A Role for Both Ets and C/EBP Transcription Factors and mRNA Stabilization in the MAPK-dependent Increase in p21Cip-1/WAF1/mda6Protein Levels in Primary Hepatocytes

作者：Jongsung Park, Liang Qiao, Donna Gilfor, Ming Yang, Philip B. Hylemon, Christopher C. Benz, Gretchen Darlington, Gary L. Firestone, Paul B. Fisher, Paul Dent · 发表于：Molecular Biology of the Cell · 年份：2000 · DOI：10.1091/mbc.11.9.2915 · 被引用次数：74 · 研究领域：Cancer-related Molecular Pathways、Liver physiology and pathology、Cell death mechanisms and regulation

In primary hepatocytes and HepG2 hepatoma cells, prolonged activation of the p42/44 mitogen-activated protein kinase (MAPK) pathway is associated with a reduction in DNA synthesis, mediated by increased expression of the cyclin-dependent kinase inhibitor protein p21 (Cip-1/WAF1/mda6) (p21). This study was performed to evaluate the contribution of transcriptional and post-transcriptional regulation in this response. Prolonged activation of the MAPK pathway in wild-type or p21 null hepatocytes caused a large decrease and increase, respectively, in DNA synthesis. Prolonged activation of the MAPK pathway in either wild-type or p21 antisense HepG2 cells also caused large decreases and increases, respectively, in DNA synthesis. MAPK signaling increased the phosphorylation of the transcription factors Ets2, C/EBPalpha, and C/EBPbeta, and rapidly increased transcription from the p21 promoter via multiple Ets- and C/EBP-elements within the enhancer region. Eight hours after MAPK activation, loss of C/EBPbeta or Ets2 function significantly reduced MAPK-stimulated transcription from the p21 promoter and abolished increased p21 protein expression. At this time, MAPK signaling increased both p21 mRNA and p21 protein stabilities that were also demonstrated to be essential for a profound increase in p21 protein levels. Thirty-six hours after MAPK activation, transcription from the p21 promoter was still significantly reduced in cells without either C/EBPbeta or Ets2 function; however, these...