The Role of Feline Retroviral Long Terminal Repeat Sequences on Virus Expression in Feline Cells

Abstract

The intracellular restriction for endogenous feline virus (RD114) replication in feline embryonic (FeF) cells has been described (Fischinger, 1975). Restriction of RD114 virus was described as the inability of Moloney Sarcoma Virus (MSV) (RD114) pseudotype to form MSV foci without Feline Leukemia Virus (FeLV) as a helper virus. A fetal feline glial cell line (G355) permissive for RD114 virus replication has also been described (Haapala, 1985). FeF and G355 cells were utilized for analysis aimed at understanding FeF restriction of RD114. Progeny virus from cells transfected with recombinant clones of RD114 or FeLV proviral DNA exhibited the same restriction properties as wild -type virus when used to infect either permissive or non -permissive cells. Virus production was measured from G418 selected colonies cotransfected with pSV2neo DNA and either FeLV or RD114 proviral DNA. FeLV cotransfectants produced a similar amount of virus in both cell lines, while RD114 colonies produced about 25 times more virus in G355 cells than FeF cells. Transcriptional activity of the FeLV and RD114 long terminal repeats (LTRs) was analyzed in FeF and G355 cells using LTRcat vectors by measuring chloramphenicol acetyl transferase (CAT) expression. It was determined that both RD114 and FeLV LTRs express about the same amount of CAT in both G355 and FeF cells. Negative regulation does not appear to be involved in the RD114 restriction in FeF cells. Collectively, these data suggest that some steps prior to integration may be involved in the restriction of RD114 virus replication in FeF cells.