Regulation of C/EBPbeta1 by Ras in mammary epithelial cells and the role of C/EBPbeta1 in oncogene-induced senescence.

Atwood AA, Sealy L
Oncogene. 2010 29 (45): 6004-15

PMID: 20818427 · PMCID: PMC2978746 · DOI:10.1038/onc.2010.336

Overexpression of Ras(V12) in MCF10A cells, an immortalized mammary epithelial cell line, leads to transformation of these cells. We demonstrate that this is accompanied by degradation of C/EBPbeta1. C/EBPbeta is a transcription factor in which three protein isoforms exist because of alternative translation at three in-frame methionines. When C/EBPbeta1 is expressed in MCF10A-Ras(V12) cells, immunoblot analysis reveals that C/EBPbeta1 is degraded in these cells. Treatment of MCF10A-Ras(V12)-C/EBPbeta1 cells with the cdk inhibitor roscovitine leads to stabilization of C/EBPbeta1. It has been previously shown that cdk2 phosphorylates C/EBPbeta on Thr235. We demonstrate that mutation of Thr235 to alanine in C/EBPbeta1 is sufficient to restore the stability of C/EBPbeta1 expression in MCF10A-Ras(V12) cells. Overexpression of Ras(V12) in primary cells induces senescence rather than transformation, thus suppressing tumorigenesis. C/EBPbeta is required for Ras(V12)-induced senescence in primary mouse embryonic fibroblasts. Upregulation of interleukin-6 (IL6) by C/EBPbeta has been shown to be necessary for oncogene-induced senescence, but the specific isoform of C/EBPbeta has not been investigated. We show that the C/EBPbeta1 isoform upregulates IL6 when introduced into normal fibroblasts. In addition, we show that C/EBPbeta1 induces senescence. Taken together, degradation of C/EBPbeta1 by Ras activation may represent a mechanism to bypass OIS.

MeSH Terms (19)

Breast CCAAT-Enhancer-Binding Protein-beta CCAAT-Enhancer-Binding Proteins Cell Line Cellular Senescence Cyclin-Dependent Kinases Epithelial Cells Fibroblasts Gene Expression Regulation Humans Infant Interleukin-6 Mutation Oncogene Protein p21(ras) Protein Kinase Inhibitors Purines ras Proteins Roscovitine Up-Regulation

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