Cell Cycle-Dependent Phosphorylation of C/EBPβ Mediates Oncogenic Cooperativity between C/EBPβ and H-RasV12
| Autor: | Philipp Kaldis, Peter F. Johnson, Songyun Zhu, Jon Shuman, Robert C. Smart, Terry D. Copeland, Thomas Sebastian |
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| Rok vydání: | 2004 |
| Předmět: |
Threonine
p38 mitogen-activated protein kinases Molecular Sequence Data Mice Cyclin-dependent kinase CDC2-CDC28 Kinases Serine Animals Protein phosphorylation Amino Acid Sequence Enzyme Inhibitors Phosphorylation Cell Growth and Development Molecular Biology Ccaat-enhancer-binding proteins biology Kinase CCAAT-Enhancer-Binding Protein-beta Cell Cycle Cyclin-Dependent Kinase 2 Cyclin-dependent kinase 2 Cell Biology Molecular biology Proto-Oncogene Proteins c-raf Cell Transformation Neoplastic Genes ras NIH 3T3 Cells ras Proteins biology.protein Mitogen-Activated Protein Kinases Sequence Alignment CDK inhibitor Signal Transduction |
| Zdroj: | Molecular and Cellular Biology. 24:7380-7391 |
| ISSN: | 1098-5549 |
| DOI: | 10.1128/mcb.24.17.7380-7391.2004 |
| Popis: | CCAAT/enhancer binding protein beta (C/EBPbeta) is a widely expressed transcription factor whose activity is regulated by oncogenic Ha-RasV12 signaling. C/EBPbeta is essential for the development of mouse skin tumors containing Ras mutations and can cooperate with RasV12 to transform NIH 3T3 cells. Here we have investigated Ras-induced phosphorylation of C/EBPbeta in fibroblasts and report a novel proline-directed phosphoacceptor site at Ser64 within the transactivation domain. Ser64 phosphorylation was induced by activated Ras and Raf but was not blocked by chemical inhibitors of MEK1/2, phosphatidylinositol 3-kinase, JNK, or p38 mitogen-activated protein kinases. Ser64 was efficiently phosphorylated in vitro by the cyclin-dependent kinases Cdk2 and Cdc2. Thr189, previously identified as an ERK1/2 phosphorylation site that regulates C/EBPbeta activity, was also a substrate for Cdk phosphorylation. Ser64 and Thr189 phosphorylation was low in serum-starved (G0) cells but was strongly increased in mid-G1 cells and in cells arrested in S or M phase. In addition, phosphorylation on both sites was blocked by treating cells with the Cdk inhibitor roscovitine. In contrast to wild-type C/EBPbeta, which enhances transformation of NIH 3T3 cells, mutants bearing alanine substitutions at Ser64 and/or Thr189 inhibited RasV12-induced focus formation. Our findings support a role for C/EBPbeta as a nuclear effector of Ras signaling and transformation, and they indicate that cell cycle-dependent phosphorylation of C/EBPbeta on Ser64 and Thr189 is required to promote Ras-induced transformation of NIH 3T3 cells. |
| Databáze: | OpenAIRE |
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