Induction of hepatitis B virus core gene in human cells by cytosine demethylation in the promoter.

A recombinant human cell line constructed by transfection of epithelial cells with a plasmid containing the hepatitis B virus core gene (HBc) was used to study the regulation of HBc gene expression. Methylation of a single Hpa II site 280 base pairs upstream from the structural gene was found to regulate the expression of the core gene. Expression increased in cells treated with 5'-azacytidine as a result of cytosine demethylation at this site, and there was a fivefold increase in the number of HBc gene transcripts in total cellular messenger RNA. The varied life cycle of hepatitis B virus in disease such as viral hepatitis and liver cancer may therefore be attributable to the site-specific regulation of the gene involved in replication of the viral DNA and to the cytophathic effects elicited by this gene in human cells.

High-frequency transfection and cytopathology of the hepatitis B virus core antigen gene in human cells.

A protoplast fusion method was developed to stably transfect human cells with pSV2-derived plasmids at frequencies greater than 10(-3). This procedure made it possible to test the biological effect of a hepatitis B virus (HBV) gene independent of the viral structures required for infection. A pSV2gpt+ plasmid constructed to carry a subgenomic fragment of HBV that contained the core antigen gene (HBc gene) was transfected into human cells. A human epithelial cell line was stably transfected with the HBc+ gene by selecting recipient cells for expression of guanine phosphoribosyl transferase expression. With this gpt+/HBc+ cell line it was shown that growth in serum-free medium or treatment with 5'-azacytidine stimulates the production of the HBV core antigen. A hepatocellular carcinoma carrying the entire HBV genome was stimulated to produce the HBc gene product in response to the same factors that stimulated HBcAg production in the gpt+/HBc+ cell line constructed by transfection. The temporal relation between the cytopathologic response and HBc gene expression was similar for both cell types, indicating a primary role for HBc gene expression in the cytopathology of HBV-infected human liver.

Transformation of human bronchial epithelial cells transfected by Harvey ras oncogene.

Transfection of normal human bronchial epithelial (NHBE) cells with a plasmid carrying the ras oncogene of Harvey murine sarcoma virus (v-Ha ras) changed the growth requirements, terminal differentiation, and tumorigenicity of the recipient cells. One of the cell lines isolated after transfection (TBE-1) was studied extensively and shown to contain v-Ha ras DNA. Total cellular RNA from TBE-1 cells hybridized to v-Ha ras structural gene fragment probes five to eight times more than RNA from parental NHBE cells. The TBE-1 cells expressed phosphorylated v-Ha ras polypeptide p21, showed a reduced requirement for growth-factor supplements, and became aneuploid as an early cellular response to v-Ha ras expression. As the transfectants acquire an indefinite life-span and anchorage independence they became transplantable tumor cells and showed many phenotypic changes suggesting a pleiotropic mechanism for the role of Ha ras in human carcinogenesis.

Preneoplastic and neoplastic growth of xenotransplanted lung-derived human cell lines using deepithelialized rat tracheas.

The human lung tumor-derived cell lines A549, Calu-1, Calu-3, HuT292, and SW900 and the transformed human bronchial epithelial cell line TBE-1, that was transfected with the v-Harvey-ras oncogene, were inoculated into deepithelialized Fisher 344 rat tracheas (5 X 10(5) cells/trachea). After the ends of the tracheas were sealed, the tracheas were transplanted into s.c. tissues of nude mice. In a parallel experiment, 1 X 10(6) cells from each of these cell lines were injected s.c. Histological examination of the tracheal transplants 2, 4, 8, 12, and 16 weeks after cell inoculation proved to be of greater usefulness than either clinical or histological observation of the s.c. injection sites. A549, Calu-1, and TBE-1 produced intratracheal neoplastic nodules as early as 2 weeks after cell inoculation. Calu-3, HuT292, and SW900 grew relatively slowly in the tracheas, and simple or stratified epithelia with slight or moderate atypia (preneoplastic lesions) were seen at 2 weeks. After the 4th week, they produced tumor nodules in the tracheal transplants, whereas no tumor cells could be seen at the s.c. injection sites. The human derivation of the cells was confirmed by in situ hybridization using human-specific DNA probes. The intratracheal inoculation and xenotransplantation of human-derived cell lines offers a time-saving alternative to the s.c. inoculation assay for tumorigenicity and is at the same time a potentially valuable approach to studying preneoplastic and neoplastic progression with human cell subpopulations.

Cross-linking and relaxation of supercoiled DNA by psoralen and light.

Photoreaction of 4,5',8-trimethylpsoralen with superhelical ColE1 and ColE1amp DNA was studied. Changes in mobilities in agarose gels, formation of interstrand cross-links, and DNA strand breaks were determined. Psoralen and light treatment removed negative superhelical turns, and extensive treatments failed to produce positive superhelical turns in covalently closed plasmid DNA. The rate of relaxation of superhelical turns by psoralen Photobinding appeared to be directly proportional to the number of superhelical turns remaining. A unique reaction mechanism is presented to explain these results. By this interpretation the initial rate of psoralen photobinding to superhelical DNA was estimated to be 3 times that for linear DNA, and the ratio of cross-linking to monofuctional adducts appears to be dependent on the superhelical conformation of the DNA. The estimated ratio of psoralen molecules bound to DNA strand breaks was 1.7 . 10(4):1, and 70% of this breakage is caused by the light alone.

Isolation of plasmids carrying either the uvrC or uvrC uvrA and ssb genes of Escherichia coli K-12.

A 3.4 kb PstI fragment containing the uvrC gene of Escherichia coli K-12 has been cloned into pBR322. Plasmids carrying this PstI fragment, in either orientation (pGY3233, pGY4211) relative to the cloning vehicle, complement uvrC mutants. A second plasmid (pGY3243) with a 21 kb HindIII fragment is shown to complement mutations in uvrA and ssb (single-strand binding protein). A composite plasmid (pGY4610) containing pBR322 and PstI fragments derived from pGY3233 (3.4 kb) and pGY3243 (11.05 kb) complements the uvrC, uvrA and ssb mutations.

Mapping a putative pyruvoyl decarboxylase active site to human cytomegalovirus open reading frame UL77.

Human cytomegalovirus is present as an apparently innocuous infection among a large proportion of the adult population that causes serious disease when congenitally transferred (1). Human cytomegalovirus disease may become life threatening when found as an infection of immunocompromised transplant and AIDS patients (1,2). We now map a putative pyruvoyl decarboxylase enzyme prosthetic group, known to be essential to the active site of this class of enzymes, to Human cytomegalovirus open reading frame UL77. The significance of finding a putative pyruvoyl decarboxylase enzyme prosthetic group among human cytomegalovirus open reading frame codons is p = 0.001. The UL77 polypeptide was aligned with human, yeast and bacterial S-AdoMet decarboxylase enzymes. Alignment of UL77 and S-AdoMet decarboxylase enzymes indicates that UL77 may contain a similar activity.

Tryptophan photoproduct(s): sensitized induction of strand breaks (or alkali-labile bonds) in bacterial deoxyribonucleic acid during near-ultraviolet irradiation.

Long-wavelength ultraviolet light (300 to 400 nm) converts L-tryptophan to a photoproduct that is toxic for bacterial cells in dark conditions. We now report that similar photoproducts of l-tryptophan sensitize bacterial deoxyribonucleic acid to 365-nm radiation, increasing the yield of deoxyribonucleic acid strand breaks (or alkali-labile bonds) by approximately 11.5-fold. Evidence is also presented which indicates that thse sensitized deoxyribonucleic acid lesions contribute to lethality for Escherichia coli irradiated with 365-nm ultraviolet light in suspensions of tryptophan photoproducts.

Role of ATP in removal of psoralen cross-links from DNA of Escherichia coli permeabilized by treatment with toluene.

Removal of interstrand cross-linked from DNA was examined in Escherichia coli permeabilized by treatment with toluene. Under these conditions, the reaction requires ATP and Mg2+, and the mechanism appears to be similar to that occurring in whole cells. Under optimum conditions, the rate constant was 0.06 min-1. Genetical, physical, and biochemical analysis of the repair process suggest the following mechanism. In an ATP-dependent reaction, the uvrA and uvrB gene products cleave a phosphodiester bond on the 5' side of one arm of the cross-link, producing a 3'-OH terminus. Subsequently, DNA polymerase I (5'-3' exonuclease activity) makes a second strand cut on the 3' side of the cross-link in the same DNA strand, completing removal of the covalent link between complementary strands. The second reaction did not occur in a uvrD- strain, which had normal levels of DNA polymerizing activity. The uvrD gene may regulate the specificity or activity of the 5'-3' exonuclease of DNA polymerase I in vivo.

The purification of the Escherichia coli UvrABC incision system.

The UvrA, UvrB and UvrC proteins of Escherichia coli have been purified in good yields to homogeneity with rapid three- or four-step purification procedures. The cloned uvrA and uvrB genes were placed under control of the E. coli bacteriophage lambda PL promoter for amplification of expression. Expression of the uvrC gene could not be amplified by this strategy, however, subcloning of this gene into the replication-defective plasmid pRLM24 led to significant overproduction of the UvrC protein. The purified UvrA protein, with its associated ATPase activity, has a molecular weight of 114,000, the purified UvrB is an 84,000 molecular weight protein and the UvrC protein has a molecular weight of 67,000.

Amplification of the uvrA gene product of Escherichia coli to 7% of cellular protein by linkage to the pL promoter of pKC30.

We have constructed a hybrid pKC30-uvrA plasmid (pGHY5003) in which transcription of the uvrA gene can be induced under pL control to amplify the uvrA gene product to 7% of cellular protein. To construct pGHY5003, we developed a genetic selection using the basal level of expression (30 degrees C) from pL in thermosensitive cI857 lysogens to isolate appropriately tailored repair genes inserted at the Hpa I site of pKC30 from recombinant DNA mixtures with a variety of products. In addition, a post-UV-irradiation radiolabeling method was adapted to screen inserts for temperature-inducible polypeptide synthesis directed by transcription under pL control rapidly. This should prove generally useful for isolating genes inserted at the Hpa I site of plasmid pKC30 with the following characteristics: (i) genetically functional hybrid plasmids selected from a large population of exonucleolytically tailored fragments ligated into Hpa I of pKC30 and (ii) production of high-level amplification for the gene product of interest by screening for post-UV-irradiation temperature inducibility of polypeptides synthesized from hybrid plasmids. The level of amplification obtained for the uvrA gene product from pGHY5003 is approximately 10,000-fold higher than estimates of the level of uvrA protein in logarithmic phase Escherichia coli.

Direct modulation of HBV surface antigen in a human, HBsAg-producing hepatocellular carcinoma cell line by alpha, beta, or gamma interferons.

A transient depression of HBV serologic markers has been reported for some chronically infected patients treated with human interferons. To determine a molecular basis for these observations, a human, HBV-carrying, hepatocellular carcinoma cell line (PLC/PRF/5) was treated with human alpha, beta, or gamma interferons. Administration of these interferons resulted in a marked depression of HBV surface antigen (HG-sAg) levels in the culture medium. This inhibition was transient, with media levels of HBsAg rising substantially within 48 hours following the termination of interferon treatment. Cell growth rates were not affected by alpha interferon treatment, indicating that overall cell protein synthesis was not substantially altered. Although all three classes of interferons were effective in lowering HBsAg levels in the culture medium, intracellular levels of HBsAg-specific RNA were unaffected. These results suggest that the transient depression of HBV serologic markers in interferon-treated patients may be a consequence of the failure to disrupt the intracellular pools of HBV RNA in the liver.

Hepadnavirus infection of peripheral blood lymphocytes in vivo: woodchuck and chimpanzee models of viral hepatitis.

The peripheral blood lymphocytes (PBL) of five hepatitis B virus (HBV)-infected chimpanzees and 17 woodchuck hepatitis virus (WHV)-infected woodchucks were examined for the presence of viral DNA and RNA. HBV DNA was detected in the PBL of three of three chronically infected chimpanzees but in neither of two animals with acute HBV infection. WHV DNA was found in the PBL of 11 of 13 chronically infected woodchucks and in the PBL and bone marrow of 1 of 4 woodchucks with antibody to WHV surface antigen. Viral DNA in the PBL and bone marrow was episomal, primarily existing as multimers with some monomeric forms. Integrated HBV DNA was detected in the PBL of one chronically infected chimpanzee, but only for a brief period. Viral RNA was also detected in the PBL, although less frequently than was DNA. HBV RNA in chimpanzee PBL existed as 3.8- and 7.5-kilobase species, while 2.3- and 3.8-kilobase WHV RNA was found in woodchuck PBL. Subfractionation of PBL isolated from the chronically infected chimpanzees demonstrated that HBV DNA and RNA were located in B and T cells. No HBV DNA was detected in the macrophages. These results, along with the recent reports of HBV nucleic acids in the PBL of human patients, suggest that infection of PBL may be a general phenomenon associated with the pathology of hepadnaviruses.

In vitro studies of human lung carcinogenesis.

Advances in the methodology to culture normal human lung cells have provided opportunities to investigate fundamental problems in biomedical research, including the mechanism(s) of carcinogenesis. Using the strategy schematically shown in Figure 1, we have initiated studies of the effects of carcinogens on the normal progenitor cells of the human cancers caused by these carcinogens. Extended lifespans and aneuploidy were found after exposure of mesothelial cells to asbestos and bronchial epithelial cells to nickel sulfate. These abnormal cells may be considered to be preneoplastic and at an intermediate position in the multistage process of carcinogenesis. Human bronchial epithelial cells can also be employed to investigate the role of specific oncogenes in carcinogenesis and tumor progression. Using the protoplast fusion method for high frequency gene transfection, vHa-ras oncogene initiates a cascade of events in the normal human bronchial cells leading to their apparent immortality, aneuploidy, and tumorigenicity in athymic nude mice. These results suggest that oncogenes may play an important role in human carcinogenesis.