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v-mos-transformed cells fail to enter quiescence but growth arrest in G1 following serum withdrawal
N Rhodes1, R Hicks, A B Kasenally
1Growth Control and Cancer Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Abstract:
The product of the mos protooncogene normally functions in the induction of meiosis and regulation of cell-cycle progression in oocytes. Here we have investigated the cell-cycle progression of NIH3T3 cells transformed by the v-mos gene. Flow cytometric analysis showed that logarithmically growing v-mos-transformed cells do not differ from their nontransformed counterparts in the distribution of cells in the G1, S, and G2/M phases. Likewise, after serum withdrawal for 48 h, both normal and v-mos-transformed NIH3T3 cells have essentially ceased proliferation, as analyzed by flow cytometry, [3H]thymidine and BrdU incorporation into newly synthesized DNA, and mitotic indexes. However, while the normal NIH3T3 cells are arrested in a quiescent state, the v-mos-transformed cells are arrested in early to mid G1, prior to the point where cells require certain amino acids for proliferation (V point). In agreement with these different arrest points, the v-mos-transformed cells enter S phase following serum stimulation within about 8 h, without the additional 4- to 6-h lag period characteristically displayed by the parental NIH3T3 cells. In addition, we show a lack of expression of a growth arrest-specific gene product, gas1, in the serum-arrested v-mos-transformed cells. These data demonstrated that v-mos-transformed cells display growth characteristics that differ fundamentally from those of normal cells or cells transformed by overexpression of myc [1]. Our results suggest that the v-mos oncoprotein transforms cells, at least in part, by preventing exit from the cell cycle into quiescence.
Insights
The v-mos oncoprotein prevents normal NIH3T3 cells from entering quiescence, causing them to arrest in early G1 phase. This leads to altered cell-cycle progression and distinct growth characteristics compared to normal cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The mos protooncogene is crucial for meiosis induction and cell-cycle regulation in oocytes.
- Understanding oncogene-induced cell transformation is key to cancer research.
Purpose of the Study:
- To investigate the cell-cycle progression of NIH3T3 cells transformed by the v-mos gene.
- To elucidate the mechanism by which v-mos oncoprotein affects cell proliferation and cell-cycle arrest.
Main Methods:
- Flow cytometry to analyze cell-cycle phase distribution (G1, S, G2/M).
- Measurement of DNA synthesis using [3H]thymidine and BrdU incorporation.
- Assessment of mitotic index and growth arrest-specific gene (gas1) expression.
Main Results:
- v-mos-transformed NIH3T3 cells, unlike normal cells, arrest in early to mid G1 phase upon serum withdrawal.
- Transformed cells re-enter the cell cycle (S phase) more rapidly after serum stimulation.
- Expression of the growth arrest-specific gene gas1 is reduced in serum-arrested v-mos-transformed cells.
Conclusions:
- The v-mos oncoprotein transforms cells by inhibiting their exit from the cell cycle into a quiescent state.
- v-mos-transformed cells exhibit fundamentally different growth characteristics compared to normal cells or those transformed by other oncogenes like myc.
- These findings offer insights into oncogenic transformation and cell-cycle control mechanisms.