Liposomes as gene carriers: efficient transformation of mouse L cells by thymidine kinase gene.

Stable transformation of mouse L cells deficient in thymidine kinase was achieved by liposome-mediated transfer of a recombinant plasmid carrying the thymidine kinase gene. Ten percent of the recipient cells expressed thymidine kinase activity. The transformed phenotype (for example, 200 out of 10(6) cells) was stable under selective and nonselective conditions. The liposome technique is compared with other methods currently used for gene transfer.

The function of KGF in morphogenesis of epithelium and reepithelialization of wounds.

The function of keratinocyte growth factor (KGF) in normal and wounded skin was assessed by expression of a dominant-negative KGF receptor transgene in basal keratinocytes. The skin of transgenic mice was characterized by epidermal atrophy, abnormalities in the hair follicles, and dermal hyperthickening. Upon skin injury, inhibition of KGF receptor signaling reduced the proliferation rate of epidermal keratinocytes at the wound edge, resulting in substantially delayed reepithelialization of the wound.

Enhanced production of hepatitis B surface antigen in NIH 3T3 mouse fibroblasts by using extrachromosomally replicating bovine papillomavirus vector.

We have constructed a recombinant pBR322 plasmid composed of a subgenomic transforming fragment of bovine papillomavirus DNA and the hepatitis B surface antigen gene from cloned hepatitis B virus DNA and used it for transfection of NIH 3T3 mouse fibroblasts. The transformed cells retain the plasmids in extrachromosomal form with a copy number of about 50 to 100 per cell. Expression of the hepatitis B surface antigen gene linked to bovine papillomavirus DNA is independent of its orientation relative to the bovine papillomavirus vector. Cell lines continuously secreting high amounts of hepatitis B surface antigen into the medium could be established. The antigen is released into the culture medium as 22-nm particles, having the same physical properties and constituent polypeptides as those found in the serum of hepatitis B virus-infected patients.

The HBV X-ORF encodes a transactivator: a potential factor in viral hepatocarcinogenesis.

We report here on a transactivating function of HBV DNA. The effect is shown by stimulation of transient expression of pSV2cat DNA in cotransfected human liver CCL13 cells. Transfection experiments with plasmid constructs containing different HBV DNA fragments and Northern analyses of RNA from cells transfected with these recombinant plasmids indicate that a transactivating function is encoded within the X-ORF. A frameshift mutation within the X gene causes loss of activity thus demonstrating requirement of a protein. The increase in the level of CAT-specific RNA suggests that the transactivation is by transcriptional enhancement. Constitutive expression of the transactivator function was also observed in cells stably transfected with HBV DNA. A number of eukaryotic promoters, SV40-early, HSV-TK, HTLV-I and RSV LTRs were responsive to transactivation by HBV DNA. However, the MMTV LTR and the human metallothionein promoter (MTIIA) were considerably less responsive than the others. The transactivational potential of HBV DNA was much higher in human cells and cells of higher primates than in rodent cells, thereby indicating interacting cellular factors. These results introduce additional considerations for the role of HBV in the development of hepatocellular tumors.

A transactivating function encoded in the hepatitis B virus X gene is conserved in the integrated state.

Recently we have shown that the hepatitis B virus (HBV) X gene encodes a transactivating factor. Here we report on the construction of a series of HBx expression plasmids which were tested for a transactivating function by cotransfections with a plasmid expressing the CAT gene under control of the SV40 early promoter. One of the plasmids, expressing a HBx specific protein, is shown to transiently transactivate CAT gene expression after cotransfection into the human cell line CC113. Furthermore, a cloned integrated HBV DNA sequence is also shown to transactivate several viral promoters and LTRs. By sequence analyses we can demonstrate that only the HBx ORF is intact and that it is fused to an ORF of at least 228 bp in the flanking cellular DNA. The HBx gene is cotranscribed with the flanking cellular DNA, resulting in a RNA of approximately 10 kb. By subcloning of the integrate we can demonstrate that the presence of the HBx gene and its expression by the HBV enhancer and/or the HBx promoter is required for the transactivating function of the integrated HBV DNA.

Characterization of essential domains for the functionality of the MHBst transcriptional activator and identification of a minimal MHBst activator.

Integrated hepatitis B virus DNA derived from hepatocellular carcinomas can express, in one third of the cases investigated so far, a transcriptional activator encoded from 3' terminal truncated surface (preS/S) genes resulting in a C-terminally truncated middle surface protein (MHBst). Since MHBst, in contrast to the secreted MHBs, is retained in the secretory pathway at the ER, the question as to whether the retention generates the transcriptional activator function was investigated. Through fusion of MHBs to the ER-retention signal KDEL, it was shown that the intracellular retention does not generate the transcriptional activator function. Tryptic digestions of microsomal vesicles revealed that the amino terminal domain of MHBst directs into the cytoplasmic compartment, whereas in MHBs this domain directs into the lumen of the ER. This structural difference appears to be why transcriptional activator function arises. Through deletion analysis it was shown that non-membrane-associated MHBst proteins are also functional activators. Nonmembrane associated MHBst proteins represent a second class of MHBst proteins. These MHBst-proteins are homogenously distributed all over the cell and show no difference in functionality as compared to the membrane-associated MHBst proteins. MHBst53 (truncated at aa53) was shown to be a minimal activator of this class. Both classes of MHBst proteins were found to form dimers; an which is involved in mediating the dimerization. The integrity of this domain was also revealed to be a prerequisite for the functionality of the activator, suggesting a linkage between dimerization and functionality.

Low mitogenic response to EGF and TGF-alpha: a characteristic feature of cultured Kaposi's sarcoma derived cells.

We have investigated the mitogenicity of Epidermal Growth Factor (EGF) and Transforming Growth Factor alpha (TGF-alpha) for cultured Kaposi's sarcoma derived cells (KS cells). In contrast to control fibroblasts from the same patients, KS cells revealed only a weak mitogenic response to these growth factors. Neither EGF nor TGF-alpha were able to substitute for Platelet-derived growth factor (PDGF) when KS cells were grown in PDGF-depleted Platelet-Poor-Plasma serum (PPPS)-supplemented medium. The low mitogenicity of EGF and TGF-alpha for KS cells is not based upon a reduced expression of EGF receptor mRNA and protein in KS cells. However, the binding of EGF to KS cells is about 50% lower than that to fibroblasts. This reduced binding is not due to an occupation of the receptors by TGF-alpha since the expression level of this mitogen in different KS cell lines does not correlate with their capacity to bind EGF. In contrast, the low EGF binding seems to be an intrinsic feature of the EGF receptors of KS cells. In spite of the low mitogenicity of EGF for the tumor cells, the expression of c-myc, PDGF-A and Fibroblast growth factor 5 (FGF-5) mRNA is equally induced by purified EGF in KS cells and fibroblasts. This shows that at least the signal transduction pathways which lead to the expression of these genes are functional in KS cells.

ER-localization and functional expression of the HBV transactivator MHBst.

In two recently reported cases, integrated hepatitis B virus (HBV) DNAs cloned from hepatocellular carcinoma were found to express a transcriptional transactivator from 3'-terminally truncated HBV surface (preS/S) genes. In this study, we characterized the transactivator at the protein level. Expression of a 3'-truncated preS2/S gene in Spodoptera frugiperda (Sf9) insect cells resulted in a C-terminally truncated middle surface protein of 76 amino acids (MHBst76), which was found to be associated with membranes of the endoplasmic reticulum and retained from Golgi processing and secretion. Accordingly, the microsome fraction of MHBst76-expressing Sf9 cells displayed transactivator activity after electric field-mediated transfer into Chang liver cells. In contrast to full-length MHBs, MHBst76 is unglycosylated, and glycosylation is not required for transactivation as shown by mutation of the glycosylation site at asparagine-4. Since highly purified MHBst76 derived from an E. coli expression system also showed transactivator activity, it is concluded that unglycosylated MHBst76 protein is the authentic transactivating factor. As the transactivator protein derives from inactive MHbs by rearrangements of integrated HBV DNA, it may be important for HBV-associated liver carcinogenesis.

Depletion of PDGF from serum inhibits growth of AIDS-related and sporadic Kaposi's sarcoma cells in culture.

We have examined the mitogenic potential of platelet-derived growth factor (PDGF) on AIDS (acquired immune deficiency syndrome)-related and sporadic Kaposi's sarcoma cells in comparison to fibroblasts at physiological and subphysiological calcium concentrations of the culture medium. At low calcium concentrations in the presence of 3% human serum the growth rate of fibroblasts and Kaposi's sarcoma (KS) cells is similarly reduced to less than half of the growth rate at physiological Ca2+ concentrations. In the presence of 3% PDGF depleted, platelet poor plasma-derived serum (PPPS) growth of KS cells ceased completely, whereas fibroblasts made 1-2 cell divisions within 15 days. At physiological Ca2+ concentrations, the reduced PDGF content in 3% PPPS had no effect on human embryonal fibroblasts and little effect on adult skin fibroblasts. In contrast, KS cells became growth-arrested after one to two doublings. This is consistent with the observation that PDGF B-chain mRNA could not be detected in our KS cells whereas PDGF receptor mRNA was expressed.

Integrated hepatitis B virus X and 3' truncated preS/S sequences derived from human hepatomas encode functionally active transactivators.

The hepatitis B virus (HBV) frequently integrates into hepatocellular genomic DNA during viral infection. Transcriptional transactivators encoded by integrated HBV X and 3' truncated preS/S sequences are known to stimulate gene expression from homologous and heterologous promoters. Here we demonstrate that 21 of 26 (81%) hepatocellular carcinoma tissues/cell lines contain coding sequences for at least one of the two known transactivators. Four integrated X and three preS/S transactivator sequences contained in five isolates from three hepatoma primary tissues or cell lines were used as examples to prove functionality of the encoded transactivators. In one case, where both X and preS/S sequences were present, dissection of X and preS/S transactivator sequences showed independent functionality. The investigation of X- and preS/S-specific RNA and protein expression revealed the existence of carboxyterminally truncated viral-cellular fusion proteins that were able to stimulate gene expression from the c-fos proto-oncogene promoter five- to ten-fold. These results demonstrate that structurally intact HBV transactivator sequences are integrated in the majority of HBV-associated HCCs/hepatoma cell lines. In all tested examples integrated DNAs had retained functionality as transactivators. This data thereby support indirectly the hypothesis of a possible involvement of HBV transactivators in liver cell proliferation and hepatocarcinogenesis.

Fibroblast growth factor 5 proto-oncogene is expressed in normal human fibroblasts and induced by serum growth factors.

Fibroblast growth factor 5 (FGF-5) is a member of the fibroblast growth factor family with transforming potential. It has been found to be expressed in several human tumor cell lines, but nothing is known about expression of this growth factor in normal cells and its biological functions. Here we show that the FGF-5 gene is expressed in exponentially growing normal human fibroblasts. In quiescent fibroblasts, expression of FGF-5 is strongly induced by serum and several growth factors such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha). This induction can be mediated by at least two different pathways involving protein kinase C or cAMP-dependent kinases. Since the effect is independent of de novo protein synthesis, FGF-5 represents the product of a primary response gene. In addition our data suggest that FGF-5 is mitogenic for human fibroblasts, indicating the existence of an FGF-5-mediated positive feedback in these cells which could amplify and prolong the cellular response to the initial stimulus.

Tumour-related expression of a translation-elongation factor-like protein.

We have identified a tumour-related 43 kd cytoplasmic protein (LC/p43) using a monoclonal antibody against the total proteins of human hepatoma cell line PLC/PRF/5. LC/p43 is preferentially expressed in a variety of tumours of human and animal origin, whereas no expression was detected in several normal adult tissues tested. LC/p43 expression was induced in rodent fibroblasts upon transfection with several viral oncogenes. Expression in non-transformed peripheral blood lymphocytes could be induced by treatment with phytohaemagglutinin (PHA) and subsequent culture with interleukin II, whereas retinoic acid treatment of transformed cells caused a drastic reduction of the antigen in the cells. Sequence analysis of three tryptic peptides of LC/p43 revealed 50-70% homology to different domains of the eukaryotic and prokaryotic translation-elongation factors EF1-alpha and EF-Tu, respectively.

Identification of interleukin-1 and platelet-derived growth factor-B as major mitogens for the spindle cells of Kaposi's sarcoma: a combined in vitro and in vivo analysis.

By means of a combined in vitro and in vivo analysis we provide evidence that IL-1 beta and PDGF-B, but not OSM (oncostatin M) or IL-6, are major mitogens for the spindle cells of Kaposi's sarcoma (KS) in vivo. PDGF-B and IL-1 beta stimulated proliferation of cultivated KS spindle cells in vitro. Analysis of gene expression in vivo revealed that both factors as well as the PDGF beta-receptor are present in KS lesions. By contrast, IL-6 had no effect and OSM inhibited proliferation of cultivated KS spindle cells. Again, the effect of these factors on cultivated KS spindle cells in vitro was reflected by the gene expression observed in KS lesions in vivo. Neither the expression of IL-6 receptor nor of OSM could be detected in KS lesions by in situ hybridization. Moreover, in situ hybridization revealed an identical pattern of gene expression in cultivated KS spindle cells and KS spindle cells in vivo with respect to the above-mentioned cytokines [PDGF-B, IL-1 beta, IL-1 alpha, IL-6, OSM] and their receptors [PDGF beta-receptor, gp130, IL-6 receptor, leukemia inhibitory factor (LIF) receptor]. This further supported the suitability of cultivated KS spindle cells as an in vitro model in order to determine which cytokines may activate proliferation of KS spindle cells in vivo.

Hepatoma-derived integrated HBV DNA causes multi-stage transformation in vitro.

The hepatoma-derived hepatitis B virus (HBV) DNA insert HU-a has recently been shown to contain two viral transactivator genes, X and preS2 /S. We report here that HU-a induces malignant transformation after stable transfection of the fetal mouse hepatocyte line FMH202, as indicated by soft agar growth and nude mouse tumorigenicity. Transfections with HU-a subclones, containing the X gene of the preS2 /S gene alone or sequences without transactivator gene, respectively, suggested that the X gene is essential for transformation. Sequential stages of transformation and tumor progression were analysed by injection of the stably transfected FMH202 lines into nude mice, explanation of the resulting tumors and re-establishment of cell lines from the tumors. Comparison of two HU-a-transformed cell lines by HBV mRNA hybridization, Southern analysis and chromosomal in situ hybridization revealed that integrated HBV DNAs were involved in major chromosomal rearrangements in both cases. Interestingly, recombination of the HBV Dna insert during the nude mouse passage had completely abolished HBV-specific transcription in one case, indicating that expression of integrated HBV genes, while presumably involved in early transformation, is dispensable at later stages of tumor progression. The sequential transformation observed in this experimental system suggests that expression of the X gene by integrated viral DNA and subsequent hepatocyte genome mutations might both contribute to HBV-associated liver carcinogenesis.

Purification and characterization of particles containing RNA-dependent DNA polymerase, in the allantoic fluid of uninfected leukosis virus-free chicken eggs.

The allantoic fluid of embryonated chicken eggs regularly contains particle-associated RNA-dependent DNA polymerase, as shown by its reaction with homopolymeric and heteropolymeric RNA and by the characterization of the products. The purification of the particles is described. The purified particles are different from the known avian RNA tumor viruses in their protein composition and their sedimentation constant. They do not exhibit biological properties typical for RNA tumour viruses, such as helper activity, interfering properties or infectivity and do not show endogenous DNA synthesis. The particles are discussed as non-viral elements.

Replication of the single-stranded DNA of the male-specific bacteriophage M13: circular forms of the replicative DNA.

Equilibrium centrifugation in caesium chloride, band sedimentation in alkaline solutions and electron microscopy have been used to study purified preparations of the M13 replicative DNA. The buoyant density of the M13 replicative DNA in a CsCl density gradient is 1.701, compared to a density of 1-710 for Escherichia coli DNA. When the replicative DNA is sedimented in alkaline solutions of CsCl (p = 1.35), two components are observed with uncorrected s-values of 48.6 +/- 0.2 and 15.2 +/- 0.5. Treatment of the replicative DNA with pancreatic DNase reduces the relative amount of the fast component in alkaline CsCl and similarly increases the relative amount of the slow component. Electron microscopic observation of the replicative DNA also shows two different forms of DNA, extended circles and condensed forms of DNA. The relative amount of condensed forms of DNA in a preparation of replicative DNA is equal to the relative amount of the fast component in alkaline velocity sedimentation. The average contour length of the extended circles is 2.19 +/- 0.07 micro.

Uber infektiöse Substrukturen aus Escherichia coli Bakteriophagen. VIII. On the tertiary structure and biological properties of phiX174 replicative form.

As already known, phiX174 replicative-form DNA is separated into two components when sedimented in a sucrose gradient. The faster component, I, is not denatured by heat treatment, whereas the slower component, II, is converted to single strands. Only the infectivity of component II increases after heat denaturation. A quantitative comparison of data obtained by band centrifugation and by electron microscopy shows that the tertiary structure of component I is a highly twisted circle and that of component II an extended circle. By treatment with DNase, component I (as observed in band centrifugation) and twisted rings (as observed by electron microscopy) are converted at the same rate to component II and to extended circles and linear molecules. The plating efficiency of replicative-form DNA, in contrast to denatured component II replicative form and to phiX174 single-stranded DNA, is diminished by the addition of Escherichia coli DNA to the adsorption medium. The inhibition by E. coli DNA at concentrations above 0.5 microg/ml. is of first order. The lower the relative plating efficiency of native replicative-form DNA, the greater is the increase of infectivity for the denatured component II. The importance of these findings with respect to normal test conditions is discussed. Some observations suggest that under ideal test conditions the relative plating efficiency of the replicative-form DNA may rise to that of phiX174 single-stranded DNA.

Uber infektiöse Substrukturen aus Bakteriophagen. VI. A simple method for separating the replicative form from single-stranded phiX174 DNA.

A selective adsorption method is presented which allows a rapid separation of phiX174 replicative form DNA from single-stranded phiX174 phage DNA, facilitating the handling of a large number of samples. The single-stranded phiX174 DNA is selectively adsorbed to silicic acid coated with methylated albumin. After removal of the adsorbent by sedimentation, at least 40% of the input replicative form DNA is recovered in the supernatant fraction; the ratio of replicative form to single-stranded phage DNA is increased 20- to 200-fold. The potential of the method for separating other nucleic acids is discussed.

Replication of the single-stranded DNA of the male-specific bacteriophage M13. Isolation of intracellular forms of phage-specific DNA.

The intracellular DNA has been isolated from Escherichia coli F+ cells infected with the small male-specific bacteriophage M13 and fractionated on a methylated albumin-kieselguhr column. Two infectious forms of phage-specific DNA were isolated and identified as a double-stranded replicative form and single-stranded DNA on the basis of their elution from the methylated albumin-kieselguhr column, infectivity to spheroplasts before and after heating, sedimentation at low ionic strength and buoyant density in CsCl. The replicative DNA was found to be resistant to thermal denaturation, suggesting that it may be a closed ring. It is estimated that there are at least 130 molecules of replicative DNA and 190 molecules of single-stranded DNA per infected bacterium.

Round table discussion 'gene therapy and society'--summary and conclusions.

An international group consisting of scientists, physicians, and one lawyer reported on the problems of gene therapy with regard to society in their respective countries and discussed ethical, legal and scientific aspects of gene therapy. Ethical questions and fear in society were addressed by Dr Odenbach, former Secretary General of the German Medical Association, member of the German Parliamentary Enquiry Commission, 'Prospects and Risks of Gene Technology' and present adviser of the Ethical Committee of the World Medical Association, and by PH Hofschneider, Professor of Virology at the Max-Planck-Institut for Biochemistry, Munich, with a long-time strong interest in medical ethics; legal aspects were addressed by H Hausheer, Professor of Civil Law with many years experience in constitutional law and jurisdiction in Switzerland. Medical and scientific aspects were discussed by R Strohman, Emeritus Professor of Molecular Biology, Berkeley, USA, F Takaku, President of the International Medical Center of Japan and Chairman of the Central Evaluation Committee of the Japanese government for gene therapy, Tokyo and J Goldman, Professor of Leukemia Biology at Hammersmith Hospital, London, and known for this pioneering work in bone marrow transplantation. The discussion was moderated by R Hehlmann, Professor of Medicine at the University of Heidelberg and member of the World Committee of the International Association.