles, the function of mitotic cyclin-cdk1 complexes, as well as of cdc25C phosphatase, is required for G2 phase progression. Accordingly, the G2 arrest induced by DNA damage is associated with a down-regulation of mitotic cyclins, cdk1, and cdc25C phosphatase expression. We found that the promoter activity of these genes is repressed in the G2 arrest induced by DNA damage. We asked whether the CCAAT-binding NF-Y modulates mitotic cyclins, cdk1, and cdc25C gene transcription during this type of G2 arrest. In our experimental conditions, the integrity of the CCAAT boxes of cyclin B1, cyclin B2, and cdc25C promoters, as well as the presence of a functional NF-Y complex, is strictly required for the transcriptional inhibition of these promoters. Furthermore, a dominant-negative p53 protein, impairing doxorubicin-induced G2 arrest, prevents transcriptional down-regulation of the mitotic cyclins, cdk1, and cdc25C genes. We conclude that, as already demonstrated for cdk1, NF-Y mediates the transcriptional inhibition of the mitotic cyclins and the cdc25C genes during p53-dependent G2 arrest induced by DNA damage. These data suggest a transcriptional regulatory role of NF-Y in the G2 checkpoint after DNA damage.

CCAAT-Binding Factor↗
PubMed2000

The tumour suppressor protein p53 can repress transcription of cyclin B.

The tumour suppressor protein p53 has functions in controlling the G(1)/S and G(2)/M transitions. Central regulators for progression from G(2) to mitosis are B-type cyclins complexed with cdc2 kinase. In mammals two cyclin B proteins are found, cyclin B1 and B2. We show that upon treatment of HepG2 cells with 5-fluorouracil or methotrexate, p53 levels increase while concentrations of cyclin B2 mRNA, measured by RT-PCR with the LightCycler system, are reduced. In DLD-1 colorectal adenocarcinoma cells (DLD-1-tet-off-p53) cyclin B1 and B2 mRNA levels drop after expression of wild-type p53 but not after induction of a DNA binding-deficient mutant of p53. Analysis of the cyclin B2 promoter reveals specific repression of this gene by p53. Transfection of wild-type p53 into SaOS-2 cells shuts off transcription from a cyclin B2 promoter-luciferase construct whereas a p53 mutant protein does not. The cyclin B2 promoter does not contain a consensus p53 binding site. Most of the p53-dependent transcriptional responsiveness resides in its 226 bp core promoter. Taken together with earlier observations on p53-dependent transcription of cyclin B1, our results suggest that one way of regulating G(2) arrest may be a reduction in cyclin B levels through p53-dependent transcriptional repression.

Cyclin B↗
PubMed2000

Activated K-ras is involved in regulation of integrin expression in human colon carcinoma cells.

Integrins participate in controlling proliferation and migration. Therefore, changes in integrin expression might be responsible for unrestrained proliferation and invasiveness of tumor cells. Alterations of integrin subunit expression have been observed in human colon carcinoma, especially loss or reduction of the alpha5 subunit, which was observed consistently. The mechanisms responsible for reduction of alpha5 expression and alteration of expression of other integrins are not fully understood. Circumstantial evidence from previous investigations points to an involvement of activated ras oncogenes in repression of integrin expression. The K-ras protooncogene is activated by point mutation in 50% of human colon carcinomas. Thus, we choose an antisense approach for specific inactivation of activated K-ras in the human colon carcinoma cell line SW 480 in order to test whether activated K-ras contributes to changes in integrin expression on colon carcinoma cells. Cell surface expression of the alpha1 and the alpha5 subunit was increased in K-ras antisense transfected clones, cell surface expression of the alpha3 subunit and the alphav subunit was decreased. This shows, in a human system, that activated K-ras is involved in diminishing cell surface expression of the alpha1beta1 collagen/laminin receptor and the alpha5beta1 fibronectin receptor, both of which are implicated in maintenance of a non-transformed phenotype. Moreover, activated K-ras contributes to increased cell surface expression of the alpha3beta1 laminin/collagen/fibronectin receptor and the alphavbeta5 vitronectin receptor, which might play a role in metastatic behavior of tumor cells.

Adenocarcinoma↗
PubMed2000

Disruption of plastid-encoded RNA polymerase genes in tobacco: expression of only a distinct set of genes is not based on selective transcription of the plastid chromosome.

Plastids of higher plants operate with at least two distinct DNA-dependent RNA polymerases, which are encoded in the organelle (PEP) and in the nucleus (NEP), respectively. Plastid run-on assays and Northern analyses were employed to analyse gene expression in tobacco mutant plastids lacking the PEP genes rpoA, rpoB or rpoC1. Hybridisation of run-on transcripts to restriction fragments representing the entire tobacco plastid chromosome, as well as to selected plastid gene-specific probes, shows that all parts of the plastid DNA are transcribed in rpo-deficient plastids. In comparison to wild-type chloroplasts, which are characterized by preferential transcription of photosynthesis-related genes in the light, mutant plastids exhibit a different transcription pattern with less pronounced differences in the hybridisation intensities between the individual genes. The analysis of steady-state transcript patterns and transcription rates of selected genes in both types of plastids demonstrates that differences in transcription rates are not necessarily paralleled by corresponding changes in transcript levels. The accumulation of large transcripts in the mutant plastids indicates that processing of primary transcripts may be impaired in the absence of PEP. These data suggest that, contrary to the prevailing view, much of the regulation of NEP-driven plastid gene expression in the rpo-deficient mutants is not based on differential promoter usage but is exerted at post-transcriptional levels.

Chloroplasts↗
PubMed2000

Molecular, functional and ultrastructural characterisation of plastids from six species of the parasitic flowering plant genus Cuscuta.

Plastids of Cuscuta reflexa Roxb., C. subinclusa D. et H., C. gronovii Willd. and C. campestris Yunck. possess thylakoids and contain both chlorophyll a and b in a ratio similar to that of stem tissue of the systematically closely related but 'normal' green Ipomoea tricolor. In contrast, plastids of C. odorata R. et P. and C. grandiflora H.B.K. do not contain any chlorophyll or possess thylakoids. Light-driven electron transport, as measured by oxygen evolution and indicated by analysis of chlorophyll fluorescence, was present in all chlorophyll-containing species. The photosystem II efficiency was low and ranged from 0.511 to 0.687. The plastid rbcL gene could not be detected in C. odorata, but was present in all other tested species. Neither rbcL transcripts nor the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) could be detected in C. odorata and C. grandiflora. Low amounts of the large subunit of Rubisco were detected immunologically in all other Cuscuta species. Apparently, the genus Cuscuta comprises species with different degrees of plastid functionality, ranging from intact chloroplasts, via plastids with impaired protein production and gene expression to plastids with reduced plastome gene content.

Blotting, Northern↗
PubMed2000

Conformational properties of a cyclic peptide bradykinin B2 receptor antagonist using experimental and theoretical methods.

The solution conformation of the cyclic peptide J324 (cyclo0,6-[Lys0,Glu6,D-Phe7]BK), an antagonist targeted at the bradykinin (BK) B2 receptor, has been investigated using experimental and theoretical methods. In order to gain insight into the structural requirements essential for BK antagonism, we carried out molecular dynamics (MD) simulations using simulated annealing as the sampling protocol. Following a free MD simulation we performed simulations using nuclear Overhauser enhancement (NOE) distance constraints determined by NMR experiments. The low-energy structures obtained were compared with each other, grouped into families and analyzed with respect to the presence of secondary structural elements in their backbone. We also introduced new ways of plotting structural data for a more comprehensive analysis of large conformational sets. Finally, the relationship between characteristic backbone conformations and the spatial arrangement of specific pharmacophore centers was investigated.

Bradykinin Receptor Antagonists↗
PubMed1999

Expression of p73 and its relation to histopathology and prognosis in hepatocellular carcinoma.

BACKGROUND: The protein p73, the first identified homologue of the tumor suppressor gene p53 (also known as TP53), has been shown to induce apoptosis (programmed cell death), but its function in tumor development has not been established. This study was undertaken to investigate the expression of p73 in liver tissue of patients with hepatocellular carcinoma (HCC) and to determine whether this expression has any impact on prognosis. METHODS: In situ hybridization and immunohistochemistry for the detection of p73 RNA transcripts and protein, respectively, were performed in tissues from 193 patients with curatively (R0-) resected HCC. Patients receiving liver transplantation were excluded. The results obtained were analyzed with respect to their association with pathohistologic stage, Edmondson grade, p53 expression status and several histopathologic factors of possible prognostic value, and, finally, with patient survival. RESULTS: RNA transcripts encoding p73 were detected by in situ hybridization in tumor cells but not in stromal, endothelial, or inflammatory cells or in cholangiocytes. Transcripts were also found occasionally in non-neoplastic hepatocytes. By immunohistochemistry, we detected p73 protein in 61 (32%) of the 193 carcinomas examined. Positive immunohistochemical staining was confined to the cell nucleus. Univariate survival analysis showed that p73 expression status was statistically significantly related to prognosis (two-sided P<.0001). Patients with p73-positive tumors had a poorer prognosis than those with p73-negative carcinomas. Multivariate Cox survival analysis identified the age of the patient, p73 expression status, co-existing cirrhosis, and Edmondson grade as independent prognostic factors. CONCLUSION: The protein p73 is overexpressed by a subset of HCCs and could serve as a useful indicator of prognosis in patients with this disease.

Apoptosis↗
PubMed1999

Chiral separations in capillary high-performance liquid chromatography and nonaqueous capillary electrochromatography using helically chiral poly(diphenyl-2-pyridylmethyl methacrylate) as chiral stationary phase.

Enantioseparations in nonaqueous capillary electrochromatography (CEC) are reported in this study for the first time, using wide-pore aminopropyl silica gel coated with helically chiral poly(diphenyl-2-pyridylmethyl methacrylate) (PDPM) as chiral stationary phase (CSP). The anodic electroosmotic flow (EOF) in a methanolic solution of ammonium acetate was used for the migration of neutral analytes through the packed bed in the capillaries. Four different techniques, high-performance liquid chromatography (HPLC) in common-size columns, capillary HPLC, pressure-assisted CEC and CEC were compared from the viewpoint of separation parameters. The latter three were performed with the same experimental setup, varying the relative contribution of the pressure-driven and the electrically driven flow to the overall mobility of the analyte. Capillary HPLC offers clear advantages compared to enantioseparations in common-size columns. However, for a given particle size of the packing material, CEC was not obviously advantageous compared to pressure-driven separations.

Chromatography, High Pressure Liquid↗
PubMed1997

Validation of the heat treatment step used in the production of diaspirin crosslinked hemoglobin (DCLHb) for viral inactivation--effect of crosslinking.

Two experiments were performed to assess viral inactivation during the crosslinking and heat treatment steps of the DCLHb manufacturing process. Stroma free hemoglobin (SFHb) collected from a large scale manufacturing lot was tested in a 1:680 scaled down system in which the key parameters used in the manufacturing process were replicated. In the first study Porcine Parvovirus (PPV), a non-enveloped virus, was used to assess inactivation, while in the second study Bovine Viral Diarrhea Virus (BVDV), an enveloped virus, was utilized. In both experiments, the SFHb solution was deoxygenated and an aliquot of virus suspension was added. To initiate the crosslinking reaction, a solution of bis (3,5-dibromosalicyl) fumarate (DBBF) in HEPES buffer was added to the test solution. In both experiments the reaction times and the degree of crosslinking were normal. After crosslinking, the reaction mixtures were heated to 74 +/- 1 degrees C over 30 minutes, held at 74 +/- 1 degrees C for 90 minutes, and cooled to less than 10 degrees C over 30 minutes. In each experiment the degree of crosslinking of final product was 100% and yield of hemoglobin recovery was normal. Samples were removed prior to crosslinking, after crosslinking and before, during and after heat treatment for determination of virus titer and evaluation of key process parameters. The results from these experiments were consistent with those obtained from the full scale manufacturing process for the deoxygenation, crosslinking and the heat treatment step during the production of DCLHb. The results of virus assays showed that crosslinking has no effect on viruses and their subsequent inactivation by heat treatment.

Animals↗
PubMed1995

Up-regulation of CYP2A5 expression by porphyrinogenic agents in mouse liver.

Coumarin 7-hydroxylase (COH) activity is catalyzed by the Cyp2a-5 gene product (CYP2A5 enzyme) in mice. Mouse hepatic CYP2A5 expression is often increased in conditions in which other P450 forms are repressed, e.g. after the administration of heavy metals and other toxic agents known to affect cellular heme balance. In this study, the effect of various porphyrinogenic chemicals on the expression CYP2A5 and the key enzymes in heme metabolism was studied. Administration of single doses of griseofulvin (1000 mg/kg), thioacetamide (10 mg/kg) and aminotriazole (1000 mg/kg) to DBA/2 and C57BL/6 mice produced up to 10-fold increases in hepatic COH catalytic activity. Dramatic, up to 130-fold increases in response to the inducers was observed in the amount of CYP2A5 steady-state mRNA. The mRNA contents of aminolevulinate synthase, ferrochelatase and heme oxygenase were also increased to a variable extent, possibly reflecting feed-back regulatory mechanisms. In D2 mice the CYP2A5 inducing effect of aminotriazole and thioacetamide, but not that of griseofulvin, pyrazole and phenobarbital, was abolished by exogenously administered heme arginate. In the B6 strain heme arginate treatment increased CYP2A5 expression but it did not affect the induction caused by porphyrinogenic agents. These results show that porphyrinogenic agents act as efficient inducers of CYP2A5, and suggest that regulation of the transcription of the Cyp2a-5 gene could in some instances involve heme-sensitive factors.

5-Aminolevulinate Synthetase↗
PubMed1995

[Aniseikonia reduces binocular summation in the VECP].

The binocular summation effect of human VECP (increase in amplitude from about 4.0 microV to about 5.4 microV) was proved and optimized in 32 subjects. Stimulus parameters: TV steady-state pattern reversal (7.0 Hz); pattern size 1 degree; stimulus contrast 5% (higher stimulus contrasts reduced considerably the selectivity of the binocular summation effect); 96 sweeps averaging (Nicolet Compaq Four); position of electrodes: 10% and 30% above Protuberantia occipitalis externa of nasioninion distance. Aniseikonia of 7 to 52% was generated by means of small Galilei telescopes. Because of comparatively large interindividual variance within the series of subjects, no decrease in binocular VECP amplitude could be demonstrated at an aniseikonia less than 52%. On one woman subject, a significant reduction in amplitude (5% level) at 14%, 26% and 52% aniseikonia was apparent, but not at 7%. Thus, for this subject, it was possible to correlate the results with the clinically known limits of toleration for aniseikonia. This result was confirmed by more than 60% of the subjects in the test group.

Adult↗
PubMed1994

[Effect of biopterin on the electroretinogram of Long-Evans rats].

Tetrahydrobiopterin (BH4) is an important cofactor in the synthesis of the leading intraretinal catecholamine derivate dopamine. According to Iuvone et al., retinal BH4-tyrosine affinity and dopamine synthesis are influenced by environmental light intensities. So far, no data are available about the in vivo effect of BH4 concentrations on the functional parameters of the retina. ERG recordings were performed after BH4 had been administered for 3 days (10 micrograms and 500 micrograms/day IP). After high-dose application a significant ERG effect was observed in a-, b-amplitudes and latencies, respectively. This is the first observation that BH4 has an in vivo effect on the functional parameters of the retina and is consistent with previous results on retinal dopamine action. This result supports the hypothesis that pterin metabolism plays an important role in the adaptive processes of the retina. It may be discussed as a model for the so far unexplained adaptation of neurons.

Animals↗
PubMed1993

Coping with cancer.

Explore the source record for details and available documents.

Adaptation, Psychological↗