Yuushi Okumura

Involvement of autophagy in trypsinogen activation within the pancreatic acinar cells

Autophagy is mostly a nonselective bulk degradation system within cells. Recent reports indicate that autophagy can act both as a protector and killer of the cell depending on the stage of the disease or the surrounding cellular environment (for review see Cuervo, A.M. 2004. Trends Cell Biol. 14:70–77). We found that cytoplasmic vacuoles induced in pancreatic acinar cells by experimental pancreatitis were autophagic in origin, as demonstrated by microtubule-associated protein 1 light chain 3 expression and electron microscopy experiments. To analyze the role of macroautophagy in acute pancreatitis, we produced conditional knockout mice lacking the autophagy-related 5 gene in acinar cells. Acute pancreatitis was not observed, except for very mild edema in a restricted area, in conditional knockout mice. Unexpectedly, trypsinogen activation was greatly reduced in the absence of autophagy. These results suggest that autophagy exerts devastating effects in pancreatic acinar cells by activation of trypsinogen to trypsin in the early stage of acute pancreatitis through delivering trypsinogen to the lysosome.

Proteolytic activation of the precursor of membrane type 1 matrix metalloproteinase by human plasmin: A possible cell surface activator

Membrane type 1 matrix metalloproteinase (MT1‐MMP) was suggested to play a critical role in the regulation of tissue invasion by normal and neoplastic cells by directly mediating the activation of pro‐gelatinase A. Recently, the proteolytic activation of a pro‐MT1‐MMP by an intracellular proprotein convertase, furin, was reported. In this study, we found that plasmin efficiently activates the pro‐MT1‐MMP by cleaving immediately downstream of Arg108 and Arg111 in the multi‐basic motif between its pro‐ and catalytic domains that participates in the activation of pro‐gelatinase A. Our present data suggest that pro‐MT1‐MMP transported to the plasma membrane is activated by plasmin extracellularly and thus it may play an important role in the matrix degradation process.

Proteases essential for human influenza virus entry into cells and their inhibitors as potential therapeutic agents

Influenza A virus (IAV) is one of the most common infectious pathogens in humans. Since IVA genome does not have the processing protease for the viral membrane fusion glycoprotein precursors, entry of this virus into cells is determined primarily by host cellular, trypsin-type, processing proteases that proteolytically activate the fusion glycoprotein precursors of IAV. At least five different processing proteases have been identified in the airways of animals and humans. These proteases determine the infectious organ tropism of IAV infection as well as the efficiency of viral multiplication in the airway, and sometimes in the brain. Proteases in the upper respiratory tract are suppressed by secretory leukoprotease inhibitor, and those in the lower respiratory tract are suppressed by pulmonary surfactant which, by adsorption, inhibits the interaction between the proteases and viral membrane proteins. Since protease activities predominate over those of endogenous inhibitory compounds under normal airway conditions, administration of protease inhibitors in the early-stage of infection significantly suppresses viral entry and viral multiplication. Several viral neuraminidase inhibitors are used clinically as anti-influenza virus agents, based on their inhibitory action on viral release from infected cells. Furthermore, protease inhibitors of viral entry could be potentially useful against influenza virus as well as neuraminidase inhibitor-resistant viruses. We also found that ambroxol, a mucolytic and anti-oxidant agent, up-regulates the levels of endogenous protease inhibitory compounds in the airway fluids in early-phase infection, and that clarithromycin, a macrolide antibiotic, increases IgA levels and mucosal immunity through augmentation of interleukin-12 levels in the airway. The combination of neuraminidase inhibitors and protease inhibitors, clarithromycin or ambroxol, could be potentially used as a potent anti-influenza therapy to minimize the emergence of drug-resistant mutant viruses.

Novel Type II Transmembrane Serine Proteases, MSPL and TMPRSS13, Proteolytically Activate Membrane Fusion Activity of the Hemagglutinin of Highly Pathogenic Avian Influenza Viruses and Induce Their Multicycle Replication

ABSTRACT Host cellular proteases induce influenza virus entry into cells by cleaving the viral surface envelope glycoprotein hemagglutinin (HA). However, details on the cellular proteases involved in this event are not fully available. We report here that ubiquitous type II transmembrane serine proteases, MSPL and its splice variant TMPRSS13, are novel candidates for proteases processing HA proteins of highly pathogenic avian influenza (HPAI) viruses, apart from the previously identified furin and proprotein convertases 5 and 6. HAs from all HPAI virus H5 and H7 strains have one of two cleavage site motifs, the R-X-K/R-R motif with R at position P4 and the K-K/R-K/T-R motif with K at position P4. In studies of synthetic 14-residue HPAI virus HA peptides with these cleavage site motifs, furin preferentially cleaved only HA peptides with the R-K-K-R motif in the presence of calcium and not peptides with the other motif, whereas MSPL and TMPRSS13 cleaved both types of HA peptides (those with the R/K-K-K-R motif) efficiently in the absence of calcium. Full-length recombinant HPAI virus HA with the K-K-K-R cleavage motif exhibited poor susceptibility to cleavage in the absence of MSPL or TMPRSS13 and the presence of furin in infected cells, but it was converted to mature HA subunits in transfected cells expressing MSPL or TMPRSS13, with membrane-fused giant-cell formation. This conversion and membrane fusion were suppressed by inhibitors of MSPL and TMPRSS13. Furthermore, infection with and multiplication of genetically modified live HPAI virus A/Crow/Kyoto/53/2004 (H5N1) with the K-K-K-R cleavage site motif were detected only in MSPL- and TMPRSS13-expressing cells.

Osteoactivin fragments produced by ectodomain shedding induce MMP-3 expression via ERK pathway in mouse NIH-3T3 fibroblasts

Intact osteoactivin, a novel type I membrane glycoprotein, were shed at a dibasic motif in the juxtamembrane region in C2C12 myoblasts. Extracellular fragments were secreted into the culture media by a putative metalloprotease. Extracellular fragments of osteoactivin, but not control protein, induced matrix metalloprotease‐3 (MMP‐3) expression in NIH‐3T3 fibroblasts. Epidermal growth factor (ERK) kinase inhibitors inhibited the osteoactivin‐mediated MMP‐3 expression, whereas the extracellular fragment of osteoactivin activated ERK1/2 and p38 in the mitogen‐activated protein kinase pathway. Our results suggest that the extracellular fragments of osteoactivin produced by shedding act as a growth factor to induce MMP‐3 expression via the ERK pathway in fibroblasts.

Host envelope glycoprotein processing proteases are indispensable for entry into human cells by seasonal and highly pathogenic avian influenza viruses

Influenza A virus (IAV) is one of the most common infectious pathogens in humans and causes considerable morbidity and mortality. The recent spread of highly-pathogenic avian IAV H5N1 viruses has reinforced the importance of pandemic preparedness. In the pathogenesis of IAV infection, cellular proteases play critical roles in the process of viral entry into cells that subsequently leads to tissue damage in the infected organs. Since there are no processing protease for the viral membrane fusion glycoprotein hemagglutinin precursor (HA0) in IAV, entry of the virus into cells is determined primarily by the host cellular HA0 processing proteases that proteolytically activate membrane fusion activity. HA0 of seasonal human IAV has the consensus cleavage site motif Q(E)-T/X-R and is selectively processed by at least seven different trypsin-type processing proteases identified to-date in animal model experiments using mouse-adapted IAV or gene expression system in MDCK cells. As is the case for the highly pathogenic avian influenza (HPAI) A virus, endoproteolytic processing of the HA0 occurs through ubiquitous cellular processing proteases, which selectively recognize the multi-basic consensus cleavage site motifs, such as R-X-K/R-R, and K-X-K/R-R. The cleavage enzymes for the R-X-K/R-R motif, but not K-X-K/R-R motif, have been reported to be furin and pro-protein convertase (PC)5/6 in the trans-Golgi network. Here we report new members of type II transmembrane serine proteases of the cell membrane, mosaic serine protease large form (MSPL) and its splice variant TMPRSS13, which recognize and cleave both R-X-K/R-R and K-X-K/R-R motifs without calcium. Furthermore, IAV infection significantly up-regulates a latent ectopic pancreatic trypsin, one of the potent HA processing proteases, and pro-matrix metalloprotease-9, in various organs. These proteases may synergistically damage the blood-brain barrier in the brain and basement membrane of blood vessels in various organs, resulting in severe edema and multiple organ failure. In this review, we discuss these proteases as new drug target molecules for IAV treatment acting by inhibition of IAV multiplication and prevention of multiple organ failure, other than anti-viral agents, viral neuraminidase inhibitors.

Ambroxol suppresses influenza-virus proliferation in the mouse airway by increasing antiviral factor levels.

The protective effect of ambroxol, a mucolytic agent which has antioxidant properties and stimulates the release of pulmonary surfactant, against influenza-virus proliferation in the airway was investigated in mice. Ambroxol or the vehicle was administered intraperitoneally twice a day for 5–7 days to mice shortly after intranasal infection with a lethal dose of influenza A/Aichi/68 (H3N2) virus, and the survival rate, virus titre and levels of factors regulating virus proliferation in the airway fluid were analysed. Ambroxol significantly suppressed virus multiplication and improved the survival rate of mice. The effect of ambroxol reached a peak at 10 mg·kg−1·day−1, higher doses being less effective. Ambroxol stimulated the release of suppressors of influenza-virus multiplication, such as pulmonary surfactant, mucus protease inhibitor, immunoglobulin (Ig)-A and IgG, although it stimulated the release of a trypsin-type protease that potentiates virus proliferation. In addition, ambroxol transiently suppressed release of the cytokines, tumour necrosis factor-α, interferon-γ and interleukin-12, into airway fluid. Although ambroxol had several negative effects on the host defence system, overall it strikingly increased the concentrations of suppressors of influenza-virus multiplication in the airway.

Glucose Infusion Suppresses Surgery-induced Muscle Protein Breakdown by Inhibiting Ubiquitin-proteasome Pathway in Rats

Background:It appears to have been well established that after surgery, protein catabolism is accelerated and glucose infusion suppresses the catabolic reactions. However, in the early postoperative period, the effects of surgical stress and glucose infusion on muscle protein catabolism and the related mechanisms remain unclear. Methods:Rats undergoing laparotomy were infused with acetated Ringer’s solution (10 ml · kg–1 · h–1) without glucose (control) or containing 1% or 5% glucose. The infusion was continued for a further 4 h after the surgical treatment. The catabolic index, excretion of urinary nitrogen and 3-methylhistidine, and release of tyrosine and 3-methylhistidine from isolated muscle were determined. Furthermore, muscular mRNA expression of proteolytic-related genes (atrogin-1/MAFbx, muscle ring finger-1, &mgr;- and m-calpain, and cathepsin L and H) and phosphorylation of components of insulin signaling (forkhead box O3 and protein kinase B) were evaluated. Results:Surgery increased the catabolic index, and this increase was suppressed by glucose infusion (both 1% and 5%). In the control group, mRNA expression of atrogin-1/MAFbx and muscle ring finger-1 was increased, and they were suppressed in the two glucose groups. Furthermore, insulin signaling (phosphorylation of protein kinase B and forkhead box O3) in muscles was stimulated by glucose infusion. Conclusion:The present study indicates that glucose infusion, even at a relatively low rate, suppresses muscle protein breakdown in the early postoperative period. The mechanism of this effect is related to the suppression of the ubiquitin-proteasome pathway, accompanied by activation of insulin signaling.

Identification of trypsin I as a candidate for influenza A virus and Sendai virus envelope glycoprotein processing protease in rat brain

Abstract Extracellular cleavage of virus envelope fusion glycoprotein hemagglutinin (HA0) by host trypsin-like proteases is a prerequisite for the infectivity and pathogenicity of human influenza A viruses and Sendai virus. The common epidemic influenza A viruses are pneumotropic, but occasionally cause encephalopathy or encephalitis, although the HA0 processing enzyme in the brain has not been identified. In searching for the brain processing proteases, we identified a processing enzyme in rat brain that was inducible by infection with these viruses. The purified enzyme exhibited an apparent molecular mass of approximately 22 kDa on SDS-PAGE and the N-terminal amino acid sequence was consistent with that of rat pancreatic trypsin I. Its substrate specificities and inhibition profiles were the same as those of pancreatic trypsin I. In situ hybridization and immunohistochemical studies on trypsin I distribution revealed heavy deposits in the brain capillaries, particularly in the allocortex, as well as in clustered neuronal cells of the hippocampus. The purified enzyme efficiently processed the HA0 of human influenza A virus and the fusion glycoprotein precursor of Sendai virus. Our results suggest that trypsin I in the brain potentiates virus multiplication in the pathogenesis and progression of influenza-associated encephalopathy or encephalitis.

Serase-1B, a new splice variant of polyserase-1/TMPRSS9, activates urokinase-type plasminogen activator and the proteolytic activation is negatively regulated by glycosaminoglycans

Polyserase-1 (polyserine protease-1)/TMPRSS9 (transmembrane serine protease 9) is a type II transmembrane serine protease (TTSP) that possesses unique three tandem serine protease domains. However, the physiological function of each protease domain remains poorly understood. We discovered a new splice variant of polyserase-1, termed Serase-1B, which contains 34 extra amino acids consisting a SEA module (a domain found in sea urchin sperm protein, enterokinase and agrin) adjacent to the transmembrane domain and the first protease domain with a mucin-like box at the C-terminus. The tissue distribution of this enzyme by RT (reverse transcription)-PCR analysis revealed high expression in the liver, small intestine, pancreas, testis and peripheral blood CD14+ and CD8+ cells. To investigate the role of Serase-1B, a full-length form recombinant protein was produced. Interestingly, recombinant Serase-1B was partly secreted as a soluble inactive precursor and it was also activated by trypsin. This activated enzyme selectively cleaved synthetic peptides for trypsin and activated protein C, and it was inhibited by several natural serine protease inhibitors, such as aprotinin, alpha2-antiplasmin and plasminogen activator inhibitor 1. In addition, Serase-1B efficiently converted pro-uPA (urokinase-type plasminogen activator) into active uPA and this activation was strongly inhibited by these natural inhibitors. Furthermore, this activation was also negatively regulated by glycosaminoglycans. Our results indicate that Serase-1B is a novel member of TTSPs that might be involved in uPA/plasmin-mediated proteolysis and possibly implicated in biological events such as fibrinolysis and tumour progression.