Hydrogen sulfide inhibits Kir2 and Kir3 channels by decreasing sensitivity to the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2).

Inwardly rectifying potassium (Kir) channels establish and regulate the resting membrane potential of excitable cells in the heart, brain, and other peripheral tissues. Phosphatidylinositol 4,5-bisphosphate (PIP2) is a key direct activator of ion channels, including Kir channels. The gasotransmitter carbon monoxide has been shown to regulate Kir channel activity by altering channel-PIP2 interactions. Here, we tested in two cellular models the effects and mechanism of action of another gasotransmitter, hydrogen sulfide (H2S), thought to play a key role in cellular responses under ischemic conditions. Direct administration of sodium hydrogen sulfide as an exogenous H2S source and expression of cystathionine γ-lyase, a key enzyme that produces endogenous H2S in specific brain tissues, resulted in comparable current inhibition of several Kir2 and Kir3 channels. This effect resulted from changes in channel-gating kinetics rather than in conductance or cell-surface localization. The extent of H2S regulation depended on the strength of the channel-PIP2 interactions. H2S regulation was attenuated when channel-PIP2 interactions were strengthened and was increased when channel-PIP2 interactions were weakened by depleting PIP2 levels. These H2S effects required specific cytoplasmic cysteine residues in Kir3.2 channels. Mutation of these residues abolished H2S inhibition, and reintroduction of specific cysteine residues back into the background of the cytoplasmic cysteine-lacking mutant rescued H2S inhibition. Molecular dynamics simulation experiments provided mechanistic insights into how potential sulfhydration of specific cysteine residues could lead to changes in channel-PIP2 interactions and channel gating.

A High Ki67/BCL2 Index Could Predict Lower Disease-Free and Overall Survival in Intestinal-Type Gastric Cancer.

BACKGROUND: The heterogeneity of gastric cancer makes the identification of potential prognostic indicators particularly important. The Ki67 and BCL2 proteins are known prognostic markers for different types of cancer. Ki67 is associated with cell proliferation, whereas BCL2 has antiproliferative roles. A combined marker based on these opposite functions might provide improved prognostic information in gastric cancer. METHOD: Ki67 and BCL2 expression was assessed in 276 gastric adenocarcinoma tissue microarrays. A Ki67/BCL2 index based on the relative expression of each protein was divided into low- and high-risk groups using receiver operating characteristic curves. RESULTS: A high Ki67/BCL2 index significantly correlated with advanced stage, recurrence, intestinal type, high histologic grade, and lymphatic and perineural invasion (all p < 0.05). Univariate and multivariate analyses revealed a significant relationship between disease-free or overall survival and the Ki67/BCL2 index in intestinal-type gastric cancer (all p < 0.05). CONCLUSIONS: A combined marker using Ki67 and BCL2 could be a useful indicator for predicting survival in patients with intestinal-type gastric cancer.

Retigabine holds KV7 channels open and stabilizes the resting potential.

The anticonvulsant Retigabine is a KV7 channel agonist used to treat hyperexcitability disorders in humans. Retigabine shifts the voltage dependence for activation of the heteromeric KV7.2/KV7.3 channel to more negative potentials, thus facilitating activation. Although the molecular mechanism underlying Retigabine's action remains unknown, previous studies have identified the pore region of KV7 channels as the drug's target. This suggested that the Retigabine-induced shift in voltage dependence likely derives from the stabilization of the pore domain in an open (conducting) conformation. Testing this idea, we show that the heteromeric KV7.2/KV7.3 channel has at least two open states, which we named O1 and O2, with O2 being more stable. The O1 state was reached after short membrane depolarizations, whereas O2 was reached after prolonged depolarization or during steady state at the typical neuronal resting potentials. We also found that activation and deactivation seem to follow distinct pathways, suggesting that the KV7.2/KV7.3 channel activity displays hysteresis. As for the action of Retigabine, we discovered that this agonist discriminates between open states, preferentially acting on the O2 state and further stabilizing it. Based on these findings, we proposed a novel mechanism for the therapeutic effect of Retigabine whereby this drug reduces excitability by enhancing the resting potential open state stability of KV7.2/KV7.3 channels. To address this hypothesis, we used a model for action potential (AP) in Xenopus laevis oocytes and found that the resting membrane potential became more negative as a function of Retigabine concentration, whereas the threshold potential for AP firing remained unaltered.

A Critical Gating Switch at a Modulatory Site in Neuronal Kir3 Channels.

Inwardly rectifying potassium channels enforce tight control of resting membrane potential in excitable cells. The Kir3.2 channel, a member of the Kir3 subfamily of G-protein-activated potassium channels (GIRKs), plays several roles in the nervous system, including key responsibility in the GABAB pathway of inhibition, in pain perception pathways via opioid receptors, and is also involved in alcoholism. PKC phosphorylation acts on the channel to reduce activity, yet the mechanism is incompletely understood. Using the heterologous Xenopus oocyte system combined with molecular dynamics simulations, we show that PKC modulation of channel activity is dependent on Ser-196 in Kir3.2 such that, when this site is phosphorylated, the channel is less sensitive to PKC inhibition. This reduced inhibition is dependent on an interaction between phospho-Ser (SEP)-196 and Arg-201, reducing Arg-201 interaction with the sodium-binding site Asp-228. Neutralization of either SEP-196 or Arg-201 leads to a channel with reduced activity and increased sensitivity to PKC inhibition. This study clarifies the role of Ser-196 as an allosteric modulator of PKC inhibition and suggests that the SEP-196/Arg-201 interaction is critical for maintaining maximal channel activity. SIGNIFICANCE STATEMENT: The inwardly rectifying potassium 3.2 (Kir3.2) channel is found principally in neurons that regulate diverse brain functions, including pain perception, alcoholism, and substance addiction. Activation or inhibition of this channel leads to changes in neuronal firing and chemical message transmission. The Kir3.2 channel is subject to regulation by intracellular signals including sodium, G-proteins, ethanol, the phospholipid phosphatidylinositol bis-phosphate, and phosphorylation by protein kinases. Here, we take advantage of the recently published structure of Kir3.2 to provide an in-depth molecular view of how phosphorylation of a specific residue previously thought to be the target of PKC promotes channel gating and acts as an allosteric modulator of PKC-mediated inhibition.

Current Issues in Duodenoscope-Associated Infections: Now Is the Time to Take Action.

A duodenoscope has a very complex structure that contains many small parts which make reprocessing more challenging. The difficulty in cleaning duodenoscopes contributes to a higher risk of infection than that of conventional gastrointestinal endoscopes. However, a duodenoscope shares similar disinfection process with other gastrointestinal endoscopes. Recent outbreaks of carbapenem-resistant Enterobacteriaceae (CRE) infections associated with duodenoscopes used for endoscopic retrograde cholangiopancreatography procedures have raised many concerns worldwide. Duodenoscope-associated infections involving CRE or other multidrug-resistant bacteria pose a great threat to patients undergoing procedures using duodenoscopes and should be dealt with a great concern. Updated guidelines regarding cleaning and disinfection of duodenoscope needs to be developed urgently to prevent transmission of infection and ensure patient safety. Meanwhile, healthcare staff should pay special attention to thorough cleaning and disinfection of duodenoscopes.

Unifying Mechanism of Controlling Kir3 Channel Activity by G Proteins and Phosphoinositides.

The question that started with the pioneering work of Otto Loewi in the 1920s, to identify how stimulation of the vagus nerve decreased heart rate, is approaching its 100th year anniversary. In the meantime, we have learned that the neurotransmitter acetylcholine acting through muscarinic M2 receptors activates cardiac potassium (Kir3) channels via the ßγ subunits of G proteins, an important effect that contributes to slowing atrial pacemaker activity. Concurrent stimulation of M1 or M3 receptors hydrolyzes PIP2, a signaling phospholipid essential to maintaining Kir3 channel activity, thus causing desensitization of channel activity and protecting the heart from overinhibition of pacemaker activity. Four mammalian members of the Kir3 subfamily, expressed in heart, brain, endocrine organs, etc., are modulated by a plethora of stimuli to regulate cellular excitability. With the recent great advances in ion channel structural biology, three-dimensional structures of Kir3 channels with PIP2 and the Gßγ subunits are now available. Mechanistic insights have emerged that explain how modulatory control of activity feeds into a core mechanism of channel-PIP2 interactions to regulate the conformation of channel gates. This complex but beautiful system continues to surprise us for almost 100 years with an apparent wisdom in its intricate design.

A Case of Anaphylaxis Induced by Contact with Young Radish (Raphanus sativus L).

Young radish (Raphanus sativus L), a member of the mustard family (Cruciferae), is a common ingredient of Kimchi. Although few reports have described anaphylaxis to cruciferous vegetables, we report the case of anaphylaxis induced by contact with young radish. A 46-year-old female with a history of contact allergy to metal presented to our emergency room (ER) with dizziness, generalized eruption and gastrointestinal upset. Her symptoms developed after re-exposure to young radish while chopping it. Hypotensive blood pressures were noted. Three days prior, the patient had experienced generalized urticaria with pruritus immediately after chopping the fresh young radish, which resolved spontaneously. In the ER, her symptoms improved by the administration of epinephrine (0.3 mL), antihistamine (chlorpheniramine) and isotonic saline hydration. A skin prick test with young radish extract showed positive reactivity. The same skin test was negative in five adult controls. IgE-mediated hypersensitivity could be an important immunologic mechanism in the development of young radish-induced anaphylaxis.

Osler-Weber-Rendu disease presenting as recurrent portosystemic encephalopathy in a 75-year-old female patient.

Osler-Weber-Rendu disease is a rare autosomal dominant disorder of fibrovascular tissues, characterized by a classic triad of mucocutaneous telangiectasias, recurrent hemorrhages, and a familial occurrence. Portosystemic encephalopathy in a patient with Osler-Weber-Rendu disease is rare, but we experienced a case presenting with recurrent portosystemic encephalopathy in Osler-Weber-Rendu disease. We report on a case of a 75-year-old female presenting with an altered mentality. Initial studies including brain imaging study did not reveal any specific cause for her mental status. She was diagnosed with the rare disease after a series of tests and received conservative treatment. Her neurological status recovered fully without complication after conservative treatment and she was discharged after 18 hospital days. This case demonstrated an extremely rare case of Osler-Weber-Rendu disease presenting as portosystemic encephalopathy treated successfully with conservative treatment. For patients who have shown hepatic encephalopathy without a definite cause, we recommend evaluation for the possibility of Osler-Weber-Rendu disease. Conservative treatment based on treatment of advanced liver cirrhosis could be an alternative solution.

The effects of bronchiectasis on asthma exacerbation.

BACKGROUND: Bronchiectasis and asthma are different in many respects, but some patients have both conditions. Studies assessing the effect of bronchiectasis on asthma exacerbation are rare. The aim of this study is to investigate the effect of bronchiectasis on asthma exacerbation. METHODS: We enrolled 2,270 asthma patients who were followed up in our hospital. Fifty patients had bronchiectasis and asthma. We selected fifty age- and sex-matched controls from the 2,220 asthma patients without bronchiectasis, and assessed asthma exacerbation and its severity based on the annual incidence of total asthma exacerbation, annual prevalence of steroid use, and frequency of emergency room visits and hospitalizations due to asthma exacerbation in each group. RESULTS: Fifty patients (2.2%) had bronchiectasis and asthma. The annual incidence of asthma exacerbation was higher in patients with asthma and bronchiectasis than in patients with asthma alone (1.08±1.68 vs. 0.35±0.42, p=0.004). The annual prevalence of steroid use (0.9±1.54 vs. 0.26±0.36, p=0.006) and the frequency of emergency room visits (0.46±0.84 vs. 0.02±0.13, p=0.001) due to asthma exacerbation were also higher in patients with asthma and bronchiectasis than in patients with asthma alone. CONCLUSION: Bronchiectasis is associated with difficult asthma control.

Controlling the intercalation chemistry to design high-performance dual-salt hybrid rechargeable batteries.

We have conducted extensive theoretical and experimental investigations to unravel the origin of the electrochemical properties of hybrid Mg(2+)/Li(+) rechargeable batteries at the atomistic and macroscopic levels. By revealing the thermodynamics of Mg(2+) and Li(+) co-insertion into the Mo6S8 cathode host using density functional theory calculations, we show that there is a threshold Li(+) activity for the pristine Mo6S8 cathode to prefer lithiation instead of magnesiation. By precisely controlling the insertion chemistry using a dual-salt electrolyte, we have enabled ultrafast discharge of our battery by achieving 93.6% capacity retention at 20 C and 87.5% at 30 C, respectively, at room temperature.

Live cell imaging reveals differential modifications to cytoplasmic dynein properties by phospho- and dephosphomimic mutations of the intermediate chain 2C S84.

Cytoplasmic dynein is a multisubunit motor protein responsible for intracellular cargo transport toward microtubule minus ends. There are multiple isoforms of the dynein intermediate chain (DYNC1I, IC), which is encoded by two genes. One way to regulate cytoplasmic dynein is by IC phosphorylation. The IC-2C isoform is expressed in all cells, and the functional significance of phosphorylation on IC-2C serine 84 was investigated by using live cell imaging of fluorescent protein-tagged IC-2C wild type (WT) and phospho- and dephosphomimic mutant isoforms in axonal transport model systems. Both mutations modulated dynein functional properties. The dephosphomimic mutant IC-2C S84A had greater colocalization with mitochondria than the IC-2C WT or the phosphomimic mutant IC-2C S84D. The dephosphomimic mutant IC-2C S84A was also more likely to be motile than the phosphomimic mutant IC-2C S84D or the IC-2C WT. In contrast, the phosphomimic mutant IC-2C S84D mutant was more likely to move in the retrograde direction than was the IC-2C S84A mutant. The phosphomimic IC-2C S84D was also as likely as the IC-2C WT to colocalize with mitochondria. Both the S84D phospho- and the S84A dephosphomimic mutants were found to be capable of microtubule minus-end-directed (retrograde) movement in axons. They were also observed to be passively transported in the anterograde direction. These data suggest that the IC-2C S84 has a role in modulating dynein properties.

Erratum: the effects of bronchiectasis on asthma exacerbation.

[This corrects the article on p. 209 in vol. 77, PMID: 25473408.].

A computational model predicts that Gßγ acts at a cleft between channel subunits to activate GIRK1 channels.

The atrial G protein (heterotrimeric guanine nucleotide-binding protein)-regulated inwardly rectifying K(+) (GIRK1 and GIRK4) heterotetrameric channels underlie the acetylcholine-induced K(+) current responsible for vagal inhibition of heart rate and are activated by the G protein ßγ subunits (Gßγ). We used a multistage protein-protein docking approach with data from published structures of GIRK1 and Gßγ to generate an experimentally testable interaction model of Gßγ docked onto the cytosolic domains of the GIRK1 homotetramer. The model suggested a mechanism by which Gßγ promotes the open state of a specific cytosolic gate in the channel, the G loop gate. The predicted structure showed that the Gß subunit interacts with the channel near the site of action for ethanol and stabilizes an intersubunit cleft formed by two loops (LM and DE) of adjacent channel subunits. Using a heterologous expression system, we disrupted the predicted GIRK1- and Gßγ-interacting residues by mutation of one protein and then rescued the regulatory activity by mutating reciprocal residues in the other protein. Disulfide cross-linking of channels and Gßγ with cysteine mutations at the predicted interacting residues yielded activated channels. The mechanism of Gßγ-induced activation of GIRK4 was distinct from GIRK1 homotetramers. However, GIRK1-GIRK4 heterotetrameric channels activated by Gßγ displayed responses indicating that the GIRK1 subunit dominated the response pattern. This work demonstrated that combining computational with experimental approaches is an effective method for elucidating interactions within protein complexes that otherwise might be challenging to decipher.

A neuron-specific cytoplasmic dynein isoform preferentially transports TrkB signaling endosomes.

Cytoplasmic dynein is the multisubunit motor protein for retrograde movement of diverse cargoes to microtubule minus ends. Here, we investigate the function of dynein variants, defined by different intermediate chain (IC) isoforms, by expressing fluorescent ICs in neuronal cells. Green fluorescent protein (GFP)-IC incorporates into functional dynein complexes that copurify with membranous organelles. In living PC12 cell neurites, GFP-dynein puncta travel in both the anterograde and retrograde directions. In cultured hippocampal neurons, neurotrophin receptor tyrosine kinase B (TrkB) signaling endosomes are transported by cytoplasmic dynein containing the neuron-specific IC-1B isoform and not by dynein containing the ubiquitous IC-2C isoform. Similarly, organelles containing TrkB isolated from brain by immunoaffinity purification also contain dynein with IC-1 but not IC-2 isoforms. These data demonstrate that the IC isoforms define dynein populations that are selectively recruited to transport distinct cargoes.