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E2F/p107 and E2F/p130 complexes are regulated by C/EBPalpha in 3T3-L1 adipocytes
N A Timchenko1, M Wilde, P Iakova
1Huffington Center on Aging, Department of Pathology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. nikolait@bcm.tmc.edu
Nucleic Acids Research
|August 14, 1999
Summary
CCAAT-enhancer-binding protein alpha (C/EBPalpha) regulates cell cycle proteins. C/EBPalpha disrupts E2F/p107 complexes and induces E2F/p130 complexes, controlling cell proliferation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- CCAAT-enhancer-binding protein alpha (C/EBPalpha) is crucial for liver cell differentiation and proliferation.
- Loss of C/EBPalpha in hepatocytes increases proliferation and alters cell cycle regulators like p21 and E2F complexes.
- E2F/Rb family complexes play a key role in cell cycle progression.
Purpose of the Study:
- To investigate the role of C/EBPalpha in regulating E2F/Rb family complexes in 3T3-L1 cells.
- To elucidate the mechanisms by which C/EBPalpha influences E2F/p107 and E2F/p130 complex formation.
- To understand the impact of C/EBPalpha on cell cycle control during differentiation.
Main Methods:
- Utilized 3T3-L1 cells and stable transformants conditionally expressing C/EBPalpha.
- Analyzed nuclear extracts for E2F complexes (cdk2/E2F/p107, E2F/p130, E2F4) during differentiation.
- Investigated the effect of purified His-C/EBPalpha and C/EBPalpha peptides on E2F complexes in vitro.
- Assessed C/EBPalpha-induced changes in p21 levels and cdk2 kinase activity.
Main Results:
- C/EBPalpha expression correlated with the reduction of S phase-specific cdk2/E2F/p107 complexes during 3T3-L1 differentiation.
- Purified C/EBPalpha and a C/EBPalpha peptide disrupted E2F/p107 complexes in vitro.
- C/EBPalpha induced E2F/p130 complexes, associated with increased p21 and reduced cdk2 kinase activity.
- C/EBPbeta did not affect E2F/p107 complexes.
Conclusions:
- C/EBPalpha regulates E2F/Rb family complexes through two distinct pathways.
- C/EBPalpha disrupts S phase-specific E2F/p107 complexes, potentially inhibiting proliferation.
- C/EBPalpha induces E2F/p130 complexes via p21-mediated inhibition of cdk2 activity, contributing to cell cycle regulation.