Biomedical subjects

Jörg Kaufmann

Publications and source records attributed to Jörg Kaufmann.

12 recordsLinked to original sources

PubMed2005

The mitochondrial protein MTP18 contributes to mitochondrial fission in mammalian cells.

Mitochondria are dynamic organelles that change morphology by controlled fission and fusion events. Mitochondrial fission is regulated by a conserved protein complex assembled at the outer membrane. Human MTP18 is a novel nuclear-encoded mitochondrial membrane protein, implicated in controlling mitochondrial fission. Upon overexpression of MTP18, mitochondrial morphology was altered from filamentous to punctate structures suggesting excessive mitochondrial fission. Mitochondrial fragmentation was blocked in cells coexpressing either the mitochondrial fusion protein Mfn1 or Drp1(K38A), a dominant negative version of the fission protein Drp1. Also, a loss-of function of endogenous MTP18 by RNA interference (RNAi) resulted in highly fused mitochondria. Moreover, MTP18 appears to be required for mitochondrial fission because it is blocked after overexpression of hFis1 in cells with RNAi-mediated MTP18 knockdown. In conclusion, we propose that MTP18 functions as an essential intramitochondrial component of the mitochondrial division apparatus, contributing to the maintenance of mitochondrial morphology.

Animals↗

PubMed2005

REDD1 integrates hypoxia-mediated survival signaling downstream of phosphatidylinositol 3-kinase.

Cancer cells frequently evade apoptosis during tumorigenesis by acquiring mutations in apoptotic regulators. Chronic activation of the PI 3-kinase-Akt pathway through loss of the tumor suppressor PTEN is one mechanism by which these cells can gain increased protection against apoptosis. We report here that REDD1 (RTP801) can act as a transcriptional downstream target of PI 3-kinase signaling in human prostate cancer cells (PC-3). REDD1 expression is markedly reduced in PC-3 cells treated with LY294002 (LY) or Rapamycin and strongly induced under hypoxic conditions in a hypoxia-inducible factor-1 (HIF-1)-dependent manner. Loss of function studies employing antisense molecules or RNA interference indicate that REDD1 is essential for invasive growth of prostate cancer cells in vitro and in vivo. Reduced REDD1 levels can sensitize cells towards apoptosis, whereas elevated levels of REDD1 induced by hypoxia or overexpression desensitize cells to apoptotic stimuli. Taken together our data designate REDD1 as a novel target for therapeutic intervention in prostate cancer.

Apoptosis↗

PubMed2005

Nonparametric methods for analysing the accuracy of diagnostic tests with multiple readers.

The evaluation of diagnostic agents or imaging procedures is governed by the same scientific and regulatory rules as that of other medical products. Receiver operating characteristic (ROC) curves, and especially the area under these ROC curves, are indices for the accuracy of a diagnostic test for continuous as well as ordinal data. The methodology of multivariate rank statistics for the nonparametric Behrens-Fisher problem is used to evaluate the accuracy of a diagnostic test in a complex factorial design with repeated measurements. Hypotheses are formulated by means of relative treatment effects and are tested by a multivariate extension of the Mann-Whitney statistic in a heteroscedastic model. The application of this method is demonstrated by the analysis of a data set from a diagnostic clinical trial.

Biometry↗

PubMed2004

PKN3 is required for malignant prostate cell growth downstream of activated PI 3-kinase.

Chronic activation of the phosphoinositide 3-kinase (PI3K)/PTEN signal transduction pathway contributes to metastatic cell growth, but up to now effectors mediating this response are poorly defined. By simulating chronic activation of PI3K signaling experimentally, combined with three-dimensional (3D) culture conditions and gene expression profiling, we aimed to identify novel effectors that contribute to malignant cell growth. Using this approach we identified and validated PKN3, a barely characterized protein kinase C-related molecule, as a novel effector mediating malignant cell growth downstream of activated PI3K. PKN3 is required for invasive prostate cell growth as assessed by 3D cell culture assays and in an orthotopic mouse tumor model by inducible expression of short hairpin RNA (shRNA). We demonstrate that PKN3 is regulated by PI3K at both the expression level and the catalytic activity level. Therefore, PKN3 might represent a preferred target for therapeutic intervention in cancers that lack tumor suppressor PTEN function or depend on chronic activation of PI3K.

Animals↗

PubMed2004

Knockdown of MTP18, a novel phosphatidylinositol 3-kinase-dependent protein, affects mitochondrial morphology and induces apoptosis.

We identified a novel human cDNA encoding a mitochondrial protein, MTP18 (mitochondrial protein, 18 kDa) as a transcriptional downstream target of phosphatidylinositol (PI) 3-kinase signaling. We demonstrate that MTP18 mRNA as well as protein expression is dependent on PI 3-kinase activity. Confocal microscopy and biochemical fractionation revealed a mitochondrial localization of MTP18. Loss-of-function analysis employing antisense molecules revealed that MTP18 is essential for cell viability in PC-3 and HaCaT cells. We show that knockdown of MTP18 protein level results in a cytochrome c release from mitochondria and consequently leads to apoptosis. In addition, HaCaT cells with reduced levels of MTP18 become more sensitive to apoptotic stimuli. This effect is accompanied by dramatic subcellular alterations. Reduction of MTP18 impairs mitochondrial morphology resulting in the formation of a highly interconnected mitochondrial reticulum in COS-7 cells. Conversely, overexpression of MTP18 induces a punctuate morphology of mitochondria suggesting also a functional role of MTP18 in maintaining the mitochondrial integrity. Hence, our data indicate an unexpected connection of PI 3-kinase signaling, apoptosis and the morphology of mammalian mitochondria.

Amino Acid Sequence↗

PubMed2003

Inducible shRNA expression for application in a prostate cancer mouse model.

RNA interference (RNAi) is a powerful tool to induce loss-of-function phenotypes by inhibiting gene expression post-transcriptionally. Synthetic short interfering RNAs (siRNAs) as well as vector-based siRNA expression systems have been used successfully to silence gene expression in a variety of biological systems. We describe the development of an inducible siRNA expression system that is based on the tetracycline repressor and eukaryotic RNA polymerase III promoters (U6 and 7SK). For proof of concept we selectively inhibited expression of two catalytic subunits of the phosphatidylinositol 3-kinase (PI 3-kinase), p110alpha and p110beta, by using vector-derived short hairpin RNAs (shRNAs). Stable pools of human prostate cancer cells (PC-3) exhibiting reduced levels of both PI 3-kinase catalytic subunits due to the expression of corresponding shRNAs in an inducible fashion were established and analyzed for their invasive potential in vitro as well as in an orthotopic metastatic mouse model. This inducible system for RNAi allows an unbiased and comparable analysis of loss-of-function phenotypes by comparing selected isogenic cell populations on the induced and non-induced level. In addition, conditional RNAi allows the study of essential and multifunctional genes involved in complex biological processes by preventing inhibitory and compensatory effects caused by constitutive knockdown.

Animals↗

PubMed2003

Structural variations and stabilising modifications of synthetic siRNAs in mammalian cells.

Double-stranded short interfering RNAs (siRNA) induce post-transcriptional silencing in a variety of biological systems. In the present study we have investigated the structural requirements of chemically synthesised siRNAs to mediate efficient gene silencing in mammalian cells. In contrast to studies with Drosophila extracts, we found that synthetic, double-stranded siRNAs without specific nucleotide overhangs are highly efficient in gene silencing. Blocking of the 5'-hydroxyl terminus of the antisense strand leads to a dramatic loss of RNA interference activity, whereas blocking of the 3' terminus or blocking of the termini of the sense strand had no negative effect. We further demonstrate that synthetic siRNA molecules with internal 2'-O-methyl modification, but not molecules with terminal modifications, are protected against serum-derived nucleases. Finally, we analysed different sets of siRNA molecules with various 2'-O-methyl modifications for stability and activity. We demonstrate that 2'-O-methyl modifications at specific positions in the molecule improve stability of siRNAs in serum and are tolerated without significant loss of RNA interference activity. These second generation siRNAs will be better suited for potential therapeutic application of synthetic siRNAs in vivo.

Endoribonucleases↗

PubMed2003

Orbital inflammatory pseudotumor due to hypersensitivity vasculitis and mononeuritis multiplex in a patient with atypical, cANCA-positive Wegener's granulomatosis.

OBJECTIVE: We report on a 60-year-old woman with a retro-orbital pseudotumor and polyneuropathy. The retro-orbital inflammation was histologically diagnosed as hypersensitivity vasculitis (HV). As cytoplasmatic antineutrophilic cytoplasmatic antibody (cANCA) and anti-proteinase-3 antibody were detected, the differential diagnosis also included atypical Wegener's granulomatosis. Hypersensitivity vasculitis is defined as small-vessel vasculitis mediated by the deposition of immune complexes (Arthus reaction) after exposure to various agents such as drugs, toxins, and infections. Since an inflammatory retro-orbital pseudotumor due to HV has not previously been reported, the following case is presented. METHODS AND MAIN OUTCOME MEASURES: Magnetic resonance imaging (MRI) revealed retro-orbital infiltrate without granuloma. Histology from an orbital biopsy confirmed HV. Electromyography was used for the diagnosis of polyneuropathy. Serum investigation indicated erythrocyte sedimentation rate (ESR) >100 mm/h, C-reactive protein (CRP) 223 mg/l, antinuclear antibodies 1:80, and cANCA 100 U/ml. RESULTS: The bilateral orbital pseudotumor, polyneuropathy, and serum levels of inflammation reactants (ESR and CRP) improved from therapy with corticosteroids (1 g of methylprednisolone initially) and azathioprine (150 mg/day). CONCLUSIONS: Because of cANCA and anti-proteinase-3 antibody positivity, this case can be viewed more as an atypical Wegener's granulomatosis than a systemic HV. The causal variety of inflammatory orbital pseudotumor, including HV and different therapeutic consequences, requires histological differentiation from usual orbital pseudotumors.

Antibodies, Antineutrophil Cytoplasmic↗

PubMed2003

[Hypersensitivity vasculitis].

BACKGROUND: Hypersensitivity vasculitis (leukocytoclastic vasculitis) is defined as small-vessel vasculitis mediated by deposition of immune complexes (Arthus reaction) after exposition to various agents, such as drugs, toxins and infections. Due to a wide spectrum of precipitating agents and symptoms, classification systems and synonyms, understanding of the disease, its diagnosis and therapeutic strategy are difficult. METHODS: Based on an extensive analysis of the literature, causal agents, etiopathogenesis as well as symptoms and their frequencies are summarized. The widespread differential diagnoses and the development of a diagnostic strategy for practical management of the disease are discussed. RESULTS AND CONCLUSIONS: The course of disease is generally benign, and spontaneous remission is often observed. Severe organ manifestations and chronic courses have, however, been described. Clinical diagnosis must be confirmed histopathologically. Once the diagnosis is made, search for etiologic agents (successful in only 50% of the cases) and an intensive organ diagnostics should be performed. Subsequently, treatment with steroids, antihistamines and slow-acting antirheumatic drugs such as cytotoxic substances and immunosuppressive drugs is planned according to severity and prognosis.

Adrenal Cortex Hormones↗

PubMed2003

Functional studies of the PI(3)-kinase signalling pathway employing synthetic and expressed siRNA.

RNA interference (RNAi) is a RNA-mediated sequence-specific gene silencing mechanism. Recently, this mechanism has been used to down-regulate protein expression in mammalian cells by applying synthetic- or vector-generated small interfering RNAs (siRNAs). However, for the evaluation of this new knockdown technology, it is crucial to demonstrate biological consequences beyond protein level reduction. Here, we demonstrate that this new siRNA-based technology is suitable to analyse protein functions using the phosphatidylinositol (PI) 3-kinase signal transduction pathway as a model system. We demonstrate stable and transient siRNA-mediated knockdown of one of the PI 3-kinase catalytic subunits, p110beta, which leads to inhibition of invasive cell growth in vitro as well as in a tumour model system. Importantly, this result is consistent with loss-of-function phenotypes induced by conventional RNase H-dependent antisense molecules or treatment with the PI 3-kinase inhibitor LY294002. RNAi knockdown of the downstream kinases Akt1 and Akt2 does not reduce cell growth on extracellular matrix. Our data show that synthetic siRNAs, as well as vector-based expression of siRNAs, are a powerful new tool to interfere with signal transduction processes for the elucidation of gene function in mammalian cells.

Animals↗

PubMed2003

Relation between body mass index and radiological progression in patients with rheumatoid arthritis.

OBJECTIVE: To determine if there is an influence of body mass index (BMI) on the radiological progression in early and longer duration rheumatoid arthritis (RA). METHODS: Fifty-four patients with RA were observed in a progressive 2 year followup for radiological progression of joint damage. At the beginning of study, 27 (50%) patients had a duration of complaints less than 6 months, grouped as early RA. BMI at the beginning and end of the study were monitored, together with HLA-DRB1 alleles, initial joint erosions, duration of disease, age, sex, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). Outcome was defined as radiographic damage according to yearly increase of Larsen score. RESULTS: Increased radiographic joint damage of patients was significantly correlated with lower BMI at the beginning of the study (r = 0.363, p < 0.05), the presence of initial joint erosions (r = 0.341, p < 0.01), ESR (r = 0.315, p < 0.05), and CRP at study entry (r = 0.427, p < 0.01). Patients with an increase of Larsen score > or = 5.8/year were found to have a lower weight at the beginning of their complaints (BMI 24.8 +/- 4.7 vs 27.8 +/- 3.8; p < 0.05) as well as after the time of observation (BMI 24.6 +/- 3.7 vs 27.6 +/- 4.9; p < 0.05). Stepwise logistic regression analysis revealed a BMI < 27 at the beginning of disease (beta = 2.04, p = 0.003, odds ratio = 7.69), the presence of HLA-DR4 shared epitope (beta = 1.76, p = 0.015, OR 5.82), and joint erosions at study entry (beta = 1.56, p = 0.044, OR 4.78) as significant predictors for rapid joint damage. CONCLUSION: Together with the presence of HLA-DR4 shared epitope and erosive disease at study entry, a low BMI at the beginning of RA was found in association with higher radiographic progression in RA. Accordingly, BMI could be of interest as a sensitive and inflammation-independent predictor for radiological outcome of RA.

Adult↗

PubMed2002

Unravelling novel intracellular pathways in cell-based assays.

The pharmaceutical industry is currently facing several challenges to identify and develop novel drug targets. Traditional drug discovery focussed on a small number of well-characterized gene products. Recently, this picture has changed with the completion of the draft sequence of the human genome, which has led to the identification of thousands of novel genes with unknown or poorly understood function. To cope with this overwhelming number of potential drug target candidates, new strategies for the elucidation of gene function, as well as their involvement in intracellular pathways, are required.

Biological Assay↗