hERG quality control and the long QT syndrome

Long-QT syndrome type-2 (LQT2) is characterized by reduced functional expression of the human ether-à-go-go related (hERG) gene product, resulting in impaired cardiac repolarization and predisposition to fatal arrhythmia. Previous studies have implicated abnormal trafficking of misfolded hERG as the primary mechanism of LQT2, with misfolding being caused by mutations in the hERG gene (inherited) or drug treatment (acquired). More generally, environmental and metabolic stresses present a constant challenge to the folding of proteins, including hERG, and must be countered by robust protein quality control (QC) systems. Disposal of partially unfolded yet functional plasma membrane (PM) proteins by protein QC contributes to the loss-of-function phenotype in various conformational diseases including cystic fibrosis (CF) and long-QT syndrome type-2 (LQT2). The prevalent view has been that the loss of PM expression of hERG is attributed to biosynthetic block by endoplasmic reticulum (ER) QC pathways. However, there is a growing appreciation for protein QC pathways acting at post-ER cellular compartments, which may contribute to conformational disease pathogenesis. This article will provide a background on the structure and cellular trafficking of hERG as well as inherited and acquired LQT2. We will review previous work on hERG ER QC and introduce the more novel view that there is a significant peripheral QC at the PM and peripheral cellular compartments. Particular attention is drawn to the unique role of the peripheral QC system in acquired LQT2. Understanding the QC process and players may provide targets for therapeutic intervention in dealing with LQT2.

Device for filamentous fungi growth monitoring using the multimodal frequency response of cantilevers

Filamentous fungi cause opportunistic infections in hospital patients. A fast assay to detect viable spores is of great interest. We present a device that is capable of monitoring fungi growth in real time via the dynamic operation of cantilevers in an array. The ability to detect minute frequency shifts for higher order flexural resonance modes is demonstrated using hydrogel functionalised cantilevers. The use of higher order resonance modes sees the sensor dependent mass responsivity enhanced by a factor of 13 in comparison to measurements utilizing the fundamental resonance mode only. As a proof of principle measurement, Aspergillus niger growth is monitored using the first two flexural resonance modes. The detection of single spore growth within 10 h is reported for the first time. The ability to detect and monitor the growth of single spores, within a small time frame, is advantageous in both clinical and industrial settings.

Establishment of the hu-PBL-SCID Mouse Model for the Investigation of Thyroid Cancer

New experimental models of human neoplastic diseases attempt to mimic the human environment that fostered the development of disease in cancer patients. The aim of the present study was to establish a human lymphocyte-engrafted, severe combined immunodeficient (hu-PBL-SCID) mouse model to investigate thyroid cancer and to evaluate the potential use of this model for cancer immunotherapy. Thyroid neoplastic tissues were obtained from ten patients (one follicular adenoma, five papillary, one follicular, one anaplastic and two medullary cancers). One 8 x 4 x 3 millimeter sample from each tumor was cut into two pieces of identical size and transplanted into two SCID mice. In each case, one of the two mice was injected intraperitoneally with lymphocytes from the same tumor patient for the reconstitution of the human immune system (Group A), while the other animal received no lymphocytes (Group B). The engraftment of the tumors was successful in all cases. The growth rate was highly dependent on the histological type. When histologies were compared before implantation and after the removal of the implants, the characters of the tumors proved to be unchanged, except one case where an anaplastic cancer arose from a papillary tumor. Macrophages were present in all but one papillary cancer. All differentiated thyroid cancers were infiltrated by T and B lymphocytes. Lymphocytes and macrophages disappeared from 19/20 grafts by week 16. However, in one case from group A lymphocytes were detected four months after the transplantation. In another case from group A, one papillary cancer spontaneously decreased in size and disappeared. Before implantation, HLA-DR expression was detected in every papillary cancer. HLA-DR expression in the grafts was not seen in 3/5 cases by week 16. In conclusion, an animal model has been established for the investigation of human thyroid cancer, by which the analysis of anti-tumor immunity, as a postulate of immune therapy, may be possible.

Biochemical methods to assess CFTR expression and membrane localization

Detection of cystic fibrosis transmembrane conductance regulator (CFTR) protein is usually a difficult task to accomplish due to the low levels of expression and high turnover that this membrane protein is submitted to in the cell. Common biochemical methods can be used for the detection of CFTR but several critical points must be taken into account. The scope of this article is to outline biochemical methods commonly used to assess CFTR expression, processing and membrane localization.

Antibodies for CFTR studies

For most expression studies focusing on the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein, sensitive and specific antibodies (Abs) are critically needed. Several Abs have been produced commercially or by research laboratories for CFTR detection in both cell lines with heterologous or endogenous expression and native cells/tissues. Here, we review the applicability of most Abs currently in use in CF research for the biochemical and/or immunocytochemical detection of CFTR.

Differentiated thyroid cancer and outcome in iodine deficiency

AIMS

Factors influencing prognosis and long-term outcome of thyroid cancer have been described by several groups. We wished to asses the previously described prognostic factors in a moderately iodine deficient region in Hungary.

METHODS

Four hundred and fifty-four out of 492 patients who had surgery for papillary thyroid cancer (PTC, 386 cases) and follicular thyroid cancer (FTC, 106 cases) between 1971 and 1998 were analyzed. Survival curves were compared using the Kaplan-Meier method and Cox regression analysis.

RESULTS

The 10 and 20-year survival rates were 87.9 and 84% for PTC, and 78.2 and 78.2% for FTC. In PTC, extrathyroidal invasion (p<0.0001), lymph node metastasis (p<0.0001), distant metastasis (p<0.0001), and age over 40 years (p=0.002) were significant adverse predictors. In FTC, extrathyroidal invasion (p=0.003) distant metastases (p<0.0001), and age over 40 years (p=0.011) were significant adverse predictors.

CONCLUSION

Iodine intake did not appear to influence survival. The incidence of follicular cancer, which has less favourable prognosis, was higher in iodine deficient regions. This supports the importance of iodine supplementation in these areas.

Endosomal recycling of the Na+/H+ exchanger NHE3 isoform is regulated by the phosphatidylinositol 3-kinase pathway

The NHE3 isoform of the Na+/H+ exchanger localizes to both the plasmalemmal and endosomal compartments in polarized epithelial and transfected Chinese hamster ovary (AP-1) cells. It is unclear how the distribution of NHE3 between these compartments is regulated. In this study, we examined the potential involvement of phosphatidylinositol 3'-kinase (PI3-K) in regulating the activity and distribution of NHE3, as this lipid kinase has been implicated in modulating vesicular traffic in the endosomal recycling pathway. Wortmannin and LY294002, both potent inhibitors of PI3-K, markedly inhibited NHE3-mediated H+ extrusion across the plasma membrane in a concentration- and time-dependent manner. The subcellular distribution of the antiporters was monitored by transfecting epitope-tagged NHE3 into AP-1 cells. In parallel with the inhibition of transport, PI3-K antagonists induced a pronounced loss of NHE3 from the cell surface and its accumulation in an intracellular compartment, as assessed by immunofluorescence microscopy and enzyme-linked immunosorbent assays. Further analysis using cells transfected with antiporters bearing an external epitope tag revealed that the redistribution reflected primarily a decrease in the rate of recycling of intracellular NHE3 to the cell surface. The wortmannin-induced inhibition and redistribution of NHE3 were prevented when cells were incubated at 4 degreesC, consistent with the known temperature dependence of the endocytic process. These observations demonstrate that NHE3 activity is controlled by dynamic endocytic and recycling events that are modulated by PI3-K.

The epithelial sodium-hydrogen antiporter Na+/H+ exchanger 3 accumulates and is functional in recycling endosomes

Na+/H+ exchangers (NHEs) mediate electroneutral exchange of Na+ for H+ and thereby play a central role in pH regulation and Na+ homeostasis. NHE3, the predominant epithelial isoform, is found in apical membranes of renal and intestinal epithelial cells, where it contributes to NaCl (re)absorption. NHE activity has been detected in endomembrane vesicles of epithelial cells, but the precise compartment involved and its functional role have not been defined. Many aspects of the targeting machinery that defines the compartmentation and polarity of epithelia are also functional in nonepithelial cells. We therefore compared the targeting of NHE1, the basolateral isoform, with that of NHE3 in Chinese hamster ovary cells. To circumvent the confounding effects of endogenous exchangers, epitope-tagged constructs of NHE1 and NHE3 were stably expressed in antiport-deficient (AP-1) cells. While NHE1 was found almost exclusively in the surface membrane, NHE3 was also found intracellularly, accumulating in a juxtanuclear compartment. Confocal microscopy showed this compartment to be distinct from the Golgi, trans-Golgi network, and lysosomes. Instead, NHE3 colocalized with transferrin receptors and with cellubrevin, markers of recycling endosomes. The activity of NHE3 in endomembranes was assessed by targeting pH-sensitive probes to the recycling endosomes using a chimeric cellubrevin construct with an accessible extracellular epitope. Fluorescence ratio imaging indicated that cellubrevin resides intracellularly in an acidic compartment. In AP-1 cells, endosomal acidification was unaffected by omission of Na+ but was dissipated entirely by concanamycin, a blocker of H(+)-ATPases. In contrast, the cellubrevin compartment was more acidic in NHE3 transfectants, and the acidification was only partially reduced by concanamycin. Moreover, removal of extracellular Na+ resulted in a significant alkalization of the endocytic compartment. These results indicate that NHE3 is present and active in recycling endosomes. By recruiting NHE3 to the plasma membrane, modulation of vesicular traffic could contribute to the regulation of Na+ reabsorption across epithelia.

Preparation and in vitro antibacterial activity of 9-O-glycosyloxime derivatives of erythromycin A, a new class of macrolide antibiotics

9-O-Glycosyloxime derivatives of erythromycin A have been synthesized and their in vitro antibacterial activity compared with that of erythromycin A (1). This new class of macrolide antibiotics showed reduced antibacterial spectrum. However, some derivatives were as or more active than erythromycin A (1) against strains, responsible for respiratory track infections, such as Haemophilus influenzae, Moraxella catarrhalis or Streptococcus pneumoniae.

Distinct structural domains confer cAMP sensitivity and ATP dependence to the Na+/H+ exchanger NHE3 isoform

Agents known to increase cAMP levels in renal and intestinal epithelia decrease sodium absorption by inhibiting NHE3, an isoform of the Na+/H+ exchanger expressed at high levels in apical membranes of these cells. In contrast, the ubiquitous, housekeeping isoform of the exchanger (NHE1) is stimulated by cAMP in some cell types. Optimal activity of NHE3 as well as NHE1 requires the presence of ATP. To gain insight into the molecular mechanisms of ATP dependence and cAMP regulation of NHE3, a series of mutations were constructed by progressively truncating segments of the C-terminal cytoplasmic domain of the transporter at amino acid positions 684, 638, and 579 (named NHE3delta684, NHE3delta638, and NHE3delta579). In addition, chimeric antiporters were constructed with the N-terminal transmembrane domain of NHE3 linked to the entire cytoplasmic region of NHE1 (chimera NHE3/1) or vice versa (chimera NHE1/3). These constructs were heterologously expressed in antiport-deficient Chinese hamster ovary cells, and their activities were assessed by fluorimetric measurements of intracellular pH and by radioisotope determinations of Na+ influx. Forskolin, which directly stimulates adenylate cyclase, inhibited NHE3 as well as NHE1/3, but not NHE3/1, suggesting that the cytoplasmic domain of NHE3 was sufficient to confer sensitivity to inhibition by cAMP. Forskolin also inhibited the truncated mutant NHE3delta684 to an extent similar to that for wild type NHE3. However, the inhibitory effect was greatly reduced in NHE3delta638 and more profound truncations (NHE3delta579 obliterated the effect of forskolin. These findings suggest that a region found between amino acids 579 and 684 is essential for the cAMP response of NHE3. In contrast, comparable ATP dependence was observed in all exchanger constructs examined. These observations indicate that ATP dependence is conferred by a region of the molecule in or adjacent to the transmembrane domain, which is most conserved between isoforms. It is concluded that different sites, and therefore different mechanisms, underlie inhibition of NHE3 by cAMP and by depletion of ATP.

Responsiveness of mutants of NHE1 isoform of Na+/H+ antiport to osmotic stress

Hypertonic activation of NHE1, the ubiquitous Na+/H+ exchanger, plays a central role in cell volume regulation, yet little is known about the underlying mechanism. We probed the osmotic responsiveness of full-length and truncated constructs of NHE1 transfected into cells lacking endogenous antiport activity. The hypertonic stimulation of NHE1 was preserved after heterologous transfection of the full-length NHE1 or of constructs truncated at positions 698 or 703. In contrast, mutants truncated at position 635 (delta 635) failed to respond to osmotic challenge. Transfectants (delta 635) behaved as if constitutively activated, having a permanently elevated cytosolic pH (pHi) under isotonic, unstimulated conditions. The delta 635 mutant displayed H+ binding with high affinity and low cooperativity. Constructs delta 582 or delta 566 had a reduced H+ sensitivity and were therefore inactive at resting pHi. Such cells were unresponsive to osmotic stress near physiological pHi but could be activated by shrinking after an acid load. Jointly, these results suggest that the H+ affinity and high cooperativity of the antiporter, earlier attributed to a single "modifier site," can be varied independently and are probably controlled by different regions of the molecule. The data indicate that volume or osmolarity-sensitive site(s) exist between the NH2-terminus and residue 566. This putative volume-sensitive site is therefore different from the site(s) postulated to mediate the stimulatory effects of calcium and growth factors.

Chemical modification of tylosin

20-Homo tylosin, 20-nor tylosin, 20-deoxy-19,20-didehydro tylosin (6-vinyl tylosin) and 2",3"-didehydro-3"-deoxy tylosin were prepared by multi-step procedures. 20-Homo tylosin was about twice less active than tylosin while the other compounds exhibited very weak antibacterial activity.

V-ATPases in phagocytic cells

V-ATPases in phagocytic cells are known to mediate the acidification of most intracellular organelles. Proton-pump-mediated acidification of these organellar compartments is vital to numerous cell processes, including receptor recycling, protein processing and sorting and microbial degradation. Recent studies have suggested a role for V-ATPases in cytoplasmic pH homeostasis. The present discussion will review the current knowledge regarding the presence of V-ATPases in both the plasmalemmal and organellar membranes of phagocytic cells, the regulation of proton pump activity in these locations and the functional significance of pump-mediated proton translocation.

Decreased leukocyte adhesion with anti-CD18 monoclonal antibodies is mediated by receptor internalization

BACKGROUND

Adhesion of polymorphonuclear leukocytes (PMNs) to endothelial cells is mediated partially by CD11/CD18 integrins. The purpose of this study was to define (1) the response of PMNs to anti-CD18 monoclonal antibody binding, and (2) the mechanism responsible for anti-CD18 monoclonal antibody-mediated decreases in PMN adhesion to endothelial cells.

METHODS

Canine PMN O2- production, myeloperoxidase, and lysozyme release in response to the anti-CD18 monoclonal antibody IB4 were measured by standard assays. To examine endocytosis of CD18 receptors, PMNs incubated with IB4 and a fluorescein isothiocyanate secondary antibody were analyzed by flow cytometry.

RESULTS

Treatment of PMNs with IB4 did not stimulate O2- production or degranulation but decreased adhesion of 51Cr-labeled PMNs to ex vivo canine aorta. Incubation of PMNs at 25 degrees C resulted in a decrease in fluorescence intensity that was not affected by NaN3 or vanadate but was blocked by NaF, 4 degrees C, and bafilomycin, which prevents endosomal acidification. Treatment with an antifluorescein antibody decreased the fluorescence intensity in NaF and 4 degrees C, but not in bafilomycin-treated neutrophils.

CONCLUSIONS

IB4 decreases PMN-endothelial cell adhesion but does not stimulate neutrophil oxidative metabolism or degranulation. These data suggest that reduced adhesion may be the result of internalization of the CD18/IB4 complex. Anti-CD18 monoclonal antibodies may be useful in preventing PMN adhesion without the potentially deleterious effects of cell activation.

Solution conformation of the disaccharide of avermectin B1a examined by NMR spectroscopy and nuclear Overhauser enhancement restrained hard-sphere exo-anomeric effect calculation

The solution conformation of the disaccharide of avermectin B1a was examined by combining NMR data with theoretical conformational energy calculations. Carbon and proton resonances were assigned unambiguously using high-field, high-resolution 2D NMR correlation spectroscopy. 3JHH coupling constants were determined at 600 MHz. The minimum-energy conformation was attained through an extended hard-sphere exo-anomeric effect (HSEA) approach. The HSEA conformation was refined by considering the experimental nuclear Overhauser enhancement contacts. The resulting three-dimensional structure was confirmed by comparing its glycosidic dihedral angles to those calculated from experimental 3JCOCH coupling constants. Differences has been found in the glycosidic dihedral angles between the solution conformation and the X-ray structure.

Synthesis and biological activity of the two isomeric 2'-C-methyl daunomycins

The title new daunorubicin analogues have been prepared from methyl 4,6-O-benzylidene-2-C-methyl-alpha-D-ribo-hexopyranosid-3-ulose and daunomycinone. The antitumor activity of these compounds was very similar to that of daunorubicin.

Structure of cervinomycin, a novel xantone antibiotic active against anaerobe and mycoplasma

The structures of cervinomycins A1 (1) and A2 (2), a potent anti-anaerobic and anti-mycoplasmal antibiotic were investigated by means of recent NMR techniques of O-methyl ether (3) and C,O-dimethyl ether (4) obtained by methylation of 2 with CH3I in the presence of Ag2O. The antibiotic 2 posesses a polycyclic structure involving a xanthone skeleton. The structure of 1 was confirmed to be a hydroquinone of 2 from the evidences that oxidation of 1 with Ag2O and acetylation of 1 with (CH3CO)2O in pyridine afforded quantitatively 2 and triacetylcervinomycin A1 (7), respectively.

Synthesis and antitumor activity of 3'-C-methyl-daunorubicin

Reaction of 1,5-anhydro-4-O-benzoyl-2,3,6-trideoxy-3-C-methyl-3-trifluoro-acetami no-L-lyxo-hex-1-enitol with daunomycinone in the presence of anhydrous toluene-p-sulfonic acid in benzene, followed by removal of the N- and O-protecting groups under mild conditions, gave 3'-C-methyldaunorubicin. The antitumor activity of the new anthracycline glycoside has been evaluated.

Etude en résonance magnétique nucléaire du 13C des paramètres de substitution de la fonction azide

The various effects (α, β, γ and δ) on the 13C nmr of azido steroids have been measured. For cyclohexane azides constrained to equatorial and axial configurations, the α-effects were determined to be 33.6 and 31.2 ppm. Both γ- and δ-effects have magnitudes near those for OH and NH2 groups. On the other hand, the β-effect of the azides is slightly smaller than those of hydroxyls or amines as its magnitude is reduced by a γ-effect of the second nitrogen atom of the azide group. This additional γ-effect is a function of the spatial arrangement of the Cβ—H bond with respect to the azide group. [Journal translation]

Studies on the biosynthesis of 16-membered macrolide antibiotics using carbon-13 nuclear magnetic resonance spectroscopy

The origin of the skeletal carbons in the lactone ring of 16-membered macrolide antiobiotics has been studied. 13C-labeled antibiotics leucomycin and tylosin, have been obtained from the culture broth of Streptomyces kitasatoensis 66-14-3 and Streptomyces fradiae C-373, respectively in the presence of appropriate 13C-labeled precursors, and 13C NMR spectra of the antibiotics thus obtained have been measured. It was shown that the aglycone of leucomycin A3 is derived from five acetates, one propionate, one butyrate, and an unknown precursor corresponding to two carbons. The formyl carbon which is characteristic of the basic 16-membered macrolides orginates from C-4 butyrate. On the other hand, the aglycone of tylosin is formed from two acetates, five propionates and one butyrate. Butyric acid and ethylmalonic acid are metabolized to propionyl-CoA or methylmolonyl-CoA through a pathway involving methylmalonyl-CoA mutase, and subsequently incorporated into the lactone ring of tylosin.