Liver tumors escape negative control of proliferation via PI3K/Akt-mediated block of C/EBP alpha growth inhibitory activity.
Liver tumor cells arise from normal hepatocytes that escape negative control of proliferation. The transcription factor C/EBPalpha maintains quiescence of hepatocytes through two pathways: inhibition of cdks and repression of E2F. Nevertheless, liver tumors and cultured hepatoma cell lines proliferate in the presence of C/EBPalpha. In this paper, we present ... evidence that the activation of the PI3K/Akt pathway in liver tumor cells blocks the growth inhibitory activity of C/EBPalpha through the PP2A-mediated dephosphorylation of C/EBPalpha on Ser 193, leading to a failure of C/EBPalpha to interact with and inhibit cdks and E2F. Mutation of Ser 193 to Ala also abolishes the ability of C/EBPalpha to cause growth arrest because of a lack of interactions with cdk2 and E2F-Rb complexes. These data provide a molecular basis for the development of liver tumors in which the activation of PI3K/Akt pathway neutralizes C/EBPalpha growth inhibitory activity.
Mesh Terms:
3T3-L1 Cells, Animals, CCAAT-Enhancer-Binding Protein-alpha, Carcinoma, Hepatocellular, Cell Division, Humans, Liver Neoplasms, Mice, Mutation, Phosphatidylinositol 3-Kinases, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-akt, Transcription Factors, Tumor Cells, Cultured
3T3-L1 Cells, Animals, CCAAT-Enhancer-Binding Protein-alpha, Carcinoma, Hepatocellular, Cell Division, Humans, Liver Neoplasms, Mice, Mutation, Phosphatidylinositol 3-Kinases, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-akt, Transcription Factors, Tumor Cells, Cultured
Genes Dev.
Date: Apr. 15, 2004
PubMed ID: 15107404
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