Journal
MOLECULAR AND CELLULAR BIOLOGY
Volume 25, Issue 4, Pages 1325-1338Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/MCB.25.4.1325-1338.2005
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Funding
- NCI NIH HHS [R01 CA100070, CA100070] Funding Source: Medline
- NIA NIH HHS [AG20752, P01 AG020752] Funding Source: Medline
- NIGMS NIH HHS [GM55188, R01 GM055188] Funding Source: Medline
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CCAAT/enhancer-binding protein alpha (C/EBPalpha) has been previously considered a strong inhibitor of cell proliferation which uses multiple pathways to cause growth arrest. In this paper, we describe a new function of C/EBPalpha, which is an acceleration of cell proliferation. This new function of C/EBPalpha is created in proliferating livers by protein phosphatase 2A-mediated dephosphorylation of C/EBPalpha at Ser193. The Ser193-dephosphorylated C/EBPalpha interacts with retinoblastoma protein (Rb) independently on E2Fs and sequesters Rb, leading to a reduction of E2F-Rb repressors and to acceleration of proliferation. This new function of C/EBPalpha requires Rb, since the dephosphorylated C/EBPalpha does not promote proliferation in Rb-negative cells. We also show that a balance of Rb and Ser193-dephosphorylated C/EBPalpha determines if the cells are growth arrested or have an increased rate of proliferation. Consistently with these findings, a significant portion of Rb is sequestered into Rb-C/EBPalpha complexes in proliferating livers, and E2F-Rb complexes are not detectable in these livers. Our data demonstrate a new pathway by which the phosphorylation-dependent switch of biological functions of C/EBPalpha promotes liver proliferation.
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