Abstracts of papers (2007)
Last Update: 10/25/2007
Abstracts of papers (2007)
[2007-1] Jin, L. et al., J. Pharmacol. Exp. Ther. 320, 47-55 (2007)
Anthraquinone spermine [N(1)-(anthraquinone-2-carbonyl)spermine; AQ343], anthraquinone homospermine [N(1)-(anthraquinone-2-carbonyl; AQ444], anthracene spermine [N(1)-(9-anthracenylmethyl)spermine; Ant343], and anthracene homospermine
[N(1)-(9-anthracenylmethyl)homospermine; Ant444] were found to be potent antagonists of recombinant N-methyl-D-aspartate (NMDA) receptors (NRs). The effects of both anthraquinone
(AQ)- and anthracene (Ant)-tetraamines were reversible and voltage-dependent.
Results of experiments using mutant NR1 and NR2B subunits of NMDA receptor
identified residues that influence block by AQ- and Ant-tetraamines. The
results indicate that the polyamine tail is crucial for block by AQ- and
Ant-tetraamines. Residues in the outer vestibule of the NR1 subunit were
more strongly involved in block by AQ-and Ant-tetraamines than residues
in the corresponding region of NR2B. Several amino acid residues in the
inner vestibule, below the level of the selectivity filter of NR1 and NR2B,
affected block by AQ444, Ant343, and Ant444, but they did not affect block
by AQ343. AQ-tetraamines could permeate the channel at very negative membrane
potentials when the narrowest constriction of the channel was expanded
by replacing the Asn residue at Asn616 of NR1 and NR2B with Gly, whereas
Ant-tetraamines did not easily pass through the channel, apparently because
of differences in the relative position of the head groups on AQ- and Ant-polyamines.
[2007-2] Masuko, T. et al., Neurochem Int. 50, 443-449 (2007)
The effects of cyclophanes (CPCn, CPPy and TGDMAP) and acyclic cyclophane
(ATGDMAP) on various glutamate receptors were studied with these receptors
expressed in Xenopus oocytes using voltage-clamp recording. CPCn, CPPy, TGDMAP and ATGDMAP
were found to inhibit macroscopic currents at heteromeric NMDA receptors
(NR1/NR2), but not Ca(2+)-permeable AMPA receptors (GluR1), Ca(2+)-nonpermeable
AMPA receptors (GluR1/GluR2) and metabotropic glutamate receptors (mGluR1alpha).
The inhibition of NR1/NR2A receptors by these compounds was more potent
than those of the other NMDA receptor subtypes. At a resting potential
(-70mV), the IC(50) values of CPCn, CPPy, TGDMAP and ATGDMAP for NR1/NR2A
receptors were 0.5+/-0.1, 1.0+/-0.2, 8.0+/-0.8 and 4.9+/-0.5[micro]M, respectively.
The inhibition by these compounds was voltage-dependent, that is, the degree
of inhibition was in the order of negative holding potentials, -100mV>-70mV>-20mV.
Results of experiments using mutant NR1 and NR2 subunits identified residues
that influence block by CPCn. The inhibition by CPCn was not altered significantly
in the mutants at the critical asparagines in the M2 loop, NR1 N616, NR2B
N615 and NR2B N616, these residues are known to form the narrowest region
of the channel and the binding site of Mg(2+). However, mutations at NR1
N650, located in the vestibule of channel pore, and NR1 D669, located in
the extracellular region, reduced the inhibition by CPCn, suggesting that
these amino acid residues interact with CPCn. These results suggest that
CPCn interacts directly with the mouth or vestibule of the ion channel,
like a lid.
[2007-3] Terui, Y. et al., J. Bacteriol. 189, 2359-2368 (2007)
Proteins whose synthesis is enhanced by polyamines at the level of translation
were identified in a polyamine-requiring mutant cultured in the presence
of 0.1% glucose and 0.02% glutamate instead of 0.4% glucose as an energy
source. Under these conditions, enhancement of cell growth by polyamines
was almost the same as that in the presence of 0.4% glucose. It was found
that synthesis of RpoN, Cra, and H-NS was enhanced by polyamines at the
level of translation at the early logarithmic phase of growth (A540 of 0.15). The effects of polyamines on synthesis of RpoN, H-NS, and Cra were due to the existence of unusual Shine-Dalgarno sequences (RpoN and H-NS) and an inefficient GUG initiation codon (Cra) in their mRNAs. Thus, rpoN, cra, and hns genes were identified as new members of the polyamine modulon. Because
most of the polyamine modulon genes thus far identified encode transcription
factors (RpoS [sigma(38)], Cya, FecI [sigma(18)], Fis, RpoN [sigma(54)],
Cra, and H-NS), DNA microarray analysis of mRNA expressed in cells was
performed. At the early logarithmic phase of growth, a total of 97 species
of mRNAs that were up-regulated by polyamines more than twofold were under
the control of seven polyamine modulon genes mentioned above.
[2007-4] Uemura, T. et al., J. Biol. Chem. 282, 7733-7741 (2007)
It has been reported that GAP1 and AGP2 catalyze the uptake of polyamines
together with amino acids in Saccharomyces cerevisiae. We have looked for polyamine-preferential uptake proteins in S. cerevisiae. DUR3 catalyzed the uptake of polyamines together with urea, and SAM3 was found to catalyze the uptake of polyamines together with S-adenosylmethionine, glutamic acid, and lysine. Polyamine uptake was greatly
decreased in both DUR3- and SAM3-deficient cells. The Km values for putrescine and spermidine of DUR3 were 479 and 21.2 [micro]M,
respectively, and those of SAM3 were 433 and 20.7 [micro]M, respectively.
Polyamine stimulation of cell growth of a polyamine requiring mutant, which
is deficient in ornithine decarboxylase, was not influenced by the disruption
of GAP1 and AGP2, but it was diminished by the disruption of DUR3 and SAM3. Furthermore, the polyamine stimulation of cell growth of a polyamine-requiring mutant was completely inhibited by the disruption of both DUR3 and SAM3. The results indicate that DUR3 and SAM3 are major polyamine uptake proteins
in yeast. We previously reported that polyamine transport protein kinase
2 regulates polyamine transport. It was found that DUR3 (but not SAM3)
was activated by phosphorylation of Thr(250), Ser(251), and Thr(684) by
polyamine transport protein kinase 2.
[2007-5] Kashiwagi, K. et al., Amino Acids 282, 299-304 (2007)
Polyamines, in particular spermine, as well as some natural and synthetic
polyamine derivatives have been found to be blockers of N-methyl-D-aspartate receptors. We developed novel, polyamine-based channel
blockers to analyze the structure of NMDA receptors. Anthraquinone polyamines
block NMDA receptors with some selectivity compared to other glutamate
receptors. Results using mutant NR1 and NR2 subunits identified amino acid
residues that influence blockade by anthraquinone polyamines. The head
group (anthraquinone) may be positioned at the selectivity filter/narrowest
constriction of the channel and the polyamine tail penetrates this constriction
into the inner vestibule below the level of the selectivity filter. The
results are consistent with other work showing that NR1 (Asn616) and NR2B
(Asn616), but not NR2B (Asn615), make the narrowest constriction of NMDA
channel, and that the M3 segments from the two subunits, which form the
outer vestibule, are likely staggered relative to each other in the vertical
axis of the channel.
[2007-6] Kaneko, S. et al., Am. J. Physiol. Cell Physiol. 293, C729-C737 (2007)
We previously showed that ornithine was mainly transported via cationic amino acid transporter (CAT)-1 in human retinal pigment epithelial (RPE) cell line, human telomerase RT (hTERT)-RPE, and that CAT-1 was involved in ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient cell produced by a OAT specific inhibitor, 5-fluoromethylornithine (5-FMO). We showed here that CAT-1 mRNA expression was increased by ornithne in OAT-deficient RPE cells, which was reversed by an inhibitor of ornithine decarboxylase (ODC), alpha-difluoromethylornithine (DFMO). Polyamines, especially spermine, one of the metabolites of ODC, also enhanced the expression of CAT-1 mRNA. ODC mRNA expression was also increased by ornithine and polyamines, and gene silencing of ODC by siRNA decreased ornithine transport activity and its cytotoxicity. In addition, the mRNA of nuclear protein c-myc was also increased in 5-FMO- and ornithine-treated hTERT-RPE cells, and gene silencing of c-myc prevented the induction of CAT-1 and ODC. Increases in expression of CAT-1, ODC, and c-myc, and the inhibition of these stimulated expression by DFMO were also observed in primary porcine RPE cells. These results suggest that spermine plays an important role in stimulation of mRNA expression of CAT-1, which is a crucial role in ornithine cytotoxicity in OAT-deficient hTERT-RPE cells.
[2007-7] Takayama, H. et al., Bioorg. Med. Chem. Lett. 17, 4729-4732 (2007)
We have developed a new class of N-methyl-D-aspartate (NMDA) channel blockers having a conjugate structure
that consists of a nitrogenous heterocyclic head and a tetraamine tail.
Among them, dihydrodibenzazepine-homospermine conjugate (8) exhibited potent
antagonistic activity at NR1/NR2A or NR1/NR2B NMDA subtype receptors compared
with the lead compound, AQ343 (1), or memantine, as well as weak cytotoxicity.
Its superior biological profiles compared with known compounds point to
its potential use as therapeutic agents for neurological disorders.
[2007-8] Masuko, T. et al., Neuropharmacology 53, 515-523 (2007)
The cleft-type cyclophanes (ACCn, DNCn and TsDCn) were found to strongly
inhibit macroscopic currents at heteromeric NMDA receptors (NR1/NR2) but
not AMPA receptors expressed in Xenopus oocytes at voltage-clamp recording. The inhibition by cleft-type cyclophanes
was voltage-dependent, because the inhibition was larger at -100 mV than
at -20 mV. Mutations at NR1 N650, located in the vestibule of the channel
pore, reduced the inhibition by DNCn and TsDCn, suggesting that the residue
(N650) interacts with these cleft-type cyclophanes. Cell toxicity of TsDCn
on SH-SY5Y cells was slightly weaker than that of memantine. The neuroprotective
effects of cleft-type cyclophanes against cell damage caused by NMDA were
investigated in cultured rat hippocampal neurons. Addition of 10 [micro]M
DNCn or TsDCn into the medium ablated the neurotoxicity induced by NMDA,
and a similar effect was also observed with memantine. The neuroprotective
effects of cleft-type cyclophanes were then assayed on NMDA-induced seizures
in mice. Intracerebroventricular injection of TsDCn (5 mg/mouse) decreased
the seizure induced by intraperitoneal injection of NMDA (115 mg/kg) in
mice. The results demonstrate that these cleft-type cyclophanes interact
directly with the extracellular mouth of the NMDA channel pore and exhibit
neuroprotective effects on NMDA-induced excitatory toxicity in primary
cultured neurons and mice.
[2007-9] Nishimura, K. et al., Biochem. Biophys. Res. Commun. 364, 124-130 (2007)
The mechanism of synthesis of ornithine decarboxylase (ODC) at the level
of translation was studied using cell culture and cell-free systems. Synthesis
of firefly luciferase (Fluc) from the second open reading frame (ORF) in
a bicistronic construct transfected into FM3A and HeLa cells was enhanced
by the presence of the 5'-untranslated region (5'-UTR) of ODC mRNA between
the two ORFs. However, cotransfection of the gene encoding 2A protease
inhibited the synthesis of Fluc. Synthesis of Fluc from the second cistron
in the bicistronic mRNA in a cell-free system was not affected significantly
by the 5'-UTR of ODC mRNA. Synthesis of ODC from ODC mRNA in a cell-free
system was inhibited by 2A protease and cap analogue (m(7)GpppG). Rapamycin
inhibited ODC synthesis by 40-50% at both the G(1)/S boundary and the G(2)/M
phase. These results indicate that an IRES in the 5'-UTR of ODC mRNA does
not function effectively.
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