Novel cell line selectively expressing neuropeptide Y-Y2 receptors

Neuropeptide Y (NPY) recognition by the human neuroblastoma cell lines SiMa, Kelly, SH-SY5Y, CHP-234, and MHH-NB-11 was analyzed in radioactive binding assays using tritiated NPY. For the cell lines CHP-234 and MHH-NB-11 binding of [3H]propionyl-NPY was observed with Kd-values of 0.64 +/- 0.07 nM and 0.53 +/- 0.12 nM, respectively, determined by saturation analysis with non-linear regression. The receptor subtype was determined by competition analysis using the subtype selective NPY analogues [Leu31, Pro34]-NPY (NPY-Y1, NPY-Y5), [Ahx(5-24)]-NPY (NPY-Y2), [Ala31, Aib32]-NPY (NPY-Y5), NPY [3-36] (NPY-Y2, NPY-Y5), and NPY [13-36] (NPY-Y2). Both cell lines, CHP-234 and MHH-NB-11, the latter one being characterized for NPY receptors for the first time, showed exclusive expression of NPY-Y2 receptors. In both cell lines binding of NPY induced signal transduction, which was monitored as reduction of forskolin-induced cAMP production in an ELISA.     

Ghrelin and body weight regulation in the obese Zucker rat in relation to feeding state and dark/light cycle

Ghrelin is a new orexigenic peptide primarily produced by the stomach but also present in the hypothalamus. It has adipogenic effects when it is chronically injected in rodents but in obese humans, its plasma concentration is decreased. It can reverse the anorectic effects of leptin when it is co-injected with this peptide in the brain ventricles. The Zucker fa/fa rat is a genetic model of obesity related to a default in the leptin receptor. It is characterized by a large dysregulation of numerous hypothalamic peptides but the ghrelin status of this rat has not yet been determined. Through several experiments, we determine in lean and obese Zucker rats its circulating form in the plasma, its tissue levels and/or expression, and studied the influence of different feeding conditions and its light/dark variations. Ghrelin expression was higher in the obese stomach and hypothalamus (P < 0.05 and P < 0.02, respectively). The ratio of [Octanoyl-Ser3]-ghrelin (active form) to [Des-Octanoyl-Ser3]-ghrelin (inactive form) was approximately 1:1 in the stomach and 2:1 in the plasma in lean and obese rats (no differences). After fasting, plasma ghrelin concentrations increased significantly in lean (+ 64%; P < 0.001) and obese (+ 60%; P < 0.02) rats. After 24 hours of refeeding, they returned to their initial ad lib levels. Ghrelin concentrations were higher in obese rats by 69% (P < 0.005), 65% (P < 0.02), and 73% (P < 0.005) in the ad libitum, fast, and refed states respectively. These results indicate that the obese Zucker rat is characterized by increases in the stomach mRNA expression and in peptide release in the circulation. They clearly support a role for ghrelin in the development of obesity in the absence of leptin signaling.     

Genes involved in the anaerobic degradation of ethylbenzene in a denitrifying bacterium,strain EbN1

Genes involved in anaerobic degradation of the petroleum hydrocarbon ethylbenzene in the denitrifying Azoarcus-like strain EbN1 were identified on a 56-kb DNA contig obtained from shotgun sequencing. Ethylbenzene is first oxidized via ethylbenzene dehydrogenase to (S)-1-phenylethanol; this is converted by (S)-1-phenylethanol dehydrogenase to acetophenone. Further degradation probably involves acetophenone carboxylase forming benzoylacetate, a ligase forming benzoylacetyl-CoA, and a thiolase forming acetyl-CoA and benzoyl-CoA. Genes of this pathway were identified via N-terminal sequences of proteins isolated from strain EbN1 and by sequence similarities to proteins from other bacteria. Ethylbenzene dehydrogenase is encoded by three genes (ebdABC), in accordance with the heterotrimeric enzyme structure. Binding domains for a molybdenum cofactor (in subunit EbdA) and iron/sulfur-clusters (in subunits EbdA and EbdB) were identified. The previously observed periplasmic location of the enzyme was corroborated by the presence of a twin-arginine leader peptide characteristic of the Tat system for protein export. A fourth gene (ebdD) was identified, the product of which may act as an enzyme-specific chaperone in the maturation of the molybdenum-containing subunit. A distinct gene (ped) coding for (S)-1-phenylethanol dehydrogenase apparently forms an operon with the ebdABCD genes. The ped gene product with its characteristic NAD(P)-binding motif in the N-terminal domain belongs to the short-chain dehydrogenase/reductase (SDR) superfamily. A further operon apparently contains five genes (apc1-5) suggested to code for subunits of acetophenone carboxylase. Four of the five gene products are similar to subunits of acetone carboxylase from Xanthobacter autotrophicus. Upstream of the apc genes, a single gene (bal) was identified which possibly codes for a benzoylacetate CoA-ligase and which is co-transcribed with the apc genes. In addition, an apparent operon containing almost all genes required for beta-oxidation of fatty acids was detected; one of the gene products may be involved in thiolytic cleavage of benzoylacetyl-CoA. The DNA fragment also included genes for regulatory systems; these were two sets of two-component systems, two LysR homologs, and a TetR homolog. Some of these proteins may be involved in ethylbenzene-dependent gene expression.     

Regulation of TonEBP transcriptional activator in MDCK cells following changes in ambient tonicity

In response to ambient hypertonicity, TonEBP (tonicity-responsive enhancer binding protein) stimulates certain genes including those encoding cytokines, transporters for organic solutes, and a molecular chaperone. TonEBP is regulated in a bidirectional manner, upregulated by an increase in ambient tonicity while downregulated by a decrease. To investigate the role of intracellular ionic strength in the activity of TonEBP, we subjected Madin-Darby canine kidney cells to a variety of conditions. Electron microprobe analysis was performed to measure intracellular electrolytes. Under conditions in which changes in cell volume were similar, TonEBP activity correlated with the intracellular ionic strength regardless of the external tonicity. On the other hand, inhibition of the Na+/K+-ATPase and high external K+ concentration led to a decreased activity of TonEBP despite a marked increase in the intracellular ionic strength. Because isotonic swelling is known to occur under these conditions, these data suggest that dilution of the cytoplasmic constituents inhibits the activity of TonEBP. We conclude that intracellular ionic strength and water content are major factors that determine the activity of TonEBP.     

Noninvasive measurement of bacterial intracellular pH on a single-cell level with green fluorescent protein and fluorescence ratio imaging microscopy

We show that a pH-sensitive derivative of the green fluorescent protein, designated ratiometric GFP, can be used to measure intracellular pH (pHi) in both gram-positive and gram-negative bacterial cells. In cells expressing ratiometric GFP, the excitation ratio (fluorescence intensity at 410 and 430 nm) is correlated to the pHi, allowing fast and noninvasive determination of pHi that is ideally suited for direct analysis of individual bacterial cells present in complex environments.     

Rapid exchange of mammalian topoisomerase II alpha at kinetochores and chromosome arms in mitosis

A stable cell line (GT2-LPk) derived from LLC-Pk was created in which endogenous DNA topoisomerase II alpha (topoII alpha) protein was downregulated and replaced by the expression of topoII alpha fused with enhanced green fluorescent protein (EGFP-topoII alpha). The EGFP-topoII alpha faithfully mimicked the distribution of the endogenous protein in both interphase and mitosis. In early stages of mitosis, EGFP-topoII alpha accumulated at kinetochores and in axial lines extending along the chromosome arms. During anaphase, EGFP-topoII alpha diminished at kinetochores and increased in the cytoplasm with a portion accumulating into large circular foci that were mobile and appeared to fuse with the reforming nuclei. These cytoplasmic foci appearing at anaphase were coincident with precursor organelles of the reforming nucleolus called nucleolus-derived foci (NDF). Photobleaching of EGFP-topoII alpha associated with kinetochores and chromosome arms showed that the majority of the protein rapidly exchanges (t1/2 of 16 s). Catalytic activity of topoII alpha was essential for rapid dynamics, as ICRF-187, an inhibitor of topoII alpha, blocked recovery after photobleaching. Although some topoII alpha may be stably associated with chromosomes, these studies indicate that the majority undergoes rapid dynamic exchange. Rapid mobility of topoII alpha in chromosomes may be essential to resolve strain imparted during chromosome condensation and segregation.     

Interactions between Multiple Phosphorylation Sites in the Inactivation Particle of a K+ Channel : Insights into the Molecular Mechanism of Protein Kinase C Action

Protein kinase C inhibits inactivation gating of Kv3.4 K⁺ channels, and at least two NH₂-terminal serines (S15 and S21) appeared involved in this interaction (Covarrubias et al. 1994. Neuron. 13:1403–1412). Here we have investigated the molecular mechanism of this regulatory process. Site-directed mutagenesis (serine → alanine) revealed two additional sites at S8 and S9. The mutation S9A inhibited the action of PKC by ∼85%, whereas S8A, S15A, and S21A exhibited smaller reductions (41, 35, and 50%, respectively). In spite of the relatively large effects of individual S → A mutations, simultaneous mutation of the four sites was necessary to completely abolish inhibition of inactivation by PKC. Accordingly, a peptide corresponding to the inactivation domain of Kv3.4 was phosphorylated by specific PKC isoforms, but the mutant peptide (S[8,9,15,21]A) was not. Substitutions of negatively charged aspartate (D) for serine at positions 8, 9, 15, and 21 closely mimicked the effect of phosphorylation on channel inactivation. S → D mutations slowed the rate of inactivation and accelerated the rate of recovery from inactivation. Thus, the negative charge of the phosphoserines is an important incentive to inhibit inactivation. Consistent with this interpretation, the effects of S8D and S8E (E = Glu) were very similar, yet S8N (N = Asn) had little effect on the onset of inactivation but accelerated the recovery from inactivation. Interestingly, the effects of single S → D mutations were unequal and the effects of combined mutations were greater than expected assuming a simple additive effect of the free energies that the single mutations contribute to impair inactivation. These observations demonstrate that the inactivation particle of Kv3.4 does not behave as a point charge and suggest that the NH₂-terminal phosphoserines interact in a cooperative manner to disrupt inactivation. Inspection of the tertiary structure of the inactivation domain of Kv3.4 revealed the topography of the phosphorylation sites and possible interactions that can explain the action of PKC on inactivation gating.