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K Haas

Publications and source records attributed to K Haas.

At least 37 records · Page 2Linked to original sources
PubMed1997

Cyclin ET, a new splice variant of human cyclin E with a unique expression pattern during cell cycle progression and differentiation.

Cyclin E is the regulatory subunit of the cdc2-related protein kinase cdk2 and is a rate limiting factor for the entry into S phase. To date, cyclin E is the only cyclin for which alternative splicing has been described. We report here the isolation of a new splice variant of cyclin E, termed cyclin ET, which has an internal deletion of 45 amino acids compared with the full-length cyclin E protein. Even though cyclin ETcontains an intact cyclin box, it is unable to complement a triple cln mutant strain of Saccharomyces cerevisiae or to interfere with rescue by cyclin E, indicating that an intact cyclin box is functionally insufficient. The expression pattern of cyclin ET during cell cycle entry, progression and differentiation differs from that of cyclin E. Thus, ET expression precedes that of the other isoforms during the G0-->S progression; it shows a sharp peak in early G1 in cells released from a mitotic block and is strongly down-regulated in terminally differentiated myeloid cells. These observations point to different functions for cyclin ET and E and show for the first time that the alternative splicing of cyclin E is a regulated mechanism governed by the cell cycle and differentiation.

Alternative Splicing↗
PubMed1997

Amino acid utilization and isotope discrimination of amino nitrogen in nitrogen metabolism of rat liver in vivo.

Urea and plasma protein differ in natural 15N abundance up to 10%. The origin of this difference is the branched nitrogen metabolism in the liver. One main branch is the protein synthesis pathway, the other the urea synthesis pathway. By this branching 15N of precursor amino acids is depleted in urea while it is enriched in protein. With the 15N abundance of precursor amino acids, which may be taken from jejunum tissue, utilization of amino acids in liver metabolism can be calculated from isotope discrimination in either pathway. This was investigated by feeding different proteins to rats. When feeding high quality protein (whey protein) utilization of amino acids in liver metabolism at requirement intake was better than at zero protein intake (> 85% vs. 70%). From this we conclude that the pattern of amino acids available from the metabolic pool at zero protein intake is characterized by an imbalance. This endogenous imbalance can be complemented by exogenous dietary amino acids so that nitrogen excretion may even be smaller than the so-called "obligatory" losses of intakes not exceeding requirement. Thus, the quality of dietary protein is reflected not only by N balance. It also may be quantified by analysis of isotope discrimination in nitrogen metabolism of the liver. In addition, the quality of amino acid pattern available from the metabolic pool is indicated by this method.

Amino Acids↗
PubMed1996

Uncoupling of DNA replication and cell cycle progression by human cyclin E.

The G1-specific D- and E-type cyclins are among the most crucial factors controlling cell cycle progression in mammalian cells and are therefore thought to play an important role in tumorigenisis. D-type cyclins have indeed been shown to be endowed with an oncogenic potential. Here, we report that the ectopic expression of human cyclin E, but not cyclin D1, deregulates DNA synthesis in both yeast and mammalian cells. In yeast, induction of DNA synthesis by cyclin E occurs even under conditions of cell cycle arrest in G1 or G2/M, indicating an uncoupling of DNA replication from cell cycle progression. In rat embryo fibroblasts, the cooperative action of Ras and cyclin E induces transformation. These cells, in contrast to those transformed by Ras and cyclin D1, show aberrant levels of DNA synthesis. Since cyclin E is commonly overexpressed in a variety of human tumors, these findings may point to a link between the uncontrolled proliferation and the genomic instability typically seen in malignant tumors. Furthermore they reveal significant differences in the functional properties of cyclin E and D1.

Animals↗
PubMed1996

Biogenesis of thermogenic mitochondria in brown adipose tissue of Djungarian hamsters during cold adaptation.

After cold exposure, cytochrome c oxidase (COX) activity increased about 2.5-fold within 2 weeks in the brown adipose tissue (BAT) of Djungarian hamsters. The mRNAs for COX subunits I and III and the 12 S rRNA, encoded on mitochondrial DNA (mtDNA), as well as mRNAs for COX subunits IV, Va and mitochondrial transcription factor A, encoded in the nucleus, were unchanged when expressed per unit of total tissue RNA. However, since total tissue RNA doubled per BAT depot, while total DNA remained unchanged, the actual levels of these transcripts were increased within BAT cells. In contrast, the abundance of mRNA for uncoupling protein was increased 10-fold, indicating specific activation of this gene. In addition, the maximal rate of protein synthesis analysed in a faithful in organello system was increased 2.5-fold in mitochondria isolated from BAT after 7 days of cold exposure. We conclude from these data that the biogenesis of thermogenic mitochondria in BAT following cold adaptation is achieved by increasing the overall capacity for synthesis of mitochondrial proteins in both compartments, by increasing their mRNAs as well as the ribosomes needed for their translation. In addition, the translational rate for COX subunits as well as all other proteins encoded on mtDNA is increased. Thus the pool of subunits encoded on mtDNA required for assembly of respiratory chain complexes is provided. By comparison with other models of increased mitochondrial biogenesis, we propose that thyroid hormone (generated within BAT cells by 5'-deiodinase, and induced upon sympathetic stimulation), which is a well known regulator of the biogenesis of mitochondria in many tissues, is also the major effector of these adaptive changes in BAT.

Acclimatization↗
PubMed1996

The mydriatic effect of topical glycopyrrolate.

BACKGROUND: Glycopyrrolate, an anticholinergic agent that does not cross the blood-brain barrier, has several indications, but its mydriatic effect has never been tested. This study was carried out in order to compare the mydriatic effect of glycopyrrolate 0.5% to that of atropine sulfate 1%. METHODS: Glycopyrrolate 0.5% and atropine 1.0% were instilled separately in the eyes of albino rabbits. Pupil diameter and intra-ocular pressure were monitored. RESULTS: Mydriasis was noted within 5 min of glycopyrrolate instillation, reached near-maximal level at 15 min and persisted for 1 week. Glycopyrrolate 0.5% showed a faster, stronger and more persistent mydriatic effect than atropine 1.0%. Administration of glycopyrrolate 0.5% solution b.i.d. for 1 week did not affect intra-ocular pressure or produce any adverse reaction. CONCLUSION: Glycopyrrolate solution has the potential to deliver an ocular anticholinergic effect without causing associated central anticholinergic hazards.

Administration, Topical↗
PubMed1996

Monoclonal antibodies Ki-S3 and Ki-S5 yield new data on the 'Ki-67' proteins.

The monoclonal antibody (mab) Ki-67 has been used for about 10 years, mainly in tissue sections, to monitor proliferating cells, but so far only very little is known about the proteins it recognizes. The new mabs Ki-S3 and Ki-S5 detect proliferating cells in frozen and paraffin-embedded tissues. They recognize proteins with the same molecular mass as Ki-67 in Western blot and for the first time also in immunoprecipitation experiments. With these mabs we were able to enrich and purify the Ki-67 proteins. Protein sequencing of four peptides of the digested proteins corresponded to the cDNA-deduced amino acid sequence already published for the Ki-67 proteins. Since we were able to immunoprecipitate the Ki-67 proteins, we performed various immunoprecipitation experiments to obtain more information about the nature of these proteins. After radiolabelling L428 cells with [35S]-methionine we were able to immunoprecipitate the Ki-67 proteins after only 5 min of labelling time. In turnover experiments the Ki-67 proteins could not be detected 3 h after the end of labelling. These data indicate a half-life of the Ki-67 proteins of about 90 min. Labelling experiments with [32P]-orthophosphate revealed that the Ki-67 proteins are phosphorylated. After dephosphorylation was blocked with okadaic acid or cell growth was arrested by means of Colcemid, the phosphorylation of the Ki-67 proteins was greatly increased, indicating that the Ki-67 proteins are phosphorylated via serine and threonine, and that the phosphorylation of the Ki-67 proteins increases in cycling cells. Labelling experiments with [3H]-mannose and [3H]-glucose revealed that the protein is weakly N-glycosylated.

Amino Acid Sequence↗
PubMed1996

Multiple regulatory steps are involved in the control of lipoprotein lipase activity in brown adipose tissue.

Lipoprotein lipase (LPL) supplies brown adipose tissue with fatty acids for nonshivering thermogenesis. In brown adipose tissue of the Djungarian hamster we studied i) the molecular mechanisms involved in cold-induced stimulation of LPL activity, ii) the adrenergic control of LPL expression, and iii) compared LPL expression in brown and white adipose tissue. i) After 8 h cold exposure we detected a 2-fold increase in LPL activity and protein level in brown adipose tissue, whereas LPL mRNA level remained unchanged. A cold-induced increase (1.5-fold) in LPL activity was observed in brown adipose tissue of hamsters treated with actinomycin D prior to 4 h cold exposure, whereas cycloheximide treatment completely abolished LPL stimulation. Thus, these data suggest that during the initial phase (< 24 h) of cold exposure the stimulation of LPL activity in brown adipose tissue is most likely due to increased translation. In contrast, during prolonged cold exposure, we detected a maximal 7-fold increase in LPL activity and a 2- to 3-fold increase in LPL mRNA level in brown adipose tissue indicating LPL regulation at the pretranslational level. Furthermore, comparison of LPL protein and activity in brown adipose tissue during prolonged (> 24 h) cold exposure provides some evidence that the active fraction of the enzyme pool in brown adipose tissue is increased in response to cold. ii) Surgical denervation and noradrenaline treatment revealed a complex role of the sympathetic innervation in the control of LPL expression in brown adipose tissue. Denervation decreased LPL mRNA level, but increased LPL activity. Noradrenaline treatment stimulated LPL activity to a similar extent as cold exposure. However, cold-induced stimulation of LPL activity was not impaired by denervation. iii) Cold exposure significantly elevated LPL mRNA content of inguinal white adipose tissue, although LPL activity was not affected. Posttranscriptional mechanisms appear to be involved in the tissue specific control of LPL expression.

Adipose Tissue↗
PubMed1993

Adventitial elastolysis is a primary event in aneurysm formation.

PURPOSE: Adventitial elastin degradation is a hallmark of abdominal aortic aneurysm (AAA) formation in human beings, although the quantitative relationship between elastin loss and AAA formation and growth is unknown. This study was undertaken to quantitate the reduction of adventitial elastin for small AAA, to determine whether the loss of this structural component parallels aneurysm growth, and to examine the ultrastructure of the remaining elastin elements. METHODS: Longitudinal strips of anterior aneurysm wall were taken from 12 patients having elective repair of small (diameter < 5 cm, n = 4), moderate (diameter < 5 to 7 cm, n = 4), or large (diameter > 7 cm, n = 4) AAA and from six normal control subjects at autopsy. Specimens were prepared with elastin and collagen stains for histologic examination or formic acid for scanning electron microscopic evaluation of elastin architecture. Adventitial elastin content of aneurysmal and control aortas was quantitated with video microscopy and compared by aneurysm diameter. RESULTS: The inner portion of adventitia of normal aortic wall was composed of densely compacted alternating lamellae of elastin and collagen, which were grossly disrupted in all aneurysms. The remaining elastin fibers were disorganized and tortuous. There was an 81.6% +/- 2.1% reduction in elastin lamellae and an 85.7% +/- 4.2% reduction in fibers per lamellae compared with the number in control aortas (p < 0.001). Size of the aneurysm made no difference in adventitial elastin content. CONCLUSION: These data strongly suggest that elastolysis is a primary event in AAA formation that occurs before over loss of adventitial structural integrity and the development of small aneurysms.

Aged↗
PubMed1993

Determination of the growth fraction in non-Hodgkin's lymphomas by monoclonal antibody Ki-S5 directed against a formalin-resistant epitope of the Ki-67 antigen.

Relevant prognostic information can be added to the histological classification of non-Hodgkin's lymphoma (NHL) by the determination of the growth fraction. In unfixed fresh tissue samples the Ki-67 antigen has proven its utility as an operational marker of proliferative activity in NHL. We have generated a monoclonal antibody directed against a formalin-resistant epitope of the Ki-67 antigen, designated Ki-S5. The immunoreactivity of Ki-S5 is confined to the nuclei of proliferating cells and, unlike Ki-67, no cross-reactivity with cytoplasmic antigens of epithelial cells occurs. In 100 cases of different NHL types, parallel staining of Ki-67 and Ki-S5 antigen yielded almost identical results in fresh tissues and fixed tissues, respectively (P < 0.00001; r = 0.95). In some cases, the Ki-S5 labeling index exceeded that of Ki-67, most probably due to a partial degradation of the epitope recognized by Ki-67 in frozen stored tissue samples. Significant differences in the median Ki-S5 labeling index could be demonstrated between high grade (> 50%) and low grade malignant NHL (< or = 30%), although the proliferative activity varied to a considerable range within identical histological categories (P < 0.001). We conclude that Ki-S5 provides a reliable means to assess proliferation in paraffin-embedded NHL specimens. Retrospective studies relating the proliferative activity to clinical outcome are thus rendered possible using archival routinely processed tissue samples.

Aged↗
PubMed1991

Contingent tolerance to carbamazepine is associated with lowering of amygdala-kindled seizure thresholds.

Amygdala-kindled seizure thresholds were studied in animals which were or were not tolerant to the anticonvulsant effects of carbamazepine. The seizure threshold was defined as the lowest current that elicited a major motor seizure (stage 3 or greater). Amygdala-kindled rats received carbamazepine, once daily, either before each electrical stimulation (carba-before) or after each stimulation (carba-after). The rats given carbamazepine before, but not after, each once-daily kindling stimulation became tolerant to its anticonvulsant effects. Following this manipulation, seizure thresholds were redetermined in both groups of animals while medication-free. The carba-before (i.e., tolerant) animals showed a decreased seizure threshold, while the carba-after (i.e., nontolerant) animals showed no change. Tolerance to carbamazepine was reversed by giving the rats kindled seizures for a period of 7 days without drug; nontolerant animals received the same stimulation and seizures. When seizure thresholds were reevaluated, the carba-before animals (now not tolerant) had returned to their pretolerance values, while the carba-after group again showed no change. This effect of carbamazepine tolerance and its reversal being associated with respective decreases and increases in basal seizure threshold was replicated two more times. In each case the change in the generalized seizure threshold mirrored the change in responsivity of the animals to carbamazepine. These findings, consistent with the formulations of Siegel regarding conditioned compensatory response mechanisms mediating contingent drug tolerance, may have important clinical and theoretical implications.

Amygdala↗
PubMed1991

Xp21 dystrophin and 6q dystrophin-related protein. Comparative immunolocalization using multiple antibodies.

A protein of Mr 400 K and slightly lower Mr than Xp21 dystrophin was detected in skeletal muscle from patients with Duchenne muscular dystrophy by three antibodies raised against the midrod and C-terminal portions of chicken dystrophin, and by antibodies to dystrophin-related protein. Immunocytochemistry showed continuous sarcolemmal staining of Duchenne muscle with these antibodies. Subcellular localization to the inner face of the plasma membrane of Duchenne muscle was demonstrated by immunoelectron microscopy using the model of a Duchenne patient deleted for most of the dystrophin gene. Other antibodies were specific for Xp21 dystrophin. In conclusion, a dystrophin homologue that may be identical to the previously described dystrophin-related protein (DRP)1 is expressed in Duchenne muscle with intracellular distribution similar to Xp21 dystrophin in normal muscle.

Antibodies, Monoclonal↗
PubMed1979

[Changes in the outer plexiform layer of the rabbit retina after long-term application of vincristine].

Rabbits which had been intravenously injected with Vincristine for six weeks showed changes in the outer plexiform layer of the retina after one year, which suggests the destruction of receptor cells, bipolar ganglion cells, and horizontal cells. Compensated cell damage accompanied by loss of microtubuli in the cytoplasma, autolytic vacuoles, granular material deposits, and membrane changes of the ribbon complex were frequently observed. A comparison between axons and dendrites showed a predominance of damaged dendritis over axons. Because short-term studies have not produced the same results, different regeneration capacities, which might have their origin in the endoplasmatic reticulum, are discussed.

Animals↗
PubMed1976

[Operative treatment of lung sequestrations (author's transl)].

In the Surgical Department of the Städtisches Krankenhaus München-Harlaching, 7 malformations of the lung in the shape of intralobar or extralobar sequestration were found among 1150 lung resections. Preoperative diagnosis caused no difficulty, even when angiography was dispensed with. In two cases a coincidence with other deformities was demonstrated. Deviations from the usual differentiation between intralobar and extralobar sequestration were found repeatedly with regard to location and vascular supply. All the 7 patients affected were cured by resection therapy.

Abnormalities, Multiple↗