Berenil-induced undercondensation in human heterochromatin

The aromatic diamidine berenil specifically inhibits the condensation of a subset of constitutive heterochromatin in human lymphocyte cultures. In the normal male chromosome complement, only the quinacrine-brilliant Y heterochromatin exhibits distinct undercondensation. The optimal culture conditions for inhibiting heterochromatin condensation are achieved when berenil is added at a final concentration of 150 micrograms/ml 24 h before cell harvest. Various examples of the use of berenil in the analysis of chromosome rearrangements involving quinacrine-brilliant heterochromatin are presented. A variant, giant-satellited chromosome 22 was found to respond to berenil treatment, although its enlarged and quinacrine-bright short-arm region did not contain Y heterochromatin. Southern blot analysis and chromosome in situ hybridization suggested that most chromosome 22 variants do not stem from Y; acrocentric translocations. The experimentally undercondensed Y heterochromatin is characterized by moderate C-band labeling, bright quinacrine fluorescence, and specific silver staining. At the ultrastructural level, undercondensation is associated with loosely packed, mutliply folded chromatin fibers with a diameter of approximately 250 A and organized probably as loops.     

The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras

Transfection of cells with cloned genes or total genomic DNA offers a means for studying aspects of neoplastic behaviour. We have used this method to examine whether incorporation of the cloned 6.6-kilobase (kb) fragment of DNA containing the mutant c-Ha-ras human oncogene can confer metastatic capability on murine NIH 3T3 cells. Cells co-transfected with the mutated ras gene and the neomycin resistance marker pSV2neo were selected by culture in neomycin. On subcutaneous inoculation into MF 1 nude mice, these cells proved to be tumourigenic with short latent periods (approximately 14 days)--nude mice were used to circumvent immunological rejection of the mouse cells expressing the product of the human oncogene. Transfectants were capable of lung colonisation after intravenous injection, but there was no evidence of spontaneous metastasis at autopsy, or on histological examination of the lungs and other organs, 90 days after inoculation. Incorporation of the transfected oncogene was confirmed by Southern blotting and its expression by dot-blot hybridisation and immunoprecipitation. The results in this experimental system indicate that transfection of a mutated human ras oncogene into non-neoplastic 3T3 cells can confer part of the metastatic phenotype, namely lung colonisation, but is not by itself sufficient to induce spontaneous metastatic behaviour.     

Immunofluorescence colocalization of the 90-kDa heat-shock protein and microtubules in interphase and mitotic mammalian cells

A mouse monoclonal antibody (AC88) that was raised against the 88-kDa heat-shock protein of the water mold, Achlya ambisexualis, and that cross-reacts with the 90-kDa mammalian heat-shock protein (hsp90), and an antibody against tubulin were used to localize hsp90 and microtubules, respectively, in the same cultured rat endothelial and PtK1 epithelial cells by indirect immunofluorescence. AC88 and tubulin antibodies labeled the same structures in cells at all stages of the cell cycle, regardless of whether cells were permeabilized before or after fixation. Labeling of cell structures by both AC88 and anti-tubulin antibodies was identically affected by treating cells with colcemid. Double labeling with AC88 and anti-tubulin antibodies in interphase and mitotic cells is consistent with the conclusion that all microtubules are labeled and that no subclass of microtubules is preferentially labeled. Fluorescent labeling by AC88 was prevented by preabsorption of the antibody with purified rat hsp90 but was unaffected by preabsorption with purified 6S tubulin dimer. In contrast to AC88, fluorescent labeling by an anti-tubulin antibody was prevented by preabsorption with tubulin dimer but was unaffected by preabsorption with rat hsp90. Western-blot analysis demonstrated no cross-reactivity of AC88 for tubulin and no cross-reactivity of the anti-tubulin antibody for hsp90. A polyclonal antiserum fraction from a rabbit immunized with the 89-kDa heat-shock protein from chicken also labeled the mitotic apparatus in dividing cells and, somewhat less distinctly, fibrous structures in interphase cells. Labeling by hsp89 anti-serum was prevented by absorption with hsp90. AC88 also labeled microtubules in cultured mouse (L929 and 3T3), rat (endothelium and TRST), hamster (CHO) and primate (BSC, COS-1 and HeLa) cell lines. The demonstration of colocalization of hsp90 with microtubules should provide a valuable clue to eventual understanding of the cellular function of this ubiquitous, conserved and abundant stress-response protein.     

Arachidonic acid-induced calcium influx in human platelets. Comparison with the effect of thrombin.

The effects of arachidonic acid and thrombin on calcium movements have been studied in fura-2-loaded platelets by a procedure which allows simultaneous monitoring of the uptake of manganese, a calcium surrogate for Ca2+ channels, and the release of Ca2+ from intracellular stores. Arachidonic acid induced both Ca2+ (Mn2+) entry through the plasma membrane and Ca2+ release from the intracellular stores. The release of Ca2+ was prevented by cyclo-oxygenase inhibitors and mimicked by the prostaglandin H2/thromboxane A2 receptor agonist U46619. Ca2+ (Mn2+) entry required higher concentrations of arachidonic acid and was not prevented by either cyclo-oxygenase or lipoxygenase inhibitors. Several polyunsaturated fatty acids reproduced the effect of arachidonic acid on Ca2+ (Mn2+) entry, but higher concentrations were required. The effects of maximal concentrations of arachidonic acid and thrombin on the uptake of Mn2+ were not additive. Both agonists induced the entry of Ca2+, Mn2+, Co2+ and Ba2+, but not Ni2+, which, in addition, blocked the entry of the other divalent cations. However, arachidonic acid, but not thrombin, increased a Ni2(+)-sensitive permeability to Mg2+. The effect of thrombin but not that of arachidonic acid was prevented either by pretreatment with phorbol ester or by an increase in cyclic-AMP levels. Arachidonic acid also accelerated the uptake of Mn2+ by human neutrophils, rat thymocytes and Ehrlich ascites-tumour cells.     

5,6,7,8-Tetrahydromethanopterin-dependent enzymes involved in methanogenesis

Abstract In the process of methanogenesis, 5,6,7,8-tetrahydromethanopterin (H₄MPT) is the carrier of the C₁ unit at the formyl through methyl state of reduction. By the transfer of a formyl group from formylmethanofuran, 5-formyl- and 10-formyl-H₄MPT are formed in hydrogenotrophic and methylotrophic organisms, respectively. Cyclohydrolysis of the 5- and 10-formyl derivatives then yields 5,10-methenyl-H₄MPT, which is reduced in two subsequent coenzyme F₄₂₀-dependent reactions to 5-methyl-H₄MPT. Following the transfer of the methyl group to coenzyme M, the substrate of the terminal step in methanogenesis, methylcoenzyme M, is produced. In this paper properties of the enzymes catalyzing the individual H₄MPT-dependent reactions are discussed.     

Biosynthesis of platelet-activating factor in glandular gastric mucosa. Evidence for the involvement of the ''de novo'' pathway and modulation by fatty acids.

The biosynthesis of platelet-activating factor (PAF), a phospholipid autocoid with potent ulcerogenic properties that is produced in secretory exocrine glands by physiological secretagogues, was assessed in microsomal preparations of glandular gastric mucosa. For this purpose, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PAF):acetyl-CoA acetyltransferase (EC 2.3.1.67); the enzymes of the 'de novo' pathway: 1-O-alkyl-2-lyso-sn-glycero-3-phosphate (alkyl-lyso-GP):acetyl-CoA acetyltransferase and 1-O-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G):CDP-choline cholinephosphotransferase (EC 2.7.8.16); and some enzymes involved in the catabolism of PAF and lyso-PAF were assayed. Only the enzymes of the 'de novo' pathway and small amounts of PAF acetylhydrolase, phospholipase A2 and a lysophospholipase D acting on either lipids could be detected in the gastric preparations, whereas lyso-PAF:acetyl-CoA acetyltransferase activity was undetectable. The specific activity of alkyl-lyso-GP:acetyl-CoA acetyltransferase in the gastric mucosa was about one-tenth of that found in spleen microsomes and its apparent Km for acetyl-CoA was 454 microM compared with 277 microM in spleen microsomes. Glandular mucosa homogenates contained preformed PAF at a concentration of 2.7 +/- 0.7 ng equivalents of PAF (hexadecyl)/mg of protein. When gastric microsomes were incubated with micromolar concentrations of fatty acids (arachidonic, palmitic and oleic) prior to the assay of dithiothreitol (DTT)-insensitive cholinephosphotransferase, a dose-dependent reduction in the formation of PAF was observed, arachidonic acid being the most potent inhibitor, followed by linoleic acid (only tested on spleen microsomes) and oleic acid. By contrast, 1,2-diolein and phosphatidylcholine (dipalmitoyl) showed no or little effect. These results indicate that glandular gastric mucosa can produce PAF through the 'de novo' pathway, and that fatty acids, especially unsaturated, can reduce that synthesis by modulating the expression of DTT-insensitive cholinephosphotransferase.     

流行性出血热病毒R22株cDNA克隆及其特异性鉴定

用家鼠型流行性出血热病毒R22株RNA,经polyA接尾,以Oligo-dT做引物,合成cDNA。用pUC18为载体转染E.coli Mc1061,建立cDNA克隆。再经菌落杂交,选择病毒特异性的5个阳性克隆制成缺口翻译探针,与病毒RNA3个片段进行反杂交,确定RNA片段的特异性。结果表明,3个克隆为中(M)片段的cDNA,另两个分别为大(L)和小(S)片段cDNA。核苷酸序列分析证明,克隆的DNA中含病毒特异的核苷酸序列。     

Phorbol esters enhance attachment of NIH/3T3 cells to laminin and type IV collagen substrates

The effect of phorbol esters on the adhesive properties of NIH/3T3 mouse fibroblasts was investigated using plastic substrates precoated with the extracellular matrix proteins fibronectin, collagen, and laminin. Treatment with phorbol 12-myristate 13-acetate (PMA) enhanced NIH/3T3 cell attachment to laminin and type IV collagen substrates but had little or no effect on attachment to fibronectin and type I collagen substrates. The effect of PMA in enhancing cell attachment to laminin and type IV collagen substrates was dose dependent between 10(-9) and 10(-7) M. PMA was effective as early as 30 min; the effect reached a maximum at 2 h and decreased gradually. Phorbol 12, 13-dibenzoate and phorbol 12, 13-diacetate were effective but to a lesser extent and phorbol 12-myristate and phorbol 13-acetate showed little or no effect. These results suggest that PMA may enhance NIH/3T3 cell adhesion through effects on laminin and type IV collagen receptors. Retinoic acid, which itself requires at least 6 h to show an effect on attachment, did not have any effect on cell attachment in 2 h and, if anything, slightly inhibited PMA-enhanced cell attachment to laminin and type IV collagen substrates.