Activation of an endogenous retrovirus from Tupaia (tree shrew)

Chemical induction of endogenous retrovirus particles from the vero cell line of African green monkeys

Endogenous retroviral sequences are present in high copy numbers in the genomes of all species and may be expressed as RNAs; however, the majority are defective for virus production. Although virus has been isolated from various Old World monkey and New World monkey species, there has been no report of endogenous retroviruses produced from African green monkey (AGM) tissues or cell lines. We have recently developed a stepwise approach for evaluating the presence of latent viruses by chemical induction (Khan et al., Biologicals 37:196-201, 2009). Based upon this strategy, optimum conditions were determined for investigating the presence of inducible, endogenous retroviruses in the AGM-derived Vero cell line. Low-level reverse transcriptase activity was produced with 5-azacytidine (AzaC) and with 5'-iodo-2'-deoxyuridine (IUdR); none was detected with sodium butyrate. Nucleotide sequence analysis of PCR-amplified fragments from the gag, pol, and env regions of RNAs, prepared from ultracentrifuged pellets of filtered supernatants, indicated that endogenous retrovirus particles related to simian endogenous type D betaretrovirus (SERV) sequences and baboon endogenous virus type C gammaretrovirus (BaEV) sequences were induced by AzaC, whereas SERV sequences were also induced by IUdR. Additionally, sequence heterogeneity was seen in the RNAs of SERV- and BaEV-related particles. Infectivity analysis of drug-treated AGM Vero cells showed no virus replication in cell lines known to be susceptible to type D simian retroviruses (SRVs) and to BaEV. The results indicated that multiple, inducible endogenous retrovirus loci are present in the AGM genome that can encode noninfectious, viruslike particles.

Characterization of the Tupaia rhabdovirus genome reveals a long open reading frame overlapping with P and a novel gene encoding a small hydrophobic protein

Rhabdoviruses are negative-stranded RNA viruses of the order Mononegavirales and have been isolated from vertebrates, insects, and plants. Members of the genus Lyssavirus cause the invariably fatal disease rabies, and a member of the genus Vesiculovirus, Chandipura virus, has recently been associated with acute encephalitis in children. We present here the complete genome sequence and transcription map of a rhabdovirus isolated from cultivated cells of hepatocellular carcinoma tissue from a moribund tree shrew. The negative-strand genome of tupaia rhabdovirus is composed of 11,440 nucleotides and encodes six genes that are separated by one or two intergenic nucleotides. In addition to the typical rhabdovirus genes in the order N-P-M-G-L, a gene encoding a small hydrophobic putative type I transmembrane protein of approximately 11 kDa was identified between the M and G genes, and the corresponding transcript was detected in infected cells. Similar to some Vesiculoviruses and many Paramyxovirinae, the P gene has a second overlapping reading frame that can be accessed by ribosomal choice and encodes a protein of 26 kDa, predicted to be the largest C protein of these virus families. Phylogenetic analyses of the tupaia rhabdovirus N and L genes show that the virus is distantly related to the Vesiculoviruses, Ephemeroviruses, and the recently characterized Flanders virus and Oita virus and further extends the sequence territory occupied by animal rhabdoviruses.

Retrovirus-like particles associated with myeloproliferative disease in the dog

A case of granulocytic myeloproliferative disease with hypercalcaemia of malignancy in a 6-year-old Golden Retriever dog is described. Numerous retrovirus-like budding particles were observed at the cell surface of the neoplastic granulocytes, suggesting the presence of a new oncogenic virus. Several attempts by other workers to demonstrate the presence of an oncogenic retrovirus in canine lymphosarcoma have produced minimal results. This study suggests that non-lymphoid canine myeloproliferative disorders warrant further investigation.

Detection of lymphocytes producing a human retrovirus associated with adult T-cell leukemia by syncytia induction assay

Recently 10 T-cell lines were established from patients with adult T-cell leukemia (ATL). During establishment of these cell lines, it was found that when T-cell lines expressing the ATL-associated retroviral antigen were cocultivated with 8C cat cells, multinucleated syncytia were formed. Retroviral antigen-negative T-cell lines did not induce syncytia. Peripheral blood lymphocytes obtained from ATL patients did not express the retroviral antigen before cultivation in vitro but became positive for the retroviral antigen after cultivation for a short period; these retroviral antigen-positive lymphocytes, but not retroviral antigen-negative lymphocytes, induced syncytia upon cocultivation with 8C cells. Peripheral blood lymphocytes isolated from patients with chronic lymphocytic leukemia of T-cell origin or Sézary syndrome or from normal adults and lymph node cells from a patient with immunoblastic lymphadenopathy-like T-cell lymphoma did not express the retroviral antigen even after cultivation in vitro and did not induce syncytia upon cocultivation with 8C cells. Thus, there was complete agreement between the presence of the retroviral antigen in established T-cell lines or freshly isolated peripheral blood lymphocytes and their ability to induce syncytia. Syncytia formation was enhanced 5- to 20-fold by the presence of Polybrene and inhibited by addition of plasma of ATL patients to the cocultures. Syncytia were detected within 4 hr on cocultivation of 8C cells with the retroviral antigen-positive T-cells, indicating that most syncytia were formed by early polykaryocytosis. After cocultivation, a clone of 8C cells that harbored the ATL virus genome and had syncytia-inducing activity was isolated. These findings indicate that the retrovirus associated with ATL has syncytia-inducing activity. Syncytia induction assay using 8C cells will be useful for detection and characterization of human retrovirus associated with T-cell malignancies.