Kir2.2v: a possible negative regulator of the inwardly rectifying K+ channel Kir2.2

We have cloned the human genes encoding the inwardly rectifying K+ (Kir) channel subunits, Kir2.2 (hKir2.2) and its variant, termed hKir2.2v. When expressed in Xenopus oocytes, hKir2.2 produced strong inwardly rectifying K+ currents, whereas the expression of hKir2.2v did not elicit significant currents. Coexpression of hKir2.2v with hKir2.2 showed an hKir2.2v inhibition of hKir2.2 K+ currents, indicating that it acts as a negative regulator of hKir2.2 channel activity. Mutational analysis of hKir2.2v and studies of chimeras between hKir2.2 and hKir2.2v suggest that the intracellular C-terminal region of hKir2.2v participates in the negative regulation of the hKir2.2v channel activity.

A family of sulfonylurea receptors determines the pharmacological properties of ATP-sensitive K+ channels

We have cloned an isoform of the sulfonylurea receptor (SUR), designated SUR2. Coexpression of SUR2 and the inward rectifier K+ channel subunit Kir6.2 in COS1 cells reconstitutes the properties of K(ATP) channels described in cardiac and skeletal muscle. The SUR2/Kir6.2 channel is less sensitive than the SUR/Kir6.2 channel (the pancreatic beta cell KATP channel) to both ATP and the sulfonylurea glibenclamide and is activated by the cardiac K(ATP) channel openers, cromakalim and pinacidil, but not by diazoxide. In addition, SUR2 binds glibenclamide with lower affinity. The present study shows that the ATP sensitivity and pharmacological properties of K(ATP) channels are determined by a family of structurally related but functionally distinct sulfonylurea receptors.

Cloning and pharmacological characterization of a fourth P2X receptor subtype widely expressed in brain and peripheral tissues including various endocrine tissues

We have isolated cDNA encoding a fourth member (P2X-4) of the ATP receptor P2X receptor family from a rat pancreatic islet cDNA library. Rat P2X-4 is a protein of 388 amino acids which shares 50%, 49%, and 47% identity with P2X-1, P2X-2, and P2X-3, respectively, and has two putative transmembrane segments. Rat P2X-4 mRNA is widely expressed in brain and peripheral tissues, including various endocrine tissues, and it is also expressed in various hormone-secreting cell lines. We have heterologously expressed the cloned P2X-4 in Xenopus laevis oocytes and have characterized its pharmacological properties. ATP, its analogs and ADP activate cation-selective ion channels. The order of agonist potency is ATP ADP 2-methyl- thioATP(2MeSATP) >> alpha beta-methelene-ATP (alpha betameATP). ATP-evoked currents are only partially blocked by suramin, reactive blue-2, or H2DIDS. The present study suggests that P2X-4, with pharmacological properties distinct from those of P2X-1+, P2X-2, and P2X-3, mediates extracellular ATP-induced biological effects in non-neuronal cells, including endocrine cells, as well as in neuronal cells.

TNF-alpha participates in an IgE-mediated cutaneous reaction in mast cell deficient, WBB6F1-W/Wv mice

The participation of tumor necrosis factor-alpha (TNF-alpha) in a IgE-mediated cutaneous reaction in WBB6F1-W/Wv (W/Wv), mast cell deficient, mice and the effect of prednisolone on this cutaneous reaction were investigated. Mice were passively sensitized by an intravenous injection of monoclonal anti-dinitrophenol (DNP) IgE, and their ears challenged epicutaneously with dinitrofluorobenzene 24 h later. The cutaneous reaction estimated by ear thickness reached a peak 48-72 h after the antigen challenge. A monoclonal anti-tumor necrosis factor (TNF)-alpha antibody inhibited the IgE-mediated cutaneous reaction. An increase of TNF-alpha mRNA was demonstrated 4 h after the application of antigen by the reverse transcriptase-polymerase chain reaction. The injection of recombinant murine TNF-alpha induced a cutaneous reaction which peaked at 24 h in nonsensitized mice. Prednisolone at doses of 3 to 10 mg/kg clearly inhibited the IgE-mediated cutaneous reaction, however, it did not affect the expression of TNF-alpha-mRNA. Prednisolone at doses of 1 to 10 mg/kg clearly inhibited the TNF-alpha-induced cutaneous reaction. These results suggest that TNF-alpha plays a role in the IgE-mediated cutaneous reaction in W/Wv mice and that prednisolone inhibits the cutaneous reaction at least in part by inhibiting the action of TNF-alpha.

Primary structure of light and heavy chain variable regions of antibodies recognizing phosphorylated vimentins

We determined the primary structure of three types of monoclonal antibodies against phosphorylated vimentin, 4A4, YT33, and MO82, which recognize phosphorylated Ser55, Ser33, and Ser82 on vimentin, respectively. The amino acid sequences between these antibodies and the anti-phosphotyrosine antibodies previously reported, (Asn/Gln)-X-(Gln/Tyr)-Ser-Tyr in the complimentarity determining region (CDR) 3 of the light chain of 4A4 and YT33, Asn-Pro-Asn-(Asn/Ser)-Gly-X-(Ser/Thr)-(Ser/Thr)-Tyr-Asn-Gln-(Arg/Lys)-Ph e-Lys in the heavy chain CDR2 of MO82, and Lys-X-Ser-(Ser/Asn) in the heavy chain CDR3 of YT33 and MO82, were highly conserved. These motifs may play a role in recognizing phosphate groups of phosphoserine and phosphotyrosine.

Detection of protein kinase activity specifically activated at metaphase-anaphase transition

We have previously reported that Ser13 and Ser34 on glial fibrillary acidic protein (GFAP) in the cleavage furrow of glioma cells are phosphorylated during late mitotic phase (Matsuoka, Y., K. Nishizawa, T. Yano, M. Shibata, S. Ando, T. Takahashi, and M. Inagaki. 1992, EMBO (Eur. Mol. Biol. Organ.) J. 11:2895-2902). This observation implies a possibility that there is a protein kinase specifically activated at metaphase-anaphase transition. To further analyze the cell cycle-dependent GFAP phosphorylation, we prepared monoclonal antibodies KT13 and KT34 which recognize the phosphorylation of GFAP at Ser13 and Ser34, respectively. Immunocytochemical studies with KT13 and KT34 revealed that the GFAP phosphorylation in the cleavage furrow during late mitotic phase occurred not only in glioma cells but also in human SW-13 and mouse Ltk- cells in which GFAP was ectopically expressed, thus the phosphorylation can be monitored in a wide range of cell types. Furthermore, we detected kinase activity which phosphorylates GFAP at Ser13 and Ser34 in the lysates of late mitotic cells but not in those of interphase cells or early mitotic cells. These results suggest that there exists a protein kinase which is specifically activated at the transition of metaphase to anaphase not only in GFAP-expressing cells but also in cells without GFAP.

Identification of microsatellite markers near the human genes encoding the beta-cell ATP-sensitive K+ channel and linkage studies with NIDDM in Japanese

ATP-sensitive K+ (KATP) channels play a key role in stimulus-secretion coupling in pancreatic beta-cells. Recent studies have shown that the beta-cell KATP channel comprises two subunits: a novel member of the inwardly rectifying K+ channel family, designated BIR and expressed at highest levels in pancreatic islets, and the sulfonylurea receptor (SUR). Moreover, the genes encoding these two proteins are adjacent to one another on human chromosome 11. Genetic factors contribute to the development of NIDDM, and it seems likely that mutations in genes encoding proteins involved in insulin secretion or action may contribute to NIDDM susceptibility. The present study examined the contribution of the linked BIR and SUR genes to the development of NIDDM. These genes were localized to the same yeast artificial chromosome as two microsatellite DNA polymorphisms, D11S902 and D11S921. These microsatellite DNA polymorphisms were typed in 140 Japanese NIDDM-affected sib pairs. There was no evidence for linkage between these markers and NIDDM, suggesting that genetic variation in the BIR and SUR genes does not play a major role in susceptibility to NIDDM in Japanese.

Carboxyl-terminal processing protease for the D1 precursor protein: cloning and sequencing of the spinach cDNA

A previous study has demonstrated that the carboxyl-terminal (C-terminal) processing protease in spinach for the D1 precursor protein (pDl) of the photosystem II reaction center is a monomeric protein of about 45 kDa. Based on the amino acid sequence data of the purified protease, a cDNA clone encoding the enzyme has been identified and sequenced, from a spinach green leaf cDNA library. In order to determine the 5' end of the transcript, the rapid amplification of cDNA end (5'-RACE) technique was applied. By these analyses, the full-length transcript was established to consist of 1906 nucleotides and a poly(A) tail, containing an open reading frame (ORF) corresponding to a protein with 539 amino acid residues. By comparing the amino acid sequence of the purified protease with that deduced from nucleotide sequence of the cDNA clones, the enzyme was shown to be furnished with an extra amino-terminal extension characteristic of both a transit peptide and a signal sequence. This suggests that the protease is synthesized in the cytosol and translocated into the lumenal space of thylakoids. The mature part of the enzyme consists of 389 amino acid residues and exhibits a significant sequence homology with two groups of proteins as demonstrated by a computer homology search, i.e. (1) the deduced sequence of a protein proposed to be the C-terminal processing protease for pD1 in Synechocystis sp. PCC 6803, based on genetic experiments and (2) proteases for C-terminal cleavage identified in Escherichia coli and Bartonella bacilliformis.

Characterization of purification-associated reduction in IgE-dependent histamine release from rat peritoneal mast cells

Histamine release from purified rat peritoneal mast cells (PMC) was examined and compared to that from a non-purified preparation (PEC). Both PEC and PMC released similar amounts of histamine upon stimulation with compound 48/80, calcium ionophore A23187 and substance P. In contrast, IgE-dependent histamine release from PMC caused by antigen, anti-IgE and concanavalin A was very low compared to that of PEC. The reduced IgE-dependent histamine release from PMC, however, was recovered when PMC was reconstituted with non-mast cells (NMC) present in the peritoneal cavity. The effect was time-dependent and reached a plateau in 30 min. NMC from both sensitized and non-sensitized rats recovered the reduced histamine release from PMC dose-dependently. The potentiating effect of NMC was observed even in the presence of excess amount of phosphatidylserine. Supernatants of NMC and a mixture of PMC and NMC incubated for 1 hr at 37 degrees C, however, failed to potentiate the histamine release. These results demonstrate that IgE-dependent histamine release from rat peritoneal mast cells is upregulated by other cells present in the peritoneal cavity, and that the mechanism involved is distinct from that of phosphatidylserine.

Reconstitution of IKATP: an inward rectifier subunit plus the sulfonylurea receptor

A member of the inwardly rectifying potassium channel family was cloned here. The channel, called BIR (Kir6.2), was expressed in large amounts in rat pancreatic islets and glucose-responsive insulin-secreting cell lines. Coexpression with the sulfonylurea receptor SUR reconstituted an inwardly rectifying potassium conductance of 76 picosiemens that was sensitive to adenosine triphosphate (ATP) (IKATP) and was inhibited by sulfonylureas and activated by diazoxide. The data indicate that these pancreatic beta cell potassium channels are a complex composed of at least two subunits--BIR, a member of the inward rectifier potassium channel family, and SUR, a member of the ATP-binding cassette superfamily. Gene mapping data show that these two potassium channel subunit genes are clustered on human chromosome 11 at position 11p15.1.

Differential targeting of protein kinase C and CaM kinase II signalings to vimentin

Hydrolysis of inositol phospholipids by receptor stimulation activates two separate signaling pathways, one leading to the activation of protein kinase C (C kinase) via formation of diacylglycerol. The other is the inositol trisphosphate (IP3)/Ca2+ pathway and a major downstream kinase which is activated is Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). To examine signaling pathways of C kinase and CaM kinase II to the cytoskeletal protein vimentin, we prepared monoclonal antibodies YT33 and MO82 which recognize the phosphorylation state of vimentin by C kinase and by CaM kinase II, respectively. Ectopic expression of constitutively active C kinase or CaM kinase II in primary cultured astrocytes by microinjection of the corresponding expression vectors induced phosphorylation of vimentin at each specific phosphorylation site, followed by reorganization of vimentin filament networks. In contrast, simultaneous activation of C kinase and CaM kinase II by inositol phospholipid hydrolysis with receptor stimulation led to an exclusive phosphorylation of vimentin at the CaM kinase II site, not at the site of C kinase. These results indicate that the intracellular targeting of C kinase and CaM kinase II signalings to vimentin is regulated separately, under physiological conditions.

Selective potentiation of IGE-dependent histamine release from rat peritoneal mast cells by stem cell factor

Effect of stem cell factor on histamine release from rat peritoneal mast cells was studied. Although stem cell factor did not evoke histamine release by itself, it clearly potentiated histamine release from sensitized mast cells caused by antigen, anti-IgE and concanavalin A. However, stem cell factor did not affect histamine release caused by compound 48/80, calcium ionophore A23187 and substance P. Although maximum potentiation of antigen-induced histamine release by stem cell factor was accomplished after 1-10 minute-preincubation, potentiation was decline after a longer incubation period. Potentiation of histamine release by phosphatidylserine and non-mast cells in the rat peritoneal cavity was incubation time-dependent. Potentiation by stem cell factor was additive to that by phosphatidylserine or non-mast cells. These results indicate that stem cell factor selectively potentiates IgE-dependent histamine release from rat peritoneal mast cells, and suggest that the mechanism involved is distinct from that of phosphatidylserine or non-mast cells in the rat peritoneal cavity.

cDNA sequence, gene structure, and chromosomal localization of the human ATP-sensitive potassium channel, uKATP-1, gene (KCNJ8)

ATP-sensitive K+ (KATP) channels play a crucial role in coupling metabolic energy to the membrane potential of cells. Recently, we have isolated a KATP channel cDNA (uKATP-1) that is expressed ubiquitously in rat tissues including pancreatic islets, pituitary, skeletal muscle, and heart. Here, we report cloning of the human cDNA and gene encoding uKATP-1. Human uKATP-1 is a protein of 424 amino acids exhibiting 98% identity with rat uKATP-1. The human gene encoding uKATP-1, designated KCNJ8, is approximately 9.7 kb in length and is composed of three exons. KCNJ8 was mapped to chromosome 12p11.23 using fluorescence in situ hybridization.

The effect of a novel leukotriene C4/D4 antagonist, BAY-x-7195, on experimental allergic reactions

The effects of a novel leukotriene (LT) C4/D4 antagonist, BAY-x-7195 on experimental allergic reactions in airway and skin were compared to that of ONO-1078. BAY-x-7195 showed an antagonistic action to LTD4-induced bronchoconstriction in vitro and in vivo. In in vitro experiments, BAY-x-7195 inhibited LTD4-induced contraction of isolated guinea pig tracheal muscle (pA2 = 8.03). BAY-x-7195 at doses of 3-30 mg/kg clearly inhibited LTD4-induced increases in respiratory resistance (Rrs) in guinea pigs. In contrast, BAY-x-7195 inhibited significantly U-46619-induced increases in Rrs at a dose of 30 mg/kg in guinea pigs. BAY-x-7195 at doses of 3-30 mg/kg inhibited the aerosolized antigen-induced biphasic increase in Rrs in guinea pigs. Moreover BAY-x-7195 inhibited repeated aeroantigen-induced airway hyperreactivity in guinea pigs. In mice, aeroantigen-induced airway inflammation were clearly inhibited by BAY-x-7195. These results show the efficacy of BAY-x-7195 against the antigen-induced increase in airway resistance and antigen-induced airway hyperreactivity in guinea pigs and mice, probably due to anti-LTD4 antagonistic action and the inhibition of antigen-induced airway inflammation.

[Silicosis associated with autoimmune hemolytic anemia]

A 60-year-old man with pneumoconiosis complained of general fatigue, exertional dyspnea, and anorexia. The patient had severe anemia, and laboratory examination revealed autoimmune hemolytic anemia with positive direct and indirect Coombs tests. After corticosteroid therapy, the anemia resolved markedly, and the antinuclear antibody test became negative. However, the silicotic shadow on chest X-ray film showed no remarkable change. The autoimmune hemolytic anemia in this case was probably due to an immunological disturbance caused by silicosis.

Characterization of TrkB receptor-mediated signaling pathways in rat cerebellar granule neurons: involvement of protein kinase C in neuronal survival

TrkB belongs to the Trk family of tyrosine kinase receptors and mediates the response to brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5). Here, we report that both truncated and full-length forms of TrkB receptors are expressed in developing cerebellar granule neurons. BDNF and NT-4/5 increased the survival of cultured cerebellar granule neurons. BDNF and NT-4/5 also induced an autophosphorylation of TrkB receptors and subsequently resulted in a phosphorylation and binding of phospholipase C-gamma (PLC-gamma) and SH2-containing sequence to the autophosphorylated TrkB receptors. Both contain src homology 2 (SH2) regions. In keeping with a signaling function of PLC-gamma, BDNF increased the phosphatidylinositol (PI) turnover and elevated intracellular calcium levels. To investigate the involvement of protein kinase C (PKC) in the survival of granular neurons, we show here activation of PKC after BDNF or TPA treatment and blocking of the observed survival-promoting effects of BDNF and TPA with calphostin C, a specific PKC inhibitor. In addition, BDNF activated c-ras in a concentration-dependent manner. These results suggest that two different pathways, the c-ras and the PLC-gamma pathway, are activated by TrkB receptors in primary neurons and that PKC activation is involved in the survival promoting effect of BDNF.

Effect of some immunosuppressors on allergic bronchial inflammation and airway hyperresponsiveness in mice

The effects of two new immunosuppressors, FK-506 and mizoribine, on antigen-induced bronchial inflammation and reactivity to acetylcholine in mice were studied in comparison with those of cyclosporin A and cyclophosphamide. Three inhalations of an antigen by actively sensitized BALB/c mice resulted in an increase in airway reactivity to acetylcholine. Twenty-four hours after the final inhalation, the number of leukocytes (mononuclear cells and eosinophils) and the amount of interleukin 5 (IL-5) increased significantly. In BALB/c nu/nu mice (athymic mice), three inhalations of antigen caused no significant change in either airway inflammation or hyperresponsiveness. The administration of each of the four immunosuppressors clearly inhibited antigen-induced airway eosinophilia. Moreover, FK-506, mizoribine and cyclophosphamide clearly inhibited the antigen-induced IL-5 production and cyclosporin A showed the tendency to inhibit IL-5 production. Whereas FK-506, mizoribine and cyclosporin A clearly inhibited the antigen-induced airway hyperreactivity in BALB/c mice, cyclophosphamide did not show a significant effect on this airway hyperreactivity. These results indicate that FK-506, mizoribine and cyclosporin A, but not cyclophosphamide, inhibit antigen-induced airway hyperreactivity in mice. The mechanism which inhibits antigen-induced airway eosinophilia and IL-5 production is not involved in the inhibitory mechanism of airway hyperreactivity by FK-506 and mizoribine.

Peritoneal mast cell hyperplasia in rats after IgE antibody-antigen interaction

Peritoneal mast cell hyperplasia was investigated in rats after evoking IgE antibody-antigen reaction. Rats were immunized with antigen and then passively sensitized with monoclonal IgE antibody before antigen challenge. A significant increase in the number of peritoneal mast cells was observed 3 weeks after the antigen challenge in the peritoneal cavity, although the histamine content of the mast cells was decreased significantly. In rats without prior immunization, these changes were not observed. Stimulation with compound 48/80 or calcium ionophore A23187 did not affect the number of mast cells. This model may prove to be a useful tool for studying the mechanisms of mast cell hyperplasia and recruitment of mast cell precursors in vivo.

The effect of a thromboxane A2 receptor antagonist BAY-u-3405 on experimental allergic reactions

The effect of a novel thromboxane A2 receptor antagonist, BAY-u-3405, on experimental allergic airway and skin reactions was studied in vivo. At doses of 3-30 mg/kg BAY-u-3405 clearly inhibited the U-46619-induced increase in respiratory resistance (Rrs) in guinea pigs. BAY-u-3405 at doses of 3 and 30 mg/kg inhibited the aerosolized antigen-induced biphasic increase in respiratory resistance in guinea pigs. Moreover, BAY-u-3405 inhibited repeated aeroantigen-induced airway hyperactivity and airway inflammation in mice. In IgE antibody-mediated biphasic skin reactions in mice, both immediate and late-phase reactions were inhibited by 10 mg/kg of BAY-u-3405. These results demonstrate the efficacy of BAY-u-3405 on the antigen-induced late-phase reactions in the airway and skin in guinea pigs and mice, and antigen-induced airway hyperactivity in mice.

The effect of a TXA2 receptor antagonist ON-579 on experimental allergic reactions

The effect of a thromboxane A2 (TXA2) receptor antagonist, ON-579, on experimental allergic skin and airway reactions was studied in vivo. ON-579 at doses of 1 and 20 mg/kg clearly inhibited U-46619-induced increases in respiratory resistance (Rrs) in guinea pigs. ON-579 at doses of 1, 20 and 50 mg/kg inhibited the aerosolized antigen-induced biphasic increase in Rrs in guinea pigs. Moreover, ON-579 clearly inhibited repeated aeroantigen-induced airway hyperreactivity in guinea pigs. ON-579, however, did not have any significant effects on allergic cutaneous reactions in rats. These results suggest that ON-579 is a relatively selective TXA2 antagonist, especially in the airways, and indicate the efficacy of ON-579 on antigen-induced increase in airway resistance and antigen-induced airway hyperreactivity in guinea pigs.

Cellular localization of synaptotagmin I, II, and III mRNAs in the central nervous system and pituitary and adrenal glands of the rat

Three isoforms of synaptotagmin, a synaptic vesicle protein involved in neurotransmitter release, have been characterized in the rat, although functional differences between these isoforms have not been reported. In situ hybridization was used to define the localization of synaptotagmin I, II, and III transcripts in the rat CNS and pituitary and adrenal glands. Each of the three synaptotagmin genes has a unique expression pattern. The synaptotagmin III gene is expressed in most neurons, but transcripts are much less abundant than the products of the synaptotagmin I and II genes. A majority of neurons in the forebrain expressed both synaptotagmin I and III mRNAs while synaptotagmin II gene expression was confined to subsets of neurons in layers IV-VI of the cerebral cortex, in the dentate granule cell region, the hilus, and the CA1-CA3 areas of the hippocampus. In the cerebellum, all three transcripts were visualized in the granule cell layer. Furthermore, synaptotagmin I probes revealed striking differences between distinct populations of neurons, as in addition to moderate labeling of granule cells, much more prominent hybridization signals were detected on scattered cell bodies likely to be Golgi interneurons. In the most caudal part of the brain, synaptotagmin II transcripts were abundant and were coexpressed with synaptotagmin III mRNAs. This pattern was found in putative motoneurons of the spinal cord, suggesting that the two isoforms might be involved in exocytosis at the neuromuscular junction. Only synaptotagmin I mRNAs were detected in the anterior and intermediate pituitary and in adrenal medullary cells. These data reveal an unexpectedly subtle segregation of the expression of synaptotagmin genes and the existence of multiple combinations of synaptotagmin isoforms which may provide diversity in the regulation of neurosecretion.

TrkA tyrosine residues involved in NGF-induced neurite outgrowth of PC12 cells

The proto-oncogene product gp140prototrk (TrkA) is the receptor tyrosine kinase that mediates nerve growth factor-induced neuronal survival and differentiation. In receptor tyrosine kinases, specific intracellular tyrosine residues become phosphorylated after ligand binding and the phosphorylated tyrosines induce the cascade of signal transduction. Here we have identified intracellular tyrosine residues of TrkA involved in nerve growth factor-induced neurite outgrowth of PC12 cells, using site-directed mutagenesis and a PC12 cell line expressing very low levels of endogenous TrkA (PC12nnr5 cells). We analysed eight conserved intracellular tyrosine residues of TrkA while the three putative autophosphorylation sites conferring tyrosine kinase activity were left intact. Five tyrosine residues, Y499, Y643, Y704, Y760 and Y794, in rat TrkA were involved in nerve growth factor-induced neurite outgrowth. None of these tyrosines mediated the full activity of wild-type TrkA, and a pair of these tyrosines, Y760 and Y794, promoted neurite outgrowth in an additive manner. These data indicate that no single tyrosine is sufficient to induce complete neurite outgrowth but the five tyrosine residues Y499, Y643, Y704, Y760 and Y794 cooperate to exhibit the full activity of wild-type TrkA.