Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.

Induction of apoptosis by the dsRNA-dependent protein kinase (PKR): mechanism of action

Interferons are a family of cytokines that exerts antiviral, antitumor and immunomodulatory actions by inducing a complex set of proteins. One of the best known IFN-induced protein is the dsRNA-dependent protein kinase (PKR), that mediates both antiviral and anticellular activities. PKR inhibits translation initiation through the phosphorylation of the alpha subunit of the initiation factor eIF-2 (eIF-2 alpha) and also controls the activation of several transcription factors such as NF-kappa B, p53, or STATs. In addition, PKR mediates apoptosis induced by many different stimuli, such as treatment with LPS, TNF-alpha, viral infection, or serum starvation. The mechanism of apoptosis induction by PKR involves phosphorylation of eIF-2 alpha and activation of NF-kappa B. In this way, expression of different genes is regulated by PKR. Among the genes upregulated in response to PKR are Fas, Bax and p53. The pathway of PKR-induced apoptosis involves FADD activation of caspase 8 by a mechanism independent of Fas and TNFR. Since IFNs are used as drugs for different disorders such as viral infection and cancer, understanding the pathway of apoptosis induction triggered by PKR should be useful in the rational design of IFN therapies.

Isolation and characterization of lamellar bodies and tubular myelin from rat lung homogenates

Three surface-active fractions which differ in their morphology have been isolated from rat lung homogenates by ultracentrifugation in a discontinuous sucrose density gradient. In order of increasing density, the fractions consisted, as shown by electron microscopy, primarily of common myelin figures, lamellar bodies, and tubular myelin figures. The lipid of all three fractions contained approximately 94% polar lipids and 2% cholesterol. In the case of the common myelin figures and the lamellar bodies, the polar lipids consisted of 73% phosphatidylcholines, 9% phosphatidylserines and inositols, and 8% phosphatidylethanolamines. In the case of the tubular myelin figures, the respective percentages were 58, 19, and 5. Over 90% of the fatty acids of the lecithins of all three fractions were saturated. Electrophoresis of the proteins of the fractions in sodium dodecyl sulfate or Triton X-100 revealed that the lamellar bodies and the tubular myelin figures differed in the mobilities of their proteins. The common myelin figures, however, contained proteins from both of the other fractions. These data indicate that, whereas the lipids of the extracellular, alveolar surfactant(s) originate in the lamellar bodies, the proteins arise from another source. It is further postulated that the tubular myelin figures represent a liquid crystalline state of the alveolar surface-active lipoproteins.

Alveolar volume-surface area relation in air- and saline-filled lungs fixed by vascular perfusion

The influence of volume changes and interfacial forces on the geometry of peripheral air spaces was studied in excised rabbit lungs inflated with either air or saline and fixed by vascular perfusion at four points of the deflation limb of the pressure-volume curve corresponding to 100, 80, 60, and 40% of the total lung capacity (TLC). In air-filled lungs pleating and folding of alveolar septa were observed, especially in alveolar corners. However, the alveolar surfaces were smooth, except at low lung volumes where some surface crumpling occurred. In saline-filled lungs pleats were absent; the alveolar surface was irregular at all inflation levels due to undulating walls and bulging capillaries. Morphometry indicated that at all alveolar volumes (VA) the surface areas (SA) were larger in saline- than air-filled lungs. No simple mathematical function was found to characterize the relation between SA and VA over the entire volume range studied. Within the range of normal breaths (80 to 40% TLC) the best fit for n in the function SA = k.VnA was 0.58 for saline-filled lungs (r = 0.93) and 0.33 for air-filled lungs (r = 0.68), suggesting different and complex deflation patterns.

A validated three-dimensional computational model of a human knee joint

This paper presents a three-dimensional finite element tibio-femoral joint model of a human knee that was validated using experimental data. The geometry of the joint model was obtained from magnetic resonance (MR) images of a cadaveric knee specimen. The same specimen was biomechanically tested using a robotic/universal force-moment sensor (UFS) system and knee kinematic data under anterior-posterior tibial loads (up to 100 N) were obtained. In the finite element model (FEM), cartilage was modeled as an elastic material, ligaments were represented as nonlinear elastic springs, and menisci were simulated by equivalent-resistance springs. Reference lengths (zero-load lengths) of the ligaments and stiffness of the meniscus springs were estimated using an optimization procedure that involved the minimization of the differences between the kinematics predicted by the model and those obtained experimentally. The joint kinematics and in-situ forces in the ligaments in response to axial tibial moments of up to 10 Nm were calculated using the model and were compared with published experimental data on knee specimens. It was also demonstrated that the equivalent-resistance springs representing the menisci are important for accurate calculation of knee kinematics. Thus, the methodology developed in this study can be a valuable tool for further analysis of knee joint function and could serve as a step toward the development of more advanced computational knee models.

Calmodulin binds to K-Ras, but not to H- or N-Ras, and modulates its downstream signaling

Activation of Ras induces a variety of cellular responses depending on the specific effector activated and the intensity and amplitude of this activation. We have previously shown that calmodulin is an essential molecule in the down-regulation of the Ras/Raf/MEK/extracellularly regulated kinase (ERK) pathway in cultured fibroblasts and that this is due at least in part to an inhibitory effect of calmodulin on Ras activation. Here we show that inhibition of calmodulin synergizes with diverse stimuli (epidermal growth factor, platelet-derived growth factor, bombesin, or fetal bovine serum) to induce ERK activation. Moreover, even in the absence of any added stimuli, activation of Ras by calmodulin inhibition was observed. To identify the calmodulin-binding protein involved in this process, calmodulin affinity chromatography was performed. We show that Ras and Raf from cellular lysates were able to bind to calmodulin. Furthermore, Ras binding to calmodulin was favored in lysates with large amounts of GTP-bound Ras, and it was Raf independent. Interestingly, only one of the Ras isoforms, K-RasB, was able to bind to calmodulin. Furthermore, calmodulin inhibition preferentially activated K-Ras. Interaction between calmodulin and K-RasB is direct and is inhibited by the calmodulin kinase II calmodulin-binding domain. Thus, GTP-bound K-RasB is a calmodulin-binding protein, and we suggest that this binding may be a key element in the modulation of Ras signaling.

Induction of apoptosis by double-stranded-RNA-dependent protein kinase (PKR) involves the alpha subunit of eukaryotic translation initiation factor 2 and NF-kappaB

The double-stranded (ds) RNA-dependent protein kinase (PKR) is a key mediator of antiviral effects of interferon (IFN) and an active player in apoptosis induced by different stimuli. The translation initiation factor eIF-2alpha (alpha subunit of eukaryotic translation initiation factor 2) and IkappaBalpha, the inhibitor of the transcription factor NF-kappaB, have been proposed as downstream mediators of PKR effects. To evaluate the involvement of NF-kappaB and eIF-2alpha in the induction of apoptosis by PKR, we have used vaccinia virus (VV) recombinants that inducibly express PKR concomitantly with a dominant negative mutant of eIF-2alpha or a repressor form of IkappaBalpha. We found that while expression of PKR by a VV vector resulted in extensive inhibition of protein synthesis and induction of apoptosis, coexpression of PKR with a dominant negative mutant of eIF-2alpha (Ser-51-->Ala) reversed both the PKR-mediated translational block and PKR-induced apoptosis. Coexpression of PKR with a repressor form of IkappaBalpha (Ser-32, 36-Ala) also leads to the inhibition of apoptosis by abolishing NF-kappaB induction, while translation remains blocked. Treating cells with two different proteasome inhibitors which block IkappaBalpha degradation, prevented PKR-induced apoptosis, supporting results from coexpression studies. Biochemical analysis and transient assays revealed that PKR expression by a VV vector induced NF-kappaB binding and transactivation. In addition, upregulation of Fas mRNA transcription occurred during PKR activation. Our findings provide direct evidence for the involvement of eIF-2alpha and NF-kappaB in the induction of apoptosis by PKR.

Reduction of annexin-V (placental anticoagulant protein-I) on placental villi of women with antiphospholipid antibodies and recurrent spontaneous abortion

OBJECTIVE

The mechanism by which antiphospholipid antibodies are associated with pregnancy loss and thromboembolic conditions has yet to be elucidated. Annexin-V, an anticoagulant phospholipid-binding protein, is normally present in syncytiotrophoblasts lining the placental villi, where it may play a role in the maintenance of intervillous blood fluidity. We therefore investigated the distribution of annexin-V in placentas of patients with antiphospholipid antibodies in situ and then used short-term villous cultures to study the direct effect of antiphospholipid antibodies on the immunolocation of annexin-V.

STUDY DESIGN

We performed a blinded study by means of computerized morphometric analysis of placental tissues that were stained for annexin-V with affinity-purified polyclonal antibody in an avidin-biotin peroxidase system. The distribution of villous surface annexin-V on cross sections of placentas of patients with antiphospholipid antibodies was compared with that of placentas from patients with uncomplicated pregnancies, elective abortions, and pregnancy losses not associated with antiphospholipid antibodies (n = 8 for each group). We quantitated villous surface annexin-V in cultured placental villi that were incubated with antiphospholipid antibodies immunoglobulin G compared with normal immunoglobulin G and measured annexin-V levels by enzyme-linked immunosorbent assay in conditioned media and in the villi.

RESULTS

The mean villous surface annexin-V of the group with antiphospholipid antibodies was 26.2% +/- 17% (SD) versus 93.9% +/- 5.7% in the normal control group (p < 0.0001). Villi from patients undergoing elective abortions and with pregnancy losses that were not attributed to antiphospholipid antibodies also showed higher mean villous surface annexin-V levels (86.9% +/- 10.6% and 83.5% +/- 11.3%, respectively, p < 0.0001). Organ culture of normal placental villi with affinity-purified immunoglobulin G from patients with antiphospholipid antibodies showed a dose-dependent decrease of villous surface annexin-V over a concentration range of 1.5 micrograms/ml to 1.5 mg/ml. Annexin-V concentrations in conditioned media were significantly lower in the presence of antiphospholipid antibodies immunoglobulin G compared with normal immunoglobulin G (49.4 +/- 8.9 ng/gm wet weight vs 57.2 +/- 11.5 ng/gm, respectively, p < 0.05). In contrast, the mean level of annexin-V in placental villi incubated with antiphospholipid antibodies immunoglobulin G was greater than in villi incubated with normal immunoglobulin G, 1328 +/- 130 ng/gm wet weight versus 1183 +/- 165 ng/gm (p < 0.02).

CONCLUSIONS

Patients with antiphospholipid antibodies and a history of previous pregnancy losses have a significant reduction in annexin-V immunostaining on placental villous surfaces, and antiphospholipid antibodies immunoglobulin G can directly decrease levels of villous surface annexin-V on cultured placental villi. Assays of annexin-V in the conditioned media and cell pellets of cultured placental villi suggest that the mechanism for antiphospholipid antibodies-mediated reduced annexin-V surface staining is an inhibition of annexin-V transport to the villous surface rather than displacement by antiphospholipid antibodies from the surface. This antiphospholipid antibodies-induced deficiency of placental surface annexin-V may contribute to the placental thrombosis observed in these patients.

Bombesin, vasopressin, and endothelin rapidly stimulate tyrosine phosphorylation in intact Swiss 3T3 cells

The mitogenic neuropeptides bombesin and vasopressin markedly increased tyrosine and serine phosphorylation of multiple substrates in quiescent Swiss 3T3 fibroblasts, including two major bands of Mr 90,000 and 115,000. Tyrosine phosphorylation of these proteins was increased as judged by immunoprecipitation of 32Pi-labeled cells and immunoblotting of unlabeled cells with monoclonal antiphosphotyrosine antibodies, elution with phenyl phosphate, and phospho amino acid analysis. Phosphotyrosyl proteins generated by bombesin and vasopressin did not correspond either by apparent molecular weight or by immunological and biochemical criteria to several known tyrosine kinase substrates, including phospholipase C gamma, the microtubule-associated protein 2 kinase, GTPase-activating protein, or phosphatidylinositol kinase. The effect was rapid (within seconds), concentration dependent, and inhibited by specific receptor antagonists for both bombesin and vasopressin. The endothelin-related peptide, vasoactive intestinal contractor, also elicited a rapid and concentration-dependent tyrosine/serine phosphorylation of a similar set of substrates. These results demonstrate that neuropeptides, acting through receptors linked to GTP-binding proteins, stimulate tyrosine phosphorylation of a common set of substrates in quiescent Swiss 3T3 cells and suggest the existence of an additional signal transduction pathway in neuropeptide-induced mitogenesis.

Vaccinia virus E3L protein is an inhibitor of the interferon (i.f.n.)-induced 2-5A synthetase enzyme

Induction of apoptosis in mammalian cells by double-stranded (ds) RNA-dependent enzymes, protein kinase (PKR), and 2-5A-synthetase/RNase L (referred to as the 2-5A system) might be a mechanism mediating anticellular and antiviral actions of interferon (i.f.n.). To counteract the effect of i.f.n., animal viruses have acquired genes that block specific i.f.n. pathways. Among poxviruses, vaccinia virus (VV) encodes E3L, a dsRNA-binding protein, which inhibits activation of i.f.n.-induced PKR. It has been proposed that E3L might also block activation of the 2-5A system, but direct proof is lacking. To establish if E3L inhibits the 2-5A system, we have developed a method to assay apoptosis induced by increased production of enzymes in the 2-5A pathway, as well as of their putative modulators. This assay is based on the use of cells derived from homozygous PKR knockout mice (Pkr-/-) infected with a VV mutant lacking E3L (delta E3L) and transiently transfected with a luciferase reporter gene together with plasmid vectors expressing 2-5A-synthetase, RNase L, or E3L, all controlled by the same inducible promoter. We found that expression of 2-5A-synthetase inhibited luciferase activity in a dose-response manner, reaching inhibition values of 80% relative to transfections with control plasmids. Similar results were obtained by transfection with an RNase L vector, although in this case the extent of inhibition was further enhanced upon coexpression of 2-5A-synthetase and RNase L. Inhibition of protein synthesis mediated by the 2-5A system correlated well with induction of apoptosis. Transfection of cells with a plasmid vector expressing E3L together with 2-5A-synthetase completely prevented apoptosis induced by this enzyme. We conclude that VV E3L acts as an inhibitor of the i.f.n.-induced 2-5A-synthetase enzyme.

Causes of death amongst French patients with amyotrophic lateral sclerosis: a prospective study

BACKGROUND AND PURPOSE

To prospectively investigate causes of death and the circumstances surrounding death in 302 patients with amyotrophic lateral sclerosis (ALS). The functional status of patients immediately before death was also determined.

METHODS

Information was obtained from neurologists at ALS centres, patients' files, and, when deaths occurred outside a medical facility, attending physicians.

RESULTS

Most patients (63%) died in a medical facility. The most frequently reported cause of death was respiratory failure (77%), including terminal respiratory insufficiency (58%), pneumonia (14%), asphyxia due to a foreign body (3%) and pulmonary embolism (2%). Ten per cent of patients died from other causes: post-surgical or traumatic conditions (5%), cardiac causes (3.4%), suicide (1.3%) and sudden death of unknown origin (0.7%). The cause of death could not be determined in 13% of cases (6% inside a medical facility and 25% outside). At the time of death, only 55% of patients were receiving riluzole, 33% were undergoing non-invasive ventilation, 3% had a tracheotomy and 37% a gastrostomy.

CONCLUSION

The information provided by this study helps to improve our understanding of the natural history of the disease and may help optimize the quality of care we can offer patients at the end of life.

Activation of NF-kappa B by the dsRNA-dependent protein kinase, PKR involves the I kappa B kinase complex

Besides its known role as a translational controlling factor, the double stranded RNA-dependent protein kinase (PKR) is a key transcriptional regulator exerting antiviral and antitumoural activities. We have recently described that induction of NF-kappa B by PKR is involved in apoptosis commitment. To define how PKR mediates NF-kappa B activation by dsRNA, we have used two different approaches, one based on expression of PKR by a vaccinia virus (VV) recombinant and the other based on induction of endogenous PKR by poly I:C (pIC) treatment. We found that NF-kappa B complexes induced by PKR are composed primarily of p50-p65 heterodimers and also of c-rel-p50 heterodimers. As described for other stimuli, following pIC treatment, PKR phosphorylates the NF-kappa B inhibitor I kappa B alpha at serine 32 before degradation. Expression by VV recombinants of IKK1 or IKK2 dominant negative mutants together with PKR showed inhibition of PKR-induced NF-kappa B activation, as measured both by gel shift and luciferase reporter assays. Immunoprecipitation analysis revealed that PKR interacts with the IKK complex. Our findings demonstrate that physiological function(s) of PKR involve activation of the I kappa B kinase complex. Oncogene (2000) 19,1369 - 1378.

A morphometric study of the carotid body in chronically hypoxic rats

We performed morphometric studies of carotid body in acutely and chronically hypoxic rats (inspired PO2 = 70 Torr, at sea level). Acute exposure was for the duration of about 10 min, and chronic exposure lasted for 28 days. We confirmed that the total volume of the organ increased by severalfold. At the light-microscopy level we found an enlargement of the volume density of the blood sinuses from 14 to 31% due to chronic hypoxia. The morphometric hematocrit increased from 39 to 70% paralleling changes in the conventionally measured venous hematocrit. These data do not show any specific plasma skimming in the carotid body blood vessels. With the electron microscope we found that the mean average volume of type I cells increased from 320 micron3 in controls to 1,120 micron3 in the chronically hypoxic rats without hyperplasia, whereas type II cells had increased in number without alteration in size. Qualitative observations revealed that the normal appearance of clusters of ovoid type I cells interspersed by capillaries had been transformed into a pattern of individual cells forming plates between expanded blood vessels with a large increase of contact area between the cells and vessels. Type II cells appeared to have proliferated without changes in individual size to cover the enlarged periphery of type I cells. The observed structural changes in the carotid body parenchyma and vasculature appear to be physiologically adaptive and provide further support for the idea that various elements in the organ are particularly sensitive to hypoxia.

Activation of caspases occurs downstream from radical oxygen species production, Bcl-xL down-regulation, and early cytochrome C release in apoptosis induced by transforming growth factor beta in rat fetal hepatocytes

Most of the morphologic changes that are observed in apoptotic cells are caused by a set of cysteine proteases (caspases) that are activated during this process. In previous works from our group we found that treatment of rat fetal hepatocytes with transforming growth factor beta1 (TGF-beta1) is followed by apoptotic cell death. TGF-beta1 mediates radical oxygen species (ROS) production that precedes bcl-xL down-regulation, loss of mitochondrial transmembrane potential, release of cytochrome c, and activation of caspase-3 (Herrera et al., FASEB J 2001;15:741-751). In this work, we have analyzed how TGF-beta1 activates the caspase cascade and whether or not caspase activation precedes the oxidative stress induced by this factor. Our results show that TGF-beta1 activates at least caspase-3, -8, and -9 in rat fetal hepatocytes, which are not required for ROS production, glutathione depletion, bcl-xL down-regulation, and initial cytochrome c release. However, caspase activation mediates cleavage of Bid and Bcl-xL that could originate an amplification loop on the mitochondrial events. An interesting result is that transmembrane potential disruption occurs later than the initial cytochrome c release and is mostly blocked by the pan-caspase inhibitor Z-VAD.fmk, indicating that the decrease in mitochondrial transmembrane potential (Delta(Psi)m) may be a consequence of caspase activity rather than the mechanism by which TGF-beta induces cytochrome c efflux. Finally, although Z-VAD.fmk completely blocks nucleosomal DNA fragmentation, it only delays cell death, which suggests that activation of the apoptotic program by TGF-beta in fetal hepatocytes inevitably leads to death, with or without caspases.

The GU-MACH study: the effect of 1-week omeprazole triple therapy on Helicobacter pylori infection in patients with gastric ulcer

AIMS

To study the efficacy of omeprazole triple therapy in the eradication of Helicobacter pylori in patients with active gastric ulcer, and to assess healing and relapse of gastric ulcer.

METHODS

A double-blind, randomized study was carried out in 18 centres in Germany, Hungary and Poland. Patients (n = 160) with gastric ulcer and a positive H. pylori screening test were randomized to a 7-day twice daily treatment with omeprazole 20 mg, clarithromycin 500 mg and amoxycillin 1000 mg (OAC) or omeprazole 20 mg, clarithromycin 250 mg and metronidazole 400 mg (OMC), or with omeprazole 20 mg once daily (O). After completion of this 1-week treatment, patients were treated with omeprazole until healing (maximum 12 weeks), and followed for 6 months. H. pylori was assessed by urea breath test (UBT) and histology.

RESULTS

Eradication rates ITT were OAC 79% (95% CI: 65-90%), OMC 86% (95% CI: 73-94%) and O 4% (95% CI: 0-14%). Eradication rates PP were OAC 83% (95% CI: 68-93%), OMC 93% (95% CI: 80-98%) and O 3% (95% CI: 0-13%). Gastric ulcer relapses occurred in 5, 0 and 11 patients in the groups, respectively.

CONCLUSIONS

The results from the study demonstrate that OMC and OAC 1-week regimens are safe and effective for eradication of H. pylori in gastric ulcer patients, and that ulcer relapse is infrequent after successful eradication.

Aspirin induces apoptosis through mitochondrial cytochrome c release

Aspirin and other non-steroidal anti-inflammatory drugs induce apoptosis in many cell types. Although the involvement of caspases has been demonstrated, the mechanism leading to caspase activation remains unknown. We have studied the role of the mitochondrial pathway in aspirin-induced apoptosis. The apoptotic effect of aspirin was analyzed in different cell lines (Jurkat, MOLT-4, Raji and HL-60) showing induction of mitochondrial cytochrome c release and caspases 9, 3 and 8 processing. Furthermore, early aspirin-induced cytochrome c release was not affected by the caspase inhibitor Z-VAD x fmk and preceded loss of mitochondrial membrane potential. Therefore, aspirin-induced apoptosis involves caspase activation through cytochrome c release.

Evaluation of different criteria for the separation of pleural transudates from exudates

OBJECTIVES

To determine the relative usefulness of different criteria for the separation of pleural transudates from exudates.

DESIGN

Prospective evaluation of patients referred for thoracentesis.

SETTING

Community teaching hospital.

PATIENTS

Three hundred fifty-one consecutive patients with pleural effusions referred for thoracentesis. Fifty-four of these patients were excluded from the analysis.

MEASUREMENTS

We recorded clinical characteristics and final diagnosis and measured pleural fluid and serum levels of total protein, lactate dehydrogenase, and cholesterol. All patients included were followed up until final diagnosis. MEAN RESULTS: Forty-four (15 percent) pleural effusions were transudates and 253 (85 percent) were exudates. The criteria of Light et al, with a sensitivity of 98 percent and a specificity of 77 percent for exudates, showed the best accuracy (95.2 percent). Moreover, when the cutoff used for the criteria of Light et al was modified according to our own laboratory results, specificity rose to 93 percent with almost a similar accuracy (94 percent). Protein pleural fluid/serum ratio > 0.5 and pleural fluid cholesterol > 60 mg/dl showed equal specificity (91 percent), but the former had better sensitivity for exudates (88 percent vs 81 percent).

CONCLUSIONS

When the proportion of exudates included is 85 percent or more, as in the present series, the criteria of Light et al remain the method that offers the highest accuracy for segregating transudates from exudates.

Klebsiella pneumoniae lipopolysaccharide O typing: revision of prototype strains and O-group distribution among clinical isolates from different sources and countries

We have previously described an inhibition enzyme-linked immunosorbent assay method for the O typing of O1 lipopolysaccharide from Klebsiella pneumoniae which overcomes the technical problems and limitations of the classical O-typing method. In this study, we have extended the method to all of the currently recognized O types. The method was validated by studying the prototype strains that have defined the O groups by the classical tube agglutinatination O-typing method. Based on these results, we confirmed the O types of 60 of 64 typeable strains, and we propose a revised O-antigenic scheme, with minor but necessary changes, consisting of serogroups or serotypes O1, O2, O2ac, O3, O4, O5, O7, O8, and O12. Application of this typing method to 638 K. pneumoniae clinical isolates from Denmark, Spain, and the United States from different sources (blood, urine, and others) showed that up to 80% of these isolates belong to serotypes or serogroups O1, O2, O3, and O5, independently of the source of isolation, and that a major group of nontypeable isolates, representing about 17% of the total, consists of half O+ and half O- strains. Differences were observed, however, in the prevalence of the lipopolysaccharide O types or groups, depending on the country and isolation source.

The interferon-induced protein kinase (PKR), triggers apoptosis through FADD-mediated activation of caspase 8 in a manner independent of Fas and TNF-alpha receptors

The interferon-induced dsRNA-dependent protein kinase (PKR) induces apoptosis of mammalian cells. Apoptosis induction by PKR involves phosphorylation of the translational factor eIF-2alpha and activation of the transcriptional factor NF-kappaB, but caspase pathways activated by PKR are not known. Upregulation of Fas mRNA by PKR has been suggested to play a role in PKR-induced apoptosis. To learn how PKR induces apoptosis, we have analysed the role of molecules in death receptor pathways. We showed the involvement of the FADD-caspase 8 pathway on PKR-induced apoptosis based on four experimental findings: upregulation of caspase 8 activity during PKR-induced apoptosis, blocking of PKR-induced apoptosis by the use of a chemical inhibitor of caspase 8, and inhibition of PKR-induced apoptosis by expression of both a FADD dominant negative or a viral FLIP molecule. Significantly, despite the PKR-mediated upregulation of Fas mRNA expression, the Fas receptor-ligand pathway is not needed for PKR-induced apoptosis. Antibodies that inhibit TNFalpha-TNFR1 or Fas-FasL interactions were not able to block PKR-induced apoptosis. Taken together, our observations establish the involvement of caspase 8 in PKR-induced apoptosis and suggest that death receptors other than Fas or TNFR1 or, alternatively, a novel mechanism involving FADD independently of death receptors, are responsible for PKR-induced apoptosis.