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Tomoko Tominaga

Publications and source records attributed to Tomoko Tominaga.

11 recordsLinked to original sources
PubMed2006

TRPM2 activation by cyclic ADP-ribose at body temperature is involved in insulin secretion.

There are eight thermosensitive TRP (transient receptor potential) channels in mammals, and there might be other TRP channels sensitive to temperature stimuli. Here, we demonstrate that TRPM2 can be activated by exposure to warm temperatures (>35 degrees C) apparently via direct heat-evoked channel gating. beta-NAD(+)- or ADP-ribose-evoked TRPM2 activity is robustly potentiated at elevated temperatures. We also show that, even though cyclic ADP-ribose (cADPR) does not activate TRPM2 at 25 degrees C, co-application of heat and intracellular cADPR dramatically potentiates TRPM2 activity. Heat and cADPR evoke similar responses in rat insulinoma RIN-5F cells, which express TRPM2 endogenously. In pancreatic islets, TRPM2 is coexpressed with insulin, and mild heating of these cells evokes increases in both cytosolic Ca(2+) and insulin release, which is K(ATP) channel-independent and protein kinase A-mediated. Heat-evoked responses in both RIN-5F cells and pancreatic islets are significantly diminished by treatment with TRPM2-specific siRNA. These results identify TRPM2 as a potential molecular target for cADPR, and suggest that TRPM2 regulates Ca(2+) entry into pancreatic beta-cells at body temperature depending on the production of cADPR-related molecules, thereby regulating insulin secretion.

Animals↗
PubMed2006

Increased sensitivity of desensitized TRPV1 by PMA occurs through PKCepsilon-mediated phosphorylation at S800.

Important mechanisms that regulate inhibitory and facilitatory effects on TRPV1-mediated nociception are desensitization and phosphorylation, respectively. Using Ca2+-imaging, we have previously shown that desensitization of TRPV1 upon successive capsaicin applications was reversed by protein kinase C activation in dorsal root ganglion neurons and CHO cells. Here, using both Ca2+-imaging and patch-clamp methods, we show that PMA-induced activation of PKCepsilon is essential for increased sensitivity of desensitized TRPV1. TRPV1 has two putative substrates S502 and S800 for PKCepsilon-mediated phosphorylation. Patch-clamp analysis showed that contribution of single mutant S502A or S800A towards increased sensitivity of desensitized TRPV1 is indistinguishable from that observed in a double mutant S502A/S800A. Since S502 is a non-specific substrate for TRPV1 phosphorylation by kinases like PKC, PKA or CAMKII, evidence for a role of PKC specific substrate S800 was investigated. Evidence for in vivo phosphorylation of TRPV1 at S800 was demonstrated for the first time. We also show that the expression level of PKCepsilon paralleled the amount of phosphorylated TRPV1 protein using an antibody specific for phosphorylated TRPV1 at S800. Furthermore, the anti-phosphoTRPV1 antibody detected phosphorylation of TRPV1 in mouse and rat DRG neurons and may be useful for research regarding nociception in native tissues. This study, therefore, identifies PKCepsilon and S800 as important therapeutic targets that may help regulate inhibitory effects on TRPV1 and hence its desensitization.

Amino Acid Sequence↗
PubMed2005

Structure and function of TRPV1.

Capsaicin, the main ingredient in hot chili peppers, elicits a sensation of burning pain by selectively activating sensory neurons that convey information about noxious stimuli to the central nervous system. The capsaicin receptor, transient receptor potential vanilloid 1 (TRPV1), is predicted to have six transmembrane (TM) domains and a short, pore-forming hydrophobic stretch between the fifth and sixth TM domains, and is activated not only by capsaicin but also by heat (>43 degrees C), acid and various lipids. Within the TPRV1 protein, many regions and amino acids involved in specific functions (multimerization, capsaicin action, proton action, heat activation, desensitization, permeability, phosphorylation and modulation by lipids) have been identified since the cloning in 1997. Given the fact that TRPV1 is a key molecule in peripheral nociception, these regions and amino acids could prove useful for the development of novel anti-nociceptive or anti-inflammatory agents.

Acids↗
PubMed2005

Sensitization of TRPV1 by EP1 and IP reveals peripheral nociceptive mechanism of prostaglandins.

Prostaglandin E2 (PGE2) and prostaglandin I2 (PGI2) are major inflammatory mediators that play important roles in pain sensation and hyperalgesia. The role of their receptors (EP and IP, respectively) in inflammation has been well documented, although the EP receptor subtypes involved in this process and the underlying cellular mechanisms remain to be elucidated. The capsaicin receptor TRPV1 is a nonselective cation channel expressed in sensory neurons and activated by various noxious stimuli. TRPV1 has been reported to be critical for inflammatory pain mediated through PKA- and PKC-dependent pathways. PGE2 or PGI2increased or sensitized TRPV1 responses through EP1 or IP receptors, respectively predominantly in a PKC-dependent manner in both HEK293 cells expressing TRPV1 and mouse DRG neurons. In the presence of PGE2 or PGI2, the temperature threshold for TRPV1 activation was reduced below 35 degrees C, so that temperatures near body temperature are sufficient to activate TRPV1. A PKA-dependent pathway was also involved in the potentiation of TRPV1 through EP4 and IP receptors upon exposure to PGE2 and PGI2, respectively. Both PGE2-induced thermal hyperalgesia and inflammatory nociceptive responses were diminished in TRPV1-deficient mice and EP1-deficient mice. IP receptor involvement was also demonstrated using TRPV1-deficient mice and IP-deficient mice. Thus, the potentiation or sensitization of TRPV1 activity through EP1 or IP activation might be one important mechanism underlying the peripheral nociceptive actions of PGE2 or PGI2.

Animals↗
PubMed2004

DIP (mDia interacting protein) is a key molecule regulating Rho and Rac in a Src-dependent manner.

Cell movement is driven by the coordinated regulation of cytoskeletal reorganization through Rho GTPases downstream of integrin and growth-factor receptor signaling. We have reported that mDia, a target protein of Rho, interacts with Src and DIP. Here we show that DIP binds to p190RhoGAP and Vav2, and that DIP is phosphorylated by Src and mediates the phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation. When endogenous DIP was inhibited by expressing dominant-negative mutants of DIP or siRNA, phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation was diminished, and EGF-induced actin organization, distribution of p190RhoGAP and Vav2, and cell movement were affected. Therefore, DIP seems to transfer the complex of the three proteins from cytosol to beneath the membrane, and the three proteins, in turn, can be phosphorylated by Src. DIP inactivated Rho and activated Rac following EGF stimulation in the membrane fraction. Thus, DIP acts as a regulatory molecule causing Src kinase-dependent feedback modulation of Rho GTPases downstream of Rho-mDia upon EGF stimulation, and plays an important role in cell motility.

Animals↗
PubMed2004

Regulation mechanisms of vanilloid receptors.

The capsaicin receptor TRPV1 (also known as the vanilloid receptor VR1) is a non-selective cation channel and is activated not only by capsaicin but also by noxious heat or protons. Tissue damage associated with infection, inflammation or ischaemia, produces an array of chemical mediators that activate or sensitize nociceptor terminals. An important component of this pro-algeic response is ATP. In cells expressing TRPV1, ATP increased the currents evoked by capsaicin or protons through activation of P2Y metabotropic receptors in a PKC-dependent manner. In the presence of ATP, the temperature threshold for TRPV1 activation was reduced from 42 degrees C to 35 degrees C, such that normal body temperature could activate TRPV1. Functional interaction between P2Y receptors and TRPV1 was confirmed in a behavioural analysis using TRPV1-deficient mice. Direct phosphorylation of TRPV1 by PKC was confirmed biochemically and the two serine residues involved were identified. Extracellular Ca2+ -dependent desensitization of TRPV1 is thought to be one mechanism underlying the paradoxical effectiveness of capsaicin as an analgesic therapy. The Ca2+ -binding protein calmodulin binds to the C-terminus of TRPV1. We found that disruption of the calmodulin binding segment prevented TRPV1 desensitization even in the presence of extracellular Ca2+.

Adenosine Triphosphate↗
PubMed2003

Structural determinant of TRPV1 desensitization interacts with calmodulin.

The capsaicin receptor, TRPV1 (VR1), is a sensory neuron-specific ion channel that serves as a polymodal detector of pain-producing chemical and physical stimuli. Extracellular Ca2+-dependent desensitization of TRPV1 observed in patch-clamp experiments when using both heterologous expression systems and native sensory ganglia is thought to be one mechanism underlying the paradoxical effectiveness of capsaicin as an analgesic therapy. Here, we show that the Ca2+-binding protein calmodulin binds to a 35-aa segment in the C terminus of TRPV1, and that disruption of the calmodulin-binding segment prevents TRPV1 desensitization. Compounds that interfere with the 35-aa segment could therefore prove useful in the treatment of pain.

Animals↗
PubMed2003

[Molecular mechanisms of nociception].

Capsaicin, the main ingredient in 'hot' chili peppers, elicits burning pain by activating nociceptors. The cloned capsaicin receptor (TRPV1) is a nonselective cation channel with six transmembrane domains, and is activated not only by capsaicin but also by noxious heat (> 43 degrees C) or protons (acidification), both of which cause pain in vivo. Furthermore, analyses of mice lacking VR1 showed that VR1 is essential for selective modalities of pain sensation and for tissue injury-induced thermal hyperalgesia. Tissue damage produces an array of chemical mediators that activate or sensitize nociceptor terminals to elicit pain. Important components of this pro-algesic response are ATP and bradykinin. In cells expressing TRPV1, ATP or bradykinin increased the currents evoked by capsaicin or protons through activation of metabotropic P2Y or B2 bradykinin receptors. In the presence of ATP or bradykinin, the temperature threshold for VR1 activation was reduced from 42 degrees C to 30-35 degrees C, such that normally non-painful normal body temperatures were capable of activating TRPV1, thereby leading to the sensation of pain. Direct phosphorylation of TRPV1 by PKC epsilon was confirmed and the involved two serine residues were determined. This represents a novel mechanism through which ATP or bradykinin in response to tissue trauma might trigger the sensation of pain.

Acid Sensing Ion Channels↗
PubMed2002

The Rho GTPase effector protein, mDia, inhibits the DNA binding ability of the transcription factor Pax6 and changes the pattern of neurite extension in cerebellar granule cells through its binding to Pax6.

mDia, one of the target proteins of the GTPase Rho, is known to be involved in cytoskeletal reorganization and cytokinesis. Here, we report that mDia enters the nucleus and binds to the transcription factor, Pax6. In cultured non-neuronal cells, overexpression of mDia with Pax6 causes redistribution of some Pax6 molecules from the nucleus to the cytosol and decreases Pax6 transcriptional activity. Because Pax6 functions in the early central nervous system morphogenesis, we also examined the effects of mDia on endogenous Pax6 localization and neurite extension in cerebellar granule cells. Here too, Pax6 was partially mislocalized to the cytosol, and its expression level was decreased by mDia overexpression. In addition, mDia overexpression in these cells led to increased neurite branching and length. These results strongly suggest that mDia influences Pax6-induced transcriptional activity and axonal pathfinding in a way opposite from ROCK (Rho kinase) and that it may act via Pax6 to modulate early neuronal development.

3T3 Cells↗
PubMed2002

Direct phosphorylation of capsaicin receptor VR1 by protein kinase Cepsilon and identification of two target serine residues.

The capsaicin receptor, VR1, is a sensory neuron-specific ion channel that serves as a polymodal detector of pain-producing chemical and physical stimuli. It has been reported that ATP, one of the inflammatory mediators, potentiates the VR1 currents evoked by capsaicin or protons and reduces the temperature threshold for activation of VR1 through metabotropic P2Y(1) receptors in a protein Kinase C (PKC)-dependent pathway, suggesting the phosphorylation of VR1 by PKC. In this study, direct phosphorylation of VR1 upon application of phorbol 12-myristate 13-acetate (PMA) was proven biochemically in cells expressing VR1. An in vitro kinase assay using glutathione S-transferase fusion proteins with cytoplasmic segments of VR1 showed that both the first intracellular loop and carboxyl terminus of VR1 were phosphorylated by PKCepsilon. Patch clamp analysis of the point mutants where Ser or Thr residues were replaced with Ala in the total 16 putative phosphorylation sites showed that two Ser residues, Ser(502) and Ser(800) were involved in the potentiation of the capsaicin-evoked currents by either PMA or ATP. In the cells expressing S502A/S800A double mutant, the temperature threshold for activation was not reduced upon PMA treatment. The two sites would be promising targets for the development of substance modulating VR1 function, thereby reducing pain.

Adenosine Triphosphate↗