Characterization of a p75(NTR) apoptotic signaling pathway using a novel cellular model

The p75 neurotrophin receptor (p75(NTR)) belongs to the tumor necrosis factor receptor/nerve growth factor receptor superfamily. In some cells derived from neuronal tissues it causes cell death through a poorly characterized pathway. We developed a neuronal system using conditionally immortalized striatal neurons, in which the expression of p75(NTR) is inducibly controlled by the ecdysone receptor. In these cells p75(NTR) induces apoptosis through its death domain in a nerve growth factor-independent manner. Caspases 9, 6, and 3 are activated by receptor expression indicating the activation of the common effector pathway of apoptosis. Cell death is blocked by a dominant negative form of caspase 9 and Bcl-X(L) consistent with a pathway that involves mitochondria. Significantly, the viral flice inhibitory protein E8 protects from p75(NTR)-induced cell death indicating that death effector domains are involved. A p75(NTR) construct with a deleted death domain dominantly interferes with p75(NTR) signaling, implying that receptor multimerization is required. However, in contrast to the other receptors of the family, p75(NTR)-mediated apoptosis does not involve the adaptor proteins Fas-associated death domain protein or tumor necrosis factor-associated death domain protein, and the apical caspase 8 is not activated. We conclude that p75(NTR) signals apoptosis by similar mechanisms as other death receptors but uses different adaptors and apical caspases.

Reconstitution of a functional core polycomb repressive complex

The opposing actions of polycomb (PcG) and trithorax group (trxG) gene products maintain essential gene expression patterns during Drosophila development. PcG proteins are thought to establish repressive chromatin structures, but the mechanisms by which this occurs are not known. Polycomb repressive complex 1 (PRC1) contains several PcG proteins and inhibits chromatin remodeling by trxG-related SWI/SNF complexes. We have defined a functional core of PRC1 by reconstituting a stable complex using four recombinant PcG proteins. One subunit, PSC, can also inhibit chromatin remodeling on its own. These PcG proteins create a chromatin structure that has normal nucleosome organization and is accessible to nucleases but excludes hSWI/SNF.

A Drosophila Polycomb group complex includes Zeste and dTAFII proteins

A goal of modern biology is to identify the physical interactions that define 'functional modules' of proteins that govern biological processes. One essential regulatory process is the maintenance of master regulatory genes, such as homeotic genes, in an appropriate 'on' or 'off' state for the lifetime of an organism. The Polycomb group (PcG) of genes maintain a repressed transcriptional state, and PcG proteins form large multiprotein complexes, but these complexes have not been described owing to inherent difficulties in purification. We previously fractionated a major PcG complex, PRC1, to 20-50% homogeneity from Drosophila embryos. Here, we identify 30 proteins in these preparations, then further fractionate the preparation and use western analyses to validate unanticipated connections. We show that the known PcG proteins Polycomb, Posterior sex combs, Polyhomeotic and dRING1 exist in robust association with the sequence-specific DNA-binding factor Zeste and with numerous TBP (TATA-binding-protein)-associated factors that are components of general transcription factor TFIID (dTAFIIs). Thus, in fly embryos, there is a direct physical connection between proteins that bind to specific regulatory sequences, PcG proteins, and proteins of the general transcription machinery.

[Study on the transformation from myelodysplastic syndromes into acute leukemias]

OBJECTIVE

To study the patterns of transformation from myelodysplastic syndromes (MDS) into acute leukemias (AL).

METHODS

Leukemic transformation of MDS patients was dynamically followed up and the clinical manifestations, peripheral blood and bone marrow pictures, karyotypes, immunophenotypes, response to treatment and prognosis of post MDS acute leukemia (postMDS-AL) were observed.

RESULTS

During the past eight year and seven months, 21 (13.91%) of 151 MDS patients progressed to overt leukemia with a median interval of 5 (1 - 21) months. There were no significant differences among the rates of leukemia from RA, RAEB and RAEB-t groups. The transformation was developed either gradually or rapidly. There were five parameters related to the leukemic transformation: under 40 years of age, pancytopenia, more than 0.15 blasts in bone marrow, at least two types of abnormal karyotype and combined chemotherapy. All of the 21 post MDS-AL were acute myeloid leukemia (AML); and most of them were M(2), M(4) and M(5). Two (9.52%) post MDS-AML developed extramedullary infiltration. Leukopenia was found in 47.62% of patients. Two third of the patients, whose bone marrows were generally hypercellular, showed neutropenias. After evolving into AML, 8 (47.06%) patients developed abnormal karyotypes. High expression of immature myeloid antigens, including CD(33) (49.83 +/- 24.50)%, CD(13) (36.38 +/- 33.84)%, monocytic antigen CD(14) (38.50 +/- 24.60)%, and stem cell marker CD(34) (34.67 +/- 30.59)% were found on bone marrow mononuclear cells of post MDS-AML cases. In some cases, lymphoid antigens, such as CD(5), CD(7), CD(9) and CD(19) were coexisted with myeloid antigens. A low complete remission rate (31.25%) and short survival duration with median survival of 6 (1 - 28) months were found in patients with post MDS-AML treated by induction therapy.

CONCLUSION

MDS was at high risk of evolving into AML, either gradually or rapidly. Patients with post MDS-AML had specific biologic features and worse prognoses.

Three-dimensional interaction of Phi29 pRNA dimer probed by chemical modification interference, cryo-AFM, and cross-linking

Six pRNAs (p for packaging) of bacterial virus phi29 form a hexamer complex that is an essential component of the viral DNA translocating motor. Dimers, the building block of pRNA hexamer, assemble in the order of dimer --> tetramer --> hexamer. The two-dimensional structure of the pRNA monomer has been investigated extensively; however, the three-dimensional structure concerning the distance constraints of the three stems and loops are unknown. In this report, we probed the three-dimensional structure of pRNA monomer and dimer by photo affinity cross-linking with azidophenacyl. Bases 75-81 of the left stem were found to be oriented toward the head loop and proximate to bases 26-31 in a parallel orientation. Chemical modification interference indicates the involvement of bases 45-71 and 82-91 in dimer formation. Dimer was formed via hand-in-hand contact, a novel RNA dimerization that in some aspects is similar to the kissing loops of the human immunodeficiency virus. The covalently linked dimers were found to be biologically active. Both the native dimer and the covalently linked dimer were found by cryo-atomic force microscopy to be similar in global conformation and size.

Optical properties of a new two-photon absorbing chromophore

A new dye, trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide, has been synthesized, and the two-photon-absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) frequency upconverted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross section of varsigma(2) = 5.7 x 10(-48) (cm(4) s(-1))/photon at 1064 nm but exhibits high lasing efficiency. The slope efficiency of the TPP cavity laser with this new dye as the laser medium is 1.6%.

Mechanisms of neuroprotection by a novel rescue factor humanin from Swedish mutant amyloid precursor protein

We report a novel gene, designated Humanin (HN) cDNA, that suppresses neuronal cell death by K595N/M596L-APP (NL-APP), a mutant causing familial Alzheimer's disease (FAD), termed Swedish mutant. Transfection of neuronal cells with HN cDNA or treatment with the coding HN polypeptide abrogated cytotoxicity by NL-APP. HN suppressed neurotoxicity by Abeta1-43 in the absence of N2 supplement, but could not inhibit Abeta secretion from NL-APP. HN could also protect neuronal cells from death by NL-APP lacking the 41st and 42nd residues of the Abeta region. Therefore, HN suppressed neuronal cell death by NL-APP not through inhibition of Abeta42 secretion, but with two targets for its inhibitory action: (i) the intracellular toxic mechanism directly triggered by NL-APP and (ii) neurotoxicity by Abeta. HN will contribute to the development of curative therapy of AD, especially as a novel reagent that could mechanistically supplement Abeta-production inhibitors.

Expression and function of c-kit receptor in bone marrow mononuclear cells of patients with myelodysplastic syndromes

OBJECTIVE

To determine the expression and function of the c-kit receptor in bone marrow mononuclear cells (BMMNC) of patients with myelodysplastic syndromes (MDS).

METHODS

Direct immunofluorescence assay and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to detect c-kit protein and c-kit mRNA expressions in the BMMNC of 29 MDS patients and 10 normal controls. Cell culture was used to detect the function of the c-kit receptor.

RESULTS

c-kit protein expression in the MDS group was significantly higher than that in the control group (8.58% +/- 5.28% vs 3.04% +/- 1.49%, P < 0.05). c-kit protein expression in the refractory anemia (RA) group was significantly lower than that in the RA with an excess of blasts (RAEB)/RAEB in transformation (RAEB-t) group (5.12% +/- 2.13% vs 10.01% +/- 5.07%, P < 0.05). The rate of c-kit protein expression was 32.43% in acute myeloblastic leukemia (AML) cases transformed from MDS (t-AML). c-kit mRNA expression in the MDS group was correlated with c-kit protein expression. Interleukin-3 (IL-3) and erythropoietin (Epo), with or without stem cell factor (SCF), upregulated c-kit protein and its mRNA expression. In the presence of IL-3 and Epo, SCF showed significant stimulating effects on the formation of CFU-GM and BFU-E in semi-solid cultures of normal BMMNC, but had no effects on those of the MDS patients.

CONCLUSION

The protein and mRNA expression of the c-kit receptor in the BMMNC of MDS patients were higher than those of normal controls, and the function of this receptor in MDS BMMNC was abnormal.

[Sequential intensified immunosuppressive therapy combining with hematopoietic growth factors in the treatment of severe aplastic anemia]

OBJECTIVE

To explore more effective regimen for reducing early mortality of severe aplastic anemia (SAA) and improving therapeutic effectiveness.

METHODS

Antilymphocyte globulin/antithymocyte globulin (ALG/ATG) and cyclosporine A (CsA) (sequential intensified immunosuppressive therapy, SIIST), with or without hematopoietic growth factors (HGFs) were administered to 73 SAA patients in a prospective randomized clinical trial to test the effectiveness of the addition of HGFs for the patients.

RESULTS

The response rate of SIIST with HGFs group was significantly higher than that of SIIST alone group (89.2% vs 63.9%), with lower rates of early infection (24.3% vs 55.3%) and mortality (4.0% vs 16.7%), shorter duration of cytopenia and blood transfusion dependence and faster recovery of bone marrow hematopoiesis. The addition of HGFs to SIIST was tolerated well in all patients. There was no difference in the treatment outcome of the two groups with GM-CSF plus Epo or G-CSF plus Epo.

CONCLUSION

The use of HGFs in combination with SIIST could reduce early infection and mortality rates and, therefore, improve the response rates in SAA patients.

Secreted Abeta does not mediate neurotoxicity by antibody-stimulated amyloid precursor protein

Antibodies against APP, a precursor of Abeta deposited in Alzheimer's disease brain, have been shown to cause neuronal death. Therefore, it is important to determine whether Abeta mediates antibody-induced neurotoxicity. When primary neurons were treated with anti-APP antibodies, Abeta40 and Abeta42 in the cultured media were undetectable by an assay capable of detecting 100 nM Abeta peptides. However, exogenously treated Abeta1-42 or Abeta1-43 required >3 microM to exert neurotoxicity, and 25 microM Abeta1-40 was not neurotoxic. Glutathione-ethyl-ester inhibited neuronal death by anti-APP antibody, but not death by Abeta1-42, whereas serum attenuated toxicity by Abeta1-42, but not by anti-APP antibody. Using immortalized neuronal cells, we specified the domain responsible for toxicity to be cytoplasmic His(657)-Lys(676), but not the Abeta1-42 region, of APP. This indicates that neuronal cell death by anti-APP antibody is not mediated by secreted Abeta.

Visualizing filamentous actin on lipid bilayers by atomic force microscopy in solution

The surface structure of actin filaments (F-actin) was visualized at high resolution, by atomic force microscopy (AFM) in aqueous solution, in large paracrystals prepared on positively charged lipid monolayers. The increased stability of these closely packed specimens allowed us to show that both the long pitch (38 nm) and the monomer (5.8 nm) can be directly resolved by AFM in the contact mode. The right-handed helical surface, distinguishable in high resolution images, was compared with reconstructed models based on electron microscopy. The height of the rafts, a measure of the actin filament diameter, was 10 +/- 1 nm, whereas the smaller inter-filament distance, 8 +/- 1 nm, was consistent with interdigitation of the filaments. The 10 +/- 1 nm F-actin diameter is in good agreement with the results of fibre X-ray diffraction. As such specimens are relatively easy to prepare without specialized equipment, this method may allow the study of the thin filaments in which F-actin-associated proteins are also present.

Signal transduction of flumazenil-induced preconditioning in myocytes

The objective of this study was to examine the role of oxygen radicals, protein kinase C (PKC), and ATP-sensitive K(+) (K(ATP)) channels in mediating flumazenil-produced preconditioning. Chick cardiomyocyte death was quantified using propidium iodide, and oxygen radical generation was assessed using 2',7'-dichlorofluorescin oxidation. Preconditioning was initiated with 10 min of ischemia followed by 10 min of reoxygenation. Alternatively, flumazenil was infused for 10 min and removed 10 min before ischemia. Flumazenil (10 microM) and preconditioning increased oxygen radicals [1,693 +/- 101 (n = 3) and 1,567 +/- 98 (n = 3), respectively, vs. 345 +/- 53 (n = 3) in control] and reduced cell death similarly [22 +/- 3% (n = 5) and 18 +/- 2% (n = 6), respectively, vs. controls 49 +/- 5% (n = 8)]. Protection and increased oxygen radicals by flumazenil were abolished by pretreatment with the antioxidant thiol reductant 2-mercaptopropionyl glycine (800 microM; 52 +/- 10%, n = 6). Specific PKC inhibitors Go-6976 (0.1 microM) and chelerythrine (2 microM), given during ischemia and reoxygenation, blocked flumazenil-produced protection (47 +/- 5%, n = 6). The PKC activator phorbol 12-myristate 13-acetate (0.2 microM), given during ischemia and reoxygenation, reduced cell death similarly to that with flumazenil [17 +/- 4% (n = 6) and 22 +/- 3% (n = 5)]. Finally, 5-hydroxydecanoate (1 mM), a selective mitochondrial K(ATP) channel antagonist given during ischemia and reoxygenation, abolished the protection of flumazenil and phorbol 12-myristate 13-acetate. Thus flumazenil mimics preconditioning to reduce cell death in cardiomyocytes. Oxygen radicals activate mitochondrial K(ATP) channels via PKC during the process.

[Immunorelated pancytopenia]

OBJECTIVE

A report of a group of patients with pancytopenia which might be related to abnormal immunity.

METHODS

The clinical and laboratory features of 29 patients with positive bone marrow mononuclear cell (BMMNC) Coombs tests were analyzed.

RESULTS

Most of these cases were pancytopenia with normal or decreased bone marrow cellularities and increased normoblasts. They were all found to have negative results of conventional hemolysis tests and hematopoietic nutrient determination and had no evidence of malignant clonal hematopoiesis. However, all of them showed positive BMMNC-Coombs test and good response to corticosteroids.

CONCLUSION

Immunorelated pancytopenia might be caused by abnormal immunity (especially autoantibody) mediated destruction or abnormal function of blood cells. It is beneficial to differentiate immunorelated pancytopenia from aplastic anemia or myelodysplastic syndromes.

Conformation transition kinetics of regenerated Bombyx mori silk fibroin membrane monitored by time-resolved FTIR spectroscopy

The ethanol-induced conformation transition of regenerated Bombyx mori silk fibroin membrane from a poorly defined to the well ordered state was monitored by time-resolved Fourier transform infrared spectroscopy (FTIR) for the first time. From the analysis of FTIR difference spectra, taken on time scales as short as 6 s and up to 1 h after addition of ethanol, intensity vs. time plots of an increasing band at 1618 cm(-1) were observed indicating formation of a beta-sheet coincident with the loss of intensity of a band at 1668 cm(-1) indicating decreases of random coil and/or silk I structure. Both infrared markers were fitted with identical biphasic exponential decay functions, however, there was a clear burst phase occurring prior to the onset of the observed transitions. The conformation transition process is indicated to either proceed sequentially through (at least) two intermediate states that contain different levels of beta-sheet structure or to have parallel pathways of initial beta-sheet formation followed by a slower 'perfection' phase. The first observed process forms in a burst phase a few seconds after mixing (or even faster), prior to the collection of the first spectrum at 6 s. The second observed process occurs with a time constant of approximately 0.5 min, the intermediate present at this stage then continues with a time constant of 5.5 min completing the observed formation of the beta-sheet. The conformation transition of this slower intermediate is not only indicated by an analysis of the kinetics of the random coil and beta-sheet-specific bands discussed above, it roughly coincides with the appearance of an additional infrared marker at 1695 cm(-1), which may be a marker for beta-sheet structure specific to the formation of the perfected structure. The conformation transition of this protein analyzed by infrared spectroscopy provides insight into a part of the fascinating process of cocoon formation in B. mori.

Qian-Kun-Nin, a Chinese herbal medicine formulation, attenuates mitochondrial oxidant stress in cardiomyocytes

Qian-Kun-Nin is a Chinese herbal medicine formulation used for several indications, including the treatment of cardiovascular diseases. This formulation contains herbs which possess antioxidant properties. In this study, Qian-Kun-Nin's ability to confer protection to cardiomyocytes against reactive oxygen species (ROS) generated during mitochondrial electron transport inhibition was tested. The intracellular fluorescent probe 2',7'-dichlorofluorescin diacetate (DCFH-DA, sensitive to H(2)O(2) and hydroxyl radicals) was used to assess intracellular ROS, and propidium iodide (PI) was used to assess viability in cultured chick embryonic cardiomyocytes. Qian-Kun-Nin significantly attenuated oxidation of DCFH in cells exposed to the mitochondrial site III inhibitor, antimycin A, consistent with a decrease in oxidative stress. These attenuated oxidant levels were associated with improved cell survival. After antimycin A exposure, Qian-Kun-Nin decreased cell death from 51. 6+/-3.3% in untreated cells to 27.3+/-3.8% in treated cells at 2 h. We conclude that Qian-Kun-Nin attenuates oxidant stress and protects cells from lethal oxidant damage during mitochondrial electron transport inhibition, and thus its therapeutic potential in treating cardiovascular diseases may relate to its antioxidant properties.

beta-Amyloid(1-42) peptide directly modulates nicotinic receptors in the rat hippocampal slice

Alzheimer's disease (AD) is a human neurological disorder characterized by an increasing loss of cognitive function and the presence of extracellular neuritic plaques composed of the beta-amyloid peptide (Abeta(1-42)). However, the link between these molecular correlates of AD and the loss of cognitive function has not been established. The pathology associated with AD includes the loss of basal forebrain cholinergic neurons, presynaptic terminals in the neocortex and hippocampus, and a decrease in the total amount of neuronal nicotinic acetylcholine receptors (nAChRs). This leads to the hypothesis that failure in the cholinergic system underlies the dementia seen in AD. Cognitive performance has been linked to nAChR function in the hippocampus, and the interneurons expressing nAChRs coordinate the activity of large numbers of principal cells and therefore have a powerful role in the regulation of hippocampal activity. We have found that Abeta(1-42) inhibits whole-cell and single-channel nicotinic currents from rat hippocampal interneurons by directly blocking the postsynaptic nAChR channels at concentrations as low as 100 nm. This inhibition appears specific for peptide sequence and neuronal nAChRs, and the magnitude of Abeta(1-42) inhibition is dependent on the nAChR channel subtype expressed. Thus, chronic inhibition of cholinergic signaling by Abeta(1-42) could contribute to the cognitive deficits associated with AD.

Single channel properties of neuronal nicotinic ACh receptors in stratum radiatum interneurons of rat hippocampal slices

The single channel properties of neuronal nicotinic ACh receptors (nAChRs) were investigated in outside-out patches from CA1 stratum radiatum interneurons from thin slices of rat hippocampus. The application of ACh (10 microM to 1 mM) induced the opening of observable single channel currents with two distinct current levels, which corresponded to conductance levels of 38 +/- 3 and 62 +/- 2 pS. The 38 pS channel was observed in 10 % (n = 260) of patches, whereas the 62 pS channel was observed in 4 % of patches; these two channel types were most often observed independently. The alpha7-selective nAChR antagonist methyllycaconitine (MLA; 50 nM) reduced the open probability of the 38 pS channel by 73 %. In contrast, the 62 pS channel was unaffected by MLA, but instead was blocked by dihydro-beta-erythroidine (DHbetaE; 10 microM), a broad spectrum nAChR antagonist. These data suggest that rat hippocampal CA1 stratum radiatum interneurons in the slice possess at least two different types of functional nAChRs, an alpha7-containing subtype with a single channel conductance of 38 pS, and a non-alpha7 subtype with a single channel conductance of 62 pS.

Probing the structure of monomers and dimers of the bacterial virus phi29 hexamer RNA complex by chemical modification

All dsDNA viruses multiply their genome and assemble a procapsid, a protein shell devoid of DNA. The genome is subsequently inserted into the procapsid. The bacterial virus phi29 DNA translocating motor contains a hexameric RNA complex composed of six pRNAs. Recently, we found that pRNA dimers are building blocks of pRNA hexamers. Here, we report the structural probing of pRNA monomers and dimers by chemical modification under native conditions and in the presence or absence of Mg2+. The chemical-modification pattern of the monomer is compared to that of the dimer. The data strongly support the previous secondary-structure prediction of the pRNA concerning the single-stranded areas, including three loops and seven bulges. However, discrepancies between the modification patterns of two predicted helical regions suggest the presence of more complicated, higher-order structure in these areas. It was found that dimers were formed via hand-in-hand and head-to-head contact, as the interacting sequence of the right and left loops and all bases in the head loop were protected from chemical modification. Cryoatomic force microscopy revealed that the monomer displayed a check-mark shape and the dimer exhibited an elongated shape. The dimer was twice as long as the monomer. Direct observation of the shape and measurement of size and thickness of the images strongly support the conclusion from chemical modification concerning the head-to-head contact in dimer formation. Our results also suggest that the role for Mg2+ in pRNA folding is to generate a proper configuration for the right and head loops, which play key roles in this symmetrical head-to-head organization. This explains why Mg2+ plays a critical role in pRNA dimer formation, procapsid binding, and phi29 DNA packaging.

[Genistein exerts multiple suppressive effects on human breast carcinoma cells]

OBJECTIVE

To study the suppressive effects of genistein on progression of breast carcinoma.

METHODS

In vitro cell culture, animal studies, zymography, Northern and Western blot were used in this study.

RESULTS

Genistein inhibited in vitro invasion of MCF-7 and MDA-MB-231 cells. This inhibition was associated with down-regulation of MMP-9 and up-regulation of TIMP-1. These effects were also demonstrated in vivo. Genistein inhibited growth of the breast cancer cells transplanted in nude mice. The growth inhibitory effect was associated with increased tumor cell apoptosis, and up-regulated p21WAF1/CIP1 expression. Furthermore, genistein inhibited angiogenesis as shown by decreased vessel density and decreased production and release of VEGF and TGF-beta 1.

CONCLUSION

Genistein exerts multiple suppressive effects on breast carcinoma. It may help halt its progression.

[Clinical implication of apoptosis of breast cancer induced by preoperative chemotherapy]

OBJECTIVE

To investigate whether apoptosis could be induced by preoperative chemotherapy in breast cancer patients, and determine if it is correlated with clinical response and patients' survival.

METHODS

Apoptosis was assayed by in situ DNA end labeling and receptors for estrogen and progesterone were examined immunohistochemically. Comparison of the differences in apoptotic index (AI) and clinical response was made between patients received preoperative chemotherapy and those did not, using the one tailed Student's t-test. The Kaplan-Meier method was utilized to calculate relapse-free and overall survival time. Cox proportional hazards model was used to conduct multivariate analysis of prognostic factors and differences in overall survival and relapse-free survival after adjustment for other variables.

RESULTS

Apoptosis was induced by preoperative chemotherapy, especially in lymph node positive patients. Post-chemotherapy AI correlated with better clinical response and increased patient survival, including relapse (disease) free survival and overall survival.

CONCLUSION

The extent of apoptosis induced by preoperative chemotherapy of primary breast cancer may possibly predict an individual patient's overall response to treatment.

A dimer as a building block in assembling RNA. A hexamer that gears bacterial virus phi29 DNA-translocating machinery

Six RNA (pRNA) molecules form a hexamer, via hand-in-hand interaction, to gear bacterial virus phi29 DNA translocation machinery. Here we report the pathway and the conditions for the hexamer formation. Stable pRNA dimers and trimers were assembled in solution, isolated from native gels, and separated by sedimentation, providing a model system for the study of RNA dimers and trimers in a protein-free environment. Cryo-atomic force microscopy revealed that monomers displayed a check mark outline, dimers exhibited an elongated shape, and trimers formed a triangle. Dimerization of pRNA was promoted by a variety of cations including spermidine, whereas procapsid binding and DNA packaging required specific divalent cations, including Mg(2+), Ca(2+), and Mn(2+). Both the tandem and fused pRNA dimers with complementary loops designed to form even-numbered rings were active in DNA packaging, whereas those without complementary loops were inactive. We conclude that dimers are the building blocks of the hexamer, and the pathway of building a hexamer is: dimer --> tetramer --> hexamer. The Hill coefficient of 2.5 suggests that there are three binding sites with cooperative binding on the surface of the procapsid. The two interacting loops played a key role in recruiting the incoming dimer, whereas the procapsid served as the foundation for hexamer assembly.

[Inner-hemangioma ligation and pingyangmycin injection in hemangioma (with 30 cases report)]

OBJECTIVE

To provide a simple and safe surgical approach in treating cavernous and racemose hemangioma.

METHODS

First cross-ligate the hemangioma, as to divide the tumor into independent compartments, them inject pingyangmycin into the compartments respectively.

RESULTS

There are 30 cases in this group (35 hemangiomas). Twenty-four cases (28 hemangiomas) were totally cured, accounting for 80%; Six cases were improved (7 hemangiomas) for 20%; There was no ineffective case.

CONCLUSION

"Inner-hemangioma ligation and injection of pingyangmycin" has broad surgical indications, with desirable outcome in treating cavernous and racemose hemangioma, especially those unsuitable for surgery, or ineffective simply by inner-hemangioma injection.

[Expression and insecticidal characteristics of cry3A in Lepidoptera-specific Bacillus thuringiensis]

The cry3A gene coding Coleoptera-specific protein was transformed into a wild strain YBT803-1 by electroporation, A transformant BMBY-001 was obtained. SDS-PAGE analysis demonstrated that cry3A could express 64 kD protein in BMBY-001. However, the expression of cry1Ab and cry1Ac were effected. Bioassay showed that BMBY-001 was not only highly toxic to Phyllodecta vulgatissima larva(LC50 0.413 microL/mL) but also toxic to Plutella xylostella(LC50 3.319 microL/mL).

[Study on clinical and laboratory features of preleukemia patients]

OBJECTIVE

To explore prospective diagnostic criteria for preleukemia.

METHODS

A case control study of the discrepancies of clinical and laboratory features between patients with preleukemia and those with chronic aplastic anemia (CAA) or atypical paroxysmal nocturnal hemoglubinuria (a-PNH).

RESULTS

There were eight variables of significance: (1) lymphocytoid micromegakaryocytes in marrow; (2) immature granulocytes in peripheral blood; (3) >or= 2% myeloblasts in marrow; (4) positive periodic acid schiff (PAS) staining of nucleated erythrocytes; (5) myeloid differentiation index >or= 1.8; (6) clonal karyotypic abnormalities; (7) negative sister chromatid differentiation; (8) > 4.0 cluster/colony ratio of granulocyte-macrophage colony-forming units (CFU-GM). The following criteria was assigned: A: To meet (1) and at least two of the other seven variables; B: To meet at least four of the eight variables. All of the patients with preleukemia met A or B and none of the patients with CAA or a-PNH did.

CONCLUSION

Preleukemia is different from CAA or a-PNH. It has its own clinical and laboratory features, which may be useful for prospective diagnosis.

[Study of the expression and function of c-kit receptor on the bone marrow mononuclear cells of the patients with myelodysplastic syndromes]

OBJECTIVE

To determine the expression and function of c-kit receptor on bone marrow mononuclear cells (BMMNC) of the patients with myelodysplastic syndromes.

METHODS

c-kit protein (CD(117)) was detected by direct immunofluorescence assay, c-kit mRNA by reverse transcriptive polymerase chain reaction (RT-PCR) and the function of c-kit receptor by cell culture.

RESULTS

c-kit protein expression in MDS was significantly higher than that in control [(8.58 +/- 5.28)% vs (3.04 +/- 1.49)%, P < 0.05]. c-kit protein expression in RA patients was significantly lower than that in RAEB/RAEB-t patients [(5.12 +/- 2.13)% vs (10.01 +/- 5.07)%, P < 0.05]. The rate of c-kit protein expression was (32.43 +/- 18.16)% in AML cases transformed from MDS (t-AML). c-kit mRNA expression in MDS was correlated with c-kit protein expression. Addition of interleukin-3 (IL-3), erythropoietin (Epo) and stem cell factor (SCF) to the semi-solid culture of BMMNC showed significant stimulating effects on CFU-GM and BFU-E formation in normal controls, but did not in MDS patients.

CONCLUSION

The protein and mRNA expressions of c-kit receptor on BMMNC in MDS are higher than those in normal control, and the function of this receptor in MDS is abnormal.

[Establishment and identification of B cell lines with PNH phenotype]

OBJECTIVE

To establish B cell lines from patients with paroxysmal nocturnal haemoglobinuria (PNH) and normal controls.

METHODS

B lymphoid cells prepared from PNH patients and normal controls were infected with EB virus. Phenotype of the immortal cells was analyzed by flow cytometry. The immunomagnetic beads were used to select CD(55)(-) and CD(59)(-) B lymphoid cells, which were cloned by limiting dilution. The clonality of the cloned cells was confirmed by testing the pattern of Ig rearrangements using polymerase chain reaction (PCR).

RESULTS

From 2 PNH patients and 2 normal controls, CD(55)(-) and CD(59)(-) B lymphoblastoid cell lines were established which had PNH phenotype and normal phenotype, respectively.

CONCLUSION

B lymphoid cell lines from PNH patients can be obtained by EB virus infection.

Cryoatomic force microscopy of filamentous actin

Cryoatomic force microscopy (cryo-AFM) was used to image phalloidin-stabilized actin filaments adsorbed to mica. The single filaments are clearly shown to be right-handed helical structures with a periodicity of approximately 38 nm. Even at a moderate concentration ( approximately 10 microg/ml), narrow, branched rafts of actin filaments and larger aggregates have been observed. The resolution achieved is sufficient to resolve actin monomers within the filaments. A closer examination of the images shows that the branched rafts are composed of up to three individual filaments with a highly regular lateral registration with a fixed axial shift of approximately 13 nm. The implications of these higher-order structures are discussed in terms of x-ray fiber diffraction and rheology of actin gels. The cryo-AFM images also indicate that the recently proposed model of left-handed F-actin is likely to be an artifact of preparation and/or low-resolution AFM imaging.

PNA-dependent gene chemistry: stable coupling of peptides and oligonucleotides to plasmid DNA

Two approaches are described for stably conjugating peptides, proteins and oligonucleotides onto plasmid DNA. Both methods use a peptide nucleic acid (PNA) clamp, which binds irreversibly and specifically to a binding site cloned into the plasmid. The first approach uses a biotin-conjugated PNA clamp that can be used to introduce functional biotin groups onto the plasmid to which streptavidin can bind. Atomic force microscopy images of linearized plasmid show streptavidin localized at the predicted PNA binding site on the DNA strand. Peptides and oligonucleotides containing free thiol groups were conjugated to maleimide streptavidin, and these streptavidin conjugates were bound to the biotin-PNA-labeled plasmid. In this way, peptides and oligonucleotides could be brought into stable association with the plasmid. A second approach used a maleimide-conjugated PNA clamp. Methods are described for conjugating thiolated peptides and oligonucleotides directly to the maleimide-PNA-DNA hybrid. This straightforward technology offers an easy approach to introduce functional groups onto plasmid DNA without disturbing its transcriptional activity.

Optimizing the window size for multiple least squares fitting of electron energy loss spectra

The purpose of this study was to determine the effect of the fitting window size used with the linear least squares fit method when quantitating trace elements with electron energy loss spectroscopy. Theory and computer simulation with a simple model of two 'signals' show that, when the background underlying the signal is slowly varying and the signal is localized, there exists a minimum window optimal for fitting raw spectra. The width of the minimum fitting window can be determined directly from the reference standard spectrum of the signal alone and the estimates of signal and background are related. Use of narrower than the minimum window will increase the fitting uncertainty of the signal and yield less reliable results. More complicated experimental spectra must be fitted to more than two standards and a simple analytical expression of the minimum fitting window cannot be derived, but can be determined empirically. Our study shows that the empirical value obtained from experimental spectra is only slightly larger than the theoretical value derived from the simple model, indicating that this conclusion is still valid. When fitting difference spectra with a slowly varying background, the estimates of signal and background are independent and windows wider than the size of the signal will yield the same fitting uncertainty. In the presence of a non-slowly varying background, common in difference spectra, the minimum window size depends on the fine structure of the signal and the background.

Atomic force microscopy in structural biology: from the subcellular to the submolecular

Atomic force microscopy (AFM) is capable of generating images within ranges of resolution that are of particular interest in biology. Although atomic resolution may not be possible with biological samples, a great deal of information can still be obtained from images that provide structures at a slightly lower level of resolution. The submolecular resolution images of bacteriorhodopsin and the chaperonin GroES, which revealed, respectively, individual loops and beta-turns, confirmed and complemented other structural investigations, while the molecular-level features in images of membrane-bound VacA, a cytotoxin from Helicobacter pylori, immediately suggested the possibility, subsequently proven, of channel-forming ability. A series of images with macromolecular resolution directly provided details on the mechanisms by which RNA polymerase nonspecifically translocates along DNA, and images with subcellular resolving power of erythrocytic cellular membranes showed, with unambiguous clarity, linear arrays of molecular complexes. In this review, we will describe some of the most biologically relevant findings that have been obtained with AFM within ranges of resolution from the submolecular to the molecular, and from the macromolecular to the subcellular. Furthermore, we will describe some of the sample conditions and imaging environments that are likely important to achieve a particular level of resolution.

A dominant negative mutant of Helicobacter pylori vacuolating toxin (VacA) inhibits VacA-induced cell vacuolation

Most Helicobacter pylori strains secrete a toxin (VacA) that causes structural and functional alterations in epithelial cells and is thought to play an important role in the pathogenesis of H. pylori-associated gastroduodenal diseases. The amino acid sequence, ultrastructural morphology, and cellular effects of VacA are unrelated to those of any other known bacterial protein toxin, and the VacA mechanism of action remains poorly understood. To analyze the functional role of a unique strongly hydrophobic region near the VacA amino terminus, we constructed an H. pylori strain that produced a mutant VacA protein (VacA-(Delta6-27)) in which this hydrophobic segment was deleted. VacA-(Delta6-27) was secreted by H. pylori, oligomerized properly, and formed two-dimensional lipid-bound crystals with structural features that were indistinguishable from those of wild-type VacA. However, VacA-(Delta6-27) formed ion-conductive channels in planar lipid bilayers significantly more slowly than did wild-type VacA, and the mutant channels were less anion-selective. Mixtures of wild-type VacA and VacA-(Delta6-27) formed membrane channels with properties intermediate between those formed by either isolated species. VacA-(Delta6-27) did not exhibit any detectable defects in binding or uptake by HeLa cells, but this mutant toxin failed to induce cell vacuolation. Moreover, when an equimolar mixture of purified VacA-(Delta6-27) and purified wild-type VacA were added simultaneously to HeLa cells, the mutant toxin exhibited a dominant negative effect, completely inhibiting the vacuolating activity of wild-type VacA. A dominant negative effect also was observed when HeLa cells were co-transfected with plasmids encoding wild-type and mutant toxins. We propose a model in which the dominant negative effects of VacA-(Delta6-27) result from protein-protein interactions between the mutant and wild-type VacA proteins, thereby resulting in the formation of mixed oligomers with defective functional activity.

Role of reactive oxygen species in acetylcholine-induced preconditioning in cardiomyocytes

We examined the ability of ACh to mimic ischemic preconditioning in cardiomyocytes and the role of ATP-sensitive potassium (KATP) channels and mitochondrial reactive oxygen species (ROS) in mediating this effect. Chick embryonic ventricular myocytes were studied in a flow-through chamber while flow rate, pH, PO2, and PCO2 were controlled. Cell viability was quantified with propidium iodide (5 microM), and production of ROS was measured using 2', 7'-dichlorofluorescin diacetate. Data were expressed as means +/- SE. Preconditioning with 10 min of ischemia followed by 10 min of reoxygenation or 10 min of ACh (1 mM) followed by a drug-free period before 1 h of ischemia and 3 h of reoxygenation reduced cell death to the same extent [preconditioning 19 +/- 2% (n = 6, P < 0.05) ACh 21 +/- 5% (n = 6, P < 0.05) vs controls 42 +/- 5% (n = 9)]. Like preconditioning, ACh increased ROS production threefold before ischemia [0.60 +/- 0.16 (n = 7, P < 0.05) vs. controls, 0.16 +/- 0. 03 (n = 6); arbitrary units]. Protection and increased ROS production during ACh preconditioning were abolished with 5-hydroxydecanoate (5-HD, 100 microM), a selective mitochondrial K(ATP) channel antagonist, and the thiol reductant 2-mercaptopropionyl glycine (2-MPG, 1 mM), an antioxidant [cell death: 5-HD+ACh 37 +/- 7% (n = 5), 2-MPG+ACh 47 +/- 6% (n = 6); ROS signals: 5-HD+ACh 0.09 +/- 0.03 (n = 5), 2-MPG+ACh 0.01 +/- 0.04 (n = 4)]. In addition, ACh-induced ROS signaling was blocked by the mitochondrial site III electron transport inhibitor myxothiazol (0.02 +/- 0.07, n = 5). These results demonstrate that activation of mitochondrial K(ATP) channels and increased ROS production from mitochondria are important intracellular signals that participate in ACh-induced preconditioning in cardiomyocytes.

Evi-1 and MDS1-Evi-1 genes in pathogenesis of myelodysplastic syndromes and post-MDS acute myeloid leukemia

OBJECTIVE

To investigate expression of Evi-1 and MDS1-Evi-1 genes in myelodysplastic syndromes (MDS) and post-MDS acute myeloid leukemia (post-MDS AML), and its role in pathogenesis or progression of MDS and post-MDS AML.

METHODS

Expression of Evi-1 and MDS1-Evi-1 genes was examined in 31 MDS, 11 post-MDS AML, and 34 de novo AML patients by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Evi-1 expression was not detected in bone marrow samples of 8 normal controls, but low MDS1-Evi-1 expression levels (MDS1-Evi-1/GAPDH < 0.1) were detected in 3 of the 8 controls. Evi-1 RNA was expressed in 1 of 8 RA, 8 of 13 RAEB and 6 of 9 RAEB-T patients, and the percentage of Evi-1 expression in RAEB(T) patients was higher than that in RA (P < 0.05). MDS1-Evi-1 expression was detected in 5 of 8 RA, 9 of 13 RAEB and 5 of 9 RAEB-T patients, and MDS1-Evi-1 expression levels (MDS1-Evi-1/GAPDH > 0.1) were markedly higher than those in the controls. Evi-1 expression was gradually increased in 4 of 5 RAEB-T patients with transformation from MDS to AML. The percentages of Evi-1 and MDS1-Evi-1 expression in post-MDS AML patients were significantly (P < 0.01 and P < 0.05 respectively) higher than those in de novo AML. The colonies of hematopoietic progenitor cells were decreased in Evi-1 and MDS1-Evi-1-positive MDS patients as compared with those in Evi-1 and MDS1-Evi-1-negative patients.

CONCLUSION

Abnormal expression of the Evi-1 gene and overexpression of MDS1-Evi-1 gene may play a role in the pathogenesis or progression of MDS and post-MDS AML.

AFM tips: how sharp are they?

From both simple estimates and a 'blind' reconstruction based on cryo-AFM images of filamentous actin, we find that the radius of curvature at the apex of Si3N4 tips can be as small as 1 nm with a conical angle in the range 30 approximately 40 degrees, revealing a relatively high aspect ratio that is much greater than previously anticipated. Our results show that commercially available cantilevers are often sharp enough for routine high resolution imaging of biological materials, and suggest that factors other than an inherent blunt tip are probably responsible for frequent occurrences of poor resolution.

[In vitro proliferation and differentiation of bone marrow stem cells of aplastic anemia patients]

OBJECTIVE

To investigate the quality of bone marrow stem cells from aplastic anemia patients and their in vitro responses to hemopoietic growth factors(HGF).

METHODS

CD34 positive bone marrow cells from 10 chronic aplastic anemia(CAA), 5 severe aplastic anemia(SAA) patients and 5 healthy subjects were detected with immunoflurescence assay, enriched by Panning way, and then cultured in vitro for CFU-GM, BFU-E and CFU-E in the presence of recombinant HGFs.

RESULTS

CD34 positive rates of the bone marrow mononuclear cells(MNC) of CAA, SAA and control groups were (1.05 +/- 0.51)%, (0.70 +/- 0.37)% and (1.27 +/- 0.45)%, respectively, and there was no difference among them (P > 0.05). After being enriched, CD34 positive cells in MNC of CAA, SAA and control groups increased to a similar level(P > 0.05). In the presence of G-CSF or GM-CSF, the enriched CD34 positive MNC of CAA and SAA patients formed similar CFU-GM number to those of normal controls. The numbers of BFU-E and CFU-E formed from the enriched CD34 positive MNC of CAA and SAA patients were also the same as that of normal control groups under the stimulation of erythropoietin and interleukin-3. Stem cell factor could cooperate with G-CSF, GM-CSF, and erythropoietin significantly increasing the numbers of CFU-GM, BFU-E and CFU-E of CAA, SAA and normal control's enriched CD34 positive MNC.

CONCLUSION

The bone marrow CD34 positive cells from aplastic anemia patients appears to be normal in percentages and in in vitro proliferation/differentiation capacities.

[The clinical implications of IgG subclass in 84 patients with autoimmune hemolytic anemia]

OBJECTIVE

To evaluate the clinical implications of IgG subclass in autoimmune hemolytic anemia(AIHA).

METHODS

Data of 84 AIHA patients were retrospectively analyzed.

RESULTS

In the 84 patients, IgG1 + IgG3 + C3d accounted for 45.0%, IgG1 + IgG3 15.5%, IgG1 + C3d 11.0%, C3d 10.7%, IgG1 9.5% and IgG3 + C3d 8.3%. IgG3 patients had the most severity of clinical and laboratory findings, followed by IgG1 patients. In IgG1 and IgG3 subgroups, the severity of hemolysis was positively correlated with the score of Coombs' test. The response rates of IgG3 and IgG1 patients were 68.2% and 100%, respectively.

CONCLUSION

In AIHA, the basic predominant IgG subclass is IgG1. IgG3 has a greater potential for red-cell destruction than IgG1 and C3d.

[Expression of c-kit receptor on the hemopoietic stem/precursor cells of aplastic anemia patients]

OBJECTIVE

To explore the expression of c-kit receptor(CD117) on the hemopoietic stem/precursor cells of aplastic anemia patients and its role in the genesis of aplastic hematopoiesis failure.

METHODS

c-kit expression on the bone marrow mononuclear cells(MNC) and CD34 positive cells from 11 chronic aplastic anemia (CAA), 9 severe aplastic anemia(SAA), 10 non-aplastic anemia(NAA) patients (5 iron deficiency anemia and 5 autoimmune hemolytic anemia) and 5 healthy controls was measured with flow cytometric immunofluorescence assay and anti-CD117 monoclonal antibody.

RESULTS

The CD117 positive rates of MNC in CAA, SAA, NAA and control groups were (2.08 +/- 1.96)%, (0.89 +/- 0.32)%, (0.67 +/- 0.39)% and (0.45 +/- 0.16)%, respectively, and the rates were significantly higher in CAA and SAA groups than in NAA and control groups(P < 0.05). The CD117 and CD34 double positive cells of MNC in CAA, SAA, NAA and control groups were (0.87 +/- 0.57)%, (0.65 +/- 0.41)%, (0.46 +/- 0.26)% and (0.41 +/- 0.15)%, respectively, and were significantly higher in CAA and SAA groups than in NAA and control groups (P < 0.05). The CD117 positive cells of CD34 positive cells were also higher in CAA[(71.6 +/- 12.4)%] and SAA[(88.9 +/- 23.5)%] groups than in NAA[(41.8 +/- 10.3)%] and control [(46.3 +/- 9.7)%] groups (P < 0.01).

CONCLUSION

Hemopoietic stem/precursor cells of aplastic anemia patients expressed more c-kit receptors than those of NAA patients and healthy controls. The hematopoiesis failure occurred in aplastic anemia is not attributed to low expression of c-kit receptor on the hemopoietic stem/precursor cells.

Recombination and chimeragenesis by in vitro heteroduplex formation and in vivo repair

We describe a simple method for creating libraries of chimeric DNA sequences derived from homologous parental sequences. A heteroduplex formed in vitro is used to transform bacterial cells where repair of regions of non-identity in the heteroduplex creates a library of new, recombined sequences composed of elements from each parent. Heteroduplex recombination provides a convenient addition to existing DNA recombination methods ('DNA shuffling') and should be particularly useful for recombining large genes or entire operons. This method can be used to create libraries of chimeric polynucleotides and proteins for directed evolution to improve their properties or to study structure-function relationships. We also describe a simple test system for evaluating the performance of DNA recombination methods in which recombination of genes encoding truncated green fluorescent protein (GFP) reconstructs the full-length gene and restores its characteristic fluorescence. Comprising seven truncated GFP constructs, this system can be used to evaluate the efficiency of recombination between mismatches separated by as few as 24 bp and as many as 463 bp. The optimized heteroduplex recombination protocol is quite efficient, generating nearly 30% fluorescent colonies for recombination between two genes containing stop codons 463 bp apart (compared to a theoretical limit of 50%).

Subclasses of warm autoantibody IgG in patients with autoimmune hemolytic anemia and their clinical implications

OBJECTIVE

To explore the mechanism of autoimmune hemolysis and establish a more sensitive test for autoimmune hemolytic anemia (AIHA).

METHODS

IgG subclasses were tested in 40 patients with idiopathic or secondary AIHA by Coombs test with monoclonal antibodies. Hb, TBil, RC and FHb, as hemolytic parameters, were used to analyze the clinical implications of subclasses of AIHA warm autoantibody IgG.

RESULTS

In most patients IgG incomplete warm autoantibody was IgG1 (27 patients), but IgG3 (20 patients), rarely IgG2 (14 patients) and IgG4 (9 patients) also occurred. Three groups were analyzed: Group A included 20 patients with IgG3; Group B included 14 patients with IgG1 bit without IgG3; Group C included 6 patients without IgG1 and IgG3. There were significant differences (P < 0.01) between groups in Hb, TBil, RC and FHb. Moreover, we also found that the sensitivity of Coombs test with polyclonal antiserums was 90.0%, while that of Coombs test with monoclonal antibodies was 97.5%. The effect of treatment was worst in patients with positive IgG3 autoantibody, whose hemolysis recurred frequently.

CONCLUSION

IgG3 autoantibody was the most effective in bringing about red cell destruction, IgG1 autoantibody was less effective, IgG2 even less, whereas IgG4 autoantibody was shown to hardly affect red cell survival. Coombs test with monoclonal antibodies was more sensitive than that with polyclonal antiserums. Patients' respondence to treatment correlated with the type of IgG subclasses.

[Mechanism of growth inhibition by genistein of human breast carcinoma]

OBJECTIVE

To study the mecnanism of inhibition of breast carcinoma cells by genistein.

METHODS

Human breast cancer cell lines were treated in vitro with genistein. Northern blot, Western blot, plasmid transfection and apoptosis assay were used to evaluate the mechanism of cell growth inhibition.

RESULTS

Genistein could inhibit proliferation of human breast carcinoma cells with different ER status and p53 status. This inhibition was associated with induction of p21WAF1/CIP1 mRNA and protein expression. Exposure of MCF-7 and MDA-MB-231 cells to genistein resulted in statistically significant increased p21WAF1/CIP1 mRNA stability, accompanied with increased p21WAF1/CIP1 protein expression. This increase in p21WAF1/CIP1 was subsequently followed by the onset of apoptosis.

CONCLUSION

The inhibitory effect of genistein on cell proliferation of breast cancer appears to be due to p21WAF1/CIP1 expression and apoptosis through mechanism independent of ER and p53. The results provide evidence for the potential usefulness of genistein in the prevention and treatment of human breast cancer.

Images of oligomeric Kv beta 2, a modulatory subunit of potassium channels

The Shaker type voltage-gated potassium (K+) channel consists of four pore-forming Kv alpha subunits. The channel expression and kinetic properties can be modulated by auxiliary hydrophilic Kv beta subunits via formation of heteromultimeric Kv alpha-Kv beta complexes. Because each (Kv alpha)4 could recruit more than one Kv beta subunit and different Kv beta subunits could potentially interact, the stoichiometry of alpha-beta and beta-beta complexes is therefore critical for understanding the functional regulation of Shaker type potassium channels. We expressed and purified Kv beta 2 subunit in Sf9 insect cells. The purified Kv beta 2, examined by atomic force and electron microscopy techniques, is found predominately as a square-shaped tetrameric complex with side dimensions of 100 x 100 A2 and height of 51 A. Thus, Kv beta 2 is capable of forming a tetramer in the absence of pore-forming alpha subunits. The center of the Kv beta 2 complex was observed to be the most heavily stained region, suggesting that this region could be part of an extended tubular structure connecting the inner mouth of the ion permeation pathway to the cytoplasmic environment.

Stabilization of chromatin structure by PRC1, a Polycomb complex

The Polycomb group (PcG) genes are required for maintenance of homeotic gene repression during development. Mutations in these genes can be suppressed by mutations in genes of the SWI/SNF family. We have purified a complex, termed PRC1 (Polycomb repressive complex 1), that contains the products of the PcG genes Polycomb, Posterior sex combs, polyhomeotic, Sex combs on midleg, and several other proteins. Preincubation of PRC1 with nucleosomal arrays blocked the ability of these arrays to be remodeled by SWI/SNF. Addition of PRC1 to arrays at the same time as SWI/SNF did not block remodeling. Thus, PRC1 and SWI/SNF might compete with each other for the nucleosomal template. Several different types of repressive complexes, including deacetylases, interact with histone tails. In contrast, PRC1 was active on nucleosomal arrays formed with tailless histones.

[Prognostic significance of cyclin-dependent kinase inhibitor p27kip1 expression in human breast cancer]

OBJECTIVE

To study the expression of p27kip1 in breast cancer in relation to biological behavior and prognosis.

METHODS

p27kip1 expression at protein level was determined by immunohistochemistry technique in 181 patients with breast cancer. In addition, p27WAF1/CIP1, p53 and mdm2 were examined in 106 cases of this series. Data about apoptotic index, bcl-2 and bax protein expression were available in the other 91 patients.

RESULTS

Of the 181 patients, p27kip1 expression was low in 121 (66.9%) and high in 60 (33.1%), respectively. p27kip1 expression level was correlated with histological grade, tumor size, axillary lymph node status, post-operative recurrence, invasion and metastasis. It was also correlated with bcl-2, bax, p53, p21WAF1/CIP1, and mdm2 expression levels. Univariate analysis demonstrated better disease-free survival in patients with higher p27kip1 expression than in those with lower expression. However, by Cox multivariate analysis, p27kip1 expression level was not found to be of independent prognostic significance.

CONCLUSION

As an inhibitor of cyclin-dependent kinase, p27kip1 favors prognosis of human breast cancer not only by arresting cell cycle in G1 phase but also inducing cancer cell apoptosis.

VacA from Helicobacter pylori: a hexameric chloride channel

VacA is a unique protein toxin secreted by the human pathogen Helicobacter pylori. At a neutral pH, the cytotoxin self-associates into predominantly dodecameric complexes. In this report, we show that at an acidic pH, VacA forms anion selective channels in planar phospholipid bilayers. Similar to several other chloride channels, the VacA channel exhibits a moderate selectivity for anions over cations (P(Cl):P(Na) = 4.2:1), inhibition by the blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and a permeability sequence, SCN- >> I- > Br- > Cl- > F, consistent with a 'weak field strength' binding site for the permeant anion. Single channel recordings reveal rapid transitions (486 s(-1)) between the closed state and a single open state of 24 pS (+60 mV, 1.5 M NaCl). Evaluation of the rate of increase in macroscopic current as well as atomic force microscopy suggest that this VacA channel is a hexamer, formed by the assembly of membrane-bound monomers. Not only are these VacA channels likely to play an important role in the pathological activity of this toxin, but they may also serve as a model system to further investigate the mechanism of anion selectivity in general.