Photoactivated gamma-secretase inhibitors directed to the active site covalently label presenilin 1

Cleavage of amyloid precursor protein (APP) by the beta- and gamma-secretases generates the amino and carboxy termini, respectively, of the A beta amyloidogenic peptides A beta40 and A beta42--the major constituents of the amyloid plaques in the brain parenchyma of Alzheimer's disease patients. There is evidence that the polytopic membrane-spanning proteins, presenilin 1 and 2 (PS1 and PS2), are important determinants of gamma-secretase activity: mutations in PS1 and PS2 that are associated with early-onset familial Alzheimer's disease increase the production of A beta42 (refs 4-6), the more amyloidogenic peptide; gamma-secretase activity is reduced in neuronal cultures derived from PS1-deficient mouse embryos; and directed mutagenesis of two conserved aspartates in transmembrane segments of PS1 inactivates the ability of gamma-secretase to catalyse processing of APP within its transmembrane domain. It is unknown, however, whether PS1 (which has little or no homology to any known aspartyl protease) is itself a transmembrane aspartyl protease or a gamma-secretase cofactor, or helps to colocalize gamma-secretase and APP. Here we report photoaffinity labelling of PS1 (and PS2) by potent gamma-secretase inhibitors that were designed to function as transition state analogue inhibitors directed to the active site of an aspartyl protease. This observation indicates that PS1 (and PS2) may contain the active site of gamma-secretase. Interestingly, the intact, single-chain form of wild-type PS1 is not labelled by an active-site-directed photoaffinity probe, suggesting that intact wild-type PS1 may be an aspartyl protease zymogen.

The plasticity of dendritic cell responses to pathogens and their components

Dendritic cells are involved in the initiation of both innate and adaptive immunity. To systematically explore how dendritic cells modulate the immune system in response to different pathogens, we used oligonucleotide microarrays to measure gene expression profiles of dendritic cells in response to Escherichia coli, Candida albicans, and influenza virus as well as to their molecular components. Both a shared core response and pathogen-specific programs of gene expression were observed upon exposure to each of these pathogens. These results reveal that dendritic cells sense diverse pathogens and elicit tailored pathogen-specific immune responses.

Superconductivity in the non-oxide perovskite MgCNi3

The interplay of magnetic interactions, the dimensionality of the crystal structure and electronic correlations in producing superconductivity is one of the dominant themes in the study of the electronic properties of complex materials. Although magnetic interactions and two-dimensional structures were long thought to be detrimental to the formation of a superconducting state, they are actually common features of both the high transition-temperature (Tc) copper oxides and low-Tc material Sr2RuO4, where they appear to be essential contributors to the exotic electronic states of these materials. Here we report that the perovskite-structured compound MgCNi3 is superconducting with a critical temperature of 8 K. This material is the three-dimensional analogue of the LnNi2B2C family of superconductors, which have critical temperatures up to 16 K (ref. 2). The itinerant electrons in both families of materials arise from the partial filling of the nickel d-states, which generally leads to ferromagnetism as is the case in metallic Ni. The high relative proportion of Ni in MgCNi3 suggests that magnetic interactions are important, and the lower Tc of this three-dimensional compound-when compared to the LnNi2B2C family-contrasts with conventional ideas regarding the origins of superconductivity.

Presenilin 1 is linked with gamma-secretase activity in the detergent solubilized state

gamma-Secretase is a membrane-associated protease that cleaves within the transmembrane region of amyloid precursor protein to generate the C termini of the two Abeta peptide isoforms, Abeta40 and Abeta42. Here we report the detergent solubilization and partial characterization of gamma-secretase. The activity of solubilized gamma-secretase was measured with a recombinant substrate, C100Flag, consisting largely of the C-terminal fragment of amyloid precursor protein downstream of the beta-secretase cleavage site. Cleavage of C100Flag by gamma-secretase was detected by electrochemiluminescence using antibodies that specifically recognize the Abeta40 or Abeta42 termini. Incubation of C100Flag with HeLa cell membranes or detergent-solubilized HeLa cell membranes generates both the Abeta40 and Abeta42 termini. Recovery of catalytically competent, soluble gamma-secretase critically depends on the choice of detergent; CHAPSO (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate) but not Triton X-100 is suitable. Solubilized gamma-secretase activity is inhibited by pepstatin and more potently by a novel aspartyl protease transition-state analog inhibitor that blocks formation of Abeta40 and Abeta42 in mammalian cells. Upon gel exclusion chromatography, solubilized gamma-secretase activity coelutes with presenilin 1 (PS1) at an apparent relative molecular weight of approximately 2.0 x 10(6). Anti-PS1 antibody immunoprecipitates gamma-secretase activity from the solubilized gamma-secretase preparation. These data suggest that gamma-secretase activity is catalyzed by a PS1-containing macromolecular complex.

Conversion of lytic to persistent alphavirus infection by the bcl-2 cellular oncogene

Little is known about virus-host cell interactions that regulate the lytic potential of viruses during productive replication. Sindbis virus (SV), a single-stranded positive-sense RNA virus in the alphavirus genus (family Togaviridae), results in lytic infection in most vertebrate cell lines, but persistent productive infection in post-mitotic neurons. The cellular oncogene bcl-2, which encodes an inner mitochondrial membrane protein of M(r) 26,000 (ref. 2), blocks programmed cell death (apoptosis) in neurons. We therefore investigated whether SV infection induces programmed cell death in non-neuronal cells, and if so, whether virus-induced programmed cell death can be blocked by transfection with bcl-2. We demonstrate that SV infection of baby hamster kidney (BHK-2), mouse neuroblastoma (N18), and rat prostatic adenocarcinoma (AT-3) cells results in programmed cell death, whereas SV infection of bcl-2-transfected AT-3 cells results in long-term persistent productive infection. Thus cellular bcl-2 oncogene expression plays a role in the establishment of persistent viral infection by blocking virus-induced programmed cell death.

Relation of alleles of the collagen type Ialpha1 gene to bone density and the risk of osteoporotic fractures in postmenopausal women

BACKGROUND

Osteoporosis is a common disorder with a strong genetic component. One way in which the genetic component could be expressed is through polymorphism of COLIA1, the gene for collagen type Ialpha1, a bone-matrix protein.

METHODS

We determined the COLIA1 genotypes SS, Ss, and ss in a population-based sample of 1778 postmenopausal women using a polymerase-chain-reaction-based assay. We then related the genotypes to bone mineral density and the occurrence of osteoporotic fractures in these women.

RESULTS

As compared with the 1194 women with the SS genotype, the 526 women with the Ss genotype had 2 percent lower bone mineral density at the femoral neck (P=0.003) and the lumbar spine (P=0.02); the 58 women with the ss genotype had reductions of 4 percent at the femoral neck (P= 0.05) and 6 percent at the lumbar spine (P=0.005). These differences increased with age (P=0.01 for modification by age of the effect of COLIA1 on femoral-neck bone density, and P=0.004 for modification of the effect on lumbar-spine bone density). Women with the Ss and ss genotypes were overrepresented among the 111 women who had incident nonvertebral fractures (relative risk per copy of the s allele, 1.5; 95 percent confidence interval, 1.1 to 2.1).

CONCLUSIONS

The COLIA1 polymorphism is associated with reduced bone density and predisposes women to osteoporotic fractures.

Disruption of alpha3 connexin gene leads to proteolysis and cataractogenesis in mice

Gap junction channels formed by alpha3 (Cx46) and alpha8 (Cx50) connexin provide pathways for communication between the fiber cells in the normal transparent lens. To determine the specific role of alpha3 connexin in vivo, the alpha3 connexin gene was disrupted in mice. Although the absence of alpha3 connexin had no obvious influence on the early stages of lens formation and the differentiation of lens fibers, mice homozygous for the disrupted alpha3 gene developed nuclear cataracts that were associated with the proteolysis of crystallins. This study establishes the importance of gap junctions in maintaining normal lens transparency by providing a cell-cell signaling pathway or structural component for the proper organization of lens membrane and cytoplasmic proteins.

Mutation R120G in alphaB-crystallin, which is linked to a desmin-related myopathy, results in an irregular structure and defective chaperone-like function

alphaB-crystallin, a member of the small heat shock protein family, possesses chaperone-like function. Recently, it has been shown that a missense mutation in alphaB-crystallin, R120G, is genetically linked to a desmin-related myopathy as well as to cataracts [Vicart, P., Caron, A., Guicheney, P., Li, A., Prevost, M.-C., Faure, A., Chateau, D., Chapon, F., Tome, F., Dupret, J.-M., et al. (1998) Nat. Genet. 20, 92-95]. By using alpha-lactalbumin, alcohol dehydrogenase, and insulin as target proteins, in vitro assays indicated that R120G alphaB-crystallin had reduced or completely lost chaperone-like function. The addition of R120G alphaB-crystallin to unfolding alpha-lactalbumin enhanced the kinetics and extent of its aggregation. R120G alphaB-crystallin became entangled with unfolding alpha-lactalbumin and was a major portion of the resulting insoluble pellet. Similarly, incubation of R120G alphaB-crystallin with alcohol dehydrogenase and insulin also resulted in the presence of R120G alphaB-crystallin in the insoluble pellets. Far and near UV CD indicate that R120G alphaB-crystallin has decreased beta-sheet secondary structure and an altered aromatic residue environment compared with wild-type alphaB-crystallin. The apparent molecular mass of R120G alphaB-crystallin, as determined by gel filtration chromatography, is 1.4 MDa, which is more than twice the molecular mass of wild-type alphaB-crystallin (650 kDa). Images obtained from cryoelectron microscopy indicate that R120G alphaB-crystallin possesses an irregular quaternary structure with an absence of a clear central cavity. The results of this study show, through biochemical analysis, that an altered structure and defective chaperone-like function of alphaB-crystallin are associated with a point mutation that leads to a desmin-related myopathy and cataracts.

Comprehensive gene expression profiling and immunohistochemical studies support application of immunophenotypic algorithm for molecular subtype classification in diffuse large B-cell lymphoma: a report from the International DLBCL Rituximab-CHOP Consortium Program Study

Gene expression profiling (GEP) has stratified diffuse large B-cell lymphoma (DLBCL) into molecular subgroups that correspond to different stages of lymphocyte development-namely germinal center B-cell like and activated B-cell like. This classification has prognostic significance, but GEP is expensive and not readily applicable into daily practice, which has lead to immunohistochemical algorithms proposed as a surrogate for GEP analysis. We assembled tissue microarrays from 475 de novo DLBCL patients who were treated with rituximab-CHOP chemotherapy. All cases were successfully profiled by GEP on formalin-fixed, paraffin-embedded tissue samples. Sections were stained with antibodies reactive with CD10, GCET1, FOXP1, MUM1 and BCL6 and cases were classified following a rationale of sequential steps of differentiation of B cells. Cutoffs for each marker were obtained using receiver-operating characteristic curves, obviating the need for any arbitrary method. An algorithm based on the expression of CD10, FOXP1 and BCL6 was developed that had a simpler structure than other recently proposed algorithms and 92.6% concordance with GEP. In multivariate analysis, both the International Prognostic Index and our proposed algorithm were significant independent predictors of progression-free and overall survival. In conclusion, this algorithm effectively predicts prognosis of DLBCL patients matching GEP subgroups in the era of rituximab therapy.

BMCP1, a novel mitochondrial carrier with high expression in the central nervous system of humans and rodents, and respiration uncoupling activity in recombinant yeast

We report here the cloning and functional analysis of a novel homologue of the mitochondrial carriers predominantly expressed in the central nervous system and referred to as BMCP1 (brain mitochondrial carrier protein-1). The predicted amino acid sequence of this novel mitochondrial carrier indicates a level of identity of 39, 31, or 30%, toward the mitochondrial oxoglutarate carrier, phosphate carrier, or adenine nucleotide translocator, respectively, and a level of identity of 34, 38, or 39% with the mitochondrial uncoupling proteins UCP1, UCP2, or UCP3, respectively. Northern analysis of mouse, rat, or human tissues demonstrated that mRNA of this novel gene is mainly expressed in brain, although it is 10-30-fold less expressed in other tissues. In situ hybridization analysis of brain showed it is particularly abundant in cortex, hippocampus, thalamus, amygdala, and hypothalamus. Chromosomal mapping indicates that BMCP1 is located on chromosome X of mice and at Xq24 in man. Expression of the protein in yeast strongly impaired growth rate. Analysis of respiration of total recombinant yeast or yeast spheroplasts and in particular of the relationship between respiratory rate and membrane potential of yeast spheroplasts revealed a marked uncoupling activity of respiration, suggesting that although BMCP1 sequence is more distant from the uncoupling proteins (UCPs), this protein could be a fourth member of the UCP family.

Initial stages of tumor cell-induced angiogenesis: evaluation via skin window chambers in rodent models

BACKGROUND

There is a paucity of information about events that follow immediately after tumor cells are triggered to initiate the process of angiogenesis (the formation of new blood vessels). Such information is relevant to the issue of when micrometastases vascularize and has implications for the accessibility of micrometastases to various treatments. In this study, we attempted to monitor events at the initiation of angiogenesis at the earliest possible stage of tumor growth in vivo.

METHODS

Two different rodent mammary tumor cell lines, R3230Ac from the Fischer 344 rat and 4T1 from the BALB/c mouse, were stably transfected with a gene that encodes an enhanced version of green fluorescence protein (GFP). GFP-labeled R3230Ac or 4T1 cells (about 20-50 cells) were implanted into dorsal skinfold window chambers of Fischer 344 rats or BALB/c mice, respectively. Tumor angiogenesis was then monitored serially and noninvasively for up to 4 weeks.

RESULTS

Clear evidence of modification of the host vasculature was observed when tumor mass reached approximately 60-80 cells, and functional new blood vessels were seen when tumor mass reached roughly 100-300 cells. Individual tumor cells exhibited a chemotaxis-like growth pattern toward the pre-existing host vasculature. When ex-flk1 (a soluble, truncated vascular endothelial cell growth factor receptor protein known to be antiangiogenic) was injected with the tumor cells, the initial angiogenic and tumor growth activities were inhibited considerably, indicating that angiogenesis inhibitors may halt tumor growth even before the onset of angiogenesis.

CONCLUSION

Angiogenesis induced by tumor cells after implantation in the host begins at a very early stage, i.e., when the tumor mass contains roughly 100-300 cells. Identification of chemotactic signals that initiate tumor cell migration toward the existing vasculature may provide valuable targets for preventing tumor progression and/or metastases.

Immunohistochemical localization of the D1 dopamine receptor in rat brain reveals its axonal transport, pre- and postsynaptic localization, and prevalence in the basal ganglia, limbic system, and thalamic reticular nucleus

D1 dopamine receptor localization was examined by immunohistochemistry using a polyclonal anti-peptide antibody which (i) immunoprecipitated a protein fragment encoded by a D1 receptor cDNA and (ii) on Western blots of solubilized striatal and hippocampal membranes recognized two proteins of approximately 50 kDa and 75 kDa, corresponding to reported sizes of D1 receptor proteins. Immunoreactivity overlapped with dopamine-containing pathways, patterns of D1 receptor binding, and mRNA expression. Staining was concentrated in prefrontal, cingulate, parietal, piriform, entorhinal, and hippocampal cortical areas and subcortically in the basal ganglia, amygdala, septal area, substantia inominata, thalamus, hypothalamus, and neurohypophysis. Prominent labeling was seen in the thalamic reticular nucleus, a region known to integrate ascending basal forebrain inputs with thalamocortical and corticothalamic pathways and in fiber bundles interconnecting limbic areas. In striatal neuropil, staining appeared in spines (heads and necks), at postsynaptic sites in dendrites, and in axon terminals; in the pars reticulata of the substantia nigra, labeling was prevalent in myelinated and unmyelinated axons and dendrites. These data provide direct evidence for the regional and subcellular distribution of D1 receptor protein in the brain and for its pre- and postsynaptic localization in the basal ganglia. The prominent immunoreactivity seen in the limbic system and thalamic reticular nucleus supports an important role for this receptor subtype in mediating integrative processes involved with learning, memory, and cognition.

Src and Cas mediate JNK activation but not ERK1/2 and p38 kinases by reactive oxygen species

c-Jun NH(2)-terminal kinase (JNK) is activated by a number of cellular stimuli such as inflammatory cytokines and environmental stresses. Reactive oxygen species also cause activation of JNK; however, the signaling cascade that leads to JNK activation remains to be elucidated. Because recent reports showed that expression of Cas, a putative Src substrate, stimulates JNK activation, we hypothesized that the Src kinase family and Cas would be involved in JNK activation by reactive oxygen species. An essential role for both Src and Cas was demonstrated. First, the specific Src family tyrosine kinase inhibitor, PP2, inhibited JNK activation by H(2)O(2) in a concentration-dependent manner but had no effect on extracellular signal-regulated kinases 1 and 2 and p38 activation. Second, JNK activation in response to H(2)O(2) was completely inhibited in cells derived from transgenic mice deficient in Src but not Fyn. Third, expression of a dominant negative mutant of Cas prevented H(2)O(2)-mediated JNK activation but had no effect on extracellular signal-regulated kinases 1 and 2 and p38 activation. Finally, the importance of Src was further supported by the inhibition of both H(2)O(2)-mediated Cas tyrosine phosphorylation and Cas.Crk complex formation in Src-/- but not Fyn-/- cells. These results demonstrate an essential role for Src and Cas in H(2)O(2)-mediated activation of JNK and suggest a new redox-sensitive pathway for JNK activation mediated by Src.

Assessment of cisplatin-induced nephrotoxicity by microarray technology

Microarrays are a new technology used to study global gene expression and to decipher biological pathways. In the current study, microarrays were used to examine gene expression patterns associated with cisplatin-mediated nephrotoxicity. Sprague-Dawley rats received either single or seven daily ip doses of cisplatin (0.5 or 1 mg/kg/day) or the inactive isomer transplatin (1 or 3 mg/kg/day). Histopathological evaluation revealed renal proximal tubular necrosis in animals that received cisplatin for 7 days, but no hepatotoxic findings. Microarray analyses were performed using rat specific arrays containing 250 toxicity-related genes. Prominent gene expression changes were observed only in the kidneys of rats that received cisplatin for 7 days. Mechanistically, the gene expression pattern elicited by cisplatin (e.g., Bax upward arrow and SMP-30 downward arrow) suggested the occurrence of apoptosis and the perturbation of intracellular calcium homeostasis. The induction of multidrug resistance genes (MDR1 upward arrow, P-gp upward arrow) and tissue remodeling proteins (clusterin upward arrow, IGFBP-1 upward arrow, and TIMP-1 upward arrow) indicated the development of cisplatin resistance and tissue regeneration. Select gene expression changes were further confirmed by TaqMan analyses. Gene expression changes were not observed in the liver following cisplatin administration. In contrast to these in vivo findings, studies using NRK-52E kidney epithelial cells and clone-9 liver cells suggested that liver cells were more sensitive to cisplatin treatment. The discrepancies between the in vivo and in vitro results suggest that caution should be taken when extrapolating data from in vivo to in vitro systems. Nonetheless, the current study elucidates the biochemical pathways involved in cisplatin toxicity and demonstrates the utility of microarrays in toxicological studies.

Anisotropy and Corotation of Galactic Cosmic Rays

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

MiR-148a promotes apoptosis by targeting Bcl-2 in colorectal cancer

Apoptosis has a vital role in maintaining tissue homeostasis, and dysregulation of the apoptotic pathway is now widely recognized as a key step in tumourigenesis. Increasingly, evidence has demonstrated that microRNA (miRNA) can exert various biological functions in tumours by targeting oncogenes or tumour suppressors. Nevertheless, the role of miRNA in apoptosis remains unclear. Here we show that ectopical expression of miR-148a can induce apoptosis in colorectal cancer cells. In addition, MYB can inhibit miR-148a by directly acting on the transcription factor binding site in miR-148a gene and miR-148a can posttranscriptionally silence Bcl-2. Subsequently, the intrinsic apoptosis pathway is activated by releasing cytochrome c, cleaving caspase 9, caspase 3 and PARP, which eventually induce cancer-cell apoptosis. These findings are part of a hitherto undocumented apoptotic regulatory pathway in which a pleiotropic transcription factor controls the expression of a miRNA and the miRNA inhibits the target, leading to activation of an intrinsic mitochondrial pathway and tumour apoptosis.

Intestinal cytokine response after gut ischemia: role of gut barrier failure

OBJECTIVE

To investigate the effect of intestinal ischemia with and without a reperfusion injury on intestinal cytokine production and gut permeability.

SUMMARY BACKGROUND DATA

In humans and in animal models, the gut has been implicated as a cytokine-producing organ after ischemia/reperfusion (I/R)-type injuries. Because of the limitations of in vivo models, it has been difficult to demonstrate directly that the gut releases cytokines after an I/R injury or whether there is a relation between the magnitude of the ischemic process and the cytokine response.

METHODS

Ileal mucosal membranes from rats subjected to sham or 45 or 75 min of superior mesenteric occlusion (SMAO) or 45 minutes of SMAO and 30 minutes of reperfusion (SMAO 45/30) were mounted in the Ussing chamber system. Levels of tumor necrosis factor-alpha and interleukin-6 were serially measured in the mucosal and serosal reservoirs of the Ussing system, as was mucosal permeability as reflected by the passage of bacteria or phenol red across the ileal membrane. In a second group of experiments, Escherichia coli C25 was added to the mucosal reservoir to determine if the cytokine response would be increased.

RESULTS

Mucosal and serosal levels of tumor necrosis factor-alpha were equally increased after SMAO, with the highest levels in the 75-minute SMAO group. The highest levels of interleukin-6 were found in rats subjected to 75 minutes of SMAO or SMAO 45/30; the serosal levels of interleukin-6 were four to sixfold higher than the mucosal levels. The addition of E. coli C25 resulted in a significant increase in the amount of interleukin-6 or tumor necrosis factor-alpha recovered from the mucosal reservoir. Increased ileal membrane permeability was observed only in rats subjected to 75 minutes of SMAO or SMAO 45/30.

CONCLUSION

These results directly document that the levels of tumor necrosis factor-alpha and interleukin-6 released from the gut increase after an ischemic or I/R injury, such as SMAO, and that there is a relation between the magnitude of the gut ischemic or I/R insult and the cytokine response.

A large-scale population-based study of the association of vitamin D receptor gene polymorphisms with bone mineral density

Conflicting results have been reported on the association between restriction fragment length polymorphisms (RFLPs) at the vitamin D receptor (VDR) gene locus (i.e., for BsmI, ApaI, and TaqI) and bone mineral density (BMD). We analyzed this association in a large population-based sample (n = 1782) of men and women aged 55-80 years using a novel direct haplotyping polymerase chain reaction (PCR) test to monitor the three polymorphic sites simultaneously. The direct haplotyping test we developed demonstrated a larger degree of genetic polymorphism at the VDR gene locus than described until now. None of the individual RFLPs were associated with BMD at the proximal femur. By analyzing allele dose effects, we identified a VDR haplotype allele weakly associated with low BMD. This allele, as one representative of the group of b alleles, is different from the BsmI allele previously reported by other groups to be associated with low BMD. This suggests allelic heterogeneity at the VDR locus in relation to BMD. Our results indicate at most a small effect of the VDR genotype on BMD in this elderly population. Since anonymous polymorphisms were analyzed, alternative explanations for our results include linkage to another nearby bone-metabolism related gene.

Structural and magnetic phase diagram of CeFeAsO(1- x)F(x) and its relation to high-temperature superconductivity

Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

Long-range magnetic order in Mn[N(CN)2]2(pyz) (pyz = pyrazine). Susceptibility, magnetization, specific heat, and neutron diffraction measurements and electronic structure calculations

Using dc magnetization, ac susceptibility, specific heat, and neutron diffraction, we have studied the magnetic properties of Mn[N(CN)2]2(pyz) (pyz = pyrazine) in detail. The material crystallizes in the monoclinic space group P2(1)/n with a = 7.3248(2), b = 16.7369(4), and c = 8.7905 (2) A, beta = 89.596 (2) degrees, V = 1077.65(7) A(3), and Z = 4, as determined by Rietveld refinement of neutron powder diffraction data at 1.35 K. The 5 K neutron powder diffraction data reflect very little variation in the crystal structure. Interpenetrating ReO3-like networks are formed from axially elongated Mn(2+) octahedra and edges made up of mu-bonded [N(CN)2](-) anions and neutral pyz ligands. A three-dimensional antiferromagnetic ordering occurs below T(N) = 2.53(2) K. The magnetic unit cell is double the nuclear one along the a- and c-axes, giving the (1/2, 0, 1/2) superstructure. The crystallographic and antiferromagnetic structures are commensurate and consist of collinear Mn(2+) moments, each with a magnitude of 4.15(6) mu(B) aligned parallel to the a-direction (Mn-pyz-Mn chains). Electronic structure calculations indicate that the exchange interaction is much stronger along the Mn-pyz-Mn chain axis than along the Mn-NCNCN-Mn axes by a factor of approximately 40, giving rise to a predominantly one-dimensional magnetic system. Thus, the variable-temperature magnetic susceptibility data are well described by a Heisenberg antiferromagnetic chain model, giving g = 2.01(1) and J/k(B) = -0.27(1) K. Owing to single-ion anisotropy of the Mn(2+) ion, field-induced phenomena ascribed to spin-flop and paramagnetic transitions are observed at 0.43 and 2.83 T, respectively.

zVAD-induced necroptosis in L929 cells depends on autocrine production of TNFα mediated by the PKC-MAPKs-AP-1 pathway

It is intriguing that some pan-caspase inhibitors such as zVAD-fmk (zVAD) are capable of inducing necrotic cell death in a selected group of cells. As earlier reports from our laboratory have ruled out the original notion that zVAD-induced necrosis in mouse fibrosarcoma L929 cells was autophagic cell death, the main objective of this study was thus to determine the underlying mechanism of this form of cell death. In this study, we provided clear evidence that zVAD-induced necroptosis in L929 cells and such cell death is dependent on autocrine production of tumor necrosis factor-α (TNFα) at the transcriptional level. More importantly, we identified that activating protein-1 (AP-1), but not nuclear factor κ-B, is the transcription factor controlling zVAD-induced TNFα transcription. Moreover, zVAD is able to activate AP-1 through activation of two upstream mitogen-activated kinases (MAPKs), c-Jun N-terminal kinase and extracellular signal-regulated kinase. Finally, we found that protein kinase C is the important upstream signaling molecule in mediating zVAD-induced activation of MAPKs and AP-1, and subsequent autocrine production of TNFα and cell death. Data from this study reveal the molecular mechanisms underlying zVAD-induced necroptosis, an important form of programmed necrotic cell death with increasing understanding of its biological significance in health and diseases.

Engineering Escherichia coli for the synthesis of taxadiene, a key intermediate in the biosynthesis of taxol

Taxadiene, the key intermediate of paclitaxel (Taxol) biosynthesis, has been prepared enzymatically from isopentenyl diphosphate in cell-free extracts of Escherichia coli by overexpressing genes encoding isopentenyl diphosphate isomerase, geranylgeranyl diphosphate synthase and taxadiene synthase. In addition, by the expression of three genes encoding four enzymes on the terpene biosynthetic pathway in a single strain of E. coli, taxadiene can be conveniently synthesized in vivo, at the unoptimized yield of 1.3mg per liter of cell culture. The success of both in vitro and in vivo synthesis of taxadiene bodes well for the future production of taxoids by non-paclitaxel producing organisms through pathway engineering.