FMP Publications

Our publications are recorded in a searchable database since 2010, updates will be added regularly.

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References
Endosomal chloride-proton exchange rather than chloride conductance is crucial for renal endocytosis
Novarino, G., Weinert, S., Rickheit, G.; Jentsch, T. J.
Science, 328:1398-1401
(2010)

Tags: Physiology and Pathology of Ion Transport (Jentsch

Abstract: Loss of the endosomal anion transport protein ClC-5 impairs renal endocytosis and underlies human Dent's disease. ClC-5 is thought to promote endocytosis by facilitating endosomal acidification through the neutralization of proton pump currents. However, ClC-5 is a 2 chloride (Cl-)/proton (H+) exchanger rather than a Cl- channel. We generated mice that carry the uncoupling E211A (unc) mutation that converts ClC-5 into a pure Cl- conductor. Adenosine triphosphate (ATP)-dependent acidification of renal endosomes was reduced in mice in which ClC-5 was knocked out, but normal in Clcn5(unc) mice. However, their proximal tubular endocytosis was also impaired. Thus, endosomal chloride concentration, which is raised by ClC-5 in exchange for protons accumulated by the H+-ATPase, may play a role in endocytosis.

Impact of membrane properties on uptake and transcytosis of colloidal nanocarriers across an epithelial cell barrier model
Orthmann(*), A., Zeisig(*), R., Koklic(*), T., Sentjurc(*), M., Wiesner, B., Lemm(*), M.; Fichtner(*), I.
Journal of pharmaceutical sciences, 99:2423-2433
(2010)

Tags: Cellular Imaging (Wiesner)

Abstract: The aim of this study was to investigate the effect of liposomal membrane properties on cellular uptake and transcytosis across a tight Madin-Darby canine kidney (MDCK) cell barrier in vitro. More than 25 small vesicles were prepared by lipid film hydration/extrusion to generate small unilamellar vesicles. The fluorescence marker calcein was encapsulated to mimic hydrophilic drug transport. Marker uptake by MDCK cells seems to be mediated by different mechanisms for the liposomes used. It was mainly depending on membrane fluidity and vesicle charge. Liposomes L2 with a positive charge (325 +/- 3 pmol/well) and vesicles L3 containing the helper lipid dioleylphosphatidylethanolamine (DOPE) in their membrane (216 +/- 42 pmol/well) were taken up to the most. Selected liposomes were tested for their transcytotic transport across a MDCK monolayer. Liposomes L4 containing equimolar DOPE and octadecyl-1,1-dimethylpiperidin-1-ium-4-yl phosphate (OPP) were the most efficient vesicles for transcellular transport resulting in 808 +/- 30 pmol calcein/cm(2) in the basal medium (28.1% of total liposomal marker added). Transcytosis was positively correlated with membrane fluidity in the outer part of the bilayer, as electron paramagnetic resonance measurements revealed. We expect that an increase in membrane fluidity of vesicles should also improve the restricted transport of hydrophilic drugs across the blood-brain barrier.

Participation of the second extracellular loop of claudin-5 in paracellular tightening against ions, small and large molecules
Piehl, C., Piontek, J., Cording, J., Wolburg(*), H.; Blasig, I. E.
Cellular and molecular life sciences : CMLS, 67:2131-2140
(2010)

Tags: Molecular Cell Physiology (Blasig, I.E.)

Abstract: Tight junctions control paracellular permeability. Here, we analyzed the impact of residues in the second extracellular loop (ECL2) of mouse claudin-5 on paracellular permeability. Stable expression of claudin-5(wild type) in MDCK-II cells-but not that of mutants R145A, Y148A, Y158A or E159Q-increased transepithelial electrical resistance and decreased fluorescein permeation. Expression of claudin-5(Y148A), (Y158A) or (E159Q) enhanced permeability of FITC-dextran(10 kDa), which was unchanged in cells expressing claudin-5(wild type) or claudin-5(R145A). In contrast, targeting to tight junctions, strand morphology and tight junction assembly were unchanged. It is concluded that R145 is unessential for trans-interaction of claudin-5, but necessary for tightening against small solutes and ions. The highly conserved residues Y148, Y158 and E159 in ECL2 of claudin-5 contribute to homo- and/or heterophilic trans-interaction between classic claudins and thereby tighten the paracellular space against ions, small and large molecules. These results provide novel insights into the molecular function of tight junctions.

Distinct Neuropathologic Phenotypes After Disrupting the Chloride Transport Proteins ClC-6 or ClC-7/Ostm1
Pressey(*), S. N. R., O'Donnell(*), K. J., Stauber, T., Fuhrmann, J. C., Tyynela(*), J., Jentsch, T. J.; Cooper(*), J. D.
J Neuropath Exp Neur, 69:1228-1246
(2010)

Tags: Physiology and Pathology of Ion Transport (Jentsch

Abstract: The proteins ClC-6 and ClC-7 are expressed in the endosomallysosomal system. Because Clcn6-deficient mice display some features of neuronal ceroid lipofuscinosis (NCL), CLCN6 may be a candidate gene for novel forms of NCL. Using landmarks of disease progression from NCL mouse models as a guide, we examined neuropathologic alterations in the central nervous system of Clcn6(-/-), Clcn7(-/-), and gl mice. gl mice bear a mutation in Ostm1, the beta-subunit critical for Clcn7 function. Severely affected Clcn7(-/-) and gl mice have remarkably similar neuropathologic phenotypes, with pronounced reactive changes and neuron loss in the thalamocortical system, similar to findings in early-onset forms of NCL. In contrast, Clcn6(-/-) mice display slowly progressive, milder neuropathologic features with very little thalamic involvement or microglial activation. These findings detail for the first time the markedly different neuropathologic consequences of mutations in these two CLC genes. Clcn7(-/-) and gl mice bear a close resemblance to the progressive neuropathologic phenotypes of early onset forms of NCL, whereas the distinct phenotype of Clcn6-deficient mice suggests that this gene could be a candidate for a later-onset form of mild neurologic dysfunction with some NCL-like features.

Disruption of the K+ Channel beta-Subunit KCNE3 Reveals an Important Role in Intestinal and Tracheal Cl- Transport
Preston, P., Wartosch, L., Günzel(*), D., Fromm(*), M., Kongsuphol(*), P., Ousingsawat(*), J., Kunzelmann(*), K., Barhanin(*), J., Warth(*), R.; Jentsch, T. J.
Journal of Biological Chemistry, 285:7165-7175
(2010)

Tags: Physiology and Pathology of Ion Transport (Jentsch

Abstract: The KCNE3 beta-subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K+ channels by abolishing their voltage-dependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K+ channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K+ channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3(-/-) mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl- secretion through basolateral recycling of K+ ions and by increasing the electrochemical driving force for apical Cl- exit. Indeed, cAMP-stimulated electrogenic Cl- secretion across tracheal and intestinal epithelia was drastically reduced in kcne3(-/-) mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3(-/-) mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis.

Amyloid beta 42 peptide (Abeta42)-lowering compounds directly bind to Abeta and interfere with amyloid precursor protein (APP) transmembrane dimerization
Richter(*), L., Munter(*), L. M., Ness(*), J., Hildebrand(*), P. W., Dasari, M., Unterreitmeier(*), S., Bulic(*), B., Beyermann, M., Gust(*), R., Reif, B., Weggen(*), S., Langosch(*), D.; Multhaup(*), G.
Proc Natl Acad Sci U S A, 107:14597-14602
(2010)

Tags: Solid-State NMR Spectroscopy (Reif), Peptide Synthesis (Beyermann)

Abstract: Following ectodomain shedding by beta-secretase, successive proteolytic cleavages within the transmembrane sequence (TMS) of the amyloid precursor protein (APP) catalyzed by gamma-secretase result in the release of amyloid-beta (Abeta) peptides of variable length. Abeta peptides with 42 amino acids appear to be the key pathogenic species in Alzheimer's disease, as they are believed to initiate neuronal degeneration. Sulindac sulfide, which is known as a potent gamma-secretase modulator (GSM), selectively reduces Abeta42 production in favor of shorter Abeta species, such as Abeta38. By studying APP-TMS dimerization we previously showed that an attenuated interaction similarly decreased Abeta42 levels and concomitantly increased Abeta38 levels. However, the precise molecular mechanism by which GSMs modulate Abeta production is still unclear. In this study, using a reporter gene-based dimerization assay, we found that APP-TMS dimers are destabilized by sulindac sulfide and related Abeta42-lowering compounds in a concentration-dependent manner. By surface plasmon resonance analysis and NMR spectroscopy, we show that sulindac sulfide and novel sulindac-derived compounds directly bind to the Abeta sequence. Strikingly, the attenuated APP-TMS interaction by GSMs correlated strongly with Abeta42-lowering activity and binding strength to the Abeta sequence. Molecular docking analyses suggest that certain GSMs bind to the GxxxG dimerization motif in the APP-TMS. We conclude that these GSMs decrease Abeta42 levels by modulating APP-TMS interactions. This effect specifically emphasizes the importance of the dimeric APP-TMS as a promising drug target in Alzheimer's disease.

Role of ClC-5 in Renal Endocytosis Is Unique among ClC Exchangers and Does Not Require PY-motif-dependent Ubiquitylation
Rickheit, G., Wartosch, L., Schaffer(*), S., Stobrawa(*), S. M., Novarino, G., Weinert, S.; Jentsch, T. J.
Journal of Biological Chemistry, 285:17595-17603
(2010)

Tags: Physiology and Pathology of Ion Transport (Jentsch

Abstract: Inactivation of the mainly endosomal 2Cl(-)/H(+)-exchanger ClC-5 severely impairs endocytosis in renal proximal tubules and underlies the human kidney stone disorder Dent's disease. In heterologous expression systems, interaction of the E3 ubiquitin ligases WWP2 and Nedd4-2 with a "PY-motif" in the cytoplasmic C terminus of ClC-5 stimulates its internalization from the plasma membrane and may influence receptor-mediated endocytosis. We asked whether this interaction is relevant in vivo and generated mice in which the PY-motif was destroyed by a point mutation. Unlike ClC-5 knock-out mice, these knock-in mice displayed neither low molecular weight proteinuria nor hyperphosphaturia, and both receptor-mediated and fluid-phase endocytosis were normal. The abundances and localizations of the endocytic receptor megalin and of the Na(+)-coupled phosphate transporter NaPi-2a (Npt2) were not changed, either. To explore whether the discrepancy in results from heterologous expression studies might be due to heteromerization of ClC-5 with ClC-3 or ClC-4 in vivo, we studied knock-in mice additionally deleted for those related transporters. Disruption of neither ClC-3 nor ClC-4 led to proteinuria or impaired proximal tubular endocytosis by itself, nor in combination with the PY-mutant of ClC-5. Endocytosis of cells lacking ClC-5 was not impaired further when ClC-3 or ClC-4 was additionally deleted. We conclude that ClC-5 is unique among CLC proteins in being crucial for proximal tubular endocytosis and that PY-motif-dependent ubiquitylation of ClC-5 is dispensable for this role.

NMR spectroscopic investigation of mobility and hydrogen bonding of the chromophore in the binding pocket of phytochrome proteins
Röben, M., Hahn, J., Klein, E., Lamparter(*), T., Psakis(*), G., Hughes(*), J.; Schmieder, P.
Chemphyschem, 11:1248-1257
(2010)

Tags: Solution NMR (Schmieder)

Abstract: For a complete understanding of the light reception of phytochrome proteins, a detailed study of the structure and dynamics of the binding pocket at atomic resolution is required. Structures from X-ray crystallography and NMR spectroscopy are available and have been able to provide a picture of the binding pocket. NMR spectroscopy has, in addition, shown that the chromophore exhibits noticeable dynamics in the binding pocket of the cyanobacterial phytochrome Cph1. Herein, NMR spectroscopy is used to investigate further the mobility of the chromophore by analyzing the line widths of the resonances of the chromophore in various environments, in particular other protein environments. It is shown that the chromophore exhibits a different mobility in the binding pocket of the bacterial phytochrome Agp1 than in that of the cyanobacterial phytochrome Cph1. Finally, it is shown that NMR spectroscopy is capable of detecting hydrogen bonds in the binding pocket of phytochromes by observing slow exchange of protons in the amino acid side chains.

Analysis of CLCN2 as Candidate Gene for Megalencephalic Leukoencephalopathy with Subcortical Cysts
Scheper(*), G. C., van Berkel(*), C. G. M., Leisle, L., de Groot(*), K. E., Errami(*), A., Jentsch, T. J.; Van der Knaap(*), M. S.
Genet Test Mol Bioma, 14:255-257
(2010)

Tags: Physiology and Pathology of Ion Transport (Jentsch

Abstract: Mutations in the gene MLC1 are found in approximately 80% of the patients with the inherited childhood white matter disorder megalencephalic leukoencephalopathy with subcortical cysts (MLC). Genetic linkage studies have not led to the identification of another disease gene. We questioned whether mutations in CLCN2, coding for the chloride channel protein 2 (ClC-2), are involved in MLC. Mice lacking this protein develop white matter abnormalities, which are characterized by vacuole formation in the myelin sheaths, strikingly similar to the intramyelinic vacuoles in MLC. Sequence analysis of CLCN2 at genomic DNA and cDNA levels in 18 MLC patients without MLC1 mutations revealed some nucleotide changes, but they were predicted to be nonpathogenic. Further, in electrophysiological experiments, one of the observed amino acid changes was shown to have no effect on the ClC-2-mediated currents. In conclusion, we found no evidence suggesting that the CLCN2 gene is involved in MLC.

The pseudo signal peptide of the corticotropin-releasing factor receptor type 2a decreases receptor expression and prevents Gi-mediated inhibition of adenylyl cyclase activity
Schulz, K., Rutz, C., Westendorf, C., Ridelis, I., Vogelbein, S., Furkert, J., Schmidt(*), A., Wiesner, B.; Schülein, R.
J Biol Chem, 285:32878-32887
(2010)

Tags: Protein Trafficking (Schülein)

Abstract: The corticotropin-releasing factor receptor type 2a (CRF(2(a))R) belongs to the family of G protein-coupled receptors. The receptor possesses an N-terminal pseudo signal peptide that is unable to mediate targeting of the nascent chain to the endoplasmic reticulum membrane during early receptor biogenesis. The pseudo signal peptide remains uncleaved and consequently forms an additional hydrophobic receptor domain with unknown function that is unique within the large G protein-coupled receptor protein family. Here, we have analyzed the functional significance of this domain in comparison with the conventional signal peptide of the homologous corticotropin-releasing factor receptor type 1 (CRF(1)R). We show that the presence of the pseudo signal peptide leads to a very low cell surface receptor expression of the CRF(2(a))R in comparison with the CRF(1)R. Moreover, whereas the presence of the pseudo signal peptide did not affect coupling to the G(s) protein, G(i)-mediated inhibition of adenylyl cyclase activity was abolished. The properties mediated by the pseudo signal peptide were entirely transferable to the CRF(1)R in signal peptide exchange experiments. Taken together, our results show that signal peptides do not only influence early protein biogenesis. In the case of the corticotropin-releasing factor receptor subtypes, the use of conventional and pseudo signal peptides have an unexpected influence on signal transduction.

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Leibniz-Forschungsinstitut für Molekulare Pharmakologie im Forschungsverbund Berlin e.V. (FMP)
Campus Berlin-Buch
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13125 Berlin, Germany
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info(at)fmp-berlin.de

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