Biomedical subjects

Motohiro Nishida

Publications and source records attributed to Motohiro Nishida.

24 records · Page 2Linked to original sources

PubMed2002

Transient receptor potential 1 regulates capacitative Ca(2+) entry and Ca(2+) release from endoplasmic reticulum in B lymphocytes.

Capacitative Ca(2+) entry (CCE) activated by release/depletion of Ca(2+) from internal stores represents a major Ca(2+) influx mechanism in lymphocytes and other nonexcitable cells. Despite the importance of CCE in antigen-mediated lymphocyte activation, molecular components constituting this mechanism remain elusive. Here we demonstrate that genetic disruption of transient receptor potential (TRP)1 significantly attenuates both Ca(2+) release-activated Ca(2+) currents and inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from endoplasmic reticulum (ER) in DT40 B cells. As a consequence, B cell antigen receptor-mediated Ca(2+) oscillations and NF-AT activation are reduced in TRP1-deficient cells. Thus, our results suggest that CCE channels, whose formation involves TRP1 as an important component, modulate IP(3) receptor function, thereby enhancing functional coupling between the ER and plasma membrane in transduction of intracellular Ca(2+) signaling in B lymphocytes.

Animals↗

PubMed2002

G beta gamma counteracts G alpha(q) signaling upon alpha(1)-adrenergic receptor stimulation.

In rat neonatal myocytes, a constitutively active G alpha(q) causes cellular injury and apoptosis. However, stimulation of the alpha(1)-adrenergic receptor, one of the G(q) protein-coupled receptors, with phenylephrine for 48 h causes little cellular injury and apoptosis. Expression of the G beta gamma-sequestering peptide beta ARK-ct increases the phenylephrine-induced cardiac injury, indicating that G beta gamma released from G(q) counteracts the G alpha(q)-mediated cellular injury. Stimulation with phenylephrine activates extracellular signal-regulated kinase (ERK) and Akt, and activation is significantly blunted by beta ARK-ct. Inhibition of Akt by inhibitors of phosphatidylinositol 3-kinase increases the cellular injury induced by phenylephrine stimulation. In contrast to the inhibition of Akt, inhibition of ERK does not affect the phenylephrine-induced cardiac injury. These results suggest that G beta gamma released from G(q) upon alpha(1)-adrenergic receptor stimulation activates ERK and Akt. However, activation of Akt but not ERK plays an important role in the protection against the G alpha(q)-induced cellular injury and apoptosis.

Animals↗

PubMed2002

Activation mechanism of Gi and Go by reactive oxygen species.

Reactive oxygen species are proposed to work as intracellular mediators. One of their target proteins is the alpha subunit of heterotrimeric GTP-binding proteins (Galpha(i) and Galpha(o)), leading to activation. H(2)O(2) is one of the reactive oxygen species and activates purified Galpha(i2). However, the activation requires the presence of Fe(2+), suggesting that H(2)O(2) is converted to more reactive species such as c*OH. The analysis with mass spectrometry shows that seven cysteine residues (Cys(66), Cys(112), Cys(140), Cys(255), Cys(287), Cys(326), and Cys(352)) of Galpha(i2) are modified by the treatment with *OH. Among these cysteine residues, Cys(66), Cys(112), Cys(140), Cys(255), and Cys(352) are not involved in *OH-induced activation of Galpha(i2). Although the modification of Cys(287) but not Cys(326) is required for subunit dissociation, the modification of both Cys(287) and Cys(326) is necessary for the activation of Galpha(i2) as determined by pertussis toxin-catalyzed ADP-ribosylation, conformation-dependent change of trypsin digestion pattern or guanosine 5'-3-O-(thio)triphosphate binding. Wild type Galpha(i2) but not Cys(287)- or Cys(326)-substituted mutants are activated by UV light, singlet oxygen, superoxide anion, and nitric oxide, indicating that these oxidative stresses activate Galpha(i2) by the mechanism similar to *OH-induced activation. Because Cys(287) exists only in G(i) family, this study explains the selective activation of G(i)/G(o) by oxidative stresses.

Adenosine Diphosphate Ribose↗

PubMed2002

Ca(2+) channel alpha(1B) subunit (Ca(V) 2.2) knockout mouse reveals a predominant role of N-type channels in the sympathetic regulation of the circulatory system.

N-type voltage-dependent Ca(2+) channels (VDCCs), predominantly localized in the nervous system, have been proposed to play vital roles in a variety of neuronal functions such as neurotransmitter release at sympathetic nerve terminals. To directly approach the elucidation of the physiological significance of N-type VDCCs in the autonomic nervous system, alpha(1B) subunit (Ca(V) 2.2)-deficient mice were generated, in which peripheral neurons showed a complete and selective elimination of N-type channel currents sensitive to omega-conotoxin GVIA (the peptide toxin from the fish-hunting cone snail Conus geographus), without a significant effect on the activity of other VDCC types. In isolated left atria prepared from N-type-deficient mice, the positive inotropic response mediated by the sympathetic nervous system was dramatically decreased, whereas the negative inotropic response mediated by parasympathetic neurons was nearly intact compared with those of normal mice. The baroreflex response to bilateral carotid occlusion was markedly reduced in the mutant mice. Interestingly, the mutant mice showed sustained elevation of heart rate and blood pressure. These results provide direct in vivo evidence for an essential role of N-type VDCCs in maintaining the normal function of the sympathetic nervous system in circulatory regulation, demonstrating a potential of N-type VDCC-deficient mice as a useful model for studying disorders attributable to sympathetic nerve dysfunction.

Animals↗

PubMed2002

LTRPC2 Ca2+-permeable channel activated by changes in redox status confers susceptibility to cell death.

Redox status changes exert critical impacts on necrotic/apoptotic and normal cellular processes. We report here a widely expressed Ca2+-permeable cation channel, LTRPC2, activated by micromolar levels of H2O2 and agents that produce reactive oxygen/nitrogen species. This sensitivity of LTRPC2 to redox state modifiers was attributable to an agonistic binding of nicotinamide adenine dinucleotide (beta-NAD+) to the MutT motif. Arachidonic acid and Ca2+ were important positive regulators for LTRPC2. Heterologous LTRPC2 expression conferred susceptibility to death on HEK cells. Antisense oligonucleotide experiments revealed physiological involvement of "native" LTRPC2 in H2O2- and TNFalpha-induced Ca2+ influx and cell death. Thus, LTRPC2 represents an important intrinsic mechanism that mediates Ca2+ and Na+ overload in response to disturbance of redox state in cell death.

Animals↗

PubMedDate not supplied

TRP channels: molecular diversity and physiological function.

Calcium ions (Ca(2+)) are particularly important in cellular homeostasis and activity. To elicit physiologically relevant timing and spatial patterns of Ca(2+) signaling, ion channels in the surface of each cell precisely control Ca(2+) influx across the plasma membrane. A group of surface membrane ion channels called receptor-activated cation/Ca(2+) channels (RACCs) are activated by diverse cellular stimuli from the surrounding extracellular environment via receptors and other pathways such as heat, osmotic pressure, and mechanical and oxidative stress. An important clue to understanding the molecular mechanisms underlying the functional diversity of RACCs was first attained by molecular identification of the transient receptor potential (trp) protein (TRP), which mediates light-induced depolarization in Drosophila photoreceptor cells, and its homologues from various biological species. Recent studies have revealed that respective TRP channels are indeed activated by characteristic cellular stimuli. Furthermore, the involvement of TRP channels has been demonstrated in the signaling pathways essential for tissue-specific functions as well as ubiquitous biological responses, such as cell proliferation, differentiation, and death. These findings encourage the usage of TRP channels and their signalplexes as powerful tools for developing novel pharmaceutical targets.

Amino Acid Sequence↗