The specific silver staining of nucleolar region organizers was applied to Daudi lymphoma control and interferon alpha-treated cells. Isolated nuclei from control and treated samples were used for the kinetic analysis of in vitro RNA and DNA synthesis. Results have shown that interferon treatment induces a reduction of the transcriptional and replicative activities within 90 min. Concomitant to these results is the modification of the organization of nucleoli. Intensity and distribution of silver grains are, in fact, different in treated cells nucleoli as compared to those of controls. Thus, the number and the arrangement of granules could be related to the functional state of the cells suggesting that the transient cascade of interferon-generated signals involves also modulation of nucleolar structure and function in accordance with the hypothesis of a relationship of cell proliferation rate to silver-stained nucleolar protein quantity.

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To study the process of nuclear envelope assembly at the end of mitosis, we developed a chromatin- free in vitro system for assembly of envelope structures in Xenopus interphase egg extract, and examined the participation of Ku-homologous protein in the assembly. The envelope structure assembled spontaneously in the absence of chromatin or DNA between glass plates under a condition that minimized generation of flow of the extract. Morphological study using an electron microscopy has revealed that the membrane surrounding the envelope structure is a double membrane that contains gaps resembling nuclear pore complex. Their assembly was dependent on ATP and was inhibited by the addition of GTP-γ-S or N-ethylmaleimide. Depletion of a prenuclear vesicle by preincubating the interphase egg extracts with large excess of sperm head chromatins impaired the assembly. The membrane vesicle, which was associated with Ku-homologous protein of Xenopus, participated in the assembly as proven by reaction with monoclonal antibody made specific for Ku p70 protein. However, the assembly process of the envelope structure was inhibited only slightly by the antibody, suggesting that the Ku-homologous protein does not participate in the fusion process of vesicles to form the envelope structure.

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Previously we described that bacterial lipopolysaccharide (LPS) promoted DNA synthesis and supported the cell viability in the factor-dependent macrophage cell lines BDM-1 and BDM-1W3 in the absence of colony-stimulating factor (CSF). To further examine this phenomenon, in the present study we examined the effects of serum on CSF-dependent proliferation and LPS-induced DNA synthesis in BDM-1 and BDM-1W3 cells. Fetal calf serum (FCS) was required for CSF-dependent proliferation in BDM-1 and BDM-1W3 cells. FCS was also required for LPS-induced DNA synthesis in BDM-1W3 cells.
However, at concentrations higher than 0.2%, FCS inhibited LPS-induced DNA synthesis in BDM-1W3 cells in a dose-dependent manner. To obtain the inhibitory activity in FCS (FCS-In) for LPS-induced DNA synthesis, FCS was fractionated by gel filtration chromatography using Sephacryl S-200, chromatography on DEAE-Sephacel, and affinity chromatography on heparin-Sepharose. FCS-In was eluted in the void volume peak from a Sephacryl S-200 column, indicating that FCS-In has a molecular weight of more than 250, 000. The molecular weight of FCS-In was apparently 270, 000 as determined by SDS-polyacrylamide gel electrophoresis (PAGE) under non-reducing conditions. Upon reduction, four components became detectable with apparent molecular weights of 170, 000, 110, 000, 67, 000, and 30, 000. The inhibitory activity in FCS-In material was inactivated by heat and trypsin treatment. The partially purified FCS-In inhibited LPS-induced DNA synthesis in BDM-1W3 cells, but did not inhibit the proliferation of BDM-1W3 cells induced by IL-3, granulocyte-macrophage CSF (GM-CSF), or macrophage CSF (M-CSF).
These results indicate that the inhibition by FCS-In is specific to LPS. Although the site and mechanism of inhibition are not known, FCS-In may function in vivo by modulating the interaction of LPS with macrophages.

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Human single-stranded DNA binding protein (hSSB/RPA) is a multimeric single-stranded DNA binding protein consisting of three subunits of 70 kDa, 34 kDa, and 11 kDa. Human SSB was isolated from HeLa cells as an essential factor for the in vitro replication of simian virus 40 DNA. We and others have isolated and sequenced cDNAs for each subunit of the SSB. The chromosome on which each gene is located was determined through the analysis of a panel of human/hamster somatic cell hybrids using the polymerase chain reaction with pairs of synthetic oligonucleotide primers from the 3'-untranslated sequences of the genes. Genomic clones for each gene were isolated from a genomic cosmid library prepared from humanlymphoblastoid cells. Using those clones as probes, we have carried out fluorescence in situ hybridization to human metaphase chromosomes and have mapped the 70 kDa subunit gene to 17p13, the 34 kDa subunit gene to 1p35-p36.1, and the 11 kDa subunit gene to 7p21-p22. Since hSSB participates in replication, recombination and repair of DNA, the physical mapping of hSSB genes may aid in the identification of human hereditary diseases associated with aberrant DNA reactions caused by genetic alterations of the hSSB.

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Cultured fibroblasts from patients with Niemann-Pick disease type C (NP-C) are characterized by the lysosomal accumulation of unesterified cholesterol and the inability of low-density lipoprotein (LDL) to stimulate cholesterol esterification, in addition to impaired LDL-mediated down-regulation of LDL receptor activity and cellular cholesterol synthesis. Although a defect in the transport of cholesterol from lysosomes to other intracellular membrane sites has been suggested, it is unclear how cells regulate the levels of cellular sterols and whether their membrane cholesterol requirements are satisfied or not. We studied the esterification of exogenously added cholesterol, total levels of cellular cholesterol and cholesteryl ester, cholesterol synthesis from a two-carbon precursor, and sensitivities to potential inhibitors of cholesterol biosynthesis in proliferating NP-C cells. We observed the following: (a) esterification of [³H]cholesterol was decreased but the total amount of cellular cholesteryl ester was not decreased; (b) synthesis of cholesterol from [³H]acetate was increased; and (c) cells were hypersensitive to cholecalciferol, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, and were resistant to filipin, which binds to membrane sterols and presumably damages the membrane. The results indicate that NP-C cells depend on the cellular cholesterol synthetic pathway for their proliferation, but the plasma membrane sterols are presumably decreased. The altered sensitivities to potential inhibitors of cholesterol biosynthesis should be a useful marker for diagnosis and genetic studies.

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Brefeldin A (BFA), an isoprenoid fungal metabolite, dramatically disrupts intracellular protein transport and protein secretion. BFA protects cells from the cytotoxicity of a plant toxin, ricin or pseudomonas toxin, but not that of diphtheria toxin (YOSHIDA et al., 1991. Expt. Cell Res., 192: 389-395.). In this study, we examined whether BFA could differentially change the cytotoxicity of ricin between BFA-sensitive cells and BFA-resistant cells. As a BFA-resistant cell line, we used a resistant cell line, KB/BF2-2, derived from BFA-sensitive human cancer KB cells. BFA treatment caused the disappearance of typical Golgi cisternae and the concomitant appearance of dilated vesicles in the cytoplasm in KB cells. By contrast, KB/BF2-2 cells had already altered Golgi structures with poor development of cisternae and also many vesicles in the absence of BFA, and BFA treatment did not further induce the morphological changes. Although a plasma membrane-specific marker protein, α-adaptin, was localized similarly in KB/BF2-2 as KB, Golgi specific markers such as β-cop and γ-adaptin were distributed in the cytoplasmic small vesicles as well as Golgi compartments in KB/BF2-2 cells in the absence of BFA, and the mutant cells showed no apparent changes in the distribution even when exposed to BFA. Ricin inhibited protein synthesis in KB and KB/BF2-2 to similar levels while pretreatment of KB cells with BFA at 0.1 μg/ml almost completely reversed the inhibitory effect of ricin. By contrast, the pre-exposure of KB/BF2-2 cells to 1.0 μg/ml BFA only partially rescued the ricin-induced inhibition of protein synthesis. Exposure to BFA at 30 min before ricin addition or at 0 min with ricin rescued the protein synthesis inhibition, but no rescue occured when BFA was added 30 min after ricin addition. BFA could not rescue the protein synthesis inhibition by another toxin, diphtheria toxin. Our results suggest that BFA-resistant mutation causes a specific change in the endocytic membrane traffic of ricin in human cells, and also that cytotoxicity of diphtheria toxin does not share a common pathway of the intracellular transport with that of ricin.

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Vitronectin is a cell-adhesive glycoprotein present in animal blood and extracellular matrix. To establish the molecular basis of vitronectin interactions with extracellular matrix macromolecules, the binding site of vitronectin to collagen has been investigated. Vitronectin fragments obtained by formic acid cleavage were separated by heparin-affinity chromatography followed by gel filtration chromatography. The collagen-binding activity of the fragments was assayed in terms of inhibitory activity on the binding of ¹²⁵I-vitronectin to immobilized collagen. There were two groups of collagen-binding fragments. One group consisted of 5 heparin-binding fragments with estimated molecular masses of 12 kDa, 14 kDa, 16 kDa, 18 kDa, and 19 kDa in SDS polyacrylamide gel electrophoresis. The other group consisted of 2 heparin-nonbinding fragments migrating at 18 kDa and 40 kDa. These results indicate that there are two collagen-binding sites in the vitronectin molecule; one located close to the heparin-binding domain in the COOH-terminal half and the other located in the NH₂-terminal half of vitronectin.

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Extrachromosomal circular DNAs isolated from a P19 embryonal carcinoma cell line were induced to differentiate into neuron-like cells by retinoic acid and cloned into an EcoRI site of a phage vector. Of the 26 DNA inserts (2.1 kb in average length) analyzed, 16 contained repetitive sequences. Out of 10 DNA inserts with unique sequence, 6 carried linear chromosomal sequences and 4 showed chromosomal rearrangements in Southern blots. Two unique fragments with germline configuration were enriched in circular DNA clone libraries. We assigned the breakpoints of 3 circular DNA fragments to positions in the germline sequence. Patchy short inverted repeats were found in the vicinity of breakpoints. An intrastrand loop structure between such inverted short homology region maybe required for the circularization of excised DNA.

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