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Regulation of cyclin D1 expression and cell cycle progression by mitogen-activated protein kinase cascade
Y Terada1, S Inoshita, O Nakashima
1Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan. yterada.med2@med.tmd.ac.jp
Abstract:
Mitogen-activated protein kinases (MAPKs) have been shown to play an important role in transducing extracellular signals into cellular responses. The classic MAPK pathway is commonly activated by growth factors and has been shown to play a crucial role in cell proliferation. Transforming growth factor-beta (TGF-beta)-activating kinase-1 (TAK1) is a novel MAPK kinase kinase that is reported to stimulate the MKK6-p38K pathway. To elucidate the functional roles of the TAK1 pathway, we transfected its constitutive active form (TAKdN) and negative form (TAKK63W) to LLC-PK1 cells. TAKdN stimulated MKK6 phosphorylation and p38K activity and inhibited the percentages of the S and G2/M phases. TAKK63W, the constitutive negative form, reduced TGF-beta-stimulated MKK6 phosphorylation and p38K activity and increased the percentages of the S and G2/M phases. The cyclin D1 protein level is reduced by the TAK1 pathway. We also examined the effects of the TAK1 pathway on cyclin D1 promoter-luciferase assay. The overexpression of TAKdN or p38K inhibited cyclin D1 promoter activity. In contrast, overexpression of the active form of MKK1, the classic MAPK-activator, MKK1 increased cyclin D1 promoter activity and protein level, as well as the percentages of S and G2/M phases.
Insights
The transforming growth factor-beta-activating kinase-1 (TAK1) pathway regulates cell cycle progression. This study shows TAK1 influences cyclin D1 levels and cell proliferation via the MKK6-p38K pathway.
Area of Science:
- Cellular Biology
- Signal Transduction
Background:
- Mitogen-activated protein kinases (MAPKs) are crucial for signal transduction and cell proliferation.
- Transforming growth factor-beta-activating kinase-1 (TAK1) is a MAPK kinase kinase linked to the MKK6-p38K pathway.
Purpose of the Study:
- To investigate the functional roles of the TAK1 pathway in regulating cell cycle progression and cyclin D1 expression.
- To elucidate the involvement of the MKK6-p38K pathway in TAK1-mediated cellular responses.
Main Methods:
- Transfection of constitutive active (TAKdN) and negative (TAKK63W) forms of TAK1 into LLC-PK1 cells.
- Assessment of MKK6 phosphorylation, p38K activity, and cell cycle phase distribution (S and G2/M phases).
- Analysis of cyclin D1 protein levels and promoter-luciferase activity.
Main Results:
- Constitutively active TAK1 (TAKdN) enhanced MKK6 phosphorylation and p38K activity, inhibiting S and G2/M phases.
- The negative form of TAK1 (TAKK63W) reduced TGF-beta-stimulated MKK6 phosphorylation and p38K activity, increasing S and G2/M phases.
- The TAK1 pathway decreased cyclin D1 protein levels and promoter activity, whereas MKK1 activation increased them.
Conclusions:
- The TAK1 pathway, through MKK6-p38K, plays a significant role in inhibiting cell proliferation by downregulating cyclin D1.
- TAK1 acts as a negative regulator of cell cycle progression, contrasting with the positive role of the classic MAPK pathway activator MKK1.