Faculty Bibliography

Previous studies from our laboratory have described two endogenous provirus-like sequences in a series of cosmids spanning the TL region of the major histocompatibility complex (MHC) of normal C57BL/10 mice. At least one of these viruses shares similarities with VL30 elements. To determine if additional VL30-like retroviral elements are integrated in the MHC, we constructed a cosmid library using DNA from a radiation leukemia virus (RadLV)-transformed cell line derived from C57BL/6 mice. The library was first screened using the H-2III (5') probe, which detects Class I genes of the H-2 complex. In the primary screening 163 H-2III positives were isolated. The H-2III-positive isolates were then hybridized with an AKR-derived virus probe, EcoB/S, which contains sequences from both the pol and the env genes of the virus. Nine virus-positive isolates were detected. Localization of these cosmid isolates containing viral sequences within the H-2 complex was done utilizing low-copy probes and confirmed using previously mapped cosmid isolates from other laboratories. We report here the isolation and characterization of VL30-like elements from the Qa and D regions of the MHC of several inbred mouse strains

The biological consequences of radiation leukemia virus (RadLV) infection include the stimulation of H-2Dd antigen expression in resistant mouse strains and thymoma induction in susceptible strains. In an effort to understand the genetic basis of these phenomena, the integrated ecotropic RadLV genome has been examined in a number of primary RadLV-induced tumors, as well as thymomas adapted to in vitro passage; considerable heterogeneity was observed. Examination of these polymorphic viral sequences should help define the viral gene(s) involved in the biological effects of RadLV infection; toward this end, integrated RadLV genomes were molecularly cloned and examined. The genomes and their flanking sequence were characterized by restriction enzyme analysis. Three unique viral genomes were obtained which represent four integration sites. The three RadLV genomes are shown to carry polymorphisms of the original tumor. Following DNA transfection, one of the three genomes replicated in and reinfected both mouse thymocytes and fibroblasts, but not mink fibroblasts in vitro. Virus encoded by the other two DNA genomes could not be recovered following transfection into any of the three cell types. One of these two apparently defective retroviruses encodes a truncated p15E molecule, while the other has elongated long terminal repeats (LTRs). The non-defective ecotropic isolate was collected from in vitro tissue culture supernatants, concentrated, and used to infect mice. Thymocytes of infected, resistant mice were shown to express elevated levels of H-2Dd antigen as early as 12 days post infection, a hallmark of RadLV infection

Our laboratory has focused on defining, localizing, and understanding the mode of action of genes involved in fractionated x-irradiation (FXI) leukemia in susceptible and restraint mouse strains. We have described the genetic and molecular evidence suggesting the existence of multiple independent loci involved in FXI-induced leukemogenesis. These studies indicated that one of these, Ril-1, a locus on the distal portion of chromosome 15, is the major locus influencing susceptibility to the disease. Our data unequivocally place Ril-1 in the gene complex Ly-6--Ril-1--Sis--H-30--Pol-5. Ril-1 appears to be closest to Ly-6 and Sis. We report that in FXI-induced leukemias there are hypomethylation changes in the Ly-6 region as compared to normal thymocytes. In contrast, Sis was found to be hypermethylated and not expressed. In addition, we have noted DNA rearrangements in the Ly-6--Pol-5 region in the majority of tumors examined using the Ly-6 and spleen focus-forming virus (SFFLV) molecular probes. Increased expression of Ly-6 and other surface markers encoded in this region has been noted in FXI-induced thymomas

Administration of the aromatic polycyclic dione compounds hypericin or pseudohypericin to experimental animals provides protection from disease induced by retroviruses that give rise to acute, as well as slowly progressive, diseases. For example, survival from Friend virus-induced leukemia is significantly prolonged by both compounds, with hypericin showing the greater potency. Viremia induced by LP-BM5 murine immunodeficiency virus is markedly suppressed after infrequent dosage of either substance. These compounds affect the retroviral infection and replication cycle at least at two different points: (i) Assembly or processing of intact virions from infected cells was shown to be affected by hypericin. Electron microscopy of hypericin-treated, virus-producing cells revealed the production of particles containing immature or abnormally assembled cores, suggesting the compounds may interfere with processing of gag-encoded precursor polyproteins. The released virions contain no detectable activity of reverse transcriptase. (ii) Hypericin and pseudohypericin also directly inactivate mature and properly assembled retroviruses as determined by assays for reverse transcriptase and infectivity. Accumulating data from our laboratories suggest that these compounds inhibit retroviruses by unconventional mechanisms and that the potential therapeutic value of hypericin and pseudohypericin should be explored in diseases such as AIDS

In this report we demonstrate that lowered expression of the H-2 antigens on RadLV-induced tumour cells is a result of depressed levels of stable mRNA in these cells. Whether this observation is a result of lowered transcription or of mRNA instability is under investigation. In an effort to determine which viral sequences are essential for mediating both the H-2 regulatory function and the transforming function of RadLV, we have begun to assemble newly integrated proviral genomes from tumours. The restriction enzyme cleavage sites of four isolates are presented; these isolates differ substantially from RadLV genomes previously presented. One of these molecular clones is shown to encode a non-defective B-tropic, ecotropic virus which when reinjected into resistant mouse strains can mediate the up-regulation of H-2Dd antigen expression. Finally, possible mechanisms of H-2 regulation are discussed

Two aromatic polycyclic diones hypericin and pseudohypericin have potent antiretroviral activity; these substances occur in plants of the Hypericum family. Both compounds are highly effective in preventing viral-induced manifestations that follow infections with a variety of retroviruses in vivo and in vitro. Pseudohypericin and hypericin probably interfere with viral infection and/or spread by direct inactivation of the virus or by preventing virus shedding, budding, or assembly at the cell membrane. These compounds have no apparent activity against the transcription, translation, or transport of viral proteins to the cell membrane and also no direct effect on the polymerase. This property distinguishes their mode of action from that of the major antiretro-virus group of nucleoside analogues. Hypericin and pseudohypericin have low in vitro cytotoxic activity at concentrations sufficient to produce dramatic antiviral effects in murine tissue culture model systems that use radiation leukemia and Friend viruses. Administration of these compounds to mice at the low doses sufficient to prevent retroviral-induced disease appears devoid of undesirable side effects. This lack of toxicity at therapeutic doses extends to humans, as these compounds have been tested in patients as antidepressants with apparent salutary effects. Our observations to date suggest that pseudohypericin and hypericin could become therapeutic tools against retroviral-induced diseases such as acquired immunodeficiency syndrome (AIDS)