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The protein SET regulates the inhibitory effect of p21(Cip1) on cyclin E-cyclin-dependent kinase 2 activity
J M Estanyol1, M Jaumot, O Casanovas
1Departament de Biologia Cellular i Anatomia Patològica, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi Sunyer, Universitat de Barcelona, 08036 Barcelona, Spain.
Abstract:
The cyclin-dependent kinase (CDK) inhibitor p21(Cip1) has a dual role in the regulation of the cell cycle; it is an activator of cyclin D1-CDK4 complexes and an inhibitor of cyclins E/A-CDK2 activity. By affinity chromatography with p21(Cip1)-Sepharose 4B columns, we purified a 39-kDa protein, which was identified by microsequence analysis as the oncoprotein SET. Complexes containing SET and p21(Cip1) were detected in vivo by immunoprecipitation of Namalwa cell extracts using specific anti-p21(Cip1) antibodies. We found that SET bound directly to p21(Cip1) in vitro by the carboxyl-terminal region of p21(Cip1). SET had no direct effect on cyclin E/A-CDK2 activity, although it reversed the inhibition of cyclin E-CDK2, but not of cyclin A-CDK2, induced by p21(Cip1). This result is specific for p21(Cip1), since SET neither bound to p27(Kip1) nor reversed its inhibitory effect on cyclin E-CDK2 or cyclin A-CDK2. Thus, SET appears to be a modulator of p21(Cip1) inhibitory function. These results suggest that SET can regulate G(1)/S transition by modulating the activity of cyclin E-CDK2.
Insights
The oncoprotein SET directly binds to the cell cycle inhibitor p21(Cip1), modulating its function. SET reverses p21(Cip1)
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Oncoprotein Function
Background:
- p21(Cip1) is a key regulator of the cell cycle with dual roles.
- p21(Cip1) inhibits cyclin E/A-CDK2 activity.
- The oncoprotein SET's role in cell cycle regulation is not fully understood.
Purpose of the Study:
- To investigate the interaction between p21(Cip1) and the oncoprotein SET.
- To determine the functional consequences of SET binding to p21(Cip1).
- To elucidate SET's role in cell cycle regulation.
Main Methods:
- Affinity chromatography using p21(Cip1)-Sepharose 4B.
- Microsequence analysis for protein identification.
- In vivo immunoprecipitation.
- In vitro binding assays.
Main Results:
- The oncoprotein SET was purified and identified as a binding partner of p21(Cip1).
- SET directly binds to the carboxyl-terminal region of p21(Cip1).
- SET reversed p21(Cip1)-induced inhibition of cyclin E-CDK2, but not cyclin A-CDK2.
Conclusions:
- SET acts as a specific modulator of p21(Cip1)'s inhibitory function.
- SET's interaction with p21(Cip1) influences cyclin E-CDK2 activity.
- SET may regulate the G(1)/S transition by modulating p21(Cip1) activity.