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Biomedical subjects

A Ebneth

Publications and source records attributed to A Ebneth.

8 recordsLinked to original sources
PubMed2001

Screening lead compounds for QT interval prolongation.

The late detection of cardiotoxic side effects, such as QT prolongation, induced by compounds of pharmacological interest can dramatically impede drug discovery and development projects, and consequently increase their cost. The launch of new drugs with undetected cardiotoxic side effects could have hazardous consequences and could trigger lethal cardiac dysrhythmias in patients. It is desirable, therefore, to test for the potential cardiotoxic side effects of compounds at an early stage of drug development. Electrophysiological test systems and cellular-based fluorometric high-throughput assays are now available for cloned human cardiac ion channels. These test systems are important tools in the preclinical safety evaluation of drugs and newly developed compounds.

Journal Article↗
PubMed1999

Phosphorylation of MAP2c and MAP4 by MARK kinases leads to the destabilization of microtubules in cells.

Microtubules serve as transport tracks in molecular mechanisms governing cellular shape and polarity. Rapid transitions between stable and dynamic microtubules are regulated by several factors, including microtubule-associated proteins (MAPs). We have shown that MAP/microtubule affinity regulating kinases (MARK) can phosphorylate the microtubule-associated-proteins MAP4, MAP2c, and tau on their microtubule-binding domain in vitro. This leads to their detachment from microtubules (MT) and an increased dynamic instability of MT. Here we show that MARK protein kinases phosphorylate MAP2 and MAP4 on their microtubule-binding domain in transfected CHO cells. In CHO cells expressing MARK1 or MARK2 under control of an inducible promoter, MARK2 phosphorylates an endogenous MAP4-related protein. Prolonged expression of MARK2 results in microtubule-disruption, detachment of cells from the substratum, and cell death. Concomitant with microtubule disruption, we also observed a breakdown of the vimentin network, whereas actin fibers remained unaffected. Thus, MARK seems to play an important role in controlling cytoskeletal dynamics.

Actins↗
PubMed1999

Tau regulates the attachment/detachment but not the speed of motors in microtubule-dependent transport of single vesicles and organelles.

We have performed a real time analysis of fluorescence-tagged vesicle and mitochondria movement in living CHO cells transfected with microtubule-associated protein tau or its microtubule-binding domain. tau does not alter the speed of moving vesicles, but it affects the frequencies of attachment and detachment to the microtubule tracks. Thus, tau decreases the run lengths both for plus-end and minus-end directed motion to an equal extent. Reversals from minus-end to plus-end directed movement of single vesicles are strongly reduced by tau, but reversals in the opposite direction (plus to minus) are not. Analogous effects are observed with the transport of mitochondria and even with that of vimentin intermediate filaments. The net effect is a directional bias in the minus-end direction of microtubules which leads to the retraction of mitochondria or vimentin IFs towards the cell center. The data suggest that tau can control intracellular trafficking by affecting the attachment and detachment cycle of the motors, in particular by reducing the attachment of kinesin to microtubules, whereas the movement itself is unaffected.

Animals↗
PubMed1998

Overexpression of tau protein inhibits kinesin-dependent trafficking of vesicles, mitochondria, and endoplasmic reticulum: implications for Alzheimer's disease.

The neuronal microtubule-associated protein tau plays an important role in establishing cell polarity by stabilizing axonal microtubules that serve as tracks for motor-protein-driven transport processes. To investigate the role of tau in intracellular transport, we studied the effects of tau expression in stably transfected CHO cells and differentiated neuroblastoma N2a cells. Tau causes a change in cell shape, retards cell growth, and dramatically alters the distribution of various organelles, known to be transported via microtubule-dependent motor proteins. Mitochondria fail to be transported to peripheral cell compartments and cluster in the vicinity of the microtubule-organizing center. The endoplasmic reticulum becomes less dense and no longer extends to the cell periphery. In differentiated N2a cells, the overexpression of tau leads to the disappearance of mitochondria from the neurites. These effects are caused by tau's binding to microtubules and slowing down intracellular transport by preferential impairment of plus-end-directed transport mediated by kinesin-like motor proteins. Since in Alzheimer's disease tau protein is elevated and mislocalized, these observations point to a possible cause for the gradual degeneration of neurons.

Alzheimer Disease↗
PubMed1998

MAPs, MARKs and microtubule dynamics.

Microtubules (MTs) serve as tracks for cellular transport, and regulate cell shape and polarity. Rapid transitions between stable and dynamic forms of MTs are central to these processes. This dynamic instability is regulated by a number of cellular factors, including the structural MT-associated proteins (MAPs), which in turn are regulated by phosphorylation. MT-affinity-regulating kinases (MARKs) are novel mammalian serine/threonine kinases that phosphorylate the tubulin-binding domain of MAPs and thereby cause their detachment from MTs and increased MT dynamics. Molecular cloning of MARKs revealed a family of four closely related protein kinases that share homology with genes from the nematode Caenorhabditis elegans and fission yeast that are involved in the generation of cell shape and polarity. Hence, MARKs might play a role in the regulation of MT stability during morphogenesis.

Animals↗
PubMed1997

MARK, a novel family of protein kinases that phosphorylate microtubule-associated proteins and trigger microtubule disruption.

MARK phosphorylates the microtubule-associated proteins tau, MAP2, and MAP4 on their microtubule-binding domain, causing their dissociation from microtubules and increased microtubule dynamics. We describe the molecular cloning, distribution, activation mechanism, and overexpression of two MARK proteins from rat that arise from distinct genes. They encode Ser/Thr kinases of 88 and 81 kDa, respectively, and show similarity to the yeast kin1+ and C. elegans par-1 genes that are involved in the establishment of cell polarity. Expression of both isoforms is ubiquitous, and homologous genes are present in humans. Catalytic activity depends on phosphorylation of two residues in subdomain VIII. Overexpression of MARK in cells leads to hyperphosphorylation of MAPs on KXGS motifs and to disruption of the microtubule array, resulting in morphological changes and cell death.

Amino Acid Sequence↗
PubMed1994

Biophysical characterization of the c-Myb DNA-binding domain.

We have examined proteins containing the DNA-binding domain of c-Myb with biophysical methods. This DNA-binding domain consists of three imperfect repeats (R1, R2, and R3) conserved among many species. Our results indicate that the DNA-binding domain forms unspecific and specific complexes with oligodeoxynucleotides. In the presence of R1, DNA sequences related to a canonical c-Myb-binding site are better discriminated. Furthermore, although R2 and R3 are sufficient for sequence-specific DNA binding, a structural change of the DNA-binding domain upon specific complex formation is induced only when R1 is present. Therefore, R1 might serve as an important element required for secondary structure alteration upon binding and its stabilization as well as for better discrimination between specific and related DNA sequences.

Base Sequence↗