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The MEK pathway is required for stimulation of p21(WAF1/CIP1) by transforming growth factor-beta
1Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Abstract:
Transforming growth factor-beta (TGF-beta)can induce the cyclin-dependent kinase inhibitors p21 and p15 in a variety of cell types. We have shown previously that Smad3 is required for the growth inhibitory activity of TGF-beta, whereas overexpression of Smads is not sufficient to activate the expression of p21 in HaCaT cells. These data suggest that an additional signaling pathway may be involved in stimulating p21 in HaCaT cells. Given the recent finding that the mitogen-activated protein kinase (MAPK) pathway can cause p21 induction and arrest cells, we examined the involvement of this pathway for p21 and p15 induction by TGF-beta. We found that TGF-beta can regulate the MAPK pathway, leading to the increased transactivation ability of transcription factor Elk. Constitutively active components in the MAPK pathway activate p21 expression, and inhibitors or dominant negative constructs for the MAPK pathway significantly decrease p21 induction by TGF-beta. Both constitutively active MEK and inhibitors for MEK have no effect on Smad activity, including DNA binding, localization, and interaction with coactivator p300/CBP. These findings suggest that the MAPK pathway may be an independent pathway that is involved in p21 and p15 induction by TGF-beta.
Insights
Transforming growth factor-beta (TGF-beta) induces cell cycle inhibitors p21 and p15. The study reveals the mitogen-activated protein kinase (MAPK) pathway independently mediates TGF-beta
Area of Science:
- Cell Biology
- Molecular Biology
- Signal Transduction
Background:
- Transforming growth factor-beta (TGF-beta) is known to induce cyclin-dependent kinase inhibitors p21 and p15.
- Smad3 is essential for TGF-beta's growth inhibitory effects, but Smad overexpression alone does not activate p21 in HaCaT cells, suggesting other pathways are involved.
- The mitogen-activated protein kinase (MAPK) pathway has been implicated in p21 induction and cell cycle arrest.
Purpose of the Study:
- To investigate the role of the MAPK pathway in TGF-beta-induced p21 and p15 expression in HaCaT cells.
- To determine if the MAPK pathway acts independently of the Smad pathway in TGF-beta signaling.
Main Methods:
- Utilized HaCaT cells treated with TGF-beta.
- Assessed MAPK pathway activation, including Elk-1 transactivation.
- Examined p21 and p15 induction using constitutively active MAPK components and pathway inhibitors.
- Evaluated Smad pathway activity (DNA binding, localization, p300/CBP interaction) under MAPK modulation.
Main Results:
- TGF-beta activates the MAPK pathway, enhancing transcription factor Elk-1 activity.
- Constitutively active MAPK components induce p21 expression.
- MAPK pathway inhibitors significantly reduce TGF-beta-induced p21.
- MEK modulation (constitutively active or inhibitors) does not affect Smad activity.
Conclusions:
- The MAPK pathway is involved in TGF-beta-induced p21 and p15 expression.
- The MAPK pathway appears to function independently of the Smad pathway in mediating TGF-beta's effects on p21 and p15 induction.