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Biomedical subjects

M Seeger

Publications and source records attributed to M Seeger.

At least 19 recordsLinked to original sources
PubMed2004

[Diagnosis of acute splenic infarction by echo-signal-enhanced ultrasound].

HISTORY AND CLINICAL FINDINGS: A 35-year-old patient with known mitral valve endocarditis presented with a stabbing pain in the left upper abdomen (patient 1). A 79-year-old patient with a history of chronic lymphocytic leukaemia (CLL) and aortic valve replacement presented with acute left upper quadrant, chest pain and impaired vision (patient 2). INVESTIGATIONS: An abdominal ultrasound revealed nonhomogeneous hypoechoic splenic lesions in both patients, which were classified as extended splenic infarctions by echo enhancer studies. The diagnosis was confirmed by computed tomography. Transesophageal echocardiography showed extensive mitral valve vegetations in patient 1. Patient 2 had a progression of the CLL without evidence of endocarditis. Magnetic resonance imaging of the brain showed infarction of the posterior cerebral artery area. DIAGNOSIS, TREATMENT AND COURSE: Patient 1: Mitral valve endocarditis with embolic splenic infarction. Patient 2: Progressive CLL with thrombotic splenic and brain infarction. In patient 1, mitral valve replacement was performed. In patient 2, chemotherapy was initiated and she was started on low molecular weight heparin s. c. and aspirin. No further embolic or thrombotic complications occurred. No splenectomy was performed. CONCLUSION: A splenic infarction is a complication pointing towards an underlying serious disorder. Echo-enhanced ultrasound is as sensitive as computed tomography for early diagnosis. Splenic infarction should trigger urgent treatment of the underlying condition.

Acute Disease↗
PubMed2003

[Chromogenic substrate as antidote against the thrombin inhibitor Melagatran?].

It could be shown in vitro that a chromogenic substrate (Chromozym TH, Roche Mannheim) acts at least partially as antidote against the new thrombin inhibitor Melagatran (AstraZeneca, Mölndal, Sweden). It is discussed that this antidote effect of a chromogenic substrate might be due to a substrate competition of fibrinogen, thrombin inhibitor, and chromogenic substrate for thrombin. Further animal experiments will clarify whether this in vitro observation is of practical relevance in vivo, too.

Antidotes↗
PubMed2001

Protein stability: the COP9 signalosome gets in on the act.

The COP9 signalosome is a multiprotein complex somewhat similar to the lid component of the 26S proteasome. Recent studies suggest that it regulates the stability of proteins by interfering with the ubiquitin-proteasome pathway via deneddylation and phosphorylation.

COP9 Signalosome Complex↗
PubMed2001

Proteins containing the UBA domain are able to bind to multi-ubiquitin chains.

The UBA domain is a motif found in a variety of proteins, some of which are associated with the ubiquitin-proteasome system. We describe the isolation of a fission-yeast gene, mud1+, which encodes a UBA domain containing protein that is able to bind multi-ubiquitin chains. We show that the UBA domain is responsible for this activity. Two other proteins containing this motif, the fission-yeast homologues of Rad23 and Dsk2, are also shown to bind multi-ubiquitin chains via their UBA domains. These two proteins are implicated, along with the fission-yeast Pus1(S5a/Rpn10) subunit of the 26 S proteasome, in the recognition and turnover of substrates by this proteolytic complex.

Amino Acid Motifs↗
PubMed2001

Dehalogenation, denitration, dehydroxylation, and angular attack on substituted biphenyls and related compounds by a biphenyl dioxygenase.

The attack by the bph-encoded biphenyl dioxygenase of Burkholderia sp. strain LB400 on a number of symmetrical ortho-substituted biphenyls or quasi ortho-substituted biphenyl analogues has been investigated. 2,2'-Difluoro-, 2,2'-dibromo-, 2,2'-dinitro-, and 2,2'-dihydroxybiphenyl were accepted as substrates. Dioxygenation of all of these compounds showed a strong preference for the semisubstituted pair of vicinal ortho and meta carbons, leading to the formation of 2'-substituted 2,3-dihydroxybiphenyls by subsequent elimination of HX (X = F, Br, NO(2), or OH). All of these products were further metabolized by 2,3-dihydroxybiphenyl 1,2-dioxygenases of Burkholderia sp. strain LB400 or of Rhodococcus globerulus P6. Dibenzofuran and dibenzodioxin, which may be regarded as analogues of doubly ortho-substituted biphenyls or diphenylethers, respectively, were attacked at the "quasi ortho" carbon (the angular position 4a) and its neighbor. This shows that an aromatic ring-hydroxylating dioxygenase of class IIB is able to attack angular carbons. The catechols formed, 2,3,2'-trihydroxybiphenyl and 2,3,2'-trihydroxydiphenylether, were further metabolized by 2,3-dihydroxybiphenyl 1,2-dioxygenase. While angular attack by the biphenyl dioxygenase was the main route of dibenzodioxin oxidation, lateral dioxygenation leading to dihydrodiols was the major reaction with dibenzofuran. These results indicate that this enzyme is capable of hydroxylating ortho or angular carbons carrying a variety of substituents which exert electron-withdrawing inductive effects. They also support the view that the conversions of phenols into catechols by ring-hydroxylating dioxygenases, such as the transformation of 2,2'-dihydroxybiphenyl into 2,3,2'-trihydroxybiphenyl, are the results of di- rather than of monooxygenations. Lateral dioxygenation of dibenzofuran and subsequent dehydrogenation and extradiol dioxygenation by a number of biphenyl-degrading strains yielded intensely colored dead-end products. Thus, dibenzofuran can be a useful chromogenic indicator for the activity of the first three enzymes of biphenyl catabolic pathways.

Benzofurans↗
PubMed2000

Mutant presenilin 1 increases the levels of Alzheimer amyloid beta-peptide Abeta42 in late compartments of the constitutive secretory pathway.

Mutations in the presenilin 1 (PS1) gene are associated with autosomal dominant, early-onset, familial Alzheimer's disease and result in increased release of the hyperaggregatable 42-amino acid form of the amyloid beta-peptide (A(beta)42). To determine which subcellular compartments are potential source(s) of released Abeta42, we compared the levels and spatial segregation of intracellular A(beta)40 and A(beta)42 peptides between N2a neuroblastoma cells doubly transfected with the "Swedish" familial Alzheimer's disease-linked amyloid precursor protein variant and either wild-type PS1 (PS1(wt)) or familial Alzheimer's disease-linked delta9 mutant PS1 (PS1delta9). As expected, PS1delta9-expressing cells had dramatically higher levels of intracellular Abeta42 than did cells expressing PS1wt. However, the highest levels of A(beta)42 colocalized not with endoplasmic reticulum or Golgi markers but with rab8, a marker for trans-Golgi network (TGN)-to-plasma membrane (PM) transport vesicles. We show that PS1 mutants are capable of causing accumulation of A(beta)42 in late compartments of the secretory pathway, generating there a readily releasable source of A(beta)42. Our findings indicate that PS1 "bioactivity" localizes to the vicinity of the TGN and/or PM and reconcile the apparent discrepancy between the preponderant concentration of PS1 protein in proximal compartments of the secretory pathway and the recent findings that PS1 "bioactivity" can control gamma-secretase-like processing of another transmembrane substrate, Notch, at or near the PM.

Alzheimer Disease↗
PubMed1999

Generation of the amyloid-beta peptide N terminus in Saccharomyces cerevisiae expressing human Alzheimer's amyloid-beta precursor protein.

The Alzheimer's amyloid-beta precursor protein (betaAPP) is a type 1 membrane-spanning protein from which the Alzheimer's disease amyloid-beta peptide (Abeta) is proteolytically derived. To date, attempts to identify the enzymes responsible for Abeta generation have failed. Here we report the accumulation of Abeta-immunoreactive peptides in yeast expressing human betaAPP. Characterization of these peptides by metabolic labeling, immunoprecipitation with Abeta-specific antibodies, and N-terminal radiosequencing indicates that these peptides include the Abeta peptide at their N termini. The Abeta-like peptides generated in yeast were recovered predominantly as 8- and 12-14-kDa species. A 4-kDa species was recovered either when a protease-deficient strain was used to prevent breakdown or when the 8- and 12-14-kDa species were treated with disaggregating agents. The likely existence in yeast of enzymes generating the Abeta N terminus indicates that the molecular identification of yeast beta-secretase-like enzymes may be accomplished using genetic screens or empirical approaches based upon the sequenced genome of Saccharomyces cerevisiae.

Alzheimer Disease↗
PubMed1999

Comparison of human COP9 signalsome and 26S proteasome lid'.

The human core COP9 signalosome consists of eight subunits which have been identified, cloned and sequenced. The components of COP9 signalosome possess homologies with eight non-ATPase regulatory subunits of the 26S proteasome. These polypeptides of the 19S regulator form a reversibly binding subcomplex called the 'lid'. We isolated the 'lid' from human red blood cells and compared it with the COP9 signalosome complex. In addition to the non-ATPase regulatory polypeptides, we found a high molecular mass ATPase copurifying with the human 'lid'. The COP9 signalosome-associated kinase activity is either not at all or only weakly affected by common kinase inhibitors such as 1-(5-Isoquinolinesulfonyl)-2-methyl-piperazine (H7), 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) or Wortmannin. Curcumin, a tumor suppressor and effector of AP-1 activation, is a potent inhibitor of the COP9 signalosome kinase activity with a Ki of about 10 microM. Since curcumin is known as an inhibitor of the c-Jun N-terminal kinase (JNK) signaling pathway acting upstream of the MAP kinase kinase kinase level, one site of action of the COP9 signalosome might be proximal to regulators on that level.

Animals↗
PubMed1999

Regiospecificity of dioxygenation of di- to pentachlorobiphenyls and their degradation to chlorobenzoates by the bph-encoded catabolic pathway of Burkholderia sp. strain LB400.

Burkholderia sp. strain LB400 is one of the most potent aerobic polychlorobiphenyl (PCB)-degrading microorganisms that have been characterized. Its PCB-dioxygenating activity originates predominantly or exclusively from the biphenyl dioxygenase encoded by its bph gene cluster. Analysis of the dioxygenation products of several di- to pentachlorinated biphenyls formed by this enzyme revealed a complex dependence of the regiospecificity and the yield of dioxygenation on the substitution patterns of both the oxidized and the nonoxidized rings. No dioxygenolytic attack involving chlorinated meta or para carbons was observed. Therefore, the ability of the enzyme to hydroxylate chlorinated carbons appears to be limited to the ortho position. However, it is not limited to monochlorinated rings, as evidenced by dioxygenation of the 2, 4-disubstituted ring at carbons 2 and 3. This site of attack is strikingly different from that of the 2,5-dichlorinated ring, which has been shown to be dihydroxylated at positions 3 and 4 (J. D. Haddock, J. R. Horton, and D. T. Gibson, J. Bacteriol. 177:20-26, 1995). These results demonstrate that a second substituent of ortho-chlorinated rings crucially influences the site of dioxygenation at this ring and thereby determines whether or not the initial chlorobiphenyl oxidation product is further metabolized through the bph-encoded pathway. The 2,4-dichlorinated ring can alternatively be attacked at carbons 5 and 6. The preferred site crucially depends on the substitution pattern of the other ring. The formation of more than a single dioxygenation product was found predominantly with congeners that contain two chlorinated rings, both of which are similarly prone to dioxygenation or one is substituted only at carbon 3.

Biodegradation, Environmental↗
PubMed1999

The netrin receptor frazzled is required in the target for establishment of retinal projections in the Drosophila visual system.

Retinal axons in Drosophila make precise topographic connections with their target cells in the optic lobe. Here we investigate the role of the Netrins and their receptor Frazzled in the establishment of retinal projections. We find that the Netrins, although expressed in the target, are not required for retinal projections. Surprisingly, Frazzled, found on both retinal fibers and target cells, is required in the target for attracting retinal fibers, while playing at best a redundant role in the retinal fibers themselves; this finding demonstrates that target attraction is necessary for topographic map formation. Finally, we show that Frazzled is not required for the differentiation of cells in the target. Our data suggest that Frazzled does not function as a Netrin receptor in attracting retinal fibers to the target; nor does it seem to act as a homotypic cell adhesion molecule. We favor the possibility that Frazzled in the target interacts with a component on the surface of retinal fibers, possibly another Netrin receptor.

Animals↗
PubMed1999

Developmental expression of wild-type and mutant presenilin-1 in hippocampal neurons from transgenic mice: evidence for novel species-specific properties of human presenilin-1.

Presenilins 1 (PS1) and 2 (PS2) are multispanning transmembrane proteins associated with familial Alzheimer disease (FAD). They are developmentally regulated, being expressed at highest levels during neuronal differentiation and are sustained at a lower level throughout life. We investigated the distribution and metabolism of endogenous murine PS1 as well as human wild-type (wtPS1) and the familial AD Met146Leu (M146L) mutant presenilins in dissociated cultures of hippocampal neurons derived from control and transgenic mice. We found that the PS1 endoproteolytic fragments and, to a lesser extent, the full-length protein, were expressed as early as day 3 post-plating. Both species increased until the cells were fully differentiated at day 12. Confocal microscopy revealed that presenilin is present in the Golgi and endoplasmic reticulum and, as in punctate, vesicle-like structures within developing neurites and growth cones. Using a human-specific PS1 antibody, we were able to independently examine the distribution of the transgenic protein which, although similar to the endogenous, showed some unique qualities. These included (i) some heterogeneity in the proteolytic fragments of human PS1; (ii) significantly reduced levels of full-length human PS1, possibly as a result of preferential processing; and (iii) a more discrete intracellular distribution of human PS1. Colocalization with organelle-specific proteins revealed that PS1 was located in a diffuse staining pattern in the MAP2-positive dendrites and in a punctate manner in GAP43-positive axons. PS1 showed considerable overlap with GAP43, particularly at the growth cones. Similar patterns of PS1 distribution were detected in cultures derived from transgenic animals expressing human wild-type or mutant presenilins. The studies demonstrate that mutant presenilins are not grossly different in their processing or distribution within cultured neurons, which may represent more physiological models as compared to transfection systems. Our data also suggest that the molecular pathology associated with PS1 mutations results from subtle alterations in presenilin function, which can be further investigated using these transgenic neuronal cell culture models.

Aging↗
PubMed1998

Involvement of cell surface glycosyl-phosphatidylinositol-linked aspartyl proteases in alpha-secretase-type cleavage and ectodomain solubilization of human Alzheimer beta-amyloid precursor protein in yeast.

Human beta-amyloid precursor protein (APP) introduced into yeast undergoes alpha-secretase-type cleavage, suggesting that yeast have alpha-secretase-like protease(s). Here we report that two structurally and functionally related glycosyl-phosphatidylinositol-linked yeast aspartyl proteases, Mkc7p and Yap3p (collectively termed yapsin), are responsible for alpha-secretase-type cleavage of APP expressed in yeast, resulting in release of soluble APP into the extracellular space. Disruption of MKC7 and YAP3 in a vacuolar protease-deficient strain abolished this APP cleavage/release, and APP cleavage/release could be restored by introduction of MKC7 or YAP3 on a single copy plasmid. Purified Mkc7p cleaved an internally quenched fluorogenic APP peptide substrate at the alpha-secretase cleavage site. Measurement of proteolytic activity either in yeast homogenates or on the yeast cell surface revealed that most Mkc7p and Yap3p activities were localized at the cell surface. These results establish a molecular basis for alpha-secretase-type cleavage in yeast and support the generally held concept that alpha-secretase cleavage of APP occurs at the cell surface.

Amyloid Precursor Protein Secretases↗
PubMed1998

The Pad1+ gene encodes a subunit of the 26 S proteasome in fission yeast.

We have isolated a fission yeast mutant, mts5-1, in a screen for mutations that confer both methyl 2-benzimidazolecarbamate resistance (MBCR) and temperature sensitivity (ts) on Schizosaccharomyces pombe. This screen has previously isolated mutations in the 26 S proteasome subunits Mts2, Mts3, and Mts4. We show that the mutation in the mts5-1 strain occurs in the pad1(+) gene. pad1(+) was originally isolated on a multicopy plasmid that was capable of conferring staurosporine resistance on a wild type strain. mts5-1/pad1-1 has a similar phenotype to 26 S proteasome mutants previously isolated in the same screen and we show that Pad1 interacts genetically with two of these subunits, Mts3 and Mts4. In this study we describe the identification of Pad1 as a subunit of the 26 S proteasome in fission yeast.

Amino Acid Sequence↗
PubMed1998

Antigen-independent suppression of the IgE immune response to bee venom phospholipase A2 by maternally derived monoclonal IgG antibodies.

The IgE immune response to ovalbumin in rats can be suppressed by prior immunization of the dams. The results reported in this paper extend this observation to include a different antigen and another species, namely the IgE immune response to bee venom phospholipase A2 (PLA2) in CBA/J mice. The degree of suppression seemed to depend on the amount of IgG antibodies transferred to the offspring. Moreover, we found that the maternally mediated suppression of the IgE response could be achieved in a completely antigen-free system in which exogenous monoclonal anti-PLA2 IgG antibodies were transferred from the dams to the offspring. The following results were obtained: (i) The IgE suppression by monoclonal IgG antibodies was induced as efficiently with one single anti-PLA2 IgG1 antibody as with a mixture of ten antibodies (nine IgG1, one IgG2b). (ii) Even after several immunizations up to an age of 6 months with a dose of PLA2 that normally induces IgE production, none of the F1 mice developed an IgE response. (iii) This long-lasting suppression was observed in mice which were first immunized at an age of 4 weeks (i.e. when low amounts of maternally derived monoclonal IgG were still present), as well as in mice which were first immunized at an age of 8 weeks, when no such maternal antibodies could be detected in their sera. The corresponding IgG responses showed, compared to normal mice, a transient enhancement in the maternally influenced mice. It is concluded that the immunological experience of the mother is of particular importance for the isotype regulation in the newborns, especially with respect to the ability to elicit an IgE response. The possible implications for the development of allergic diseases in humans are discussed.

Animals↗
PubMed1998

Estrogen reduces neuronal generation of Alzheimer beta-amyloid peptides.

Alzheimer's disease (AD) is characterized by the accumulation of cerebral plaques composed of 40- and 42-amino acid beta-amyloid (Abeta) peptides, and autosomal dominant forms of AD appear to cause disease by promoting brain Abeta accumulation. Recent studies indicate that postmenopausal estrogen replacement therapy may prevent or delay the onset of AD. Here we present evidence that physiological levels of 17beta-estradiol reduce the generation of Abeta by neuroblastoma cells and by primary cultures of rat, mouse and human embryonic cerebrocortical neurons. These results suggest a mechanism by which estrogen replacement therapy can delay or prevent AD.

Alzheimer Disease↗
PubMed1998

A novel protein complex involved in signal transduction possessing similarities to 26S proteasome subunits.

A novel protein complex has been identified in human cells that has a molecular mass of approximately 450 kDa. It consists of at least eight different subunits including JAB1, the Jun activation-domain binding protein 1, and Trip15, the thyroid hormone receptor-interacting protein 15. The purified complex contains COP9 and COP11 protein homologs and is very similar, if not identical, to the plant COP9 complex involved in light-mediated signal transduction. The isolated JAB1-containing particle has kinase activity that phosphorylates IkappaBalpha, the carboxy terminus of p105, and Ser63 and/or Ser73 of the amino-terminal activation domain of c-Jun. The phosphorylation of c-Jun requires the carboxy terminus of the protein containing the DNA binding and dimerization domains. Three subunits of the new complex--Sgn3, Sgn5/JAB1, and Sgn6--exhibit sequence similarities to regulatory components of the 26S proteasome, which could indicate the existence of common substrate binding sites. Immunofluorescence staining reveals that the new complex shows a subcellular distribution similar to that of the 26S proteasome. The functional relationship of the two particles in regulating transcriptional activity is discussed. Considering the putative role of the complex in signal transduction and its widespread occurrence, we suggest the name JAB1-containing signalosome.

Amino Acid Sequence↗
PubMed1997

Resistance to diverse drugs and ultraviolet light conferred by overexpression of a novel human 26 S proteasome subunit.

We have investigated the usefulness of the fission yeast Schizosaccharomyces pombe as a model organism for the discovery of novel modes of drug resistance in human cells. In fission yeast, overexpression of the essential pad1(+) gene confers pleiotropic drug resistance through a pathway involving an AP-1 transcription factor encoded by pap1(+). We have identified POH1, a human pad1 homologue that can substitute fully for pad1(+) and induce AP-1-dependent drug resistance in fission yeast. POH1 also confers P-glycoprotein-independent resistance to taxol (paclitaxel), doxorubicin, 7-hydroxystaurosporine, and ultraviolet light when transiently overexpressed in mammalian cells. Poh1 is a previously unidentified component of the human 26 S proteasome, a multiprotein complex that degrades proteins targeted for destruction by the ubiquitin pathway. Hence, Poh1 is part of a conserved mechanism that determines cellular susceptibility to cytotoxic agents, perhaps by influencing the ubiquitin-dependent proteolysis of transcription factors.

Amino Acid Sequence↗