A novel mechanism for CTCF in the epigenetic regulation of Bax in breast cancer cells.

Abstract

We previously reported the association of elevated levels of the multifunctional transcription factor, CCCTC binding factor (CTCF), in breast cancer cells with the specific anti-apoptotic function of CTCF. To understand the molecular mechanisms of this phenomenon, we investigated regulation of the human Bax gene by CTCF in breast and non-breast cells. Two CTCF binding sites (CTSs) within the Bax promoter were identified. In all cells, breast and non-breast, active histone modifications were present at these CTSs, DNA harboring this region was unmethylated, and levels of Bax mRNA and protein were similar. Nevertheless, up-regulation of Bax mRNA and protein and apoptotic cell death were observed only in breast cancer cells depleted of CTCF. We proposed that increased CTCF binding to the Bax promoter in breast cancer cells, by comparison with non-breast cells, may be mechanistically linked to the specific apoptotic phenotype in CTCF-depleted breast cancer cells. In this study, we show that CTCF binding was enriched at the Bax CTSs in breast cancer cells and tumors; in contrast, binding of other transcription factors (SP1, WT1, EGR1, and c-Myc) was generally increased in non-breast cells and normal breast tissues. Our findings suggest a novel mechanism for CTCF in the epigenetic regulation of Bax in breast cancer cells, whereby elevated levels of CTCF support preferential binding of CTCF to the Bax CTSs. In this context, CTCF functions as a transcriptional repressor counteracting influences of positive regulatory factors; depletion of breast cancer cells from CTCF therefore results in the activation of Bax and apoptosis.

• Authors: Claudia Fabiola Méndez-Catalá, Svetlana Gretton, Alexander Vostrov, Elena Pugacheva, Dawn Farrar, Yoko Ito, France Docquier, Georgia-Xanthi Kita, Adele Murrell, Victor Lobanenkov, Elena Klenova
• Journal: Neoplasia (New York, N.Y.) (Neoplasia) Vol. 15 Issue 8 Pg. 898-912 (Aug 2013) ISSN: 1476-5586 [Electronic] United States
• PMID: 23908591 (Publication Type: Journal Article, Research Support, N.I.H., Intramural, Research Support, Non-U.S. Gov't)

Chemical References

• CCCTC-Binding Factor
• CTCF protein, human
• Repressor Proteins
• bcl-2-Associated X Protein

Topics

• Apoptosis (genetics)
• Base Sequence
• Binding Sites (genetics)
• Binding, Competitive
• Blotting, Western
• Breast Neoplasms (genetics, metabolism, pathology)
• CCCTC-Binding Factor
• Cell Line, Tumor
• Epigenesis, Genetic
• Female
• Gene Expression Regulation, Neoplastic
• HEK293 Cells
• HeLa Cells
• Humans
• K562 Cells
• MCF-7 Cells
• Molecular Sequence Data
• Promoter Regions, Genetic (genetics)
• Protein Binding
• RNA Interference
• Repressor Proteins (genetics, metabolism)
• Reverse Transcriptase Polymerase Chain Reaction
• bcl-2-Associated X Protein (genetics, metabolism)