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Initiation of growth inhibition by TGF beta 1 is unlikely to occur in G1
I M Kramer1, R Patel, D Spargo
1Department of Pharmacology, University College London, UK.
Abstract:
Type beta transforming growth factors represent a family of polypeptides that modulate growth and differentiation. They exert their effect on target cells through interaction with multiple cell surface receptors. Transforming growth factor-beta 1 has a strong inhibitory action on cell division in mink lung CC164 cells, a process that is initiated by immediate induction of junB and phosphorylation of nuclear protein followed by a reduced expression of cdk4. However, its signal transduction pathways are still unresolved. In this study we report a detailed analysis of cell kinetic events following addition of transforming growth factor-beta 1 to mink lung CCL64 cells. We show that transforming growth factor-beta 1 reduces [3H]thymidine incorporation after a delay of 8 hours, which reaches its nadir at 16 hours. The reduced growth rate is maintained for at least 48 hours as shown by flow cytometric analysis of DNA content. Using time-lapse video microscopy it was shown that control cells double on average every 14.4 hours, whereas the transforming growth factor-beta 1-treated cells have a doubling time of on average 20.3 hours. The difference in intermitotic time is a consequence of a prolonged G1 phase (a shift from 7.5 to 13.5 hours on average). However, changes in intermitotic times occur only after cells have undergone division in the presence of transforming growth factor-beta 1 and treated cells finish the ongoing cell cycle exactly like control cells. From these findings we conclude that transforming growth factor-beta 1 may change cell cycle parameters by interfering with cellular events prior to G1.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Transforming growth factor-beta 1 (TGF-β1) inhibits mink lung cell division by prolonging the G1 phase. This cell cycle delay occurs after the initial cell division, impacting subsequent cell cycle progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Transforming growth factors (TGFs) are key regulators of cell growth and differentiation.
- TGF-beta 1 (TGF-β1) inhibits cell division in mink lung cells, but its precise signaling pathways remain unclear.
- TGF-β1 interacts with cell surface receptors to mediate its effects.
Purpose of the Study:
- To analyze the cell kinetic effects of TGF-β1 on mink lung CCL64 cells.
- To elucidate the specific cell cycle phases affected by TGF-β1 treatment.
- To understand the temporal dynamics of TGF-β1's inhibitory action on cell proliferation.
Main Methods:
- Treatment of mink lung CCL64 cells with TGF-β1.
- Measurement of [3H]thymidine incorporation to assess DNA synthesis.
- Flow cytometry to analyze DNA content and cell cycle distribution.
- Time-lapse video microscopy to determine cell doubling times and intermitotic intervals.
Main Results:
- TGF-β1 delayed [3H]thymidine incorporation by 8 hours, reaching a minimum at 16 hours.
- Cell proliferation inhibition was sustained for at least 48 hours.
- Cell doubling time increased from 14.4 to 20.3 hours due to a prolonged G1 phase (7.5 to 13.5 hours).
- Cell cycle changes were observed only after the first division in the presence of TGF-β1.
Conclusions:
- TGF-β1 significantly alters cell cycle kinetics in mink lung cells.
- The primary effect of TGF-β1 is the extension of the G1 phase, leading to reduced proliferation.
- TGF-β1 likely interferes with pre-G1 cellular events, influencing subsequent cell cycle progression.