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Serum starved v-mos-transformed cells are unable to appropriately downregulate cyclins and CDKs
N Rhodes1, C L Innes, F Propst
1Growth Control and Cancer Group, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Abstract:
Serum deprived v-mos-transformed NIH3T3 cells are unable to enter a true quiescent state, but instead, arrest in the early G1 phase of the cell cycle. We have analysed several cell cycle regulatory proteins in these G1 arrested cells and show altered regulation in the expression and activity of certain cyclins and cyclin-dependent kinases. In particular, p34cdc2, cyclin A, cyclin D and cyclin E are not appropriately down-regulated in serum starved, G1 arrested, v-mos-transformed cells as compared with quiescent NIH3T3 cells. Furthermore, serum starved v-mos-transformed cells have elevated histone H1 kinase activity associated with cyclin A, cyclin E, p33cdk2, and p34cdc2. Using a metallothionein-inducible c-mos(mu) expression system, we show that c-mos(mu) induction in quiescent NIH3T3 cells causes elevated expression of p34cdc2. However, this induction of c-mos(mu) and subsequent expression of p34cdc2 was not sufficient to promote significant entry of cells into S phase. Analysis of extracts from serum starved v-H-ras, v-src, and tpr-met transformed NIH3T3 cells demonstrates that these oncogene-transformed cells also contain elevated levels of p34cdc2. We propose that the altered regulation of these critical cell cycle regulatory molecules, and specifically the inability to fully downregulate their activity, contributes significantly to neoplastic transformation and subsequent unregulated growth of tumor cells.
Insights
v-mos-transformed cells exhibit cell cycle dysregulation, failing to down-regulate key proteins like p34cdc2 and cyclins. This altered regulation contributes to uncontrolled tumor cell growth and neoplastic transformation.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Oncogenesis
Background:
- v-mos-transformed NIH3T3 cells arrest in early G1 phase when serum-deprived, unlike normal quiescent cells.
- Cell cycle regulatory proteins, including cyclins and cyclin-dependent kinases, are implicated in uncontrolled cell proliferation.
Purpose of the Study:
- To investigate the altered regulation of cell cycle proteins in v-mos-transformed NIH3T3 cells.
- To determine the role of c-mos(mu) induction in cell cycle progression.
- To examine cell cycle protein levels in other oncogene-transformed cells.
Main Methods:
- Analysis of cell cycle regulatory proteins (cyclins, cyclin-dependent kinases) in serum-starved, G1-arrested cells.
- Utilizing a metallothionein-inducible c-mos(mu) expression system.
- Assessing histone H1 kinase activity.
- Examining protein extracts from v-H-ras, v-src, and tpr-met transformed cells.
Main Results:
- v-mos-transformed cells show failure to down-regulate p34cdc2, cyclin A, cyclin D, and cyclin E.
- Elevated histone H1 kinase activity associated with cyclin A, cyclin E, p33cdk2, and p34cdc2 was observed.
- c-mos(mu) induction increased p34cdc2 expression but did not drive significant S phase entry.
- Other oncogene-transformed cells also displayed elevated p34cdc2 levels.
Conclusions:
- Altered regulation and inability to down-regulate cell cycle proteins contribute to neoplastic transformation.
- Dysregulation of p34cdc2 and associated kinases plays a significant role in tumor cell growth.