Michael M. Lieber

Mink cell line MvlLu (CCL 64): Focus formation and the generation of “nonproducer” transformed cell lines with murine and feline sarcoma viruses

Abstract Because of its flat regular growth in monolayer culture and its broad host range as a permissive cell for replication of a variety of mammalian type C viruses, the MvlLu mink cell line (CCL 64) has been found to be useful for focus forming assays of murine and feline sarcoma viruses, the generation of nonproducer murine and feline sarcoma virus-transformed cell lines, and the construction of sarcoma virus pseudotypes of mammalian type C viruses.

Characterization of a type C virus released from the porcine cell line PK(15)

Abstract The PK(15) pig kidney cell line produces type C viral particles which are not infectious for a variety of mammalian cell lines. The PK(15) virions contain reverse transcriptase with a molecular weight of 70,000 and a “gs protein” with a molecular weight of 30,000. The reverse transcriptase and gs protein are antigenically related to the homologous proteins of previously studied mammalian type C viruses; however, RNA-DNA hybridization shows that the PK(15) RNA genome is essentially unrelated to known murine, feline, rat, hamster, and primate type C viruses. Normal pig liver contains DNA which is homologous to the PK(15) viral genome, indicating that pigs have endogenous type C viral genetic information.

Mammalian Cells in Culture Frequently Release Type C Viruses

Cell cultures commonly used in animal cell research, both cell strains and continuous cell lines from various mammalian species, spontaneously produce type C RNA viruses.

Type C viruses of baboons: Isolation from normal cell cultures

Abstract Four new type C viruses were isolated from putatively virus-negative baboon lung, kidney, and testicular cells by cocultivation with several permissive host cell lines. The baboon type C viruses are infectious for cells from various mammalian species, but do not replicate in any baboon cell lines so far tested. These viruses can be distinguished from other major classes of mammalian type C viruses, including previous isolates from primates, but are most closely related to endogenous feline viruses of the RD-114/CCC group. By immunologic criteria, viral host range, and nucleic acid hybridization studies, the baboon type C viruses are highly related to one another and represent a distinct new class of endogenous primate type C viruses.

Biologic and immunologic properties of porcine type C viruses

Six different porcine cell lines spontaneously begin to release type C viruses after long-term propagation in vitro. Reverse transcriptases from all of the viral isolates are inhibited by immune IgG directed against the polymerase from the endogenous porcine type C virus PK(15). Two of the isolates are capable of replicating in the pig cell line, ST-Iowa, and the third isolate, while unable to initiate productive infection, can rescue murine sarcoma virus genomes from transformed nonproducer cell lines.

Infectious primate type C viruses: Three isolates belonging to a new subgroup from the brains of normal gibbons

Abstract Three type C viruses (GBr-1, GBr-2, and GBr-3) were isolated by coculativation of normal gibbon brain tissues with cultured mammalian cell lines. The tissues, all frozen since 1968, were obtained from two animals inoculated with brain extracts from human patients with kuru and from one uninoculated cagemate. By viral interference tests and by immunologic studies of the viral polymerases and major internal structural proteins (p30), the new isolates are typical members of a group of mammalian type C viruses infectious for primates. By nucleic acid hybridization, the viruses isolated from the gibbon brains, while highly related to one another, can be readily distinguished from the previously isolated type C viruses of this group. The infectious primate type C viruses isolated to date can be classified into four distinct subgroups.

Endogenous baboon type C virus (M7): Biochemical and immunologic characterization

Abstract A type C virus (M7) was isolated from a baboon placenta and grown to high titer in a canine thymus cell line. M7 virions contain a 70,000 molecular weight reverse transcriptase and a group specific (gs) protein of approximately 30,000 molecular weight which are antigenically related to the homologous proteins of other mammalian type C viruses. The M7 viral polymerase is not inhibited by antisera prepared against viral polymerases of a woolly monkey type C virus or Rauscher murine leukemia virus (R-MuLV), but is partially inhibited by antisera prepared against the polymerase of the feline virus, RD-114. A competitive radioimmunoassay for the gs protein of RD-114 also detects the gs protein of the M7 virus, indicating the presence of cross-reacting antigenic determinants not detected in the gs proteins of other type C viruses. In contrast, the M7 gs protein is only minimally detected in an assay for interspecies (gs-3) determinants which detects the gs proteins of other mammalian type C viruses. While the M7 virus and viruses of the RD -114 CCC group replicate readily in certain cell lines of canine and human origin, the M7 virus cannot be propagated on a cat cell strain which is permissive for endogenous feline viruses of the RD -114 CCC group. Two previously described type C viruses, isolated from primates, show no immunologic relationship to the M7 virus.

Infectious type C viruses released by normal cat embryo cells

Abstract Type C viruses with antigenic and host range properties similar to the RD114 virus and to a virus from a continuous line of cat kidney cells, CCC, have been isolated from six of ten diploid fetal cat cell cultures. Each of the new viruses replicates readily in human and rhesus monkey cells, but not in most other cat cell strains tested. However, a cat cell strain, FFc60WF, was found that is permissive for replication of the RD/CCC group of type C viruses produced by other cat cell strains. The host range of these endogenous type C viruses includes bat, dog, mink, and rabbit cells, as well as primate cells. Type C viruses of the FeLV group could not be detected in any of these ten fetal cat cell cultures. Viral RNA from one of the new isolates, from the CCC virus, and from RD114 virus each specifically anneal S 1 to an [ 3 H]DNA transcript of the RD114 genome.

Mammalian Type C RNA Viruses

Type C RNA viruses are a distinct class of vertebrate viruses which share a common morphology, protein composition, and viral life cycle, have single-stranded RNA as their viral genome, and contain an RNA-directed DNA polymerase (reverse transcriptase).

Isolation of a type C virus (FS-1) from the European wildcat (Felis sylvestris)

Abstract The DNA of the European wildcat ( Felis sylvestris ) contains sequences which hybridize to [ 3 H]DNA transcripts of the RNA of domestic cat type C viruses of the RD-114/CCC group. To determine if the sequences could code for the production of infectious virions, tissues from a European wildcat were cocultivated with established cell lines from heterologous species known to be permissive for the replication of endogenous domestic cat type C viruses. Both a syncytium-forming (“foamy”) and a type C virus were isolated, and the type C viral component was resolved by passaging the mixed virus stock in cells which are relatively resistant to infection by feline syncytium-forming viruses. The European wildcat type C virus (FS-1) is highly related to viruses of the RD-114/CCC group by viral host range and interference critera. FS-1 contains a reverse transcriptase and major group-specific protein (p30) with antigenic determinants similar to those of the homologous proteins of RD-114, and [ 3 H]DNA transcripts of FS-1 RNA hybridize extensively to the RNA of endogenous domestic cat type C viruses. Like viruses of the RD-114/CCC group, FS-1 is related by several criteria to endogenous baboon type C viruses. The results indicate that European wildcats contain endogenous type C virogenes which can code for the production of infectious type C particles.