| Abstract |
Mouse mammary tumor cell lines were established in culture from a tumor
arising spontaneously in a female mouse of DD/Tbr strain. Two epithelial
(DD-762 and DD-763) and one spindle-shaped (DD-764) cell lines were
isolated from DD-761 by single cell cloning. Cytological and growth
properties in vitro, ability to produce viruses, the characteristics of
produced viruses, kinetics of virus production, and effects of
dexamethasone (DXM) on virus production were examined in these cell lines,
and following results were obtained. 1) The chromosome number and
population-doubling time were 80 and 18 hours respectively in all cell
lines except DD-764. 2) The virus produced by these cell lines was
considered to be B-type RNA virus (MuMTV) according to the following
evidence: a) the culture harvest contained virus particles with a density
of 1.17g/ml, and 70S RNA was extracted from the particles, b) the viral
RNA-dependent DNA polymerase (RDDP) prefers rather Mg" than Mn" with poly
(rA).(dT)12-14 as synthetic template-primer, c) no murine leukemia virus
(MuLV) was detected by the UV-XC test and Mink S+L- focus induction assay.
3) The kinetics of virus release into culture fluid was studied by RDDP
assay. MuMTV production was not observed in the epithelial cell lines at
the logarithmic phase of cell growth, but was observed at the stationary
phase. 4) The levels of MuMTV production in 4 different cell lines were
compared by RDDP assays. DD-762 produced approximately 0.8mg viral
protein/l/day and is considered an excellent source of MuMTV. 5) DXM
(5mug/ml) resulted in about a 15-fold increase in MuMTV production in the
presence of insulin (10/mug/ml). This enhancing effect was reversible.
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