Accumulation of high levels of the p53 and p130 growth-suppressing proteins in cell lines stably over-expressing cyclin-dependent kinase 6 (cdk6)

Cyclin-dependent kinase 6(cdk6) is present in randomly proliferating cultures of 3T3 cells but has little detectable enzymatic activity. Significant activity is detected only during a short period in early G1 phase. To examine the possible functions of cdk6 in 3T3 cells, lines stably over-expressing cdk6 were constructed and compared to normal 3T3 cells or cell lines with reduced cdk6 levels due to expression of a dominant-negative form of the protein. Over-expression of cdk6 in cells, which led to high levels of activity even in proliferating cultures, had dramatic effects. Cell lines stably over-expressing wild-type cdk6 had a markedly reduced growth rate compared to parental 3T3 cells or lines expressing a dominant-negative form of cdk6. They also over-produced the p53 and p130 proteins and had increased sensitivity to UV-irradiation. Irradiation resulted in accumulation of the Bax protein and rapid cell death. Levels of p53 and p130 proteins were down-regulated and the growth rate of the cells was increased by introduction of the dominant-negative form of cdk6 into cells over-expressing cdk6, indicating that cdk6 is involved in the overproduction of p53 and p130. The results suggest that cdk6, through regulation of growth-suppressing molecules, may play a role in halting cellular growth when proliferation is inappropriate.

Effect of a combined administration of 5-fluorouracil and medroxyprogesterone acetate on pyrimidine nucleoside phosphorylases and thymidylate synthetase in 7,12-dimethylbenz

The effect of a combined therapy of medroxyprogesterone acetate (MPA) and 5-fluorouracil (5-FU) on tumor size, pyrimidine nucleoside phosphorylase (PyNPase) activity, and thymidylate synthetase (TS) activity was examined in Sprague-Dawley (SD) rats with 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors. MPA augmented the antitumor activity of 5-FU and protected against body weight-loss due to 5-FU administration. PyNPase activity of both the MPA group and the MPA+5-FU group tended to increase compared with that of the 5-FU alone group. TS inhibition levels in the MPA+5-FU group tended to increase compared with those in the 5-FU alone group. These results indicate that MPA tended to augment antitumor activity of 5-FU and to reduce the side effects caused by 5-FU.

Effects of a novel hepatoprotective drug, ZNC-2381, on fas-induced hepatocellular caspase-3 activity and apoptosis in mice

We examined the effects of ZNC-2381 (1-(4-aminophenyl)methyl-3-(3-nitrophenyl)-1,3-dihydroimidazo[4,5-b] pyridine-2-one), a new oral hepatoprotective agent, on hepatocellular caspase-3 activity and apoptosis induced by anti-mouse Fas antibody (anti-Fas ab) in mice. Oral ZNC-2381, administered at doses of 10, 30 and 100 mg/kg 1 h before inducing hepatic injury with anti-Fas ab, dose-dependently inhibited the increase in serum alanine aminotransferase (s-ALT) activity 8 h after injection of anti-Fas ab. Increases in DNA fragmentation (nucleosome assay) and caspase-3 activity in the liver 2 h after injection of anti-Fas ab were also inhibited by ZNC-2381 in a dose-dependent manner. As shown by histopathological examination, ZNC-2381 dose-dependently inhibited the appearance of TUNEL-positive apoptotic cells in the liver. Moreover, in studies in vitro, ZNC-2381 (1- 100 micromol/l) concentration-dependently inhibited increases in DNA fragmentation and caspase-3 activity caused by anti-Fas ab in isolated mouse hepatocytes. N- Acetyl-Asp-Glu-Val-Asp aldehyde (Ac-DEVD-cho), a caspase-3-specific inhibitor, inhibited hepatocellular apoptosis caused by anti-Fas ab both in vivo and in vitro, as well as the increase in s-ALT activity in vivo. These results demonstrate that orally administered ZNC-2381 inhibits hepatocellular apoptosis induced by anti-Fas ab and presents the progression of hepatic injury. We propose that the mechanism of action of ZNC-2381 may involve blockade of the signal transduction pathway (caspase-3) of apoptosis mediated by anti-Fas ab.

Thymoma. Analysis of prognostic factors

OBJECTIVE

We evaluated the prognostic factors for thymoma that remain controversial.

METHODS

We studied 72 consecutive patients treated for thymoma during the period between 1966 and 1997. Recurrence-free interval rates and overall survival rates calculated by the Kaplan-Meier method were compared using log-rank test by the Masaoka stage, extent of surgical resection, histology, or associated disease(s). Multivariate analysis was performed using Cox's proportional hazards model.

RESULTS

Thirty-two thymomas were at Masaoka stage I, 9 at stage II, 15 at stage III, and 16 were at stage IV. There were 56 complete resections, 7 incomplete resections (2 at stage III and 5 at stage IV), and 9 biopsies (1 at stage III and 8 at stage IV). Forty-one thymomas were cortical, 16 medullary, and 15 were mixed form. Association of myasthenia gravis was found in 20 patients, and pure red cell aplasia in 7. After an average follow-up period of 103 months, the recurrence-free 5-, 10-, 15-year interval rate was 89%, 80%, 80%, respectively, and overall 5-, 10-, 15-year survival rate was 86%, 71%, 59%, respectively. Factors influencing the recurrence-free interval and overall survival included the Masaoka stage, extent of surgical resection, and association with pure red cell aplasia. Multivariate analysis revealed stage IV tumor and association with pure red cell aplasia as risk factors for recurrence. Pure red cell aplasia indicated poor prognosis for overall survival.

CONCLUSIONS

Masaoka stage, extent of surgical resection, and association with pure red cell aplasia were prognostic factors for thymoma. Multidisciplinary treatment for stage IV tumors and better control of pure red cell aplasia, if associated, should be investigated.

Enhanced hepatic lipid peroxidation in patients with primary biliary cirrhosis

OBJECTIVE

The mechanisms responsible for hepatic injury have not been fully clarified in primary biliary cirrhosis (PBC). It has recently been suggested that hepatic lipid peroxidation may be involved in the pathogenesis of PBC. The aims of the current study were to determine whether patients with PBC have evidence of enhanced hepatic lipid peroxidation and to evaluate its relationship to clinicopathological features.

METHODS

Immunohistochemical detection of 4-hydroxynonenal (HNE) protein adducts was performed in the liver biopsies of 20 patients with PBC. Histological stages of PBC were evaluated. Orcein or Victoria blue staining was performed for detection of copper-associated proteins. The size of bile ducts was defined as the smallest diameter between the subepithelial basement membranes.

RESULTS

All 20 patients had immunodetectable HNE protein adducts in the cytoplasm of damaged, but also intact, biliary cells. The mean diameter of bile ducts with HNE protein adducts was smaller than those without the adducts (61.0 +/- 1.9 vs 122.5 +/- 24.4 microm, respectively, p < 0.01). Out of 20 patients, 6 (30%) also had immunodetectable HNE protein adducts in hepatocytes preferentially located around the portal tracts. Most of the patients with hepatocytic HNE protein adducts had copper-associated protein granules in hepatocytes around the portal tracts and were classified as histological stage 3, whereas all of the patients without the adducts lacked copper-associated protein granules and were classified as histological stage 1 or 2. The patients with hepatocytic HNE protein adducts had higher levels of serum total bilirubin than did those without the adducts (2.9 +/- 0.9 vs 0.7 +/- 0.1 mg/dl, respectively, p < 0.01).

CONCLUSIONS

Hepatic lipid peroxidation can occur in PBC and may be an early event in bile duct destruction. At advanced stages of PBC, hepatocellular lipid peroxidation may play a role in hepatocyte injury during cholestasis.

Analysis of risk factors in bronchopleural fistula after pulmonary resection for primary lung cancer

OBJECTIVES

Despite the advances in surgical technology, bronchopleural fistulas (BPFs) still occur and are often fatal. We studied the risk factors for BPF formation after lung cancer operation to clarify the indication of preventive bronchial stump coverage. In addition, the reliability of our methods of bronchial closure was evaluated.

METHODS

We reviewed 557 consecutive bronchial stumps, corresponding to 547 patients without any coverage in pulmonary resection for lung cancer between 1989 and 1998. According to nine variables, stumps that made dehiscence were compared with uneventful ones using contingency table analysis. The incidence of BPFs according to each method of bronchial closure was calculated.

RESULTS

BPFs developed in ten patients (1.8%). Compared with the lobar bronchus (LB), the main bronchus (MB; P<0.01; odds ratio, 23.0) and the intermediate bronchus (IB; P=0.03; odds ratio, 10.7) carried a high risk. Previous ipsilateral thoracotomy (P<0.01; odds ratio, 37.9) and preoperative chemotherapy and/or radiotherapy (P=0.02; odds ratio, 13.2) increased the risk. The incidence of BPFs with manual suture, stapling devices only, reinforcement suture at the distal side of staplers, or reinforcement suture at the proximal side of staplers was 1.8, 5.0, 1.9 and 1.0%, respectively.

CONCLUSIONS

The main and intermediate bronchial stumps, and the stumps in cases with previous ipsilateral thoracotomy or receiving induction therapy are prone to BPFs. Preventive coverage should be considered for these stumps. Our methods for reinforcement of stapled stumps are thought to be reliable.

[The effects of human atrial natriuretic peptide on the pediatric recipients of living-related renal transplantation]

We evaluated the effects of human natriuretic peptide (hANP) on the recipients of living-related renal transplantation in children. Anesthesia was maintained with nitrous-oxide and isoflurane in oxygen. The recipients were divided into two groups: the hANP group (n = 8) received continuous infusion of hANP (0.1 microgram.kg-1.min-1), and the control group (n = 5) received no hANP infusion. Intravenous hANP infusion was started at the loading time of fresh frozen plasma in the recipients until the 12 hours after operation. There were no differences between the groups with regards to age, height, body weight, changes in heart rate and systolic arterial pressure, urine volume during operation, and the levels of blood uremic nitrogen and creatinine. The hANP group showed minimal change in CVP during operation and body weight between the values during and after operation compared with control group. The control group needed significantly more fluid than hANP group during operation. We concluded that continuous i.v. hANP infusion in the pediatric recipients of living-related renal transplantation was useful for maintaining sufficient urination and prevention of heart failure or lung edema.

Dual nature of the distal histidine residue in the autoxidation reaction of myoglobin and hemoglobin comparison of the H64 mutants

The oxygenated form of myoglobin or hemoglobin is oxidized easily to the ferric met-form with generation of the superoxide anion. To make clear the possible role(s) of the distal histidine (H64) residue in the reaction, we have carried out detailed pH-dependence studies of the autoxidation rate, using some typical H64 mutants of sperm whale myoglobin, over the wide range of pH 5-12 in 0.1 M buffer at 25 degrees C. Each mutation caused a dramatic increase in the autoxidation rate with the trend H64V >/= H64G >/= H64L >> H64Q > H64 (wild-type) at pH 7.0, whereas each mutant protein showed a characteristic pH-profile which is essentially different from that of the wild-type or native sperm whale MbO2. In particular, all the mutants have lost the acid-catalyzed process that can play a dominant role in the autoxidation reaction of most mammalian myoglobins or hemoglobins. Kinetic analyses of various types of pH-profiles lead us to conclude that the distal histidine residue can play a dual role in the nucleophilic displacement of O2- from MbO2 or HbO2 in protic, aqueous solution. One is in a proton-relay mechanism via its imidazole ring, and the other is in the maximum protection of the FeO2 center against a water molecule or an hydroxyl ion that can enter the heme pocket from the surrounding solvent.

Stable expression of Epstein-Barr virus BZLF-1-encoded ZEBRA protein activates p53-dependent transcription in human Jurkat T-lymphoblastoid cells

Interaction between viral proteins and tumor suppressor p53 is a common mechanism of viral pathogenesis. The Epstein-Barr virus (EBV) BZLF-1 ORF-encoded ZEBRA protein (also denoted EB1, Z, Zta) binds to p53 in vitro and has been associated with the altered transcription of p53-regulated genes in B lymphocytes and epithelial cells. In this work, Jurkat T-lymphoblastoid cells that express ZEBRA were characterized by the use of transiently transfected p53 and p53 reporter genes. Stable expression of ZEBRA was associated with the activation of p53-dependent transcription and increased p53 dependent apoptotic cell death. In Jurkat cell lines, stably expressed ZEBRA protein was apparently localized to the cell cytoplasm, in contrast to the typical nuclear localization of this protein in other cell types. Previous studies have suggested that EBV infection of T lymphocytes may contribute to the malignant transformation of T cells and the increased replication of human immunodeficiency virus. Our observations suggest a mechanism through which ZEBRA protein expressed in human T lymphocytes could alter T-cell proliferation and apoptosis during EBV infection. (Blood. 2000;96:625-634)

Fatigue behavior of the zinc-phosphate cement layer

PURPOSE

Fatigue behavior of luting cement film between model fixed partial dentures (FPD) and their dies was investigated to gain a better understanding of the mechanical properties of zinc-phosphate cement.

MATERIALS AND METHODS

Fifty-six brass dies were made, half of them with grooves and half without grooves. A cantilever FPD for each die was cast in Au-Pd-Ag alloy. Four linear strain gauges were attached to the marginal portions of each retainer. The FPDs were cemented to the dies using zinc-phosphate cement. A fatigue test machine was used to cyclically load the specimens with 50 or 100 N for 5.5 x 10(5) cycles (1 Hz) in 37 degrees C water. During the fatigue test, strain measurements were made after every 0.5 x 10(5) load cycles to discover if strain response was altered. After completion of the fatigue test, ultimate tensile strength of each specimen was measured and statistically analyzed by 2-way analysis of variance.

RESULTS

With or without grooves, strain responses were the same at every periodic strain measurement throughout the 50-N fatigue test. For the 100-N fatigue test, strain responses for the specimens without grooves were different before and after cyclic testing, but there was no difference for the specimens with grooves. There were no significant differences in tensile strength among the specimens after the fatigue tests.

CONCLUSION

No fatigue fracture was observed in zinc-phosphate cement film after repetitive loading. Repetitive loading may improve stress transmission within the zinc-phosphate cement film.

Effects of ZNC-2381, a new oral compound, on several hepatic injury models and on hepatocellular apoptosis in mice and rats

The hepatoprotective effect of ZNC-2381 (1-(4-aminophenyl) methyl-3-(3-nitrophenyl)-1,3-dihydroimidazo[4,5-b]pyridine-2-one), a novel 2-one dihydroimidazopyridine derivative, has been evaluated in several experimental models of hepatic injury. In mice, oral ZNC-2381, administered at doses of 3, 10 or 30 mgkg(-1), 1 h before induction of hepatic injury with concanavalin A, dose-dependently inhibited increases in serum alanine aminotransferase (ALT) activity. Apoptosis of liver cells, as indicated by DNA fragmentation (nucleosome assay) and DNA-ladder formation (electrophoresis), was also inhibited dose-dependently. ZNC-2381 dose-dependently inhibited concanavalin A-induced increases in serum tumour necrosis factor (TNF)-alpha levels, and TNF-alpha mRNA expression in the liver. Oral ZNC-2381 also dose-dependently inhibited increases in serum ALT activity in mice with hepatic injury induced by Propionibacterium acnes and a bacterial lipopolysaccharide (LPS) or D-galactosamine-LPS, and in rats with D-galactosamine-induced hepatic injury. These results indicate that oral ZNC-2381 inhibits cytokine (TNF-alpha) production and cytokine-related hepatocellular apoptosis, and might thus prevent different types of hepatic injury.

[Effects of 4-hydroxybenzoic acid methyl ester on the Ca(2+)-related functions of skinned skeletal muscle fibers from the guinea pig]

The amide-linked local anesthetics can be used safely in patients susceptible to malignant hyperthermia (MH). 4-Hydroxybenzoic acid methyl ester contained as a preservative in local anesthetic solution was suspected to have triggered MH in a patient who had received nerve block with lidocaine solution. The author investigated the effects of 4-hydroxybenzoic acid methyl ester on Ca(2+)-related functions of the skeletal muscle using saponin-treated skinned fibers from the extensor digitorum longus muscle of guinea pigs. 4-Hydroxybenzoic acid methyl ester accelerated the Ca2+ induced Ca2+ release (CICR) rate from the sarcoplasmic reticulum (SR) in a dose-dependent manner, and the Ca2+ concentration-CICR rate curves were shifted to the left with 4-hydroxybenzoic acid methyl ester at concentrations above 30 microM. 30 microM of 4-hydroxybenzoic acid methyl ester is associated with a plasma concentration of lidocaine intoxication which induces general convulsion. Ca2+ uptake, initial rate of Ca2+ uptake by the SR and Ca2+ sensitivity of the contractile system were not affected by 100 microM of 4-hydroxybenzoic acid methyl ester. These results suggest that amide-type local anesthetic solutions and agents containing 4-hydroxybenzoic acid methyl ester as a preservative may trigger MH in MH susceptible patients, if they are accidentally administered into the blood vessel.

Evaluation of portosystemic collaterals by SPECT imaging after endoscopic variceal sclerotherapy: usefulness for predicting recurrence

Bleeding from esophageal varices is a major cause of morbidity and mortality in cirrhotic patients. Identification of patients at high risk for bleeding is particularly important. The aim of this study was to determine whether detection of portosystemic collaterals by SPECT could predict the outcome of endoscopic injection sclerotherapy of esophageal varices and be useful for selecting appropriate therapy.

METHODS

Sixty-two patients with liver cirrhosis who were considered at high risk of bleeding were treated with endoscopic injection sclerotherapy. Endoscopy was performed every 3 mo after therapy or until bleeding occurred. Before and within 2 wk after therapy, tomographic images of intra-abdominal blood pool were constructed by SPECT.

RESULTS

Before therapy, the following portosystemic collateral routes were observed: coronary veins in 53 (85.5%) of 62 patients, short gastric veins in 8 patients (12.9%), splenorenal shunts in 10 patients (16.1%), and paraumbilical veins in 6 patients (9.7%). Patients positive for imaging of coronary veins were divided into 3 groups on the basis of changes in images after therapy: complete responders (n = 17), whose coronary vein images disappeared completely; partial responders (n = 18), whose images became smaller; and nonresponders (n = 18), whose images did not change significantly before or after therapy. The rates of recurrence after endoscopic injection sclerotherapy until 6 mo in complete responders (4/17, 23.5%) and partial responders (7/18, 38.9%) were significantly less (P < 0.05) than that in nonresponders (11/13, 84.6%). The rate of recurrence of esophageal varices until 6 mo in nonresponders treated with additional submucosal injection sclerotherapy (1/5, 20.0%) was significantly less (P < 0.05) than that in nonresponders without additional submucosal injection sclerotherapy (11/13, 84.6%).

CONCLUSION

Abdominal blood-pool SPECT, a noninvasive method, is useful for evaluating the therapeutic effectiveness of endoscopic sclerotherapy, for predicting the recurrence of varices, and for selecting appropriate management after sclerotherapy.

Descending necrotizing mediastinitis with sternocostoclavicular osteomyelitis and partial thoracic empyema: report of a case

We present herein the case of a 50-year-old woman in whom descending necrotizing mediastinitis originating from an anterior neck abscess spread to the left upper bony thorax, resulting in osteomyelitis of the left sternocostoclavicular articulation and left partial thoracic empyema. Transcervical mediastinal irrigation and drainage was performed with aggressive antibiotic therapy, followed by resection of the left sternocostoclavicular joint and debridement of the anterior mediastinum. The patient had an uneventful postoperative course, and her left arm and shoulder mobility was well preserved.

Trends in antimicrobial-drug resistance in Japan

Multidrug resistance in gram-positive bacteria has become common worldwide. In Japan until recently, gram-negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Serratia marcescens were controlled by carbapenems, fluoroquinolones, and aminoglycosides. However, several of these microorganisms have recently developed resistance against many antimicrobial drugs.

["What an ideal clinical microbiological laboratory should be"--from the position of medical technologist]

The evolution of the microbiology laboratory is necessary for correspondence to the transfiguration of infection and contribution to clinical applications. Especially, the correspondence of emergency tests such as smear strain and antigen detection, the report added value and the infection surveillance in team medical treatment are indispensable. Also, medical technologists need to be knowledge able about techniques related to infection overall, and participation in infection diagnosis and social responsibility are indispensable.

[Proceeding of the workshop "What an ideal clinical microbiological laboratory should be". The 33rd in-service training course for medical technologists of university hospitals in 1999]

In the workshop of the 33rd in-service training course for University Hospital Medical Technologists in 1999(sponsorship: the ministry of Education), all groups of participants were charged with discussing an ideal clinical microbiology laboratory. In conclusion, the successful operation of the ideal system of clinical microbiology should require a high level of competence in every staff member of the hospital. It must not be focused solely on the sophistication of laboratory methods. We must modify our behavior effectively and establish a good collaborative partnership with physicians and other health care professionals.

Successful treatment of percutaneous transhepatic papillary dilation in patients with obstructive jaundice due to common bile duct stones after Billroth II gastrectomy: report of two emergent cases

Successful treatment of two patients with obstructive jaundice due to choledocholithiasis after Billroth II gastrectomy was performed by elimination of stones by percutaneous transhepatic balloon dilatation of the sphincter of Oddi. Patient 1 was an 82-year-old man and Patient 2 was a 73-year-old man. Both patients presented with obstructive jaundice. The papilla was not observed in either patient because of previous Billroth II gastrectomy. Because an endoscopic approach was impossible, percutaneous transhepatic cholangiodrainage (PTCD) was performed to alleviate jaundice. Choledocholithiasis was treated as follows: The sphincter of Oddi was dilated by percutaneous transhepatic balloon, and stone particles were removed from the papilla with a stone-eliminating balloon catheter via the same route of PTCD. This method is less invasive than the percutaneous transhepatic cholangioscopic method, and the use of existing appliances such as a balloon for papillary dilation is possible. Hence, this method appears to be an effective and simple method for the treatment of choledocholithiasis after gastrectomy that is difficult to treat endoscopically.

Regulation of estrogen receptor and epidermal growth factor receptor by tamoxifen under high and low estrogen environments in MCF-7 cells grown in athymic mice

The purpose of this study was to investigate whether tamoxifen (TAM) treatment causes a downregulation of estrogen receptor (ER) and whether TAM induces epidermal growth factor receptor-1 (EGFR). We investigated the expression of ER and EGFR after the treatment of TAM in MCF-7 tumors grown in athymic mice under high and low estrogen environments. MCF-7 tumors were grown in ovariectomized athymic mice by implanting a sustained release 17beta-estradiol (E2) pellet. The E2 pellets were removed after 3 weeks of E2 treatment. Animals were then divided into the following 4 groups: i) an E2 (0. 72 mg/pellet) pellet [E2(+)]; ii) an E2 and a TAM (5 mg/pellet) pellets [E2(+)TAM]; iii) no treatment [E2(-)]; iv) a TAM pellet [E2(-)TAM]. A significant reduction in tumor size was observed in the estrogen-depleted group [E2(-) and E2(-)TAM] compared with the estrogen-completed group [E2(+) and E2(+)TAM]. TAM inhibited estrogen-stimulated growth in the estrogen-completed mice. No additional reduction of the tumor by TAM was observed in the estrogen-depleted mice. Both ER and EGFR protein levels in the tumors of the estrogen-depleted mice were higher than in the estrogen-completed mice. Expression of ER and EGFR protein was increased by TAM in the estrogen-completed mice, however it was decreased by TAM in the estrogen-depleted mice. Changes of ER and EGFR protein levels were similar in all treatments. Transforming growth factor-alpha (TGF-alpha) in tumors, which is known as a ligand of EGFR and as an estrogen-inducible protein in ER positive MCF-7 cells, was decreased by TAM in the estrogen-completed mice, by contrast, it was increased by TAM in the estrogen-depleted mice. Downregulation of ER was observed in TAM-treated mice in an estrogen-depleted environment, this action of TAM was similar to E2. These results suggest that increase of EGFR expression does not lead to a loss of ER after short-term TAM treatment in MCF-7 tumors.

Inactivation of NF-kappaB by EBV BZLF-1-encoded ZEBRA protein in human T cells

We have previously shown that the EBV ZEBRA protein (also denoted EB1, Z, or Zta) encoded by the BZLF open reading frame is expressed in primary human thymocytes and in human T lymphoblastoid cell lines infected by EBV. Expression of EBV-encoded gene products in T lymphocytes could contribute to viral pathogenesis during acute EBV infection as well as in individuals coinfected with EBV and HIV. HPB-ALL and Jurkat T lymphoblastoid cell lines transiently and stably expressing ZEBRA were characterized in this work. Expression of ZEBRA protein in human T lymphoblastoid cells was associated with decreased expression of an NF-kappaB reporter gene, altered expression of the NF-kappaB p50 protein subunit, and decreased DNA binding by components of NF-kappaB. These observations suggest that inactivation of NF-kappaB transcription by ZEBRA in EBV-infected T cells may be a novel mechanism of viral pathogenesis analogous in part to over-expression of the endogenous cytoplasmic inhibitor of NF-kappaB, IkappaBalpha.

Characterization of the angR gene of Vibrio anguillarum: essential role in virulence

The ability to utilize the iron bound by high-affinity iron-binding proteins in the vertebrate host is an important virulence factor for the marine fish pathogen Vibrio anguillarum. Virulence in septicemic infections is due to the presence of a highly efficient plasmid-encoded iron transport system. AngR, a 110-kDa protein component of this system, appears to play a role in both regulation of the expression of the iron transport genes fatDCBA and the production of the siderophore anguibactin. Therefore, study of the expression of the angR gene and the properties of its product, the AngR protein, may contribute to the understanding of the mechanisms of virulence of this pathogen. In this work, we present genetic and molecular evidence from transposition mutagenesis experiments and RNA analysis that angR, which maps immediately downstream of the fatA gene, is part of a polycistronic transcript that also includes the iron transport genes fatDCBA and angT, a gene located downstream of angR which showed domain homology to certain thioesterases involved in nonribosomal peptide synthesis of siderophores and antibiotics. In order to dissect the specific domains of AngR associated with regulation of iron transport gene expression, anguibactin production, and virulence, we also generated a panel of site-directed angR mutants, as well as deletion derivatives. Both virulence and anguibactin production were dramatically affected by each one of the angR modifications. In contrast to the need for an intact AngR molecule for anguibactin production and virulence, the regulation of iron transport gene expression does not require the entire AngR molecule, since truncation of the carboxy terminus carrying the nonribosomal peptide synthetase cores, as well as the site-directed mutations, resulted in derivatives that retained their ability to regulate gene expression which was only abolished after truncation of amino-terminal sequences containing helix-turn-helix and leucine zipper motifs and a specialized heterocyclization and condensation domain found in certain nonribosomal peptide synthetases. The evidence, while not rigorously eliminating the possibility that a separate regulatory polypeptide exists and is encoded somewhere within the 5'-end region of the angR gene, strongly supports the idea that AngR is a bifunctional protein and that it plays an essential role in the virulence mechanisms of V. anguillarum. We also show in this study that the angT gene, found downstream of angR, intervenes in the mechanism of anguibactin production but is not essential for virulence or iron transport gene expression.