Inflammasomes regulate innate immune responses by facilitating maturation of inflammatory cytokines, interleukin (IL)-1β and IL-18. NACHT, LRR and PYD domains-containing protein 7 (NALP7) is one inflammasome constituent, but little is known about its cellular handling. Here we show a mechanism for NALP7 protein stabilization and activation of the inflammasome by Toll-like receptor (TLR) agonism with bacterial lipopolysaccharide (LPS) and the synthetic acylated lipopeptide Pam3CSK4. NALP7 is constitutively ubiquitinated and recruited to the endolysosome for degradation. With TLR ligation, the deubiquitinase enzyme, STAM-binding protein (STAMBP) impedes NALP7 trafficking to lysosomes to increase NALP7 abundance. STAMBP deubiquitinates NALP7 and STAMBP knockdown abrogates LPS or Pam3CSK4-induced increases in NALP7 protein. A small-molecule inhibitor of STAMBP deubiquitinase activity, BC-1471, decreases NALP7 protein levels and suppresses IL-1β release after TLR agonism. These findings describe a unique pathway of inflammasome regulation with the identification of STAMBP as a potential therapeutic target to reduce pro-inflammatory stress.

We sought to determine the mechanisms by which influenza infection of human epithelial cells decreases cystic fibrosis transmembrane conductance regulator (CFTR) expression and function. We infected human bronchial epithelial (NHBE) cells and murine nasal epithelial (MNE) cells with various strains of influenza A virus. Influenza infection significantly reduced CFTR short circuit currents (Isc) and protein levels at 8 hours postinfection. We then infected CFTR expressing human embryonic kidney (HEK)‐293 cells (HEK‐293 CFTRwt) with influenza virus encoding a green fluorescent protein (GFP) tag and performed whole‐cell and cell‐attached patch clamp recordings. Forskolin‐stimulated, GlyH‐101‐sensitive CFTR conductances, and CFTR open probabilities were reduced by 80% in GFP‐positive cells; Western blots also showed significant reduction in total and plasma membrane CFTR levels. Knockdown of the influenza matrix protein 2 (M2) with siRNA, or inhibition of its activity by amantadine, prevented the decrease in CFTR expression and function. Lysosome inhibition (bafilomycin‐A1), but not proteasome inhibition (lactacystin), prevented the reduction in CFTR levels. Western blots of immunoprecipitated CFTR from influenza‐infected cells, treated with BafA1, and probed with antibodies against lysine 63‐linked (K‐63) or lysine 48‐linked (K‐48) polyubiquitin chains supported lysosomal targeting. These results highlight CFTR damage, leading to early degradation as an important contributing factor to influenza infection‐associated ion transport defects.—Londino, J. D., Lazrak, A., Noah, J. W., Aggarwal, S., Bali, V., Woodworth, B. A., Bebok, Z., Matalon, S. Influenza virus M2 targets cystic fibrosis transmembrane conductance regulator for lysosomal degradation during viral infection. FASEB J. 29, 2712–2725 (2015). http://www.fasebj.org

We investigated the mechanisms by which chlorine (Cl 2 ) and its reactive byproducts inhibit Na ؉ -dependent alveolar fluid clearance (AFC) in vivo and the activity of amiloridesensitive epithelial Na ؉ channels (ENaC) by measuring AFC in mice exposed to Cl 2 (0 -500 ppm for 30 min) and Na ؉ and amiloride-sensitive currents (I Na and I amil , respectively) across Xenopus oocytes expressing human ␣-, ␤-, and ␥-ENaC incubated with HOCl (1-2000 M). Both Cl 2 and HOCl-derived products decreased AFC in mice and whole cell and single channel I Na in a dose-dependent manner; these effects were counteracted by serine proteases. Mass spectrometry analysis of the oocyte recording medium identified organic chloramines formed by the interaction of HOCl with HEPES (used as an extracellular buffer). In addition, chloramines formed by the interaction of HOCl with taurine or glycine decreased I Na in a similar fashion. Preincubation of oocytes with serine proteases prevented the decrease of I Na by HOCl, whereas perfusion of oocytes with a synthetic 51-mer peptide corresponding to the putative furin and plasmin cleaving segment in the ␥-ENaC subunit restored the ability of HOCl to inhibit I Na . Finally, I Na of oocytes expressing wild type ␣-and ␥-ENaC and a mutant form of ␤ENaC (S520K), known to result in ENaC channels locked in the open position, were not altered by HOCl. We concluded that HOCl and its reactive intermediates (such as organic chloramines) inhibit ENaC by affecting channel gating, which could be relieved by proteases cleavage.The balance of fluid covering the respiratory and alveolar epithelia is determined in part by the ability of these cells to transport sodium (Na ϩ ) and chloride (Cl Ϫ ) ions in a vectorial fashion. Active Na ϩ reabsorption across lung epithelia requires the coordinated entry of Na ϩ ions through cation-and Na ϩ -selective amiloride-sensitive channels (ENaC) 5 located at the apical membranes, their extrusion across the basolateral membranes by the electrogenic Na ϩ -K ϩ -ATPase, and the passive movement of K ϩ ions through basolateral K ϩ channels. The entry of Na ϩ ions through apical pathways is thought to be the rate-limiting step in this process (1-3). To preserve neutrality, Cl Ϫ ions follow Na ϩ ions both through transcellular and paracellular pathways (4, 5). The coordinated movement of Na ϩ and Cl Ϫ ions creates an oncotic gradient favoring the absorption of alveolar fluid.Injury to either apical or basolateral pathways by partially reduced intermediates may lead to impairment of fluid reabsorption, which in turn may result in pulmonary edema, hypoxemia, and eventually death from respiratory failure (6 -9). One such specie is hypochlorous acid (HOCl) 6 , which may be generated either endogenously or exogenously. Millimolar concentrations of HOCl may be generated by activated neutrophils and eosinophils by the catalytic actions of neutrophil-and eosinophil-derived myeloperoxidases on chloride (Cl Ϫ ) and hydrogen peroxide (H 2 O 2 ) in close proximity of the apical and basolatera...

The human cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-activated chloride (Cl(-)) channel in the lung epithelium that helps regulate the thickness and composition of the lung epithelial lining fluid. We investigated whether influenza M2 protein, a pH-activated proton (H(+)) channel that traffics to the plasma membrane of infected cells, altered CFTR expression and function. M2 decreased CFTR activity in 1) Xenopus oocytes injected with human CFTR, 2) epithelial cells (HEK-293) stably transfected with CFTR, and 3) human bronchial epithelial cells (16HBE14o-) expressing native CFTR. This inhibition was partially reversed by an inhibitor of the ubiquitin-activating enzyme E1. Next we investigated whether the M2 inhibition of CFTR activity was due to an increase of secretory organelle pH by M2. Incubation of Xenopus oocytes expressing CFTR with ammonium chloride or concanamycin A, two agents that alkalinize the secretory pathway, inhibited CFTR activity in a dose-dependent manner. Treatment of M2- and CFTR-expressing oocytes with the M2 ion channel inhibitor amantadine prevented the loss in CFTR expression and activity; in addition, M2 mutants, lacking the ability to transport H(+), did not alter CFTR activity in Xenopus oocytes and HEK cells. Expression of an M2 mutant retained in the endoplasmic reticulum also failed to alter CFTR activity. In summary, our data show that M2 decreases CFTR activity by increasing secretory organelle pH, which targets CFTR for destruction by the ubiquitin system. Alteration of CFTR activity has important consequences for fluid regulation and may potentially modify the immune response to viral infection.