In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus.

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid-like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse-based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI-277 and FTI-2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration-of-treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

Molecular cloning, genomic characterization and expression of novel human alpha1A-adrenoceptor isoforms.

We have isolated and characterized from human prostate novel splice variants of the human alpha1A-adrenoceptor, several of which generate truncated products and one isoform, alpha(1A-4), which has the identical splice site as the three previously described isoforms. Long-PCR on human genomic DNA showed that the alpha(1A-4) exon is located between those encoding the alpha(1A-1) and alpha(1A-3) variants. CHO-K1 cells stably expressing alpha(1A-4) showed ligand binding properties similar to those of the other functional isoforms as well as agonist-stimulated inositol phosphate accumulation. Quantitative PCR analyses revealed that alpha(1A-4) is the most abundant isoform expressed in the prostate with high levels also detected in liver and heart.

The pharmacology and distribution of human 5-hydroxytryptamine2B (5-HT2B) receptor gene products: comparison with 5-HT2A and 5-HT2C receptors.

1. Full length clones of the human 5-HT2B receptor were isolated from human liver, kidney and pancreas. The cloned human 5-HT2B receptors had a high degree of homology (approximately 80%) with the rat and mouse 5-HT2B receptors. 2. PCR amplification was used to determine the tissue distribution of human 5-HT2B receptor mRNA. mRNA encoding the 5-HT2B receptor was expressed with greatest abundance in human liver and kidney. Lower levels of expression were detected in cerebral cortex, whole brain, pancreas and spleen. Expression was not detected in heart. 3. Northern blot analysis confirmed the presence of 5-HT2B receptor mRNA (a 2.4 kB sized band) in pancreas, liver and kidney. An additional 3.2 kB sized band of hybridization was detected in liver and kidney. This raises the possibility of a splice variant of the receptor or the presence of an additional homologous receptor. 4. The human 5-HT2B receptor was expressed in Cos-7 cells and its ligand binding characteristics were compared to similarly expressed human 5-HT2A and 5-HT2C receptors. The ligand specificity of the human 5-HT2B receptor (5-HT > ritanserin > SB 204741 > spiperone) was distinct from that of the human 5-HT2A (ritanserin > spiperone > 5-HT > SB 204741) and 5-HT2C (ritanserin > 5-HT > spiperone = SB 204741) receptors. On the basis of a higher affinity for ketanserin and a lower affinity for yohimbine the human 5-HT2B receptor also appeared to differ from the rat 5-HT2B receptor. 5. These findings confirm the sequence of the human 5-HT2B receptor and they demonstrate that the receptor has a widespread tissue distribution. In addition, these data suggest that there are differences in ligand affinities between different species homologues of the receptor. Finally, the finding of two distinct bands on the Northern blots of liver and kidney raises the possibility of splice variants or subtypes of 5-HT2B receptors, within these tissues.

Host Susceptibility to endogenous viruses: defective, glycoprotein-expressing proviruses interfere with infections.

Three defective endogenous avian leukosis viruses, ev3, ev6 and ev9, interfered with subgroup E virus infections, ev3, ev6, and ev9 expressed high levels of subgroup E envelope glycoproteins. These glycoproteins reduced the activity of cellular receptors for subgroup E viruses. ev3 and ev6 protected chickens and cultured cells from subgroup E virus infections.

Polypeptides of hepatitis B virus surface antigen produced by a hepatoma cell line.

The PLC/PRF/5 cell line derived from a human hepatoma produces hepatitis B surface antigen (HBsAg) in 22-nm particles of the same buoyant density as those found in the serum of infected patients. The HBsAg particles from this cell line were labeled with [35S]methionine and purified, and the polypeptides were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with those of serum-derived particles. The two major polypeptides of serum-derived HBsAg particles (p20 and p23) were found in the same relative amounts in the particles from the cell line. The three smallest of the five minor components observed in HBsAg particles from serum were present in particles from the cell line. These polypeptides (p31, p36, and p43), as well as p20 and p23, were precipitated with anti-HBs-containing serum. The two largest polypeptides of serum particles (p49 and p66) were not detected in particles from these cells. When the PLC/PRF/5 HBsAg particles were radiolabeled with tritiated sugars, p23, and not p20, was found to contain radioactivity, indicating that the pattern of polypeptide glycosylation is similar to that of serum HBsAg. None of the other possible gene products of hepatitis B virus was detected in the PLC/PRF/5-derived HBsAg particles, in the cells, or in the cell supernatants.

State of hepatitis B viral DNA in a human hepatoma cell line.

PLC/PRF/5, a tissue culture cell line isolated from a human hepatocellular carcinoma and producing hepatitis B surface antigen, was studied for the presence of hepatitis B virus (HBV)-specific DNA and RNA. PLC/PRF/5 cell DNA accelerated the rate of reassociation of HBV [32P]DNA, and quantitative experiments indicated that the cells contained approximately four copies of viral DNA per haploid, mammalian cell DNA equivalent. PLC/PRF/5 DNA accelerated the rate of reassociation of all individual restriction endonucleases HincII and HaeIII fragments of HBV [32P]DNA, indicating that DNA from all regions of the viral genome is present in the cells. This suggests that these cells contain at least most, and possibly all, of the viral genome. Digestion of PLC/PRF/5 cell DNA with restriction endonuclease HindIII (an enzyme found not to cleave the DNA of any HBV isolate so far examined) yielded only three fragments, all larger than virion DNA, which contained HBV DNA base sequences, suggesting that HBV DNA is integrated in high-molecular-weight DNA at three different sites in these cells and that there is no viral DNA in an episomal form. PLC/PRF/5 cell [32P]RNA was found to hybridize with all restriction fragments of HBV DNA adequately tested, indicating that at least most, and possibly all, of the viral DNA in these cells is transcribed.

Purification and structural characterization of the putative gag-pol protease of human immunodeficiency virus.

We have purified a 10,774-dalton protein from human immunodeficiency virus (HIV) type 1 that is encoded in the protease domain of the pol open reading frame (ORF). Radiochemical amino acid microsequencing identified 12 amino acids from the stretch of 39 N-terminal residues of this protein, beginning with a PQITLW sequence at position 69 of the pol ORF. Radiosequencing of selected tryptic peptides of the protein identified 11 additional residues (Leu-9 and Val-2) in six peptides encompassing the entire molecule of 99 residues. A protein of similar size and identical N-terminal sequence (determined through the first 39 residues) was present among the processed HIV pol gene products in Escherichia coli which expressed the entire HIV pol ORF. The C terminus of both the viral and E. coli-expressed proteins was inferred to be contiguous with the N terminus of the p64-p51 reverse transcriptase on the basis of tryptic mapping and specific immunoreactivity with an antiserum against a dodecapeptide located upstream of the reverse transcriptase. Thus, the initial processing of the pol precursor that generates the native protease is apparently preserved across phylogenetic barriers. Although the purified viral protease lacked measurable proteolytic activity, the bacterial extracts were capable of processing an HIV gag precursor protein synthesized in E. coli.

The gag gene products of human immunodeficiency virus type 1: alignment within the gag open reading frame, identification of posttranslational modifications, and evidence for alternative gag precursors.

Seven human immunodeficiency virus gag polypeptides were identified in the purified virus and in infected CD4+ lymphocytes by peptide mapping and limited amino acid sequencing of immune-purified proteins. Two gag polyproteins of 55,000 (p55) and 41,000 (p41) daltons were rapidly labeled and readily processed into the major internal gag proteins that were aligned within the gag open reading frame (ORF) as NH2-p16 (MA)-p24 (CA)-p9 (NC)-p7-COOH. The myristoylated p16 (matrix, MA) protein was processed from the myristoylated p55 gag precursor protein. The immunoreactivity of the p16 (MA) protein with region-specific gag antisera and the conservation of the N-terminal myristyl group of the p55 precursor protein in p16 (MA) confirmed its position as the N-terminal-most protein. The p9 (nucleocapsid, NC) protein was localized to residue 378 of the gag ORF, next to the C terminus of the p24/p25 (core antigen, CA) protein. The p9 protein had a repeating Cys residue containing motif which is found in the nucleic acid-binding Cys residue-containing proteins of retroviruses. The p24 (CA) protein, which was localized to residue 133 of the gag ORF, was apparently derived by C-terminal processing of an intermediate polypeptide, p25. Both the mature p24 (CA) and p16 (MA) proteins were phosphorylated at Ser residue(s). We also identified two forms of gag p41 species, one resulting from the C-terminal processing of p55 and the other originating either from N-terminal processing of p55 or from de novo synthesis.

Expression of K99 adhesion antigen controlled by the Escherichia coli tryptophan operon promoter.

The genetic determinant for the K99 adhesin of enterotoxigenic Escherichia coli B41 [O101:K99] has been cloned as a 7.0-kilobase BamHI-generated DNA fragment into the vector pBR322 by us and others (J. D. A. van Embden, F. K. de Graaf, L. M. Schouls, and J. S. Teppma, Infect. Immun. 29:1125-1133, 1980). Cells harboring one such construction, known as pK99-64, are capable of expressing K99 antigen on the cell surface. We replaced the natural promoter sequence for the gene encoding the K99 pilus subunit with a strong, inducible exogenous promoter, the E. coli tryptophan (trp) operon promoter, to construct the plasmid pBR-TrpK99. E. coli cells harboring pBR-TrpK99 or a similar construction in the plasmid pDR540, known as pKO-TrpK99, upon induction with 3-beta-indoleacrylic acid, produced about fourfold more K99 antigen than did cells bearing pK99-64 with the natural promoter. Expression of the pilus antigen was found to be under control of the tryptophan promoter. Plasmid instability was encountered, however, in cells bearing pKO-TrpK99 when the trp promoter was derepressed. Introduction of the aminoglycoside 3'-phosphotransferase gene of transposable element Tn5 into pKO-TrpK99 to generate pKON-TrpK99 effectively stabilized the plasmid in cells grown under identical conditions in medium containing kanamycin.

Hepatocellular carcinoma in ground squirrels persistently infected with ground squirrel hepatitis virus.

Although persistent infection with hepatitis B virus and woodchuck hepatitis virus has been associated with development of hepatocellular carcinoma in the host, little has been known of such an association with ground squirrel hepatitis virus (GSHV), which is closely related to the woodchuck virus. Colonies of GSHV-infected and -uninfected Beechey ground squirrels were observed for tumors for a period of 5 years. Tumors developed in seven squirrels after a minimum of 2.4 years of observation per animal; each of the seven animals was over 4 years old when the tumor was detected. The predominant type of tumor was hepatocellular carcinoma, which appeared in 2 of 28 GSHV-bearing animals studied and in 1 of 23 squirrels with antibody to the virus. No hepatocellular carcinoma appeared in 24 GSHV marker-free squirrels. Integrated GSHV DNA was found in the hepatocellular carcinoma tissue of the one carrier animal examined, paralleling the frequent findings of integrated hepatitis B and woodchuck hepatitis viral DNA in human and woodchuck hepatocellular carcinoma. Although the incidence of liver carcinoma reported here in carrier ground squirrels is neither as great as that in carrier woodchucks nor statistically different from the incidence in noncarrier squirrels, the data presented suggest that persistent infection with GSHV may also be associated with hepatocellular carcinoma.