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Changes in retrovirus expression in mouse mammary tumor cells in culture
Abstract:
Mouse mammary tumor cells (Mm5Mt/c1) produced mouse mammary tumor virus (MMTV) (type B retrovirus) at early passages in culture. They apparently produced predominently type C retrovirus(es) at late passages in culture. The decline in MMTV production during passage was not accompanied by an apparent decrease in the synthesis or accumulation of intracellular MMTV-specific RNA. As judged by the concentration of RNA (mol/titer) x half-time (sec) of hybridization of cellular RNA with MMTV complementary DNA, the intracellular concentration MMTV-specific RNA did not change significantly during passage in culture. Since late-passage RNA, particularly polysomal poly(adenylic acid)-containing RNA, yielded lower apparent maximum hybridization of MMTV complementary DNA as compared with early-passage RNA, it was possible that the complexity or base sequence of MMTV-specific RNA in late-passage cultures was not identical with that in early-passage cultures. The data on thermal transitions of hybrids were in accord with this possibility. In contrast, the steady-state level of type C virus-specific RNA in late-passage cultures was orders of magnitude higher than that in early-passage cultures. The production of type C retrovirus(es) at later passages was apparently accompanied by increased transcription of type c retrovirus DNA.
Insights
Mouse mammary tumor cells shifted from producing mouse mammary tumor virus (MMTV) to type C retroviruses over time. This change correlated with altered MMTV-specific RNA complexity and increased type C retrovirus RNA transcription.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Mouse mammary tumor cells (Mm5Mt/c1) initially produce mouse mammary tumor virus (MMTV), a type B retrovirus.
- Over time in culture, these cells appear to shift to producing type C retroviruses.
Purpose of the Study:
- To investigate the changes in retroviral production and associated RNA in Mm5Mt/c1 cells during prolonged culture.
- To understand the molecular mechanisms underlying the shift from MMTV to type C retrovirus production.
Main Methods:
- Analysis of retroviral production at early and late passages.
- Quantification of intracellular MMTV-specific RNA using hybridization assays with MMTV complementary DNA.
- Assessment of RNA complexity and base sequence through hybridization thermal transitions.
- Measurement of steady-state levels of type C virus-specific RNA.
Main Results:
- MMTV production declined in late-passage cells, without a decrease in intracellular MMTV-specific RNA concentration.
- Late-passage RNA showed altered hybridization characteristics with MMTV complementary DNA, suggesting changes in MMTV-specific RNA complexity.
- Steady-state levels of type C virus-specific RNA significantly increased in late-passage cultures.
- Increased type C retrovirus production correlated with enhanced transcription of type C retroviral DNA.
Conclusions:
- The shift in retroviral production in Mm5Mt/c1 cells involves a decrease in MMTV production and an increase in type C retrovirus production.
- Changes in MMTV-specific RNA complexity may contribute to the observed decline in MMTV production.
- Increased transcription of type C retroviral DNA underlies the enhanced production of type C retroviruses in late-passage cells.