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S phase mouse embryo fibroblasts secrete varying amounts of a 45,000 dalton protein
Abstract:
Synchronized cultures of mouse embryo fibroblasts upon release from hydroxyurea (HOU) arrest, secreted several proteins of which a polypeptide of molecular weight 45,000 (45K) was barely visible in the conditioned medium of cells that synthesized DNA at peak levels. The quantity of the 45K protein was higher in the medium of HOU arrested cells and the level got progressively reduced as the cells entered into the DNA synthetic phase. Conditioned media containing the 45K protein inhibit DNA synthesis when added to synchronized cultures. These results suggest that the 45K secreted protein may be involved in the autocrine regulation of turning-off of DNA synthesis at the end of S phase.
Insights
A secreted 45K protein inhibits DNA synthesis in mouse embryo fibroblasts. Its levels decrease as cells enter DNA synthesis, suggesting a role in regulating the cell cycle and turning off DNA replication.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cell cycle regulation is crucial for normal development and preventing disease.
- Autocrine signaling plays a role in controlling cellular proliferation.
Purpose of the Study:
- To investigate the role of secreted proteins in regulating DNA synthesis in mouse embryo fibroblasts.
- To identify specific proteins involved in the termination of the S phase.
Main Methods:
- Utilized synchronized mouse embryo fibroblast cultures.
- Analyzed protein secretion during cell cycle progression using hydroxyurea (HOU) arrest.
- Assessed the impact of conditioned media on DNA synthesis.
Main Results:
- A 45,000 molecular weight (45K) protein was identified in conditioned media.
- 45K protein levels were inversely correlated with DNA synthesis rates.
- Conditioned media containing 45K protein inhibited DNA synthesis.
Conclusions:
- The secreted 45K protein may function as an autocrine factor.
- This protein appears to be involved in the process of turning off DNA synthesis at the end of S phase.