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Transforming growth factor beta 1 inhibits mouse keratinocytes late in G1 independent of effects on gene
1Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2175, USA.
Abstract:
Potential mechanisms by which transforming growth factor beta 1 (TGF beta 1) inhibits cell growth include suppression of transcription of genes required for proliferation and inactivation of enzymatic activities that regulate progression through G1. To clarify which events are important for TGF beta 1 signaling, we have defined more precisely the times in G1 when the mouse keratinocyte cell line BALB/MK is sensitive to TGF beta 1-induced inhibition. TGF beta 1 is capable of inhibiting BALB/MK cell growth when the inhibitory factor is added to cells at any point before the G1-S transition. Synchronization at the G1-S boundary with mimosine, an inhibitor of initiation of origins of DNA replication, followed by release into S phase in the presence of TGF beta 1, indicated that cells lose sensitivity to TGF beta 1 as they enter the replicative phase. It is interesting that TGF beta 1 can inhibit BALB/MK cell growth late in G1, at a time when cell cycle progression is not blocked by an inhibitor of RNA polymerase II-mediated transcription. 5,6-dichlorobenzimidazole riboside (DRB). In addition, the ability of TGF beta 1 to inhibit entry into S phase in late G1 is unaffected by concurrent treatment with DRB. The data suggest that, at least when added to cultures that are in the latter few hours of G1, TGF beta 1 can inhibit cell cycle progression through mechanisms that do not involve stimulation or inhibition of gene expression at the transcriptional level.
Insights
Transforming growth factor beta 1 (TGF-β1) inhibits cell growth by affecting G1 phase progression. This inhibition occurs late in G1, independent of transcriptional regulation, suggesting non-genomic mechanisms.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Transforming growth factor beta 1 (TGF-β1) is known to inhibit cell proliferation through various mechanisms.
- Key proposed mechanisms include transcriptional suppression of proliferation genes and enzymatic inactivation impacting G1 phase progression.
Purpose of the Study:
- To precisely define the timing of TGF-β1 sensitivity during the G1 phase of the cell cycle in mouse keratinocytes (BALB/MK cells).
- To elucidate the specific molecular events targeted by TGF-β1 during G1 phase arrest.
Main Methods:
- Utilized the BALB/MK mouse keratinocyte cell line.
- Employed mimosine to synchronize cells at the G1-S boundary.
- Assessed TGF-β1 sensitivity at different G1 time points.
- Investigated the role of transcriptional regulation using 5,6-dichlorobenzimidazole riboside (DRB), an RNA polymerase II inhibitor.
Main Results:
- TGF-β1 inhibited BALB/MK cell growth when added at any point before the G1-S transition.
- Cells lost sensitivity to TGF-β1 as they entered the S phase.
- TGF-β1 effectively inhibited late G1 progression, even when transcription was blocked by DRB.
- Concurrent treatment with DRB did not affect TGF-β1's ability to inhibit entry into S phase.
Conclusions:
- TGF-β1 can inhibit cell cycle progression in late G1 through mechanisms independent of transcriptional gene regulation.
- These findings suggest that TGF-β1 utilizes non-transcriptional pathways to control cell cycle progression, particularly in the critical late G1 phase.