BACE inhibitor treatment of mice induces hyperactivity in a Seizure-related gene 6 family dependent manner without altering learning and memory.

BACE inhibitors, which decrease BACE1 (ß-secretase 1) cleavage of the amyloid precursor protein, are a potential treatment for Alzheimer's disease. Clinical trials using BACE inhibitors have reported a lack of positive effect on patient symptoms and, in some cases, have led to increased adverse events, cognitive worsening and hippocampal atrophy. A potential drawback of this strategy is the effect of BACE inhibition on other BACE1 substrates such as Seizure-related gene 6 (Sez6) family proteins which are known to have a role in neuronal function. Mice were treated with an in-diet BACE inhibitor for 4-8 weeks to achieve a clinically-relevant level of amyloid-ß40 reduction in the brain. Mice underwent behavioural testing and postmortem analysis of dendritic spine number and morphology with Golgi-Cox staining. Sez6 family triple knockout mice were tested alongside wild-type mice to identify whether any effects of the treatment were due to altered cleavage of Sez6 family proteins. Wild-type mice treated with BACE inhibitor displayed hyperactivity on the elevated open field, as indicated by greater distance travelled, but this effect was not observed in treated Sez6 triple knockout mice. BACE inhibitor treatment did not lead to significant changes in spatial or fear learning, reference memory, cognitive flexibility or anxiety in mice as assessed by the Morris water maze, context fear conditioning, or light-dark box tests. Chronic BACE inhibitor treatment reduced the density of mushroom-type spines in the somatosensory cortex, regardless of genotype, but did not affect steady-state dendritic spine density or morphology in the CA1 region of the hippocampus. Chronic BACE inhibition for 1-2 months in mice led to increased locomotor output but did not alter memory or cognitive flexibility. While the mechanism underlying the treatment-induced hyperactivity is unknown, the absence of this response in Sez6 triple knockout mice indicates that blocking ectodomain shedding of Sez6 family proteins is a contributing factor. In contrast, the decrease in mature spine density in cortical neurons was not attributable to lack of shed Sez6 family protein ectodomains. Therefore, other BACE1 substrates are implicated in this effect and, potentially, in the cognitive decline in longer-term chronically treated patients.

Important role of junctophilin in nematode motor function.

Junctional complexes between the plasma membrane and endoplasmic/sarcoplasmic reticulum are shared by excitable cells and seem to be the structural ground for cross-talk between cell-surface and intracellular ionic channels. Our current studies have identified junctophilins (JPs) as members of a novel transmembrane protein family in the junctional membrane complex. Biochemical and gene-knockout studies have suggested that JPs contribute to the formation of the junctional membrane complex by spanning the intracellular store membrane and interacting with the plasma membrane. We report here invertebrate JPs in fruit fly and nematode. Three distinct JP subtype genes are found in the mammalian genome, while a single JP gene exists in either invertebrate genome. Mammalian and invertebrate JPs share characteristic structural features, although some intervening sequences are found in invertebrate JPs. A reporter assay indicated that the JP gene is predominantly activated in muscle cells in nematode. Nematodes, in which expression of JP was inhibited by RNA-mediated interference (RNAi), showed hypolocomotion. Taking account of the cell-type-specific expression and data from previous reports, the hypolocomotion is likely to be due to the deficiency of junctional membrane structures and the resulting reduction of Ca(2+) signaling during excitation-contraction coupling in muscle cells.

A region of the sulfonylurea receptor critical for a modulation of ATP-sensitive K(+) channels by G-protein betagamma-subunits.

To determine the interaction site(s) of ATP-sensitive K(+) (K(ATP)) channels for G-proteins, sulfonylurea receptor (SUR2A or SUR1) and pore-forming (Kir6.2) subunits were reconstituted in the mammalian cell line, COS-7. Intracellular application of the G-protein betagamma2-subunits (G(betagamma)(2)) caused a reduction of ATP-induced inhibition of Kir6.2/SUR channel activities by lessening the ATP sensitivity of the channels. G(betagamma)(2) bound in vitro to both intracellular (loop-NBD) and C-terminal segments of SUR2A, each containing a nucleotide-binding domain (NBD). Furthermore, a single amino acid substitution in the loop-NBD of SUR (Arg656Ala in SUR2A or Arg665Ala in SUR1) abolished the G(betagamma)(2)-dependent alteration of the channel activities. These findings provide evidence that G(betagamma) modulates K(ATP) channels through a direct interaction with the loop-NBD of SUR.

Molecular cloning of cDNA encoding a drosophila ryanodine receptor and functional studies of the carboxyl-terminal calcium release channel.

Ryanodine is a plant alkaloid that was originally used as an insecticide. To study the function and regulation of the ryanodine receptor (RyR) from insect cells, we have cloned the entire cDNA sequence of RyR from the fruit fly Drosophila melanogaster. The primary sequence of the Drosophila RyR contains 5134 amino acids, which shares approximately 45% identity with RyRs from mammalian cells, with a large cytoplasmic domain at the amino-terminal end and a small transmembrane domain at the carboxyl-terminal end. To characterize the Ca(2+) release channel activity of the cloned Drosophila RyR, we expressed both full-length and a deletion mutant of Drosophila RyR lacking amino acids 277-3650 (Drosophila RyR-C) in Chinese hamster ovary cells. For subcellular localization of the expressed Drosophila RyR and Drosophila RyR-C proteins, green fluorescent protein (GFP)-Drosophila RyR and GFP-Drosophila RyR-C fusion constructs were generated. Confocal microscopic imaging identified GFP-Drosophila RyR and GFP-Drosophila RyR-C on the endoplasmic reticulum membranes of transfected cells. Upon reconstitution into the lipid bilayer membrane, Drosophila RyR-C formed a large conductance cation-selective channel, which was sensitive to modulation by ryanodine. Opening of the Drosophila RyR-C channel required the presence of microM concentration of Ca(2+) in the cytosolic solution, but the channel was insensitive to inhibition by Ca(2+) at concentrations as high as 20 mM. Our data are consistent with our previous observation with the mammalian RyR that the conduction pore of the calcium release channel resides within the carboxyl-terminal end of the protein and further demonstrate that structural and functional features are essentially shared by mammalian and insect RyRs.

Effects of graded levels of dietary casein and corn oil on total cholesterol and triacylglycerol in plasma and liver of rats.

With the intention of examining the effects of dietary protein and oil levels on total cholesterol (T-CHOL) and triacylglycerol (TG) concentrations in the plasma and liver, male Wistar rats, weighing about 170 g, were fed diets containing graded levels of casein and corn oil for 2 wk. At the 5, 20, and 30% levels of dietary corn oil, plasma T-CHOL concentrations were generally enhanced in proportion to the rise of dietary casein level, but plasma TG contents were scarcely influenced by the level. At the 8 to 35% casein levels, plasma T-CHOL and TG concentrations were the highest at the 5% corn oil level, followed in order by the 20 and 30% levels of oil. At the 5 and 20% oil levels, hepatic T-CHOL contents were hardly changed at the 8 to 30% casein levels, but enhanced at the 35% casein level. At the 30% oil level, the T-CHOL contents tended to be changed proportionally to casein levels. At all levels of casein, hepatic T-CHOL contents tended to be relatively high at the 30% corn oil, middle at the 20% oil, and low at the 5% one. At each corn oil level, TG contents in the liver tended to be elevated at the 8 to 15% casein levels and highly preserved at the 15 to 25% ones. Then, the raised TG contents declined at the 5 and 20% levels of corn oil and remained constant at the 30% oil. At each casein level, the contents of hepatic TG were generally high at the 30% oil level, followed in order by the 20 and 5% oil levels. These results indicated that plasma and liver T-CHOL concentrations were proportionately enhnaced by the increase in casein level, and plasma TG contents were hardly affected by the level and hepatic TG ones were lowered by relatively lower or higher casein level, and the rise in corn oil level generally reduced plasma T-CHOL and TG concentrations, but raised hepatic ones.

[Cases of refractory testicular cancer treated with all trans-retinoic acid].

We reported two cases of chemotherapy-refractory testicular cancer treated with all trans-retinoic acid (ATRA). Case 1. A 21-year-old male patient underwent salvage surgery for lung metastasis which had developed after treatment with three different cisplatin-based chemotherapy regimens for malignant teratoma. After recovery from surgery, he was treated with oral ATRA at daily dose 80 mg/m2 for four weeks. Case 2. A-45-year-old patient suffered from lung metastasis after orchiectomy for teratocarcinoma. The patient failed to achieve a complete response despite two different cisplatin-based chemotherapy and high dose chemotherapy regimens with bone marrow rescue. He was treated with oral ATRA for five weeks. Both patients showed disease progression with increase in tumor size and elevation of tumor marker during ATRA therapy. Side effects were acceptable except the headache in Case 2, who needed a dose reduction of ATRA. In conclusion, oral ATRA with this dose failed to show clinical antitumor activity in patients with refractory testicular cancer.

Excitation-contraction uncoupling and muscular degeneration in mice lacking functional skeletal muscle ryanodine-receptor gene.

Contraction of skeletal muscle is triggered by the release of Ca2+ from the sarcoplasmic reticulum (SR) after depolarization of transverse tubules. The ryanodine receptor exists as a 'foot' protein in the junctional gap between the sarcoplasmic reticulum and the transverse tubule in skeletal muscle, and is proposed to function as a calcium-release channel during excitation-contraction (E-C) coupling. Previous complementary DNA-cloning studies have defined three distinct subtypes of the ryanodine receptor in mammalian tissues, namely skeletal muscle, cardiac and brain types. We report here mice with a targeted mutation in the skeletal muscle ryanodine receptor gene. Mice homozygous for the mutation die perinatally with gross abnormalities of the skeletal muscle. The contractile response to electrical stimulation under physiological conditions is totally abolished in the mutant muscle, although ryanodine receptors other than the skeletal-muscle type seem to exist because the response to caffeine is retained. Our results show that the skeletal muscle ryanodine receptor is essential for both muscular maturation and E-C coupling, and also imply that the function of the skeletal muscle ryanodine receptor during E-C coupling cannot be substituted by other subtypes of the receptor.

cDNA cloning and regional distribution of a novel member of the opioid receptor family.

We have cloned a cDNA for a novel member of the opioid receptor family, designated as ROR-C, from the rat cerebrum cDNA library using the probe derived from the delta-opioid receptor subtype cDNA. The deduced amino acid sequence of ROR-C shows high homology with those of ROR-A (rat delta-opioid receptor subtype), ROR-B (rat mu-subtype) and ROR-D (rat kappa-subtype). RNA blot hybridization and in situ hybridization analysis revealed that ROR-C mRNA is expressed in discrete regions of the rat central nervous system.

Isolation and characterization of a gene for a ryanodine receptor/calcium release channel in Drosophila melanogaster.

The nucleotide sequence of a 25.7 kilobase Drosophila melanogaster genomic DNA segment containing a gene for a ryanodine receptor/calcium release channel homologue has been determined. Computer analysis and partial cDNA cloning revealed 26 exons comprising the protein-coding sequence in this gene. The predicted protein is homologous in amino acid sequence and shares characteristic structural features with the mammalian ryanodine receptors. In blot hybridization analysis, a approximately 16 kilobase RNA species was identified abundantly in a 6-12 h embryo as the transcript from this gene. In situ hybridization to polytene chromosomes indicated that this gene locates at band position 44F on the second chromosome.

Primary structure and functional expression of the cardiac dihydropyridine-sensitive calcium channel.

In cardiac muscle, where Ca2+ influx across the sarcolemma is essential for contraction, the dihydropyridine (DHP)-sensitive L-type calcium channel represents the major entry pathway of extracellular Ca2+. We have previously elucidated the primary structure of the rabbit skeletal muscle DHP receptor by cloning and sequencing the complementary DNA. An expression plasmid carrying this cDNA, microinjected into cultured skeletal muscle cells from mice with muscular dysgenesis, has been shown to restore both excitation-contraction coupling and slow calcium current missing from these cells, so that a dual role for the DHP receptor in skeletal muscle transverse tubules is suggested. We report here the complete amino-acid sequence of the rabbit cardiac DHP receptor, deduced from the cDNA sequence. We also show that messenger RNA derived from the cardiac DHP receptor cDNA is sufficient to direct the formation of a functional DHP-sensitive calcium channel in Xenopus oocytes. Furthermore, higher calcium-channel activity is observed when mRNA specific for the polypeptide of relative molecular mass approximately 140,000 (alpha 2-subunit) associated with skeletal muscle DHP receptor is co-injected.

Primary structure and expression from complementary DNA of skeletal muscle ryanodine receptor.

The sequence of 5,037 amino acids composing the ryanodine receptor from rabbit skeletal muscle sarcoplasmic reticulum has been deduced by cloning and sequencing the complementary DNA. The predicted structure suggests that the calcium release channel activity resides in the C-terminal region of the receptor molecule, whereas the remaining portion constitutes the 'foot' structure spanning the junctional gap between the sarcoplasmic reticulum and the transverse tubule.

Primary structure of the receptor for calcium channel blockers from skeletal muscle.

The complete amino-acid sequence of the receptor for dihydropyridine calcium channel blockers from rabbit skeletal muscle is predicted by cloning and sequence analysis of DNA complementary to its messenger RNA. Structural and sequence similarities to the voltage-dependent sodium channel suggest that in the transverse tubule membrane of skeletal muscle the dihydropyridine receptor may act both as voltage sensor in excitation-contraction coupling and as a calcium channel.

Screening and isolation of penicillinase inhibitor, KA-107.

It is known that penicillin resistance of bacteria is mainly caused by the inactivation of penicillin by penicillinase derived from such strains. We have developed a screening procedure for penicillinase inhibitors. Several microorganisms were found to produce such inhibitors, and from the culture filtrate of Streptomyces gedanensis ATCC 4880 a penicillinase inhibitor, named KA-107, was isolated. The characteristics of this inhibitor were revealed by an in vitro test by using penicillinase derived from penicillin resistant Staphylococcus aureus, FS-1277. When KA-107 was used in combination with penicillin-G, ampicillin, d- or l-phenethicillin, the growth inhibitory activity of these penicillins was maintained.