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Transforming growth factor beta induces the cyclin-dependent kinase inhibitor p21 through a p53-independent mechanism
1Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA.
Abstract:
The transforming growth factor beta s (TGF-beta s) are a group of multifunctional growth factors which inhibit cell cycle progression in many cell types. The TGF-beta-induced cell cycle arrest has been partially attributed to the regulatory effects of TGF-beta on both the levels and the activities of the G1 cyclins and their kinase partners. The activities of these kinases are negatively regulated by a number of small proteins, p21 (WAF1, Cip1), p27Kip1, p16, and p15INK4B, that physically associate with cyclins, cyclin-dependent kinases, or cyclin-Cdk complexes. p21 has been previously shown to be transcriptionally induced by DNA damage through p53 as a mediator. We demonstrate that TGF-beta also causes a rapid transcriptional induction of p21, suggesting that p21 can respond to both intracellular and extracellular signals for cell cycle arrest. In contrast to DNA damage, however, induction of p21 by TGF-beta is not dependent on wild-type p53. The cell line studied in these experiments, HaCaT, contains two mutant alleles of p53, which are unable to activate transcription from the p21 promoter when overexpressed. In addition, TGF-beta and p53 act through distinct elements in the p21 promoter. Taken together, these findings suggest that TGF-beta can induce p21 through a p53-independent pathway. Previous findings have implicated p27Kip1 and p15INK2B as effectors mediating the TGF-beta growth inhibitory effect. These results demonstrate that a single extracellular antiproliferative signal, TGF-beta, can act through multiple signaling pathways to elicit a growth arrest response.
Insights
Transforming growth factor-beta (TGF-β) induces cell cycle arrest by upregulating p21 protein. This TGF-β-induced p21 expression occurs independently of the p53 pathway, highlighting a novel mechanism for cell cycle regulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Transforming growth factor-beta (TGF-β) is a key regulator of cell proliferation and differentiation.
- TGF-β signaling inhibits cell cycle progression by modulating G1 cyclins and cyclin-dependent kinases (CDKs).
- The cyclin-dependent kinase inhibitors (CKIs) p21, p27, p16, and p15 are crucial negative regulators of the cell cycle.
Purpose of the Study:
- To investigate the role of p21 in TGF-β-induced cell cycle arrest.
- To determine whether TGF-β-mediated p21 induction is dependent on p53.
- To elucidate the signaling pathways involved in TGF-β's antiproliferative effects.
Main Methods:
- Cell culture experiments using HaCaT cells (with mutant p53).
- Analysis of p21 gene transcription and protein levels.
- Examination of TGF-β and p53 interactions with the p21 promoter.
Main Results:
- TGF-β rapidly induces the transcription of p21 in HaCaT cells.
- TGF-β-induced p21 expression is independent of wild-type p53.
- TGF-β and p53 bind to distinct elements in the p21 promoter.
- TGF-β utilizes multiple signaling pathways, including p21 induction, to inhibit cell growth.
Conclusions:
- TGF-β can induce cell cycle arrest via a p53-independent pathway involving p21.
- p21 acts as a critical mediator of TGF-β's antiproliferative effects.
- This study reveals a novel mechanism for extracellular signal-induced cell cycle arrest.