TMPRSS2 Activates Hemagglutinin-Esterase Glycoprotein of Influenza C Virus.

Influenza C virus (ICV) has only one kind of spike protein, the hemagglutinin-esterase (HE) glycoprotein. HE functions similarly to hemagglutinin (HA) and neuraminidase of the influenza A and B viruses (IAV and IBV, respectively). It has a monobasic site, which is cleaved by some host enzymes. The cleavage is essential to activating the virus, but the enzyme or enzymes in the respiratory tract have not been identified. This study investigated whether the host serine proteases, transmembrane protease serine S1 member 2 (TMPRSS2) and human airway trypsin-like protease (HAT), which reportedly cleave HA of IAV/IBV, are involved in HE cleavage. We established TMPRSS2- and HAT-expressing MDCK cells (MDCK-TMPRSS2 and MDCK-HAT). ICV showed multicycle replication with HE cleavage without trypsin in MDCK-TMPRSS2 cells as well as IAV did. The HE cleavage and multicycle replication did not appear in MDCK-HAT cells infected with ICV without trypsin, while HA cleavage and multistep growth of IAV appeared in the cells. Amino acid sequences of the HE cleavage site in 352 ICV strains were completely preserved. Camostat and nafamostat suppressed the growth of ICV and IAV in human nasal surface epithelial (HNE) cells. Therefore, this study revealed that, at least, TMPRSS2 is involved in HE cleavage and suggested that nafamostat could be a candidate for therapeutic drugs for ICV infection. IMPORTANCE Influenza C virus (ICV) is a pathogen that causes acute respiratory illness, mostly in children, but there are no anti-ICV drugs. ICV has only one kind of spike protein, the hemagglutinin-esterase (HE) glycoprotein on the virion surface, which possesses receptor-binding, receptor-destroying, and membrane fusion activities. The HE cleavage is essential for the virus to be activated, but the enzyme or enzymes in the respiratory tract have not been identified. This study revealed that transmembrane protease serine S1 member 2 (TMPRSS2), and not human airway trypsin-like protease (HAT), is involved in HE cleavage. This is a novel study on the host enzymes involved in HE cleavage, and the result suggests that the host enzymes, such as TMPRSS2, may be a target for therapeutic drugs of ICV infection.

Acinar Cell Carcinoma with Morphological Change in One Month.

A 64-year-old man was admitted to our hospital to undergo examination of a pancreatic tumor accompanied by sudden epigastric pain. The tumor had a well-defined oval shape that was mostly less enhanced, with the exception of part of the tumor on the pancreatic head side, on contrast enhanced (CE)-CT. However, CE-CT performed one-month later revealed that the viable part of the tumor grew toward the pancreatic tail with the reduction of necrotic tissue. We performed distal pancreatectomy and the tumor was diagnosed as acinar cell carcinoma (ACC). One important characteristic of ACC is that it may develop morphological changes within a short period of time.

IgG4-related Diaphragmatic Inflammatory Pseudotumor.

A 71-year-old man underwent surgery for a pancreatic neuroendocrine tumor. Follow-up imaging showed swelling of the remnant pancreas, and he was histologically diagnosed with autoimmune pancreatitis based on endoscopic ultrasonography-guided fine-needle aspiration specimens. After two years, a tumor appeared on the liver surface. Although we planned to perform laparoscopic partial hepatectomy, the intraoperative findings showed that the tumor was located in the diaphragm. Partial resection of the diaphragm was performed, and the final diagnosis was an immunoglobulin G4-related inflammatory pseudotumor in the diaphragm. To our knowledge, this is the first reported case of an immunoglobulin G4-related diaphragmatic inflammatory pseudotumor.

Estimated model of psychotropic polypharmacy for bipolar disorder: Analysis using patients' and practitioners' parameters in the MUSUBI study.

OBJECTIVE: This study aims to clarify the relevant factors influencing practitioners' methods of prescribing medications for bipolar disorder, in a nation-wide survey in Japan. METHODS: The clinical records of 3130 outpatients with bipolar disorder were consecutively reviewed from 176 psychiatric outpatient clinics. Fifteen parameters, that is, five patients' including five general characteristics (sex, age, education, occupation, and social adjustment), five patients' aspects of mental functioning (onset age, comorbid mental illness, rapid-cycling, psychopathologic severity, and followed-up years), and five practitioners' characteristics (sex, age, specialist experience, clinic standing years, and location), were evaluated. The number of psychotropic drugs (mood stabilizers, antidepressants, antipsychotic drugs, anxiolytics, and hypnotics) was used as an index of pharmacotherapy. Converted data from each practitioner-unit were analyzed. RESULTS: Seven factors (patient's social adjustment, patient's psychopathology, patient's comorbid mental disorders, patient's followed-up years, doctor's age, clinic running years, and patient's education years) were correlated to the number of psychotropic drugs. Multiple regression analysis showed that the severity of illness (poor social adjustment, and comorbid mental illness) and an intractable disease course (long followed-up years), were significantly associated with the number of psychotropic drugs. CONCLUSION: Our findings indicated that patient-related conditions affected psychotropic polypharmacy more strongly than did practitioner-related conditions.

New-Onset or Exacerbation of Diabetes Mellitus Is a Clue to the Early Diagnosis of Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC), which accounts for majority of pancreatic cancers, is one of the most lethal human malignancies. Most patients are diagnosed at an advanced stage after symptom development. Early diagnosis of PDAC in asymptomatic subjects is important to improve prognosis. Diabetes mellitus (DM) is a risk factor for PDAC, and DM, especially new-onset DM, has attracted attentions as a diagnostic clue to PDAC. However, the impact of DM as a diagnostic opportunity on the prognosis of PDAC is unclear. We here retrospectively reviewed 489 PDAC patients and compared the clinical characteristics and prognosis according to the opportunities for PDAC diagnosis. PDAC was diagnosed upon presentation of symptoms, such as pain and jaundice, in 318 cases including 151 DM patients, upon new-onset or exacerbation of long-standing DM in 53 asymptomatic patients, and upon incidental detection by medical check-up or follow-up/work-up of other diseases in 118 asymptomatic patients. Asymptomatic patients including those with DM had smaller tumors, earlier disease stage, and higher resectability rates than symptomatic patients. Asymptomatic patients diagnosed in association with DM had better prognosis (median survival time, 771 days) than those diagnosed due to symptoms (343 days, P < 0.001), and similar to those diagnosed by incidental detection (869 days). The survival advantage was not evident in symptomatic patients with DM-associated signs. In conclusion, patients diagnosed in association with DM at asymptomatic stages had better prognosis than those diagnosed with symptoms. DM-associated signs might provide a clue to the early diagnosis of PDAC among asymptomatic subjects.

Focal Parenchymal Atrophy and Fat Replacement Are Clues for Early Diagnosis of Pancreatic Cancer with Abnormalities of the Main Pancreatic Duct.

Pancreatic cancer is one of the most dangerous solid tumors, but its early diagnosis is difficult. The abnormality of the main pancreatic duct (MPD), such as a single localized stricture and upstream dilatation, might be useful in the early detection of pancreatic cancer. However, these findings are often observed in benign inflammatory cases. This study aimed to clarify whether early pancreatic cancer presenting MPD abnormalities has characteristic features different from those of benign cases. This is a single-center, retrospective study. We analyzed 20 patients who underwent pancreatectomy presenting with a single, localized MPD stricture without identifiable masses on imaging: 10 patients with pancreatic ductal adenocarcinoma (cancer group; 6 with stage 0 and 4 with stage I) and 10 patients with benign strictures (benign group; 8 with inflammation and 2 with low-grade pancreatic intraepithelial neoplasms). Pancreatectomy was performed in these benign cases because high-grade intraepithelial neoplasm was suspected. Although the proportion of patients with diabetes mellitus tended to be higher in the cancer group (6/10) than that in the benign group (1/10) (P = 0.058), other clinical characteristics were not different between the groups. Preoperative cytological malignancies were detected in four patients in the cancer group (4/10) but not in the benign group (P = 0.09). Focal parenchymal atrophy and fat replacement were more frequently detected on computed tomography in the cancer group (7/10) than in the benign group (1/10) (P = 0.02). In conclusion, focal parenchymal atrophy and fat replacement may provide clues for the early diagnosis of pancreatic cancer.

Antigenic changes among the predominantly circulating C/Sao Paulo lineage strains of influenza C virus in Yamagata, Japan, between 2015 and 2018.

Influenza C virus is a pathogen that causes acute respiratory illness in children and results in the hospitalization of infants. The antigenicity of the hemagglutinin esterase (HE) glycoprotein is highly stable, and it is not yet known whether antigenic changes contribute to the worldwide transmission and the occurrence of outbreaks of influenza C virus. Here, we performed antigenic analysis of 84 influenza C viruses isolated in Yamagata, Japan, during a 4-year period from 2015 to 2018 and analyzed sequence data for strains of the virus from Japan and many other parts of the world. Antigenic and phylogenetic analyses revealed that 83 strains belonged to the C/Sao Paulo lineage, and two sublineage strains, the Aichi99 sublineage and Victoria2012 sublineage, cocirculated between 2016 and 2018. Aichi99 sublineage strains exhibiting decreased reactivity with the monoclonal antibody YA3 became predominant after 2016, and these strains possessed the K190N mutation. Residue 190 is located in the 190-loop on the top side of the HE protein within a region that is known to show variation that does not impair the biological activity of the protein. The Aichi99 sublineage strains possessing the K190N mutation were detected after 2012 in Europe, Australia, the USA, and Asia as well as Japan. These observations suggest that antigenic variants with K190N mutations have circulated extensively around the world and caused outbreaks in Japan between 2016 and 2018. Our study indicated that the 190-loop is an important antigenic region, and the results suggested that changes in the 190-loop have contributed to the extensive transmission of the virus.

Pancreatic Acinar Cell Carcinoma with Multiple Liver Metastases Effectively Treated by S-1 Chemotherapy.

A 79-year-old woman was referred for pancreatic tail cancer with multiple liver metastases. The pancreatic tail tumor was diagnosed as acinar cell carcinoma (ACC) histologically by endoscopic ultrasound-guided fine-needle aspiration. Because of multiple liver metastases, S-1 chemotherapy was administered, resulting in a partial response to chemotherapy one year later. After approximately three years, liver atrophy and esophageal varices developed. We suspected S-1 as the cause of the liver cirrhosis. S-1 cessation minimized ascites and improved the esophageal varices. Although S-1 can potentially treat ACC, we should be watchful for liver cirrhosis caused by its long-term administration.

Neutralizing Epitopes and Residues Mediating the Potential Antigenic Drift of the Hemagglutinin-Esterase Protein of Influenza C Virus.

We mapped the hemagglutinin-esterase (HE) antigenic epitopes of the influenza C virus on the three-dimensional (3D) structure of the HE glycoprotein using 246 escape mutants that were selected by a panel of nine anti-HE monoclonal antibodies (MAbs), including seven of the C/Ann Arbor/1/50 virus and two of the C/Yamagata/15/2004 virus. The frequency of variant selection in the presence of anti-HE MAbs was very low, with frequencies ranging from 10-4.62 to 10-7.58 for the C/Ann Arbor/1/50 virus and from 10-7.11 to 10-9.25 for the C/Yamagata/15/2004 virus. Sequencing of mutant HE genes revealed 25 amino acid substitutions at 16 positions in three antigenic sites: A-1, A-2, and A-3, and a newly designated Y-1 site. In the 3D structure, the A-1 site was widely located around the receptor-binding site, the A-2 site was near the receptor-destroying enzyme site, and the Y-1 site was located in the loop on the topside of HE. The hemagglutination inhibition reactions of the MAbs with influenza C viruses, circulating between 1947 and 2016, were consistent with the antigenic-site amino acid changes. We also found some amino acid variations in the antigenic site of recently circulating strains with antigenic changes, suggesting that viruses that have the potential to alter antigenicity continue to circulate in humans.

Effect of Phosphorylation of CM2 Protein on Influenza C Virus Replication.

CM2 is the second membrane protein of the influenza C virus and has been demonstrated to play a role in the uncoating and genome packaging processes in influenza C virus replication. Although the effects of N-linked glycosylation, disulfide-linked oligomerization, and palmitoylation of CM2 on virus replication have been analyzed, the effect of the phosphorylation of CM2 on virus replication remains to be determined. In this study, a phosphorylation site(s) at residue 78 and/or 103 of CM2 was replaced with an alanine residue(s), and the effects of the loss of phosphorylation on influenza C virus replication were analyzed. No significant differences were observed in the packaging of the reporter gene between influenza C virus-like particles (VLPs) produced from 293T cells expressing wild-type CM2 and those from the cells expressing the CM2 mutants lacking the phosphorylation site(s). Reporter gene expression in HMV-II cells infected with VLPs containing the CM2 mutants was inhibited in comparison with that in cells infected with wild-type VLPs. The virus production of the recombinant influenza C virus possessing CM2 mutants containing a serine-to-alanine change at residue 78 was significantly lower than that of wild-type recombinant influenza C virus. Furthermore, the virus growth of the recombinant viruses possessing CM2 with a serine-to-aspartic acid change at position 78, to mimic constitutive phosphorylation, was virtually identical to that of the wild-type virus. These results suggest that phosphorylation of CM2 plays a role in efficient virus replication, probably through the addition of a negative charge to the Ser78 phosphorylation site.IMPORTANCE It is well-known that many host and viral proteins are posttranslationally modified by phosphorylation, which plays a role in the functions of these proteins. In influenza A and B viruses, phosphorylation of viral proteins NP, M1, NS1, and the nuclear export protein (NEP), which are not integrated into the membranes, affects the functions of these proteins, thereby affecting virus replication. However, it was reported that phosphorylation of the influenza A virus M2 ion channel protein, which is integrated into the membrane, has no effect on virus replication in vitro or in vivo We previously demonstrated that the influenza C virus CM2 ion channel protein is modified by N-glycosylation, oligomerization, palmitoylation, and phosphorylation and have analyzed the effects of these modifications, except phosphorylation, on virus replication. This is the first report demonstrating that phosphorylation of the influenza C virus CM2 ion channel protein, unlike that of the influenza A virus M2 protein, plays a role in virus replication.

Ectopic Opening of the Common Bile Duct Accompanied by Choledochocele and Pancreas Divisum.

A 32-year-old woman was referred due to abdominal pain and elevated liver enzymes. Computed tomography and magnetic resonance imaging showed ectopic opening of the common bile duct (CBD) into the duodenal bulb. Esophagogastroduodenoscopy showed a hemispheric bulge in the duodenal bulb. Endoscopic retrograde cholangiopancreatography (ERCP) revealed the bulge to be cystic dilatation of the CBD. ERCP also showed no communication between the ventral and dorsal pancreatic ducts. We diagnosed the patient with ectopic opening of the CBD accompanied by choledochocele and pancreas divisum. Endoscopic incision was performed for the treatment of the choledochocele. The patient's symptoms and elevated liver enzymes improved after treatment.

IgG4-unrelated type 1 autoimmune pancreatitis.

A 50-year-old male was referred to our hospital for the evaluation of hyperproteinemia. Fluorodeoxyglucose positron emission tomography revealed high fluorodeoxyglucose uptake in the pancreas, bilateral lacrimal glands, submandibular glands, parotid glands, bilateral pulmonary hilar lymph nodes, and kidneys. Laboratory data showed an elevation of hepatobiliary enzymes, renal dysfunction, and remarkably high immunoglobulin (Ig) G levels, without elevated serum IgG4. Abdominal computed tomography revealed swelling of the pancreatic head and bilateral kidneys. Endoscopic retrograde cholangiopancreatography showed an irregular narrowing of the main pancreatic duct in the pancreatic head and stricture of the lower common bile duct. Histological examination by endoscopic ultrasonography-guided fine-needle aspiration revealed findings of lymphoplasmacytic sclerosing pancreatitis without IgG4-positive plasma cells. Abnormal laboratory values and the swelling of several organs were improved by the treatment with steroids. The patient was diagnosed as having type 1 autoimmune pancreatitis (AIP) based on the International Consensus Diagnostic Criteria. Therefore, we encountered a case of compatible type 1 AIP without elevated levels of serum IgG4 or IgG4-positive plasma cells. This case suggests that AIP phenotypes are not always associated with IgG4.

Epstein-Barr virus in the enlarged salivary tissues of patients with IgG4-related disease.

OBJECTIVE: Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized disease entity characterized by high-serum IgG4 concentration and IgG4-producing plasma cell production with fibrotic or sclerotic changes in affected organs. We aimed to clarify the roles of Epstein-Barr virus (EBV) in patients with IgG4-RDs. STUDY DESIGN AND SETTING: A retrospective clinical study at the Yamagata University School of Medicine, Yamagata, Japan. METHODS: The patient group consisted of four males and four females with an average age of 62 years (range: 48-73). Expression of IgG4, latent member protein 1, EBV nuclear antigens-2, and EBV-encoded RNA in affected salivary glands from patients with IgG4-RD was examined by using immunohistochemistry and in situ hybridization. The copy number of EBV DNA in the salivary glands was also investigated by real-time polymerase chain reaction. RESULTS: All patients had hard masses in the salivary or lacrimal glands, or both, bilaterally. Serum concentrations of IgG4 were elevated in all cases (mean 589.1, range 129-1750), and IgG4-positive plasmacytes were observed in the involved salivary glands. Four patients developed potentially life-threatening systemic involvement after initial salivary gland swelling. EBV-associated molecules (EBNA and EBER) were overexpressed in the affected salivary glands. The copy number of EBV DNA was significantly higher in patients with potentially life-threatening systemic involvement than in patients without systemic involvement (P < 0.05). CONCLUSION: These results suggest that the copy number of EBV DNA could be useful as diagnostic findings in IgG4-RD to predict potentially life-threatening systemic involvement. LEVEL OF EVIDENCE: 4.

The serine protease inhibitor camostat inhibits influenza virus replication and cytokine production in primary cultures of human tracheal epithelial cells.

BACKGROUND: Serine proteases act through the proteolytic cleavage of the hemagglutinin (HA) of influenza viruses for the entry of influenza virus into cells, resulting in infection. However, the inhibitory effects of serine protease inhibitors on influenza virus infection of human airway epithelial cells, and on their production of inflammatory cytokines are unclear. METHODS: Primary cultures of human tracheal epithelial cells were treated with four types of serine protease inhibitors, including camostat, and infected with A/Sendai-H/108/2009/(H1N1) pdm09 or A/New York/55/2004(H3N2). RESULTS: Camostat reduced the amounts of influenza viruses in the supernatants and viral RNA in the cells. It reduced the cleavage of an influenza virus precursor protein, HA0, into the subunit HA1. Camostat also reduced the concentrations of the cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α in the supernatants. Gabexate and aprotinin reduced the viral titers and RNA levels in the cells, and aprotinin reduced the concentrations of TNF-α in the supernatants. The proteases transmembrane protease serine S1 member (TMPRSS) 2 and HAT (human trypsin-like protease: TMPRSS11D), which are known to cleave HA0 and to activate the virus, were detected at the cell membrane and in the cytoplasm. mRNA encoding TMPRSS2, TMPRSS4 and TMPRSS11D was detectable in the cells, and the expression levels were not affected by camostat. CONCLUSIONS: These findings suggest that human airway epithelial cells express these serine proteases and that serine protease inhibitors, especially camostat, may reduce influenza viral replication and the resultant production of inflammatory cytokines possibly through inhibition of activities of these proteases.

Bismuth classification is associated with the requirement for multiple biliary drainage in preoperative patients with malignant perihilar biliary stricture.

BACKGROUND: Single preoperative biliary drainage for malignant perihilar biliary stricture occasionally fails to control jaundice and cholangitis. Multiple biliary drainage is required in such cases, but their clinical background is unclear. We determined the clinical characteristics associated with the requirement for multiple biliary drainage. METHODS: The consecutive 122 patients with malignant perihilar biliary stricture were enrolled in a single-center retrospective study. Preoperative biliary drainage was initially performed on the future remnant hepatic lobe. Additional drainage was performed if jaundice failed to improve or cholangitis developed in undrained hepatic lobes. Detailed clinical characteristics and the number of preoperative biliary drainage procedures required before operation were analyzed. RESULTS: Thirty-one patients (25.4%) initially underwent multiple biliary drainage. However, 69 (56.7%) required multiple biliary drainage by the time of the operation. In the univariate analysis, the initial serum bilirubin level, cholangitis, percutaneous portal vein embolization, history of inserted endoscopic biliary stenting, length of preoperative period, operative procedure, and Bismuth classification were significant factors. In the multivariate analysis using these factors, Bismuth classification was independently associated with the requirement for multiple biliary drainage. The number of patients who required multiple biliary drainage was higher in those with Bismuth-II (91.9%), Bismuth-IIIa (65.7%), and Bismuth-IV (92.9%) than in those with Bismuth-I (22.2%) and Bismuth-IIIb (18.2%). CONCLUSIONS: Patients with Bismuth-II, Bismuth-IIIa, and Bismuth-IV are at higher risk for multiple biliary drainage. A strategy based on the Bismuth classification for performing preoperative biliary drainage is important for patients with malignant perihilar biliary stricture.

Molecular epidemiology of enterovirus 71 strains isolated from children in Yamagata, Japan, between 1990 and 2013.

Enterovirus 71 infections have become a major public issue in the Asia-Pacific region due to the large number of fatal cases. To clarify the longitudinal molecular epidemiology of enterovirus 71 (EV71) in a community, we isolated 240 strains from children, mainly with hand-foot-and-mouth diseases, between 1990 and 2013 in Yamagata, Japan. We carried out a sequence analysis of the VP1 region (891 bp) using 223 isolates and identified six subgenogroups (B2, B4, B5, C1, C2 and C4) during the study period. Subgenogroups C1 and B2 were found only between 1990 and 1993 and have not reappeared since. In contrast, strains in subgenogroups C2, C4 and B5 appeared repeatedly with genomic variations. Recent reports from several local communities in Japan have suggested that identical predominant subgenogroup strains, which have also been found in the Asia-Pacific region, have been circulating in a wide area in Japan. However, it is likely that there is a discrepancy between the major subgenogroups circulating in the Asia-Pacific region and those in Europe. It is necessary to continue the analysis of the longitudinal epidemiology of EV71 in local communities, as well as on regional and global levels, to develop strategies against severe EV71 infections.

Quantitative analyses of schizophrenia-associated metabolites in serum: serum D-lactate levels are negatively correlated with gamma-glutamylcysteine in medicated schizophrenia patients.

The serum levels of several metabolites are significantly altered in schizophrenia patients. In this study, we performed a targeted analysis of 34 candidate metabolites in schizophrenia patients (n = 25) and compared them with those in age- and gender-matched healthy subjects (n = 27). Orthogonal partial least square-discriminant analysis revealed that complete separation between controls and patients was achieved based on these metabolites. We found that the levels of γ-glutamylcysteine (γ-GluCys), linoleic acid, arachidonic acid, D-serine, 3-hydroxybutyrate, glutathione (GSH), 5-hydroxytryptamine, threonine, and tyrosine were significantly lower, while D-lactate, tryptophan, kynurenine, and glutamate levels were significantly higher in schizophrenia patients compared to controls. Using receiver operating characteristics (ROC) curve analysis, the sensitivity, specificity, and the area under curve of γ-GluCys, a precursor of GSH, and D-lactate, a terminal metabolite of methylglyoxal, were 88.00%, 81.48%, and 0.8874, and 88.00%, 77.78%, and 0.8415, respectively. In addition, serum levels of D-lactate were negatively correlated with γ-GluCys levels in patients, but not in controls. The present results suggest that oxidative stress-induced damage may be involved in the pathogenesis of schizophrenia.

Effect of cysteine mutations in the extracellular domain of CM2 on the influenza C virus replication.

CM2 is the second membrane protein of influenza C virus and possesses three conserved cysteines at residue 1, 6 and 20 in its extracellular domain, all of which are involved in the formation of disulfide-linked oligomers of the molecule. In the present study, to examine the effect of CM2 oligomerization on virus replication, we generated a mutant recombinant virus, rC1620A, in which all three cysteines on CM2 were substituted to alanines. The rC1620A virus was more attenuated than the recombinant wild-type (rWT) virus in cultured cells. The CM2 protein synthesized in rC1620A-infected cells could not apparently be detected as a tetramer and was transported to the cell surface less efficiently than was authentic CM2. The amount of CM2 protein incorporated into the rC1620A virions was comparable to that into the rWT virions, although the main CM2 species in the rC1620A virions was in the form of a dimer. Analyses of one-step grown virions and virus-infected cells could not provide evidence for any difference in growth between rC1620A and rWT. On the other hand, the amount of genome present in VLPs possessing the mutant CM2 (C1620A-VLPs) was approximately 31% of that in VLPs possessing wild-type CM2 (WT-VLPs). The incoming genome from VLPs was less efficiently transported to the nucleus in the C1620A-VLP-infected cells than in WT-VLP-infected cells, leading to reduced reporter gene expression in the C1620A-VLP-infected cells. Taken together, these findings demonstrate that CM2 oligomerization affects the packaging and uncoating processes. Thus, we concluded that disulfide-linked CM2 oligomers facilitate virus growth by affecting the replication processes.

Intrinsic temperature sensitivity of influenza C virus hemagglutinin-esterase-fusion protein.

Influenza C virus replicates more efficiently at 33°C than at 37°C. To determine whether hemagglutinin-esterase-fusion protein (HEF), a surface glycoprotein of influenza C virus, is a restricting factor for this temperature sensitivity, we analyzed the biological and biochemical properties of HEF at 33°C and 37°C. We found that HEF exhibits intrinsic temperature sensitivities for surface expression and fusion activity.

Palmitoylation of CM2 is dispensable to influenza C virus replication.

CM2 is the second membrane protein of influenza C virus. The significance of the posttranslational modifications of CM2 remains to be clarified in the context of viral replication, although the positions of the modified amino acids on CM2 have been determined. In the present study, using reverse genetics we generated rCM2-C65A, a recombinant influenza C virus lacking CM2 palmitoylation site, in which cysteine at residue 65 of CM2 was mutated to alanine, and examined viral growth and viral protein synthesis in the recombinant-infected cells. The rCM2-C65A virus grew as efficiently as did the parental virus in cultured HMV-II cells as well as in embryonated chicken eggs. The synthesis and biochemical features of HEF, NP, M1 and mutant CM2 in the rCM2-C65A-infected HMV-II cells were similar to those in the parental virus-infected cells. Furthermore, membrane flotation analysis of the infected cells revealed that equal amount of viral proteins was recovered in the plasma membrane fractions of the rCM2-C65A-infected cells to that in the parental virus-infected cells. These findings indicate that defect in palmitoylation of CM2 does not affect transport and maturation of HEF, NP and M1 as well as CM2 in virus-infected cells, and palmitoylation of CM2 is dispensable to influenza C virus replication.