Isolation and characterization of a rice cDNA similar to the bovine brain-specific 14-3-3 protein gene

We isolated a rice cDNA clone which is similar to the bovine brain-specific 14-3-3 protein (an activator protein of tyrosine and tryptophan hydroxylase involved in the synthetic pathway of monoamine) gene. The deduced amino acid sequence of the cDNA indicated a surprising similarity to a potent inhibitor of Ca²⁺-phospholipid-dependent protein kinase C. DNA blot analysis indicated that this gene is located at more than a single locus in rice genome DNA. Expression of this gene is regulated by external stresses.     

Homologous Desensitization of Serotonin 5-HT2 Receptor-Stimulated Intracellular Calcium Mobilization in C6BU-1 Glioma Cells via a Mechanism Involving a Calmodulin Pathway

Abstract: Serotonin 5-HT₂ receptor-mediated intracellular Ca²⁺ mobilization was investigated in rat glioma C6BU-1 cells. The receptors became desensitized after previous exposure to 5-HT in a time-and concentration-dependent manner. The desensitization of 5-HT₂ receptor-mediated intracellular signaling appeared to be homologous because previous exposure to 5-HT did not alter the response to other transmitters such as thrombin or isoproterenol and because previous exposure to thrombin or isoproterenol did not diminish the response to 5-HT. The desensitization induced by pretreatment with 5-HT was potently prevented by the naphthalenesulfonamide derivative W-7, a calmodulin antagonist, when it was cosupplied with 5-HT. Furthermore, the preventive effect of W-7 was greater than that of W-5, a weak analogue of W-7, and than that of H-7, a nonselective inhibitor of protein kinases. These results suggest that 5-HT₂ receptor-mediated Ca²⁺ mobilization can be desensitized homologously after prolonged exposure to 5-HT in a calmodulin-dependent manner in rat glioma C6BU-1 cells.     

Molecular characterization of rice genes specifically expressed in the anther tapetum

In situ localization of mRNA was carried out on two cDNAs (Osc4 and Osc6) that had been isolated from rice anthers at the microspore stage. The mRNA corresponding to each cDNA was shown to be localized only in the tapetal cells of the rice immature anthers, but not in the microspores or the mature pollen. The corresponding genomic clone, Osg6B, was isolated, and its 5-upstream region was found to regulate -glucuronidase expression in the tapetum of transgenic tobacco. A set of 5 deletions was also generated and a 1095 bp 5 region was revealed to be necessary for activation of the Osg6B promoter in transgenic tobacco.     

Crystal structure of the drug discharge outer membrane protein, OprM, of Pseudomonas aeruginosa: dual modes of membrane anchoring and occluded cavity end

The OprM lipoprotein of Pseudomonas aeruginosa is a member of the MexAB-OprM xenobiotic-antibiotic transporter subunits that is assumed to serve as the drug discharge duct across the outer membrane. The channel structure must differ from that of the porin-type open pore because the protein facilitates the exit of antibiotics but not the entry. For better understanding of the structure-function linkage of this important pump subunit, we studied the x-ray crystallographic structure of OprM at the 2.56-angstroms resolution. The overall structure exhibited trimeric assembly of the OprM monomer that consisted mainly of two domains: the membrane-anchoring beta-barrel and the cavity-forming alpha-barrel. OprM anchors the outer membrane by two modes of membrane insertions. One is via the covalently attached NH(2)-terminal fatty acids and the other is the beta-barrel structure consensus on the outer membrane-spanning proteins. The beta-barrel had a pore opening with a diameter of about 6-8 angstroms, which is not large enough to accommodate the exit of any antibiotics. The periplasmic alpha-barrel was about 100 angstroms long formed mainly by a bundle of alpha-helices that formed a solvent-filled cavity of about 25,000 angstroms(3). The proximal end of the cavity was tightly sealed, thereby not permitting the entry of any molecule. The result of this structure was that the resting state of OprM had a small outer membrane pore and a tightly closed periplasmic end, which sounds plausible because the protein should not allow free access of antibiotics. However, these observations raised another unsolved problem about the mechanism of opening of the OprM cavity ends. The crystal structure offers possible mechanisms of pore opening and pump assembly.     

Effects of psychotomimetic and antipsychotic agents on neocortical and striatal concentrations of various amino acids in the rat

A subcutaneous injection of small and moderate doses (1.6, 3.2, 4.0 and 4.8 mg/kg) of the schizophrenomimetic methamphetamine caused a dose-related increase in the tissue content (the net content) of L-Arg and L-Asn in the neocortex and striatum at 60 min, but not at 360 min, after injection. The methamphetamine-induced (4.8 mg/kg) increases in levels of these amino acids were significantly attenuated by pretreatment with an antipsychotic drug, haloperidol (1 mg/kg) or clozapine (10 mg/kg). In the neocortex, a clozapine-reversible increase in the level of L-Thr was also observed 60 min after methamphetamine administration. Striatal concentrations of L-Glu, L-Ser, LThr, Gly and L-Ala were augmented by the same regimen in a haloperidol- and clozapine-sensitive fashion. A moderate dose of another schizophrenomimetic phencyclidine (7.5 mg/kg) given subcutaneously induced robust abnormal behavior, a diminution in the neocortical and striatal levels of L-Asp and an increase in the striatal L-Ala content without significant effects on the other amino acids studied. These results suggest that neocortical and striatal L-Arg, L-Asn, L-Thr, Gly, L-Ala or L-Ser may be implicated in the psychotomimetic effects of methamphetamine and might display mutual interaction with cerebral dopaminergic transmission. The differential effects of methamphetamine and phencyclidine on the net neocortical and striatal concentrations of various amino acids might, at least in part, underlie the distinct features of psychoses induced by these two drugs.     

Transforming activity of the lymphotoxin-beta receptor revealed by expression screening

Pancreatic ductal carcinoma (PDC) remains one of the most intractable human malignancies. To obtain insight into the molecular pathogenesis of PDC, we constructed a retroviral cDNA expression library with total RNA isolated from the PDC cell line MiaPaCa-2. Screening of this library with the use of a focus formation assay with NIH 3T3 mouse fibroblasts resulted in the identification of 13 independent genes with transforming activity. One of the cDNAs thus identified encodes an NH(2)-terminally truncated form of the lymphotoxin-beta receptor (LTBR). The transforming activity of this short-type LTBR in 3T3 cells was confirmed by both an in vitro assay of cell growth in soft agar and an in vivo assay of tumorigenicity in nude mice. The full-length (wild-type) LTBR protein was also found to manifest similar transforming activity. These observations suggest that LTBR, which belongs to the tumor necrosis factor receptor superfamily of proteins, may contribute to human carcinogenesis.     

Depletion of vesicle-tethering factor p115 causes mini-stacked Golgi fragments with delayed protein transport

Depletion of p115 with small interfering RNA caused fragmentation of the Golgi apparatus, resulting in dispersed distribution of stacked short cisternae and a vesicular structure (mini-stacked Golgi). The mini-stacked Golgi with cis- and trans-organization is functional in protein transport and glycosylation, although secretion is considerably retarded in p115 knockdown cells. The fragmented Golgi was further disrupted by treatment with breferdin A and reassembled into the mini-stacked Golgi by removal of the drug, as observed in control cells. In addition, p115 knockdown cells maintained retrograde transport from the Golgi to the endoplasmic reticulum, although the rate was not as efficient as in control cells. While no alternation of microtubule networks was found in p115 knockdown cells, the fragmented Golgi resembled those in cells treated with anti-microtubule drugs. The results suggest that p115 is involved in vesicular transport between endoplasmic reticulum and the Golgi, along with microtubule networks.     

Convergence of cell cycle regulation and growth factor signals on GRASP65

Together with other Golgi matrix components, GRASP65 contributes to the stacking of Golgi cisternae in interphase cells. During mitosis, GRASP65 is heavily phosphorylated, and in turn, cisternal stacking is inhibited leading to the breakdown of the Golgi apparatus. Here we show that GRASP65 is phosphorylated on serine 277 in interphase cells, and this is strongly enhanced in response to the addition of serum or epidermal growth factor. This is directly mediated by ERK suggesting that GRASP65 has some role in growth factor signal transduction. Phosphorylation of Ser-277 is also dramatically increased during mitosis, however this is mediated by Cdk1 and not by ERK. The microinjection of recombinant GRASP65 without N-terminal myristoylation or a peptide fragment containing Ser-277 into the cytosol of normal rat kidney cells inhibits passage through mitosis. This effect is abolished when Ser-277 is replaced with alanine suggesting the phosphorylation of Ser-277 plays an important role in cell cycle regulation. The convergence of cell cycle regulation and growth factor signals on GRASP65 Ser-277 suggests that GRASP65 may function as a signal integrator controlling the cell growth.