Role of poly(ADPribosyl)ation of CTCF in cancer and normal breast cells

Background

CTCF is a conserved, ubiquitous and multifunctional transcription factor with features of a tumour suppressor. We have previously reported that CTCF function is modulated by post-translational poly(ADPribosyl)ation [1, 2]. Poly(ADPribosyl)ation of CTCF protein results in two isoforms: a highly poly(ADPribosyl)ated form (called CTCF180) and a hypopoly(ADPribosyl)ated form (called CTCF130). In this study we assessed the presence of both CTCF isoforms in normal and cancer breast tissues and investigated their function using immortalised cell lines.

Methods

CTCF expression was analysed in breast tissues and breast cancer cell lines by western blotting, immunohistochemistry and immunofluorescence, using antibodies that specifically recognise different CTCF isoforms. Functional investigations of CTCF isoforms in cell culture included induction of apoptosis, senescence and cell-cycle arrest using various chemical treatments and analysis of cells by flow cytometry.

Results

We discovered, using a large panel of breast tumours and paired peripheral tissues, that only the CTCF180 isoform was present in normal breast tissues, whereas CTCF130 was exclusively detected in breast tumour tissues and immortalised cell lines. Immunohistochemical staining revealed that 91% of the breast tumours contained CTCF130. In addition, correlations were found between the levels of CTCF130 and tumour grade, lymph node metastases and neoadjuvant chemotherapy treatment. In breast cancer cell lines, induction of cell death by apoptosis and senescence resulted in a transition from the CTCF130 to the CTCF180 isoform. This shift was not observed following cell-cycle arrest.

Conclusion

The present study demonstrates that CTCF180 is characteristic for normal breast tissues, whereas CTCF130 is specific for breast tumours and breast cancer cell lines. The CTCF130 isoform may therefore be used as a specific biological marker for breast tumourigenesis. Our data indicate that loss of CTCF poly(ADPribosyl)ation may be involved in breast tumour development. Poly(ADPribosyl)ation of CTCF, on the other hand, correlates with induction of cell death in breast cancer cell lines.