In vivo induction of endogenous retroviruses in BALB/c mouse hepatocytes by successive treatments with carbon tetrachloride and bromodeoxyuridine

The effects of bromodeoxyuridine (BrdUrd) incorporation into hepatocytes of carbon tetrachloride (CCl₄)‐induced regenerating liver of BALB/c mice on the induction of endogenous retroviruses was examined. From the nucleic acid hybridization studies, the maximum levels of hybridization were obtained for both N‐ and X‐tropic BALB/c endogenous retrovirus specific [³H]‐cDNAs with liver RNA from animals receiving BrdUrd at 40 and 44 h post‐CCl₄ treatment, and killed on the fourth day following BrdUrd injection. Media from NIH‐3T3 (Swiss mouse) and mink cell cultures, infected with liver homogenates from animals treated as above, gave significant levels of reverse transcriptase activity. The observations made in the present study show that BrdUrd incorporation into cell DNA can cause induction of both N‐ and X‐tropic endogenous retroviruses in BALB/c mouse hepatocytes in vivo, and such induction is probably a transient event.