Identification of a Src tyrosine kinase/SIAH2 E3 ubiquitin ligase pathway that regulates C/EBPδ expression and contributes to transformation of breast tumor cells.

Abstract

The transcription factor CCAAT/enhancer-binding protein delta (C/EBPδ, CEBPD) is a tumor suppressor that is downregulated during breast cancer progression but may also promote metastasis. Here, we have investigated the mechanism(s) regulating C/EBPδ expression and its role in human breast cancer cells. We describe a novel pathway by which the tyrosine kinase Src downregulates C/EBPδ through the SIAH2 E3 ubiquitin ligase. Src phosphorylates SIAH2 in vitro and leads to tyrosine phosphorylation and activation of SIAH2 in breast tumor cell lines. SIAH2 interacts with C/EBPδ, but not C/EBPβ, and promotes its polyubiquitination and proteasomal degradation. Src/SIAH2-mediated inhibition of C/EBPδ expression supports elevated cyclin D1 levels, phosphorylation of retinoblastoma protein (Rb), motility, invasive properties, and survival of transformed cells. Pharmacological inhibition of Src family kinases by SKI-606 (bosutinib) induces C/EBPδ expression in an SIAH2-dependent manner, which is necessary for "therapeutic" responses to SKI-606 in vitro. Ectopic expression of degradation-resistant mutants of C/EBPδ, which do not interact with SIAH2 and/or cannot be polyubiquitinated, prevents full transformation of MCF-10A cells by activated Src (Src truncated at amino acid 531 [Src-531]) in vitro. These data reveal that C/EBPδ expression can be regulated at the protein level by oncogenic Src kinase signals through SIAH2, thus contributing to breast epithelial cell transformation.

• Authors: Tapasree Roy Sarkar, Shikha Sharan, Jun Wang, Snehalata A Pawar, Carrie A Cantwell, Peter F Johnson, Deborah K Morrison, Ju-Ming Wang, Esta Sterneck
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 32 Issue 2 Pg. 320-32 (Jan 2012) ISSN: 1098-5549 [Electronic] United States
• PMID: 22037769 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, N.I.H., Intramural)

Chemical References

• Nuclear Proteins
• RNA, Messenger
• Cyclin D1
• CCAAT-Enhancer-Binding Protein-delta
• Ubiquitin-Protein Ligases
• seven in absentia proteins
• src-Family Kinases

Topics

• Breast (metabolism, pathology)
• Breast Neoplasms (genetics, metabolism, pathology)
• CCAAT-Enhancer-Binding Protein-delta (genetics, metabolism)
• Cell Line, Tumor
• Cell Transformation, Neoplastic (genetics, metabolism, pathology)
• Cyclin D1 (genetics)
• Female
• Gene Expression Regulation, Neoplastic
• Humans
• Nuclear Proteins (metabolism)
• RNA, Messenger (genetics)
• Signal Transduction
• Ubiquitin-Protein Ligases (metabolism)
• Ubiquitination
• src-Family Kinases (metabolism)